Biodegradable plastics in the air and soil environment: Low degradation rate and high microplastics formation

In recent years, the promotion and use of biodegradable plastics (BPs) are growing into a general trend. Here the degradation performance of different types of BPs was investigated in the natural environment. Their degradation levels followed the order of pure BPs> BP blends> claimed "BP"≈ non-biodegradable plastic after 6-month incubation. Photo- and biodegradation were the main degradation mechanisms of these plastics in the air and soil, respectively. Poly(p-dioxanone) (PPDO) exhibited the highest weight loss potentials in both air (54.7 ± 9.1%) and soil (56.8 ± 4.8%), due to its special ether bond and the rich and diverse microorganisms on its biofilms. The microbiota on PPDO was distinct and enriched with Chloroflexi and Firmicutes that responsible for carbon cycle and organic degradation. The weight loss was only 1.1-8.0% for poly(lactic acid), and 0.8-6.8% for poly(butylene adipate-co-terephthalate), and other plastics are basically non-degradable. Of note, numerous microplastics were formed after PPDO degradation, with 441 ± 326 and 2103 ± 131 item/g plastic in the air and soil, respectively. Taken together, the monitoring of BP biodegradation in the natural environment is of vital importance, and it is risky to promote large-scale application of BPs if the knowledge gap of their environmental behavior has not been well addressed.