Effects of composite microplastics on soil properties and the physiological and biochemical characteristics of Chinese cabbage

Microplastics (MPs), as a novel environmental pollutant, are widely distributed in the environment and negatively impact ecosystems and biodiversity, posing potential risks to human health through the food chain. However, there is limited knowledge about the adverse effects of composite MPs on soil-plant systems. To address this lack of data, a pot experiment was conducted using polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyolefin (PO) in various combinations: PP-PE-PVC, PP-PE-PO, PE-PVC-PO, PVC-PO-PP, and PP-PO-PE-PVC. The study investigated composite MPs effects on soil properties and physiological-biochemical indicators of Chinese cabbage (Brassica napus L.). The results indicated that 2% concentration of different types of composite MP pollution significantly increased soil pH while reducing soil water content, organic matter, ammonium nitrogen, nitrate nitrogen, available phosphorus, sucrase activity, urease activity, and soil microbial numbers. Soil catalase (CAT) activity initially increased and then decreased. The effect of composite MP pollution on Chinese cabbage revealed that it significantly reduced water content, plant height, and chlorophyll content, while promoting root length growth. Additionally, it had a negative effect on the activities of CAT, peroxidase, and superoxide dismutase activity in Chinese cabbage, with a significant declines. The study found that the degree of risk associated with composite MP pollution was related to the types of MP combinations. This study provides valuable insights into the environmental effects of MPs on the soil ecosystem and plants, while offering scientific support for formulating agricultural food safety control strategies.