Experimental Studies of Molybdenum Physiology and Toxicity
Molybdenum toxicity studies with fish
| Substance |
Toxicity/ mg/l |
||
| |
acute fish a |
acute daphnids b |
algal growth c |
| |
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.
| LD50/mg/l |
|||||
| Compound |
Species |
24h |
48h |
96h |
No 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] organisms Chironomus plumosus larvae and Tubifex 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.
|
|
C. plumosus |
T. 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.
| Chemical |
48 h LC50/mg L-1 |
95% confidence limit |
| Sodium dichromate |
0.29 |
0.269-0.315 |
| Sodium molybdate |
2848 |
2839-2857 |
| Chemical |
Total growth |
Reproduction |
Mortality |
||||||
| |
NOEC |
LOEC |
EC50 |
NOEC |
LOEC |
EC50 |
NOEC |
LOEC |
EC50 |
| 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 |
| Chemical |
NOEC/mg L-1 |
LOEC/mg L-1 |
EC50 /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 towards Daphnia magna than is sodium dichromate.