Emission characteristics of volatile organic compounds from plastics exposed to sunlight

Fossil fuel-based synthetic polymers release substantial amounts of chemicals throughout their life cycle. Given their potential for accumulation and persistence in the environment, plastic-associated chemicals released into the surrounding matrix during weathering have gained attention due to potential hazards to both the environment and human health. Particularly, volatile organic compounds (VOCs), characterized by their high vapor pressure, can be emitted into the atmosphere as degradation products from plastics. Despite their significant impacts, the emission characteristics of these VOCs during the weathering process remain poorly understood. This study aims to fill this knowledge gap by systematically characterizing the VOC emissions from plastics exposed to outdoor conditions. Pellets of five types of plastic (low- and high-density polyethylene, LDPE and HDPE; polypropylene, PP; expanded polystyrene, EPS; polyethylene terephthalate, PET) prevalent in marine environments as debris were subjected to year-long outdoor exposure. Physical and chemical transformations were examined through Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrometry (FTIR), respectively, while VOCs were measured using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) under controlled heating conditions of 60℃ in a chamber. Over the course of a year, noticeable alterations in color, fragmentation, and the occurrence of cracks were evident in EPS, PP, and LDPE plastics with considerable chemical modifications. Mass spectra of VOCs from plastics susceptible to weathering exhibited increased peak intensity and the number of peaks over time. The proportion of oxygen-containing compounds increased as a function of exposure time, indicating photooxidation of the plastic backbone. VOC emissions in the control group exhibited a decreasing trend throughout the year, indicating their source from residuals contained in the pellets. In contrast, those of the exposure group showed an increasing trend, particularly in LDPE, PP, and EPS, attributed to the production of degradation products. Calculations of potential annual emissions using annual concentration changes revealed a 2.25-fold increase in VOC emissions in sunlight exposure compared with the control group. These findings emphasize the significance of evaluating VOC emissions originating from plastics in environments with direct sunlight exposure, especially beaches, which frequently serve as hotspots for the accumulation of marine plastic debris.

Acknowledgement: This study was supported by the grant “Development of technology for impact assessment of plastic debris on marine ecosystem” from the Korea Institute of Ocean Science and Technology (PEA0204).