Residues of pesticides in the water of the Depression Central rivers in the State of Rio Grande do Sul, Brazil

The rice-growing activity is conducted out with intensive use of agrochemicals, which, depending on the management and rainfall can reach rivers. The study aimed to determine the residues of herbicides clomazone, quinclorac, propanil, bentazone, 2,4-D and imazethapyr and insecticides carbofuran and fipronil in the Vacacai and Vacacai-Mirim rivers, located in the Central Depression of Rio Grande do Sul, in the crop of 2003/04 until( 2007/08. Samples were collected from November to February (rice growing season). Analysis of herbicides and carbofuran were performed by HPLC-DAD and fipronil by GC-ECD. During 2003/04, in both rivers, the herbicide clomazone, 2,4-D and propanil were the most frequent in water samples. In 2004/05, the quinclorac was detected in many samples and in 2005/06 and 2006/07 season's fipronil was the most common pesticide in the samples in Vacacai and Vacacai-Mirim rivers. In the 2007/08 crop, there were less residues of pesticides in Vacacai and Vacacai-Mirim rivers. There is presence of pesticides used in rice farming in the Vacacai and Vacacai-Mirim rivers during the rice crop, especially among those analyzed, the herbicides clomazone and quinclorac and the insecticide fipronil.