Aging of biodegradable-mulch-derived microplastics reduces their sorption capacity of atrazine

Degradable plastics are gradually regarded as alternatives of conventional, synthetic organic polymers to reduce the plastics or microplastics (MPs) pollution; however, the reports upon environmental risk of degradable plastics are still limited. In order to evaluate the potential vector effect of biodegradable MPs on coexisting contaminants, sorption of atrazine onto pristine and ultraviolet-aged (UV) polybutylene adipate co-terephthalate (PBAT) MPs and polybutylene succinate co-terephthalate (PBST) MPs were investigated. The results showed that, UV aging led to more wrinkles and cracks on the surface, increased homogeneous chains proportion, enhanced hydrophobicity, and enlarged crystallinity of both MPs. The sorption kinetics of atrazine to MPs fitted well into pseudo-first-order (R² = 0.809-0.996) and pseudo-second-order (R² = 0.889-0.994) models. In the concentration range of 0.5-25 mg L^-1, the sorption isotherm fitted into linear (R² = 0.967-0.996) and Freundlich model (R² = 0.972-0.997), indicating that the absorption partitioning was the dominant sorption mechanism. The partition coefficient (K_d) of atrazine to PBAT- MPs (40.11-66.01 L kg^-1) was higher than that of PBST- MPs (34.34-57.96 L kg^-1), and the K_d values of both MPs declined for aged MPs. The specific surface area, hydrophobicity, polarity and crystallinity of MPs jointly interpreted the changing sorption capacity of the MPs. In the present study, both aged PBAT- and aged PBST- MPs exhibited lower vector potential to atrazine than pristine MPs, suggesting reduced risk of being a pollutant carrier, which is of great significance for the development of biodegradable plastics.