Children more vulnerable to pesticides until age 7 due to lower enzyme level

Huen K, K Harley, J Brooks, A Hubbard, A Bradman, B Eskenazi and N Holland. 2009. Developmental changes in PON1 enzyme activity in young children and effects of PON1 polymorphisms. Environmental Health Perspectives doi:10.1289/ehp.0900870.
Synopsis by Kim Harley, Ph.D.

Children are more susceptible to the toxic effects of certain pesticides than adults, and this vulnerability lasts longer than previously believed.

A new study finds that young children have significantly lower levels of a key enzyme that protects against the toxic effects of certain pesticides. The youngsters' enzyme levels do not catch up to an adult's until after age seven – far longer than previously thought.
In addition, a person's genes dictate how effective the enzyme is at breaking down the pesticides. This is one reason why some people are more susceptible to the effects of pesticides than others.
Regulations governing organophosphate pesticide use should recognize that some individuals are more susceptible to the toxic effects of pesticides, say the researchers from the University of California, Berkeley who authored the study. Children are also more susceptible and this increased vulnerability appears to continue into school age.
The enzyme, called paraoxonase, plays a key role in helping the body neutralize and eliminate organophosphate pesticides. Organophosphates are a class of acutely toxic insecticides that have been largely banned for home use, but continue to be widely used in agriculture. Organophosphate pesticides target the nervous systems of insects, but have similar effects on humans. Some studies have shown reduced IQs among young children whose mothers were exposed to these pesticides during pregnancy.
Although it has been known that newborns have low levels of the paraoxonase enzyme, it was previously believed that paraoxonase concentrations reached adult levels by 2 years of age.
This assumption was based on one earlier study of 9 children. Now a new study of 458 children followed from birth to age 7 shows that paraoxonase levels continue to increase steadily until age 7. At age 7, the average paraoxonase level in children was similar to, but still lower than, adult levels.
Researchers measured paraoxonase levels in children’s blood at birth and at 1, 2, 5 and 7 years of age. They compared these levels with those of their mothers.
In addition to the gains with age, paraoxonase also varied by a child's genetics. Both the quantity and the quality (i.e. how fast it detoxifies the pesticide) of the enzyme are dependent of variations in the paraoxonase gene. Children with certain variations of the gene had significantly lower enzyme levels and activity.