Response of Physico-Chemical Properties and Cd Adsorption Capacity of Microplastics to Simulated Environmental Conditions in Sludge-Amended Soil

Abstract

Sludge microplastics (MPs) enter the soil with soil amendment by sludge and are exposed to complex environmental conditions. Changes in the physico-chemical properties and adsorption capacity of MPs deserve attention. In this study, three environmental conditions, dry-wet alternation, microbial addition, and Ultraviolet irradiation were simulated to investigate their effects on the properties and Cd adsorption capacity of polyethylene (PE), polypropylene (PP), and polystyrene (PS) in sludge-amended soil. The results showed that UV irradiation enhanced the average Cd adsorption capacity of MPs. After microbial addition and UV irradiation, the adsorption sites number, specific surface area and oxygen content of the MPs increased rather than dry-wet alternation. It has been speculated that Streptomyces may play a positive role in the Cd adsorption by MPs. Ultraviolet irradiation caused cracks on the MP surfaces, increased the alkoxy, and carbonyl groups and the crystallinity increased or new crystals were produced, which may promote Cd adsorption by MPs. The results will aid our understanding of how environmental conditions alter the properties and Cd adsorption capacity of MPs in sludge-amended soil. This has significance for controlling sludge MPs and the potential export risk of carrying heavy metals.

Keywords: Microplastics, Cd, Physico-chemical characteristics, Adsorption capacity, environmental conditions