Pesticides in soil sediment, and water samples from a small microbasin in the Brazilian cerrados

The expansion of intensive agriculture in the tropics is leading to increasing concern about environmental pollution from pesticides in these regions. This study was conducted in the Brazilian savannas, also known as the Cerrados near Uberlândia, to determine the magnitude of biocide concentrations in the small catchment of the Pantaninho stream and its reservoirs. Samples of soils, surface and well water, and sediments were collected on 10-12 December 1995, and analyzed for 15 herbicides and insecticides. In all surface-water samples, atrazine was detected at concentrations of 0.05-0.13 micro g/L. The sampled well water (used for drinking) on farms did not contain detectable residues of biocides. Sediments, taken from the stream's banks, were contaminated at two sampling locations with either X-cyhalothrin (at 4.0 micro g/kg) or simazine (at 3.2 micro g/kg). Soil samples from maize fields usually showed higher concentrations of simazine, atrazine, and chlorpyrifos (ranging from 80 to 180 micro g/kg at 18 to 35 days after application) than did those from soybean fields. Fluazifop-butyl, monocrotophos, and x-cyhalothrin were found 0-8 days after application at concentrations between 5 and 25 microg/kg. Carry-over residues of metolachlor, atrazine, simazine, cyanazine, and trifluralin were also detected at concentrations of around 2-15 micro g/kg, indicating that pesticides can accumulate in tropical soils. Sampling at depth in a maize field proved that simazine and atrazine, although mainly restricted to the top 10-cm layer (40-120 micro g/kg), are highly mobile, as was triazine, which was continuously detected at the maximum sampling depth (70 cm) in concentrations of 2-4 micro g/kg. Although, when compared with temperate regions, these concentration levels of biocides were medium to low, they showed a potential for accumulation and leaching, which, over the long term, may lead to pollution of water resources.