Impacto de lavouras na qualidade de águas de fontes naturais em propriedades do sul do Brasil

Abstract

Agricultural activities are strongly related to the environment, causing changes in soil and water. In small rural properties in the south of Brazil, it is common practice to consume water from wells and springs, often inserted within the cultivation areas. Therefore, the environmental monitoring of these waters, inserted in these areas, becomes important, in order to measure the effects of agricultural activities on the environment, and consequently, on the health of those who depend on it. Therefore, the objective of this study is to investigate whether agricultural activity, practiced in these places, causes changes in the quality of water from natural sources and their surroundings. For this evaluation, three sites were selected, one in each state in the southern region of Brazil (Paraná, Santa Catarina and Rio Grande do Sul), and studied for one year. Four soil and water samples were taken, one in each season, in the three properties. Physico-chemical, microbiological and ecotoxicological parameters of waters and soils were analyzed. The ecotoxicological tests performed were cytotoxicity and mutagenicity with Allium cepa and with the bioluminescent bacterium Vibrio Fischeri (Microtox®). The analyzes showed that the waters of PR and SC are unfit for consumption due to the presence of Escherichia coli, in addition to having pH values below or very close to the minimum required by Brazilian legislation. In the summer and autumn, the water samples showed high concentrations of COD and BOD and the lowest mitotic indices. Also in the summer, the water from the RS source showed high concentrations of nitrogen. Two soil samplings in the area adjacent to the PR and SC sources were found to be cytotoxic to A. cepa, however, without effects on the mutagenicity test. The source waters were not cytotoxic or mutagenic for the same test organism, however, there are micronuclei indicating contamination by chemical substances. The acute toxicity test with V. fischeri showed that water samples from PR (spring) and RS (autumn) showed high toxicity. In the integration of soil and water analysis, the fragility of the sources was evidenced, with changes in characteristics following the period of more intense cultivation in the crops. Studies like this are important to verify the environmental quality of areas of natural sources under the influence of anthropic activities, allowing to evaluate and implement measures to protect water quality.