Predicting algal sensitivity to a pesticide stress

Abstract

AbstractTwelve freshwater phytoplankton species were used to investigate the factors affecting the toxicity of the organo‐phosphorus insecticide fenitrothion (O,O‐dimethyl‐O‐nitro‐m‐tolyl phosphorothioate) to algae. The unicellular chlorophytesAnkistrodesmus falcatus, Chlamydomonas segnis, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Chlorella vulgaris, Cosmariumsp.,Pediastrumsp.,Scenedesmus obliquus, Selenastrum capricornutum, and Staurastrumsp.; the bacillariophyteNaviculasp.; and the cyanophyteAnabaenasp. were exposed to three concentrations (0.1, 1.0, and 10.0 mg/L) of fenitrothion. Differential growth effects were observed among the species exposed to fenitrothion over short (96 h) and long‐term (14 d) durations. Fenitrothion concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 0.8 to 24.4 mg/L. Selected properties of the test algae (cell size, lipid content, and bioconcentration capacity) were measured and examined for their relationship to fenitrothion sensitivity. Strong correlations were obtained between fenitrothion sensitivity and cell surface area/volume (S/V) ratios, cell lipid content, and fenitrothion bioconcentration capacity of the cells, suggesting that these attributes may be useful predictors of differential sensitivity to lipophilic xenobiotics in unicellular phytoplankton. A positive relationship observed between cell S/V ratio and the bioconcentration of fenitrothion further implicates algal cell size as a significant factor in alga/pesticide interaction and subsequent vulnerability to lipophilic xenobiotics.