‘Acid Rain’ Amplifies the Impacts of Polyvinyl Chloride Microplastics on Heavy Metal Toxicity and Transfer in Soil-Lettuce Systems

Microplastic pollution, particularly from persistent polyvinyl chloride (PVC) plastics, and the increasing prevalence of “acid rain” (AR) pose considerable environmental risks to food crops. However, the coexposure effects of PVC and AR on heavy metal transfer in soil-crop systems and the associated underlying mechanisms remain poorly understood. This study employed multiomic approaches to investigate the synergistic effects of PVC and AR on Cd and As bioavailability, bacterial diversity, metabolites, and microbial functional genes in a soil–lettuce pot system. The results showed that PVC and AR coexposure increased Cd accumulation by 51.9% and decreased As uptake by 32.5%. This was likely due to changes in soil pH and metal mobility. The microbial analysis identified Sphingopyxis and Bacillus as key genera linked to plant Cd and As accumulation. The metabolomic analysis revealed suppressed energy balance and cellular growth, coupled with enhanced lipid-related pathways, suggesting an adaptive response in the soil system to environmental stress. The metagenomic analysis further revealed the downregulation of essential metabolic genes and upregulation of adaptive pathways, including ABC transporters and nitrogen metabolism. This study provides critical insights into the effects of coexposure to PVC and AR on heavy metal transfer, highlighting the need for sustainable agricultural practices to ensure safe crop production in contaminated areas.