Role of soil microplastic pollution in climate change

In recent decades, environmental pollution from microplastic (MPs: <5 mm) and climate change have received international attention. However, these two issues have been primarily investigated separately hitherto, although they exhibit a cause-and-effect relationship. Studies considering MPs and climate change as causal entities have focused only on MP pollution in marine environments as a contributor to climate change. Meanwhile, systematic causal studies have not been performed inadequately to understand the role of soil, which is a primary terrestrial sink of greenhouse gases (GHGs) in the context of MP pollution, in climate change. In this study, the causal effect of soil MP pollution on GHG emissions as direct and indirect contributors to climate change is systematically analyzed. The mechanisms underlying the contribution of soil MPs to climate change are discussed, and future research perspectives are suggested. Approximately 121 research manuscripts pertaining to MP pollution and its associated effects on GHGs, carbon sinks, and soil respiration, recorded between 2018 and 2023, are selected and cataloged from seven database categories in PubMed, Google Scholar, Nature's database, and Web of Science. Several studies demonstrated that soil MP pollution directly contributes to climate change by accelerating the emission of GHGs from the soil to the atmosphere and indirectly by promoting soil respiration and adversely affecting natural carbon sinks, such as trees. Other studies correlated the release of GHGs from the soil to mechanisms such as the alteration of soil aeration, methanogen activity, and carbon and nitrogen cycles, and improved the abundance of carbon and nitrogen soil microbial functional genes adhering to plant roots to create anoxic conditions for plant growth. In general, soil MP pollution increases the release of GHGs into the atmosphere, thereby contributing to climate change. However, further research is to be conducted by investigating the underlying mechanisms using more practical field-scale data.