BioEd Online

Song birds, mammals and amphibians alike are being exposed to toxic amounts of mercury, according to a report released today by the National Wildlife Federation (NWF) in the United States.

Fish have long been blamed for bringing mercury into the food chain, and the Environmental Protection Agency has issued guidelines to pregnant women since 2004 warning them to limit their fish intake for this reason. But the NWF report highlights that the threat is much wider than that.

Forest birds, raccoons, bats and bullfrogs are all being exposed to harmful levels of mercury, the report, Poisoning wildlife: The reality of mercury pollution¹ says.

"The more places we look for mercury, the more places we find it," says David Evers from the Biodiversity Research Institute, Gorham, Maine.

The NWF collated more than 65 scientific studies documenting the levels of mercury in wildlife and their effects. The results were clear: "There is harm that is happening to these species," says the report's principal author Catherine Bowes.

Whereas previous research focused on birds that eat fish, showing how mercury accumulates in birds' bodies and eggs, newer work has shown that forest birds are also exposed to mercury from their diet of bugs and insects. This can cause developmental and behavioural problems that make them produce fewer chicks, as well as neurological problems causing tremors and difficulties walking and flying.

"Given the wide range of threats to these species habitat loss, climate change having this heavy load of toxic mercury is not helping," says Bowes.

Web of poison

"It is clear to me that the mercury story is much more complex than scientists initially thought," says Jrg Feldmann, an environmental chemist at Aberdeen University, UK.

Highlighting the extent of mercury contamination is one thing, but to understand mercury accumulation more information is needed about specific mercury species, he says. Mercury in the natural environment predominantly exists as methylmercury and ionic mercury; both of these can bind to biomolecules, and the way in which they bind can influence mercury accumulation in biological systems.

"There is a real need for mercury speciation studies in order to predict dispersion and accumulation in the food web," Feldmann says.

Bowes and the report authors called on federal government to mandate coal-powered power stations a major source of mercury in the environment to install mercury filtration devices. "Our federal government is not doing enough," says Bowes. In US states where these measures have been introduced, for example Florida, Wisconsin, New Hampshire and Massachusetts, mercury levels in wildlife dropped dramatically: in just a few years, rather than the predicted decades.

The report follows news that energy-saving fluorescent light bulbs are adding an extra mercury burden to the planet. Thomas Goonan, a materials specialist with the US Geological Survey in Reston, Virginia, recently presented results at an international mercury conference showing that only 20% of mercury-containing bulbs used in the United States were recycled the rest may end up in landfills or incinerators, or break in transport, potentially releasing mercury into the environment.

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