Herbicide use, mainly glyphosate, has been intense in worldwide agriculture, including in the Brazilian Amazon region. This study aimed to validate a method for determining glyphosate and its degradation product, AMPA, and glufosinate by HPLC-FL in 58 water samples collected at the Santarém plateau region (Planalto Santareno), in the western of Pará state, Brazil. The method involves filtration and direct injection in the HPLC-FL for AMPA analysis, or previous concentration (10×) by lyophilization for glufosinate and glyphosate analysis. Analytes were oxidized and complexed with o-phthalaldehyde and 2-mercaptoethanol in a post-column reaction before fluorescence detection. LOQs for AMPA, glyphosate and glufosinate were established at 0.5, 0.2 and 0.3 μg L-1, respectively. A total of 58 samples were collected. Glyphosate and glufosinate were not detected in any of the 30 surface water samples collected in 2015 (<LOQ), and AMPA was detected in 6 samples (0.65-1.93 μg L-1). A total of 28 ground and surface water samples were collected in 2017 and analyzed for glyphosate, which was detected in 11 samples (7 ground water samples), with concentrations between 1.5 and 9.7 μg L-1. A continuous pesticide monitoring of the Amazonian water system is essential to guarantee the preservation of this important ecosystem.
Keywords: Brazilian Amazon; HPLC-FL; ground water; superficial water.