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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The growth rate of algae was determined as ErC50 (0-72 h) = 62.24 mg/L. Furthermore, a NOEC of 25.0 mg/L and a LOEC of 50.0 mg/L was calculated.

Key value for chemical safety assessment

EC50 for freshwater algae:
62.24 mg/L
EC10 or NOEC for freshwater algae:
25 mg/L

Additional information

In order to test acute toxicity to algae of 1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, Desmodesmus subspicatus was exposed to the test solution of five nominal concentrations of the test substance ( 6.3, 12.5, 25, 50 and 100 mg/L) and blank control solution for a period of 72 hours under static conditions. The cell densities were measured at 24 hours intervals. Inhibition of the algal population was measured as reduction in growth rate (index r), relative to control cultures grown under identical conditions. The measured concentrations confirm that deviation from the nominal concentrations was less than 30 % ( measured concentrations were in the range of 97.0 - 101.8 % of nominal concentrations). The growth rate of algae was determined as ErC50 (0-72 h) = 62.24 mg/L. Furthermore, a NOEC of 25.0 mg/L and a LOEC of 50.0 mg/L was calculated. This toxicity study is classified as acceptable and satisfies the guideline requirements for the acute algae study.