Ocorrência de pesticidas em águas superficiais, subterrâneas e pluviais em três microbacias do Rio São Lourenço, Mato Grosso

Abstract

In Mato Grosso's crops, especially soybean, corn and cotton, high plant productivity is achieved by using multiple pesticides to prevent or control pests. Once applied in the field, these compounds can, by various processes, contaminate water resources and considering the incipience of comprehensive studies in this state, the present work aimed to evaluate the occurrence of pesticides in three perennial watercourses of three microbasins of the São Lourenço River, using point and passive sampling techniques. This evaluation was based on the identification and quantification of 47 pesticides by ultra-high performance liquid chromatography coupled with sequence mass spectrometer (UHPLC-MS / MS). Surface, groundwater and rainwater samples were collected from December 2017 to November 2018. The method for pesticide extraction from the solid phase of the passive samplers was developed and validated, obtaining precision and acceptable accuracy for the determination of thirty pesticides and while for grab samples the extraction method used was adequate for thirty-four. Among the thirty-four pesticides studied, twenty-seven were detected in at least one kind of point sample. The pesticides atrazine, azoxystrobin, carbendazim, carbofuran, cyproconazole, clomazone, chlorantraniliprole, chlorpyrifos, diphenoconazole, malationa and metolachlor were observed in all three sample types and seven pesticides (fomesafem, haloxyphop-p- methyl, novaluron, pyriproxyfen, s-indoxacarb, sulfentrazone and teflubenzuron) were not detected in any sample, falling below concentrations detectable by the method. The highest concentrations and detection percentages were observed in rainwater samples due to the design of the collectors that accumulate dry as well as wet precipitation. The passive sampling technique applied in surface water confirmed the presence of the fifteen analytes detected by the grab sampling technique, and identified the pesticides acetamiprid, diuron, epoxiconazole, imazetapyr, imidacloprid, tebuconazole and thiodicarb that were not found in the grab samples and increased the percentage of detection of the active ingredients analyzed. Therefore, it is inferred that the use of passive sampler is a promising methodology for detection of pesticides at low concentrations. Since the pesticides studied were present at low concentrations in most samples, no risk to aquatic organisms was identified. Although, in some cases there was a high percentage of detection and considering that the collection points were selected considering conditions of greater vulnerability to contamination, it is suggested to continue monitoring to allow a more detailed risk assessment.