(Beyond Pesticides, January, 21, 2009)
A new study concludes that exposures during pregnancy and childhood to insecticides that target the nervous system, such as organophosphates (OPs) and carbamates, are associated with childhood brain tumors. The researchers hypothesize that this susceptibility might be increased in children with genetic variations that affect the metabolism of these chemicals.
The study, “Childhood Brain Tumors, Residential Insecticide Exposure, and Pesticide Metabolism Genes,” examines whether childhood brain tumors (CBT) are associated with the functional genetic variations. The study provides evidence that exposure to insecticides, paired with specific metabolism gene variants, may increase the risk of CBT. DNA was extracted from archival screening samples for 201 cases, 10 years of age and born in California or Washington State between 1978 and 1990. Insecticide exposures during pregnancy and childhood were classified based on interviews with participants’ mothers. The children’s mothers reported whether they or anyone else had chemically treated the child’s home for insects including termites, fleas, ants, cockroaches, silverfish, or “other” pests.
The results are consistent with the possibility that children with a reduced ability to metabolize organophosphate and carbamate insecticides might be at increased risk of CBT when sufficiently exposed. The researchers observed multiplicative interactions between insecticide exposure during childhood and variant genes relevant to insecticide metabolism. Among exposed children, CBT risk increased with PON1—108T allele – a gene which reduces the activity of paraoxonase (PON1), a key enzyme in the metabolism and neutralization of acetylcholinesterase (AChE ) inhibitors: notably OPs such as chlorpyrifos and diazinon. In other words, children with brain tumors were more likely to carry the enzyme-inhibiting gene variant PON1—108T than other children.
The authors state that even though certain OPs have been phased out of residential use in the U.S., children remain exposed to these and other AChE inhibitors not only via the diet but also potentially via drift from use in agricultural areas, on golf courses, and for mosquito control. In the home, OP and carbamate insecticides remain, for example, in topical treatments for lice (malathion) and flea collars (tetrachlorvinphos, carbaryl, propoxur). Even though previous studies have also shown that farmworkers and persons exposed to high levels of pesticides have an increased risk of developing brain tumors, this study’s result most strongly indicate the importance of exposures during early childhood and interaction with genotypes and enzyme levels. However, other periods are important, notably prenatal development, and need to be further explored. Larger studies are needed to confirm the findings, and environmental and biological measurements of specific pesticides and the inclusion of more gene interactions.
Children face unique hazards from pesticide exposure. They take in more pesticides relative to their body weight than adults in the food they eat and air they breathe. Their developing organ systems often make them more sensitive to toxic exposure. The U.S. EPA, National Academy of Sciences, and American Public Health Association, among others, have voiced concerns about the danger that pesticides pose to children. The body of evidence in the scientific literature shows that pesticide exposure can adversely affect a child’s neurological, respiratory, immune, and endocrine system, even at low levels.
Source: Environmental Health Perspectives