Integrated approach for the assessment of impacts from pesticide use in transgenic crop productive system in the pampa´s plains of Argentina. Part 2: Water-sediment physico chemical characterization

MUGNI, H.; MARINO, D.J.G.; CREMONTE, C.; PERUZZO, P.J.; GUSTINCIC, M.V.; PORTA, A.A.; RONCO, A.E.; BONETTO, C.

Vilnius

Simposio; 11th International Symposium on Toxicity Assessment; 2003

Pesticide, nutrients, and basic physico-chemical parameters were determined in water, bottom sediments and surrounding soils of a first order stream draining a soybean-corn field. The stream traverse an adjacent breeding cattle field and about three km downstream goes through a widening colonized by a dense stand of Thypha sp. developing a small (20x100 m) natural  wetland. Cultures were applied twice, the first application was performed with a mixture of glifosate and cypermethrin and the second one with glifosate and clorpirifos. Nitrate and ammonium concentrations were comparatively small in the soy bean field, highest in the cattle field and lowest downstream the wetland, suggesting a large direct contribution from the cattle and eventual release from the bottom instertitial pool by cattle disturbance, followed by marsh downstream retention. Soluble reactive phosphorus (SRP) on the contrary increased downstream the marsh, simultaneously with oxygen depletion suggesting SRP release from the reduced bottom sediments, a  condition denoted by strong sulphur smell. Nutrients concentrations were higher during flood peaks caused by rain events, suggesting rain-mediated stream incorporation from the sorrounding soils. A detailed sampling event showed maximum nutrient concentrations in coincidence with peak discharge. Heavy metal distribution in water and sediment are within background regional concentrations. Low levels of insecticides were only detected in bottom sediments (below 0.030 mg cypermethrin /Kg wet) with highest concentrations in the wetland after spray, suggesting net retention within the marsh. Prediction of pesticide fate, analyzed by means of a MacKay?s type multimedia fate model, is in general agreement with chemical analyses.