Effects of biodegradable poly(butylene adipate-co-terephthalate) and poly(lactic acid) plastic degradation on soil ecosystems

Despite that biodegradable plastics are perceived as environmentally friendly, there is a lack of comprehensive understanding of their fate in soil. Current Environmental, Social, and Governance (ESG) frameworks, along with new UNEP regulations on plastic pollution, necessitate scientific information on plastic degradation in soils for developing sustainable biodegradable plastics. In this study, we examined the degradation rates of two biodegradable plastics, poly(butylene adipate-co-terephthalate) (PBAT) and poly(lactic acid) (PLA), in a laboratory microcosm experiment using uncontaminated soil, with PBAT or PLA added at 8.3% (w/w). Our aim was to further understand the impact of these plastic types on soil properties and microbial communities under different incubation temperatures. Both PBAT and PLA treatments elevated cumulative CO₂ efflux compared with the control soil incubated at 25 and 58°C. After 33 weeks, 9.2% and 6.1% of the added PBAT and PLA degraded, respectively, at 58°C, while only 2.3% of PBAT and 1.7% of PLA degraded at 25°C, implying slower degradation rates of PBAT and PLA under the lower temperature. Degradation at 58°C increased total soil carbon by 0.6%, 1.9%, and 4.3% for Control, PBAT, and PLA, respectively, and soil electrical conductivity by 0.17, 0.33, and 2.38 dS m⁻¹, respectively, but decreased soil pH. Microbial diversity and richness decreased under thermophilic conditions at 58°C compared with that at 25°C. We conclude that the degradation of PBAT and PLA varies with environmental condition, and influences soil properties.