Abstract
Nonylphenol (NP), a kind of alkylphenol, is the chemical having toxicity for mainly reproduction to organisms. Toxicity of NP has been evaluated as a mixture because commercial and industrial NP product is isomeric mixture. However, limited information on toxicity of each isomer to aquatic organisms is available. To determine the fundamental toxicity of NP isomers, we performed acute toxicity test of a linear isomer (4-n-NP), 18 kinds of branched isomers, and an equivalent mixture of 19 isomers (linear and branched isomers) to larval medaka (Oryzias latipes). As a result of the test on OECD test guideline 203, median lethal concentration (96 h-LC50) of each isomer to Oryzias latipes was as follows: 4-n-NP, 439 μg/L; equivalent mixture, 265 μg/L; 18 branched isomers, 193 (NP-O)-450 (NP-A) μg/L. The 96 h-LC50 values of 17 branched isomers (except for NP-A) were lower than those of 4-n-NP. The relationship of NP isomers between 96 h-LC50 and molecular structure in this study differed from the report of relationship between estrogen activity and molecular structure.
