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Long-term toxicity to aquatic invertebrates

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Description of key information

The long-term toxicity of hydroquinone was investigated in a GLP-study conducted according to OECD Guideline 211 (Daphnia magna Reproduction Test). A 21 d NOEC (reproduction)=0.0057 mg/L based on recalculated measured initial concentration was found.

Key value for chemical safety assessment

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

Additional information

The long-term toxicity of hydroquinone was investigated in a study conducted according to OECD Guideline 211 (Daphnia magnaReproduction Test) under GLP. Daphnids were exposed to nominal concentrations of 0 (control), 0.0081, 0.016, 0.033, 0.065, and 0.13 mg/L under semi-static conditions with a 24 hour renewal period of the test water. The test concentrations were monitored via HPLC/UV in three exposure periods on days 0 -1, 10 -11 and 20 -21. The mean values of the measured initial concentrations were

0.0057. 0.012, 0.027, 0.054 and 0.106 mg/L. During the 24 hour test period the hydroquinone concentration decreased rapidly.

The authors used the mean measured concentrations for the evaluation. The mean measured concentrations (time-weighted average) were 0 (control), 0.0029, 0.0049, 0.014, 0.039, and 0.076 mg/L for 21 d. Effect parameters observed were inhibition of reproduction, cumulative number of surviving offspring, first day of birth, death and body length of parent daphnias, occurrence of aborted eggs and male individuals. The 21 d LC50 for parental daphnids was calculated to be 0.061 mg/L based on mean measured concentrations. The calculated 21 d EC50, NOEC and LOEC for inhibition of reproduction were calculated to be 0.080, 0.0029, and 0.0049 mg/L based on mean measured concentrations.

However, hydroquinone is known to be fast degraded to several toxic degradation products depending on the environmental conditions like oxygen, pH and light (e.g. p-benzoquinone). The degradation products were not analyses in this study.

Provided that the formed degradation products are also of high ecotoxicity the evaluation of the test based on the concentration of the parent compound alone may overestimate its toxicity. Provided further that the total amount of toxic equivalents is stable during the exposure period the initial concentration is regarded as relevant concentration. Therefore, the daphnia test was re-evaluated based on the measured initial concentration. Thus, a 21 d NOEC=0.0057 mg/L based on recalculated measured initial concentration was found.