Effects of agriculture on ground water in a recharge area of Guarany Aquifer in Brazil.

The region of Ribeirão Preto City located in São Paulo State, southeastern Brazil, is an important and highly mechanized sugar cane producing area. It is also an important recharge area of the Guarany aquifer, which provides water to several cities and rural communities in the region. Research has been conducted in this region since 1995 to assess the behavior of herbicides, such as atrazine, simazine, ametryn, tebuthiuron, diuron, 2,4-D, picloram, and hexazinone, applied in the area. Nitrate applied as nitrogen fertilizer was also evaluated. Espraiado watershed, located over the recharge area, was chosen for this study. Water samples were collected from seven wells located inside the watershed and from surface water of Espraiado stream. Other samples were taken from city wells located at the edge of the recharge area with exception of the control samples that were collected from downtown wells. Results have shown that no residue of herbicide was found in ground water wells and only ametryn was found at levels higher than the Maximum Concentration Level (MCL) of 0.1 ?g/L in surface water of the watershed. However, nitrate was detected at levels close to the MCL of 10 mg/L in wells located in downtown, far away from the sugar cane area