Determinação de resíduos de pesticidas, em amostras de água e sedimento, na bacia hidrográfica do Rio Cuiabá, Mato Grosso

Abstract

The Cuiabá River is a major tributary of the Paraguay River, whose basin is of great importance in Brazil and internationally, for the Pantanal, one of the most extensive wetlands on the planet. Among the economic activities in the region of Cuiabá River basin agriculture has an important role, representing the region's economic base. To maintain high productivity the agricultural production requires high amount of agrochemicals such as pesticides that once introduced into the environment can undergo various processes of dispersion and reach different environmental matrices such as surface water. The present study therefore aimed to assess contamination by pesticides used on crops grown in the drainage area of the Rio Cuiaba in Mato Grosso. For this, we collected monthly samples of surface water and bottom sediment, from August 2011 to July 2012. Two multiresidue methods based on solid phase extraction were used for analysis of pesticide residues in water, both described in the literature. One employs gas chromatography coupled to mass spectrometry (GC/MS) to determine atrazine, cypermethrin, chlorpyrifos, endosulfan (α, β and sulfate), lambda cyhalothrin, malathion, metolachlor, metribuzin, methyl parathion, permethrin and trifuralin. For the determination of the same molecules in bottom sediment, a validated method described in the literature which consists of solid-liquid extraction by mechanical agitation followed by purification by liquid-liquid extraction with identification and quantification by GC/MS was used. The other method for analysis of water consists on the identification and quantification of pesticides carbendazim, carbosulfan, carbofuran, clomazone, diuron, imidacloprid, methomyl, pyraclostrobin, and thiamethoxam tebuconaloze by high performance liquid chromatography coupled to UV diode array detector (HPLC/DAD). For glyphosate, it was necessary to perform a validation procedure of the analytical method for water samples by ion exchange chromatography, where analytical parameters such as selectivity, linearity, precision, accuracy, limit of detection (LD), limit of quantification (LQ) were evaluated. Satisfactory results were obtained, indicating good performance of the method, recoveries of 84-101% and coefficient of variation lower than 8%; LD equal to 0.013 mg L-1

and LQ 0.038 mg L-1 . In surface water samples, the presence of only four active ingredients were identified once, which were α - endosulfan at a concentration of 0.36 μg L -1 , β-endosulfan at

0.12 μg L-1

, clomazone at 2.8 μg L-1

and malathion at 0.54 μg L-1

. In samples of bottom sediments pesticide residues were identified in samples collected in August and September 2011 and in January, February, April and July 2012, at concentrations ranging from 5.7 to 79.3 μg kg-1

. The two matrices studied showed pesticide contamination at sampling points in the Pantanal. Although the frequency of detection was low, the results indicate that there is a potential for transport of pesticides used in Cuiabá river basin and its tributaries which can reach the Pantanal.