Molybdenum in the Geosphere

SOIL LEACHING

Long-term environmental impacts of BUILDING COMPOSITES containing waste materials.: Evaluation of the leaching protocols

The NEN 7375 test has been proposed for evaluating the long-term environmental impacts caused by the release of contaminants from monolithic building and waste materials. Over a period of 64 days, at specific points in time, the leaching solution (demineralised water) is replenished. By applying the NEN 7375 test, leaching of contaminants that is based mainly on diffusion is followed. In the present work, the results from modified leaching protocols were evaluated against those obtained by NEN 7375 test. In modified protocols, synthetic sea, surface and MilliQ water were used for the leaching of selected elements and chromate, molybdate and vanadate from compact and ground building composites (98% mixture of fly ash (80%) and cement (20%), and 2% of electric arc furnace (EAF) dust) over 6 months. The leaching solutions were not replenished, imitating both the diffusion and the dissolution of contaminants. The data revealed larger extent of leaching when the leaching solution was not replenished. More extensive was also leaching from ground composites, which simulated the disintegration of the material over time. The composition of the leaching solution influenced the release of the matrix constituents from the composites and, consequently, the amount of elements and their chemical species. Synthetic sea and surface water used as leaching solutions, without replenishing, were found to be suitable to simulate the conditions when the building material is immersed in stagnant environmental waters. (C) 2016 Elsevier Ltd. All rights reserved.

Drincic, A., Nikolic, I., Zuliani, T., Milacic, R., and Scancar, J.,Long-term environmental impacts of building composites containing waste materials.: Evaluation of the leaching protocols, Waste Management, 2017, 59, 340-349.

 

Effects of LAND USE on Selected Properties and Heavy Metal Concentration for Soil in the US Great Plains

There is increasing interest in the current conditions of dynamic soil properties and element concentration in the US Great Plains as well as the nature and magnitude of change due to land use and management practices. The study was conducted on Pawnee soil, a major U.S. benchmark soil in the Great Plains. The objectives were to investigate the effects of four common land uses [NoTill (NT), Conventional Till (CT), Grass (G), and Conservation Reserve Program (CRP)] on: i) selected soil properties [total organic carbon (TOC), bulk density (BD), pH, cation exchange capacity (CEC), and electric conductivity (EC)] and ii) water-soluble concentration of 14 heavy metals and micronutrients. The analysis of variance (ANOVA test) indicated that the land use had significant effects on the TOC, CEC, and EC, whereas no relation was detected for BD and pH. Irrespective of land use, the mean element concentration in soil could be arranged in the order: Si (Silicon) > Al (Aluminum) > Fe (Iron) > Mn (Manganese) > B (Boron) > Zn (Zinc) > Cr (Chromium) > Ni (Nickel) > Cu (Copper) > As (Arsenic) > Pb (Lead) > Co (Cobalt) > Mo (Molybdenum) > Cd (Cadmium). Silicon, Al, and Fe which are usually form the major components of soil minerals were present in much higher levels (91 to 308mg/kg) than other elements in soil. Essential plant micronutrients such as B, Cu, Mn, Mo, and Zn, generally presented moderate levels in soil (7 to 698 mu g/kg), whereas toxic heavy metals such as As, Cd, Co, Ni, and Pb were present in the lowest values (0.7-96.2 mu g/kg). The ANOVA test indicated land use had significant effects on As, B, Cd, Co, Cu, Ni, and Si concentration in soil while effects were insignificant for other elements. The data proved the important effects of land use on dynamic soil properties as well as nutrient and heavy metal for a major benchmark soil. Thus, more studies on other major soils are warranted. The information is needed to modify and adapt management practices to improve and sustain soil health and water quality in the US Great Plains.

Elrashidi, M., Wysocki, D., and Schoeneberger, P.,Effects of Land Use on Selected Properties and Heavy Metal Concentration for Soil in the US Great Plains, Communications in Soil Science and Plant Analysis, 2016, 47, 2465-2478.

 

Distribution and mobility of geogenic molybdenum and arsenic in a LIMESTONE AQUIFER matrix

To investigate the potential of Mo and As as possible geogenic contaminants, three sediment cores were examined to evaluate their mineralogical association, distribution and mobility.

The cores were described and analyzed for total organic carbon (TOC), Ca, Mg, Si, Al, P, Sr, As, Mo, Fe, and S content. Except in the uppermost segment, limestone was the main lithology with the occasional presence of dolomite and clay. That change in lithology was also observed in the bulk chemical composition, where Ca, Mg and Sr concentrations increased with depth, while Si, Al and P concentrations decreased with depth. Minor minerals included pyrite (FeS2), powellite (CaMoO4) and ferrihydrite.

The minimum, maximum, median and standard deviations for all analyzed elements, including As and Mo were comparable for all three cores. Molybdenum and As, however, varied significantly with depth and median As and Mo values were above their respective crustal averages of approximately 1.1 mg/kg and 1.5 mg/kg.

The median values for As were 1.9 mg/kg in core DEP-1, 3.3 mg/kg in DEP-2 and 1 mg/kg in DEP-5.

The median values for Mo were 2.3 mg/kg in core DEP-1, 2.5 mg/kg in DEP-2 and 2.5 mg/kg in DEP-5.

Maximum concentrations for As were 101.9 mg/kg, 47.5 mg/kg and 56.2 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively.

Maximum concentrations for Mo were 880 mg/kg, 123 mg/kg and 225 mg/kg in cores DEP-1, DEP-2 and DEP-5, respectively.

Electron microprobe analyses of individual minerals revealed variable concentrations of As ranging from approximately 300 to 9000 mg/kg, in pyrite and up to 17,600 mg/kg in powellite (CaMoO4).

The Mo concentration in pyrite was consistently below the detection limit of approximately 100 mg/kg.

In powellite the Mo concentration was up to 42 wt%.

A subset of 10 samples from different stratigraphic sections and with different As and Mo concentrations was further investigated to assess As and Mo mobility under changing physicochemical conditions. Leaching the aquifer matrix with a 1 M NaOAc solution at a pH of 8.1 removed more than 70% Mo in 8 of the 10 samples. The maximum value was 97%.

In contrast to Mo, As was mobilized to a lesser degree. In 8 of the samples less than 30% were removed and the maximum was only 50%.

Molybdenum, which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix, while As on the other hand should be much less mobile, because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite.

Thus, it is advisable to include Mo in the analytical program whenever elevated As concentrations are encountered in groundwater. (C) 2015 Elsevier Ltd. All rights reserved.

Pichler, T., and Mozaffari, A.,Distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix, Applied Geochemistry, 2015, 63, 623-633.

Molybdenum in soil and rocks

Molybdate in soil adsorption by manganese oxide

Molybdate (MoO42-) adsorption by manganese (Mn) oxide was investigated using a synthetic birnessite. Experiments were carried out in a batch experiment as a function of time (1 min to 28 d), pH (2-10) and the competitive anions sulphate (SO42-), phosphate (PO43-selenate (SeO42-) and selenite (SeO43-).

Furthermore, MoO42- adsorption was described as a function of equilibrium concentration at pH 4-7 and the data were evaluated with the Freundlich and Langmuir equations.

The amount of adsorbed MoO42- was strongly dependent on time and reached roughly an equilibrium after three days. An increase in the pH by 1.15 units within 28 days indicates ligand exchange of surface hydroxyls with MoO42-. Molybdate adsorption showed high sensitivity to pH and reached a maximum at pH 3, near the pK(a1) and pK(a2) for molybdic acid. The Freundlich equation adequately reconstructed the adsorption data. Molybdate adsorption also conformed to the Langmuir equation for the investigated pH values.

The competition sequence of anions for MoO42- adsorption by Mn oxide was SeO 43-> SeO42-> PO 43- > SO 42-, assuming a strong adsorption mechanism of MoO42- onto the surface of birnessite.

These results indicate that Mn oxides have a strong effect on the adsorption of MoO42- especially due to their higher specific surface area compared to aluminium or iron oxides. This is important regarding the availability of MoO42-in soils under agricultural conditions (pH 4-7) as well as for the treatment of soils and groundwater affected by elevated intake from industries. (C) 2015 Elsevier B.V. All rights reserved

 

Matem, K. and Mansfeldt, T., Molybdate adsorption by birnessite, Applied Clay Science, 2015, 108, 78-83.

[Birnessite: (Na, Ca)0.5(Mn4+,Mn3+)2O4 • 1.5H2O. Handbook of Mineralogy.]

Molybdate binding in soil

Metals in soils may positively or negatively affect plants as well as soil micro-organisms and mesofauna, depending on their abundance and bioavailability. Atmospheric deposition and biological uplift commonly result in metal enrichment in surface soils, but the relative importance of these processes is not always resolved. Here, we used an integrated approach to study the cycling of phosphorus and a suite of metals from the soil to the canopy (and back) in a temperate watershed.

The behavior of elements in these surface soils fell into three categories. First, Al, Fe, V, Co, and Cr showed little to no enrichment in the top soil layers, and their concentrations were determined primarily by soil production fluxes with little influence of either atmospheric inputs or biological activity.

Second, P, Cu, Zn and Cd were moderately enriched in surface soils due to a combination of atmospheric deposition and biological uplift. Among the metals we studied, Cu, Zn and Cd concentrations in surface soils were the most sensitive to changes in atmospheric deposition fluxes.

Finally, Mo and Mn showed strong enrichment in the top soil layer that could not be explained strictly by either current atmospheric deposition or biological recycling processes, but may reflect both their unique chemistry and remnants of past anthropogenic fluxes.

Mn has a long residence time in the soil partly due to intense biological uplift that retains Mn in the top soil layer.

Mo, in spite of the high solubility of molybdate, remains in the soil because of strong binding to natural organic matter.

This study demonstrates the need to consider simultaneously the vegetation and the soils to understand elemental distribution within soil profiles as well as cycling within watersheds

Kraepiel, A. M. L., Dere, A. L., Herndon, E. M., and Brantley, S. L., Natural and anthropogenic processes contributing to metal enrichment in surface soils of central Pennsylvania, Biogeochemistry, 2015, 123, 265-283.

Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge

Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed. (C) 2015 Elsevier Ltd. All rights reserved.

Chen, J. Y., Luong, H. V. T., and Liu, J. C.,Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge, Water Research, 2015, 82, 86-93.

 

Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant

This study investigated the leaching yields of Mo, Ni and Co from a mineral sludge of a metal recycling plant generated by rainfalls. The investigated mineral sludge had a complex heterogeneous composition, consisting of particles of settled soil combined with the metal bearing particles (produced by catalysts, metallic oxides and battery recycling). The leaching potential of different leaching reagents (stand-alone strong acids (HNO3 (68%), H2SO4 (98%) and HCl (36%)) and acid mixtures (aqua regia (nitric + hydrochloric (1:3)), nitric + sulfuric (1:1) and nitric + sulfuric + hydrochloric (2:1:1))) was investigated at changing operational parameters (solid - liquid (S/L) ratio, leaching time and temperature), in order to select the leaching reagent which achieves the highest metal leaching yields. Sulfuric acid (98% H2SO4) was found to be the leachant with the highest metal leaching potential. The optimal leaching conditions were a three stage successive leaching at 80 degrees C with a leaching time of 2 h and S/L ratio 0.25 g L-1. Under these conditions, the achieved mineral sludge sample leaching yields were 85.5, 40.5 and 93.8% for Mo, Ni and Co, respectively. The higher metal leaching potential of H2SO4 in comparison with the other strong acids/acid mixtures is attributed to the fact that H2SO4 is a diacidic compound, thus it has more H+ ions, resulting in its stronger oxidising power and corrosiveness.

Vemic, M., Bordas, F., Guibaud, G., Joussein, E., Lens, P. N., and van Hullebusch, E. D.,Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant, Environmental technology, 2015, 1-33.

