Toxic Metals Lurk in Ghana’s Greater Amanzule Wetlands, Testing the Safety of Local Seafood

Deep in southwestern Ghana, where the Greater Amanzule Wetland threads its way through mangrove forests, lagoons, and fishing villages along the Atlantic coast, scientists have been quietly taking the pulse of one of West Africa’s most ecologically valuable coastal ecosystems. What they found is a story of contamination that is both reassuring and alarming at the same time. A new study published in Environmental Monitoring and Assessment reports widespread heavy metal pollution in the wetland’s waters, yet the levels of toxic metals in the seafood that local communities depend on remain below thresholds that would signal immediate harm to human health. The tension between those two findings is precisely what makes the research so important.

The research team, led by Francis Adarkwah of the Institute of Environment and Sanitation Studies at the University of Ghana, together with colleagues from institutions in Ghana, the Czech Republic, and beyond, set out to answer a deceptively simple question: how contaminated is the water in the Greater Amanzule Wetland, and does that contamination find its way into the fish and shrimp that people eat? To do this, they collected 126 water samples from communities across the wetland during three separate sampling periods in 2024, analysing each for six metals of concern: cadmium, copper, arsenic, lead, nickel, and mercury. They also gathered 36 samples of seafood, including Bagrid catfish (Chrysichthys nigrodigitatus), black-chinned tilapia (Sarotherodon melanotheron), and black tiger shrimp (Penaeus monodon), testing them for cadmium, lead, and mercury.

The results paint a detailed picture of a wetland under pressure. Across most of the sampling communities, the researchers detected heavy metal contamination, with the average concentrations of the six metals in the water following a consistent pattern: arsenic was the least abundant, followed by mercury, cadmium, lead, nickel, and finally copper, which was the most prevalent. That ordering matters, because copper and nickel, while less notorious than lead or mercury, can still exert toxic effects on aquatic organisms and human health when concentrations climb high enough. The fact that copper topped the list suggests that sources such as domestic waste, small-scale industry, and agricultural runoff may be playing a significant role in shaping the wetland’s chemistry.

To move beyond simple concentration measurements, the team deployed a battery of analytical tools that are standard in environmental monitoring but rarely combined in a single study of a West African wetland. The heavy metal pollution index and the heavy metal evaluation index are composite metrics that translate raw concentration data into a single score reflecting how contaminated a water body is relative to guideline values. Principal component analysis, a statistical technique that identifies hidden patterns in complex datasets, was used to trace which metals varied together and therefore likely shared common sources. And the bioconcentration factor measured how efficiently metals moved from the water into the tissues of fish and shrimp, a key step in understanding how contamination travels through the food web.

The pollution indices revealed a striking gradient across the wetland. In some communities, contamination was moderate, while in others it reached very high levels, indicating that the problem is not uniform but concentrated in specific, impacted locations. The principal component analysis added a crucial layer of interpretation: copper, nickel, lead, cadmium, arsenic, and mercury all contributed substantially to the variation in water quality across sites. This pattern points to a mixture of anthropogenic influences, meaning human activities such as waste discharge and land-use change, and geochemical influences, meaning the natural release of metals from underlying rocks and soils. In other words, the wetland’s contamination story is not one single villain but a cast of interacting sources.

The bioconcentration findings and the seafood analysis then allowed the team to ask the question that matters most to the people who live around the wetland: is it safe to eat what you catch? Using the estimated daily intake approach, the researchers calculated how much of each metal a typical consumer would ingest through a diet of local catfish, tilapia, and shrimp. They then compared those intakes against reference doses, the toxicological benchmarks that define how much of a substance can be consumed daily over a lifetime without appreciable risk. Every estimated daily intake value fell below its corresponding reference dose.

The team went further, computing the hazard quotient for each metal and the hazard index, which sums the individual quotients to capture the combined effect of exposure to multiple metals. In every case, the values came in below unity, the threshold beyond which non-carcinogenic health effects would be expected. Under the exposure conditions evaluated in the study, the researchers found no immediate non-carcinogenic health risk from eating seafood drawn from the Greater Amanzule Wetland. For fishing families whose livelihoods and nutrition depend on the daily catch, that conclusion offers genuine reassurance, at least for now.

Yet the researchers are careful not to let that reassurance become complacency. The persistent occurrence of toxic metals, including lead, cadmium, and mercury, in both the water and the seafood signals potential ecological and public health concerns that cannot be dismissed. Lead exposure, even at low levels, is associated with neurodevelopmental harm, while cadmium accumulates in the kidneys over years of chronic exposure and mercury is a potent neurotoxin, particularly dangerous to developing foetuses and young children. The hazard index framework used in this study captures non-carcinogenic risks under current exposure conditions, but it does not eliminate the possibility of longer-term, chronic effects, especially if contamination continues to rise or if consumption patterns change.

The study’s recommendations reflect that caution. The authors call for integrated wetland management strategies that treat the Greater Amanzule as a single connected ecosystem rather than a patchwork of separate communities. They urge strengthened regulation of pollution sources, arguing that the mixed anthropogenic signature identified by the principal component analysis demands attention to the human activities driving contamination. They also recommend routine monitoring of heavy metal levels in aquatic ecosystems, so that trends can be detected before they become crises, and increased community awareness about sustainable seafood consumption, empowering residents to make informed choices about the fish and shrimp they eat.

Looking ahead, the researchers identify two critical gaps in the current picture. First, the study focused on water and seafood, but sediments, the muddy floors of lagoons and channels where metals tend to accumulate over time, were not assessed. Because sediments can act as both sinks and secondary sources of contamination, releasing stored metals back into the water under changing chemical conditions, future work that includes sediment analysis will be essential for understanding the full contaminant dynamics of the wetland. Second, the study captured a snapshot in time during 2024, whereas chronic health implications unfold over years and decades. Long-term monitoring studies will be needed to determine whether the contamination documented today is stable, worsening, or improving, and whether the communities that depend on the Greater Amanzule Wetland face accumulating risks that today’s hazard indices cannot yet reveal. For now, the wetland’s waters carry a warning that is quiet but unmistakable: the metals are there, the ecosystem is under strain, and the time to act is before the numbers cross the line.

Subject of Research: Heavy metal contamination of water and seafood in the Greater Amanzule Wetland in southwestern Ghana and its ecological and human health risks

Article Title: Heavy metal contamination in the Greater Amanzule Wetlands: a public health concern and a threat to seafood provision

Article References: Adarkwah, F., Odoom, E. S., Afful, R., Baidoo, E. K., Awuni, S., & Mattah, M. M. (2026). Heavy metal contamination in the Greater Amanzule Wetlands: a public health concern and a threat to seafood provision. Environmental Monitoring and Assessment, 198(10), Article 1044. https://doi.org/10.1007/s10661-026-15855-4

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15855-4

Keywords: Greater Amanzule Wetland, Ghana, heavy metals, water contamination, seafood safety, cadmium, lead, mercury, health risk assessment, wetland conservation, bioconcentration, environmental monitoring