Insights on the characteristics of plastic surface degradation and biofilm microorganisms: Exploring the impacts of three aerobic composting (AC) as well as UV irradiation and cycles of freeze-thaw (CFTs)

Abstract

Organic fertilizers applied to soil often contain significant amounts of plastics, which typically undergo a process of aerobic composting (AC) that induces specific physical and chemical changes on their surfaces. In this study, we simulated the environmental actions of AC source plastic film under typical soil environmental exposure, exploring how AC affects the response of plastics to ultraviolet (UV) radiation and cycles of freeze-thaw (CFTs). The results showed that varying composting conditions significantly impacted the fungal and bacterial community structures on the plastic surface; and plastic degradation under AC present various surface properties, including embrittlement, wear, corrosion, and reduced transparency, with specific yellowing and breakage, and strong microbial adhesion. UV exposure exacerbated the degradation of plastics sourced from AC. Plastics subjected to both AC and UV displayed significant changes after experiencing intense stress from CFTs. The structures of polyethylene (PE) and polylactic acid (PLA) were severely disrupted, resulting in the formation of powder or debris. Moreover, PLA and polyvinyl chloride (PVC) showed slightly reduced yellowing and unsaturation, while releasing total dissolved solids (TDS), micro/nanoplastics and additives. This study highlights the distinct characteristics of plastic pollution originating from AC processes associated with organic fertilizer land-use.

Keywords: Aerobic composting; Cycles of freeze-thaw; Degradation; Metabolites; Plastic; Ultraviolet.