Plasma-mediated aging process of different microplastics: Release of dissolved organic matter and formation of disinfection by-products

Abstract

The release of dissolved organic matter (DOM) from microplastics (MPs) in the water environment under physical, chemical, and biological transformation has been widely concerned. However, the impacts of released DOM on the subsequent generation of chlorinated disinfection by-products (DBPs) are still unknown. In this study, the leaching behaviors of organic matter from four types of MPs by plasma treatment were investigated, with polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) as the model MPs. The plasma treatment led to cracks, pits, and loose porous surfaces of MPs, and the C/O ratios of these four MPs significantly decreased. Simultaneously, the long-chain alkyl groups of the four MPs were weakened, and O-containing functional groups were introduced after the plasma treatment. As a result, the dissolved organic carbon (DOC) released from PP, PVC, PS, and PE after 120 min of plasma treatment were 4.35, 4.33, 5.09, and 14.0 mg L−1, respectively. The released conjugated organic compounds contained aromatic hydrocarbons and double bonds or hydroxyl groups, which were soluble microbial byproduct-like and humic acid-like substances. Trichloromethane (TCM) and dichloroacetic acid (DCAA) were the main DBPs in trihalomethanes (THMs) and haloacetic acids (HAAs). The DBPs in the four MPs filtrates were mainly HAAs, which reached 811.2, 780.2, 1234.7, and 420.7 μg L−1 in the PVC, PP, PE, and PS filtrates after 120 min of plasma treatment, respectively. Correlations among DBPs, UV–visible and fluorescence components of these four MPs were established. Overall, the released byproducts of MPs had the potential to be the precursors of DBPs, and thus their risks deserve more attention.