SUBLETHAL EFFECTS OF THE INSECTICIDE FENITROTHION ON FRESH-WATER PHYTOPLANKTON

The effects of the insecticide fenitrothion ethyl-O-(3-methyl-4-nitrop henyl)-phosphorothioate) were investigated on the unicellular phytopla nkton Ankistrodesmus falcatus, Chlamydomonas reinhardtii, Chlamydomona s segnis, Chlorella pyenoidosa, Navicula sp., Scenedesmus obliquus, Se lenastrum capricornutum, and Staurastrum sp. at concentrations of 0.1, 1.0, and 10 mg.L(-1). Following a 24-h exposure, total lipids, fatty acid profiles, and bioaccumulation of fenitrothion into algal cells we re determined for the above species. Total lipids may play an importan t role in determining sensitivity of phytoplankton to fenitrothion str ess over 96-h exposures. A saturation occurred in A. falcatus membrane s represented by the 5.4 and 4.3% increases in palmitic (16:0) and ole ic (18:1) acids, respectively, and 1.8 and 7.6% decreases in linoleic (18:2) and linolenic (18:3) acids, respectively. This resulted in a sh ift from a profile dominated by linolenic (18:3) acid to one dominated by the more saturated oleic (18:1) acid. Bioconcentration factors (BC F), or the ratio of the total radiocarbon associated with algae, calcu lated for viable Chlamydomonas reinhardtii and Chlamydomonas segnis ce lls were 293 and 124, respectively. BCFs for dead cells were 1261 and 1025 for the same species, respectively. These investigations showed d ifferential insecticide bioaccumulation between species. This bioaccum ulation was shown to be correlated with the total lipid content of alg al cells.