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Short-term toxicity to fish

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The acute toxicity and the prolonged toxicity of CBS to fish (Oryzias latipes) were tested according to OECD TG 203 "Fish, acute toxicity test" and OECD TG 204 "Fish, prolonged toxicity test: 14-day Study", respectively. After 96 hours of exposure a LC50 of 2.1 mg/L was obtained for acute effect and after 14 days of exposure a LC50 of 0.78 mg/L and a NOEC of 0.14 mg/l were obtained for prolonged effect (National Institute of Technology and Evaluation, 1996). 
CBS is rapidly degraded by hydrolysis and benzothiazole (BT) is the main degradation product appearing during the time frame of acute tests. The most sensitive results of the acute toxicity of BT to fish (96h-LC50=8.1 mg/l) and the prolonged toxicity of BT to fish (14d-LC50=5.6 mg/l) are reported by SRI International (1981) using a flow-through sys-tem with Oncorhynchus mykiss.
Some further data are available for another main metabolite from CBS, like MBT and MBTS. The most sensitive results of the toxicity of MBT to fish (4d-LC50=0.73 mg/l and 8d-LC50=0.67 mg/l) are reported by Monsanto (1981) using a flow-through system with Oncorhynchus mykiss. For MBTS no toxic effect was observed to fish (Oncorhynchus mykiss) up to its water solubility (Monsanto, 1981).
Regarding the data summarized here, the described metabolites of CBS are less toxic to fish than CBS itself.

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Additional information

A hydrolysis half-life time of CBS of 12.5 h and a complete hydrolysis of CBS in 24.9 h were observed in deionized water buffered at pH 7.0 and at 25°C (Monsanto, 1984). MITI online did not provide detailed information, whether the effect concentrations were nominal concentrations or from analytical monitoring. The observed effect is most probably a combined effect from both CBS and its hydrolysis products. Because the reported LC50 is higher than the water solubility of CBS (i.e. 0.32 mg/l), vehicle was most probably used in the study however detailed information regarding this issue is also not available.

Two Monsanto studies from 1979 with Pimephales promelas and from 1976 with Salmo gairdneri and Lepomis macrochirus are considered as invalid. The reason for Monsanto (1979) is the lack of analytical monitoring and the observable precipitation. The reason for Monsanto (1976) is the lack of aeration inducing that the oxygen saturation at the end of the study was less than 30%.