 

 

Solid-solution phase partitioning coefficients

The authors' aim was to develop rapid and inexpensive regression models for the
prediction of partitioning coefficients (Kd ), defined as the ratio of the total
or surface-bound metal/metalloid concentration of the solid phase to the total
concentration in the solution phase. Values of Kd were measured for boric acid
(B[OH]3 (0) ) and selected added soluble oxoanions: molybdate (MoO42- ),
antimonate (Sb[OH]6- ), selenate (SeO42-), tellurate (TeO42- ) and
vanadate (VO43- ). Models were developed using approximately 500 spectrally
representative soils of the Geochemical Mapping of Agricultural Soils of Europe
(GEMAS) program. These calibration soils represented the major properties of the
entire 4813 soils of the GEMAS project. Multiple linear regression (MLR) from
soil properties, partial least-squares regression (PLSR) using mid-infrared
diffuse reflectance Fourier-transformed (DRIFT) spectra, and models using DRIFT
spectra plus analytical pH values (DRIFT?+?pH), were compared with predicted log
Kd?+?1 values. Apart from selenate (R(2) ?=?0.43), the DRIFT?+?pH calibrations
resulted in marginally better models to predict log Kd?+?1 values (R(2)
?=?0.62-0.79), compared with those from PSLR-DRIFT (R(2) ?=?0.61-0.72) and MLR
(R(2) ?=?0.54-0.79). The DRIFT?+?pH calibrations were applied to the prediction
of log Kd?+?1 values in the remaining 4313 soils. An example map of predicted log
KKd?+?1 values for added soluble MoO4 (2-) in soils across Europe is presented.
The DRIFT?+?pH PLSR models provided a rapid and inexpensive tool to assess the
risk of mobility and potential availability of boric acid and selected oxoanions
in European soils. For these models to be used in the prediction of log Kd?+?1
values in soils globally, additional research will be needed to determine if soil
variability is accounted on the calibration. Environ Toxicol Chem 2014;9999:1-12.

Janik LJ, Forrester ST, Soriano-Disla JM, Kirby JK, McLaughlin MJ, Reimann C;
GEMAS Project Team. GEMAS: Prediction of solid-solution phase partitioning coefficients (Kd ) for
oxoanions and boric acid in soils using mid-infrared diffuse reflectance spectroscopy. Environ Toxicol Chem. 2015 Feb;34(2):235-46. doi: 10.1002/etc.2821. Epub 2015 Jan 8. © 2014 SETAC.

Effect of long-term equilibration on the toxicity of molybdenum to soil organisms

To determine if long-term equilibration may alleviate molybdenum toxicity, earthworms, enchytraeids, collembolans and four plant species were exposed to three soils freshly spiked with Na2MoO4.2H2O and equilibrated for 6 or 11 months in the field with free drainage.

Total Mo concentrations in soil decreased by leaching, most (up to 98%) in sandy soil and less (54-62%) in silty and clayey soils.

Changes in residual Mo toxicity with time were inconclusive in sandy soil.

In the other two soils, toxicity of residual total Mo was significantly reduced after 11 months equilibration with a median 5.5-fold increase in ED50s.

Mo fixation in soil, i.e. the decrease of soil solution Mo concentrations at equivalent residual total soil Mo, was maximally a factor of 2.1 only.

This experiment shows natural attenuation of molybdate ecotoxicity under field conditions is related to leaching of excess Mo and other ions as well as to slow ageing reactions. (C) 2011 Elsevier Ltd. All rights reserved

van Gestel, C. A. M., McGrath, S. P., Smolders, E., Ortiz, M. D., Borgman, E., Verweij, R. A., Buekers, J., and Oorts, K., Effect of long-term equilibration on the toxicity of molybdenum to soil organisms, Environmental Pollution, 2012, 162, 1-7.

The Mo concentration in soil of the Pamperan region of Argentina was

Lavado, R.S., Porcelli, C.A., Alvarez, iR., Concentration and distribution of extractable elements in a soil as affected by tillage systems and fertilization, Science Of The Total Environment, 1999, 232, 3, 185-191.

Average and "normal" concentration levels for various metals including molybdenum have been proposed in order to establish a base line from which to assess contamination and pollution of the environment. Suggested levels are based on experience in Canada, Great Britain and two small areas in Wisconsin, U.S.A., but the general applicability of these levels especially in the U.S.A., remains to be established. For soils an average molybdenum concentration of 1.5 ppm is suggested with a normal range of 0.2-5 ppm. Similarly, average trace element contents of some vegetables have been suggested.

Warren, H . V., Delavault, R. E., Fletcher, K. W., Geology Environ. Contr. Bull., 1971, 6, 34.

Aging

Aging reactions in soils can influence the lability and hence bioavailability of added metals in soils through their removal from labile pools into pools from which desorption is slow (non-labile pools). The aims of this study were to examine the effect of aging reactions on the lability of soluble molybdate (MoO42-) added into soils with varying physical and chemical properties and develop models to predict changes in the labile pool of MoO42- in soils with incubation time. Soils were spiked with soluble MoO42- at quantities sufficient to inhibit barley root growth by 10% (EC10) or 90% (EC90) and incubated for up to 18 months. The labile pool of MoO42- (E value) was observed to decrease in soils with incubation time, particularly in soils with high clay content. A strong relationship was observed between measures of MoO42- lability in soils determined using E value [sampling the solution phase]and L value [use of a biological component (e.g. plant or earthworm) grown directly in the labelled soil] techniques (R2 = 0.98) suggesting E values provided a good measure of the potential plant available pool of MoO42- in soils. A regression model was developed that indicates clay content and incubation time were the most important factors affecting the labile pool of MoO42- in soils with time after addition (R2 = 0.70-0.75). The aging model developed suggests soluble MoO42-will be removed into non-labile pools more rapidly with time in neutral to alkaline clay soils than in acidic sandy soils. Labile MoO42- concentrations in molybdenum contaminated soils was found to be <10% of the total molybdenum concentrations in soils. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved

Kirby, Jason K., McLaughlin, Michael J., Ma, Yibing, and Ajiboye, Babasola, Aging effects on molybdate lability in soils, Chemosphere, 2012, 89, 876-883.

Metal and nanoparticle occurrence in biosolid-amended soils
Metals can accumulate in soils amended with biosolids in which metals have been concentrated during wastewater treatment.

The goal of this study is to inspect agricultural sites with long-term biosolid application for a suite of regulated and unregulated metals, including some potentially present as commonly used engineered nanomaterials (ENMs).
Sampling occurred in fields at a municipal and a privately operated biosolid recycling facilities in Texas. Depth profiles of various metals were developed for control soils without biosolid amendment and soils with different rates of biosolid application (6.6 to 74 dry tons per hectare per year) over 5 to 25 years.

Regulated metals of known toxicity, including chromium, copper, cadmium, lead, and zinc, had higher concentrations in the upper layer of biosolid-amended soils (top 0-30 cm or 0-15 cm) than in control soils.
The depth profiles of unregulated metals (antimony, hafnium, molybdenum, niobium, gold, silver, tantalum, tin, tungsten, and zirconium) indicate higher concentrations in the 0-30 cm soil increment than in the 70-100 cm soil increment, indicating low vertical mobility after entering the soils.

Titanium-containing particles between 50 nm and 250 nm in diameter were identified in soil by transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDX) analysis.

In conjunction with other studies, this research shows the potential for nanomaterials used in society that enter the sewer system to be removed at municipal biological wastewater treatment plants and accumulate in agricultural fields. The metal concentrations observed herein could be used as representative exposure levels for eco-toxicological studies in these soils. (C) 2014 Elsevier B.V. All rights reserved

Yang, Y., Wang, Y. F., Westerhoff, P., Hristovski, K., Jin, V. L., Johnson, M. V. V., and Arnold, J. G., Metal and nanoparticle occurrence in biosolid-amended soils, Science of the Total Environment, 2014, 485, 441-449.

Derivation of ecological standards for risk assessment of molybdate in SOIL

Environmental context

In order to assess the potential risks of elevated molybdenum concentrations in soil due to anthropogenic activities, toxicity thresholds must be known and environmental criteria defined. Setting such criteria for metals is not straightforward because of varying natural background concentrations and differences in toxicity between typical laboratory and field conditions and across soil types. Toxicity data and models were derived that account for these parameters so that soil quality criteria can be derived based on total molybdenum concentrations in soil.

Abstract

An extensive testing programme on the toxicity of sodium molybdate dihydrate in soil was initiated to comply with the European REACH Regulation.

The molybdate toxicity was assayed with 11 different bioassays, 10 different soils, soil chemical studies on aging reactions, and toxicity tests before and after 1-year equilibration in field conditions.

Differences in molybdate toxicity among soils were best explained by soil pH and clay content.

A correction factor of 2.0 was selected to account for the difference in molybdate toxicity between laboratory and field conditions due to leaching and aging processes.

Toxicity thresholds were determined as the HC5-50 (median hazardous concentration for 5% of the species, i.e. median 95% protection level) derived from the species sensitivity distribution of ecotoxicity data after bioavailability corrections. Uncertainty analysis illustrated that the HC5-50 provides a robust and ecologically relevant predicted no-effect concentration (PNEC) for risk characterisation.

The 10th and 90th percentiles for site-specific PNEC values in European agricultural soil are 10.7 and 168 (mgMo) kg-1 dry weight respectively based on a large survey of metal concentrations and soil properties in arable land soils. Total soil Mo concentrations in these soils are below corresponding PNEC values at most locations, suggesting no regional risks of molybdate to soil organisms at this scale.

The information presented can be used in the EU risk-assessment framework as well as for national and international regulatory purposes for the setting of soil quality criteria based on total molybdenum concentrations, soil pH and clay content.

Oorts, K., Smolders, E., McGrath, S. P., van Gestel, C. A. M., McLaughlin, M. J., and Carey, S.,Derivation of ecological standards for risk assessment of molybdate in soil, Environmental Chemistry, 2016, 13, 168-180.

Surface complexation modelling in variable charge SOILS: charge characterization by potentiometric titration

Intrinsic equilibrium constants of 17 representative Brazilian Oxisols were estimated from potentiometric titration measuring the adsorption of H+ and OH- on amphoteric surfaces in suspensions of varying ionic strength. Equilibrium constants were fitted to two surface complexation models: diffuse layer and constant capacitance. The former was fitted by calculating total site concentration from curve fitting estimates and pH-extrapolation of the intrinsic equilibrium constants to the PZNPC (hand calculation), considering one and two reactive sites, and by the FITEQL software. The latter was fitted only by FITEQL, with one reactive site. Soil chemical and physical properties were correlated to the intrinsic equilibrium constants. Both surface complexation models satisfactorily fit our experimental data, but for results at low ionic strength, optimization did not converge in FITEQL. Data were incorporated in Visual MINTEQ and they provide a modeling system that can predict protonation-dissociation reactions in the soil surface under changing environmental conditions.

Marchi, G., Vilar, C. C., O'Connor, G., and Silva, M. L. N.,SURFACE COMPLEXATION MODELING IN VARIABLE CHARGE SOILS: CHARGE CHARACTERIZATION BY POTENTIOMETRIC TITRATION, Revista Brasileira De Ciencia Do Solo, 2015, 39, 1386-1394.

Molybdate. Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant

This study investigated the leaching yields of Mo, Ni and Co from a mineral sludge of a metal recycling plant generated by rainfalls. The investigated mineral sludge had a complex heterogeneous composition, consisting of particles of settled soil combined with metal-bearing particles (produced by catalysts, metallic oxides and battery recycling). The leaching potential of different leaching reagents (stand-alone strong acids (HNO3 (68%), H2SO4 (98%) and HCl (36%)) and acid mixtures (aqua regia (nitric + hydrochloric (1:3)), nitric + sulphuric (1:1) and nitric + sulphuric + hydrochloric (2:1:1)) was investigated at changing operational parameters (solid-liquid (S/L) ratio, leaching time and temperature), in order to select the leaching reagent which achieves the highest metal leaching yields. Sulphuric acid (98% H2SO4) was found to be the leachant with the highest metal leaching potential. The optimal leaching conditions were a three-stage successive leaching at 80 degrees C with a leaching time of 2 h and S/L ratio of 0.25 g L-1. Under these conditions, the achieved mineral sludge sample leaching yields were 85.5%, 40.5% and 93.8% for Mo, Ni and Co, respectively. The higher metal leaching potential of H2SO4 in comparison with the other strong acids/acid mixtures is attributed to the fact that H2SO4 is a diacidic compound, thus it has more H+ ions, resulting in its stronger oxidizing power and corrosiveness.

