Investigation of microplastics release behavior from ozone-exposed plastic pipe materials

Microplastics (MPs) are detected in drinking water and plastic used during water treatment and distribution is one of the possible sources of MPs. This work aimed to investigate the MPs release behavior from ozone-exposed plastic pipe materials. The changes on physicochemical properties of the plastic materials were analyzed. The carbonyl groups introduction, the oxidation induction time variation, and the surface topography altering were detected after ozone exposure. The MPs release behavior varied between different plastic materials. As the ozone exposure duration of plastic materials prolonged, the released MPs abundance from the materials sharply increased, especially for LDPE, HDPE and PP. PVC was an exception where the released MPs abundance had little changes (p > 0.05). The total released MPs concentration from 20 h-aged samples could be ranked in order as follows: LDPE (656 ± 20 MP L^-1) > PP (349 ± 20 MP L^-1) > HDPE (337 ± 22 MP L^-1) > PVC (63 ± 13 MP L^-1). MPs release behavior was more likely to occur for LDPE, which was possibly related to the low oxidation resistance and weak stability of LDPE under ozone exposure. There was a more dominant contribution to MPs abundance increase caused by MPs release from aged plastic pipe materials than secondary MPs generation from original plastic particles. The generated MPs from 20 h-aged LDPE, HDPE, and PP accounted for 88.4%, 82.2%, and 88.3% of the total released MPs, respectively. For ozone-exposed plastic materials, the surface crack propagation and fragmentation posed an entry point for MPs generation. The proportion of generated MPs with polymer composition consistent with pipe materials (PE/PP) increased as the ozone exposure proceeded. Small-sized particles, especially 1-10 μm, were released more predominantly. This study provides an implication that possible MPs release from long-term aged plastic pipe materials under proper conditions could not be ignored.