Potential Toxicity of Microplastics in Wheat and Maize—A Pilot Pot Experiment

Most agricultural plastic products are single-use and often remain in the environment long after they have fulfilled their intended purpose. From the soil, they may transfer to living organisms, where they can alter biological functions, physiological processes, and reproduction, and can also lead to pollutant accumulation in biomass; through food chains, they may increase risks to human health. This study analyzes the uptake of polyethylene microplastics (MPs) in wheat and maize, and their impact on plant development. Two types of fluorescent polyethylene spheres were used in a pot experiment—27–32 µm and 75–90 µm in diameter, as these sizes are reported to penetrate plant root tissues most efficiently. After 50 days, MPs accumulated in all organs of the test plants—roots, stem, and leaves. The average relative growth rate (RGR) shows that the two plant species respond differently to the applied microplastics. In maize, the control plants recorded the highest RGR (0.039 day−1), while both MP treatments decreased RGR (0.034 day−1 for 75–90 µm and 0.026 day−1 for 27–32 µm). In wheat, the lowest RGR was recorded under 75–90 µm MPs exposure (0.016 day−1), while at 27–32 µm MPs the RGR value (0.024 day−1) practically coincides with that of the control plants. MPs significantly affected growth and biomass synthesis in both underground and aboveground organs, with the degree of impact depending on plant type and MP size. Polyethylene microplastics positively affect photosynthetic pigment biosynthesis in maize and negatively affect it in wheat. Future comprehensive studies in real field conditions are needed to reveal the impact of MPs on plants and their ability to be transmitted through food chains, thus assessing the risk to food security and human health.