Abstract
Fish oils, such as cod liver oil or shark liver oil, are a valuable source of essential omega-3 unsaturated fatty acids (EFAs) (mainly DHA and EPA) and vitamins A and D, which are crucial for the proper functioning of the body, including neurological development, vision and the cardiovascular system. Due to the low consumption of fish in Poland, dietary supplements containing these oils have gained popularity. However, a significant problem is the potential contamination of fish and fish products with heavy metals, especially mercury. Mercury, mainly in the form of methylmercury, accumulates in aquatic organisms, especially in predatory and long-lived fish, due to environmental pollution. Methylmercury is highly toxic. It penetrates the blood-brain and blood-placenta barriers, posing a risk of neurotoxicity, developmental problems and a negative impact on the circulatory, immune, urinary and hormonal systems. The applicable regulations (e.g. Commission Regulation (EC) No. 629/2008, ICH Q3D guidelines) specify permissible levels of mercury in food, dietary supplements and medicinal products, with the standards for supplements being more stringent than for fish meat. Studies have shown that commercially available fish oil supplements usually contain mercury in amounts below the established limits, making them safe for consumption. Nevertheless, due to the dynamic development of the market and the lack of mandatory control before placing on the market, the need for constant quality monitoring and possible tightening of legal requirements for dietary supplements is postulated.