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Long-term toxicity to fish

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Based on the available results on short-term toxicity of thiourea to algae, daphnia and fish, as well as on the available long-term toxicity data on daphnia and subchronic toxicity data on fish, fish is expected to be the least sensitive species. Thus it is expected that additional long-term toxicity testing on fish according to OECD 210, 212, or 215 would not result in NOEC/EC10 values lower than the available NOEC values of 0.1 mg/L and 0.3 mg/L for invertebrates and algae, respectively. Therefore, additional long-term toxicity testing is deemed scientifically unjustified. Considering this and also due to animal welfare reasons a study proposal is not included in this dossier.

Key value for chemical safety assessment

Additional information

Friesel et al. (1984) determined the sub-chronic toxicity (lethal and sublethal effects) of thiourea to the freshwater fish species Brachydanio rerio according to the German Guideline "Subletale toxische Wirkungen beim Zebrabärbling Brachydanio rerio (Schwellenniveau der letalen und anderer Wirkungen, NOEC, mindestens 14-Tage)" which is similar to the OECD Guideline 204 (Fish, Prolonged Toxicity Test: 14-day Study).

The 14 -d NOEC was found to be 5,000 mg/L. At 10,000 mg/L all animals were alive after 14 d exposure.

With regard to sublethal effects (swimming behaviour, morphology, feed intake, and reaction to external environmental stimuli) the LOEC was determined to be 7,000 mg/L.

Tests performed according to OECD 204 (Fish, Prolonged Toxicity Test: 14-Day Study (OECD 1984)) or similar guidelines cannot be considered as suitable long-term tests (see ECHA guidance R.7b, p. 25). They are, in effect, prolonged acute studies with fish mortality as the major endpoint examined.

However, the ECHA guidance further states (see p. 51) that in case suitable long-term toxicity data on fish according to OECD 215, 212, or 210 are not available, standard testing data might be substituted by a reliable non-standard study for fish. In addition, if there is evidence to suggest that fish are likely to be at least a factor of about 10 less sensitive than invertebrates or algae there are no further requirements for fish testing according to the ECHA guidance.

The test conducted by Friesel et al. (1984) was rated Klimisch III (not reliable) due to insufficient documentation of study design/set-up and results. However, this study was conducted in the context of a research project of the German Federal Environmental Agency (UBA). Thus, it is assumed that the test was conducted in an adequate and reliable manner. Therefore, the 14-d NOEC of 5000 mg/L for Brachydanio rerio is used to assess the relative sensitivity of fish compared to algae and daphnids:

The key values for freshwater invertebrates and algae that are used in the chemical safety assessment are NOEC = 0.1 mg/L and NOEC = 0.3 mg/L, respectively. Hence the NOEC for fish is ca. a factor 17,000 to 50,000 higher than the NOEC values for algae and daphnia, respectively and it can be stated with sufficient reliabilty that fish is the least sensitive species with regard to toxicity of thiourea. This finding is further supported by the available results on short-term toxicity of thiourea to daphnia, algae and fish.

Thus it is expected that additional long-term toxicity testing on fish according to OECD 210, 212, or 215 would not result in NOEC/EC10 values lower than the available NOEC values of 0.1 mg/L and 0.3 mg/L for invertebrates and algae, respectively. Therefore, additional long-term toxicity testing is deemed scientifically unjustified. Considering this and also for animal welfare reasons a study proposal is not included in this dossier.

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