Molybdenum in Human Health

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.

Mo uptake 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.

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.

Regulatory controls and legislation

Threshold Limit Values of Some Common Metals

Metal	TLV/mg Mo/m3
	soluble	insoluble
molybdenum	5	10
tungsten	1	5
iron oxide		5
tantalum		5
nickel	0.1	1
copper dust	1	1
copper fume		0.2
chromium		0.5
lead	0.15	0.15
cobalt	0.02	0.02
chromium(VI)	0.05	0.01
cadmium	0.01	0.01
arsenic	0.01	0.01

TLV, threshold limit value

International Molybdenum Association (IMOA), Report 1995, p. 5

Molybdenum Regulatory Limits

Process or material	Limit	Units	Averaging period	Source 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.

MAC Limits for Insoluble and Soluble Molybdenum Compounds

Country	MAC 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.

Workplace Exposure TLV USA

Material	TLV-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 5 mg/m³ for soluble molybdenum compounds and 10 mg/m³ for insoluble molybdenum.