MICROPLASTICS IN AGRICULTURAL SOIL AMENDED WITH ALKALINE-TREATED BIOSOLIDS

Abstract

Microplastics (MPs) are emerging ubiquitous environmental contaminants that risk agricultural sustainability and food security through the land application of biosolids. This research quantified MPs in alkaline-treated biosolids (ATBs) and evaluated their accumulation, persistence, and vertical movement in agricultural soils over 15 years. ATBs contained an average of 138 600 MP particles kg⁻¹ (dry weight), predominantly fragments. Repeated ATB applications led to significant MP accumulation in surface soils (0–15 cm), with an 8.7-fold increase observed under 14 tonnes ha⁻¹ applications. MPs persisted long-term, even in single-application plots, and smaller MPs preferentially migrated deeper into the soil profile. To enhance MP characterisation, thermogravimetric analysis (TGA) paired with differential scanning calorimetry (DSC) and Fourier-transformed infrared (FTIR) spectroscopy was used to successfully identify polypropylene (PP), polyethene (PE), and polystyrene (PS). These findings underscore the need for improved regulatory oversight and monitoring strategies to mitigate MP contamination and protect agricultural sustainability and food security.