Mercury is a toxic heavy metal that is present in the environment both naturally (e.g. volcanic eruptions) and as a result of industrial processes (e.g. mining, burning coal or heating oil). Mercury also enters the food chain through deposits in the soil and water and thus into food. There are different forms of mercury, which have different health effects: elemental (metallic) mercury (Hg0), inorganic mercury (iHg) and organic mercury compounds such as methylmercury (MeHg).

Inorganic mercury can be found in all food groups: in fish and seafood as well as in plant products and in animal products from land animals. In water, the inorganic mercury is converted by bacteria into the even more harmful organic methylmercury. Aquatic organisms take it up, which in turn feed on some fish. Long-living predatory fish, which feed on fish already contaminated with methylmercury, contain particularly high concentrations of methylmercury. This is why this mercury compound is found exclusively in fish and seafood (crustaceans, mussels, squid).

Elemental mercury is primarily absorbed by inhalation via the respiratory tract, whereas the dietary intake of elemental mercury via the gastrointestinal tract is negligible and therefore of no significance.

Inorganic mercury mainly accumulates in the kidneys. It can also affect the liver, the nervous system, the reproductive system and the immune system.

Organic mercury compounds, such as methylmercury, are considered a particularly dangerous form of mercury in food. Methylmercury can cross the blood-brain barrier and the placenta, which can lead to neurological damage. The development of the nervous system in the unborn child is particularly sensitive to these mercury compounds.

The European Food Safety Authority (EFSA) has derived TWI values for inorganic mercury and methylmercury. TWI stands for tolerable weekly intake. This refers to the amount of a substance that can be ingested per week over a lifetime without causing health effects. The TWI value for inorganic mercury is 4 µg/kg body weight (bw) per week and the TWI value for methylmercury is 1.3 µg/kg body weight per week. A 70 kg person may ingest 91 µg of methylmercury per week without any health effects. A child weighing 30 kg may ingest 39 µg of methylmercury per week without any health effects.

Results from Austria and the EU show that the contamination of mercury in foods of terrestrial origin, i.e. in plant products and animal products from land animals, is very low. In the majority of these foods, the concentrations of mercury were so low that they could not be measured. The situation regarding mercury in fish and seafood is different: Here, measurable concentrations are present in most cases. In fish, 80 to 100 per cent of the total mercury is present as methylmercury, while in seafood (shrimps, mussels, squid) 50 to 80 per cent of the total mercury is methylmercury and 20 to 50 per cent is inorganic mercury.

Maximum levels for mercury in food

Mercury is regulated as total mercury in fish, seafood, food supplements and salt in Regulation (EU) No. 2023/915 as amended. While a maximum level of 300 µg/kg is set for some fish and seafood, the maximum level for the majority of fish is 500 µg/kg. The maximum level of 1,000 µg/kg applies to certain fatty fish, especially predatory fish, which are at the end of the food chain and can accumulate more harmful substances. Foodstuffs may only be placed on the market if their contaminant content does not exceed the specified maximum levels. A parameter value of 1 μg/l applies to drinking water and natural mineral waters in Austria in accordance with the Drinking Water Ordinance and the Mineral Water and Spring Water Ordinance.

Furthermore, maximum residue levels for mercury in other foods are regulated in accordance with the Pesticides Regulation (EC) No. 396/2005. On 18 January 2018, new maximum residue levels were published in the Official Journal of the European Union in Regulation (EU) No. 2018/73, which have been valid since 7 February 2018. In Austria, the use of mercury compounds in plant protection products is prohibited (ban on plant protection products containing certain active substances, Federal Law Gazette II No. 308/2002).

In addition, mercury is regulated in Directive 2002/32/EC on undesirable substances in animal feed.

Analyses of mercury in fish

We analyse mercury in fish and seafood as well as in foods of terrestrial origin such as cereals, fruit, vegetables, dairy products, meat, baby food and food supplements. In the years 2016 to 2022, a total of 1,099 samples of fish and seafood were analysed for their mercury content. In the case of freshwater fish, mainly trout, carp, char, catfish and pikeperch, both from domestic waters and imported products, were analysed. Exotic freshwater fish such as pangasius and tilapia and popular marine fish such as tuna, cod, herring, mackerel, sardine, anchovy, plaice, gilthead bream, halibut, Alaska pollack, sea bass and butter mackerel were also analysed. In addition, crustaceans (shrimps), aquatic molluscs (squid and mussels) and fish products (canned fish, fish fingers, spreads) were analysed.

