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

Plastic biodegradability governs its environmental fate and sustainability. However, most degradation studies have been limited to closed systems, relying on physical disintegration and CO₂ evolution. Thus, we present a field-applicable methodology to evaluate plastic degradation under natural soil conditions. Biodegradable polymers—polybutylene succinate (PBS), polybutylene adipate-co-terephthalate (PBAT), poly3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV), and polylactic acid (PLA) were buried in lysimeter-equipped soils that preserve the in situ environmental dynamics. Over two years, we monitored the soil electrical conductivity (EC), temperature, water content, and the plastic degradation-derived monomers in the leachate. The seasonal fluctuations in soil EC proved the plastic degradation, with increased monomer concentrations mostly spiking during the summer months. A correlation between the soil EC and monomer concentration was observed through the electrochemical footprint of degradation. The soil resilience remained intact despite the degradation-derived soil properties fluctuating with seasonal changes. We elucidated the seasonal changes and environmental drivers of plastic degradation in soil and proposed a non-intrusive methodology to assess biodegradability. These insights provide the scientific basis for the evaluation of biodegradable plastics in the real environment.