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Long-term toxicity to aquatic invertebrates

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Description of key information

After 21 days of exposure a NOEC (reproduction) of 0.0346 mg/L (measured) and a LOEC (reproduction) of 0.1035 mg/L (measured) for the substance was determined.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.035 mg/L

Additional information

A study was performed to assess the effects of 1,3-Dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione on the reproductive output of parthenogenetic Daphnia magna STRAUS under semi static conditions. The study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.20 'Daphnia magna Reproduction Test'' (2008), which equals in all relevant parts to the OECD Test guideline 211 (Daphnia magna Reproduction Test; adopted: Oct. 03, 2008).

Young female Daphnia, aged less than 24 hours at the start of the test, were exposed to a range of concentrations, nominally 0.01, 0.04, 0.13 and 0.4 mg/L of 1,3-Dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione dissolved in water. Auxiliaries used to prepare the test media were an ultrasonic bath, a magnetic stirrer and aseptic filters. After a 21d-exposure period, the total number of living offspring produced per parent animal alive at the end of the test was assessed. The reproductive output of the Daphnia exposed to the test item was compared to that of the control in order to determine the Lowest Observed Effect Concentration (LOEC) and the No Observed Effect Concentration (NOEC) according to Williams Multiple Sequential t-Test Procedure. Additionally, the Lowest Observed Effect Concentration (LOEC) and the No Observed Effect Concentration (NOEC) of the survival of the parent Daphnia was determined according to Williams Multiple Sequential t-Test Procedure and the time to production of first brood was determined.

The results are expressed in terms of time-weighted mean measured concentrations. Effective concentrations ranged from 75.38 % to 97.00 % of the nominal values in the freshly prepared media and from 73.85 % to 96.25 % in the media after 48 hours, or 72 hours of exposure.

This toxicity study is classified asacceptable and satisfies the guideline requirements for the chronic Daphnia study.