Acute toxicity of chlorophenols to green algae, Selenastrum capricornutum and Chlorella vulgaris, and quantitative structure‐activity relationships

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Abstract
The growth inhibition (96‐h EC50) of two species of green algae, Selenastrum capricornutum and Chlorella vulgaris, caused by phenol and 12 chlorophenols (from mono‐Cl to penta‐Cl) was determined according to the Organization for Economic Cooperation and Development guidelines for testing chemicals. The responses of the algae to the chemicals were measured by cell counting, and 96‐h EC50 values were correlated with six physicochemical parameters of chlorophenols. The parameters employed in the quantitative structure‐activity relationship (QSAR) analyses were n‐octanol/water partition coefficient (log Pow), dissociation constant (pKa), Hammett Σσ constant, index of valence molecular connectivity (1χv), perimeter of the efficient cross section of molecule (ΣD) and melting point (F). In the S. capricornutum assay, the toxicity increased as the number of substituted chlorine atoms increased. In the C. vulgaris assay, although toxicity increased from phenol to dichlorophenol, the toxicities of di‐, tri‐, tetra‐ and pentachlorophenol were almost the same. QSAR study shows that log Pow gives the best correlation, even in the C. vulgaris assay, by the use of the square of log Pow. Therefore, the growth inhibition of these algae caused by chlorophenols is mostly influenced by lipophilicity, as is stated frequently in toxicity studies using aquatic animals.