Long-term biodegradability of Poly-Lactic Acid (PLA) in soil by measuring carbon dioxide evolution in a closed system

Plastics have become an integral part of our lives due to their versatility and durability. Conventional plastics are made from non-renewable resources that are harmful to humans and the environment. They release toxic substances and break down into microparticles. The use of biodegradable plastics, such as polylactic acid (PLA), is a viable alternative to reduce the above-mentioned problematics. This study investigates the long-term (9 months) biodegradability of PLA in soil under laboratory conditions in a closed chamber system. The experiment was set up according to the European standard ISO 17556:2012. The biodegradability percentage of the plastic was calculated by measuring the production of CO₂ by microorganisms in the soil on PLA. The percentage biodegradability of the PLA was calculated using soil CO₂ emission rates (measured by titration method). PLA was used in net and film forms under two experimental conditions: untreated soil and soil modified with two natural soil amendments (natural zeolites and biochar) to evaluate their potential impacts on PLA decomposition rates and CO₂ emissions. Cellulose (100% biodegradable) was used as a positive control.  For comparison, PLA degradation was also studied under temperature-controlled composting conditions (58°C) with the same experimental setup.  The morphological changes of PLA were analysed using a scanning electron microscope. The results showed different trends over time and significant differences between the treatments, especially concerning the presence of soil amendments, highlighting the complexity of the interactions between PLA and the soil microbial community and physico-chemistry of the substrate.