Combined effects of UV exposure and mechanical abrasion on microplastic fragmentation by polymer types

Abstract

Fragmented secondary microplastic particles account for the majority of microplastics in the field and have various origins, which makes proper control to be difficult. Scientific information is, however, quite limited, and this hypothesis is not tested yet. Therefore, effects of UV irradiation and (or) mechanical abrasion on fragmentation of polyethylene (PE), polypropylene (PP) and expanded polystyrene (EPS), the top three polymer types in marine debris monitoring study, was evaluated in laboratory condition. The apparent surface damage of PE and PP pellets and EPS spherules exposed to UV for 180 d was observed by SEM, FT-IR microscope and naked eyes. The surface damage of PP was faster than PE. After 120 d, the cracks on the surface of PE could be identified by naked eyes, while, after 60 d, the weakened PP was embrittled and easily broken down and fine cracks appeared. In case of EPS, yellow color appeared on 60 d after UV exposure and the surface was embrittled and started to create the fine particles on the surface. In the only mechanical abrasion experiment for 60 d, the average fragmented particles per bottle produced from PE, PP and EPS were 174±51, 214±14 and 57,339±7,504, respectively. In combination of UV exposure and subsequent mechanical abrasion for 60 d, the mean fragmented particles from PE, PP and EPS were 73±49, 1,442±123 and 723±134, respectively. In case of PE, 60 days of exposure period tois not tested yet. Therefore, effects of UV irradiation and (or) mechanical abrasion on fragmentation of polyethylene (PE), polypropylene (PP) and expanded polystyrene (EPS), the top three polymer types in marine debris monitoring study, was evaluated in laboratory condition. The apparent surface damage of PE and PP pellets and EPS spherules exposed to UV for 180 d was observed by SEM, FT-IR microscope and naked eyes. The surface damage of PP was faster than PE. After 120 d, the cracks on the surface of PE could be identified by naked eyes, while, after 60 d, the weakened PP was embrittled and easily broken down and fine cracks appeared. In case of EPS, yellow color appeared on 60 d after UV exposure and the surface was embrittled and started to create the fine particles on the surface. In the only mechanical abrasion experiment for 60 d, the average fragmented particles per bottle produced from PE, PP and EPS were 174±51, 214±14 and 57,339±7,504, respectively. In combination of UV exposure and subsequent mechanical abrasion for 60 d, the mean fragmented particles from PE, PP and EPS were 73±49, 1,442±123 and 723±134, respectively. In case of PE, 60 days of exposure period to