The effects of different types microplastics on soil properties and the biochemistry of Chinese cabbage under different dosages and exposure times

The impact of microplastics (MP) on agricultural ecosystems has drawn widespread attention around the world. This study aims to evaluate the impacts of MP with different types, doses and exposure times on the soil-plant system. A pot experiment was conducted to explore the impacts of four common MP, namely polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polyolefin resin (PO), at different dosages (0.1 and 20 g MP/kg soil) and exposure times (10 d, 20 d, and 30 d) on soil properties and the physiology and biochemistry of Chinese cabbage (Brassica chinensis L.). The results demonstrated the following: (1) In terms of soil properties, with the increase of exposure time, high-concentration MP led to an elevation of soil pH, among which PE had the most significant impact. High-concentration PVC remarkably reduced water content, nitrate nitrogen content, and catalase (CAT) activity, increased available phosphorus content and the quantity of microorganisms. All four types of MP were capable of decreasing soil organic matter, ammonium nitrogen content, and sucrase activity. At low concentrations, they significantly reduced soil urease activity. (2) Regarding Chinese cabbage, MP could reduce its water content. 0.1% PE significantly inhibited the plant height, and promoted root length. Different concentrations of MP could significantly enhance the chlorophyll content. High-concentration MP increased the peroxidase activity of Chinese cabbage while decreasing the superoxide dismutase and CAT activity. This study indicates that the risks of MP to the soil-plant system are dependent on type, dosages, and exposure times.