Millions of microplastics released from a biodegradable polymer during biodegradation/enzymatic hydrolysis

In this article, we show that enzymatic hydrolysis of a biodegradable polyester (poly(e-caprolactone)) by Amano Lipase PS in an aqueous (buffer) environment yielded rapidly an excessive number of microplastic particles; merely 0.1 g of poly(e-caprolactone) film was demonstrated to yield millions of particles. There were also indications of non-enzymatic hydrolysis at the same conditions, but this did not yield any particles within the time frame of the experiment (up to 6 days). Microplastic particles formed had irregular shapes with an average size of around 10 pm, with only a few reaching 60 pm. The formation of microplastic particles resulted from the uneven hydrolysis/erosion rate across the polymer film surface, which led to a rough and undulating surface with ridge, branch, and rod-shaped micro-protruding structures. The consequent detachment and fragmentation of these micro-sized protruding structures resulted in the release of microplastics to the surroundings. Together with microplastics, hydrolysis products such as acidic monomers and oligomers were also released during the enzymatic hydrolysis process, causing a pH decrease in the surrounding liquid. The results suggest that the risk of microplastic pollution from biodegradable plastics is notable despite their biodegradation. Special attention needs to be paid when using and disposing of biodegradable plastics, considering the enormous impact of the paradigm shift towards more biodegradable products on the environment.

Automated summary

In this study, it was found that enzymatic hydrolysis of a biodegradable polyester in an aqueous environment resulted in the formation of a large number of microplastic particles. Non-enzymatic hydrolysis was also observed but did not produce particles within the experimental timeframe. The formation of microplastics was attributed to the uneven hydrolysis/erosion rate across the polymer film surface, resulting in the release of fragmented micro-sized protruding structures. Additionally, acidic monomers and oligomers were released during the enzymatic hydrolysis process, causing a decrease in pH. These findings highlight the significant risk of microplastic pollution from biodegradable plastics.