Multi-element isotope fractionation analysis to investigate the photosensitized reactions of humic substance with 3-chloroaniline

This is the authors' abstract. We don't add key points for this paper.

• Multi-isotope fractionation analysis has potential to characterize photosensitized reactions of 3-chloroaniline. • Reactions of humic substances with 3-CA in aquatic environments exposed to sunlight. • Exited states induce parallel reactions with specific inverse C, normal H, N and Cl fractionation of 3-CA. • The enrichment factors (ε) for 2 H, 13 C, 15 N and 37 Cl of 3-CA allows analysis of degradation pathways. Dissolved organic matter including humic-like substances (HS), acting as photosensitizers participating in electron transfer reactions, can generate a variety of reactive species, such as OH radicals and excited triplet state HS ( 3 HS*) and related, which promote the degradation of organic contaminants such as 3-chloroaniline (3-CA). Multi-element-compound-specific stable isotope analysis (ME-CSIA) was applied to characterize photosensitized mechanisms employing 3-CA as a probe. HS were irradiated with artificial sunlight for elucidation of the reaction mechanisms by studying the kinetic isotope effect ( 2 H, 13 C, 15 N and 37 Cl) to characterize the first irreversible bond change reaction. Unique enrichment factors (-1.0 ± 0.3 ‰ for 13 C, 7.4 ± 1.7 ‰ for 2 H and 2.3 ± 0.7 ‰ for 37 Cl) have been detected in HS/UV experiments (OH radical and triplet state), which indicate complex reaction mechanisms. Triplet state reference experiments with the artificial photosensitizers 4,5,6,7-tetrachloro-2′,4′,5′,7′-tetraiodofluorescein in the presence of O 2 (Rose Bengal-O 2 ) or absence of O 2 (Rose Bengal-O 2 free) yielded characteristic enrichment factors (-0.3 ± 0.2 ‰ and -1.2 ± 0.2 ‰ for 13 C, 2.7 ± 0.5 ‰ and 4.8 ± 1.0 ‰ for 15 N and 8.4 ± 3.3 ‰ and 11.2 ± 6.8 ‰ for 37 Cl), allowing interpretation of reaction mechanisms of triplet state with 3-CA. The correlation of 2 H vs 13 C, 15 N vs 13 C and 37 N vs 13 C fractions could be used diagnostically to determine photosensitized reactions in the environment and to differentiate between biodegradation, hydrolysis and photosensitized HS reaction.