Abstract:

Nanoplastics (NPs) are an emerging class of environmental pollutants, characterized by their strong potential to adsorb and transport coexisting contaminants in aquatic environments. The ecological risks and environmental fate of NPs are dynamically regulated by their environmental stability, which is closely linked to water chemistry and the synergistic interaction of multiple environmental factors. Although existing studies have primarily focused on the distribution patterns and toxicological effects of microplastics (MPs) and NPs in atmospheric, terrestrial, and select aquatic systems (e.g., groundwater and rivers), there remains a significant lack of systematic understanding of the occurrence, transport mechanisms, and associated health risks of NPs in marine and freshwater environments. These water bodies serve as major sources of drinking water and as critical conduits for the pollutant transmission. This review offers a comprehensive synthesis of the occurrence characteristics, environmental behaviors, and ecological effects of NPs in marine and freshwater systems, articulating the following key insights: 1) Polymer types and morphological diversity: NPs can be classified into primary and secondary sources based on their origin and morphological characteristics. Primary NPs are manufactured at the nanoscale during production processes, whereas secondary NPs are generated through mechanical abrasion, usage, or natural weathering and the fragmentation of larger plastic polymers. The predominant types of plastic polymers commonly found in aquatic environments include polyethylene (PE), polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). In marine and freshwater environments, NPs have been identified in at least four morphological types: fibers, fragments, films, and spheres. NPs may exhibit a wide range of colors, including transparent, white, black, blue, green, red, yellow, brown, gray, silver, and pink. Such diversity in shape and color reflects the complexity of plastic sources and indicates a broad spectrum of transformation pathways under aquatic conditions. 2) Environmental factors influencing transport and fate: Once released into marine and freshwater systems, the transport and fate of NPs are governed by the interplay between their intrinsic physicochemical properties (e.g., polymer type, morphology, size, concentration, and color) and a suite of environmental factors. Factors such as water chemistry (e.g., pH, electrolyte type, and ionic strength), the presence of heavy metals, coexisting colloids, light irradiation, dissolved organic matter (DOM), interaction sequence, and hydrodynamic conditions play critical roles in shaping the migration behavior of NPs in aquatic systems. Notably, extreme conditions, such as high salinity, strong hydrodynamic turbulence, and intense sunlight exposure, especially in estuarine or open ocean systems, further complicate NP dynamics, making their fate highly unpredictable and distinct from terrestrial or atmospheric environments. 3) Environmental behavior and ecological risks: The environmental behavior of NPs fundamentally determines their environmental fate and associated ecological risks in aquatic ecosystems. NPs that aggregate rapidly tend to form large aggregates that are readily removed by sedimentation. In contrast, NPs that remain in a highly dispersed state possess larger specific surface areas and stronger mobilities, enabling them to travel across extensive aquatic regions. This increases the likelihood of interactions with aquatic organisms, thereby enhancing bioaccessibility and exposure risk. In addition, NPs can access to aquatic food webs, where they may amplify along the food chain, posing a long-term threat to higher trophic-level organisms and public health. As the largest dynamic carbon reservoir and a key site for the cycling of various elements, oceans are particularly vulnerable to the accumulation of NPs, which may interfere with biogeochemical processes and energy flow in marine ecosystems. Moreover, NPs often act as vectors for other environmental pollutants, modulating their environmental and biological distribution through adsorption and desorption processes. This vector effect significantly enhances the bioavailability and bioaccumulation potential of the associated pollutants, leading to synergistic pollution effects with ecological toxicity that often surpass those of individual pollutants. Additionally, the interplay between NPs and microbial communities may alter nutrient cycling and microbial diversity, further intensifying their ecological consequences in the pelagic and benthic zones of aquatic ecosystems. This review highlights that NP pollution in marine and freshwater systems has emerged as one of the most pressing and complex challenges in environmental science, owing to its global dispersibility, ecological amplification effects, and intractable remediation difficulties. The long-term sedimentation of NPs in deep-sea environments further exacerbates this issue, as it contributes to irreversible ecological burdens that persist over geological timescales. Simultaneously, there are significant technical bottlenecks in the identification and management of NPs, such as the high similarity between NPs and natural colloidal particles (e.g., humic acid) in terms of their physical and chemical properties, which makes it difficult to detect and separate NPs. The transboundary mobility of pollution requires coordinated management by multiple countries, highlighting the special characteristics of NPs that distinguish them from pollution in other environmental media. However, current detection methods for NPs lack unified standards, with fundamental differences in analytical principles across methodologies hindering data comparability, and the generalization of research findings. Future studies should build on existing knowledge to develop standardized and rigorously validated experimental frameworks and analytical protocols, thereby improving the consistency and reliability of the results across different investigations. Moreover, this review emphasizes the importance of employing environmentally representative plastic types in future NP studies to ensure the ecological relevance of the results. For research on NP aggregation and transport, it is recommended that nanoparticle tracking analysis (NTA) and dynamic light scattering (DLS) be integrated to construct multi-factor-coupled transport models. In terms of toxicity assessment, future research should move beyond the traditional “single-pollutant, static-system” paradigm and establish multi-pollutant interfacial reaction platforms to better simulate realistic environmental exposure scenarios. Future pollution control strategies may include the development of magnetic nanoreactors for the targeted capture of NPs, the design of biomimetic adhesive materials to enhance the retention efficiency of biofilms, and the optimization of ultraviolet (UV)/persulfate-based advanced oxidation processes to achieve low-energy, high-efficiency mineralization of NPs. Only through interdisciplinary innovation and the integration of advanced techniques across fields can we achieve a comprehensive understanding of the environmental behavior of NPs and provide a solid scientific foundation for the effective management and mitigation of global plastic pollution.

Key words: nanoplastics (NPs), oceans and freshwater, migration and fate, aggregation, dispersion, environmental risks

摘要：

纳米塑料（NPs）是一种具有较强污染物传递和吸附能力的新型污染物。NPs的生态风险受其稳定性影响，而其稳定性又取决于各种环境因素。现有研究主要关注微/纳米塑料在大气、土壤及特定水环境（如地下水、河流、陆地径流）中的分布与毒性。海洋与淡水是饮用水来源及污染物输移载体，目前人们对其NPs的赋存、迁移及健康风险的系统归纳仍显不足。该文概括了这几方面的研究，得出如下的若干结果。海洋和淡水中的NPs存在至少4种形状（纤维、碎片、薄膜、颗粒）和11种颜色（透明、白、黑、蓝、绿、红、黄、棕、灰、银、粉）。NPs进入海洋和淡水后的迁移与归趋会受其自身性质（类型、形状、尺寸、浓度、颜色）及环境因素（水化学条件、重金属、其他胶体、水体类型、光照、溶解性有机物、相互作用顺序、水动力条件）影响。NPs在海洋和淡水中凝聚越快，可能越有利于其沉积以被清除；反之，高度分散的NPs会迁移更远的距离，可能增大生物可及性。NPs会通过食物链影响水生生物和人体健康。最后，该文强调了应深入研究真实环境NPs的凝聚与分散程度及其携带污染物的释放对水生生态系统功能的影响。开展相应的研究有助于了解NPs在复杂水生环境中的命运。

关键词: 纳米塑料, 海洋和淡水, 迁移与归趋, 凝聚, 分散, 环境风险