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Mercury and Fish Consumption

The Food Safety Authority of Ireland (FSAI) is providing important precautionary advice in relation to the consumption of fish following the publication of studies, which indicate the presence of mercury in top predatory fish species. The FSAI is advising pregnant and breastfeeding women, women of childbearing age and young children to limit their intake of predatory fish (shark, swordfish, tuna, etc.) while continuing to consume other fish as part of a balanced diet. It recommends that these groups select fish from a wide range of species but not to eat swordfish, marlin and shark, and to limit consumption of tuna to one fresh tuna steak or two 225 g/8 oz cans of tuna per week.

The FSAI states that mercury is a metal, which is found both naturally in the environment and also as a result of disposal of waste or releases from industrial activities. It is a contaminant and can build up in the food chain. A recent European Food Safety Authority study undertaken by its Scientific Panel on Contaminants in the Food Chain has shown that its chemical form, methylmercury, is prevalent in all fish and can build up to significant levels in large predatory fish as these fish consume smaller species that have taken up mercury in the environment. These predatory fish thus have a larger store of mercury, which is found to affect the human nervous system and the developing brain. It is on this basis the FSAI is making this recommendation to pregnant, breastfeeding and women of child bearing age so as to protect unborn, newborn and young children against the negative effects of the build up of methylmercury.

FSAI stated it is important that consumers including pregnant and breastfeeding women continue to appreciate the role and benefits of fish in a healthy diet. Everyone should continue to eat one to two portions of fish per week including one portion of oily fish such as salmon.

In Ireland, the consumption of shark, swordfish, marlin and fresh tuna is relatively low. Consumption however in relation to tuna is increasing especially in relation to canned tuna, so we would caution pregnant and breastfeeding women as well as young children to not exceed the consumption of two 225 g/8 oz cans of tuna per week. All other adults and young people should continue to eat tuna and fish products as vital component of a healthy diet. This precautionary advice purely relates to the potential impact mercury can have on unborn, newborn and young children. Exposure during pregnancy is considered the most critical period for methylmercury toxicity, and the unborn child and young children are the most vulnerable to its effects out of all groups.

In Ireland, a mercury monitoring programme was put in place for fish landed at all major Irish fishing ports, following the introduction of maximum limits for mercury in fishery product in 1993. This programme is now carried out by the Marine Institute under service contract to the FSAI.

The mercury levels in commercial fish catches landed at Irish ports and in shellfish from shellfish growing areas are low. Over the past number of years, the concentration of mercury in the edible portion of the fish analysed has ranged from 0.02 to 0.27 mg/kg wet weight which is well within the European Union human consumption tolerance level of 1.6 micrograms (µg) per kg body weight. These catches do not however normally include the deep water species such as shark, swordfish, marlin and tuna.

In order to protect the developing fetus, breast-fed babies and young children, the FSAI advises the following:

  • Women of childbearing age (in particular, those intending to become pregnant), pregnant and breastfeeding women should avoid eating shark, swordfish and marlin and should limit their consumption of tuna to not more than 1 fresh tuna steak (approximately 225 g/8 oz) or 2 medium cans (225 g/8 oz) of canned tuna per week. 
  • The diet of young children should also not include shark, swordfish and marlin and intake of tuna should be limited as above; 
  • Consumers other than the above groups should restrict their consumption of shark, swordfish or marlin to not more than one portion per week, but do not need to limit their consumption of tuna.

The nutritional important contribution that fish can make to the diet and the healthy development of children should not be underestimated. The proven association between omega-3-fatty acids found in oily fish and reduced heart disease is a strong motivator for people to consume fish and we would hope that people continue to consume fish – there is a wide range of fish available offering everyone a range of healthy options.