Plastic-derived dissolved organic matter release from agricultural mulch films: Impacts of solar UV weathering

Plastic mulch film coverings are increasingly used in sustainable agriculture production to better use water resources. As mulches weather in fields in contact with rainfall or irrigation water, they have potential to release a complex mixture of organic chemicals, often called plastic-derived dissolved organic matter (plastic-DOM). Photodegradation is a potentially important pathway for plastic-DOM generation, yet little is known about the quantities of plastic-DOM released from commercial biodegradable mulches during use. To address this unknown, we investigated the release of plastic-DOM from agricultural mulch films during ultraviolet (UV) weathering over growing season relevant timescales (months). We quantified the amount of plastic-DOM released from polyethylene (PE) and biodegradable mulches as a function of weathering conditions (in air or water) and time. We further assessed the composition of the mulch film plastic-DOM generated during weathering using fluorescence excitation-emission matrices (EEMs), which revealed formation of humic-like fluorescence signals in plastic-DOM from biodegradable mulch films with UV weathering. Results advance understanding on the quantities and composition of plastic-DOM released from mulches throughout the growing season, as a first step to estimate plastic-DOM's impact on receiving soils, groundwaters, and surface waters.