DISSIPATION AND DISTRIBUTION OF ATRAZINE, SIMAZINE, CHLORPYRIFOS, ANDTETRADIFON RESIDUES IN CITRUS ORCHARD SOIL

An environmental fate study was conducted in a citrus orchard plot in Valencia (Spain) In the fall of 1993. Dissipation and distribution of atrazine, simazine, chlorpyrifos and tetradifon residues following the ir controlled addition for agricultural purposes in a mediterranean re d soil (Luvic Calcisol, Rhodoxeralf) were evaluated. During a two-mont h period, the amounts of applied pesticides in different soil layers ( 0-0.05, 0.05-0.22, 0.22-0.42, and 0.42-0.52 m) were monitored, In addi tion, information on soils, weather and agricultural practice were col lected. Degradation half-lives were calculated, assuming zero-order ki netics: 11 days far atrazine, 12 days for simazine, 10 days for chlorp yrifos, and 18 for tetradifon. The distribution through the soil profi le shows that the pesticide concentrations: were always highest in the upper layer (0-0.05 m) of soil, and that atrazine was the most mobile of all the four pesticides investigated.