Acute Toxicity and Hatching Inhibition of Chlorophenols to Japanese Medaka, Oryzias latipes and Structure-Activity Relationships

Abstract

Acute toxicities and hatching inhibitions of embryo by 14 chlorophenols from mono-Cl to penta-Cl and phenol to Japanese Medaka, Oryzias latipes, have been determined as 96 h-LC₅₀ and 15 d-EC₅₀, respectively and studied in terms of quantitative structure-activity relationship (QSAR). The 6 physico-chemical parameters of chlorophenols employed in this study were : n-octanol/water partition coefficient, log P_ow ; dissociation constant, pK_a ; Hammett constant, Σσ ; index of valence molecular connectivity, ¹X^v ; perimeter of the efficient cross section of molecule, ΣD ; melting point, F. On the whole, acute toxicity and hatching inhibition of chlorophenols increase with a degree of chlorination and ortho-isomers appear as less toxic than meta-and para-isomers. QSAR study shows that log P_ow, a parameter of hydrophobicity, gives the best correlation with the activity. With regard to each chlorophenol, 96 h-LC₅₀ of Oryzias latipes agrees with that of another kind of fish, Lebistes reticulatus (guppy). High correlations were found among 96 h-LC₅₀ and 15 d-EC₅₀ values of Oryzias latipes, EC₅₀ values of growth inhibition of green algae, Selenastrum capricornutum and EC₅₀ values of immobilization of Daphnia magna, Daphnia carinata and Daphnia pulex.