ARTICLES>> Mercury in Swordfish

Why the concern?
It has been found that large predatory fish like swordfish,
shark and marlin are contaminated with toxic substances
containing mercury beyond the safe limits allowed by the WHO.

Is this a new thing ?
The contamination of large fish with mercury has been known or under investigation across the globe for the last 10 years. However, it is only in the last two years that food safety warnings have begun to be issued. Now, several countries including the United States, Canada, Australia, New Zealand and the UK have issued safety warnings.

Why has it taken so long in Gibraltar ?
By its very nature, the contamination of food can be a very geographically specific thing. It is not reasonable to assume that what happens in one distant country, also applies here. Tests in Gibraltar were begun soon after the UK issued food warnings in May this year. The contamination of mercury in locally sold fish was confirmed only last week.

What is the position in Gibraltar ?
Tests carried out for the Environment Agency by the UK accredited laboratory show that locally consumed swordfish is contaminated with mercury above the WHO safety levels. Our samples actually came out with slightly higher readings than the UK, but this is not significant without large scale studies.

Where does this mercury come from ?
Mercury is a widely available element that can harm health in many ways through both inorganic and organic forms. The most important food source is fish. The organic variant methylmercury is consumed by small fish, which in turn are consumed by larger fish, until the greatest concentrations are achieved at the top of the food chain.

How is mercury harmful to health ?
Mercury is excreted by the human body very slowly and is therefore a cumulative poison. Even if very small doses are taken, if they are taken regularly, toxic levels can build up over time.
Mercury damages the nervous system. In adults, symptoms like creeping or tingling sensation in the skin only occur with very high exposures, but in children the developing nervous system may be affected, which could affect mental skills, memory and co-ordination. With pregnant women, unborn babies may be affected.

Is there a safe level ?
This is not clear. Some studies of children born to women who eat fish every day have not given convincing evidence of harmful effects. However, the WHO recommends safe levels based on studies across the world. The WHO recommends that adults should receive no more than 3.3 µg/kg of body weight of methylmercury per week. For an average sized adult, this would mean not more than about 200 grams of swordfish per week. For children, because of the higher vulnerability, there is no safe level. The same applies to unborn children.

So what is the advice ?

There is at present no risk from other fish (tuna, salmon, sardines, mackerel, etc) and the general advice to consume at least one portion of oily fish per week still holds good.

 

Dr. Vijay Kumar
Director of Public Health 05 November 2002