For many Egyptian families, fish is a staple on the table: affordable, rich in protein and widely considered a healthier alternative to red meat. However, a new study suggests that some popular marine fish sold in Egyptian markets may also carry a hidden risk, as they can contain heavy metals that accumulate in the body over time.
Published in Scientific Reports, the study examined 250 samples of three commonly consumed fish species: flathead grey mullet, known locally as bouri, sardines and mackerel. The samples were collected from local markets in Mansoura, Egypt, over 10 sampling rounds between August 2023 and March 2024. Researchers tested the fish muscle for four toxic metals: mercury, arsenic, lead and cadmium.
According to Hend Ali Elshebrawy of the Department of Food Hygiene, Safety and Technology at Mansoura University’s Faculty of Veterinary Medicine, and lead author of the study, the research went beyond simply measuring contamination. The team also sought to assess what the detected levels could mean for consumers’ health, particularly among people who eat fish frequently.
Fish remains an important source of high-quality protein, minerals and omega-3 fatty acids. However, marine fish can absorb pollutants from water, sediment and food, particularly in environments affected by industrial waste, agricultural runoff, sewage and other human activities. Once accumulated in fish tissue, these metals can reach people through regular consumption.
The results showed that arsenic had the highest average concentration across the three fish species, while cadmium had the lowest. Flathead grey mullet recorded the highest average levels of mercury and arsenic, at 0.313 and 2.13 micrograms per gram of wet weight, respectively. Sardines had the highest average lead concentration, at 0.472 micrograms per gram, while mackerel recorded the highest cadmium level, although cadmium concentrations remained comparatively low.
A significant share of the samples exceeded the maximum permissible limits used in the study. For mercury, 20% of mullet samples, 9% of sardine samples and 12% of mackerel samples were above the permitted limit. Arsenic showed higher exceedance rates, with 56% of mullet, 41% of sardine and 22% of mackerel samples crossing the relevant limit.
Lead also raised concerns, with 58% of sardine samples, 45% of mackerel samples and 20% of mullet samples exceeding the permissible level. Cadmium, by contrast, remained within the permitted limits in all samples.
The health-risk calculations added another layer to the findings. For the general population, defined in the study as people consuming about 57 grams of fish per day, most estimated daily intakes remained below safety thresholds, except for mercury from flathead grey mullet, which slightly exceeded the recommended limit.
The picture changed considerably for high-fish consumers, defined as people consuming 200 grams per day. In this group, mercury intake exceeded safety limits for all three fish species. Arsenic exceeded the limit for mullet and sardines, while lead exceeded the limit for sardines and mackerel.
The study also assessed potential non-cancer health risks using a standard measure known as the target hazard quotient. Values above 1 indicate a potential health concern. For all three fish species, the combined risk values exceeded this threshold, mainly due to mercury and arsenic.
The estimated cancer risk associated with arsenic was also above the acceptable safety level for all three fish species among both general and high-fish consumers. By contrast, the risks associated with lead and cadmium remained within safer ranges.
However, the authors point to important limitations that should be considered when interpreting the findings. The study tested raw fish muscle, while cooking methods such as frying and grilling may alter metal concentrations.
More importantly, the researchers measured total arsenic rather than distinguishing between its different chemical forms. This is significant because most arsenic found in marine fish is typically present in organic forms that are considerably less toxic, while inorganic arsenic is the form most strongly associated with cancer. As a result, the study’s estimate of arsenic-related cancer risk may be higher than the actual risk.
The findings do not mean Egyptians should stop eating fish. Rather, they underscore the need for regular monitoring of fish sold in markets, tighter control of pollution sources and clearer public guidance on safe fish consumption. They also highlight the importance of considering both contamination levels and the amount and frequency of fish consumed when assessing potential health risks.
