LAUSR

Despite the high algogenic dissolved organic matter (A-DOM) content in the marine environment, the impact of A-DOM on the environmental behavior of alkylated polycyclic aromatic hydrocarbons (A-PAHs) has rarely been reported. Thus, this study sought to investigate the changes in A-DOM and its interaction with phenanthrene (Phe) and 3-methylphenanthrene (3-MPhe). The results showed that the spectroscopic characteristics of A-DOM changed dynamically during the entire growth period of Prorocentrum donghaiense. The total proportions of humic-like components in A-DOM, including marine humic-like and longer wavelength humic-like components, increased from 26.30% at the initial phase to 40.42% at the decline phase, but those of protein-like components decreased. Humic-like components showed stronger interaction capabilities with Phe/3-MPhe than that of protein-like components. The interaction characteristics and increased the humic-like components content indicated their prominent role in the interaction of A-DOM and Phe/3-MPhe. 3-MPhe had stronger hydrophobic interactions with the humic-like components and the methyl group increased π-π interactions with A-DOM on day 28. Methyl group also increased the molecular weight and steric hindrance of 3-MPhe, resulting in a lower interaction capability with A-DOM than that of Phe on day 16. The diverse interaction behaviors of A-DOM fluorescent components with Phe and 3-MPhe were largely attributed to dynamic changes in the A-DOM characteristics. Methyl substitution varied the hydrophobicity and molecular weight of Phe and 3-MPhe, and further influenced the interactions with A-DOM fluorescent components. These results highlight the vital impact of dynamic A-DOM on the environmental behavior of PAHs, and the differences in the environmental behavior between parent and alkylated PAHs should also receive additional attention.