Occurrence in food
Mercury is a toxic heavy metal occurring naturally in the environment. Mercury is also released into the environment as a result of burning fossil fuels, especially coal. Air flows can result in mercury spreading far from the source of emission. The amount of mercury released into the environment as a result of human activity is limited by environmental legislation.
Mercury occurs in various forms in nature: metallic mercury, inorganic mercury salts and organic mercury compounds (in particular methylmercury). Methylmercury is the most toxic form of mercury. Human exposure to mercury is primarily through food. Mercury is present mainly in foodstuffs of animal origin. Fish accounts for most of the mercury intake from daily food. As much as 90% of the mercury contained in fish is toxic methylmercury. However, mercury levels in fish vary widely depending on the species and their origin. Good quality feedstuffs mean that mercury levels in farmed fish, milk and dairy products, eggs and meat are generally very low.
Adverse health effects
The symptoms of acute mercury poisoning are central nervous system related: tremors of the hands, impaired concentration, sensory, visual and auditory disorders, and numbness of the limbs. With prolonged exposure, methylmercury damages the central nervous system. Foetal exposure to methylmercury can cause a delay in the development of the child. Methylmercury may also increase the risk of cardiovascular disease.
The European Food Safety Authority (EFSA) has determined the tolerable weekly intake (TWI) of methylmercury to be 1.3 μg/kg bw/week.
Maximum levels in food
EU regulation, ((EU) 2023/915 as amended) sets maximum levels for mercury in fishery products, muscle meat of fish, crustaceans and food supplements.