title: Acute toxicity of benzoic acids to the crustacean Daphnia magna.
abstract: The acute immobilization toxicity of benzoic acids substituted with hydroxyl and/or methoxyl groups on the aromatic ring was determined for the freshwater crustacean Daphnia magna under neutralized condition (initial pH: 7.45+/-0.05). Toxicity, expressed as EC50 value, varied depending largely on the number and position of phenolic hydroxyl groups. Especially, benzoic acids with ortho-substituted hydroxyl groups were more toxic than benzoic acids with meta- and/or para-substituted hydroxyl groups. Whereas the limited data indicated that methoxyl substitution had relatively small and variable effects on the toxicity. Of the tested compounds, 2,4,6-trihydroxybenzoic acid showed the highest toxicity with the 48 h EC50 of 10 micromol l-1. This was 700 times as toxic as the parent benzoic acid (48 h EC50=7.0 mmol l-1) and about two orders of magnitude higher than those previously reported for monohalogenated benzoic acid derivatives in Daphnia. Within the subgroups based on the number of hydroxyl groups (N(OH)), the toxicity variations due to the position of hydroxyl groups appeared to be correlated with the logarithms of n-octanol/water partition coefficients (logPow). The toxicity of benzoic acids existing almost entirely as their ionized forms could be expressed as simple structure-toxicity relationships using these two descriptors (N(OH) and logPow).
authors.affiliation: Department of Environmental Science for Human Life, Faculty of Agriculture, Shizuoka University, 836 Ohya, Shizuoka 422-8529, Japan. ahykama@agr.shizuoka.ac.jp
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kamaya
authors.forename: Yuki
authors.initials: Y
authors.lastname: Fukaya
authors.forename: Kyoji
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D001565:Benzoates / Q000737:chemistry / Q000633:toxicity*; D003621:Daphnia / Q000187:drug effects* / Q000378:metabolism; D005618:Fresh Water; D062385:Hydroxybenzoates / Q000633:toxicity; D017665:Hydroxyl Radical / Q000737:chemistry; D020128:Inhibitory Concentration 50; D021281:Quantitative Structure-Activity Relationship; D012044:Regression Analysis; D023382:Toxicity Tests, Acute
chemical_list: D001565:Benzoates; D062385:Hydroxybenzoates; D017665:Hydroxyl Radical; C470931:2,4,6-trihydroxybenzoic acid