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*, & sdot;OH, and 1O2, with apparent quantum yields of 4.75 x 10-2, 4.35 x 10-5, and 4.01 x 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 phototransformation pathway leading to decreased environmental risk-associated amide pesticides.