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Description of key information

There are no study data available for the toxicokinetic of the test substance TBBS. Based on physico-chemical parameters of TBBS and potential metabolites, the ADME properties of TBBS are predicted.

Key value for chemical safety assessment

Bioaccumulation potential:
low bioaccumulation potential

Additional information

There are no study data available for the toxicokinetic of the test substance TBBS. However, considering the experiences with TBBS in acute and repeated dose toxicity studies, a characterization of TBBS toxicokinetics can be conducted as discussed in the OECD SIDS 2003:

The test material is a solid. No details of particle size distribution have been given, but a repeated-dose toxicity study using the inhalation route indicates some systemic toxicity. The vapour pressure value for the test material is low (< 0.21 x 10-5 hPa at 25 °C, OECD SIDS 2003).

The test material is expected to hydrolyse readily at pH values below 9. This suggests that systemic exposure to degradants can be expected, particularly following oral ingestion. The log oil/water partition coefficient value is moderate (log Pow 3.9 at room temperature), which suggests that test material passage across biological membranes is possible.

Absorption

The results of the acute and repeated dose oral toxicity studies in the rat suggest that the test material is absorbed from the gastro-intestinal tract. Systemic effects are observed, particularly with cumulative exposure. Because of the rapid hydrolysis of the test material, it is likely that toxicity is a result of exposure to degradants. The test material has low water solubility (0.345 mg/l at 20°C, OECD SIDS 2003) which may restrict absorption of the parent molecule but hydrolysis may enhance water solubility. The moderate log oil/water partition coefficient of the parent molecule will allow passage across the biological membranes of the gastro-intestinal tract. The results of the acute dermal toxicity studies in the rabbit show that the test material is not more toxic by this route. The results of human patch tests and a sensitisation study in the guinea pig show that the test material (or a product of hydrolysis, mercaptobenzothiazole) is absorbed through the skin.

Distribution

The results of the oral repeated dose studies in the rat suggest some systemic distribution. Following oral ingestion it is likely that the test material (or hydrolysis products) is distributed via the porta circulation system. The positive sensitisation response suggests that the hydrolysis products may bind to circulatory proteins. The moderate log oil/water partition coefficient value suggests that the test material could potentially accumulate in body fat. Because the test material hydrolyses, it is likely to result in products with a lower partition coefficient value.

Metabolism

The widespread distribution throughout tissues such as the gastro-intestinal tract, and the tendency of the test material to undergo hydrolysis suggest that initial metabolism of the material will be widespread and non-specific. The results of the oral repeated dose studies in the rat do show microscopic changes in the liver. This may be indicative of further metabolism of hydrolysis products. The results of in vitro mammalian cell genotoxicity studies show that a positive genotoxic effect is seen, but only in the presence of S9 metabolising system. This indicates that metabolism of the parent test material or a hydrolysis product is required to produce a positive response. The results of separate reproduction/developmental toxicity studies in the rat with the test material and an analogue (either N-cyclohexylbenzothiazole-2-sulfenamide or N, N-dicyclohexylbenzothiazole-2-sulfenamide) show differences in developmental toxicity. If, as expected, the analogues undergo hydrolysis/metabolism as does the test material, it may be suggested that the profile of the metabolites may be significant in the toxicity of the product.

Excretion

The results of some of the repeated dose oral toxicity studies show changes in the kidneys of rats. This suggests that urinary excretion is a significant route for removal of test material (OECD SIDS 2003).