Sorption and desorption of organophosphate pesticides, parathion and cadusafos, on tropical agricultural soils
Olvera-Velona , Angeluz (Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos(Mexique). Centro de Investigacion en Biotecnologia) | Benoit , Pierre (INRA , Thiverval-Grignon (France). UMR 1091 Environnement et Grandes Cultures) | Barriuso , Enrique (INRA , Thiverval-Grignon (France). UMR 1091 Environnement et Grandes Cultures) | Ortiz-Hernandez , Laura (Universidad Autónoma del Estado de Morelos, Cuernavaca, Morelos(Mexique). Centro de Investigacion en Biotecnologia)
Ecotoxicological impacts of organic pesticides on soil and aquatic ecosystems depend primarily on their behavior in soils. Actual pesticide knowledge is mostly restricted to soils from temperate climates, whereas knowledge of pesticide behavior in tropical soils is scarce. Here, the sorption behavior of two organophosphorous insecticides, parathion and cadusafos, was studied in three agricultural soil samples from central Mexico, Vertisols and Andosols. Using 14C-labeled substances, we assessed sorption and desorption properties in classical batch equilibrium and static soil incubation experiments. Our results show that cadusafos was less sorbed by the various soils (Kd values 7.6-12.7 L kg-1) compared with parathion (Kd values 38.6-74.9 L kg-1), despite similar log Kow values. Cadusafos exhibited a greater reversibility of sorption than parathion in both soil types. Time-dependent sorption was quantitatively significant, leading to a rapid decrease in the concentration of available insecticide. This finding is partly due to the formation of non-extractable, bound residues. The decrease in the available concentration of both insecticides was greater in the Andosol compared with the Vertisols. Soil organic matter clearly influenced the sorption behavior and availability of parathion. On the other hand, the sorption of cadusafos was more influenced by other soil properties such as clay content and cation exchange capacity. Calculation of residual insecticide levels in the soil solution suggests that both insecticides may have persistent toxic effects in the studied soils.
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