Carbon and nitrogen stable isotope fractionation during abiotic hydrolysis of pesticides

摘要

Compound-specific Stable Isotope Analysis (CSIA) has been recently established as a tool to study pesticide degradation in the environment. Among degradative processes, hydrolysis is environmentally relevant as it can be chemically or enzymatically mediated. Here, CSIA was used to examine stable carbon and nitrogen isotope fractionation during abiotic hydrolysis of legacy or currently used pesticides (chloroacetanilide herbicides: Acetochlor, Alachlor, S-Metolachlor and Butachlor, acylalanine fungicide: Metalaxyl, and triazine herbicide: Atrazine). Degradation products analysis and C-N dual-CSIA allowed to infer hydrolytic degradation pathways from carbon and nitrogen isotopic fractionation. Carbon isotopic fractionation for alkaline hydrolysis revealed similar apparent kinetic isotope effects (AKIE(c) = 1.03-1.07) for the 6 pesticides, which were consistent with SN2 type nucleophilic substitutions. Neither enantio-selectivity (EF approximate to 0.5) nor enantio-specific isotope fractionation occurred during hydrolysis of R (AKIE(c) = 1.04 0.01) and S (AKIE(c) = 1.04 +/- 0.02) enantiomers of a racemic mixture of Metalaxyl. Dual element isotope plots enabled to tease apart C-Cl bond breaking of alkane (Lambda approximate to epsilon(N)/epsilon(c) approximate to 0, Acetochlor, Butachlor) and aromatic pi-system (Lambda approximate to 0.2, Atrazine) from C-O bond breaking by dealkylation (Lambda approximate to 0.9, Metalaxyl). Reference values for abiotic versus biotic S(N)2 reactions derived from carbon and nitrogen CSIA may be used to untangle pesticide degradation pathways and evaluate in situ degradation during natural and engineered remediation. (C) 2018 Elsevier Ltd. All rights reserved.