New research reveals dangerous levels of mercury and arsenic in local fish, raising urgent concerns for child health and food safety in Ghana’s Keta Lagoon communities.
Study: Cancer risk from heavy metal contamination in fish and implications for public health. Image Credit: schusterbauer.com / Shutterstock
In a recent article published in the journal Scientific Reports, researchers assessed levels of heavy metal contamination in fish and evaluated the associated risks and implications for public health. They detected high concentrations of arsenic and mercury in fish samples, with arsenic exceeding the World Health Organization (WHO) safety limit in 75% of samples and mercury exceeding the WHO limit in all samples.
Cadmium only exceeded the permissible level in two out of twelve samples. These contaminants could increase the risk of cancers and other adverse health effects, including neurological and organ toxicity, particularly in children.
Background
Heavy metal contamination in aquatic environments poses a serious threat to both ecosystems and public health. Fish, which are a major source of protein globally, can absorb and accumulate toxic metals from their habitats, making them useful indicators of water pollution. Consuming contaminated fish can have harmful health effects, including cancer risks, due to metals like arsenic, mercury, cadmium, and lead.
Heavy metals are dense elements that can be toxic even in small amounts. While some, such as iron (essential for red blood cell development), copper (which supports iron absorption and metabolism), and manganese (which aids in connective tissue formation and bone health), are essential to the body in trace amounts, they become toxic at higher levels. Others, such as lead and cadmium, have no known biological benefits and can enter the body through exposure to sediment, food, and water.
Coastal lagoons are particularly vulnerable to heavy metal pollution due to their ecological sensitivity and proximity to industrial, agricultural, and urban waste sources. These lagoons support communities that rely heavily on fishing for nutrition and livelihood.
Fish in these environments often feed on materials in the sediment and can accumulate heavy metals over time. As a result, fish are frequently used as biological markers to monitor pollution levels in lagoons, making them central to research on environmental contamination and food safety.
About the Study
This study examined the cancer risk associated with consuming fish contaminated by heavy metals, using Keta Lagoon in southeastern Ghana as a case study.
Sampling was conducted during the minor rainy season, with twelve fish collected from randomly chosen locations. Upon collection, the live fish were humanely euthanized in an ice slurry and transported on ice to a certified laboratory, in accordance with ethical animal research guidelines and with the approval of the KNUST Animal Research Ethics Committee (AREC/024).
In the laboratory, all glassware underwent rigorous cleaning, including acid soaking, to prevent sample contamination.
For metal analysis, the study used specific instrumental techniques: arsenic was quantified using an atomic absorption spectrometer with hydride generation, mercury was measured with an automatic mercury analyzer, and other metals were detected using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS).
Before analysis, homogenized fish samples were digested using a three-acid mixture at 200 °C to ensure complete breakdown of the tissue. Quality control was maintained through the use of standard solutions and blank samples.
Finally, health risk assessments were conducted via target hazard quotient calculations for non-carcinogenic risks and by comparing estimated daily metal intakes to established cancer slope factors, with statistical analyses verifying differences across sample sites.
Statistical analysis included a one-way ANOVA, which showed significant differences in metal concentrations between sample groups (F-value = 184.13, p = 1.53 × 10⁻⁸³). Correlation analysis (e.g., arsenic and zinc, r = 0.75; chromium and copper, r = -0.42) further explored potential relationships and sources of contamination. Principal Component Analysis (PCA) identified distinct clustering of samples F3, F4, and F12, suggesting shared contamination sources, while other samples had unique metal profiles.
Key Findings
The study revealed notable variation in heavy metal levels across fish samples from Keta Lagoon.
Arsenic concentrations ranged from 0.9 to 3.2 mg/kg, with an average of 2.24 mg/kg, exceeding WHO’s safety limit in 75% of samples. Mercury levels averaged 1.49 mg/kg, surpassing the 0.5 mg/kg limit in all samples.
Cadmium exceeded permissible levels in two samples, while chromium, lead, and zinc remained within safe ranges. Copper and chromium showed the highest average concentrations and variability, likely due to localized industrial or agricultural inputs.
Statistical analysis revealed significant differences in metal concentrations among sample groups, likely due to environmental conditions and pollution sources. Correlation analysis revealed the co-occurrence of certain metals, such as arsenic and zinc, and inverse relationships between others, indicating diverse contamination pathways.
Principal Component Analysis revealed distinct clustering of some samples, indicating shared contamination sources, while others exhibited unique metal profiles. Health risk assessments revealed that for adults, arsenic, chromium, and mercury posed significant non-carcinogenic risks (hazard quotient (THQ) > 1), while for children, all metals except zinc exceeded this threshold. The THQ values for adults were: As (4.40), Cr (4.77), Hg (2.91); for children: As (13.4), Cr (14.6), Hg (8.93).
The hazard index (HI, the sum of THQs) was 14.5 for adults and 44.1 for children, exceeding the safe threshold (HI > 1) for both groups.
Carcinogenic risk assessments showed that only cadmium did not present a significant cancer risk for adults, while all metals except cadmium presented a significant cancer risk for children, underlining their heightened vulnerability.
For non-carcinogenic risk, the order of concern was chromium > arsenic > mercury > cadmium > copper > lead > zinc.
Conclusions
This study highlights substantial heavy metal contamination in fish from Keta Lagoon, especially arsenic and mercury, posing serious health risks to consumers.
The elevated non-carcinogenic and carcinogenic risk levels, particularly for children, emphasize the urgent need for regulatory action and environmental monitoring. Statistical analyses confirmed significant variation in metal concentrations, likely due to differing pollution sources and ecological conditions.
A strength of the study lies in its comprehensive analytical approach, using validated methods and robust risk models to assess both exposure and health risks. The integration of correlation analysis helped identify potential metal sources and contamination patterns.
However, limitations include the small sample size and seasonal sampling, which may not reflect long-term trends. Future research should expand the sample size, include data from different seasons, and investigate potential sources in greater detail.
Overall, the findings support the need for stricter regulation, community education, and sustainable fisheries management.
Journal reference:
- Cancer risk from heavy metal contamination in fish and implications for public health. Cobbinah, R.T., Boadi, N.O., Saah, S.A., Agorku, E.S., Badu, M., Kortei, N.K. Scientific Reports (2025). DOI: 10.1038/s41598-025-08488-z, https://www.nature.com/articles/s41598-025-08488-z