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Toxicity to microorganisms

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Description of key information

According to the guideline ISO 8192 (Test for Inhibition of Oxygen

Consumption by Activated Sludge) a 3h-EC50 of 1220 mg/l was observed for ZMBT (Bayer AG, 1990). For the nitrification inhibition by 2 -mercaptobenzothiazole an EC75 of 3 mg/L during a 2 -4 h incubation period was obtained (Tomlinson et al., 1966). The effect concentration of MBT is lower than the one of ZMBT; and hence it is used as a worst case consideration for the further risk assessment of ZMBT.

Key value for chemical safety assessment

EC50 for microorganisms:
3 mg/L

Additional information

Data from MBT and ZMBT. The key value reported in the study was an EC75 from MBT.

ZMBT is an organic complex with where the relation of Zn to Sulfur bridge is considered to be ionic.

Meanwhile MBT is often found as impurity in ZMBT with variable percentage. The dissolution of MBT determines the hazard profile of ZMBT aqueous solution; and hence a read-across approach from MBT is used to support the risk assessment of ZMBT as a worst-case. The read-across is justified as ZMBT has an ionic structure where MBT is contained.

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