Vemic, M., Bordas, F., Guibaud, G., Comte, S., Joussein, E., Lens, P. N., and Hullebusch, E. D.,Acid extraction of molybdenum, nickel and cobalt from mineral sludge generated by rainfall water at a metal recycling plant, Environmental technology, 2015, 1-10.

Molybdate. Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge

 Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed.

Chen, J. Y., Luong, H. V., and Liu, J. C.,Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge, Water research, 2015, 82, 86-93.

Assessment of sampling and analytical uncertainty of trace element contents in arable field soils

Assessment of trace element contents in soils is required in Germany (and other countries) before sewage sludge application on arable soils. The reliability of measured element contents is affected by measurement uncertainty, which consists of components due to (1) sampling, (2) laboratory repeatability (intra-lab) and (3) reproducibility (between-lab). A complete characterization of average trace element contents in field soils should encompass the uncertainty of all these components. The objectives of this study were to elucidate the magnitude and relative proportions of uncertainty components for the metals As, B, Cd, Co, Cr, Mo, Ni, Pb, Tl and Zn in three arable fields of different field-scale heterogeneity, based on a collaborative trial (CT) (standardized procedure) and two sampling proficiency tests (PT) (individual sampling procedure). To obtain reference values and estimates of field-scale heterogeneity, a detailed reference sampling was conducted. Components of uncertainty (sampling person, sampling repetition, laboratory) were estimated by variance component analysis, whereas reproducibility uncertainty was estimated using results from numerous laboratory proficiency tests. Sampling uncertainty in general increased with field-scale heterogeneity; however, total uncertainty was mostly dominated by (total) laboratory uncertainty. Reproducibility analytical uncertainty was on average by a factor of about 3 higher than repeatability uncertainty. Therefore, analysis within one single laboratory and, for heterogeneous fields, a reduction of sampling uncertainty (for instance by larger numbers of sample increments and/or a denser coverage of the field area) would be most effective to reduce total uncertainty. On the other hand, when only intra-laboratory analytical uncertainty was considered, total sampling uncertainty on average prevailed over analytical uncertainty by a factor of 2. Both sampling and laboratory repeatability uncertainty were highly variable depending not only on the analyte but also on the field and the sampling trial. Comparison of PT with CT sampling suggests that standardization of sampling protocols reduces sampling uncertainty, especially for fields of low heterogeneity

Buczko, Uwe, Kuchenbuch, Rolf O., Uebelhoer, Walter, and Naetscher, Ludwig, Assessment of sampling and analytical uncertainty of trace element contents in arable field soils, Environmental Monitoring and Assessment, 2012, 184, 4517-4538.

Soil:Standards for the contents of heavy metals and metalloids in soils

In line with the present-day ecological and toxicological data obtained by Dutch ecologists, heavy metals/metalloids form the following succession according to their hazard degree in soils: Se > Tl > Sb > Cd > V > Hg > Ni > Cu > Cr > As > Ba.

This sequence substantially differs from the succession of heavy elements presented in the general toxicological GOST (State Norms and Standards) 17.4.1.02-8, which considers As, Cd, Hg, Se, Pb, and Zn to be strongly hazardous elements, whereas Co, Ni, Mo, Sb, and Cr to be moderately hazardous.

As compared to the general toxicological approach, the hazard of lead, zinc, and cobalt is lower in soils, and that of vanadium, antimony, and barium is higher.

The new sequence also differs from that of the metal hazard in soils according to the Russian standard on the maximal permissible concentration of mobile metal forms (MPCmob): Cu > Ni > Co > Cr > Zn. Neither an MPCmob nor an APC(mob) has been adopted for strongly hazardous thallium, selenium, and vanadium in Russia.

The content of heavy metals in contaminated soils is very unevenly studied: 11 of them, i.e., Cu, Zn, Pb, Ni, Cd, Cr, As, Mn, Co, Hg, and Se, are better known, while the rest, much worse, although there are dangerous elements (Ba, V, Tl) among them

Vodyanitskii, Yu, Standards for the contents of heavy metals and metalloids in soils, Eurasian Soil Science, 2012, 45, 321-328.

Soil: Mathematical models to predict soil heavy metal toxicity in the 2012 Olympic site

Heavy metal concentrations in samples collected from the London 2012 Olympic Village were determined using a three-step sequential extraction and a rapid extraction method. Metal toxicity was measured by employing the Microtox(A (R)) solid phase analysis. Both extraction methods produced comparable results (p = 0.996), but the rapid method produced higher readings.

A number of heavy metals were detected using the two extraction methods, including aluminum, arsenic, cadmium, chromium, copper, iron, nickel, lead and zinc; beryllium, molybdenum, niobium and titanium were also found in low concentration ranging between 0.16 and 27.10 mg/kg in the total acid digestion.

The total metal levels in all the soil samples were within the UK Soil Guideline Value (SGV) except for lead which ranged between 62.9 and 776.2 mg/kg.

The 30 min EC50 of different soil fractions was 2-5.8 g/L.

In the absence of any of heavy metals in the SGV, the Dutch Guideline values were referred.

Mathematical models for a number of metals were generated based on the changes in EC50 values between each (F1, F2 and F3) soil fractions and the initial toxicity in the non-fractionated samples. The resulting models produced good R-2 values (> 96%) for predicting the change in toxicity of lead, cadmium, zinc and copper by measuring their changes in concentrations. These models could substantially reduce the time requires to determine the toxicity in the samples; they would be a useful tool in the clean up process where monitoring of metal toxicity is required

Radiar, A. R. B. and Purchase, D., Mathematical models to predict soil heavy metal toxicity in the 2012 Olympic site, International Journal of Environmental Science and Technology, 2012, 9, 219-226.

Molybdate and soil

Soil-to-plant transfer of elements is not linear

Element-specific concentration ratios (CRs) assuming that plant uptake of elements is linear are commonly used in radioecological modelling to describe the soil-to-plant transfer of elements. The goal of this study was to investigate the validity of the linearity assumption in boreal forest plants, for which only limited relevant data are available. The soil-to-plant transfer of three essential (Mo, Ni, Zn) and two non-essential (Pb, U) elements relevant to the safety of radioactive waste disposal was studied. Three understory species (blueberry, narrow buckler fern and May lily) and two tree species (Norway spruce and rowan) were included. Examining CRs as a function of soil concentration showed that CR was not constant but decreased with increasing soil concentrations for all elements and plant species. A non-linear equation fitted fairly well with the empirical data; the R(2)-values for this equation were constantly higher than those for the linear fit. The difference between the two fits was most evident at low soil concentrations where the use of constant CRs underestimated transfer from soil to plants. Site-specific factors affected the transfer of Mo and Ni. The results suggested that systematic variation with soil concentrations explains a part of the large variation of empirically determined CRs, and the accuracy of modelling the soil-to-plant transfer might be improved by using non-linear methods. Non-linearity of soil-to-plant transfer has been previously reported for a few different species, elements and environments. The present study systematically tested the linearity assumption for five elements (both essential and non-essential) and in five boreal forest species representing different growth traits and phylogenies. The data supported non-linearity in all cases.

Tuovinen, Tiina S.; Roivainen, Paivi; Makkonen, Sari; Kolehmainen, Mikko; Holopainen, Toini; Juutilainen, Jukka. Soil-to-plant transfer of elements is not linear: Results for five elements relevant to radioactive waste in five boreal forest species. Science of the Total Environment, 2011, 410,191-197.

Metals in industrially contaminated soil

The concentrations of heavy metals (As, Ba, Co, Cr, Cu, Ni, Mo, Pb, Sr, V and Zn) were studied in soils to understand metal contamination due to industrialization and urbanization around Manali industrial area in Chennai, Southern India. This area is affected by the industrial activity and saturated by industries like petrochemicals, refineries, and fertilizers generating hazardous wastes. The data revealed elevated concentrations of chromium (149.8-418.0 mg/kg), copper (22.4-372.0 mg/kg), nickel (11.8-78.8 mg/kg), zinc (63.5-213.6 mg/kg) and molybdenum (2.3-15.3 mg/kg).

Krishna, A.K. and Govil, P. K., Assessment of heavy metal contamination in soils around Manali industrial area, Chennai, Southern India, Environmental Geology, 2008, 54, 1465-1472.

Molybdenum availability in forest soils

The oxalate-extractable Mo concentrations of acid forest soils, the Mo, nitrate, phosphate, and sulfate fluxes from the organic forest floor into the mineral soil using resin tubes and the Mo concentrations of the Norway spruce tree needles were measured. The supply of oxalate-extractable Mo varied from 51 to 3400 g.ha- 1, with the lowest values occurring in sandstone-derived soils (370 +/- 212 g.ha- 1; mean +/- SD). Molybdenum concentrations of current-year needles were in the range of 5 to 48 ng.g- 1. The Mo needle concentrations and oxalate-extractable Mo of soils did not correlate. Mo fluxes (6-60 g.ha- 1.a- 1from the organic forest floor into the mineral soils were correlated to needle concentrations and to the NO3 fluxes. Mo turnover within forest ecosystems is governed by Mo plant availability of mineral soils as well as by plant Mo uptake. In addition, Mo cycling strongly affects Mo distribution within soil profiles and Mo fluxes out of the organic layer

Lang, F. and Kaupenjohann, M., Molybdenum at German Norway spruce sites: contents and mobility, Canadian Journal of Forest Research-Revue Canadienne De Recherche Forestiere, 2000, 30, 1034-1040.

A low level of available Mo in a soil may result from a low content of total Mo, a strong adsorption or fixation of molybdate ions by kaolinitic clay or hydrous oxides of iron or aluminum, leaching of available forms, or perhaps from a combination of these influences. Surface samples of 33 serpentine soils and 22 non-serpentine soils from the North Coast Range of California, southwestern Oregon and western Washington State, were analysed for available molybdenum. The serpentine soils show a generally low level of available Mo, with 26 of the 32 soils classified as deficient or very deficient. In contrast the non-serpentine soils were mostly only slightly deficient or not deficient. Recovery from visible Mo-deficiency symptoms in lettuce and tomato plants grown on two of the serpentine soils was obtained with Mo fertilization. Analyses for total Mo In a few of the soils did not show exceptionally low values, suggesting that the low available Mo status of the serpentine soils is probably due to adsorption or fixation of this element, and possibly also due to leaching of available forms of Mo. Mo levels were

Total and available molybdenum in soils
Total Mo/mg (kg)-1Available Mo/ mg (kg)-1
Non-serpentine soils
2.38 0.034
8.73 0.217
Serpentine soils
3.04 0.0075
4.14 0.013
6.11 0.036
8.63 0.034
9.5 0.17

Available Mo was determined using the fungus Aspergillus niger.

Walker, R.B., Low molybdenum status of serpentine soils of western North America, South African Journal of Science, 2001, 97, 565-568.

Molybdenum deficiency in soil in Nepal

Micronutrient problems in the food systems of the Himalaya are wide spread due to bedrock with low nutrient content, high erosion rates, poverty, subsistence agriculture, and increasing cropping intensity. Agriculturally based strategies for the reduction of micronutrient malnutrition will require knowledge of the scale and spatial patterns of soil deficiencies or excesses of some elements. The present article documents current knowledge about the micronutrient status of cultivated soil in Nepal. Most studies have recorded largely the same magnitude of deficiencies in this country. Some 80 to 90% of soil samples were deficient in boron (B), 20 to 50% in zinc (Zn), and 10 to 15% in molybdenum (Mo). These are important micronutrient deficiencies because they limit agricultural production and affect human nutrition directly or indirectly

Andersen, P., A review of micronutrient problems in the cultivated soil of Nepal - An issue with implications for agriculture and human health, Mountain Research and Development, 2007, 27, 331-335.

Molybdenum adsorption capacities of soils

Mo maximum adsorption capacities (MoMAC) of 16 soils, primarily Oxisols, from Minas Gerais, Brazil were determined. The MoMAC varied from 0.15 to 2.02 mg g-1 and there were good correlations between MoMAC and soil clay content as well as between MoMAC and soil organic carbon content. The molybdate-catalysed reaction of potassium iodide and hydrogen peroxide was used to determine molybdenum (Mo) in Mehlich 1 (1:10) soil test extracts.

