Differential release and transformation of dissolved organic matter from common plastics in coastal waters

Plastics are a major source of anthropogenic pollution in coastal waters and can modify dissolved organic matter (DOM) depending on polymer type. A 21-day microcosm experiment incubating polypropylene (PP), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and nylon (Nyl) in autoclaved seawater under natural light was conducted to assess DOM release and transformation. FTIR spectroscopy indicated oxidative and hydrolytic degradation. Dissolved organic carbon (DOC) release followed the order PP, LDPE > Nyl > HDPE, reflecting differences in polymer structure and crystallinity. PARAFAC analysis of excitation–emission matrix (EEM) spectra identified humic-like (C, M) and protein-like (T, B) fluorophores. Blueshifts in C and M and a redshift in T fluorescence indicated the release of labile, less aromatic DOM. A strong positive correlation between DOC and the B fluorophore, along with elevated T:B and M:C ratios, confirmed enhanced bioavailable DOM, highlighting the role of polymer heterogeneity in altering coastal carbon cycling.