A new research by Johns Hopkins University suggests that an earlier exposure to some pollutants can cause harm that shows up only years later, according to media reports Monday.

Sharp cuts in environmental lead levels more than 20 years ago didn't stop its widespread effects, said the researcher.

"We're trying to offer a caution that a portion of what has been called normal aging might in fact be due to ubiquitous environmental exposures like lead," said Dr. Brian Schwartz of Johns Hopkins University.

Animal studies showed that infant mice exposed to chemicals took on very subtle effects in young adulthood. But more dramatic harm in areas like movement and learning appeared when they reached old age.

Researchers contributed this prolonged effect to the fact that when some brain cells are destroyed in early life, the brain draws on its reserve capacity until it loses more cells with aging hence symptoms like forgetfulness or tremors appear.

Other pollutants like mercury and pesticides may do the same thing, said Schwartz.

The long-delayed effects have also been found in tobacco and asbestos which can lead to cancer.

(Agencies via Xinhua January 28, 2008)