Microplastic contamination in Ramsar wetlands: a systematic review of global sources, ecological impacts, and policy implications.

Ramsar wetlands, globally recognized for their ecological, hydrological, and socio-economic significance, are increasingly threatened by microplastic (MP) contamination. Despite mounting evidence of MPs in freshwater and coastal environments, no global synthesis has focused on MP contamination in Ramsar-designated wetlands. This study presents the first systematic global review of MP contamination in Ramsar wetlands by compiling peer-reviewed studies (April 2012-May 2025). This review addresses MP sources, transport pathways, contamination levels in surface water, sediment, and biota especially in threatened species, ecosystem impacts, and mitigation efforts. Key findings from quartile analysis and descriptive statistics reveal that MPs are ubiquitous across Ramsar wetland compartments, with spatial patterns showing higher contamination in Asia, North and South America, and lower levels in Europe and Australia. Certain countries' Ramsar wetlands consistently emerged as hotspots across all three environmental compartments, surface water, sediments, and biota, including Ecuador, China, India, and Ghana. Temporal trends indicate rising MP loads over the past decade, and seasonal peaks linked to runoff in some regions. Polyethylene and polypropylene were the most common polymers (> 80%), with fibres and fragments as the predominant morphotypes. Sediments generally harboured the highest MP concentrations, while biota exhibited variable uptake. These results underscore an urgent need for standardized monitoring methods and more geographically balanced research, especially in under-studied regions such as Africa and South America, to enable robust global comparisons. We recommend prioritizing plastic source reduction, enhancing international collaboration, and integrating MP pollution control into wetland conservation policies to safeguard the ecological integrity of Ramsar wetlands.