UC Berkeley and University of Washington Children's Centers Find Susceptibility to Pesticides is Highly Variable Among Latina Women and Children
(March 2, 2006)
Some children may be 26 to 50 times more susceptible to exposure to certain organophosphate (OP) pesticides than other newborns, and 65 to 130 times more sensitive than some adults, according to a new study from the University of California, Berkeley, and the University of Washington Children's Centers. The study, published in the journal Pharmacogenetics and Genomics, reveals far greater variability in susceptibility to pesticides than previously predicted.
Since 2001, home use of OP pesticides, specifically diazinon and chlorpyrifos, has been restricted by the EPA, mainly because of risk to children. However, the researchers said there may still be residual exposure to diazinon and chlorpyrifos from household use before they were banned, and some structural uses for the pesticides are still approved, including treatment of house foundations with chlorpyrifos, and these and other OP pesticides are still widely used in agriculture.
Approximately 143,000 pounds of diazinon and 52,000 pounds of chlorpyrifos are used annually in the region studied - California's Salinas Valley, an agricultural community. The study, conducted through UC Berkeley's Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), included 130 Latina women and their newborns living in the valley. The researchers report that approximately 28 percent of the women in the study had worked in the fields during their pregnancies, and another 14 percent had other jobs in agriculture that included nursery or greenhouse work. Overall, 82 percent of the women had agricultural workers living in their homes during their pregnancies.
The researchers used levels of the OP detoxifying enzyme paraoxonase 1 (PON1) activity measured in blood samples as a marker for pesticide susceptibility. PON1 breaks down the toxic metabolites of OP pesticides, including diazinon and chlorpyrifos, and lower enzyme levels means less protection.
Current EPA standards require an extra tenfold safety factor to protect children compared with adults if there are gaps in information about the children's susceptibility. The EPA may select a lower safety factor if it determines that enough information is available, and based on an EPA review, many other pesticides have lower or no additional safety factors.
The ability of the PON1 enzyme to protect the body from the toxicity of pesticides is determined by whether a person has the Q or R form of the PON1 gene at position 192 on the chromosome. People with the QQ genotype have two copies of the Q variant of the PON1 gene, producing a PON1 enzyme that is significantly less efficient at detoxifying OP pesticides, while people with the RR genotype have two copies of the R variant of the PON1 gene, producing a PON1 enzyme that is more resistant to OP pesticides. Inheriting one type of gene from each parent leads to a QR genotype with intermediate sensitivity to OPs. In addition to the factors affecting the type of PON1 enzyme produced, there are additional genetic variants that affect the levels of enzyme available, which also affects detoxifying ability. For all groups, infants are at particular risk because the level of PON1 enzyme in newborns averages one-third or less than that of adults. It can take six months to two years for a baby to develop mature levels of PON1. The results of this analysis predict that some newborns may be 26 times more susceptible to diazinon and diazoxon exposure than newborns with the highest PON 1 enzyme levels and up to 65 times more susceptible than adults with the highest enzyme levels. The differences are even greater when predicting susceptibility to chlorpyrifos and chlorpyrifos oxon. Some of the QQ newborns may be 50 times more susceptible to this pesticide than RR newborns with high PON1 levels, and 130 to 164 times more susceptible than some of the RR adults.