Biodegradation of Plastics

Abstract

The consumption of plastic products has increased significantly with the rapid development of the global economy. The total output of virgin plastics has already reached eight billion tons, and the annual global plastic consumption has reached 2.8 billion tons. In parallel with this high consumption rate, a staggering amount of plastic waste is generated annually. As a consequence of incorrect disposal of waste plastics and plastic longevity, this plastic waste is accumulating in the environment at an increasing rate. Moreover, since most plastic waste is corrosion resistant, these plastics do not decompose in the natural environment and can cause serious environmental pollution. In particular, petroleum-based synthetic polymers, including polyethylene, polyvinyl chloride, polystyrene, polypropylene, polyethylene terephthalate, and polyurethanes need hundreds of years to completely degrade in the natural environment. Moreover, although some aliphatic polyesters, such as polybutylene succinate, polycaprolactone, and polylactic acid are considered biodegradable, degradation of these plastics occurs only under specific microorganism activity and under specific conditions. Sometimes the apparent degradation is initiated by hydrolytic activity and not microorganism or enzymatic activity. Large-scale synthesis and application of plastics only began after 1950. Hence, the time span of plastic exposure in the environment has been too short for the adaptive evolution of natural microorganisms. Indeed, natural microorganisms showing high specificity for plastics and a high degradation efficiency are extremely scarce. Because of the inability of most natural microorganisms to recognize and degrade plastics, enzymes that can specifically degrade plastics are also scarce. Many of the enzymes which are known have either an unclear mechanism of the action on the polymer, a poor affinity for their substrates, a low efficiency, or enzyme production yield is currently low. To address these problems, new biotechnology strategies need to be implemented. In particular, new microorganisms and their enzymes need to be identified, and pathways for plastic degradation and molecular modification need to be clarified to enhance the activity and stability of the degrading enzymes. The current Research Topic aims to cover the recent and novel research trends in the development of plastics biodegradation (including petroleum-based plastics and bio-based plastics) under soil, composted, microbial and enzymatic conditions. The recycling technology of degraded products is also of interest.