Aging of polyethylene microplastics in agricultural soils has minimal effect on sorption and desorption of wastewater-derived organic contaminants

Microplastics in agricultural soils may act as sorptive agents for organic contaminants. This study investigated the effect of soil aging of linear low-density polyethylene (LLDPE) microplastics on the sorption and desorption of wastewater-derived organic contaminants. LLDPE microparticles 1% (w/w) were aged in three arable Entisols. Soil sampling was conducted after 0, 6, 11, 15, and 20 months of aging. At each sampling time, microparticles were extracted, characterized, and used as sorbents for 48 organic contaminants. Soil aging resulted in pronounced modifications of the LLDPE surface, mostly during the early stages of aging. These changes included an increase in polar surface characteristics, primarily due to the formation of an organic surface coating. Despite these changes, for most tested contaminants, the change in sorption affinity with aging time was relatively limited. Only six contaminants exhibited an increased sorption affinity exceeding one order of magnitude, primarily during the first 11 months of aging. Desorption experiments further indicated that, for most contaminants, sorption was reversible and independent of soil aging. Our data show that the soil organic matter or clay contents had little to no effect on the aging of LLDPE microplastics, in terms of both surface properties and organic contaminant sorption affinities. From an environmental perspective, these results quantitatively confirm that the contribution of LLDPE microplastics (700-1000 μm) to the overall sorption affinity of the receiving soils is limited, mainly due to their low specific surface area and relatively low abundance in soils. Accordingly, the presence of LLDPE microplastics in agricultural soils is expected to influence contaminant behavior primarily at the local, microscale level rather than altering the overall sorption balance of the soil. • 20-month soil aging modifies polyethylene (PE) microplastic surfaces • Surface modifications of PE microplastic were driven by organic matter coating • Surface modification occurred primarily within early stages of incubation • Soil properties did not affect the aging or sorptive properties of PE microplastics • Sorption of organic contaminants to PE microplastics was reversible