Advances in environmental degradation and impact of degradable plastics

Plastic pollution has become a global environmental issue. With the implementation of plastic bans, degradable plastics (DPs) have been widely used as a substitute for traditional plastics in the fields of express delivery, takeout packaging, and disposable products. DPs undergo degradation under the influence of abiotic and biotic factors in different environments, and their residence time is shorter compared to traditional plastics, even though certain persistence still occurs. Researching the degradation characteristics of DPs in different environments helps promote the development of the industry. It is an indispensable link in the improvement of the comprehensive management of plastic pollution with practical significance. In this paper, various definitions and classifications of DPs were clarified, and the degradation characteristics of DPs with different polymer components in water and soil environments were summarized. The degradation in aerobic composting and anaerobic digestion were reviewed, and the potential and limitations of DPs through biological treatment of organic solid waste in urban areas were analyzed. In addition, the potential environmental and biological impacts of intermediate products such as microplastics and additives released by DPs were also introduced. Current research shows that DPs exhibit conditional degradability in natural environments, which depends on specific polymer types, temperature conditions, or duration to complete the degradation. Incomplete degradation of DPs can lead to the release of plasticizers and microplastics, impacting on the ecological environment. DPs are widely used as substitutes for traditional plastics but are still processed according to the classification and treatment/disposal procedures of traditional plastics, mainly through incineration, which increases treatment costs without bringing significant environmental benefits. The following prospects are proposed for the promotion, application, and treatment of DPs: (1) Investigate and monitor the occurrence of DPs in the natural environment. The laboratory conditions cannot replicate the effects of seasonal changes, weather, and water shear on the fragmentation and degradation of DPs. There is still a lack of systematic understanding of the environmental degradation and transformation of DPs, as well as the presence and persistence of intermediate products. (2) Establish standards based on the application scenario and degradation capability of DPs. In the field of recycling and reuse, priority should be given to recycling rather than biodegradability. For application scenario with high leakage risk, low reuse value, and difficulty in recycling or cleaning, the treatment and degradability of DPs should be clearly defined. (3) Improve the full-process management and optimize the classification system of plastic waste. Fill the gap in the classification of DPs to avoid mixing them with other waste for incineration. Co-processing of DPs with municipal organic solid waste such as kitchen waste is an effective measure to reduce environmental risks and achieve a circular economy, which also meets the needs of waste sorting and low-carbon development. (4) Continuously carry out research and development on DPs. Develop materials for different application scenarios, through blending and modification of various polymer materials, to meet the requirements of commodity use, mechanical properties, and degradation capabilities, and provide technical support for the development of the DP industry. (5) Strengthen the research on the residual characteristics of DPs. DPs are more prone to degradation, microplastics production and plasticizers and additives release. The sustainability of these incomplete degradation products in the environment and their impacts on ecosystems need further investigation.