Adsorption of neonicotinoid insecticides by mulch film-derived microplastics and their combined toxicity

Mulch films allow for efficient crop production, yet their low recovery after use causes severe microplastics (MPs) pollution in agricultural soils. MPs in agricultural environments undergo complex ageing processes, which can alter their interactions with coexisting neonicotinoids and result in unpredictable ecological risks. Here, polyethylene (PE) and polybutylene adipate terephthalate (PBAT), typical mulch films, were chosen for the preparation of PE-MPs and PBAT-MPs. The adsorption of two common neonicotinoids, imidacloprid and dinotefuran, by the two MPs and their joint toxicity were examined. We found that the specific surface area of PBAT-MPs (7.59 m g) is greater than that of PE-MPs (2.83 m g), which results in a greater adsorption capacity for neonicotinoids. Additionally, ageing increased the adsorption capacity of MPs for neonicotinoids by 37.50-40.68 % for PBAT-MPs and 44.23-72.34 % for PE-MPs. This enhancement is attributed to the introduction of additional oxygen-containing functional groups on the MPs' surfaces, which can form hydrogen bonds with the amino groups in imidacloprid and dinotefuran. Furthermore, compared to single MPs and neonicotinoids, stronger inhibition in the growth of Escherichia coli and the germination of lettuce seeds was observed when they coexisted. This study highlights the importance of assessing the interactions between MPs and neonicotinoids and their joint toxicity, thereby improving our understanding of the potential risks of MPs towards the agricultural ecosystems.