Dimolybdenum carbide

Endpoint summary

Description of key information

Data on toxicokinetics was retrieved from the Handbook of Toxicology of Metals. Fourth edition. Edited by: Nordberg, G.F., Fowler, B.A. and Nordberg, M.)

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Absorption

Inhalation

No human data on the absorption of molybdenum after inhalation could be identified. In guinea pigs no noticeable absorption was reported after exposure through inhalation to 285mg Mo/m3 as molybdenum disulfide. Hexavalent molybdenum compounds were absorbed to an appreciable extent, although no qualitative data was available.

Ingestion

Oral absorption is high in both animals and humans. Animal data from single exposure studies demonstrate that hexavalent molybdenum is readily absorbed from the gastrointestinal tract (40 and 85% in guinea pigs, rats, and goats). Molybdenum is well absorbed by humans, with values ranging from 57 to 93% of dietary intake. Molybdenum is an essential trace element for several enzymes important to animal and plant metabolism.

Distribution

In guinea pigs and rats molybdenum trioxide show an immediate accumulation in the kidneys, liver, and bone after acute exposure. A similar distribution is seen in rats, cows, and goats after prolonged exposure. The highest concentrations are found in the kidneys.

In the blood, molybdenum is bound in the form of molybdate, specifically to armacroglobulin, and in erythrocytes to proteins of the erythrocyte membrane, especially spectrin. In controlled human studies, plasma concentrations increased from 4 to 44 nmol/L when the dietary intake increased from 22 to 1400µg/day. Concentrations are usually <10nmol/L. Blood concentrations rise after meals and then return to basal levels. Infused tracer doses disappear rapidly, with 2.5-5% remaining after an hour.

Excretion

The pattern and route of molybdenum excretion in humans is influenced by the dietary intake. Increased molybdenum intake results in increased absorption and urinary excretion (primary route), whereas the fraction deposited in the tissues is decreased. Human studies have demonstrated that when intake is very low, approximately 60% of the amount of ingested molybdenum is excreted in the urine and approximately 40% is eliminated in the stools. When intake is high, > 90% is excreted in the urine and < 10% in the stools. The source of molybdenum in the stools is partly unabsorbed dietary molybdenum and partly endogenous molybdenum excreted into the gastrointestinal tract through the bile.

Biological Half-Life

Based on data on excretion and rapid clearance from the liver, kidney, spleen, testis, and hard tissues of animal the biological half-life is expected to be in the order of hours, extending to a maximum of 1 day in laboratory animals.

(Data on toxicokinetics was retrieved from the Handbook of Toxicology of Metals. Fourth edition. Edited by: Nordberg, G.F., Fowler, B.A. and Nordberg, M.)