Increasing amounts of microplastic (MP) in soils may pose a hazard to agricultural ecosystems. To date, research has largely concentrated on MP quantification in environmental samples and MP impacts on aquatic organisms, humans and food chains, whereas responses of crop and fodder plants to MP particles and their respective leachates remain a knowledge gap. The present study evaluated the effects of two MP types - polyvinylchloride (PVC) and recycled tire crumb (RTC; proxy for tire wear particles, TWP) - and their respective leachates on germination and early growth of Lolium multiflorum in a laboratory trial. For fragment treatments, different concentrations and RTC size fractions were applied, whereas leachate treatments were applied at a single extract ratio, to disentangle chemical from physical MP effects. Leaf δ13C-signatures were additionally measured as a proxy for early physiological responses. Exposure to fragments or leachates reduced normal germination and increased the proportion of ungerminated and abnormally germinated seeds. Leachates predominantly affected germination and root elongation, but not biomass production; the strongest effects were observed for PVC leachates. Fragments generally caused stronger adverse effects than leachates, and PVC affected growth parameters more than RTC. Contrary to expectations, the smallest RTC size did not induce the strongest responses, and no consistent interaction between RTC fragment size and concentration was observed. Leaf δ13C-signatures showed treatment-related trends, but values were depleted rather than enriched, consistent with altered carbon isotope discrimination and early physiological functioning during seedling growth. This study focused on comparatively large concentrations of MP; therefore, our results should be interpreted in terms of hazard potential rather than as a direct representation of MP loads under field conditions. Overall, the findings confirm that MP can impair plant establishment and affect early physiological processes. Chemical (leachate-mediated) and physical (fragment-mediated) effects are both relevant in this context.
Cornelsen et al. (Fri,) studied this question.