Herbicidas ácidos e resíduos conjugados em serapilheira foliar e amendoim: desenvolvimento analítico, validação e monitoramento por QuEChERS-UHPLC-MS/MS

Abstract

Acidic herbicides are a class of pesticides widely used in agriculture and, more recently, associated with illegal chemical deforestation practices in the Brazilian Legal Amazon, with significant implications for human health and the environment. However, the reliable quantification of these compounds, especially their conjugated residues, remains an analytical challenge due to the complexity of environmental and food matrices. This study aimed to optimize, and validate analytical methods for the determination of 11 acidic herbicides and their conjugated residues in leaf litter, and 9 compounds in peanut-derived products, using QuEChERS-based extraction with alkaline hydrolysis and analysis by UHPLC-MS/MS. The hydrolytic extraction of leaf litter was performed using 5.00 g of sample, 1.70 mL of 5,0 mol L⁻¹ NaOH, under heating at 60 °C for 100 min, followed by freeze-out and dispersive solid-phase extraction (MgSO₄, C18, and graphitized carbon black). For peanut samples, 5.00 g of sample and 1.00 mL of the same alkaline solution was used, with hydrolysis at 60 °C for 30 min, and only freeze-out for clean-up. The methods achieved quantification limits of 0.040 mg kg⁻¹ (leaf litter) and 0.010 mg kg⁻¹ (peanut), with recoveries ranging from 70.0 to 118.6% and acceptable precision (<20%). Analysis of leaf litter samples collected from areas under investigation for chemical deforestation revealed the presence of 2,4-D and/or fluroxypyr at levels up to 40 mg kg⁻¹, both active ingredients used in defoliant formulations. In peanut-derived products, 2,4-D, haloxyfop-P, fluazifop-P, and fluroxypyr were detected. Although residue levels were below the maximum limits set by Anvisa, 45% of the samples exceeded the limits established by the European Food Safety Authority. For both matrices, comparative analyses without hydrolysis resulted in lower residue levels, highlighting the importance of deconjugation to avoid underreporting. The method developed for leaf litter proved to be a promising forensic tool for investigating environmental crimes related to chemical deforestation, while the method for food showed applicability in monitoring acidic herbicides in high-lipid content products.