Dissolved black carbon mediated photo-transformation of tetrachlorantraniliprole: Kinetics, pathways, and adverse effects of the photoproduct

Abstract

The combustion of agricultural and forestry residues, along with subsequent runoff, can lead to the production of a significant quantities of dissolved black carbon (DBC), which plays a pivotal role in the photo-transformation of organic pesticides. As a result, the photochemical activity of DBC and its associated photo-transformation mechanisms must elucidate. This study investigated the effect of DBC on tetrachlorantraniliprole (TCTP) photo-transformation, a new type of pesticide independently developed and widely used in China, using photochemical simulation experiments. The results revealed that the prepared DBC had a smaller molecular weight and higher aromaticity, generating 3DBC*, ·OH, and 1O2, with apparent quantum yields of 4.75 × 10−2, 4.35 × 10−5, and 4.01 × 10−2, respectively. 3DBC* was the dominant intermediate reactive responsible for accelerating TCTP photolysis by determining its direct photolysis rate constant as 0.278 min−1. The degradation pathway of TCTP mainly involved nucleophilic substitution, dechlorination, and cleavage of the C–N bond. Notably, TCTP can photo-generate the cross-condensation products only in the presence of DBC. Ecotoxicity and organ-specific toxicity analysis demonstrated reduced environmental risks compared to TCTP for both direct photoproducts, as well as those mediated by DBC. These findings highlighted how DBC altered the photo-transformation pathway leading to decreased environmental risk-associated amide pesticides.