Molybdenum toxicological studies with fish

Toxicological Testing Programme: Aquatic organisms

IMOA Toxicological Testing Programme: Aquatic organisms
SubstanceToxicity/ mg/l
acute fishaacute daphnidsbalgal growthc
96 h LC50 48 h EC50 72 h IC50
Molybdenum trioxide (pure) 130 150 100
Molybdenum trioxide (tech)d 77 88 100
Ammonium dimolybdatee 420 140 41
Sodium molybdate 7600 330 >100
Risk phrase required if: <100 <100 < 100

Notes

a Acute fish toxicity is representive of relative toxicity to aquatic vertebrates. Trout used because of large data base and sensitivity. Rainbow trout (10/concentration) exposed to various concentrations under semi-static conditions for 96 hours.

b Acute daphnia toxicity is representative of relative toxicity to aquatic invertebrates. Dapnids are ubiquitous thoughout the world in fresh water ponds and lakes, important link in food chain. Daphnids (20/concentation) exposed to various concentrations under static conditions for 48 hours. Daphnids observed for immobilization and Effective Concentration, EC50 calculated.

c Algal growth inhibition is representative of relative toxicity to aquatic plants. Algae are primary producers in the food chain. Inhibition can alter food web and reduce productivity of ecosystems. Stimulation may cause algal blooms, causing anoxic conditions, negative anaesthetic effects, etc. Test cultures of algae were prepared and added to solutions of test material and incubated for 72 hours. Growth was monitored by measuring the absorbance of each culture at 665 nm. The median effective concentration for inhibition of growth (IC50 ) after 72 hours was calculated.

d The aquatic toxicity of technical oxide varied with the level of impurities, particularly copper. High copper content samples gave lower results in the daphnia studies.

e The toxicity of ammonium molybdate to algae is not unexpected considering the the known toxicity of ammonia, which is commonly used as a bactericide and disinfectant.

Acute toxicities of molybdenum compounds towards fish

Acute toxicities of molybdenum compounds towards fish
LD50/mg/l
CompoundSpecies24h48h96hNo effect Level
MoO3[1] bluegill 87-120 87-120 87 75
  rainbow trout 102 65-87 65-87 65
Ammonium dimolybdate[2] bluegill 166 157 157 140
  rainbow trout 138 135 120 87
Sodium molybdate [2] bluegill > 10,000 - 6,790 2,400
  rainbow trout > 10,000 - 7,340 3,200
  channel catfish > 10,000 - > 10,000 7,500
  fathead minnow > 10,000 - 7,630 5,600
Sodium molybdate [3] shrimp 3997 - - -
  minnow 6590 - - -
  American oyster (EC50) 3526 - - -

[1] Bentley, R. E., Acute Toxicity of Ammonium Molybdate and Molybdic Trioxide to Bluegill (Lepomis macrochirus) and Rainbow Trout (Salmo gairdneri),Bionomics, Wareham, Massachusetts, 1975, January
[2] Bentley, R. E., Acute Toxicity of Sodium Molybdate to Bluegill (Lepomis macrochirus), Rainbow Trout (Salmo gairdneri), Fathead Minnow (Pimephales promeals), Channel Catfish (Ictalurus punctatus), Water Flea (Daphnia magna) and Scud (Gammarus fasciatus),Bionomics, Wareham, Massachusetts, 1973, December.
[3] Knothe, D. W. and van Riper, G. G., Bull. Environ. Contam. and Toxicol., 1988, 40, 785.

Sodium molybdate was found to be significantly less toxic to several varieties of fish than either molybdic oxide or ammonium dimolybdate [ Bentley, 1973; 1975].

Bentley, R. E., Acute Toxicity of Sodium Molybdate to Bluegill (Lepomis macrochirus), Rainbow Trout (Salmo gairdneri), Fathead Minnow (Pimephales promeals), Channel Catfish (Ictalurus punctatus), Water Flea (Daphnia magna) and Scud (Gammarus fasciatus), Bionomics, Wareham, Massachusetts, 1973.
Bentley, R. E., Acute Toxicity of Ammonium Molybdate and Molybdic Trioxide to Bluegill (Lepomis macrochirus) and Rainbow Trout (Salmo gairdneri), Bionomics, Wareham, Massachusetts, 1975.

Toxicity rainbow trout

The purpose of the study was to resolve inconsistencies in reported bioassays of the toxicity of molybdenum (as sodium molybdate in water) to fertilized rainbow trout eggs and alevins (EA) for which a wide toxicity range (LC50 0.73 to >90 mg/L Mo) has been reported. Molybdenum was not acutely toxic to the early life stages of rainbow trout (32 d, maximum molybdenum concentration 400 mg l-1). When early life stages of rainbow trout were exposed to a maximum molybdenum concentration of 1500 mg l-1 for 32 d there was not sufficient mortality for an LC50 to be calculated. The importance of careful control of the water chemistry in the bioassay was emphasized.

