Photochemistry of dissolved organic matter extracted from coastal seawater: Excited triplet-states and contents of phenolic moieties

Coastal seawater constitutes an important ecosystem receiving inputs of organic micropollutants (OMPs) such as sulfa antibiotics from land-based sources or mariculture activities. It is necessary to investigate photodegradation of OMPs in coastal seawaters for assessing their environmental fate and risks. However, effects of coastal seawater dissolved organic matter (S-DOM) on OMPs photodegradation are largely unknown, given that chemical compositions of S-DOM are different from those of freshwater DOM. Herein, photochemical characteristics of S-DOM extracted from Dalian coastal seawaters were investigated by simulating photochemical experiment adopting sulfachloropyridazine as a case. Results show that S-DOM accelerates the photodegradation mainly through excited triplet-state DOM ((DOM)-D-3*) with an apparent rate constant (4.43 x 10(8) M-1 s(-1)) ten folds of that of freshwater DOM, which is mainly due to much lower phenol contents detected in the S-DOM (0.022 mg-Gallic acid mg-C-1). The S-DOM impacted by mariculture can photogenerate more high-energy (DOM)-D-3* than those less impacted by mariculture, further contributing to the high (DOM)-D-3* reactivity. The study shows that to accurately predict photolytic persistence of OMPs in field water bodies, it is of significance to determine the second-order reaction rate constants between (DOM)-D-3* and target OMPs using DOM extracted from relevant water bodies. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study investigated the photochemical characteristics of S-DOM extracted from coastal seawaters and found that S-DOM accelerates the photodegradation of OMPs mainly through (DOM)-D-3*. Furthermore, the impact of mariculture on S-DOM influences the generation of (DOM)-D-3*, affecting the efficiency of photodegradation.