Warming exponentially stimulates photoleaching of dissolved organic matter from multiple microplastics

The substantial release of microplastics (MPs) into the marine environment is now deeply integrated into Earth’s carbon cycle. However, the mechanisms by which warming regulates the release of MP-leached dissolved organic matter (MP-DOM) in seawater media remain highly uncertain. This work considers four typical MPs that enter the ocean (polyethylene, PE; polypropylene, PP; polyethylene terephthalate, PET; and polyvinyl chloride, PVC) over 1-week experiments under UV light and dark conditions at a narrow temperature interval of 5 °C between10-35 °C. The results indicate that different MPs have variable photoleaching rates of dissolved organic carbon (MP-DOC, 0.06 ± 0.01 to 0.61 ± 0.07 mg-C/g-MP/week) and fluorescent DOM (MP-FDOM). An unexpected inconsistency emerged in the photoleaching of MP-DOC and MP-FDOM, with dominant MP-DOC release for PE, PP and PVC, while PET showed substantial release of both. The humification index and biological index pair is a useful indicator to distinguish MP-DOM versus natural DOM. The Q₁₀ values, which reflect the temperature sensitivity of MP-DOC photoleaching, ranged from 1.62 (PVC) to 1.93 (PET) indicating an exponential increase in MP-DOC leaching rates with rising temperature. These findings highlight the need for incorporating ocean warming into predicting the effects of plastic pollution on the marine carbon cycle.