Industrial and Environmental Exposure of Humans

Humans are exposed to molybdenum compounds in industrial operations and in the environment. As with other elements maximum exposure limits for molybdenum are laid down in government legislation and regulatory controls. The limits may vary from country to country and are not always consistent. The basis for the limits is not always clear. Here we list the regulatory limits, the natural levels of molybdenum and the levels derived from industrial activity including mining.

Workplace exposure to molybdenum and molybdenum compounds and regulatory limits

Regulatory limits are listed in a number of publications. Useful summaries are at

http://www.3rd1000.com/elements/Molybdenum.htm#RegulatoryHealth
http://nj.gov/health/eoh/rtkweb/documents/fs/0105.pdf

We take as an example regulatory data from the United States. Other data are listed later in this section.

Note that the values are listed on the basis of the molybdenum content of a substance.

In the United States the National Institute for Occupational Safety and Health (NIOSH) conducts studies of workplace hazards and proposes standards to the Federal Occupational Safety and Health Administration (OSHA), which adopts and enforces health and safety standards.

The OSHA legal airborne Permissible Exposure Limit (PEL) for insoluble molybdenum compounds, expressed as the eight-hour Time Weighted Averages (TWA,average value of exposure over the course of an 8 hour work shift), is15 mg Mo/m3 (date last revised 09/06/2012) (http://www.osha.gov/dts/chemicalsampling/data/CH_255100.html and for soluble compounds is 5 mg/m3 (revision date:01/15/1993) (http://www.osha.gov/dts/chemicalsampling/data/CH_255100.html).

The American Conference of Governmental Industrial Hygienists (ACGIH) publishes guidelines called threshold limit values (TVLs) for exposure to workplace chemicals, the respirable fraction averaged over an eight hour work shift. The TLV for molybdenum compounds is 0.5 mg (Mo)/m3.

The National Institute for Occupational Safety and Health (NIOSH) publishes Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs). For soluble molybdenum compounds a revised IDLHis 1,000 mg Mo/m3 (May 1994).

A background account of molybdenum PELs and TLVs is in Hamilton and Hardy’s Industrial Toxicology 2015 p. 170. Quote:

‘The permissible exposure limit (PEL) values are established by the Occupational Safety and Health Administration (OSHA) and the threshold limit values (TLV) are set by the ACGIH. The PEL for insoluble molybdenum compounds (e.g. molybdenum disulphide), molybdenum dioxide and metallic molybdenum) is 15 mg/m3 total dust and 5 mg/m3 for respirable dust (OSHA 2008). These values were promulgated in 1971 as part of the original establishment of the OSHA, and have not changed (Federal Register, 1971). The ACGIH TLV for insoluble molybdenum is 10 mg/m3 total dust and 3 mg/m3 respirable dust. The TLV for insoluble molybdenum compounds is based on ACGIH’s intent to bring TLV values for low toxicity, poorly absorbed materials into agreement with each other. The TLV for soluble molybdenum compounds of 0.5 mg/m3 (respirable fraction) is based on the NTP (1979) inhalation study of molybdenum trioxide wherein the observed no effect level was 10 mg/m3 (ACGIH, 2008). Several safety factors were then incorporated for the development of this criterion.’

Workplace Exposure TLV-TWA USA

Workplace Exposure TLV USA
MaterialTLV-TWA /mg m-3
Soluble Mo
respirable particulate

0.5
Insoluble Mo
inhalable particulate
respirable particulate

10
3

Threshold Limit Values and Biological Exposure Indices for 2001: American Conference of Governmental Industrial Hygienists (ACGIH), Cincinatti, Ohio, 2001.

Notes

The number of workers in the United States potentially exposed to molybdenum trioxide during the years 1981 to 1983 was approximately 17,072

National Occupational Exposure Survey (NOES): National Institute for Occupational Safety and Health (NIOSH), 1995.

