Microplastic accumulation in soils: Unlocking the mechanism and biodegradation pathway

• Microplastic pollution in soil poses a significant environmental challenge. • Biodegradation offers a promising method for reducing soil microplastic pollution. • Optimizing conditions for microplastic-degrading microbes is essential for success. • Research is needed to develop strategies to protect ecosystems from microplastics. Plastic pollution has become a pressing environmental issue, with significant quantities of microplastics (MPs) contaminating terrestrial ecosystems. In agro-environments and soils, the abundance of MPs has been reported to range from 3.7 to 40,800 items per kilogram. Once MPs enter the soil, their accumulation can have several detrimental effects on the soil environment and ecosystems. This review summarizes current research on the biodegradation of MP-contaminated soils. The primary mechanism of MP biodegradation involves enzymatic oxidation and hydrolysis, leading to the formation of functional groups. The interaction between microorganisms and polymers involves various processes, including colonization, biofilm formation, and biodegradation. Microorganisms can adhere to polymer surfaces where they build biofilms as complex microbial communities embedded in an extracellular polymeric matrix. These biofilms facilitate microbial activity and can boost their ability to degrade polymers. The biodegradation of MPs in soil is a promising strategy to address MPs pollution. However, further research is needed to optimize degradation conditions, identify MPs-degrading microorganisms, and assess the long-term environmental impacts of biodegradation techniques. Several key factors, including pH, temperature, salinity, moisture, and oxygen content as environmental conditions, as well as specific enzyme activities, should be considered to promote biodegradation. This review also suggests future research directions to increase our understanding of this important area and develop effective strategies to mitigate MP contamination in soil ecosystems. Further research should focus on identifying new types of microbes that degrade plastics and engineering enzymes that degrade MPs.