Fontes, R.L.F., Dallpai, D. L., Braga, J. M., and Alvarez, V. H., Determination of molybdenum in soil test extracts with potassium iodide plus hydrogen peroxide reaction, Communications in Soil Science and Plant Analysis, 2000, 31, 2671-2683.

Molybdenum adsorption to goethite

The interaction (adsorption) of molybdate and goethite displayed a fast relaxation time (reciprocal of rate constant, about 4 ms), that decreased with increasing temperature (283 to 303 K) and a slow time (about 60 ms) that did not depend on temperature. Activation energy of the fast process was 76 kJ mol-1. The fast relaxation, which was not affected by incubation time, represents Mo chemisorption to the goethite. The amount of Mo sorbed to the iron oxide increased with increasing incubation time. Slow relaxation is due to Mo transport within the suspension.

Lang, F., Pohlmeier, A., and Kaupenjohann, M., Mechanism of molybdenum sorption to iron oxides using pressure- jump relaxation, Journal of Plant Nutrition and Soil Science-Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, 2000, 163, 571-575.

The mobility of Mo in soils and sediments depends on several factors including soil mineralogy and the presence of other oxyanions that compete with Mo for the adsorbent's retention sites. Tungstate and phosphate appear to be the strongest competitors of Mo for the adsorption sites of goethite, whereas little competitive effects were observed in the case of silicate and sulfate. The dominant complexes of adsorbed W and Mo on goethite 110 faces at low pH were diprotonated monodentate complexes, FeOW(OH)(5)(-0.5) and FcOMo(OH)(5)(-0.5) Mo and W are retained mainly by the formation of monodentate complexes on the goethite surface.

Xu, N., Christodoulatos, C., and Braida, W., Modeling the competitive effect of phosphate, sulfate, silicate, and tungstate anions on the adsorption of molybdate onto goethite, Chemosphere, 2006, 64, 1325-1333.

Molybdenum adsorption on soil minerals

Goldberg, S., Brown, G. E., Johnston, C. T., and Suarez, D. L., Mechanism of molybdenum adsorption on soil minerals evaluated using vibrational spectroscopy and surface complexation modeling, Abstracts of Papers of the American Chemical Society, 2006, 231

Influence of soil solution salinity on molybdenum adsorption by soils

Molybdenum adsorption on five arid-zone soils from California was investigated as a function of equilibrium solution molybdenum concentration (0 30 mg L-1), solution pH (4-8), and electrical conductivity. Molybdenum adsorption decreased with increasing pH. An adsorption maximum was found near pH 4. Molybdenum adsorption as a function of solution pH was independent of solution salinity from pH 4 to 8. Molybdenum adsorption for five soils as a function of solution molybdenum concentration obeyed the Langmuir adsorption isotherm equation. The constant capacitance model, a surface complexation model, was able to describe molybdenum adsorption as a function of solution molybdenum concentration and solution pH. Molybdenum adsorption was predicted using the soil chemical properties: cation exchange capacity, organic carbon content, inorganic carbon content, and iron oxide content. Under agricultural conditions (pit 4-8), molybdenum adsorption can be described without consideration of changes in soil solution salinity

The following surface complexation reactions were considered and the surface complexation constants were determined:

SOH + H+ = SOH2+

SOH = SO- + H+

SOH + H2MoO4 = SHMo4 + H2O

SOH + H2MoO4 = SMoO4- + H+ + H2O

where SOH, the surface functional group, represents both reactive surface hydroxyl groups on oxides and aluminol groupson clay mineral edges in soils.

Molybdenum adsorption isotherms were determined on five soils under conditions of low (EC = 0.32 dS m I) and high(EC = 7.9 dS m) electrolyte concentration. The Langmuir isotherm equation was fitted to the experimental adsorption data using nonlinear least-squares optimization (Kinniburgh. 1986).

Moads = (KMoeqM)/(1+KMoeq)

Here Moads is the molybdenum adsorption, Moeq is the equilibrium molybdenum solution concentration, M is the maximum molybdenum adsorption and K is a parameter fitted to the molybdenum adsorption data. With the exception of the Arlington subsoil, the molybdenum adsorption was not different at the 95% level of confidence for the two electrical conductivities. This result indicates that in the range of EC = 0.32 to 7.9 dS m, the magnitude of molybdenum adsorption is independent of soil solution salinity.

Goldberg, S., Influence of Soil Solution Salinity on Molybdenum Adsorption by Soils, Soil Science, 2009, 174, 9-13.

Mo in soil: availability enhanced by increased pH

The Mo availability in the soil was highest for soil application of lime (0.5 tonne/ha) followed by Mo @ 0.5 kg/ha

Hamza, S. and Sadanandan, A. K., Soil amendments and molybdenum on yield and quality of black pepper (Piper nigrum), Indian Journal of Agricultural Sciences, 2005, 75, 735-737.

Bioaccumulation of molybdenum in cabbage and broccoli grown in sewage sludge and chicken manure amended soil

The mobility of heavy metals from soil into the food chain and their subsequent bioaccumulation has increased the attention they receive as major environmental pollutants. The objectives of this investigation were to: i) study the impact of mixing native agricultural soil with municipal sewage sludge (SS) or chicken manure (CM) on yield and quality of cabbage and broccoli, ii) quantify the concentration of seven heavy metals (Cd, Cr, Mo, Cu, Zn, Pb, and Ni) in soil amended with SS or CM, and iii) determine bioavailability of heavy metals to cabbage leaves and broccoli heads at harvest. Analysis of the two soil amendments used in this investigation indicated that Cr, Ni, Cu, Zn, Mo, Cd, Pb, and organic matter content were significantly greater (P < 0.05) in premixed sewage sludge than premixed chicken manure. Total cabbage and broccoli yields obtained from SS and CM mixed soil were both greater than those obtained from no-mulch (bare) soil. Concentration of Ni in cabbage leaves of plants grown in soil amended with CM was low compared to plants grown in no-mulch soil. No significant differences were found in Cd and Pb accumulation between cabbage and broccoli. Concentrations of Ni, Cu, Zn, and Mo were greater in broccoli than cabbage. Total metals and plant available metals were also determined in the native and amended soils. Results indicated that the concentration of heavy metals in soils did not necessary reflect metals available to plants. Regardless of soil amendments, the overall bioaccumulation factor (BAF) of seven heavy metals in cabbage leaves and broccoli heads revealed that cabbage and broccoli were poor accumulators of Cr, Ni, Cu, Cd, and Pb (BAF <1), while BAF values were >1 for Zn and Mo. Elevated Ni and Mo bioaccumulation factor (BAF >1) of cabbage grown in chicken manure mixed soil is a characteristic that would be less favorable when cabbage is grown on sites having high concentrations of these two metals

Antonious, George F., Kochhar, Tejinder S., and Coolong, Timothy, Yield, quality, and concentration of seven heavy metals in cabbage and broccoli grown in sewage sludge and chicken manure amended soil, Journal of Environmental Science and Health Part A-Toxic/Hazardous Substances & Environmental Engineering, 2012, 47, 1955-1965.

Competitive molybdate and phosphate sorption and soil properties

We have examined the effects of both pH and phosphate concentrations on molybdate sorption by four Chilean Andisols with varying chemical properties. For both anions adsorption decreased with an increase in soil pH and also with organic matter content in the soils. In general, more phosphate than molybdate was sorbed by the soils. The Freundlich equation adequately described adsorption of both anions. Differences in the extent of sorption of molybdate and phosphate and in isotherm shape between soils were ascribed to variations in soil properties. The competitive sorption data were adequately described by the multicomponent Freundlich equations. Phosphate strongly competed with molybdate for sorption sites on the Andisols, causing molybdate sorption to decrease by 10-27%. The competition coefficients for phosphate and molybdate sorption were variable, indicating that competition between the two anions was not symmetrical. The present results provide further evidence to indicate that the surfaces of Andisols are rich in reactive Al-OH and Fe-OH groups, exposed at colloidal particle surfaces. Molybdate sorption appeared to be mainly associated with free Al- and Fe-oxides, while phosphate sorption was primarily regulated by Al- and Fe-humus complexes

Vistoso, E., Theng, B., Bolan, N., Parfitt, R., and Mora, M., Competitive sorption of molybdate and phosphate in Andisols, Journal of Soil Science and Plant Nutrition, 2012, 12, 59-72.

Molybdenum Foliar Fertilization of Oilseed Rape - Influence of Soil Reaction

The effect of foliar fertilization with molybdenum on oilseed rape in thirty-three field trials on soils of different acidity (pH=4.1-7.1) is reported. Molybdenum at 30, 60 and 120 g Mo ha-1 was applied: in the spring, a few days after the growing season started; and during the early stem formation stage.

On very acidic and acidic soils, seed yields were 0.08 t ha-1 higher. A relative seed yield increase obtained through molybdenum fertilization depended on the concentration of manganese and percentage of the silt fraction in the soil.

Oilseed rape grown on slightly acidic and neutral soils responded to molybdenum fertilization with an average seed yield increase of 0.02t ha-1.

The amount of molybdenum added affected oilseed rape yields only for slightly acidic and neutral soils. Molybdenum at 30 g Mo. ha-1was less effective than molybdenum at 60 and 120 g Mo. ha-1.

Seed yields did not depend on the date of molybdenum application. There was no interaction between molybdenum application rates and application dates in either group of the trials.

Stanislawska-Glubiak, E., The Influence of Soil Reaction on the Effects of Molybdenum Foliar Fertilization of Oilseed Rape, Journal of Elementology, 2008, 13, 647-654.

Acidic agricultural soils molybdenum addition and liming

Most soils in sub-Saharan Africa are acidic and have low calcium (Ca2+), magnesium (Mg2+) and molybdenum (Mo). Higher concentrations and contents of hydrogen ion (H+), aluminium (Al3+) and manganese (Mn2+) found in these acidic soils are the major causes of poor plant growth due to their toxicity to plants and micro organisms such as N-fixing bacteria. Molybdenum is a component of some bacterial nitrogenase and is important for plants that live in symbiosis with nitrogen-fixing bacteria such as Rhizobium. Calcium, magnesium and molybdenum deficient plants exhibit poor growth. The most common management practice to ameliorate these acidic soil problems is through the surface application of lime or molybdenum and/ or seed pelleting. The potential role(s) of lime and Mo in legumes with respect to growth, assimilation of metabolites, N-fixation and growth is given special attention in this review

Bambara, S. and Ndakidemi, P. A., The potential roles of lime and molybdenum on the growth, nitrogen fixation and assimilation of metabolites in nodulated legume: A special reference to Phaseolus vulgaris L, African Journal of Biotechnology, 2010, 9, 2482-2489.

Phosphorus-Molybdenum Relationship in Soil and Red Clover

The phosphorus and molybdenum relationship in soil and red clover (Trifolium pratense L.) in a non-limed and limed acid Andisol of Southern Chile was studied.

The effect of different liming (0 and 2000 mg kg(-1)), P (0, 200 and 400 mg kg(-1)), and Mo (0, 0.58 and 0.96 mg kg(-1)) doses supply on soil available Mo was evaluated. The availability of P and calcium (Ca) in treated soils was determined.

Lime and more strongly P and Mo additions significantly (P <= 0.05) increased soil Mo availability.

Soil available P was not significantly (P <= 0.05) affected by liming and Mo treatments.

A significant high correlation (r = 0.579, at P <= 0.05) was observed among soil Mo availability and shoot Mo concentrations, and between soil available P and shoot concentration of P (r = 0.844, at P <= 0.01).

For all fertilization treatments, shoot Cu concentrations reached values considered normal for forage species. Simultaneous applications of high P and Mo rates could produce red clover shoot Cu/Mo ratios that should provoke Mo-induced Cu deficiency (molybdenosis) for cattle.

Red clover yield was not significantly different in limed and non limed soils. Red clover yield increased at increasing rates of P and Mo in both non-limed and limed soil.

The major practical implication of these results is that the application of Mo doses equal or superior to 200 g ha-1 to acid Andisols, is recommendable to obtain appropriate Mo shoot content on red clover.

