Effects of Combined Pollution of Microplastics and Lead on Maize Seed Germination and Growth

Abstract

Microplastics are a new contaminant that are causing worldwide concern. However, an understanding of their impact on agricultural seed germination remains inadequate. To investigate the effects of combined microplastic and heavy metal contamination on crop seed germination and growth, the effects of exposure to different single and combined concentrations of lead (Pb) and three microplastics[polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)] on maize seed germination and growth were investigated using maize seeds. The results showed that:the inhibition of maize seed germination by Pb single exposure generally increased with Pb concentration. Compared with that in CK, 500, 1000, and 1500 mg·L-1 PE exposure significantly inhibited maize seed germination, but 100 and 300 mg·L-1 exposure had no significant effect (except at d 5). All PP concentration exposures significantly inhibited maize seed germination, with higher concentrations resulting in stronger inhibition. Compared to that under PP and PE exposure, PVC single exposure inhibited maize germination less, and 500, 1000, and 1500 mg·L-1 exposures produced a facilitative effect at the later stages of germination. The germination index, germination potential, and vigor index of maize seeds decreased with the increase in the single exposure concentration of lead and three types of microplastics, significantly decreased compared with that of CK under the combined exposure of Pb and PE, and did not change significantly under the combined exposure of PP and Pb or PVC and Pb. Among the three types of microplastics, PVC had the least effect on corn seed vigor. Both single exposures of 10 mg·L-1Pb and 100 mg·L-1 of the three microplastics promoted maize stalk and root growth, whereas other concentrations showed mostly inhibitory effects. When the PE concentration was 500 mg·L-1, the 10 and 20 mg·L-1Pb exposures both promoted maize seed stalk and root growth; however, the combined PP and Pb exposures did not produce significant inhibition, whereas 500 mg·L-1PVC and 10 mg·L-1Pb showed the strongest inhibition of maize stalk and root growth under combined PVC and Pb exposures. The effects of combined exposure to microplastics and Pb on the germination and growth of maize seeds were essentially antagonistic, thus slowing down the toxic effects of their respective single exposures on maize seeds.