Site-Specific Occurrence of Microplastics and Soil Chemical Profiles in Grazed Pastures

Plastic use in livestock systems may create sources of microplastics (MPs) and promote their dispersion into surrounding pastures. This study evaluated MP concentration, polymer composition, soil chemical properties, and enzyme activities in six pasture areas located 53–534 m from the boundary of a localized plastic-use area in southern Chile. Five composite samples were collected per area from the 0–30 cm soil layer. MPs were confirmed by FTIR–ATR, particle counts were analyzed using a Poisson generalized linear model, and global and pasture-area-adjusted Spearman correlations were calculated. MPs occurred in all pasture areas at 12–76 items kg−1 dry soil. Expected particle counts decreased by 19.3% per 100 m (incidence rate ratio: 0.807; 95% CI: 0.725–0.898), although area means were not strictly monotonic. PE predominated, while PE, PP, PVC, PA, and EVA occurred in source inputs and soils. Soil chemical properties and enzyme activities showed spatial heterogeneity. No pasture-area-adjusted pairwise correlations remained significant. The results support the plastic-use area as a plausible contributor to MP distribution, while soil fertility and biological activity reflected area-specific variability; however, the observational design does not establish causal effects of distance or MPs.