Davies, T. D., Pickard, J., and Hall, K. J., Acute molybdenum toxicity to rainbow trout and other fish, Journal of Environmental Engineering and Science, 2005, 4, 481-485.

Aquatic Organisms

The benthic [sediment] organismsChironomus plumosus larvae andTubifex tubifex worms may be used as aquatic toxicity indicators of metals which may accumulate in freshwater sediments as a consequence of heavy metal contamination of water. The LC50 values after 96 h are given in the Table. The tests were carried out in boiled tap water (20 C, pH 7 - 8, calcium carbonate hardness 80 mg l-1). Molybdate (supplied as ammonium hepatamolybdate) is the least toxic of the metals on both a mass and molar basis and is non-toxic, its LC50 value being less than concentrations found in the environment.

Toxicities of metals towards aquatic organisms
 C. plumosusT. tubifex
Compound 103LC50/mg l-1 103LC50/ mol l-1 103LC50/mg l-1 103LC50/ mol l-1
V2O5 218 4.28 211 4.14
(NH4)6Mo7O24.4H2O 455 4.74 4563 47.6
MnSO4.H2O 68 1.24 295 5.37
NiSO4.7H2O 266 4.53 537 9.15
CuSO4.5H2O 0.105 0.00165 2 0.0315
Cu2Cl2 0.927 0.0146 6 0.0945

Fargasova, A, Comparative acute toxicity of Cu2+, Cu+, Mn2+, Mo6+, Ni2+ and V5+ to Chironomus plumosus larvae and Tubifex tubifex worms, Biologia, 1998, 53, 315-319.

Mo toxicity towards flannelmouth sucker

Larval flannelmouth sucker (Catostomus latipinnis) were exposed to inorganics which simulated environmental ratios reported for sites along the San Juan River. The toxicity rank order was copper > zinc >vanadium > selenite > selenate > arsenate > uranium > boron > molybdenum.

Hamilton, S.J., Buhl, K.J., Hazard evaluation of inorganics, singly and in mixtures, to flannelmouth sucker Catostomus latipinnis in the San Juan River, New Mexico, Ecotoxicology And Environmental Safety, 1997, 38, 296-308.

Toxicity towards Daphnia

Molybdates are alternatives to toxic chromates in industrial applications, e.g. passivation of zinc coatings in the automobile industry. Molybdates are much less toxic than chromates although both molybdenum and chromium and their compounds are included in th List II of European dangerous substances directive (Council of the European Communities (1976). Directive of 4 May 1976 on Pollution Caused by Certain Dangerous Substances and Discharged into the Aquatic Environment of the Community (76/464/EEC, OJL 129, 18 May). The purpose of the work described in this paper was to compare the aquatic acute and chronic toxicity of Mo and Cr in standard tests with the organism Daphnia magna, and in acetylcholinesterase inhibition.

Acute toxicity towardsDaphnia magnain ASTM hard water
Chemical48 h LC50/mg L-195% confidence limit
Sodium dichromate 0.29 0.269-0.315
Sodium molybdate 2848 2839-2857
Chronic toxicity towardsDaphnia magnain ASTM hard water
ChemicalTotal growthReproductionMortality
NOEC
/mg L-1
LOEC
/mg L-1
EC50
/mg L-1
NOEC
/mg L-1
LOEC
/mg L-1
EC50
/mg L-1
NOEC
/mg L-1
LOEC
/mg L-1
EC50
/mg L-1
Sodium dichromate 0.0125 0.025 0.233 0.0125 0.025 0.047 0.075 0.01 0.524
Sodium molybdate 50 75 204 50 75 102 75 100 255
Daphnia magnaacetylcholinesterase inhibition in vivoa
ChemicalNOEC/mg L-1LOEC/mg L-1EC50 /mg L-1
Sodium dichromate 0.075 0.15 0.632
Sodium molybdate 750 1500 26.5

a No inhibition in vitro

The study shows that sodium molybdate is much less toxic towardsDaphnia magna than is sodium dichromate.

Diamantino, T.C., Guilhermino, L., Almeida, E., and Soares, A. M. V. M., Toxicity of sodium molybdate and sodium dichromate to Daphnia magna Straus evaluated in acute, chronic, and acetylcholinesterase inhibition tests, Ecotoxicology and Environmental Safety, 2000, 45, 253-259.