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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The toxicity of hydroquinone to algae was investigated in a study conducted equivalent or similar to OECD Guideline 201 (Alga, Growth Inhibition Test). The 72 h ErC50 and NOEC (growth rate) were determined to be 0.330 mg/L and 0.019 mg/L (based on recalculated measured initial concentrations). The 72 h EyC50 and NOEC (yield) were determined to be 0.041 mg/L and 0.0085 mg/L (based on recalculated measured initial concentrations).

Key value for chemical safety assessment

EC50 for freshwater algae:
0.33 mg/L
EC10 or NOEC for freshwater algae:
0.019 mg/L

Additional information

The toxicity of hydroquinone to algae was investigated in a GLP-study conducted equivalent to OECD Guideline 201 (Alga, Growth Inhibition Test). Cultures ofPseudokirchnerella subcapitatawere exposed to nominal concentrations of 0.005, 0.01, 0.02, 0.040, 0.10, 0.25, 0.63, 1.6, and 3.9 mg/L in two separate tests. The test substance concentrations were monitored by HPLC/UV. At test start the initial concentrations were between 82 and 100% of the nominal values and were between 1.4 and 5.2% at test end. The mean measured concentrations (0-72 h geom. mean) were 0.0057, 0.018, 0.056, 0.11, 0.24, 0.45 mg/L and 0.00085, 0.0015, and 0.0033 mg/L (additional test) for 72 h under static conditions. As a result of measuring the concentration after 72 h, the 0.04 mg/L test concentration was below the lower LOQ. Therefore, the decrease of concentration with time was determined using an initial nominal concentration of 0.63 mg/L. Based on the decay curve, concentrations below the LOQ were calculated. The 72 h NOEC and EC50 (growth rate each) were determined to be 0.0015 mg/L and 0.053 mg/L, respectively.

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 algal test was re-evaluated based on the measured initial concentrations. The 72 h ErC50 and NOEC (growth rate) were determined to be 0.330 mg/L and 0.019 mg/L (based on recalculated measured initial concentrations). The 72 h EyC50 and NOEC (yield) were determined to be 0.041 mg/L and 0.0085 mg/L (based on recalculated measured initial concentrations). The validity criteria according to OECD Guideline 201 were fulfilled and this study is regarded as reliable without restriction.

For the hazard and risk assessment the effect concentrations for growth rate should be used: ErC50 and NOEC (growth rate) of 0.330 mg/L and 0.019 mg/L, respectively.