Fish contamination with heavy metals – Causes and health effects

The main contributor is the contamination of aquatic environments due to industrial activity, intensive farming, oil spills, municipal and industrial effluents. Harmful chemicals enter the human body through consumption, particularly of fish and seafood, which are often laden with heavy metals, pesticides, and dioxins. Long-lived fish species accumulate more toxins than short-lived ones.

Among the hazardous heavy metals are mercury, cadmium, and lead. Mercury primarily exists in organic and inorganic compounds. The most toxic form is organic mercury, which arises from the transformation of inorganic compounds in aquatic environments. The primary source of human exposure to mercury is the consumption of fish and seafood. Mercury has a detrimental effect on the nervous system. According to Commission Regulation (EC) No 1881/2006 of 19 December 2006, the maximum permissible mercury content in fishery products is 0.050 mg/kg; for certain species such as pike, grouper, pelamid, eel, halibut, marlin, tuna, perch, sea bream, pike-perch, grenadier, hake, cod, swordfish, and sturgeon, the limit is 1.0 mg/kg. Cadmium occurs as chlorides and sulfates, negatively impacting the entire body, particularly the reproductive system. According to Commission Regulation (EU) No 488/2014 of 12 May 2014, the permissible cadmium content in fishery products is 0.50 mg/kg, with exceptions for mackerel and tuna (0.10 mg/kg), tazan marun (0.15 mg/kg), sardines, anchovies, and sardines (0.25 mg/kg), shellfish (0.50 mg/kg), and mollusks (1.0 mg/kg). Lead exists as nitrates and acetates, and excessive amounts disrupt respiratory and circulatory functions. According to Commission Regulation (EU) No 2015/1005 of 25 June 2015, the permissible mercury content in fish is 0.30 mg/kg.

Pregnant women must exercise caution, as certain chemical compounds can cross the placenta and impair fetal development. Among the most hazardous substances is methylmercury, a potent neurotoxin that can lead to severe developmental disorders, including cognitive impairment and damage to sensory organs such as vision and hearing. Consequently, expectant mothers should avoid consuming fish contaminated with methylmercury, including marlin, swordfish, pike, sharks, tuna, and to a lesser extent, mackerel and halibut.

Undoubtedly, all predatory fish, which accumulate harmful substances by consuming other animals, should be avoided. When making a purchase, one should pay attention to the fish's origin and whether it bears an MSC certification, which ensures it comes from sustainable and properly managed fisheries. Additionally, it is advisable to opt for fish from local fisheries to reduce transportation. Diversity is key. One should purchase various fish species to limit the overfishing of the most popular ones. Before buying, it is essential to inquire with the seller about the fish's origin. When deciding to purchase fish, it is also crucial to be informed about the safety of fishing practices and to avoid species threatened with extinction. The table presents the possibility of purchasing fish based on the species' extinction risk. Table 1: Fish Purchase Possibility Based on Extinction Risk. Fish that can be purchased, caution advised, not to buy. Cod (eastern stock), Cod (western stock), Atlantic halibut, Flounder, Smelt, Redfish, Lesser spotted dogfish, Norwegian lobster, Tropical shrimp, Lobster, Crab, Baltic salmon, Carp, Northern shrimp, Sharks and rays, Pacific salmon, Farmed salmon, Sole, Mackerel, Plaice, Bluefin tuna, Pollock, Pangasius, Eel, Perch, Pike-perch, Edible mussel, Rainbow trout, Zander, Pike, Whitefish, Sprat, Tilapia, Herring, Tuna, and all with MSC certification. WWF, What Fish for Dinner, WWF Ecological Guide. Fish are highly recommended in everyone's diet. Remember that in addition to nutrients, they can also be a source of harmful substances such as heavy metals. Therefore, it is best to consume them 2-3 times per week. Pregnant or breastfeeding women should limit consumption frequency, particularly of large predatory fish. Additionally, when buying fish, only choose from reliable sources.