Environmental behavior and mechanistic interactions of biochar-derived dissolved organic matter with microplastics

Biochar-derived dissolved organic matter (BC-DOM), a critical byproduct of biochar aging, plays a pivotal role in governing the fate of microplastics (MPs) in terrestrial and aquatic ecosystems. As MPs (<5 mm) proliferate globally, their persistence and ecotoxicity threaten soil health, water quality, and food security, depending on the composition and content of organic compounds. The purpose of this review was to examine and analyze the existing studies to explore and summarize the properties and environmental behavior of BC-DOM, and emerging evidence on how BC-DOM interacts with MPs to influence their environmental behavior. BC-DOM, rich in reactive oxygen species-generating aromatic and lipid-like compounds, accelerates MP degradation by promoting photoaging processes (e.g., via singlet oxygen and hydroxyl radicals) that fragment MPs into smaller, more biodegradable particles. Concurrently, BC-DOM alters MP surface properties, enhancing their hydrophobicity and adsorption capacity for co-contaminants like heavy metals, thereby modulating MP mobility and retention in soils and sediments. For instance, BC-DOM with high SUVA 254 values increases MP aggregation in aquatic systems, reducing their bioavailability but potentially prolonging environmental persistence. These interactions carry significant environmental implications: BC-DOM-driven MP degradation could mitigate long-term ecological risks, while its role in MP adsorption may influence contaminant transport across ecosystems. Therefore, long-term studies need to be carried out to fully understand the interaction mechanism between BC-DOM and MPs and its environmental impact to provide a scientific basis for the safe application of BC in soil and aquatic ecosystems.