Methylmercury content in fish from the Austrian food analyses for the years 2016-2022:

Mercury is mainly present in fish and seafood in the form of methylmercury (80 - 100% of total mercury). The level of methylmercury contamination is highly dependent on the type of fish: Fish fillets of fatty predatory fish at the end of the food chain, such as swordfish, butter mackerel and tuna, contain particularly high concentrations of mercury. Tinned tuna contains significantly lower concentrations of mercury compared to tuna fillets. The size of the processed fish may play a role here, as the accumulation of mercury in the fish increases with age.

Of the fish species popular in Austria, trout, carp, char, herring, salmon and "Alaska pollock", which is often processed into fish fingers, were slightly contaminated.

According to the data from the years 2016-2022, seafood such as shrimp, squid and mussels were slightly contaminated.

Exceedances of the maximum levels for methylmercury were found in three tuna samples, two swordfish samples and one sample each of bluefish, butter mackerel and butterfish, which is contained in certain sushi dishes.

Fish recommendations

Fish is rich in iodine, contains high-quality protein, omega-3 fatty acids and significant amounts of vitamin D. The Austrian Ministry of Health therefore recommends eating 1 portion of local fish (such as char, trout, carp) and 1 portion of oily sea fish (such as salmon, mackerel, herring, tuna) per week (1 portion = 1 palm-sized, finger-thick piece).

Table: Number of portions of selected fish species that could be consumed per week without exhausting the TWI (portion size: adults: 150 g, children: 70 g)

Recommendations for sensitive groups:

• When following the recommendations for fish consumption, care should be taken to ensure that children do not eat predatory fish such as tuna, swordfish, halibut, pike, butterfish, snapper, shark, marlin, swordfish, king mackerel, tilefish and butter/snake mackerel every week. Babies, small children, pregnant women, breastfeeding mothers and women who wish to have children should avoid these predatory fish altogether
• In this way, the positive nutritional and physiological effects of regular fish consumption can be achieved without ingesting harmful amounts of organic mercury compounds such as methylmercury. If you avoid sea fish altogether, it is recommended that you also eat 1 tablespoon of rapeseed oil per day

Recommendations on fish consumption from the National Nutrition Commission

With our mercury calculator you can easily find out how much mercury you are ingesting through fish.

You enter how much fish you eat, your body weight and which fish you eat.

The result shows you what proportion of your tolerable weekly intake (TWI) of mercury you have reached. As long as you remain below 100%, there is no health risk.

AGES report - Intake of mercury via food (2016-2022)

TWI values were derived by the European Food Safety Authority (EFSA) for inorganic mercury and methylmercury. TWI means tolerable weekly intake or tolerable weekly intake. This refers to the amount of a substance that can be ingested per week over a lifetime without causing health effects.

The TWI value for inorganic mercury is 4 µg/kg body weight (bw) per week and the TWI value for methylmercury is 1.3 µg/kg body weight per week. A 70 kg person may ingest 91 µg of methylmercury per week without any health effects. A child weighing 30 kg may ingest 39 µg of methylmercury per week without any health effects.

To estimate exposure to methylmercury, the tolerable weekly intake was compared with the calculated intake based on data on fish consumption by the Austrian population (Austrian Nutrition Report 2017).

Utilisation of the tolerable daily intake of mercury in Austria

With an average consumption of fish fillets, 9% of adults and 24% of children utilise the TWI value for methylmercury. With a high consumption of fish fillets, adults utilise 74% of the TWI value and children 162%. This means that the TWI value is exceeded in children. However, the type of fish consumed plays a major role. If only less contaminated fish such as trout, char, carp, salmon or fish fingers are consumed, even very high consumption does not lead to the TWI being exceeded. In the case of highly contaminated species such as tuna, for example, the consumption of 2 portions of tuna (fillet) per week can lead to an exceedance. However, the utilisation of the TWI value is significantly lower when canned tuna is consumed.