Vertical profiling of micro-plastics in agricultural soils: polymer types, metal interactions, and implication on crop rooting zones.

Microplastics are emerging pollutants of interest in agricultural soils, as they are persistent and may have significant ecological effects. The paper examined the occurrence, properties, and distribution of microplastics in peri-urban agricultural soils in Ranchi, Jharkhand. Soil samples (n = 165; 11 sites × 3 depths × 5 replicates) were collected from ten agricultural fields and one control area at three depths (0-15 cm, 15-30 cm, and 30-45 cm). Microplastics were isolated using density separation and oxidation methods, and then morphologically categorized. FTIR spectroscopy was employed to analyze the polymer composition. Quantification of associated metals was performed using atomic absorption spectrophotometry (AAS) after acid digestion, while physicochemical parameters of the soils were measured following the protocols of APHA to establish their relationships with the presence of microplastic. The findings showed that fibers had the highest prevalence at all depths (80 ± 8 to 3320 ± 36 particles kg dry soil) with the highest concentration in the surface layers. Fragments, films, and microbeads were found to decrease significantly with depth, suggesting a lack of vertical migration, except in finer fibers. Polymers were mainly polypropylene (34.3%), polyethylene (16.7%), polypropylene diene rubber (14.7%), LDPE and polyethylene-based foaming material (11.8% each), and polypropylene copolymer (10.8%). The Microplastic Pollution Load Index (MPPLI) was used to identify pollution hotspots associated with the intensive use of plastics. The interrelations between microplastic abundance and soil organic matter, as well as electrical conductivity, suggest the potential impact of microplastic on soil quality and properties (Supplementary Figs. 1, 2, and 3). Vertical distribution of microplastics shows that shallow-rooted crops face surface microplastics, while deep-rooted crops interact with finer particles in soil highlighting the need to enhance the management of plastic waste to protect soil health and sustainability in agriculture.