Microplastic abundance and characterization in municipal sewage sludge from cities across upper Ganga River, India: Apprising microplastic uptakes and their toxicity in the plant during sludge application in agriculture

Abstract

This study investigates the occurrence and characterization of microplastic (MP) in sewage sludge from 3 different cities along the Ganga River, India and their toxic impact while applying sludge for crop production. MP occurred in the ranges of 29.2–60.8 × 103 particles kg−1 with an abundance of 1–5 mm (11.12%), <1 mm–100 μm (32.65%), and 20–100 μm (56.23%) size particles. ATR-FTIR analysis suggested polypropylene, polyethylene, nylon, and polycarbonate as sludge's most common MP polymer. In lab scale trials, sludge MP showed significant toxicity in Vigna radiata and reduced vegetative growth and plant weight was recorded with sludge-inoculated setups. Seedlings with sludge exhibited higher activities of catalase, superoxide dismutase, hydrogen peroxide (H2O2), and malondialdehyde than the control setups. Furthermore, fluorescence microscopy confirmed the MP bioaccumulation in tested seedlings. In summary, our results suggested that wastewater treatment plants (WWTPs) sink large volumes of MP in sewage sludge, which could be hazardous while applying such biosolids for crop production. MP seasonal dynamics in local WWTPs and their role in the mobilization of other toxicant chemicals could be investigated in future studies in this series.