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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

A study with the green alga Scendesmus subspicatus, resulted in EC10and EC50 values based on growth rate inhibition (ErCx) of 2.0 and 6.5 mg/L, respectively.  The 72 hr NOEC = <1.2 mg.L, based on growth.

Key value for chemical safety assessment

EC50 for freshwater algae:
6.5 mg/L
EC10 or NOEC for freshwater algae:
1.2 mg/L

Additional information

Reliable (Klimisch 1 or 2) toxicity studies with algae have been conducted for o-tert-butylphenol and included in this dossier. Reliable toxicity studies for algae conducted with the structural analogue, o-sec-butylphenol, are included as supporting studies.

Schulz (1994) conducted a reliable (Klimisch 2) GLP compliant study according to OECD 201 methods. In a 72-hour toxicity study, cultures of the green alga Scendesmus subspicatus (CHODAT 86.81 SAG) were exposed to o-tert-butylphenol at nominal concentrations of 1.2, 2.4, 5, 10, 20, and 40 mg/L under static conditions in accordance with EU method C.3 (Directive 92/69/EEC) and OECD guideline 201 (1984). The EC10and EC50values based on growth rate inhibition (ErCx) were 2.0 and 6.5 mg/L, respectively. The 72 hr NOEC is <1.2 mg/L, based on growth.

MOE Japan (1999) conducted a reliable (Klimisch 1) GLP compliant study according to OECD 201 methods. In a 72-hour toxicity study, cultures of the alga, Pseudokirchneriella subcapitata, were exposed to the analogue, o-sec-butylphenol, at nominal concentrations of 1.0, 1.8, 3.2, 5.6, 10, 18 and 32 mg/Lunder static conditions in accordance with OECD guideline 201 (1984). The 72 -hr NOEC and EC50 values, based on growth rate inhibition (ErCx) were 1.8 and 6.9 mg/L, respectively.

Adequate reliable measured data exists for toxicity to algae to o-tert-butylphenol and the analogue, o-sec-butylphenol. The data point of highest concern for this endpoint has been identified in a reliable study which reports a measured 72 hr EC50 of 6.5 mg/L and 72 hr NOEC of <1.2 mg/L, based on growth, for toxicity to aquatic algae. Consequently these values will be taken as the toxicity in aquatic algae endpoint for o-tert-butylphenol.