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Data on aquatic effects of thymol are available on three trophic levels (fish, daphnia and algae) for short-term toxicity and on two trophic levels (daphnia and algae) for long-term toxicity. The most sensitive short-term toxicity was observed for fish and daphnia with 96h-LC50 for fish of 3.2 mg/l and 48h-LC50 for daphnia of 3.2 mg/l, respectively. The most sensitive long-term effect was to algae with 72h-NOEC of 1.9 mg/l. Meanwhile a 3h-EC50 of 39.6 mg/l to activated sludge was also reported as the toxicity of thymol to microorganism.

The effect concentrations reported in this chapter are mostly nominal concentrations. Although the test concentrations of thymol were not analytically confirmed, the nominal concentrations are expected to remain constant throughout the experiments as thymol is considered hydrolytically stable based on its chemical structure.

According to column 2 of REACH Annex IX, further long-term toxicity tests should be proposed by the registrant if the chemical safety assessment indicates the need to further investigate effects on aquatic organisms as indicated by a PEC/PNEC ratio > 1. Having a PEC/PNEC ratio<1 for all exposure scenarios, there is no need to perform a long-term assay as the risk towards aquatic organisms is sufficiently controlled based on the already available information.