Rice Culture and Heavy Metal Contamination in the D’Una River Hydrographic Basin, Santa Catarina State, Brazil.

Abstract

Irrigated rice is grown in large areas from the coastal part of the Santa Catarina State, and constitutes a major economic activity; but it gives also rise to many conflicts because of soil and hydric resources use. This is the case for the D’Una River Hydrographic Basin, whose waters are defined as “class 1” by state regulations: the population from Imbituba, whose water supply comes from this river, and fishers from the lagoon complex which receives it’s waters, are in permanent conflict with the rice growers. In the rice culture many agrochemicals are used, especially to prevent herbs infestation. To evaluate the heavy metal contamination related to the rice culture in the Rio D’Una basin, samples were collected in two distinct periods: during May, 1997, and during February-March, 1998. The samples were analysed at the Chemistry Department, Federal University of Santa Catarina (UFSC), by Inductively Coupled Plasma Mass Spectrometry (ICP-MS); analysed parameters were Cr, Co, Ni, Cu, Zn, As, Cd, Hg, Tl and Pb. Considering all results, data for Pb, Cd, Hg and Ni are especially worrying, since the toxicity of these elements is well known. The presence of metal concentrations in levels highly above accepted limits put in evidence the interference of the rice culture in the area of study. Complementary studies shall be undertaken in the area, to evaluate the water quality related to the drainage of the rice squares, just before the rice sowing. On the other hand, considering the graveness of the problem represented by the contamination of the water collected for the public supply of the population of Imbituba, a thorough monitoring program should be undertaken, observing the periods relative to the several rice cultivation procedures. Besides that, a monitoring program in the Mirim Lagoon can lead to more objective answers about the possible relation between fisher’s denunciations and water contamination in this environment. Key Words: Rice, Water Contamination.