关键词: 微塑料, 矿物质, 相互作用, 界面反应, 环境影响因子

Abstract:

Plastic pollution has emerged as a global environmental crisis. Currently, the annual global plastic production continues to rise, exceeding 320 million tons, with massive amounts of plastic products flowing into the natural environment through various pathways. Under the combined effects of physical fragmentation, photochemical oxidation, and biodegradation, these plastics gradually break into microplastics (MPs) with particle sizes less than 5 mm, and even nanoplastics (NPs) smaller than 1 μm. Based on differences in their sources, MPs and NPs can be divided into two categories, either primary, originating from intentionally added plastic microbeads in products such as cosmetics and detergents, or secondary, formed through the fragmentation of larger plastic debris in the environment due to long-term weathering, mechanical abrasion, and ultraviolet radiation. Existing research indicates that MPs are now widely distributed across all environmental media globally, including soil, water bodies, the atmosphere, and even polar glaciers and deep-sea sediments, with their concentrations showing significant spatiotemporal heterogeneity. Due to the characteristics of large specific surface area, strong hydrophobicity, and high chemical stability, most types of MPs are difficult to be completely degraded in the environment. The longer they persist in the environment, the more pronounced their cumulative effects become, leading to escalating ecological risks. Based on a search of relevant literature from 2021 to 2025 in Web of Science, this paper systematically reviews the interfacial reaction rules and interaction mechanisms between various micro/nanoplastics and typical minerals in aquatic and soil environments. Additionally, we discussed in detail the effects of environmental factors (e.g., temperature, pH, and ionic strength) and microorganisms on these reaction processes. Existing research has delineated three primary mechanistic pathways underlying these interactions. 1) Electrostatic attraction. A subset of minerals, exemplified by iron oxides including goethite, hematite, and magnetite, exhibit positively charged surfaces under typical environmental conditions. In contrast, microplastic surfaces, particularly those subjected to aging processes, develop negative charges due to the formation of oxygen-containing functional groups (such as C=O and −OH). When these oppositely charged entities encounter one another in aquatic or soil matrices, electrostatic attractive forces drive their mutual adhesion. 2) Coordination complexation. The edge sites of minerals are typically enriched with reactive hydroxyl groups, which serve as critical binding moieties. Concurrently, the weathering and aging of MPs in natural environments lead to the gradual formation of surface oxygen-containing functional groups, including carboxyls and hydroxyls. Upon contact, the hydroxyl groups on mineral edges undergo ligand exchange reactions with the oxygen-containing functional groups on MPs surfaces, resulting in the formation of stable coordination bonds. Notably, the reactivity of mineral edge hydroxyls varies across mineral species, while the type and density of functional groups on microplastics directly modulate binding strength. 3) Cation bridging. Divalent cations such as Ca²⁺ and Mg²⁺, which are abundant in natural water bodies and soil solutions, act as “bridging agents” that facilitate the association between MPs and minerals. These cations first form inner-sphere or outer-sphere complexes with carboxyl and hydroxyl groups on MPs surfaces, while simultaneously interacting with negatively charged sites on mineral surfaces. In terms of catalytic degradation, mineral phases can not only immobilize microplastics through physical adsorption but also generate reactive oxygen species (ROS) via Fenton-like or photocatalytic reactions, including hydroxyl radicals (·OH), superoxide anions (O₂·⁻), singlet oxygen ⁽¹O₂), and sulfate radicals (SO₄·⁻). These highly oxidative species can attack the carbon-carbon backbone and carbon-hydrogen bonds of microplastics, triggering reactions such as chain scission, oxidation, and dechlorination, thereby accelerating the chemical degradation process of microplastics. The study innovatively proposes a ternary synergistic mechanism involving “minerals-microorganisms-microplastics,” revealing the multifaceted roles of microplastics as novel mobile environmental matrices in microbial-mediated geochemical processes. On one hand, microplastic surfaces provide unique ecological niches for microorganisms, forming distinct microbial community structures compared to surrounding environments. On the other hand, oxygen-containing functional groups enriched on microplastic surfaces act as electron donors or acceptors, participating in microbial redox reactions. Specifically, microplastics can sequester metal ions through complexation, serving as electron transfer mediators for functional microorganisms such as iron-manganese oxidizing bacteria and sulfate-reducing bacteria, thereby facilitating microbial-induced carbonate precipitation (MICP) and iron-manganese oxidation mineralization processes. During these processes, extracellular polymeric substances (EPS) secreted by microorganisms play a critical role. Their surface negative charge functional groups (carboxyl groups, hydroxyl groups, phosphate groups, etc.) adsorb metal ions like Ca²⁺, Fe²⁺/Fe³⁺, and Mn²⁺, providing templates and sites for mineral nucleation that accelerate the biogenic precipitation of minerals such as calcite, siderite, and hydromanganite. The formation of these “microplastic-mineral” complexes may either immobilize microplastics through physical encapsulation to reduce their mobility and bioavailability, or increase surface active sites to synergistically accumulate heavy metals and organic pollutants, potentially becoming secondary pollution sources that amplify ecological risks through food chain transmission. The study conducted a detailed analysis of the complex interactions between microplastics and minerals, examining factors such as pH, temperature, ionic strength, dissolved organic matter, degree of aging and microbial activity. Results indicate that pH and ionic strength serve as primary regulatory factors in these interactions. pH determines the adsorption and desorption thresholds by altering the charge characteristics and protonation states of microplastics and mineral surfaces, while ionic strength modulates the intensity of electrostatic interactions through charge screening effects and double-layer compression. Among these, divalent cations play a more significant role in promoting the formation of microplastic-mineral aggregates due to their stronger charge screening capacity and cationic bridging effects. At the same time, it is proposed that future research should focus on developing combined confocal Raman and synchrotron infrared microspectroscopy techniques to visualize interfacial reactions; enhance the molecular characterization of microplastic degradation intermediates (such as oligomers and oxygen-containing functional groups); and optimize microorganism-mediated mineralization technologies to achieve environmental immobilization of microplastics and control ecological risks through the enrichment of functional microbial communities and the overexpression of mineralization-related genes. Therefore, unraveling the microscopic mechanisms underlying MP-mineral interface interactions and their associated environmental regulatory factors not only carries profound theoretical and practical significance for accurate assessment of MPs’ ecological risks and environmental fate but also lays a scientific foundation for developing targeted, high-efficiency pollution control technologies.

Key words: microplastics, minerals, interaction mechanism, interfacial reaction, environmental impact factors