ECOTOXICOLOGICAL ASSESSMENT, USING BIOASSAYS WITH Daphnia magna, OF THE WATER IN RICE FARM, MUNICIPALITY OF MOSTARDAS, RS, BRAZIL.

Abstract

This study aimed to evaluate the acute toxicity of the water from the channels of rice fields irrigated by the Lagoa dos Patos, in the town of Mostardas,/RS, through the use of bioassays with the test organism Daphnia magna. Three sampling locations we selected: one near the point of water catchments (P1), an output of an area planting (P2), and another on the drain water return to the Patos Lagoon (P3). Samples were collected at three times during the production cycle: before, during and after irrigation, corresponding to the months of November 2007, January and March 2008. The tests were performed at the Laboratory of Ecotoxicology of UNISC, following the technical standard ABNT 12713. After 48h, the number of immobile individuals for concentration was observed, and from these data the percentage of immobility was calculated. The test result is expressed in Median Initial Effective Concentration - CE (I) 50 48h, which corresponds to the sample concentration at the beginning of the test, which causes acute effect of 50% of exposed organisms. The results indicated, in different sampling sites and stages of crop management, a low toxicity for this biological indicator, or even absence of toxicity, since it showed an EC (I) 50 48h more than 75% in the range of toxicity relative, according to the monitoring system established, an specific period that included the production cycle. In this sense, aimed at corroborating the results, it is suggested to increase the frequency of experimental design and conduct the sampling closer to the period of agrochemicals application.