Single and Combined Effects of Microplastics and Cadmium on Oxidative Responses, Antioxidant System and Cadmium Phytoavailability of Chinese Cabbage (Brassica campestris L.)

Microplastics (MPs) and cadmium (Cd) are both common contaminants in agro-systems, but research on the synthetic effects remains limited. This study focuses on the eco-physiological responses and assess whether co-contamination of microplastics affects the bioavailability of Cd. Our results found that the co-existing MPs with Cd resulted in a significant increase in malondialdehyde (MDA) compared to the exposure to single MPs. Under the single MPs treatment, MDA content in plants increased first and then decreased with the increase of MPs content. This trend is also manifested in the co-existing polyethylene (PE) with Cd. However, polyvinyl chloride (PVC) co-existing with Cd caused decreases of the content of MDA. The exposure to single polyethylene (PE), polyvinyl chloride (PVC), and co-existing MPs with Cd significantly increased the electrical conductivity of Chinese cabbage, and they showed a fluctuating upward trend, with the increase of the content of added MPs. Both MPs single exposure and co-contaminated with Cd stimulated the antioxidant system, caused in a higher superoxide dismutase and peroxidase activities at lower content of MPs (p < 0.05). The addition of MPs was able to alleviate the stress effects of Cd. Under the same content of Cd and MPs, PE treatment absorbed less Cd than PVC. Under co-existing of PE, the absorption of Cd in stems and roots of Chinese cabbage decreased by 16.20% and 9.12% on average, while with co-presence of PVC, it decreased by 14.21% and 4.98% on average. TF and BCF also showed a similar trend. These results unraveled that the relieving effect of PE on Cd stress was better than that of PVC and it has a better retention capacity for heavy metals. PE and PVC can reduce the Cd transport from the root system to the stem and leaf parts. The findings of this study provide reference to further understanding of the effects of MPs and Cd synergies on the plant-soil system, and also offer a physiological and ecological basis for the construction of synergistic governance strategies for new pollutants in agricultural ecosystems.