Fish contaminated with mercury 'pose worldwide threat to health'

By Jeremy Laurance, Health Editor
Published: 08 March 2007

A worldwide warning about the risks of eating mercury-contaminated fish is to be issued by an international group of scientists today.

Three times more mercury is falling from the sky than before the Industrial Revolution 200 years ago, the scientists say.

Fish absorb the toxic chemical, which pollutes the seas, posing a risk especially to children and women of childbearing age. The role of low-level pollutants such as lead and mercury on the growing brain has been known for decades and measures have been taken to reduce exposure to a minimum. But the scientists say more must be done.

The warning is based on five papers by mercury specialists summarising the current state of knowledge on the chemical published in the international science journal Ambio. Called the Madison Declaration on Mercury Pollution, it presents 33 key findings from four expert panels over the past year. Every member of the four panels backed the declaration which was endorsed by more than 1,000 scientists at an international conference on mercury pollution in Madison, Wisconsin, in the US last August.

However, it runs counter to research by British scientists last month which found pregnant women who ate the most fish had children who were more advanced, with higher IQs and better physical abilities.

The British researchers said that while mercury is known to harm brain development, fish also contain omega-3 fatty acids and other nutrients which are essential to brain development. They studied 9,000 families taking part in the Children of the 90s project at the University of Bristol and concluded, in The Lancet, that the risks of eating fish were outweighed by the benefits.

The US scientists focused on the risks of mercury which they say now constitute a "public health problem in most regions of the world". In addition to its toxic effects on the human foetus, new evidence indicates it may increase the risk of heart disease, particularly in adult men.

While developed countries have reduced mercury emissions over the past 30 years, these have been offset by increased emissions from developing nations.

The uncontrolled use of the metal in small-scale gold mining is contaminating thousands of sites around the world, putting 50 million inhabitants of mining regions at risk and contributing 10 per cent of the global burden of the pollutant attributable to human activities in the atmosphere.

The global spread of the threat is revealed in increased mercury concentrations now being detected in fish-eating species in remote areas of the planet. The impact on marine eco-systems may lead to population declines in these species and in fish stocks.

Professor James Wiener, of the University of Wisconsin, said: "The policy implications of these findings are clear. Effective national and international policies are needed to combat this global problem."

In the US, official government advice is for pregnant women to limit their consumption of all seafood, including white fish, oily fish and shellfish, to no more than 12oz (340g) a week in order to limit their exposure to mercury.

In the UK, the Food Standards Agency advises expectant mothers to avoid shark, swordfish and marlin and to limit their consumption of tuna, because these are the fish with the highest levels of mercury.

The key findings

* Three times more mercury is falling from the sky today than before the Industrial Revolution

* Eating fish is the primary way most people are exposed to the toxic metal

* There is solid scientific evidence of the toxic effects of mercury on the developing foetus

* Mercury exposure now constitutes a public health problem in most regions of the world

* New evidence suggests exposure to mercury may increase the risk of heart disease and stroke in men

* Increased mercury emissions from developing countries over the past 30 years have outstripped declines in the developed world

* Increasing mercury concentrations are now being detected in fish-eating wildlife in remote areas of the planet