P supply to these soils, rather than liming, is necessary to obtain sufficient values of shoot Mo concentrations in red clove

Ribera, A. E., Mora, M. D., Ghiselini, V., Demanet, R., and Gallardo, F., Phosphorus-Molybdenum Relationship in Soil and Red Clover (Trifolium Pratense L.) on An Acid Andisol, Revista de la Ciencia del Suelo y Nutricion Vegetal, 2010, 10, 78-91.

Molybdenum in agriculture: application of molybdenum to leaves of winter beans

The objective was to evaluate the performance of irrigated winter beans, in a no-tillage system, with increasing levels of side dressing nitrogen application (zero, 30, 60, 90 and 120 kg ha-1) and its interaction with leaf application of molybdenum (zero and 80 g ha-1). The common bean can fix nitrogen in symbiosis with Rhizobium, but the fixed nitrogen is not enough to meet the nitrogen requirement of the plant. Molybdenum application aims to improve symbiosis in the Rhizobium-common bean plant, given its importance in the metabolism nitrogen, thus being able to reduce the application of nitrogen fertilizer. The research was carried out on soil previously cultivated with corn culture. The levels of nitrogen proved consistent regarding the effects on some production components, and on dry mass of plants, providing better development of irrigated beans cultivated under no-tillage. The application of molybdenum in leaves did not influence the majority of evaluated parameters

Barbosa, G. F., Arf, O., do Nascimento, M. S., Buzetti, S., and Freddi, O. D., Side dressing nitrogen and leaf molybdenum in the winter common bean plant, Acta Scientiarum-Agronomy, 2010, 32, 117-123.

Plants agriculture seed treatment

Molybdenum was applied as a concentrated suspension of Mo trioxide in waterto soybean seeds resulting in in higher soybean yields than in a control.

Lana, R. M. Q., de Faria, M. V., Bonotto, I., and Lana, A. M. Q., Cobalt and Molybdenum Concentrated Suspension for Soybean Seed Treatment, Revista Brasileira de Ciencia do Solo, 2009, 33, 1715-1720.

Plants rice beneficial effect of Mo and Ni interaction on plant growth

This is the first evidence for a beneficial effect of Mo and Ni interaction on plant growth. Upland rice plants, cultivar 'IAC 202,' were grown in nutrient solution until full tillering. Treatments consisted of ammonium nitrate or urea as nitrogen source plus molybdenum and/or nickel.

Moraes, M. F., Reis, A. R., Moraes, L. A. C., Lavres, J., Vivian, R., Cabral, C. P., and Malavolta, E., Effects of Molybdenum, Nickel, and Nitrogen Sources on the Mineral Nutrition and Growth of Rice Plants, Communications in Soil Science and Plant Analysis, 2009, 40, 3238-3251.

Plants alfalfa

Alfalfa crops were grown in the field at the University of Ankara over two seasons between 2001 and 2003 with sulfur supplied as gypsum at rates of 0 (control), 160 (S1), and 240 (S2) kg /ha.Sulfur fertilization increased sulfur concentrations and improved alfalfa hay yield for both years. Molybdenum concentration of the alfalfa was significantly reduced by S1 treatment in year 1. Applied S had no effect on copper.

Gunes, A., Inal, A., Pilbeam, D. J., and Kadioglu, Y. K., Effect of Sulfur on the Yield and Essential and Nonessential Element Composition of Alfalfa Determined by Polarized Energy Dispersive X-ray Fluorescence, Communications in Soil Science and Plant Analysis, 2009, 40, 2264-2284.

Plants lettuce accumulation of molybdenum in plants and soils following amendments of molybdenum compost

A limit for molybdenum loading of soil developed from compost additions is proposed as 55 mg Mo/ kg soil, a value which is presently greater than the Canadian Council for Ministers of the Environment (CCME) Guidelines for the use of type B compost in Canada

The growth of lettuce (Lactuca sativa L.) and barley (Hordeum vulgar) and accumulation of molybdenum in plants and soils were evaluated in a pot experiment following amendments of molybdenum compost (1.0 g/ kg) to a Truro sandy loam. Dry-matter yield: up to 25% molybdenum compost, no effect; at the 50% compost treatment dry-matter yield decreased.

pH: 50% compost treatments, soil pH increased an average of 0.5 units.

Extractable molybdenum:

50% compost treatments:

in the growth medium increased the nitric acid extractable molybdenum to 150 mg/ kg and diethylenetriaminepentaacetic acid extractable molybdenum to 100 mg/ kg;

tissue Mo concentration to 569 and 478 mg/ kg in the lettuce and barley.

25% compost treatment:

in the growth medium produced about 55 mg/ kg of total molybdenum;

tissue Mo concentration of 348 mg/ kg in lettuce and 274 mg/ kg in barley without any phytotoxicity.

Kashem, M. A. and Warman, P. R., Effect of High-Molybdenum Compost on Soils and the Growth of Lettuce and Barley, Communications in Soil Science and Plant Analysis, 2009, 40, 2225-2233.

Agriculture molybdenum application lettuce effect on nutrients

Ammonium heptamolybdate, (NH4)6Mo7O24 .4H2O, was applied under greenhouse conditions to head lettuce at doses Mo mg/kg 0, 0.25, 0.5. Nitrogen fertilizerNH4NO3 100 mg/kg phosphorus fertilizer KH2PO4 50 mg/ kg .

With increasing added molybdate

N, P and K contents of head lettuce increased;

Fe, Zn and Mn contents of plant decreased;

Cu content of plant was not affected.

Adiloglu, S., Adiloglu, A., Sumer, A., and Satana, A., Molybdenum Application on the Growth and Nutrient Element Contents of Head Lettuce (Lactuca sativa L.) in Acid Soils, Asian Journal of Chemistry, 2011, 23, 937-938.

Molybdenum and soil

Liming an acid soil increases molybdenum content in the root and leaf of Dutch tomato

Pseudogley is a typical acid soil predominating in Serbia and the wider region. Acid soils are not suitable for the cultivation of agricultural crops due to the hampered uptake of most nutrients owing to increased hydrogen ions.

In order to make pseudogley soil suitable for crop production, pH improvement measures should be employed. Soil acidity was neutralised by liming and the effect was evaluated of soil pH improvement on the Mo content in root and leaf of the Dutch tomato (Lycopericon esculentum Mill.) hybrid Belle planted under controlled conditions on pseudogley soil.

Three liming treatments were employed (1, 3 and 4 t/ha CaCO3). Liming of pseudogley caused an increase of molybdenum ion absorption into the root system of tomato. The root and leaf molybdenum content of tomato in each treatment were very low and insufficient for growth of tomato. To make pseudogley suitable for agricultural production soil pH must be increased and the available molybdenum in the soil.

Djuric, M.; Mladenovic, J.; Radovanovic, B.; Murtic, S.; Acamovic-Djokovic, G.; Pavlovic, R.; Boskovic-Rakocevic, Lj. Effect of liming on the molybdenum content in the root and leaf of tomato grown on pseudogley under controlled conditionsAfrican Journal of Biotechnology, 2011, 10, 83, 19402-19406.

Toxicity of molybdenum to soil organisms

To determine if long-term equilibration may alleviate molybdenum toxicity, earthworms, enchytraeids, collembolans and four plant species were exposed to three soils freshly spiked with sodium molybdate dihydrate, Na2MoO4.2H2O, and equilibrated for 6 or 11 months in the field with free drainage.

Total molybdenum concentrations in soil decreased by leaching, most (up to 98%) in sandy soil and less (54-62%) in silty and clayey soils.

Changes in residual molybdenum toxicity with time were inconclusive in sandy soil. In the other two soils, toxicity of residual total molybdenumwas significantly reduced after 11 months equilibration, with a median 5.5-fold increase in ED50s.

Molybdenumfixation in soil, i.e. the decrease of soil solution molybdenum concentrations at equivalent residual total soil molybdenum , was maximally a factor of 2.1 only.

This experiment shows natural attenuation of molybdate ecotoxicity under field conditions is related to leaching of excess molybdenumand other ions as well as to slow ageing reactions.

van Gestel, Cornelis A M; McGrath, Steve P; Smolders, Erik; Ortiz, Maria Diez; Borgman, Eef; Verweij, Rudo A; Buekers, Jurgen; Oorts, KoenEffect of long-term equilibration on the toxicity of molybdenum to soil organisms.Environmental pollution,2012, 162, 1-7.

Molybdenum in soil applications

Mo in fly ash

The concentrations of As, Cd, Hg, Mo, Ni, and Pb in fly ash are related to the S content of the coal. Generally, those feed coals with a high S content contain higher concentrations of these elements.

Goodarzi, F., Characteristics and composition of fly ash from Canadian coal-fired power plants, Fuel, 2006, 85, 1418-1427

Molybdenum and trace elements in bottom ash and fly ash

Two ash samples were taken from the 77 MW multi-fuel boiler (MFB) at the power plant of Stora Enso Oyj Heinola fluting board mill in Finland. The samples were analysed by X-ray diffraction (XRD) and inductively coupled plasma optic emission spectroscopy (ICP-OES).

Hematite (Fe2O3) and quartz (SiO2) were found in both the bottom ash and fly ash; anorthite (CaAl2Si2O8) and anhydrite (CaSO4) were detected only in the bottom ash.

Element concentrations in the fly ash were higher than in the bottom ash except sulfur which was more concentrated in the bottom ash (8030 mg/kg; d.w.) was than in the fly ash (5380 mg/kg; d.w.).

In the bottom ash, extractable molybdenum (8.2 mg/kg; d.w.) and sulfate (15.900 mg/kg; d.w.) concentrations exceeded the limit values for the acceptance of waste at inert waste landfills.

In the fly ash, the extractable concentration of chromium (1.8 mg/kg; d.w.) and sulfate (7200 mg/kg; d.w.) exceeded the limit values for the acceptance of waste at inert waste landfills. The extractable concentration of molybdenum (37.0 mg/kg; d.w.) exceeded the limit value for the acceptance of waste at non-hazardous waste landfills.

According to a three-stage sequential extraction procedure, in which elements in the bottom ash and fly ash were fractionated between acid-soluble (CH3COOH), reducible (NH2OH-HCl) and oxidisable (H2O2) + CH3COONH4) fractions, the concentrations of most elements were higher in all fractions of the fly ash than those in the bottom ash.

In the bottom ash, the extractable concentration of molybdenum (8.2 mg/kg; d.w.) in the acid-soluble fraction (CH3COOH), was higher than in the fly ash.

Approximately 52.7% of molybdenum in the fly ash was partitioned in the oxidisable fraction. Thus, molybdenum is not considered to be very mobile or bioavailable.

Poykio, R., Manskinen, K., Nurmesniemi, H., and Dahl, O., Comparison of trace elements in bottom ash and fly ash from a large-sized (77 MW) multi-fuel boiler at the power plant of a fluting board mill, Finland, Energy Exploration & Exploitation, 2011, 29, 217-233.

NOTE

From http://www.scotash.com/pdfs/FBA.pdf

Furnace Bottom Ash (FBA) is the coarse ash fraction produced in the furnaces of coal fired power stations when pulverised coal is fed into the boilers and burnt at high temperatures and pressures. [Incinerator bottom ash (IBA) is a form of ash produced in incineration facilities. This material is discharged from the moving grate of municipal solid waste incinerators.] Once combustion has taken place, the finer particles of ash of

Pulverised Fuel Ash (PFA) [Fly Ash: one of the residues generated in combustion, and comprises the fine particles that rise with the flue gases.] are carried out in the flue gases and captured in the precipitators. The coarser material (FBA) drops to the bottom of the boiler into a hopper. It is then removed by high-pressure water and pumped into storage lagoons where it can be dredged, stockpiled and allowed to drain. Chemically, FBA has similar properties to Pulverised Fuel Ash with the three predominant elements being silica, aluminum and iron, the oxides of which together account for approximately 85% of the material. There can be a small percentage of carbon particulate resulting from incomplete combustion, but percentage is low.

