GLOBAL warming could lead to raised levels of toxic mercury in the fish we eat, research suggests.

Increased rainfall and melting snow and ice is expected to increase the flow of organic matter into aquatic ecosystems in large parts of the northern hemisphere.

Research conducted in Sweden predicts this could lead to a sevenfold increase in the mercury content of zooplankton, tiny marine animals at the base of the ocean food chain.

Herald View: Dangers in discarding the monitoring of fish stocks

As the small creatures are eaten, the mercury is concentrated until it reaches high enough levels in large fish, such as cod, to pose a potential risk to human health.

Mercury can damage nerves. Children may be especially at risk from exposure to fish-derived mercury while their brains and nervous systems develop in the womb.

Up to 17 per 1,000 children from subsistence fishing communities in Brazil, Canada, China, Columbia and Greenland have been shown to suffer from mental impairment due to the consumption of mercury-contaminated sea food, according to the World Health Organisation.

In fish and other sea creatures, the metal is present in an organic form called methylmercury.

Herald View: Dangers in discarding the monitoring of fish stocks

The research shows organic run-off linked to global warming is likely to encourage the growth of bacteria, which go on to dominate the aquatic food web. A “heterotrophic” food web based around bacteria generally has more levels of organisms than an “autotrophic” food web founded on microscopic ocean plants.

With a greater number of stages, a heterotropic food web may have the effect of increasing mercury concentrations, experts believe.