Microplastic and cadmium contamination: Impact on the soil by inhibiting the growth of pak choi (Brassica rapa subsp. chinensis)

Microplastics are persistent pollutants that elicit significant environmental and health concerns; however, little is known about their interactions with cadmium (Cd) and their toxic effects on soil and plant growth. A pot study was conducted to examine the effects of polyethylene (PE; 0.05% w/w), polylactic acid (PLA; 0.05% w/w), and Cd application (5 mg kg-1 soil) in a soil-plant system. Sole application of PE and soil contamination with Cd negatively influenced the biomass, soil properties, Cd accumulation, photosynthetic properties, chlorophyll content, root growth traits, and antioxidant enzyme activity. PE+Cd exerted stronger adverse effects on biomass, soil properties, Cd accumulation, photosynthetic properties, chlorophyll content, root growth traits, and antioxidant enzyme activity. PLA+Cd decreased Cd uptake and accumulation in leaves and roots. PE+Cd upregulated the antioxidant activities (APX, CAT, POD, and SOD contents) in the root and leaves, compared to that by PLA. Both types of microplastics, especially PE, are affected by oxidative stress caused by Cd-contaminated soil. In conclusion, PE+Cd had stronger adverse effects on soil health and pak choi physiology, thereby affecting roots and leaf biomass. Long-term experiments are required to enhance our understanding of microplastic in bioremediation.