Blood Lead Levels Well Below "Safe" Threshold Harm Children's Development

Main Category: Pediatrics / Children's Health
Article Date: 18 Sep 2009 - 0:00 PDT

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Blood levels well below the accepted "safe" threshold harm young children's intellectual and emotional development, reveals research published ahead of print in the Archives of Disease in Childhood.

The current safety threshold above which blood lead levels give cause for concern is 10 µg/dl, which was set by the US Centers for Disease Control in 1991. But concerns have been voiced that this may be too high.

Researchers from the University of Bristol took blood samples from 582 children all of whom were part of the Avon Longitudinal Study of Parents and Children (ALSPAC), to check on blood lead levels at 30 months of age.

They then assessed these children's academic performance and behavioural patterns when they were 7 to 8 years old, obtaining complete information for 488 of the children.

After taking account of factors likely to influence the results, they found a clear link between blood lead levels in early childhood and academic performance and behaviour by the ages of 7 and 8.

The higher the level of lead in the blood at the age of 30 months, the poorer were reading, writing, and spelling grades on the Standard Assessment Tests (SATS), and the greater were the chances of antisocial behaviour.

With lead levels up 5 µg/dl, no obvious effect on intellectual capacity or behaviour was apparent.

But lead levels of between 5 and 10 µg/dl were associated with significantly poorer scores for reading (49% lower) and writing (51% lower). A doubling in lead level from 5 to 10 µg/dl was associated with a 0.3 point fall in SAT scores.

Children with lead levels higher than10 µg/dl were almost three times as likely to display antisocial behaviour patterns and be hyperactive as children whose blood levels were between 0 and 2 µg/dl.

The authors point out that although the effect sizes were small, the impact is substantial at a population level.

The effects of lead exposure are greater when children are very young, say the authors, because the toxin is readily absorbed into their developing bodies, and their tissues are especially vulnerable to damage.

They also process lead differently from adults, absorbing up to 50% of the lead content they take in, compared with around 15% for adults.

Once absorbed, most lead is stored in the bones, where it can remain for up to 30 years, and irreversibly damage the central nervous system.

"The clinical importance of these findings is that exposure to lead may interact with other environmental factors associated with educational disadvantage to have a cumulative long term impact," they write.

They argue that the current threshold of10 µg/dl should be halved to 5 µg/dl.

The World Health Organization estimates that globally, half of all children living in cities and towns under the age of 5 have blood lead levels above 10 µg/dl.

Source
Archives of Disease in Childhood

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