Occupational standards of exposure established by the Occupational Safety and Health Administration (OSHA) are 5 mg/m3 for soluble molybdenum compounds and 15 mg/m3 for insoluble molybdenum compounds

Hammond, P.B. and Beliles, R.P. Metals. In Casarett and Doull's Toxicology:The Basic Science of Poisons ,ed. Doull, J., Klaasen C. D. and Amdur, M. O., Macmillan, New York, 2nd Ed. 1980, 409.

The American Conference of Governmental Industrial Hygienists [ACGIH, 1995, 2001] recommends a threshold limit value-time-weighted average of  0.5 mg/m3 for soluble molybdenum compounds and 10 mg/m3 for insoluble molybdenum.

Maximum Allowable Concentration (MAC) Limits for Insoluble and Soluble Molybdenum Compounds

Maximum Allowable Concentration (MAC) Limits for Insoluble and Soluble Molybdenum Compounds
CountryMAC Limit (mg/m3) 
Insoluble molybdenum compounds
Holland 10 (mean)  
Romania 5 (mean)  
Germany 15 (mean)  
Russia (USSR), Hungary, Bulgaria 6 (peak)  
USA 20 (peak) 10 as TWA
Soluble molybdenum compounds
Holland 5 (mean)  
Romania 2 (mean)  
Germany, USA, Austria, Belgium, Italy 5 (mean)  
Russia (USSR), Bulgaria, Poland 4 (peak)  
Romania, USA 10 (peak) 5 as TWA

ILO, Occupational Exposure Limits, 2nd (revised) Ed., Occupational Safety and Health Series, 1980, 37, ILO Geneva.

Molybdenum Regulatory Limits International

Molybdenum Regulatory Limits
Process or materialLimitUnitsAveraging periodSource of limit
Air emission
Dust collectors 15 mg Mo dust/m3   Holland-permit
Calciner dust collector 0.126 kg Mo oxide/h   Holland-permit
Dryer dust collector 0.024 kg ADM/h   Holland-permit
As dust 10 mg/m3   NER (Dutch emission guidelines)
Soluble compounds 5 mg Mo/m3   UK Health and Safety Executive
Insoluble compounds 10 mg Mo/m3   UK Health and Safety Executive
Exhaust air from production plants 5 mg Mo/m3 0.5 - 3 h total Austria
For non-ferrous metals after filter stations 0.2 mg Mo/m3 0.5 - 3 h Austria-regional authority
Soluble Mo TLV 5 mg Mo/m3 0.5 - 3 h Austria
Insoluble Mo TLV 15 mg Mo/m3 0.5 - 3 h Austria
Water quality
Drinking 0.07 mg/l   Austria-WHO guideline
  0.01 mg/l   Chile-N Ch 1333 - 1978
Industrial 1 - 2 kg/day   Holland-permit
  5 mg/l   Austria-country
  5 mg/l 2 h average Germany-municipal authorities
Ground 300 mg/l   Holland-intervention values
  5 ppm   Holland-authorisation
  none     Belgium-80/68/EEC
  0.1 mg/l   US EPA
  0.07 mg/l   Japan
target limit 5 mg/l   Belgium-MILBOWA (DBO 07494013)
intervention limit 300 mg/l   Belgium-MILBOWA (DBO 07494013)
Soil
soil sanitation 200 mg/kg   Holland-intervention values
arableland pastures 10 mg/kg dry   Austria-TLV
  30 kg/ha   Austria-TLV
  3 g/m2   Austria-TLV
target limit 10 mg/kg dry   Belgium-MILBOWA (DBO 0749013)
intervention limit 200 mg/kg dry   Belgium-MILBOWA (DBO 0749013)
emission limit 150 mg/kg dry   Belgium-MILBOWA (DBO 0749013)
Solid waste
waste 5000 mg/kg   Holland-(BAGA)
to landfill 50 mg/l   Germany-approval DIN 38414
landfill leachate limit 125 mg/kg dry   OVAM proposals to Belgium Government
leachate limit 35 mg/m2   OVAM proposals to Belgium Government
  150 mg/m3/100y   Belgium-NEM 7340 Decision 23/11/95
sludge from dredging 10 mg/kg dry   Belgium-Decision 25/11/93
fly ash leachate limit 3 mg/kg   Belgium- NEM 7343 Decision 20/1/93
Sewage sludge
agricultural disposal 20 mg/kg dry   Austria
  0.5 mg/l   Chile
land application ceiling concentration 75 mg/kg   US EPA
Milk
  0.2 mg/kg   Austria