MOLYBDATE (?) SOIL

Metals can accumulate in soils amended with biosolids in which metals have been concentrated during wastewater treatment. The goal of this study is to inspect agricultural sites with long-term biosolid application for a suite of regulated and unregulated metals, including some potentially present as commonly used engineered nanomaterials (ENMs). Sampling occurred in fields at a municipal and a privately operated biosolid recycling facilities in Texas. Depth profiles of various metals were developed for control soils without biosolid amendment and soils with different rates of biosolid application (6.6 to 74 dry tons per hectare per year) over 5 to 25 years. Regulated metals of known toxicity, including chromium, copper, cadmium, lead, and zinc, had higher concentrations in the upper layer of biosolid-amended soils (top 0-30 cm or 0-15 cm) than in control soils. The depth profiles of unregulated metals (antimony, hafnium, molybdenum, niobium, gold, silver, tantalum, tin, tungsten, and zirconium) indicate higher concentrations in the 0-30 cm soil increment than in the 70-100 cm soil increment, indicating low vertical mobility after entering the soils. Titanium-containing particles between 50 nm and 250 nm in diameter were identified in soil by transmission electron microscopy (TEM) coupled with energy dispersive x-ray spectroscopy (EDX) analysis. In conjunction with other studies, this research shows the potential for nanomaterials used in society that enter the sewer system to be removed at municipal biological wastewater treatment plants and accumulate in agricultural fields. The metal concentrations observed herein could be used as representative exposure levels for eco-toxicological studies in these soils.

Yang, Y., Wang, Y., Westerhoff, P., Hristovski, K., Jin, V. L., Johnson, M. V., and Arnold, J. G.,Metal and nanoparticle occurrence in biosolid-amended soils, Sci Total Environ, 2014, 485-486, 441.

 

Mo from biosolids application to soil

Metal concentrations (As, Cd, Cu, Pb, Hg, Mo, Ni, Se, and Zn) in soil and bermudagrass [Cynodon dactylon (L.) Pers.] and forage from 10 fields were determined in the following categories of biosolids application: six or more years, less than six years and no applications Soil metal concentrations in all groups were similar to values reported for mineral soils in Georgia. The study indicated that toxic levels of metals had not accumulated in the soils due to long-term biosolids application.

Gaskin, J.W., Brobst, R. B., Miller, W. P., and Tollner, E. W., Long-term biosolids application effects on metal concentrations in soil and bermudagrass forage, Journal of Environmental Quality, 2003, 32, 146-152.

Alkaline-stabilized biosolids

Agricultural utilization of biosolids poses a potential risk to ruminant animals due to transfer of Mo from biosolids to forage to the animal in amounts large enough to suppress Cu uptake by the animal. Alkaline-stabilized biosolids (ASB) must be given particular consideration in assessment of Mo risk because the high pH of these biosolids could increase Mo and decrease Cu uptake by forage legumes. Application of ASB did not detectably increase extractable soil Mo (0- to 15-cm depth), but increased alfalfa Mo uptake in all cuttings. Although ASB increased extractable soil Cu, and alfalfa Cu content the Cu to Mo ratio was decreased by ASB to levels near 3. These results suggest that ASB may have a greater effect on Mo uptake and Cu to Mo ratio of forage legumes than do other biosolids.

Stehouwer, R.C. and Macneal, K. E., Effect of alkaline-stabilized biosolids on alfalfa molybdenum and copper content, Journal of Environmental Quality, 2004, 33, 133-140.

Molybdenum accumulation in plants onbiosolid- amended soils

Accumulation of heavy metals in soils amended with biosolids and the risk of their uptake into different parts of plants are topics of great concern.

This research reports the accumulation of several heavy metals and nutrients in soybeans grown on biosolid-applied soils and the use of remote sensing to monitor the metal uptake and plant stress. Field and greenhouse studies were conducted with soybeans grown on soils applied with biosolids at varying rates.

The plant growth was monitored using Landsat TM imagery in field studies and handheld spectroradiometer in greenhouse studies.

Soil and plant samples were collected and then analyzed for several elemental concentrations.

The chemical concentrations in soils and roots increased significantly with increase in applied biosolid concentrations.

Copper and molybdenum accumulated in the shoots of the metal-treated plants.

The spectral and Landsat TM image analysis revealed that the Normalized Difference Vegetative Index (NDVI) can be used to distinguish the metal stressed plants.

The NDVI showed significant negative correlation with increase in soil Cu concentrations followed by other elements.

The use of remote sensing to monitor soybean stress patterns and indirectly assesses soil chemical characteristics. (C) 2011 Elsevier B.V. All rights reserved

Sridhar, B. B. M., Vincent, R. K., Roberts, S. J., and Czajkowski, K., Remote sensing of soybean stress as an indicator of chemical concentration of biosolid amended surface soils, International Journal of Applied Earth Observation and Geoinformation, 2011, 13, 676-681.

Mo in phosphate fertilisers
SubstanceMo/mg/kg
mean, median
triple superphosphate 8-17, 13
monoammonium phosphate 12-17, 15
diammonium phosphate 10-21, 14
phosphate rock
(Africa,USA,Peru)
2-21, 6

commercial phosphate fertilisers, Iowa USA

Charter, R.A., Tabatabai, M.A., Schafer, J.W., Arsenic, Molybdenum, Selenium, And Tungsten Contents Of Fertilizers And Phosphate Rocks, Communications In Soil Science And Plant Analysis, 1995, 26, 3051-3062.

MOLYBDATE (?) INDUSTRIAL SLUDGE

In France, more than 250 million metric tons of sludges need to be treated each year. These sludges are either dumped on the landfills or reused as secondary resources in order to preserve natural resources. A large portions of these sludges are mineral sludges, originating from metal recycling plants. In order to estimate their metal recovery potential, these mineral sludges were characterized. Four types of mineral sludge samples were collected from a metal recycling plant (3 from the recycling plant storage areas (bulk storage, barrel storage and storage shed) and 1 from the collection basin). The sludges were characterized, wherein the Mo, Ni, Cr, Co, Zn and W content and speciation were quantified. The samples had pH values between 5.9 and 10.3 with organic matter contents varying between 6.3% (storage shed) and 29.5% (bulk storage) (loss on ignition at 500 degrees C). Based on their leaching properties, the four mineral sludge samples (in the case of Mo) and the bulk storage sludge (in the case of Ni and Zn) were classified as potentially hazardous regarding the EN 12457-1 and EN 12457-2 method. Mineralogical results reveal that both bulk storage and the storage shed give the highest contributions to the metal content of the collection basin sample. Sequential extraction of the collection basin samples indicated that Mo is bound to the oxidizable and residual fraction, while Ni, Cr and Co were bound to the residual fraction, and Zn to the soluble acid fraction, respectively. W tends to be equally distributed among all extracted fractions. A strong correlation existed between Mo and Co, as well as between Ni, Zn and Cr, respectively. (C) 2015 Elsevier Ltd. All rights reserved.

Vemic, M., Bordas, F., Guibaud, G., Joussein, E., Labanowski, J., Lens, P. N. L., and van Hullebusch, E. D.,Mineralogy and metals speciation in Mo rich mineral sludges generated at a metal recycling plant, Waste Management, 2015, 38, 303.

 

 

MOLYBDATE (?) INDUSTRIAL SLUDGE

Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed.

Chen, J. Y., Luong, H. V., and Liu, J. C.,Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge, Water Res, 2015.

 

 

Sewage Sludge and municipal wastes

Mo in sewage sludge av 15 mg Mo/kg , range 1 – 40 mg Mo/kg
A.K. Furr, Lawrence, A.W., and Tong, S.S.C., Multielement and chlorinated hydrocarbons analysis of municipal sewege sludges of American cities, Environ. Sci. Technol., 1976, 10, 683 – 687.

Mo uptake from sewage sludge

The use of sewage sludge as a fertiliser continues to be controversial. Sewage sludge, a byproduct of wastewater treatment, consists mainly of human excreta plus inputs from industrial discharges. The sludge is contaminated with metals including Mo. The particular problem with Mo is the Mo-Cu antagonism leading to molybdenosis in cattle and other ruminants. A recent news item (Renner,R., Scientists debate fertilizing soils with sewage sludge, Environmental Science and Technology News, 2000, June 1, 243A) reports a Water Environment Research Foundation study which concludes that the danger to grazing animals associated with sludge derived Mo is small provided the sludge (20 - 30 mg Mo/kg dry weight) is applied at 'reasonable' rates to farms that follow good practice (cutting and drying animal forage before it is eaten, augmenting cattle diets with copper).
On the contrary a paper by McBride et al.(following paragraph) concludes that on pastures of alfalfa and clover Mo in forages can be elevated to 'unacceptable' levels by one or two sewage sludge applications. The McBride paper provides a useful review of Mo in soil and forage as well as results of their detailed study.

Sewage sludges, which are commonly applied to farmlands, can contain Mo in the range 5 - 50 mg Mo/kg.
Mo supplied from sludge is readily taken up by legumes in particular. Excessive uptake into red clover (Trifolium pratense L.) (>30 mg/kg) was seen in a soil that had been heavily amended with sewage sludge 20 y earlier, where the soil contained about 3 mg Mo/kg soil, three times the background soil concentration. Mo can have a long residual availability in sludge amended soils. The effect of sludge application was to decrease Cu to Mo ratios in legume forages, canola (Brassica napus var, napus) and soybeans [Glycine max (L.) Merr,] below the recommended limit of 2:1 for ruminant diets, a consequence of high bioavailability of Mo and low uptake of Cu added in sludge. Molybdenum uptake coefficients for alkaline-stabilized sludge were higher than for dewatered sludge, presumably due to the greater solubility of Mo measured in the more alkaline sludges and soils. Based on these molybdenum uptake coefficients, it is tentatively recommended that cumulative Mo loadings on forages grown on nonacid soils should not exceed
from alkaline-stabilized sludge 1.0 kg Mo/ha
from dewatered sludge 4.0 kg Mo/ha .

McBride, M.B., Richards, B. K., Steenhuis, T., and Spiers, G., Molybdenum uptake by forage crops grown on sewage sludge- amended soils in the field and greenhouse, Journal of Environmental Quality, 2000, 29, 848-854.

Heavy metals in municipal solid waste incineration bottom ash (MSWIBA) may leach into soil and groundwater and pose long-term risks to the environment. Toxicity characteristic leaching procedure (TCLP) was carried out on the MSWIBA from Macao. Heavy metals in leachates were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES), and genotoxicity of leachates was also evaluated by micronucleus (MN) assay with Vicia faba root tip cells.

Concentrations of aluminium (Al), manganese (Mn), cobalt (Co), cadmium (Cd) and mercury (Hg) in the leachates were less than 0.01 mg l(-1), and those of iron (Fe), copper (Cu) and molybdenum (Mo) were less than 0.1 mg l(-1) The concentrations of chromium (Cr), zinc (Zn), selemium. (Se), strontium (Sr), barium (Ba) and caesium (Cs) were between 0.11 mg l(-1) and 2.19 mg l(-1). Lead (Pb) concentrations, in particular, reached as high as 19.6 mg l(-1), significantly exceeding the maximum concentration limit (5 mg l(-1) for lead by TCLP).

Compared with the negative group, a significant increase of MN frequencies was observed in the leachate-exposed groups (P < 0.05).

With the increase of heavy metals in the leachates, the toxic effects on the Vicia faba root tip cells increased, implying that heavy metals were the main factors causing the genotoxic effects.

Apart from chemical analysis, bioassays like the MN assay of Vicia faba root tip cells should also be included in a battery of tests to assess the eco-environmental risks of bottom ashes before decisions can be made on the utilization, treatment or disposal.

Feng, S. L., Wang, X. M., Wei, G. J., Peng, P. G., Yang, Y., and Cao, Z. H., Leachates of municipal solid waste incineration bottom ash from Macao: Heavy metal concentrations and genotoxicity, Chemosphere, 2007, 67, 1133-1137.

Molybdenum in sediments

This paper presents the results of measurements of the Mo isotopic composition in the bottom sediments (BS) of freshwater basins. Mo isotopic ratios were measured using a multicollector inductively coupled plasma mass spectrometer (MC ICP MS).

Malinovskii, D. N., Rodyushkin, I. V., and Ohlander, V., Determination of the isotopic composition of molybdenum in the bottom sediments of freshwater basins, Geochemistry International, 2007, 45, 381-389.

In one perennially oxic and three seasonally anoxic lakes in Eastern Canada the authors measured

  • in sediment porewater the vertical distributions of Mo, Fe; Mn, sulfide, sulfate, organic carbon, major ions, and pH
  • in sediment cores from the same sites Mo, acid volatile sulfide, Fe, Mn, Al, organic C, Pb-210 and Cs-137.

