Phytoplankton differential sensitivity to pesticide stress: Predicting vulnerability and identifying response mechanisms in freshwater algae exposed to the insecticide fenitrothion.

Abstract

Axenic batch cultures of twelve freshwater phytoplankton species were used to study the molecular, cellular and population effects of the organophosphorus insecticide fenitrothion (O,O-Dimethyl-O-nitro-m-tolyl phosphorothioate) on algae. The unicellular chlorophytes Ankistrodesmus falcatus, Chlamydomonas segnis, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Chlorella vulgaris, Cosmarium sp., Pediastrum sp., Scenedesmus obliquus, Selenastrum capricomutum and Staurastrum sp., the bacillariophyte Navicula sp., and the cyanophyte Anabaena sp. were exposed to three treatment levels of fenitrothion. Differential algistasis was observed among the species exposed to fenitrothion over short and long-term durations. Effects on growth included an extension in lag-phase and/or alterations in growth rate and/or final standing crop. At the molecular level, alterations in the fatty acid composition of total lipids suggest that fenitrothion disrupts lipid synthesis and membrane structure. We hypothesize that fenitrothion prevented normal mitotic divisional processes from occurring. Uninhibited biomolecular synthesis resulted in an accumulation of macromolecules and subsequent cell weight augmentation. The ecological implications of the observed effects were discussed. In addition to effects studies, selected properties of the test algae (cell size functions, lipid content and fenitrothion bioaccumulation capacity) were measured and examined for their relationship to fenitrothion sensitivity. (Abstract shortened by UMI.)