The European Food Safety Authority (EFSA) has established Tolerable Weekly Intakes (TWIs), or ‘safe levels’, intended to protect consumers from adverse health effects posed by the possible presence of the main forms of mercury found in food: methylmercury and inorganic mercury. Recommendations of the EFSA Panel on Contaminants in the food chain where published online on Thursday Dec. 20.
Background: Mercury is a metal that is released into the environment from both natural sources and as a result of human activity. Besides the element mercury, it can occur as inorganic mercury (mercurous (Hg
22+) and mercuric (Hg
2+) cations); Mainly through the activity of microbes, inorganic mercury is transformed to organic mercury. Methylmercury (MeHg) is by far the most common form of organic mercury in the food chain.
Since both inorganic mercury as well as organic mercury are strong toxins, their presence in foodstuff is undesirable. Due to risks for human health, uptake of such contaminants should be restricted to a tolerable limit. A Tolerable Daily or Weekly Intake (TDI/TWI) is an estimate of the average quantity of a chemical contaminant that can be ingested daily or weekly over a lifetime without posing a significant risk to health. Exposure to such contaminants whilst not desirable may not be avoidable as some may be found in foods as a result of environmental pollution.
A call for annual collection of chemical contaminant occurrence data in food and feed, including mercury, was issued by EFSA in December 2010. In response EFSA has received 59,820 results from testing of the presence of mercury in food from 20 European countries, covering 2002 to 2011. Because of the lack of specific information on methylmercury and inorganic mercury in data collected, the exposure assessment (except for human milk) was based on the data submitted for total mercury.
EFSA's scientific opinion on the risk for public health related to the presence of mercury and methylmercury in food:At the request of the European Commission, EFSA’s Scientific Panel on Contaminants in the Food Chain (CONTAM Panel) considered new scientific information regarding the toxicity of these forms of mercury and evaluated provisional TWIs established in 2003 and 2010 by the Joint FAO/WHO Expert Committee on Food Additives (JECFA).
More precise data on food consumption and on mercury levels in food have allowed the Panel to more accurately assess human exposure to methylmercury through the diet. Fish meat, particularly tuna, swordfish, cod, whiting and pike were identified as the most important contributors of methylmercury exposure in Europe for all age groups, with the addition of hake for children. Exposure in women of child-bearing age was especially considered and found not to be different from adults in general. Exposure through food in high and frequent fish consumers was in general some two-fold higher than for the total population.
In its opinion, the CONTAM Panel has established a TWI for inorganic mercury of 4 µg/kg body weight (bw) which is in line with JECFA. For methylmercury, new studies indicate that beneficial effects related to long chain omega 3 fatty acids present in fish may have previously led to an underestimation of the potential adverse effects of methylmercury in fish. The Panel has therefore proposed a TWI for methylmercury of 1.3 µg/kg bw, which is lower than JECFA’s 1.6 µg/kg bw.
Whereas average exposure to methylmercury in food is unlikely to exceed the TWI, the likelihood of reaching such a level increases for high and frequent fish consumers. This group may include pregnant women, resulting in exposure of the fetus at a critical period in brain development. Inorganic mercury is less toxic and can also be found in fish and other seafood as well as ready-made meals. Exposure to inorganic mercury through food is unlikely to exceed the TWI for most people, unless combined with other sources of exposure.
This opinion focuses only on the risks related to inorganic mercury and methylmercury exposure through the diet and does not assess the nutritional benefits linked to certain foods (e.g. fish and other seafood). However, the CONTAM Panel added that if measures to reduce methylmercury exposure are considered by risk managers, the potential beneficial effects of fish consumption should also be taken into account.
The estimated exposure to inorganic mercury in Europe from the diet alone does not exceed the TWI. Inhaled elemental mercury vapour from dental amalgam, which after absorption is converted to inorganic mercury, is an additional source that is likely to increase the internal inorganic mercury exposure; thus the TWI might be exceeded.
The CONTAM Panel recommends to develop certified reference materials and proficiency testing schemes for inorganic mercury in foodstuffs other than fish and seafood. Further effort should be made to increase the number of methylmercury and inorganic mercury data in all food groups that contribute significantly to overall exposure. In order to decrease the uncertainty in the point of departure derived from the epidemiological studies, more reliable definition of the dose response taking confounding factors into account is needed. Future studies should elucidate the relevance of additional endpoints, such as immunological and cardiovascular endpoints.
Source: adapted from EFSA
The cited report:
EFSA: Scientific Opinion on the risk for public health related to the presence of mercury and methylmercury in food Related Reports BRI
- Report: Mercury in the Global Environment: Patterns of Global Seafood
Mercury Concentrations and their Relationship with Human Health Zero Mercury Working Group - Report: Mercury Contamination, Exposures and Risk: A New Global Picture Emerges, December 2012 Zero
Mercury Working Group - Report: An Overview of Epidemiological Evidence
on the Effects of Methylmercury on Brain Development, and A Rationale
for a Lower Definition of Tolerable Exposure, December 2012 
Related EVISA Resources Link database: Mercury exposure through the diet Link database: Environmental cycling of mercury Link database: Toxicity of Organo-mercury compounds Link database: Research projects related to organo-mercury compounds
Related EVISA News December 9, 2012: Mercury in fish more dangerous than previously believed; Scientists urge for effective treaty ahead of UN talks October 12, 2012: Prenatal mercury intake linked to ADHD
July 31, 2012: FDA Lands in Court Over Mercury in Fish June 17, 2012: Factors Affecting Methylmercury Accumulation in the Food Chain March 1, 2012: High levels of mercury in newborns likely from mothers eating contaminated fish October 15, 2011: Mercury pollution in the Great Lakes region -- nearly forgotten, but not gone August 16, 2010: Methylmercury: What have we learned from Minamata Bay? August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide May 3, 2009: Ocean mercury on the rise February 11, 2009: Mercury in Fish is a Global Health Concern October 30, 2008: Precautionary approach to methylmercury needed
March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning October 9, 2006: Linking atmospheric mercury to methylmercury in fish August 16, 2006: Mercury pollution threatens health worldwide, scientists say June 8, 2006: Methylmercury in fish: Can you cook it out ? February 17, 2006: Study shows link between clear lakes and methylmercury contamination in fish
February 9, 2006: Study show high levels of mercury in women related to fish consumption August 29, 2005: Is methyl mercury limiting the delight of
seafood ? - To answer this question is a challenge for elemental
speciation analysis January 12, 2005: Number of fish meals is a good predictor for the mercury found in hair of environmental journalists April 27, 2004: New kind of mercury found in fish April 27, 2004: FDA/EPA recommends pregnant women to restrict their fish consumption because of methylmercury contentlast time modified: December 24, 2012
