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The short-term toxicity of the substance 4-phenylbutan-2-one to aquatic invertebrates was studied in a limit test in accordance with OECD TG 202. No effects were seen at a nominal test concentration of 100 mg/L (95.4 mg/L as determined by TOC analysis). Studies on the short-term toxicity of the substance to fish and algae are not available. These endpoints were covered by studies with the structurally similar substance acetophenone, for which valid and reliable studies in accordance with official testing guidelines are available. The study of acute toxicity of acetophenone to fish (Pimephales promelas) over a period of 96 hours under flow-through conditions resulted in a LC50 value of 162 mg/L (converted to 199.8 mg/L for 4-phenylbutan-2-one). The study of acute algal toxicity of acetophenone was conducted under static conditions over a period of 72 hours with Pseudokirchneriella subcapitata. The EC50 and NOEC values based on the inhibition of growth rate were 86.4 mg/L and 24.8 mg/L (converted to 106.6 mg/L and 30.6 mg/L for 4-phenylbutan-2-one). It appears from the available data on aquatic short-term toxicity of the substance and structurally similar substances that freshwater algae are most sensitive to acute exposure to 4-phenylbutan-2-one or to the structurally related substance acetophenone. Since studies on the long-term aquatic toxicity of the substance are not available, the PNEC values will be derived from the converted EC50 value based on algal growth rate of 106.6 mg/L by applying appropriate assessment factors.

No microbial toxicity of 4-phenylbutan-2-one was seen in a toxicity control conducted in the course of the study on the ready biodegradability of the substance at a nominal concentration of 5 mg/L. The substance was readily biodegradable at this test concentration. Further testing of the inhibition of activated sludge respiration is therefore not necessary.