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Abstract

The middle valley of the "Rio Itajaí" is an important agricultural region in Santa Catarina state, producing mainly rice, corn and bananas. In these farming areas several different kinds of agrotoxics are used (among them "Round-up") in order to increase productivity and decrease the competition of weeds that grow among the crops. Round-up (C3H8NO3P) is too know by N-phosphonomethyl-glycine or isopropylaminic salt or glyphosate, and is used as herbicide. Round-up causes irritation in the skin, eyes and mucuous membrane of those who use it. A lethal oral dose for 50% of the sampling of rats is 4,320 mg/kg and a cutaneous dose for rabbits is 7,940 mg/kg. The analysis of the microalgae flora in the waters under investigation, showed very little microalgae in some places, and in others an indication of microalgae pollution by toxic substances. Aquatic organisms can acquire, accumulate and transfer these pollutants to higher trophic levels. The extent of this transfer depends on the microalgae's capacity to tolerate high concentrations of these substances. The pH in the environment may or may not influence the toxicity of the herbicide in question. Chloroficean Chlorella sp. was isolated from the rivers that received the herbicide (through surface draining), as well as pure incubated cultures at different pH values and different concentration of Round-up. The concentration reference was considered to be the one in the manufacture's instructions. The pure cultures which grew at pH values of 6.8 and 10.0, show the same growth pattern, in different concentrations of Round-up. The pH values for both changed to 7.0, and the cultures that grew at 4.0 initial pH, showed a much lower growth rate, compared with the first two.