Toxicological Effects of Coexistence of Tire Microplastics on Wheat Seedlings Under Cadmium Contamination

Rapid industry development has led to the accumulation of tire plastic particles and heavy metals in the environment, posing a serious threat to plant growth. This study explored the toxic effects of tire microplastics (TMPs) (0, 100, 250, 500, 1000, 2500, and 5000 mg/L) and cadmium (Cd) (0, 2, 5, 10, 20, and 50 mg/L), both individually and in mixture, on the germination characteristics, growth, and oxidative response of wheat. Results indicated that TMPs-only (0~5000 mg/L) and Cd-only (0~50 mg/L) treatments had no effects on the germination rates of wheat seeds. TMPs at concentrations ranging from 0 to 2500 mg/L exhibited an antagonistic effect when combined with Cd (2 and 20 mg/L) on the germination potential and germination index of wheat seed. High concentration Cd alone (50 mg/L) significantly inhibited the root length and shoot length of wheat seedlings (p < 0.05), but TMPs alone had no effect on it, indicating that the toxic effect of Cd on the growth of wheat seedlings was greater than that of TMPs. TMPs reduced the inhibitory effects of Cd (20 mg/L) on root length in wheat seedlings. Compared with single pollution, the combined effects of TMPs and Cd on wheat seeds-related indices (e.g., GP, GI, and VI), root length, and shoot length generally showed an antagonistic effect, which may reduce the toxic effect of Cd as a single pollutant to a certain extent. Co-exposure to TMPs and Cd resulted in elevated SOD and POD activities and a reduction in MDA content in wheat seedlings compared with the Cd-only treatment.