Impact of Long Term Applications of Cotton Pesticides on Soil Biological Properties, Dissipation of [c]-methyl Parathion and Persistence of Multi-pesticide Residues*

Biological parameters were followed in soils from a cotton farm (Tatui) where the recommended pesticides have been used for years, and from an experimental field (São Paulo) which was subdivided in two areas: one received the recommended pesticides and the other was maintained untreated. The soil bioactivities monitored from 1995 to 1998, after different pesticide applications, were: basal and glucose-induced respiration; anaerobic activity; nitrification rate; activity of the enzymes: dehydrogenase, aryl sulfatase and arginine deaminase; the soil capacity to mineralize an aromatic pesticide molecule ([C]-2,4-D), fungal and bacterial contributions for soil respiration until the beginning of 1998, and fungal and bacterial numbers from the beginning of 1998. The dissipation of [C]-methyl parathion one of the recommended pesticides was followed by radiometric techniques only in São Paulo, but persistence of multi-residues was determined in both soils by gas-liquid chromatography. All the biological parameters varied each sampling time and values also varied among soil samples, being inhibited or stimulated by the different pesticide applications, but they mostly recovered the initially detected activity. Dissipation of methyl parathion was fast and not affected by the other pesticide applications. Pesticide residues varied between the two soils but were mostly low after all applications, which indicates their dissipation.