Differential Impacts of Conventional and Biodegradable Microplastics on Cadmium Transfer in a Soil-Earthworm-Lettuce System

Microplastics (MPs) and cadmium (Cd) are widespread agricultural contaminants, yet the interactions of MPs with Cd in agroecosystems are unknown. Here, we conducted a microcosm experiment to investigate the impacts of different MP types, including conventional (CMPs) and biodegradable MPs (BMPs), on the transfer of Cd in a soil-earthworm-lettuce system. The high dose (2%) of CMPs significantly increased the Cd concentration in plant shoots and earthworms by 54.1% and 79.9%, respectively. However, high-dose BMP exposure decreased the shoot Cd concentration by 30.3%. This could be explained by significant changes in soil properties, available Cd, and microbial communities after CMP and BMP exposure. Metabolomic analysis revealed that the CMP was significantly more enriched than the BMP group in metabolic pathways related to organic acid biosynthesis, which may increase soil Cd availability. Our study provides important insights for understanding the potential risk of Cd contamination of the food chain under MP exposure.