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

National Waterway-3 stretches roughly 205 kilometres through the southern Indian state of Kerala, with the study focusing on a 168-kilometre navigable segment running from Kollam to the bar mouth of the Cochin estuary. The route carries enormous economic weight: it serves the booming houseboat tourism industry centred on Kollam, Alappuzha and Ernakulam, supports traditional fisheries, and passes through Kuttanad, the famously low-lying region known as the rice bowl of Kerala. Yet the same waters receive untreated urban sewage, industrial effluent from the Periyar and Muvattupuzha river catchments, and discharges linked to shipbuilding and repair activities concentrated near Kochi.

To capture the full chemical complexity of the system, researchers from Cochin University of Science and Technology and the CSIR National Institute of Oceanography sampled water, suspended particulate matter and sediments at seventeen stations along the entire corridor. Each station told a different story. One site sat near a boat jetty influenced by poultry units and medical facilities, another directly beside the titanium-bearing minerals producer Kerala Metals and Minerals Limited at Chavara, where two industrial effluent outlets discharge into the channel, while downstream stations captured the effects of dredging, tidal stagnation and vessel construction near the Marine Science jetty. Water was collected with a Niskin bottle, sediments with a Van Veen grab sampler, and all metal determinations were performed by inductively coupled plasma atomic emission spectroscopy, with certified reference material confirming recoveries between 95 and 105 percent.

The nine metals examined, iron, manganese, chromium, cobalt, nickel, copper, zinc, cadmium and lead, behaved very differently depending on which compartment of the ecosystem they occupied. In the dissolved phase, iron dominated with concentrations reaching 350.63 micrograms per litre during the monsoon, followed by zinc and copper. But the real surprise lay in the particles. Suspended particulate matter and sediments showed striking enrichment, with zinc climbing as high as 4,012 milligrams per kilogram in particulates during the non-monsoon season, and cobalt reaching 582 milligrams per kilogram during the monsoon. This pattern of low dissolved concentrations paired with particle-bound enrichment points to a fundamental truth about estuarine chemistry: metals rarely travel freely in solution for long.

That truth was quantified through partition coefficients, the ratio of a metal’s particulate concentration to its dissolved concentration. Log-transformed values exceeding three for essentially every metal in both seasons indicate an overwhelming affinity for solid phases. The chemistry behind this behaviour is intricate. Salinity, pH, dissolved oxygen and organic matter all shape how metals split between water and particles. Lead, with its small ionic radius, adsorbs efficiently onto suspended solids in both seasons. Copper, unusually, clings to the dissolved phase, likely because it forms stable compounds with water. Cadmium and nickel favour solution, with cadmium forming stable chloro-complexes as salinity rises and nickel binding to dissolved organic matter. Iron and manganese oxyhydroxides, meanwhile, act as microscopic scavengers, co-precipitating and adsorbing other metals onto their surfaces as water chemistry shifts along the salinity gradient.

Seasonality proved decisive. During the southwest monsoon, heavy rainfall dilutes salinity, flushes the estuary and floods the waterway with suspended sediment, so more metals become trapped on particles and partition coefficients rise for elements such as nickel, cobalt and cadmium. In the drier non-monsoon months, higher salinity and pH promote flocculation and sedimentation, driving iron, manganese, zinc and lead onto the particulate phase. Two-way analysis of variance confirmed that these swings were statistically robust, with chromium and cadmium showing extreme seasonal variation in the dissolved fraction, and nickel, cobalt and zinc doing the same in suspended particulates. The takeaway is that any monitoring programme sampling only one season would badly misjudge the true contaminant burden of the system.

To translate raw concentrations into a verdict on pollution, the team deployed a battery of geochemical indices. Enrichment factors normalised to iron, which is naturally abundant and rarely enriched by human activity, revealed very high to extremely high enrichment of cadmium and cobalt in suspended matter during the monsoon and of zinc during the non-monsoon. Contamination factors, the geo-accumulation index and the pollution load index converged on the same conclusion: the upper and central reaches of the waterway remain comparatively clean, with sediment pollution load indices below one, while the downstream segment of the Cochin estuary, fed by the Periyar and Muvattupuzha rivers, crossed the alarming threshold with values at or above one. The potential ecological risk index, which weights cadmium with a toxicity factor thirty times that of zinc, showed very low comprehensive risk in the southern Ashtamudi sector but very high risk in the northern Cochin sector.

Principal component analysis added a source-detective layer to the picture. For dissolved metals, the first component, explaining 39 percent of variance, grouped nutrients such as nitrate, phosphate, ammonium and silicate with iron and chromium, a fingerprint of anthropogenic nutrient and metal inputs travelling together through river runoff. In sediments, one component loaded on nickel, copper, lead and grain size, showing that fine, carbon-rich particles are the principal controllers of metal deposition, while another clustered iron, manganese, cobalt, zinc and chromium, consistent with the scavenging role of iron-manganese oxyhydroxides. Cadmium stood apart, correlating with salinity rather than any single environmental parameter, hinting at discrete industrial sources. Together the statistics point to a mixed origin: natural weathering and tidal cycling on one hand, and agricultural runoff, urban effluent and industrial discharge on the other.

The most consequential findings concern living organisms. When sediment metal concentrations were benchmarked against the National Oceanic and Atmospheric Administration’s sediment quality guidelines, cadmium exceeded the Effects Range-Low threshold at nearly every station in both seasons, with only a couple of exceptions, and chromium exceeded it across most monsoon stations. Concentrations above these thresholds are those at which adverse effects on sediment-dwelling fauna begin to appear with meaningful frequency. The toxic risk index, a consensus-based measure combining threshold and probable effect concentrations, rated the northern sector of the waterway at moderate ecological risk. Because benthic communities sit at the base of estuarine food webs, accumulating metals and passing them upward to fish and, ultimately, to people, these exceedances matter well beyond the mudflats themselves.

The authors also note a striking context for their numbers: measured concentrations were generally lower than those reported in earlier decades of Cochin estuary research, possibly because the catastrophic 2018 Kerala floods scoured and flushed the estuarine system, and because pandemic-era restrictions briefly curtailed industrial discharge. That the waterway still shows severe cadmium and zinc contamination despite these partial resets underscores how persistent the pollution sources are. The study closes with a five-point prescription: continuous seasonal monitoring of all three metal compartments, stricter treatment of effluents entering through the Periyar and Muvattupuzha catchments, environmentally sound dredging practices that avoid remobilising contaminated sediment, tougher regulation of navigation, harbour and shipbuilding activity, and integrated watershed management to protect the Ramsar wetlands. As cargo and tourists increasingly return to this historic waterway, the chemistry of its mud will determine whether the route can carry commerce without quietly carrying poison through the heart of Kerala’s most precious ecosystems.

Subject of Research: Heavy metal contamination and ecological risk in the National Waterway-3 estuarine system of Kerala, South India

Article Title: Geochemical and ecological assessment of heavy metals in a National Waterway in South India

Article References: Ragi, A. S., Gireeshkumar, T. R., Habeeb Rahman, K., Snigtha, S., Abhina, C., Muhammed Aquib, T. P., Nayana, C., & Martin, G. D. (2026). Geochemical and ecological assessment of heavy metals in a National Waterway in South India. Discover Oceans, 3(1), Article 43. https://doi.org/10.1007/s44289-026-00154-0

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00154-0

Keywords: heavy metals, cadmium, zinc, National Waterway-3, Cochin estuary, Ashtamudi Lake, Ramsar wetlands, sediment contamination, partition coefficient, ecological risk assessment, estuarine pollution, Kerala