The only input of anthropogenic Mo to these lakes comes from atmospheric deposition.

In the porewater of three seasonally anoxic basins the distribution of Mo was relatively monotonous: Mo is not redistributed in the sedimentary column during periods of anoxia.

In the porewater in a perennially oxic basin Mo profiles obtained at three sampling dates display sharp Mo peaks below the sediment-water interface, indicating redistribution subsequent to deposition. Diagenetic modeling of these latter porewater Mo profiles reveal that

  • Mo is released at 1-2 cm depth as a consequence of the reductive dissolution of Fe oxyhydroxides
  • scavenged both at the vicinity of the sediment-water interface, by re-adsorption onto authigenic Fe oxyhydroxides, and deeper in the sediments where dissolved sulfide concentrations are higher.

The estimated rate constant for the adsorption of Mo onto Fe oxyhydroxides is 36 ± 45 cm3mol-1s-1.

In sediments of the perennially oxic basin diagenetic modeling indicates that authigenic Mo represents about one-third of the total solid phase Mo in the first cm below the sediment-water interface and only one tenth below this horizon.

The sediment Mo concentrations are up to 3-16 times higher than the average lithogenic composition, depending on the lake. SedimentMo is mainly due to atmospheric deposition of anthropogenic Mo and not to the formation of authigenic Mo phases if it is assumed that no authigenicMo is accumulated in the seasonally anoxic lake sediments.

Reconstructed historical records of the atmospheric Mo deposition indicate maximum values in the 1970s and 1980s and significant decreases since then.

Emissions to the atmosphere associated with the smelting of non-ferrous ores and coal combustion appear to be the most important sources of anthropogenic Mo.
[Anthropogenic: derived from human activities.

Diagenesis: any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification.

Authigenic: of minerals, formed in place, rather than having been transported and deposited there.

Lithogenic:coming from rock.]

Chappaz, A., Gobeil, C., and Tessier, A., Geochemical and anthropogenic enrichments of Mo in sediments from perennially oxic and seasonally anoxic lakes in Eastern Canada, Geochimica et Cosmochimica Acta, 2008, 72, 170-184.

Molybdenum is a trace metal used as a marker of paleoredox conditions of ancient depositional settings.

Pyrite is an important molybdenum host for enriched sedimentary rocks.

The relationship between Mo and pyrite in the Bancs Jumeaux Formation, a Jurassic succession in northern France consisting of limestone and pyrite-rich marls, has been studied. This formation is enriched in Mo compared to other redox-sensitive trace metals.

Their approach is grounded on bulk rock chemical analysis and delineation of two contrasting types of pyrite that can be extracted from the rocks: polyframboids and nonframboidal concretionary masses.

The morphological characteristics of both morphotypes were studied using scanning electronic microscopy. The polyframboids are richer in Mo than the concretions but are not markedly enriched in other trace metals. This discrepancy in geochemical composition could result from pyrite precipitation at different times during early diagenesis.

Their results indicate that the polyframboids would have formed very early in reducing "microniches", within dominantly dysoxic sediment. This early pyrite precipitation occurred at shallow depth below the sediment-water interface close to the abundant Mo source in overlying oxic seawater (molybdate ions), and would have fostered Mo-capture by the polyframboids in relatively large amounts. The concretions would have formed later during early diagenesis (within the sulfidic zone) under conditions of more limited Mo availability

Tribovillardi, N., Lyons, T. W., Riboulleau, A., and Bout-Roumazeilles, V., A possible capture of molybdenum during early diagenesis of dysoxic sediments, Bulletin de la Societe Geologique de France, 2008, 179, 3-12.

MOLYBDATE (?) SEDIMENTS

This research focuses on determination of the mineralogical composition, geochemical characteristics and evaluationof pollution status of the Makirina Bay sediments. Calculated enrichment factor (EF) values show no enrichment (< 1) for Cd, Ni, and Zn, minor enrichment (< 3) for As, Cu, and Pb, and minor to moderate enrichment for Mo. The resultsof the sequential leaching procedure for the aforementioned potentially toxic elements (PTE) indicates that the mobilityand bioavailability characteristics of the PTE studied declined in the following order: Mo > Cd > Pb > Ni > Zn > Cu > As. Principal component analysis (PCA) and correlation analysis confirmed the PTE distribution depends mainly on thegeogenic mineral components and anthropogenic activities in the areas surrounding the bay. Calculated transfer factor(TF) values from sediment to seagrass Cymodocea nodosa (C. nodosa) were < 1, showing that despite the results of thesequential extraction procedure, PTE transfer from sediment to roots was not effective.

Darja, K., Matej, D., Zivana, L. B., Slavica, M. S., Sonja, L., Goran, K., Petra, V., Tadej, D., and Nastja, R. S.,Geochemical characterization and environmental status of Makirina Bay sediments (northern Dalmatia, Republic of Croatia), Geologia Croatica, 2015, 68, 79.

 

Molydenum isotopes in black shales - redox evolution of the Earth's oceans

The first complete suite of molybdenum isotope fractionation observations is reported for a sulfidic water column and sediment system, the meromictic Lake Cadagno, Switzerland, a small alpine lake with a pronounced oxygen-sulfide transition reaching up to H2S ca 200 microM in the bottom waters (or about 300 microM total sulfide: ΣS2- = H2S + HS- + S2-).

Molybdenum isotope studies in black shales can provide information about the redox evolution of the Earth's oceans, provided the isotopic consequences of molybdenum burial into its major sinks are well understood.

Previous applications of the molybdenum isotope paleo-ocean redox proxy assumed quantitative scavenging of molybdenum when buried into sulfidic sediments.

Molybdenum behaves conservatively in the oxic zone and non-conservatively in the sulfidic zone, where dissolved molybdenum concentrations decrease from 14 nM to 2-8 nM across this transition.

Dissolved molybdenumin the upper oxic waters has a δ98Mo (oxic) = 0.9 ± 0.1 parts per thousand, which matches that of the riverine input, δ98Mo (river) = 0.9 ± 0.1 parts per thousand.

In the deeper sulfidic waters, a subaquatic source delivers molybdenum at 1.55 ± 0.1 parts per thousand, but the dissolved Mo is even heavier at δ98Mo (sulfidic) = 1.8 parts per thousand. Sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in molybdenum with depth, with de δ98Mo values significantly fractionated at -0.8 parts per thousand to -1.2 parts per thousand both near the chemocline and in the deepest trap.

Suspended particulates in the sulfidic waters carry lighter molybdenum than the ambient dissolved molybdenum pool by ca 0.3-1.5 parts per thousand.

Sedimentary molybdenumconcentrations correlate with total organic carbon and yield molybdenum levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area.

Solid-phase molybdenum in the sediment shows a slightly positive δ98Motrend with depth, from δ98Mo= 1.2 parts per thousand to 1.4 parts per thousand

while the pore waters show dramatic enrichments of molybdenum (>2000 nM) with a relatively light isotope signature of δ98Mo= 0.9-1.0 parts per thousand.

These data are explained if molybdenum is converted to particle-reactive oxothiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles. Isotope fractionation is expressed in the water column, despite the high sulfide concentrations, because the rate of molybdenum removal is fast compared to the slow reaction kinetics of thiomolybdate formation. However, elemental and isotopic mass balances show that molybdenum is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water. This efficient molybdenum drawdown is expected to occur in settings where H2S is very much in excess over molybdenum or in a restricted setting where the water renewal rate is slow compared to the molybdenum burial rate.

A model for the molybdenum isotope fractionation in sulfidic systems is presented.

Dahl, T. W., Anbar, A. D., Gordon, G. W., Rosing, M. T., Frei, R., and Canfield, D. E., The behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic Lake Cadagno, Switzerland, Geochimica et Cosmochimica Acta, 2010, 74, 144-163.

Molybdenum isotopes weathering

Pearce, C. R., Burton, K. W., von Strandmann, P. A. E. P., James, R. H., and Gislason, S. R., Molybdenum isotope behaviour accompanying weathering and riverine transport in a basaltic terrain, Earth and Planetary Science Letters, 2010, 295, 104-114.

E. Germany

The Malter Reservoir is about 30 km south of Dresden (eastern Germany) in a historical mining area of the eastern Erzgebirge. Within the whole core recovered from the deepest point of the lake, heavy metals are strongly enriched (parentheses refer to enrichment factors as compared with average shale): cadmium (290), silver (140), bismuth (90), antimony (25), lead (21), zinc (14), tin (13), uranium (9), tungsten (9), molybdenum (5), copper (4), thallium (3) and chromium (2). Enrichments are detectable for the whole registered time-period of 81 years. Peaks of up to 27 mg/kg silver, 37 mg/kg bismuth, 91 mg/kg cadmium, 410 mg/kg chromium, 240 mg/kg copper, 20 mg/kg molybdenum, 14000 mg/kg phosphorus, 740 mg/kg lead, 6,5 mg/kg antimony, 74 mg/kg tin, 52 mg/kg tungsten and 1900 mg/kg zinc reflect local events caused by human impact.

Muller, J., Ruppert, H., Muramatsu, Y., and Schneider, J., Reservoir sediments - a witness of mining and industrial development (Malter Reservoir, eastern Erzgebirge, Germany), Environmental Geology, 2000, 39, 1341-1351.

British Columbia

Sediment geochemical patterns in lakes in British Columbia are strongly influenced by proximity to Mo mineralization, with the highest Mo concentrations (max: 165 ppm) downslope of known prospects. Elevated centre-basin Mo concentrations of at least 12 ppm reflect the presence of adjacent porphyry Mo mineralization. Sediments at Tatin, Hanson and the Counts Lakes contain elevated median Mo concentrations of 8 ppm (max: 23 ppm), 7 ppm (max: 55 ppm) and 42 ppm (max: 165 ppm), respectively, relative to regional background of 1-2 pm. Mo Centre-basin results from Tatin Lake (12, 7-10, 23 ppm), Hanson Lake (11-12 ppm) and the Counts lakes (49, 160, 60, 33, 38, 56, 54, 83 ppm) exceed regional background by 3-80x.

Cook, S.J., Distribution and dispersion of molybdenum in lake sediments adjacent to porphyry molybdenum mineralization, central British Columbia, Journal of Geochemical Exploration, 2000, 71, 13-50.

The concentrations of dissolved trace elements (Li, B, Mn, Cu, As, Rb, Sr, Mo, Cd, Ba, Pb) in the Marne and Seine rivers in the Paris urban area were monitored over a 2-year period. Dissolved Mn, Cu and Cd increased rapidly in summer, whereas the concentration of Mo decreased. These variations were attributed to redox processes. During summer when the dissolved oxygen concentrations decrease, Mn, Cu, Cd and Pb are released into solution whereas Mo is immobilised.

Elbaz-Poulichet, F., Seidel, J. L., Casiot, C., and Tusseau-Vuillemin, M. H., Short-term variability of dissolved trace element concentrations in the Marne and Seine Rivers near Paris, Science of the Total Environment, 2006, 367, 278-287.

Fe, Mn, Cu, Zn, Mo and Cr were determined in May 2002 at 25 locations in the sediments of Laguna Caren. Mo showed homogeneous concentrations at all stations, with average level 160 mu g/g dry weight. High Cu/Fe and Mo/Fe ratios indicate the accumulation of these metals in sediments. Cu and Mo were found to be mainly associated to the organic matter-sulfides fraction

Pizarro, J., Rubio, M. A., Henriquez, J., and Gonzalez, M., Metals in sediments of an urban shallow lake in Santiago (Chile), Fresenius Environmental Bulletin, 2006, 15, 524-529.

Molybdenum isotopic composition in the bottom sediments (BS) of freshwater basins.

This paper presents the results of measurements of the Mo isotopic composition in the bottom sediments (BS) of freshwater basins. Mo isotopic ratios were measured using a multicollector inductively coupled plasma mass spectrometer (MC ICP MS).

Malinovskii, D. N., Rodyushkin, I. V., and Ohlander, V., Determination of the isotopic composition of molybdenum in the bottom sediments of freshwater basins, Geochemistry International, 2007, 45, 381-389.

