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

Organophosphate pesticides are among the most heavily used chemical pest controls on Earth, accounting for roughly 40 percent of global pesticide consumption. They were widely adopted as replacements for the notoriously persistent organochlorine pesticides of the mid-twentieth century because they break down more quickly in the environment. Yet that relative impermanence has not kept them out of aquatic ecosystems. Spray drift, agricultural runoff, groundwater leaching, careless disposal of empty containers, and the washing of application equipment all provide routes by which these compounds reach lakes and rivers, where they can persist long enough to be taken up by organisms. In Ethiopia, chlorpyrifos-methyl is commonly applied in crop production, while diazinon finds its way into the environment partly through flea collars used on sheep, dogs, and cats in rural areas.

The research team, led by Tarekegn Fentie Yimer of the University of Gondar, targeted Lake Tana and Lake Hayqe because neither had ever been assessed for the ecological and human health risks of these compounds, despite intensive pesticide use by smallholder farmers and horticulture companies in their catchments. Lake Tana covers 3,150 square kilometers at an altitude of 1,786 meters, is recognized by UNESCO as a Biosphere Reserve, and supports endemic fish, bird, and plant species alongside a fishery with an estimated potential of 10,000 tons per year. Lake Hayqe, by contrast, is a closed-basin lake with a watershed of only about 77 square kilometers but an average depth of 37 meters and a maximum depth of 81 meters. Both lakes supply Nile tilapia, a staple food for surrounding communities, making them ideal natural laboratories for tracing pesticides from farm fields to dinner plates.

Between February and May 2023, the researchers collected water from 20 sites on Lake Tana and 5 sites on Lake Hayqe, along with 30 Nile tilapia from three Lake Tana fishing districts and 10 fish, five tilapia and five common carp, from Lake Hayqe. Fish muscle tissue was freeze-dried, homogenized, and extracted using the QuEChERS method, a technique whose acronym promises a process that is quick, easy, cheap, effective, rugged, and safe. All samples were then analyzed by gas chromatography coupled with triple quadrupole mass spectrometry, one of the most sensitive analytical approaches available for trace organic contaminants. The method performed well: recoveries ranged from 96.7 to 106.0 percent, well within the accepted 80 to 120 percent window, and detection limits were low enough to quantify every residue found.

Of the eighteen organophosphate pesticides screened, only a handful appeared. In water, chlorpyrifos-methyl, ethion, and malathion were detected at every site sampled, with chlorpyrifos-methyl ranging from 1.41 to 1.91 micrograms per liter. That figure is dramatic when set against the United Kingdom Environment Agency’s non-statutory maximum acceptable concentration of just 0.01 micrograms per liter for the protection of freshwater life, meaning the lakes carry concentrations more than a hundred times that benchmark. Malathion, by contrast, remained below the World Health Organization’s drinking-water guideline of 2 micrograms per liter. In fish muscle, four compounds were detected: chlorpyrifos-methyl, diazinon, ethion, and malathion, at concentrations generally between about 11 and 25 micrograms per kilogram. Notably, malathion levels in fish exceeded the WHO maximum residue limit of 2 micrograms per kilogram, while diazinon stayed comfortably within its 200 to 500 microgram limit.

The spatial patterns told a story about sources. Statistical analysis revealed significant differences among sampling sites for every detected compound, with the highest chlorpyrifos-methyl and malathion values clustering near the mouths of tributary rivers such as the Gumara, Rib, and Megech, which drain intensive agricultural areas like Fogera and Gorgora, and near Bahir Dar, the region’s largest city. Principal component analysis, a multivariate technique that condenses many correlated measurements into a few underlying axes of variation, confirmed that ethion and chlorpyrifos-methyl dominated the first component explaining nearly 60 percent of the variance in water data, while malathion distinguished the Megech site. Tilapia consistently accumulated more pesticide than common carp in Lake Hayqe, suggesting species-specific differences in uptake and metabolism.

The ecological risk assessment produced the study’s most alarming numbers. The team calculated risk quotients by dividing measured environmental concentrations by predicted no-effect concentrations derived from acute toxicity data for three representative organisms: fish, Daphnia, and algae, chosen to span primary producers, primary consumers, and higher trophic levels. For Daphnia, the risk quotients for chlorpyrifos-methyl reached 275 in Lake Tana and 268 in Lake Hayqe, values far above the threshold of 1 that signals high risk. Ethion also posed high risk to Daphnia, with quotients between roughly 19 and 22, while malathion registered a medium risk. Fish and algae fared considerably better, with low to medium risk quotients across the board. The pattern identifies Daphnia as by far the most sensitive receptor, a finding consistent with studies in Ethiopia’s Lake Hawassa and in surface waters of northwestern Bangladesh and Greece.

The human health picture was far more reassuring. Using standard exposure assumptions, a fish consumption rate of 30 grams per day and an adult body weight of 60 kilograms, the researchers estimated daily intakes and hazard quotients for each pesticide. Every hazard quotient came in well below 1, and the combined hazard index was approximately 0.06 for both lakes, indicating a negligible non-carcinogenic risk from eating fish under the conditions assessed. Diazinon contributed the largest share of the hazard index, yet even at maximum detected concentrations the total remained an order of magnitude below the level of concern. The authors caution, however, that these estimates rest on generalized consumption and body weight assumptions that may not reflect every local community, and that the assessment addressed only non-cancer endpoints.

The study’s authors are candid about its limitations. Composite sampling, while analytically practical, blurred spatial resolution, particularly in Lake Hayqe where all water samples were merged into a single composite. Sampling occurred during a single season, so rainfall-driven pulses of pesticide runoff may have gone unmeasured, and the smaller sample size from Lake Hayqe limits direct comparison between the lakes. Still, the baseline established here carries a clear message for policymakers: pesticide governance in Ethiopia remains underdeveloped, many generic pesticides circulate without full registration, and farmers often handle chemicals without precautions. The researchers call for multi-season monitoring, larger and non-composited samples, and site-specific exposure data, alongside improved management practices to stem the flow of organophosphates into lakes that sustain fisheries, tourism, and hydropower. Protecting the plankton at the base of these ecosystems, the data suggest, may be the most urgent task of all.

Subject of Research: Ecological and human health risk assessment of organophosphate pesticide residues in water and fish from two Ethiopian highland lakes

Article Title: Ecological and human health risk assessments of organophosphate pesticide residues in water and fish from two highland lakes in Ethiopia

Article References: Yimer, T. F., Kassa, Y., Mulugeta, M., Akele, M. L., Alemu, A. K., Yenealem, D., Amare, A., Moges, Z., Birhan, T. A., & Tibebe, D. (2026). Ecological and human health risk assessments of organophosphate pesticide residues in water and fish from two highland lakes in Ethiopia. Heliyon, 12(15), Article e45551. https://doi.org/10.1016/j.heliyon.2026.e45551

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45551

Keywords: organophosphate pesticides, Lake Tana, Lake Hayqe, Ethiopia, chlorpyrifos-methyl, Daphnia, ecological risk assessment, bioconcentration, Nile tilapia, water contamination, fish consumption, risk quotient