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Long-term toxicity to fish

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The chronic toxicity of bronopol to rainbow trout (Oncorhynchus mykiss) was investigated in a 49 -day flow-through test according to OECD guideline 210 [Knoll Pharmaceuticals 1996]. Test parameters observed were mortality, sublethal effects, body length, body weight and condition indices.

A LC50 value of nominal 39.1 mg/L was determined. Survival of early life stage rainbow trout was significantly affected by a chronic treatment at nominal test concentrations of 40 mg/L. Mortality for all other test concentrations (2.25 - 21.50 mg/L) was within the control range. For the control, a mortality of 11.25 % was reported, which was in accordance with the validity criteria of OECD guideline 210 requesting a hatching success > 60 % and a post-hatch survival of 70 % for the control gourp. None of the treated groups differed significantly from the control in terms of body weight, length and condition indices. The resulting NOEC, based on mortalilty was 21.5 mg/L.

Analytical monitoring of the test substance revealed a recovery rate which was within 1.6 and 19.5 % of the nominal concentrations. A comparison to reference standards showed that at elevated pH values (8.16 - 8.23) and under aerobic conditions, bronopol seems to preferentially degrade to 2 -bromo-2 -nitroethanol.

Conclusively, there was no evidence for bronopol-related effects on fish growth and a NOEC of 21.5 mg/L could be derived.