British researchers found that children with blood lead levels of above five micrograms per decilitre had much poorer SAT scores than those with modest lead levels of between two and five micrograms per decilitre. (CBC)

Lead in children's bloodstreams, even at levels considered modest by scientific authorities, still leads to behavioural changes and cognitive impairment, suggests new research in the U.K.

Published Thursday in the online edition of the journal Archives of Diseases in Childhood, the findings, drawn from the long-term Avon Longitudinal Study of Parents and Children, shows that the higher the blood lead level, the poorer a child's performance in school.

In recent years, toymakers have issued numerous recalls due to lead found in toys. It has been found in paints, children's jewelry and toys from vending machines.

British researchers administered Standard Assessment Tasks (SATs), which measure how well pupils process and retain information they learn in school, to 500 seven-year-olds who had their blood lead levels measured when they were eight months and two years old. They found that children with modest blood lead levels of above five micrograms per decilitre had much poorer SAT scores than those with lead levels of between two and five micrograms per decilitre.

According to the World Health Organization, an "acceptable" level of lead in the blood is 10 micrograms per decilitre.

"Our results suggest that the threshold for clinical concern should be reduced to five micrograms per decilitre," said Prof. Alan Edmond, the study's lead author, in a release.

Edmond said interviews with teachers in the course of the study also revealed that children with lead levels above 10 micrograms per decilitre were almost three times as likely to be hyperactive and display anti-social behaviour than those children with modest lead levels.

The researchers said that children absorb lead through lead water pipes, old lead paint and soil predominantly between the ages of two and three. Edmond says that absorption of lead at this age is high, adding that while adults absorb 10 to 15 per cent of ingested lead, young children can absorb up to 50 per cent.

"Lead gets incorporated into the bones and is gradually released into the blood and circulates throughout the body," said Edmond. "It interferes with enzymes and affects many systems — including the central nervous system."

More than 14,000 mothers enrolled during pregnancy in 1991 and 1992 in the Avon Longitudinal Study. The development of their children has been tracked since that time.