In situ soil environment-based evaluation on degradation of biodegradable plastics

Abstract

The biodegradability of plastic is a critical factor in environmental sustainability. However, plastic degradation has been focused on closed systems via physical changes and CO₂ generation. We innovated a methodology on open system degradation in soil environments to reveal the authentic process of plastic degradation in nature. Polybutylene succinate (PBS), polybutylene adipate-co-terephthalate (PBAT), poly3-hydroxybutyrate-co-3-hydroxyvalerate (PHVB), and polylactic acid (PLA) were buried in a soil equipped with the lysimeter, the field applicable instrument that preserves and measures the in-situ soil conditions. Over two years, we tracked the soil electrical conductivity (EC), temperature, water content, and the plastic degradation products in the leachate−the monomers. The seasonal change in soil EC proved the plastic degradation, due to the decomposed plastic particles increasing the electrolyte concentration. The quantity of monomers increased over time, spiking during the summer months. A correlation was observed between the soil EC and monomer concentration. Despite the degradation-derived soil properties fluctuating with seasonal changes, the resilience of soils was maintained. Through long-term field experiments, we identified the seasonal degradation conditions of the actual soil environment and proposed a methodology of degradability that allows plastic targeting without disturbing the degradation media. These insights provide crucial knowledge for the biodegradable plastics market.