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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The potential for bioaccumuation of disulfiram is expected to be low based on all available data.

Key value for chemical safety assessment

Additional information

The experimental partition coefficient value of tetraethylthiuram disulfide (CAS No. 97-77-8), reported to be 3.6 suggests potential of the substance to bioaccumulate. However, the information gathered on environmental behavior and metabolism in combination with the experimental and QSAR-estimated BCF values provide enough evidence (in accordance to the REACh Regulation (EC) No. 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2, to cover the data requirements of Regulation (EC) No. 1907/2006, Annex IX) to state that tetraethylthiuram disulfide is likely to show low bioaccumulation potential.

Experimental data

One study evaluating the bioaccumulation potential of tetraethylthiuram disulfide (CAS No. 97-77-8) is available (van Leeuwen, 1986). In this test, the bioaccumulation of radio-labeled tetraethylthiuram disulfide was evaluated in Rainbow trout (Oncorhynchus mykiss) after an exposure of 96 hours, within a static water regime. The results of the study shows that no steady-state conditions were reached for fish exposed to the test substance, and therefore the BCF value in steady-state could not be determined. In order to determine the BCF value, three biotransformation constants were introduced in the equation, leading to an estimated BCF value of 225. According to Regulation (EC) No. 1907/2006, Annex XIII, 1.1.2, a substance only fulfills the bioaccumulation criterion (B) when BCF values are > 2000 L/kg. Since the BCF value obtained for tetraethylthiuram disulfide is well below the trigger value of 2000 L/kg, this substance is considered to have a low bioaccumulation potential.

QSAR data

Additional information on the bioaccumulation of tetraethylthiuram disulfide in fish species is available. Estimated bioconcentration (BCF) and bioaccumulation (BAF) factors were calculated using the regression and Arnot-Gobas methods (BCFBAF v3.01 program, Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA). The resulting BCF/BAF values are in the same order of magnitude than the one from the experimental study (110-182.8 L/kg), thus supporting the assumption of the expected low bioaccumulation potential of tetraethylthiuram disulfide.

Intrinsic properties and environmental fate

Regarding the relation between partition coefficient and bioaccumulation potential, the Guidance on information requirements and chemical safety assessment, Chapter R.11 (PBT Assessment; ECHA, 2012) states that substances with a log Kow ≤ 4.5 can be considered not to be bioaccumulative (B) or very bioaccumulative (vB). Furthermore, tetraethylthiuram disulfide does not meet either the bioaccumulation criteria set in the Guidance on the application of the CLP criteria (ECHA, 2012), since the available BCF values for the substance are well below 500 L/kg and the partition coefficient value is below 4.

Tetraethylthiuram disulfide is expected to be rapidly degraded in water/sediment systems considering its potential for hydrolysis (especially under neutral and alkaline conditions, with half-lives of 3.5 days and 6.9 hours, respectively; Norris, 1991) and photolysis in water (half-life < 10 hours; Norris, 1990, Knoch, 1994). According to the Guidance on information requirements and chemical safety assessment, Chapter R7.C (ECHA, 2012), the likelihood of bioaccumulation is greatly reduced for hydrolytically unstable substances, since the rate of hydrolysis is expected to be greater than that of the uptake of exposed organisms. In most cases, hydrolysis products are more hydrophilic than the parent substance, and as a consequence their bioaccumulation potential is expected to be even lower than for tetraethylthiuram disulfide. This is the case for the main metabolites (based on chemical structure) of tetraethylthiuram disulfide: diethyldithiocarbamate (DDTC) and carbon disulfide (CS2). Estimated log Kow values for these two substances are calculated with the KOWWIN v1.68 program (Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US EPA). The resulting values of 1.67 and 1.94 for DDTC and CS2 (respectively) show that indeed the bioaccumulation potential of the metabolites is lower than that of the parent substance.

Metabolism

The available information on mammalian toxicokinetics (IUCLID section 7.1) also indicate that tetraethylthiuram disulfide (CAS No. 97-77-8) has a low bioaccumulation potential in mammals, since its main by-products, diethyldithiocarbamate (DDTC) and carbon disulfide (CS2) are rapidly and effectively excreted (in humans, after 3 days in the form of DDC and other minor metabolites in the case of DDTC, and through respiration in the case of CS2; Peachey, 1981).

Conclusion

In conclusion, all information above provides strong evidence supporting the statement that tetraethythiuram disulfide (CAS No. 97-77-8) has low potential for bioaccumulation in biota.

References

European Chemicals Agency (ECHA, 2012). Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance.

European Chemicals Agency (ECHA, 2012). Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment.

European Chemicals Agency (ECHA, 2012). Guidance on application of the CLP criteria.

Knoch, E. (1994). Determination of the direct phototransformation of 14C-Thiram in a buffered medium at pH 7. Unpublished study. Report No. 449600. Taminco BVBA.

Norris, K.J. (1991). Determination of the hydrolysis of 14C-Thiram. Unpublished study. Report No. 1156. Taminco BVBA.

Norris, K.J. (1990). Determination of the aqueous degradation of 14C-Thiram. Unpublished study. Report No. 1157. Taminco BVBA.

Peachey, J.E. et al. (1981). A comparative review of the pharmacological and toxicological properties of disulfiram and calcium carbimide. Journal of Clinical Psychopharmacoly, 1(1):21-6.

Van Leeuwen, C.J. (1986). Ecotoxicological aspects of dithiocarbamates: Chapter 9. Uptake, distribution and retention of zineb and ziram in rainbow trout (Salmo gairdneri). Report No. 44/1986. Rijkswaterstaat/University of Utrecht.