Aqueous picloram degradation by hydroxyl radicals: Unveiling mechanism, kinetics, and ecotoxicity through experimental and theoretical approaches

Autor(es)

Sanches-Neto, Flavio O. ^[1] ; Ramos, Bruno ^[2] ; Lastre-Acosta, Arlen M. ^[2] ; Teixeira, Antonio Carlos S. C. ^[2] ; Carvalho-Silva, Valter H. ^{[1, 3]}

Afiliação do(s) autor(es)

^[1] Univ Brasilia, Inst Quim, Caixa Postal 4478, BR-70904970 Caixa Postal, DF - Brazil

^[2] Univ Sao Paulo, Escola Politecn, Dept Chem Engn, Res Grp Adv Oxidat Proc AdOx, BR-05508010 Sao Paulo - Brazil

^[3] Goias State Univ, Res & Postgrad Ctr, Modeling Phys & Chem Transformat Div, Theoret & Struct Chem Grp, BR-75132903 Anapolis, Go - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Chemosphere; v. 278, SEP 2021.
• Citações Web of Science: 0

Resumo

Pesticides are chemical compounds widely used to combat pests in crops, and they thus play a key role in agricultural production. However, due to their persistence in aquatic environments, even at low concentrations, their use has been considered an environmental problem and caused concern regarding the adverse effects on human health. This paper reports, for the first time, the mechanisms, kinetics, and an evaluation of the toxicity of picloram degradation initiated by center dot OH radicals in the aqueous environment using quantum chemistry and computational toxicology calculations. The rate constants are calculated using a combination of formulations derived from the Transition State Theory in a realistic temperature range (250-310 K). The results indicate that the two favorable pathways (R1 and R5) of center dot OH -based reactions occur by addition to the pyridine ring. The calculated rate constant at 298 K is compared with the overall second-order reaction rate constant, quantified herein experimentally via the competition kinetics method and data available in the literature showing an excellent agreement. The toxicity assessment and a photolysis study provide important information: i) picloram and the majority of degradation products are estimated as harmful; however, ii) these compounds can suffer photolysis in sunlight. The results of the present study can help understand the mechanism of picloram, also providing important clues regarding risk assessment in aquatic environments as well as novel experimental information. (C) 2021 Elsevier Ltd. All rights reserved. (AU)

• Processo FAPESP: 19/24158-9 - Destinação ambiental de poluentes emergentes em águas superficiais e alternativas sustentáveis de mitigação: abordagem híbrida experimental-computacional
• Beneficiário: Antonio Carlos Silva Costa Teixeira
• Modalidade de apoio: Auxílio à Pesquisa - Regular