Data assembled by IMOA Health and Safety Committee, 1999.

Health surveillance study of workers who manufacture multi-walled carbon nanotubes

While many in vivo and in vitro toxicology studies of multi-walled carbon nanotubes (MWCNTs) have already indicated that exposure to MWCNTs can potentially induce health effects in humans, the actual health effects of MWCNTs among exposed workers are not yet known. Moreover, the levels of exposure and internal doses of MWCNTs are becoming more and more important for estimating the health effects resulting from exposure to MWCNTs. However, information on biomonitoring and exposure to MWCNTs remains limited. Therefore, the authors conducted a health surveillance study in a workplace that manufactures MWCNTs, including assessment of the personal and area exposure levels to MWCNTs, a walk-through evaluation of the manufacturing process, and collection of blood and exhaled breath condensates (EBCs) from the MWCNT manufacturing and office workers. In addition, a pulmonary function test was also conducted on the MWCNT manufacturing workers (9) and office workers (4). The worker exposure to elemental carbon was found to be 6.2-9.3 mug/m3 in the personal samplings and 5.5-7.3 mug/m3 in the area samplings. Notwithstanding, the workers exhibited a normal range of hematology and blood biochemistry values and normal lung function parameters. When analyzing the EBCs, the malondialdehyde (MDA), 4-hydroxy-2-hexenal (4-HHE) and n-hexanal levels in the MWCNT manufacturing workers were significantly higher than those in the office workers. The MDA and n-hexanal levels were also significantly correlated with the blood molybdenum concentration, suggesting MDA, n-hexanal and molybdenum as useful biomarkers of MWCNT exposure.

Lee, J. S., Choi, Y. C., Shin, J. H., Lee, J. H., Lee, Y., Park, S. Y., Baek, J. E., Park, J. D., Ahn, K., and Yu, I. J.,Health surveillance study of workers who manufacture multi-walled carbon nanotubes, Nanotoxicology, 2015, 9, 802-11.

Molybdenum trioxide (?) welding fumes

Studies in the field of environmental epidemiology indicate that for the adverse effect of inhaled particles not only particle mass is crucial but also particle size is. Ultrafine particles with diameters below 100 nm are of special interest since these particles have high surface area to mass ratio and have properties which differ from those of larger particles. In this paper, particle size distributions of various welding and joining techniques were measured close to the welding process using a fast mobility particle sizer (FMPS). It turned out that welding processes with high mass emission rates (manual metal arc welding, metal active gas welding, metal inert gas welding, metal inert gas soldering, and laser welding) show mainly agglomerated particles with diameters above 100 nm and only few particles in the size range below 50 nm (10 to 15%). Welding processes with low mass emission rates (tungsten inert gas welding and resistance spot welding) emit predominantly ultrafine particles with diameters well below 100 nm. This finding can be explained by considerably faster agglomeration processes in welding processes with high mass emission rates. Although mass emission is low for tungsten inert gas welding and resistance spot welding, due to the low particle size of the fume, these processes cannot be labeled as toxicologically irrelevant and should be further investigated.

Brand, P., Lenz, K., Reisgen, U., and Kraus, T.,Number size distribution of fine and ultrafine fume particles from various welding processes, Ann Occup Hyg, 2013, 57, 305.

