Weathering of agricultural polyethylene films in cold climate regions: which parameters influence fragmentation?†

Plastic agricultural mulch films are used to improve the productivity of cultivable fields; however, their weathering and fragmentation could lead to release of microplastics and nanoplastics, both of which are considered potential health and environmental hazards. In this study, we examined the changes in physical and chemical properties of various plastic mulch films as they underwent different weathering processes. For this purpose, three commercially available polyethylene mulch films (one clear and two dark films) were evaluated under the following weathering conditions: laboratory treatments to evaluate the impacts of moisture, ultraviolet irradiation, pH, and freeze–thaw, as well as natural weathering conditions of a cold climate region. The morphologies and physicochemical properties of the polyethylene films were systematically studied following exposure to controlled and natural weathering. The three films, one of which was marketed as UV-resistant, underwent significant modifications. All weathered films were found to have increased surface roughness, suggesting that this could be the origin of microplastics or nanoplastics. While the dark pigments in the UV-resistant film protected the film against UV oxidation to some degree, they did not prevent deterioration caused by other types of weathering such as moisture, freeze–thaw, or natural weathering. The results of this study provide insights to understanding the fragmentation of polyethylene films into microplastics in winter and cold climate conditions.