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DDT linked to smaller brains in birds

DDT linked to smaller bird brains

DDT linked to smaller brains in birds
July 14, 2006

For the first time researchers have found evidence that natural exposure to a contaminant damages the brain of a wild animal.

Scientists at the University of Alberta discovered that the regions in robins’ brains responsible for singing and mating shrink when exposed to high levels of DDT.

The new study, published in the current issue of Behavioural Brain Research, suggests that exposure to environmental levels of DDT can cause significant changes in the brains of songbirds.

“These residues have been persisting since the late 1960s–that’s what is really disturbing,” said author Dr. Andrew Iwaniuk, a researchers at the Department of Psychology at the University of Alberta. “It has been years since it has been used and still has this effect.”

Earlier studies had suggested that exposure to DDT affects the brain, but none have actually demonstrated it, according to Iwaniuk.

The researchers used the American Robin (Turdus migratorius), a migratory songbird the breeds throughout Canada and the United States, to test the theory.

“Birds are more susceptible to the effects of pesticide residues and other contaminants in the environment than other animals,” read a release from the research team. “As well, American robins are often exposed to high levels of DDT and other chemicals because they rely heavily on earthworms as part of their diet.”

“We found that the regions sensitive to reproductive hormones–song production and courtship behaviour–were most affected by DDT,” said Iwaniuk. “Song production is extremely important in attracting a mate or to mark out a territory.”

“The issue is not that DDT is killing these robins but if they are growing up in this one area and then move to another, they won’t be able to attract any females,” he added.

The researchers found the effects were most prominent in the males, especially significant since the use songs to attract mates. Some males “experienced up to a 30 percent reduction in brain region size compared to males at lower DDT exposure levels” according to the study.

While the researchers can’t say whether these finding apply to humans and other animals, they warn that it is possible that exposure to similar levels of DDT could increase the risk of neurological damage.

“The take-home message is that people need to be more cognizant of their use of pesticides and herbicides,” said Iwaniuk. “People need to be careful about using chemicals in their homes or farms. Who knows the effects these will have down the road.”

DDT, dichloro-diphenyl-trichloroethane, was developed as an insecticide during the second World War. Paul Hermann, a Swiss chemist credited with the discovery of the compounds effectiveness as an insect killer, was awarded the Nobel Prize in 1948. DDT was used widely to control mosquitos and other pests.

In 1962, American biologist Rachel Carson published Silent Spring, which alleged that DDT caused cancer and harmed bird reproduction by thinning egg shells. The book stirred public outcry which eventually led to the ban of DDT for agricultural use in the United States. Its publication is often cited as one of the key events in the birth of the modern environmental movement. Other countries followed suit with the ban in the 1970s due to health concerns.

This is article is based on a news release from the University of Alberta.

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