Reported daily molybdenum intakes from industrial sources

Molybdenum dusts and fumes, as can be generated by mining or metalworking, are not toxic. There are no long-term effects associated with exposure to molybdenum; however, prolonged exposure (to high levels) can cause irritation to the eyes and skin. The direct inhalation or ingestion of molybdenum should be avoided.

Inhaling molybdenum dust can irritate the nose and throat and may cause coughing and wheezing. Mining and metallurgy workers chronically exposed to 60 to 600 mg Mo/m3 reported an increased incidence of nonspecific symptoms that included weakness, fatigue, headache, anorexia, and joint and muscle pain.

Lener J. and Bibr B., J Hyg Epidemiol Microbiol Immunol, 1984, 29:405-419. Effects of molybdenum on the organism: a review.

Routes of Exposure areinhalation; ingestion; skin and eye contact.

Target Organs areeyes, respiratory system, liver, kidneys.

Levels In Humans: naturally occurring levels of molybdenum in the typical human (NOT recommended daily allowances) are reported 

·Blood/mg dm-3: 0.001

·Bone/p.p.m: <0.7

·Liver/p.p.m: 1.3-5.8

·Muscle/p.p.m: 0.018

·Daily Dietary Intake: 0.05-0.35 mg

-Total Mass In Avg. 70kg human: 5 mg

http://www.3rd1000.com/elements/Molybdenum.htm#Regulatory%20/%20Health

Reported daily molybdenum intakes from industrial sources

Average daily intakes of Mo 0.1 – 0.5 mg Mo increasing to 1 mg if contamination from industrial sources

Friberg, L., Lener, J., Molybdenum, in Handbook on the Toxicology of Metals Vol II, Friberg, L., Nordberg, G.F., and Vouk, V.B., eds., Elsevier, 1986, 446 – 461.

56 adults in Germany 47 – 89 microg

Anke, M., Groppel, B., Krause, U., Arnhold, W., Langer, M., Trace element intake of humans , J. Trace Elemen. Electrolytes Health Dis., 1991, 5, 69 – 74.

Adults in Denver 120 – 240 microg Mo/d av 180

Tsongas, T.A., Meglen, R.R., Walravens, P.A., Chappell W.R., Molybdenum in the diet, Am. J. Clin. Nutr., 1980, 33, 1103 –1107.

NE US 74 – 126 microg Mo/d

Pennington, J.A.T., Young, B.E., Wilson, D., Nutritional elements in US diets, J. Am. Diet. Assoc., 1989, 89, 659 – 664.

Average daily intakes of Mo 0.1 – 0.5 mg Mo increasing to 1 mg if contamination from industrial sources

Friberg, L., Lener, J., Molybdenum, in Handbook on the Toxicology of Metals Vol II, Friberg, L., Nordberg, G.F., and Vouk, V.B., eds., Elsevier, 1986, 446 – 461.

56 adults in Germany 47 – 89 microg

Anke, M., Groppel, B., Krause, U., Arnhold, W., Langer, M., Trace element intake of humans , J. Trace Elemen. Electrolytes Health Dis., 1991, 5, 69 – 74.

Adults in Denver 120 – 240 microg Mo/d av 180

Tsongas, T.A., Meglen, R.R., Walravens, P.A., Chappell W.R., Molybdenum in the diet, Am. J. Clin. Nutr., 1980, 33, 1103 –1107.

NE US 74 – 126 microg Mo/d

Pennington, J.A.T., Young, B.E., Wilson, D., Nutritional elements in US diets, J. Am. Diet. Assoc., 1989, 89, 659 – 664.

Mo uptake from industrial sources: Impact of Dust Filter Installation in Ironworks and Construction on Brownfield Area on the Toxic Metal Concentration in Street and House Dust (Celje, Slovenia)

This article presents the impact of the ecological investment in ironworks (dust filter installation) and construction works at a highly contaminated brownfield site on the chemical composition of household dust (HD) and street sediment (SS) in Celje, Slovenia.

