Effect of Temperature, Snow-Ice, Particle Size, and Polymer Type on Photolysis of Polycyclic Aromatic Hydrocarbons Adsorbed on Microplastics under UV Irradiation

Microplastics (MPs) can adsorb polycyclic aromatic hydrocarbons (PAHs) and potentially transfer them to biota in aquatic environments. However, the environmental fate of PAHs adsorbed on MPs remains unclear. Recent studies suggest that photolysis may dominate the fate of the MP-adsorbed PAHs. Here, we show that high temperature and snow-ice enhanced the photolysis of MP-sorbed PAHs, while their first-order photolysis rate constants were independent of the size of MPs (170–850 μm). A correlation between the enhancement factor of snow and activation energy demonstrated that the enhancement effect of snow strongly affected relatively stable PAHs adsorbed on MPs. A comparison of the quantum yields of PAHs adsorbed onto MPs and soil revealed that the suppressive effect of soil on the photolysis of PAHs was greater than that of MPs. Among the tested polymers, polypropylene (PP) showed the lowest quantum yields (3.3 × 10^–6 (benzo[a]pyrene) – 2.9 × 10^–4 (fluorene)), followed by polystyrene (PS), polyethylene terephthalate (PET), and polyethylene (PE). This study contributes to estimate the environmental fate of MPs-sorbed PAHs, as there is a concern about the environmental impact of photodegradation of MPs-sorbed PAHs in Southeast Asia, where there are high emissions of PAHs under high sea temperature, and in polar regions where they are covered by snow-ice, which enhances the photolysis.