1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione

Endpoint summary

Description of key information

Data on aquatic effects of the substance are available on three trophic levels (fish, daphnia and algae) for acute and chronic toxicity. Acute toxicity to fish (Danio rerio) was determined according to "Letale Wirkung beim Zebrabärbling -Brachydanio rerio-". During 96 hours exposure the LC0 was measured at 22 mg/L and LC100 at 63 mg/L; and goemetric mean LC0/LC100 was calculated at 37.2 mg/L.

Concerning the toxicity towards aquatic invertebrates, an acute toxicity test to Daphnia magna was determined according to OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test). As analytical monitoring was performed showing stability of the test substance, the result of EC 50 1.9 mg/L relates to nominal concentrations.

The most sensitive toxicity was observed for chronic toxicity to daphnia magna. The Chronic toxicity of the substance to invertebrates (Daphnia magna) was conducted under Semi-Static Reproduction test according to OECD Guideline 211. After 21 days of exposure an NOEC of 0.0346 mg/L (measured) was obtained.

The acute toxicity of the substance to alga (Desmodesmus subspicatus was tested according to OECD guideline 201 ' Alga, Growth Inhibition Test' (2006). During 72 hours exposure an EC50 of 62.24 mg/L and a NOEC of 50.0 mg/L was calculated.

The effect of the substance towards the growth of activated sludge was investigated according to OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test). The test item showed 43 % and 44.4 % respiration inhibition of activated sludge at the highest test item concentration of 10000 mg/L. An EC50 of >10000 mg/L were obtained in this test. The effect value relates to nominal concentration, since no analytical monitoring was performed.

Additional information

According to ECHA Decision on Substance Evaluation (SEV) for 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt (CAS 61617-00-3), requesting an Amphibian Metamorphosis Assay (AMA - OECD TG 231) with 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione (CAS 53988-10-6), this study was performed and summarised in the section 6.1.8 Endocrine disrupter testing in aquatic vertebrates - in vivo.

This AMA study was performed to identify whether the registered substance may interfere with the normal function of the hypothalamic-pituitary-thyroid (HPT) axis, according to OECD Test Guideline 231 with GLP statement. According to a 14-day preliminary toxicity test, Xenopus laevis tadpoles were exposed to the test item at analytically confirmed nominal concentrations of 0.0048, 0.024, 0.12, 0.60, 3.0 and 15 mg/L and to a control, over a period of 21 days under flow-through conditions. The study met the acceptability criteria and was considered valid. According to the results of this study, neither advanced, nor asynchronous development were observed in the present study. However, remarkable histological effects were noted at concentrations of 0.12 mg/L and higher, including assignment of ‘severe degree’ grading for the core assessed criteria at 3.0 mg/L and 15 mg/L. Consequently, following the decision logic presented in OECD TG 231, the registered substance is concluded to be thyroid active.