The spread of mercury in spiders, and how DDT lives on…

| 1st June 2008
The pathways of contamination highlighted in Rachel Carson’s 'Silent Spring' are still being found, research shows

Man-made pollutants are continuing to find new routes into food chains and habitats, new research has shown.

A paper published in the journal Science by researchers from the Institute for Integrated Bird Behavior at the College of William and Mary, in Virginia, has demonstrated for the first time how mercury river pollution can find its way into land-based ecosystems – through spiders.

The researchers were surprised that even though the birds they were monitoring were known not to eat fish from a polluted river, they still displayed high levels of mercury in their bodies. By studying the birds’ diet, the scientists discovered that spiders they had eaten had acted as ‘bioaccumulators’ – concentrating levels of mercury contamination found in the soils and organisms on the river banks and then delivering the dose up the food chain.

Lead author Dan Cristol said when examining mercury pollution in watercourses it was important to look beyond fish and other aquatic organisms that were directly exposed to mercury.

‘It’s not just about the fish, the people who eat the fish and the animals that eat the fish,’ he said. ‘We’ve also got to look at a strip of habitat all the way around the lake or river that is affected.’

Cristol’s paper is published as separate research in the journal Environmental Science and Technology poses an answer as to why levels of the pesticide DDT have remained the same in the bodies of Adeìlie penguins, despite a widespread ban on the use of the chemical in 1980s.

Heidi Geisz and colleagues, of the Virginia Institute of Marine Science, analysed the fat deposits on dead penguins and discovered that the birds were being exposed to old sources of DDT that had somehow persisted in the environment for decades. The researchers then measured levels of the chemical in Antarctic glacial meltwaters. They discovered that, as glaciers melt, DDT that was at one stage deposited in snowfall is delivered directly to the Antarctic ecosystem and the penguins’ food chain.

Geisz said that although the levels of DDT were low, persistent exposure could cause problems:

‘We can never really know where these chemicals are hiding,’ she said. ‘They show up in places that have no point source.’

Meanwhile, scientists in Asia have identified a cause behind the rapid decline of the whitebacked vulture. The birds suffer kidney failure within days of feasting on cattle carcases treated with the anti-inflammatory drug Diclofenac, which is regularly – though illegally –given by farmers to treat livestock infections.


This article first appeared in the Ecologist June 2008

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