Virgin and Photoaged Polyethylene Microplastics Have Different Effects on Collembola and Enchytraeids

Wariness is increasing about resident times of microplastics (MPs) in soils; however, limited knowledge is available on ultraviolet (UV) light exposure of MPs to soil fauna. This study investigated the effects of virgin and photoaged polyethylene microplastics (PE MPs) on soil mesofauna (enchytraeids and collembolans) at environmentally relevant concentrations in a microcosm incubation experiment. Ten individuals of each Enchytraeus crypticus and Folsomia candida and twenty Proisotoma minuta were exposed separately to virgin and photoaged PE MPs (40–48 μm) admixed in agricultural soil (0.2–2000 mg/kg) to evaluate reproduction and survival. After 28 d of exposure to photoaged PE MPs, there was a moderate survival reduction but reproduction promotion of E. crypticus. Contrastingly, F. candida exhibited an opposite trend, with survival enhancement and reproduction depression rates when exposed to both PE MP contaminated soils. However, P. minuta was the only species with significant apical endpoint changes after PE MP exposure; at 20 mg/kg photoaged and 2000 mg/kg virgin PE MP exposure, there was a 34% and 31% decrease in survival, respectively, and at 200 mg/kg photoaged PE MP exposure, an increase of 39% for reproduction. PE MPs had contrasting impacts on soil mesofauna species, which highlights the need to account for these variable results when understanding the repercussions of MP pollution on community assemblage and population dynamics in soils.