Ramsar wetlands occupy a special place in global conservation. Designated under an international treaty signed in 1971 in the Iranian city of Ramsar, these sites include marshes, lakes, mangroves, estuaries and coastal lagoons that serve as critical habitat for waterbirds, fish and countless other species, while also providing flood control, water purification and livelihoods for millions of people. The review’s authors set out to answer a deceptively simple question: how contaminated are these protected areas with microplastics, defined broadly as plastic particles smaller than five millimetres? The answer, they found, is that contamination is essentially ubiquitous. Wherever scientists have looked, from the water column to the sediment and inside the bodies of fish, clams and crabs, microplastics have been detected.

The geographic pattern that emerges from the synthesis is strikingly uneven. Contamination levels are highest in Ramsar wetlands across Asia and in North and South America, while Europe and Australia show comparatively lower concentrations. Certain countries emerged repeatedly as hotspots across all three environmental compartments examined, surface water, sediments and biota. Ecuador, China, India and Ghana consistently ranked among the most contaminated, a finding that reflects both genuine pollution pressures and the distribution of research effort itself. The authors caution that the map is incomplete: Africa and South America remain dramatically under-studied, meaning the true global picture could be worse than the data suggest.

Underlying the spatial patterns is a familiar polymer chemistry. More than 80 percent of the particles identified across the reviewed studies were polyethylene and polypropylene, the two most widely produced commodity plastics on Earth. These polymers dominate packaging, bags, bottles, fishing gear and agricultural films, and their low density and resistance to degradation allow them to persist and disperse widely in aquatic environments. In terms of shape, fibres and fragments predominated. Fibres, shed from synthetic textiles during washing and from weathered ropes and nets, are particularly insidious because their elongated form makes them readily ingested by filter feeders and other organisms, and because they are small enough to slip through many wastewater treatment systems.

The transport pathways delivering these particles to protected wetlands are as varied as the wetlands themselves. Rivers act as the primary arteries, carrying plastic debris from urban and agricultural catchments downstream into deltas, estuaries and coastal lagoons. Urban runoff after rainfall delivers pulses of microplastics from roads and storm drains, and the review found that seasonal peaks in contamination in some regions align with these runoff events. Wastewater treatment plants, despite their filtering role, discharge significant numbers of microplastics because conventional treatment was never designed to capture particles of this size. Atmospheric deposition adds another route, with fibres transported by wind and rained out even in remote locations. Once inside a wetland, particles are trapped by the dense vegetation and fine, organic-rich sediments that characterize these ecosystems, turning wetlands into effective sinks for plastic pollution.

Sediments generally harboured the highest microplastic concentrations of the three compartments examined, a finding consistent with the physical behaviour of most plastic particles. As polymers weather and biofouling organisms colonize their surfaces, many particles gain density and sink, becoming buried in layers of accumulating silt. This makes wetland sediment both a long-term archive of plastic pollution and a persistent exposure source for the benthic organisms that live in and feed on it. Biota exhibited more variable uptake, shaped by feeding strategy, habitat and body size. Filter-feeding molluscs, sediment-ingesting worms and crabs, and fish at multiple trophic levels have all been documented with microplastics in their digestive tracts, and studies cited in the review report trophic transfer through aquatic food webs, including in the Sundarbans mangrove forest shared by Bangladesh and India.

The ecological consequences extend well beyond simple ingestion. Laboratory and field studies compiled in the review document a cascade of sub-lethal effects: reduced feeding and growth, altered reproduction, oxidative stress and tissue damage in invertebrates and fish. In seabirds, chronic plastic exposure has been linked to a fibrosis-like condition researchers have dubbed plasticosis. Perhaps most concerning for wetland function specifically, emerging research shows that microplastics and nanoplastics can alter the microbial communities and biogeochemical processes that make wetlands so valuable. Studies cited in the review report effects on nitrogen and phosphorus cycling in sediments and changes to denitrification in wetland soils, suggesting that plastic pollution may be quietly rewiring the nutrient-processing machinery on which water quality depends. Microplastic surfaces also act as adsorption sites for heavy metals, pesticides and other organic contaminants, potentially creating concentrated packets of toxicity that organisms ingest along with the plastic itself.

Temporal trends add urgency to the picture. The review found that microplastic loads in Ramsar wetlands have risen over the past decade, tracking the relentless growth in global plastic production and waste, which projections suggest will continue climbing toward mid-century without aggressive intervention. Because monitoring began at different times in different places and methods vary widely between studies, the authors emphasize that the temporal signal is approximate. But the direction is clear, and it points upward. The fact that contamination is increasing inside areas nominally protected by an international treaty underscores a uncomfortable truth: designation alone does not shield an ecosystem from a pollutant that ignores boundaries entirely.

That methodological fragmentation is itself a central finding. Studies of microplastics in water, sediment and biota use different sampling gear, size definitions, digestion protocols and reporting units, making robust cross-site and cross-country comparison genuinely difficult. The review’s authors call urgently for standardized monitoring methods and for a more geographically balanced research agenda, particularly in under-studied regions of Africa and South America, so that future assessments can distinguish real differences in contamination from artefacts of inconsistent technique. Without harmonized data, they argue, it is impossible to set meaningful baselines, track progress or identify the sites most in need of intervention.

On the policy front, the review’s recommendations are direct. The authors urge prioritizing plastic source reduction, the only intervention that addresses the root of the problem, alongside enhanced international collaboration and the explicit integration of microplastic pollution control into wetland conservation policy under the Ramsar framework. Practical measures highlighted across the reviewed literature include improving wastewater treatment, curbing single-use plastics, managing fishing gear and agricultural plastic waste, and supporting biodegradable alternatives where they genuinely perform. With wetlands disappearing globally at roughly three times the rate of forests, according to conservation assessments cited in the study, the window for protecting these ecosystems from a compounding threat is narrowing. The review makes clear that the world’s Ramsar wetlands, symbols of international environmental commitment for more than half a century, cannot be safeguarded by protection on paper alone; they will need a global plastics problem to be solved at its source.

Subject of Research: Microplastic contamination in Ramsar-designated wetlands worldwide

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

Article References: Das, U. C., Shuvo, M. S. I., Ghosh, R., Akter, M. F., Ab. Hannan, M., Acharjee, M. R., Mehedi, L. B., Islam, S., Saha, P., Khatoon, H., Habibullah-Al-Mamun, M., & Faruque, M. H. (2026). Microplastic contamination in Ramsar wetlands: a systematic review of global sources, ecological impacts, and policy implications. Environmental Monitoring and Assessment, 198(11), Article 1158. https://doi.org/10.1007/s10661-026-15994-8

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15994-8

Keywords: microplastics, Ramsar wetlands, wetland conservation, polyethylene, polypropylene, sediment contamination, biota, plastic pollution, environmental monitoring, trophic transfer, wastewater treatment, environmental policy