Mercury is a heavy metal that is present in the environment both naturally (e.g. evaporation, volcanic eruptions) and through industrial processes (e.g. mining, waste incineration, coal combustion). Mercury enters the food chain and thus food through deposition in soil and water. A distinction is made between elemental mercury (Hg0), inorganic mercury (iHg) and organic mercury compounds. Elemental mercury is not significant as a food contaminant. Inorganic mercury can occur as a contaminant in all food groups. The most significant organic mercury compound in food is methylmercury (MeHg). Methylmercury is particularly hazardous to health and is found only in fish and seafood (crustaceans, mollusks, squid). Therefore, the topic of mercury is discussed in connection with fish consumption.

Inorganic mercury and methylmercury have very different toxicological properties and must be considered separately in risk assessments. Inorganic mercury accumulates primarily in the kidney and can cause kidney damage. Methylmercury is able to cross the blood-brain barrier and placenta and can cause neurological damage. Particularly sensitive to methylmercury is the development of the nervous system in the unborn child. The Tolerable Weekly Intake (TWI) for inorganic mercury is 4 μg per kg body weight per week. The TWI for methylmercury is 1.3 μg per kg body weight per week. The TWI indicates the amount of a substance that can be ingested weekly over a lifetime without causing health effects.

In this report, the occurrence of mercury in food in Austria was investigated. The report includes data from food surveys conducted by AGES from 2007 to 2015. By linking these results with consumption data from the Austrian Nutrition Report 2012, the intake of inorganic mercury and methlymercury (exposure) in adults and children (6 - 9 years) was estimated. Intake values were compared to TWI values to assess health risk.

Occurrence of mercury in food on the Austrian market

Mercury levels in food were measured as total mercury. Subsequently, the proportion of inorganic mercury and methylmercury was calculated using standard factors. In foods of terrestrial origin, all mercury is present as inorganic mercury. Terrestrial origin includes all food groups except fish and seafood, i.e., plant products and products from terrestrial animals. In fish, 80-100% of the total mercury is present as methylmercury, and in seafood, 50-80%. The remaining mercury in fish and seafood is present as inorganic mercury.

In all foods of terrestrial origin, mercury levels were very low. In 93% of the total of 3,695 samples of terrestrial origin, the total mercury content was below the limit of quantification, i.e. no measurable concentrations of mercury were found. Since no measured values are available in such a case, two calculation methods were used to calculate the mean value. The Lower Bound (LB) method results in an underestimate, while the Upper Bound (UB) method results in an overestimate. The mean value calculated in this way for total mercury in food of terrestrial origin was 1 - 7 μg/kg (LB-UB).

In the "fish and seafood" group, a total of 1,751 samples were analyzed and the mean value for total mercury was 64 - 66 μg/kg (LB-UB). There were significant differences in mercury content of different fish species. Long-lived predatory fish, which are at the bottom of the food chain, are the most contaminated.

Exposure to inorganic merc ury The exposure estimate for inorganic mercury assumed that 100% of the total mercury measured was present as inorganic mercury in terrestrial foods, 20% in fish, and 50% in seafood. The calculated total inorganic mercury intake did not result in any exceedance of the TWI. The average intake was no more than 50% of the TWI value (UB) for adults and no more than 71% of the TWI value (UB) for children. Adults with high seafood consumption (95th percentile of consumption values) exhausted at most 54% of the TWI for inorganic mercury (UB), and children with high consumption exhausted at most 78% (UB).

Exposure to methylmercury

In the exposure assessment for methylmercury, it was assumed that 100% of the total mercury measured was present as methylmercury in fish and 80% in seafood. In Austria, adults consume an average of about 111 g of fish and seafood per week, thereby ingesting methylmercury at the rate of 9% of the TWI value. Children aged 6-9 years consume on average about 124 g of fish per week, reaching 18% of the TWI value. Adults with high consumption of fish and seafood (95th percentile of consumption values, i.e., approximately 750 g per week) exhaust 66% of the TWI value. Children with high consumption (about 570 g per week) exceed the TWI for methylmercury by 116%.

It plays a major role which kind of fish is consumed. Based on Austrian mercury data, adults, for example, consume only 3% of the TWI value with a weekly portion (150 g) of trout, while children consume 8%. In contrast, with one portion of tuna per week, adults consume 30% of the TWI value, children 71%.

According to the Austrian food pyramid, one portion of domestic fish (such as char, trout, carp) and one portion of fatty sea fish (such as salmon, mackerel, herring, tuna) should be consumed weekly. Adhering to this consumption recommendation, adults exhaust the TWI for methylmercury to 7 - 35 %, children to 17 - 84 %, depending on which fish species are combined.

In tendency, the Austrian mean values for mercury in fish and seafood were below the European mean values of EFSA (European Food Safety Authority). While the Austrian data for freshwater fish were particularly meaningful for the domestic market, it can be assumed that the international market for marine fish was better covered by EFSA's Europe-wide data collection. For example, based on the European mean values for mercury, one serving of tuna alone will result in 48% of the TWI for methylmercury being consumed by adults, and 112% by children. Therefore, when following fish consumption recommendations, care should be taken to ensure that children do not eat predatory fish (tuna, swordfish, halibut, and pike) every week. Young children, pregnant women, nursing mothers and women of childbearing potential are generally advised against eating these types of fish. Thus, the positive nutritional effects of regular fish consumption can be achieved without ingesting alarming amounts of methylmercury.