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Toxicity to microorganisms

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Description of key information

EC50 (5 h) = 168 mg/L (ISO DIS 9509)

Key value for chemical safety assessment

EC50 for microorganisms:
168 mg/L

Additional information

For the toxicity of 1,3,5-triazine-2,4,6(1H,3H,5H)-trithione, trisodium salt (CAS No. 17766-26-6) towards microorganisms, two studies are available.

The key study is a nitrification inhibition test with TMT 15 according to ISO DIS 9509 (91-0180-DKO). Activated sludge was used in this non-GLP study that consisted of two parts. In the first part, the test substance was administered once for an exposure period of 5 hours. In the second part, the test substance was continuously administered over a period of 23 days to a model activated sludge unit simulating a sewage treatment plant. The first approach resulted in an EC50 (5 h) > 1120 mg/L TMT 15 concentration, corresponding to 168 mg/L anhydrous TMT. This value was used for further assessment. The second approach resulted in an EC50 (23 d) > 448 mg/L TMT 15 concentration, corresponding to 67.2 mg/L anhydrous TMT.

The supporting study is a dehydrogenase activity inhibition test with TMT 60 according to DIN 38412 and GLP regulations (87-0022-DGO). Domestic activated sludge was used in the test. An EC10 (3 h) of 115 mg/L is reported for TMT 60, this corresponds to 69 mg/L for anhydrous TMT. A number of microbial inhibition test approaches such as the dehydrogenase inhibition test exist which are based on subcellular systems. Such in-vitro systems based on a single reaction have not been sufficiently validated in the context of STP risk assessment, and their use is therefore not accepted (ECHA (2008), Guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance). Therefore, the result from the nitrification inhibition test was used for further assessment.