Microplastic Contamination in Sewage Sludge–Amended Soils and Plant Uptake

Abstract

The application of sewage sludge as agricultural fertilizer introduces microplastics into arable soils, raising concerns about long-term soil health and food safety. This study investigated the abundance, distribution, and polymer composition of microplastics in soils receiving sewage sludge amendments over varying durations (0, 3, 6, and 10 years) at three agricultural sites in the Indo-Gangetic Plain, India. Additionally, the uptake and translocation of microplastics in wheat (Triticum aestivum) and lettuce (Lactuca sativa) cultivated in sludge-amended soils were examined. Soil samples were collected at two depth intervals (0–20 cm and 20–40 cm), and microplastics were extracted using density separation with ZnCl₂ solution (1.6 g/cm³) followed by identification via micro-FTIR spectroscopy. Results indicated that microplastic concentrations increased significantly with sludge amendment duration, ranging from 320 ± 45 particles/kg in unamended control soils to 2,870 ± 410 particles/kg in soils with ten years of amendment history. Polyethylene, polypropylene, and polyester fibres constituted over 78% of all recovered particles. Root tissues of both crop species contained microplastics in the size range of 10–150 µm, with lettuce accumulating significantly higher concentrations than wheat. These findings underscore the role of sewage sludge application as a persistent pathway of microplastic entry into agricultural ecosystems and the human food chain.