Chemical Dissipation from Outdoor Plastics: The Significant Impact of Transformation Processes Revealed by Adjusted Mass Transfer Modeling

Chemicals in plastics raise significant concerns for potential adverse environmental and health impacts. However, dissipation kinetics and fluxes of chemicals from outdoor plastic products remain largely uncharacterized, hindering the accurate assessment of their environmental exposure. This study quantified outdoor dissipation profiles for 20 "priority" chemicals, including sunscreens (benzophenone, benzophenone-3, octyl salicylate, etc.), phthalates, benzotriazole ultraviolet stabilizers (UV-P, UV-326, UV-327, etc.), and polycyclic aromatic hydrocarbons (PAHs), from 3 types of plastic protective nets over 180 days. Results revealed that levels of sunscreens and PAHs decreased to less than 50% of their initial concentrations within 5 days. Adjusted mass transfer modeling by integrating transformation processes well reproduced the dissipation kinetics (median determination coefficients R² = 0.82) and revealed synchronous release and transformation in the dissipation. Average dissipation half-lives of the chemicals were 19.7 days and positively correlated with the number of electron lone pairs and carbon atoms in the molecules. Unexpectedly, the transformation contributed 82.1% to the total chemical dissipation, especially for di(2-ethylhexyl) phthalate (DEHP) and UV-326. Suspect screening of formed products in PPNs suggested photolysis, ozone, and hydroxyl radical-induced oxidation as the primary transformation processes, supported by a high concentration of 2-ethylhexyl benzoate product comparable to its parent DEHP. These insights underscore the pivotal role of transformation in chemical dissipation from plastics, informing more precise emission assessment of chemicals and future efforts toward developing environmentally benign plastics.