Molybdenum Concentrations in Soils
CountrySoil typeMedian Concentration/ppm
[1] Soil 0.2 - 5
[1] Igneous rocks 1.5
[1] Shales 2.6
[1] Sandstones 0.2
[1] Limestones 0.4
[2] Coal 10
Canada[3] Calcareous 6.0
Western US[1] Calcareous 6.0
Eastern US[3] Acidic 0.5
Irish Cattle Farms[4] dry mass 0.03 - 6.5mg/kg
British Columbia[5] dry mass 24 microg/g
World maximum[6] dry mass 17 microg/g

[1] Kubota, J., Molybdenum Status of United States Soils and Plants, in: Chappell, W. R. and Petersen, K. K. (ed.), Molybdenum in the Environment, 1977, 2, Ch. 6. Marcel Dekker, New York.
[2] Stone, L. R., Erdman, J. A., Fedder, G. L. and Holland, H. D., Molybdenum in an Area Underlain with Uranium Bearing Lignites in the Northern Great Plains, J. Range Manag. ,1983, 36, 280.
[3] Boila, R. J., Devlin, T. J., Drysdale, R. A. and Lillie, L. E., The Severity of Hypocupremia in Selected Herds of Beef Cattle in Northwestern Manitoba, Can. J. Anim. Sci., 1984a, 64, 899.
Boila, R. J., Devlin, T. J., Drysdale, R. A. and Lillie, L. E. (1984b), Geographic Variation in the Copper and Molybdenum Contents of Forages Grown in Northwest Mantiboa (Canada), Can. J. Anim. Sci. , 1984b, 64, 919.
[4] Mee, J.F., Rogers, P.A.M., Prevalence Of Iodine, Selenium, Copper And Cobalt Deficiencies On Irish Cattle Farms, Irish Veterinary Journal, 1996, 49, 160.
[5] Depieri, L.A., Buckley, W.T., Kowalenko, C.G., Micronutrient Concentrations Of Commercially Grown Vegetables And Of Soils In The Lower Fraser Valley Of British-Columbia, Canadian Journal Of Soil Science, 1996, 76, 173-182.
[6] Kabata-Pendias, A.and Pendias, H., Trace elements in soils and plants, CRC Press, Second edition, 1992.

Mo in soil
Av 1 –2 mg Mo/kg

Jarrell, W.M., Page, A.L, and Elseewi, A.A., Molybdenum in the environment, Residue Rev., 1980, 7, 41 – 43.

Mo-deficient < 0.2 mg Mo/kg
Mo-excessive > 0.7 mg Mo/ kg

Lener, J., Bibr, B., Effects of molybdenum on the organism, J. Hyg. Epidemiol. Microbiol. Immunol., 1984, 4, 405 – 419.

Molybdenum in barley on fly ash treated soil

A clay loam topsoil that tends to form surface crusts was mixed with unweathered fly ash from a western Canada coal burning power plant in mixtures ranging from 0 to 100% fly ash (v/v). Fly ash increased plant Mo concentrations to alter Cu/Mo such that it could be a concern for ruminant diets.

Sale, L.Y., Naeth, M.A., Chanasyk, D.S., Plant And Environment Interactions - Growth-Response Of Barley On Unweathered Fly Ash-Amended Soil, Journal Of Environmental Quality, 1996, 25, 684-691

Molybdenum and Cu in barley grown on fly ash treated soils
Fly ash/%Mo/mg kg-1Cu/mg kg-1
 SilageGrainStrawSilageGrainStraw
0 0.02 0.02 0.02 4.33 3.73 2.67
6.25 3.67 0.02 5.33 7.47 4.77 5.67
12.5 7.33 3.33 15.67 8.33 8.83 7.13
25 12.33 4.00 21.33 7.90 6.23 9.77

Clay loam topsoil mixed with unweathered fly ash from a western Canada coal burning power plant in mixtures ranging from 0 to 100% fly ash (v/v).

Sale, L.Y., Naeth, M.A., Chanasyk, D.S., Plant And Environment Interactions - Growth-Response Of Barley On Unweathered Fly Ash-Amended Soil, Journal Of Environmental Quality, 1996, 25, 684-691.

Trace elements including molybdenum in industrially contaminated soils in India

The concentrations were determined of heavy metals (As, Ba, Co, Cr, Cu, Ni, Mo, Pb, Sr, V and Zn) in soils around Manali industrial area in Chennai, Southern India having petrochemicals, refineries, and fertilizers generating hazardous wastes. There were elevated concentrations of chromium (149.8-418.0 mg/kg), copper (22.4-372.0 mg/kg), nickel (11.8-78.8 mg/kg), zinc (63.5-213.6 mg/kg) and molybdenum (2.3-15.3 mg/kg).

Krishna, A.K. and Govil, P. K., Assessment of heavy metal contamination in soils around Manali industrial area, Chennai, Southern India, Environmental Geology, 2008, 54, 1465-1472.

Polish Soil Quality Standards Versus Risk-Based Soil Screening Levels for Metals and Arsenic

The main objective of the study was derivation of risk-based soil screening levels (RBSSLs) under two basic exposure scenarios-industrial and residential, and their comparison with the relevant soil quality standards (SQSs), applied in Poland as remedial targets. The RBSSLs were derived from standardized sets of equations that are based on the recently updated U. S. Environmental Protection Agency's human health risk assessment methods. The article presents the results concerning 12 contaminants listed in the SQS ordinance: arsenic, barium, cadmium, cobalt, chromium, copper, mercury, molybdenum, nickel, lead, tin, and zinc. Taking only the human health protection criterion into account, most of SQSs for non-carcinogenic metals under both industrial and residential scenarios seem to be too stringent if used as the remedial levels, which may lead to unnecessary remediation. On the other hand, the SQSs for carcinogenic contaminants (As, Cr(VI)) correspond to cancer risk levels significantly higher than the acceptable level of 1E-06. The findings of the study may constitute the first step to justify the amendment of the Polish SQS ordinance aimed at establishing the new soil quality values based on clearly defined criteria

Wcislo, Eleonora, Polish Soil Quality Standards Versus Risk-Based Soil Screening Levels for Metals and Arsenic, Human and Ecological Risk Assessment, 2012, 18, 569-587.

Industrial Wastes - spent catalysts

Spent catalysts hazardous waste

Bioleaching of nickel, vanadium and molybdenum from hazardous spent refinery hydroprocessing catalysts by means of iron/sulfur oxidizing bacteria

Spent catalysts represent a large amount of refinery solid waste. These wastes have been classified as hazardous by the US Environmental Protection Agency. Hydroprocessing catalysts contain valuable base metals, nickel, vanadium and molybdenum. The exhaust catalyst was rich in nickel (45 mg/g), vanadium (44 mg/g) and molybdenum (94 mg/g). Before bioleaching, the solid was washed with Tween 80 and ethyl alcohol for hydrocarbon removal. Iron(II) was essential for metal extraction and for bacteria adaptation. In the presence of iron 83% nickel and 90% vanadium were bioleached but only 50% extraction with iron absent. For molybdenum, the highest extraction was about 50% after 26 days bioleaching in the presence of iron and 25 % extraction without iron.

Beolchini, F., Fonti, V., Ferella, F., Centofanti, M., and Veglio, F., Bioleaching of nickel, vanadium and molybdenum from spent refinery catalysts, J. Advanced Materials Research, Biohydrometallurgy, 2009, 71 - 73, 657-660.

Road dust Tunnel and road dusts in Houston, Texas - anthropogenic metals from motor vehicles

Platinum group elements (PGEs) including Rh. Pd, and Pt are important tracers for vehicular emissions, though their measurement is often challenging and difficult to replicate in environmental campaigns. These challenges arise from sample preparation steps required for PGE quantitation, which often cause severe isobaric interferences and spectral overlaps from polyatomic species of other anthropogenically emitted metals. Consequently, most previous road dust studies have either only quantified PGEs or included a small number of anthropogenic elements. Therefore a novel analytical method was developed to simultaneously measure PGEs, lanthanoids, transition and main group elements to comprehensively characterize the elemental composition of urban road and tunnel dusts.

Dust samples collected from the vicinity of high-traffic roadways and a busy underwater tunnel restricted to single-axle (predominantly gasoline-driven) vehicles in Houston, TX were analyzed for 45 metals with the newly developed method using dynamic reaction cell-quadrupole-inductively coupled plasma-mass spectrometry (DRC-q-ICP-MS).

Average Rh, Pd and Pt concentrations were 152 +/- 52, 770 +/- 208 and 529 +/- 130 ng g-1 respectively in tunnel dusts while they varied between 6 and 8 ng g-1, 10 and 88 ng g-1 and 35 and 131 ng g-1 in surface road dusts. Elemental ratios and enrichment factors demonstrated that PGEs in dusts originated from autocatalyst attrition/abrasion.

Strong evidence is also presented for mobile source emissions of Cu, Zn, Ga, As, Mo, Cd, Sn, Sb, Ba, W and Pb.

However, all other elements including rare earths most likely arose from weathering, erosion and resuspension of crustal material.

These are the first such detailed measurements in Houston, the largest city in TX and fourth largest in the United States. We posit that such investigations will assist in better understanding PGE concentrations in urban environments while providing elemental data necessary to better understand anthropogenic influences on their biogeochemical cycling. (C) 2012 Elsevier B.V. All rights reserved

Spada, Nicholas, Bozlaker, Ayse, and Chellam, Shankararaman, Multi-elemental characterization of tunnel and road dusts in Houston, Texas using dynamic reaction cell-quadrupole-inductively coupled plasma-mass spectrometry: Evidence for the release of platinum group and anthropogenic metals from motor vehicles, Analytica Chimica Acta, 2012, 735, 1-8.

Dust

Chemical composition of PM10 in Switzerland: An analysis for 2008/2009 and changes since 1998/1999

In this study, the chemical composition of PM10 at various sites in Switzerland during a one year period in 2008/2009 and changes since the time of a similar characterisation campaign in 1998/1999 are investigated.

The concentrations of main components of PM10 were found to be similar at different site types north of the Alps (i.e. urban background, suburban and rural sites).

Secondary inorganic PM10 components (nitrate, sulphate and ammonium) constituted the largest PM10 mass fraction, followed by carbonaceous matter (OM and EC), while the abundance of mineral dust and trace elements was small (both <10%).

At a rural site south of the Alps the concentrations of secondary inorganic components were much lower and the concentrations of OM and EC clearly higher than north of the Alps.

Enhanced concentrations of EC, trace elements and to a lesser extent of OM and mineral dust were found at an urban roadside site. At this site, typical traffic related trace elements like Cu, Fe, Mo, Sb and Ba were highly enriched.

This paper indicates clear positive effects of emission reduction strategies for PM10 and precursors implemented during the past ten and more years.

The concentrations of sulphate and EC declined during the considered time period, EC reductions were especially strong at the urban roadside site (-2.4 mu g m-3).

In contrast, the concentration of nitrate slightly increased at all of the considered sites (0.2-0.5 mu g m-3.

Large reductions in the concentrations of many trace elements in PM10 during the past ten years are evident. As an example, the observed relative decrease of Pb is about -80%, which is a success of the ban of leaded gasoline in Switzerland and in the EU. (C) 2012 Elsevier Ltd. All rights reserved

Gianini, M. F. D., Gehrig, R., Fischer, A., Ulrich, A., Wichser, A., and Hueglin, C., Chemical composition of PM10 in Switzerland: An analysis for 2008/2009 and changes since 1998/1999, Atmospheric Environment, 2012, 54, 97-106.

[PM10: particulate matter with an aerodynamic diameter below 10 μm (PM10). See Swiss Agency for the Environment,Forests and Landscape SAEFL, ENVIRONMENTAL DOCUMENTATION No. 169.

Atmospheric particulate matter (PM) collected on air filters. Mean annual concentrations (ng m-3) Mo: Urban Roadside Mo 4.37, Urban background 1.16, Suburban 0.53, Rural 0.25 0.85. Associated with non-exhaust road traffic emissions due to abrasion of brake wear (Ba, Cr, Cu, Mo, Sb and Fe).Elements reported to beemitted by abrasion of brake and tyre wear Mo, Sb, Cu, Ba and Zn.]