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Children in communities around Ghana’s Keta Lagoon face a high risk of cancer from consuming locally caught fish contaminated with dangerous levels of mercury and arsenic, according to a study published in the journal Scientific Reports on July 7, 2025.
Researchers found that 75 per cent of the fish samples collected from the lagoon exceeded the World Health Organization’s (WHO) safety limit for arsenic, while mercury levels in all samples surpassed the WHO threshold.
The study, led by Richard Tsiwah Cobbinah of Kwame Nkrumah University of Science and Technology, assessed the long-term cancer and non-cancer risks from exposure to heavy metals through fish consumption.
Cancer risk assessments painted a grim picture, the study noted, with all metals except cadmium posing long-term cancer risks for children. Arsenic, mercury and chromium were found to be the most concerning.
The researchers analysed 12 randomly selected fish samples from various parts of the Keta Lagoon, the largest lagoon complex in Ghana and a designated Ramsar site. The lagoon, a closed system separated from the Gulf of Guinea by a sandbar, is especially vulnerable to the accumulation of pollutants due to limited water exchange.
Mean arsenic concentrations were recorded at 2.24 milligrammes per kilogramme (mg/kg) — above the WHO limit of 2 mg/kg in three-quarters of the samples. Mercury averaged 1.49 mg/kg, nearly three times the WHO safety limit of 0.5 mg/kg. Cadmium levels exceeded the permissible limit (1 mg/kg) in two samples, while chromium, lead and zinc remained within acceptable ranges.
However, copper and chromium showed the highest variability and concentrations, likely due to industrial or agricultural runoff.
Beyond cancer risks, the study also assessed potential non-carcinogenic effects using the Target Hazard Quotient (THQ) approach, which compares estimated daily metal intake against safe reference doses. In adults, arsenic, chromium and mercury each exceeded the THQ threshold of 1, signalling potential health concerns. Children were found to be more vulnerable, with only zinc falling below the risk threshold.
The cumulative hazard index showed that both adults and children were at risk, with children disproportionately affected due to lower body weight and greater metal absorption.
The researchers highlighted the role of sediment-feeding fish in bioaccumulating toxins over time, making them reliable indicators of aquatic pollution. Fish, a major protein source for millions, often accumulate toxic metals from polluted habitats, making them key indicators of water quality, the study stated.
Despite its small sample size and seasonal scope, the study raises urgent questions for Ghanaian authorities and environmental regulators. It calls for stricter pollution control, improved monitoring and public health campaigns to protect communities dependent on the lagoon’s fish as a dietary staple.
“Implementing stricter regulations, monitoring programs and public awareness campaigns are critical to mitigating the risks associated with metal-contaminated fish consumption,” it stated.
