Effects of mixtures of oleic acid with chlorinated herbicides on Vibrio fischeri bacteria

Abstract

Abbreviations: D, diuron; EC50, effective concentration,causing the inhibition of function fifty per cent; EDTA, ethylenediamine tetraacetic acid; FAs, fatty acids; M, monuron; OA, oleic acid; OP, organochlorine pollutants; POM, particular organic matter The toxicity of chlorinated phenylurea herbicides and their mixtures with monounsaturated oleic (fatty) acid, OA, to bioluminescence of Vibrio fischeri was investigated. The EC50 of the inhibition of bioluminescence by mono- and di-chlorinated phenylureas such as monuron (M) and diuron (D) was found to be 13.5 and 1.05 ppm at 30 min. of exposure, respectively. The monuron at a concentration of 8 ppm inhibited bioluminescence by 40–43%, while diuron (0.6 ppm) decreased bioluminescence by 18% after 15 min of exposure. The toxicity of M and D at these concentrations was enhanced to 90% and 80%, respectively, by OA (up to 190 ppb) during the same exposure time. Different effects of phenylureas and OA were observed during a prolonged time of exposure up to 2 hours: (a) an increase in inhibition of bioluminescence during exposure to D and M at concentrations exceeding 0.8 and 10 ppm, respectively, and (b) slow recovery of bioluminescence after highest inhibition at 5–15 min of exposure to OA. Combined effects of OA and phenylurea herbicides depended on the time of exposure: an additive effect was observed after 5–15 min and synergistic after 1 h. The data show that monounsaturated fatty acid, which is usually used in formulations of technical pesticide preparations or is formed during (bio)degradation of the adjuvants to active ingredients (herbicides) can enhance the toxicity of herbicides to non-target species. Keywords: Vibrio fischeri, bioluminescence, toxicity, oleic acid, mixtures, monuron, diuron