PARTITION OF PESTICIDES OF THE COUMARIN FAMILY BETWEEN WATER AND AMPHIPHILIC AGGREGATES

Coumarin derivatives used as pesticides may accumulate in hydrophobic microstructures, such as biological membranes, aggregates of humic and fulvic acids, and micelles of pollutant surface active agents. In thi s work, we present a comparison of three photophysical methods for the determination of the membrane-water and micelle-water partition const ants, K-p, of two pesticides O,O-diethyl-O-(4-methylcoumarin-7-yl)thio phosphate (potasan) and O,O-diethyl-O-(3-chloro-4-methyl coumarin-7-yl )thiophosphate (coumaphos) and their parent compounds 4-methyl-7-metho xy coumarin and 3-chloro-4-methyl-7-methoxy coumarin (MMC and CIMMC), respectively. Micelles of an anionic surfactant, sodium dodecyl sulfat e (SDS); a nonionic surfactant, polyoxyethylene(10) lauryl ether (C(12 )E(10)); and bilayers of a zwitterionic phospholipid 1,2-dimiristoyl-s n-glycerophosphocholine (DMPC) in aqueous suspensions buffered at pH 7 .4 are used. The values of the partition coefficients obtained by the fluorescence anisotropy method proved to be more universal and reliabl e than those based upon the medium dependence of the fluorescence quan tum yield and lifetime. The obtained partition constants are compared with the universal predictor, K-OW, and with the solubility in water. In this family of com pounds, there is no correlation between the K-p and the hydrophobicity. The results are analyzed in terms of the molec ular interactions and the solubilization site of the solutes in the ag gregates, and the use of hydrophobicity in the analysis of bioconcentr ation of these compounds is discussed.