From Enrichment to Fate: Transport, Transformation, and Fate of Micro- and Nanoplastics in Marine Environments.

With the increasing detection of micro- and nanoplastics (MNPs) in marine environments and the expanding body of related research, their environmental behavior and ecological effects have become central topics in marine environmental science. This review addresses the growing concern over MNP pollution in the marine realm, encompassing their primary sources, spatial accumulation and distribution, environmental transport and transformation dynamics, and ecotoxicological effects on marine organisms and ecosystems, as well as the ecological risks they pose within key habitats such as seagrass beds and coral reefs. We synthesize evidence on the biological impacts of MNPs, including oxidative stress, tissue accumulation, metabolic disturbances, and immune impairment, as well as the heightened risk of pathogen transmission facilitated by the so-called "Plastisphere". Moreover, we explore the potential implications of MNP exposure on oceanic carbon cycling and net primary productivity. The reviewed literature suggests that MNPs are capable of long-range transport and progressive fragmentation into ultrafine particles, which are readily ingested and retained by a wide array of marine organisms, subsequently inducing toxicological effects and compromising both organismal health and ecological integrity. Such disturbances may undermine critical ecosystem services, including carbon sequestration capacity and food web stability. Finally, based on the current research landscape, we outline future research priorities: improving environmental detection and toxicological evaluation of MNPs, elucidating their long-term effects at the ecosystem scale, and investigating their interactions with co-occurring pollutants under complex, multi-stressor scenarios. These efforts are essential to support science-based assessment and effective management strategies for marine MNP pollution.