The evaluation is based on two sampling campaigns: the first was undertaken 1 month before the ecological investment became operational and the second 3 years later.

The results show that dust filter installations reduced the content of Co, Cr, Fe, Mn, Mo, W and Zn on average by 58% in HD and by 51% in SS. No reduction was observed at sampling points in the upwind direction from the ironworks.

By contrast, the impact of the construction works on the highly contaminated brownfield site was detected by a significant increase (on average by 37%) of elements connected to the brownfield contamination in SS. Such increase was not detected in HD

Zibret, Gorazd, Impact of Dust Filter Installation in Ironworks and Construction on Brownfield Area on the Toxic Metal Concentration in Street and House Dust (Celje, Slovenia), Ambio, 2012, 41, 292-301.

Ergonomic study of an operator's work of a molybdenum plant

This study was part of an ergonomic program which is being carried out through an agreement between the University of Concepcion and a Chilean private mining company. The purpose of this case study was to identify working conditions in which the physical and mental workload could be over the capabilities of the operator. He was responsible for loading trucks with sacks of molybdenum and for downloading reagents and handles them. The methods employed in this study included electronic records, interviews, surveys, review of the company standards, a time study and physical and mental workload analysis. Results showed that 84% of the time the operator was carrying out principal and secondary activities and no break periods were detected. It was found that the pace of work and the shift system generated unfavorable conditions by imbalance in the workload on the different days of the week. In the light of the results recommendations were made for a number of ergonomic changes. Most of them were accepted by the company. The most important achievement was a change in the shift system. The overload of the operator was due to the fact that he was in a shift working 5 days and resting on weekends. The imbalance was mainly because the work of the week end was accumulated for Monday. As a result of the study, the company contracted a second worker for this job and adopted a 7x7 shift system, meaning that they work seven days and rest seven days. An evaluation carried out two month after adopting the new shift revealed that changes were well accepted by the worker

Onate,E. and Meyer, F., Ergonomic study of an operator's work of a molybdenum plant, Work-A Journal of Prevention Assessment & Rehabilitation, 2012, 41, 5950-5955.

Guinea pigs exposed to the dust or fumes of molybdenum trioxide

For guinea pigs exposed to the dust or fumes of molybdenum trioxide (150-300 mg/m3) for 1 h per day, 5 times per week, for 5 weeks [Fairhall et al., 1945]. Low concentrations of molybdenum (20-270 microg/10g fresh tissue) were found in the lungs, liver, kidneys, spleen and bone. The molybdenum concentrations in these tissues decreased after exposure was stopped to 20% of the original level after 2 weeks. After an oral gavage dose of 50 mg molybdenum trioxide was administered to guinea pigs, molybdenum was distributed to the kidneys, spleen, blood, bile, liver, and lungs within 4 h. The concentrations of molybdenum in the organs decreased, whereas in the blood and bile molybdenum titres were higher at 48 h. Bone retained molybdenum longer than any other tissues [Fairhall et al., 1945]. Based on the amount recovered in faeces for up to 48 h, Fairhall et al. (1945) calculated that 85 % of the oral dose was absorbed. Excess hexavalent forms of molybdenum are excreted rapidly through the kidneys and the bile. Twice as much molybdenum is eliminated in urine as in the faeces. The urinary and faecal concentrations of molybdenum returned to normal after an oral dose of molybdenum trioxide was administered to guinea pigs [Fairhall et al., 1945]. The predominant urinary metabolite of molybdenum was in the form of molybdate complexes [Venugopal and Luckey, 1978].

Fairhall, L. T., Dunn, R. C., Sharpless, N. E. and Pritchard, E. A., U. S. Public Health Bull., 1945, 293, 1.
Venugopal, B. and Luckey, T. D., Metal Toxicity in Mammals, 1978, Vol. 2, Chemical Toxicity of Metals and Metalloids, Plenum Press, New York.