Pesticidas em sedimentos de fundo de cursos d’água em áreas agrícolas de Mato Grosso

Abstract

Sediment plays an important environmental role as it has a high potential to retain and accumulate chemical species, and its study in water resources quality monitoring programs is essential. The objective of this study was to determine the susceptibility to contamination by pesticides of bottom sediments from three microbasins within the São Lourenço watershed, whose areas are occupied predominantly by soybean, maize and cotton cultures which apply considerable amounts of pesticides. Bottom sediment samples were collected monthly for one year, at six sampling points located in the Pulador stream, Entre Rios stream and Ponte de Pedra stream, totaling 72 samples. Twenty-three pesticides were analyzed. The extraction of pesticide molecules from the sediment samples was performed by the QuEChERS method and the identification and quantification was done by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). Glyphosate residues determination was carried out by ion exchange chromatography (CTI). A total of 19 molecules were detected at concentrations ranging from 0.0054 mg.kg-1 to 0.769 mg kg-1. Bifenthrin was the active ingredient detected more frequently and at the highest concentration (0.769 mg kg-1). In the Pulador stream, the highest number of active ingredients was detected (17). From the pesticide residues found, the physical and chemical properties of the sediments and the landscape characteristics of the surrounding area and the water course, it is possible to infer that the Pulador stream, which has a lentic environment characteristic, is more susceptible to contamination by pesticides applied to agricultural crops. In the other two microbasins, there was only an eventual detection of pesticides at lower concentrations. The relatively low concentrations and detection frequency, in most cases, allow us to conclude that there is a low risk to the aquatic environment in the studied area. However, it is important to continue this monitoring in order to produce long-term information that supports the taking of mitigation measures in order to avoid possible contamination identified by the detection of some molecules in the studied sediments.