New insight into environmental photochemistry of PAHs induced by dissolved organic matters: A model of naphthalene in seawater

The photochemical behavior of a model PAH, naphthalene, was investigated under simulated sunlight ir-radiation with different dissolved organic matter (DOM) in seawater. The results revealed that naphthalene was prone to direct photolysis (Phi(d) = 1.34 x 10(-3)) and could be degraded by (DOM)-D-3*/O-1(2)-induced reactions with fulvic acid (FA) and humic acid (HA) at low concentrations. However, the DOM at a high level dramatically decreased the k(obs) due to the higher light attenuation and radical competition effect. The presence of FA resulted in lower (DOM)-D-3*/O-1(2) generation and quantum yield compared with HA, but it achieved higher degradation kinetics due to the higher reactivity between (3)FA* and naphthalene and their lower binding effect. The naphthalene degradation in natural water with different depths and DOM were modeled based on the experimental results, which revealed the important role of indirect photolysis initiated by inorganic constituents. Moreover, several degradation intermediates were identified by GC-MS and three possible pathways were proposed. The Quantitative Structure Activity Relationships (QSAR) evaluation revealed that some intermediates are more toxic than original naphthalene. This study offers further insights into the photochemical behavior of PAHs, which will facilitate our understanding of the persistence and ecological risks of organic contaminants in natural waters. (C) 2022 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights reserved.

Automated summary

The photochemical behavior of naphthalene, a model PAH, was investigated under simulated sunlight irradiation in seawater with different dissolved organic matter (DOM). The results showed that naphthalene could undergo direct photolysis and degradation reactions induced by DOM and reactive oxygen species. The presence of fulvic acid and humic acid in DOM promoted the degradation kinetics of naphthalene. However, high levels of DOM led to reduced degradation rates. The study also identified degradation intermediates and found that some of them were more toxic than the original naphthalene.