Avaliação integrada de qualidade da água e de multiresíduos de agrotóxicos do rio Ijuí no município de Cerro Largo/RS

Abstract

Currently the release of effluents, the drainage of contaminated areas and the use of pesticides are important sources of contamination of surface waters. In this sense, the objective of this work was to determine the quality of the water and to identify the presence of multiresidue of pesticides in five sampling points along the Ijuí River, in a stretch of the Municipality of Cerro Largo/RS. In the Resolution of the National Environment Council (CONAMA) n° 357/2005, such as UV absorbance (λ - 254 nm), positive/negative total coliforms (P/N), Escherichia Coli coliforms (P/N), electrical conductivity (μs cm-1 ), apparent color (uH), dissolved oxygen (OD) (mg L-1), nitrate (mg L-1), pH, sedimentable solids (mg L-1), turbidity (uT), temperature (°C), and by means of High Performance Liquid Chromatography coupled to a Mass Spectrometer (HPLC-MS) 24 pesticide compounds were determined. Four surface water collected were carried out, corresponding to the summer (03/18/2019), autumn (04/30/2019), winter (07/02/2019) and spring (10/23/2019), at five sampling points. The results referring to the physical-chemical parameters showed turbidity values higher than the Maximum Allowable Values (MAV) foreseen in CONAMA Resolution n° 357/2005 in the summer season, at the point CB, the values of the other physical-chemical parameters were accordingly, or MAVs were not established by the resolution. Regarding microbiological parameters, the presence of total coliforms and Escherichia coli was identified in 100% of the analyzed samples. Were detected, above the method limit of quantification (LOQm) in at least one of the analyzes, the multiresidues of pesticides, atrazine, azoxystrobin, cyproconazole, diphenoconazole, fipronil, imazetapyr, malathione, penoxsulam, pyrazosulfuron, profenophos and trifloxystrobin. Among the pesticides determined, CONAMA Resolution n° 357/2005 establishes MAV for atrazina, malathion and simazine. At the points where there was quantification of atrazine and simazina residues in the water samples from the Ijuí River, the values were within the MAV established by the resolution. However, the results obtained for malationa at PO and SC points, in the summer season and for atrazine, did not meet the limits established by the resolution. Although, in the majority, the parameters determined met the MAV of CONAMA Resolution n° 357/2005, it is pertinent to emphasize that continuous monitoring, as well as the analysis of a greater number of parameters, is fundamental to accurately determine the water quality of the Ijuí River.