Registration Dossier

Administrative data

Link to relevant study record(s)

Description of key information

Short description of key information on bioaccumulation potential result: 
Basic toxicokinetic assessment taken from the accepted NONS dossier (1999).

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

The substance is an organo-molybdenum complex reaction mixture of molecular weights which do not preclude absorption.  Predictions of toxicokinetic behaviour cannot be made by SAAR.  The substance is a non-volatile paste, therefore inhalation exposure is not expected.  Rapid hydrolysis is likely and, hence, exposure to degradants is anticipated.

Absorption: An acute oral toxicity study showed no treatment-related effects but a 28-day repeated dose oral toxicity study and a 14 and 21 day range finding study (to support a 2-generation reproductive toxicity study) showed effects which demonstrate that absorption does occur from the gastro-intestinal tract.  An acute dermal study also showed no effects but this does not necessarily preclude absorption.  The substance is poorly water soluble and could, theoretically, be deposited at the dosage site but the hydrolysis products are likely to include water soluble molybdenum-containing compounds.  The high log Pow of many constituents of the parent substance would indicate ready diffusion across membranes but this is of little relevance in view of the rapid hydrolysis.  The parent constituents do not contain ionisable organic groups but the putative, poorly water soluble organic degradants may and the water soluble molybdenum-containing degradants will also be ionic.  Hence absorption may be pH dependent.

Distribution: The repeated dose oral toxicity study shows that the substance or a degradant/metabolite reaches the kidneys because treatment related renal changes were detected. Presumably transport occurs via the blood stream but there is no experimental evidence of partitioning into other tissues.  A contact sensitisation study was negative so the substance may not become bound to proteins.

Metabolism: There is no experimental evidence of metabolism although hydrolysis may be further enhanced by the action of hydrolase enzymes.  Molybdenum itself is an essential trace element and could enter the normal body pool.  In vitromutagenicity studies showed no differences in cell toxicity in the presence or absence of S9 so these do not provide any information relating to metabolism.  Rapid biotransformation of any absorbed parent constituents to more water soluble metabolites would however, be expected.

Excretion: Evidence from the repeated dose oral toxicity study indicates that a major route of elimination is via the kidneys in urine.  This is also the expected route of elimination for molybdenum itself or any low molecular weight water soluble metabolites or degradants.  Excretion of larger degradants or conjugates in the bile is also possible, but there is no experimental evidence of this.