Pesticide Exposure Linked to Childhood Blood Cancers

Roxanne Nelson RN, BSN

September 21, 2015

Exposure to pesticides that are used inside the home was associated with an increased risk of developing childhood leukemia and lymphoma, according to new data.

The study was published in the October issue of Pediatrics.

In this meta-analysis of 16 epidemiologic studies, researchers from the Harvard TH Chan School of Public Health in Boston, Massachusetts, examined the possible association between residential pesticide exposure during childhood and childhood cancers.

They found that exposure to indoor insecticides was associated with a significant increase in the risk for childhood leukemia (odds ratio [OR], 1.47; 95% confidence interval [CI], 1.26 - 1.72; I 2 = 30%) and lymphomas (OR, 1.43; 95% CI, 1.15 - 1.78; I 2 = 0%).

In addition, the authors found that there was a positive association between childhood home pesticide or herbicide exposure and childhood brain tumors, but it did not reach statistical significance.

"Using pesticides in the indoor environment where young children live is the most unwise decision that parents can make, because of the close proximity, lack to adequate ventilation, and deposition of residues on the surface in which children come into contact with," said senior author Chensheng Lu, PhD, associate professor of environmental exposure biology in the department of environmental health, Harvard School of Public Health.

While the data isn't conclusive and additional research is needed to confirm the association between residential indoor pesticide exposures and childhood cancers, the findings of this meta-analysis should prompt more attention to childhood exposure, explained Dr Lu.

Preventive measures should be considered to reduce children's exposure to pesticides at home, he said.

"Making your homes pest-proof or pest-free is the best way to prevent your children from developing childhood cancers," Dr Lu told Medscape Medical News. "Also there are so many non-chemical treatments that can be used, such as using screen windows or fixing cracks and crevices to prevent insects from getting inside."

There are also safer types of chemical treatments that can be used for pest control. "Parents also should be aware of whether the school, playground, sports field, or parks have been treated with pesticides because children often spend many hours in these environments," he pointed out.

AAP Statement Urges Caution

In 2012, the American Academy of Pediatrics (AAP) issued a policy statement and an accompanying technical report noting that prenatal and early childhood exposure to pesticides is associated with several childhood cancers as well as with decreased cognitive function and behavioral problems (Pediatrics. 2012;130(6):e1757-1763).

In their statement, they recommended that pediatricians become familiar with the effects of acute and chronic exposures to pesticides, and learn what resources are available for both treatment of acute poisoning and addressing lower-dose chronic exposures in children.

In an interview with Medscape at the time, James Roberts, MD, MPH, professor of pediatrics at Medical University of South Carolina in Charleston and lead author of the AAP documents, noted that "this report really has been a long time in coming."

"Most people think of pesticide poisoning as happening in an agricultural area," he said. "Certainly, to some extent, these are high-use areas, and there may be some more exposure both through proximity to the fields and take-home exposure from parents who work in the fields."

"However, poisonings in the home do occur as a result of treatment for nuisance pests such as cockroaches, mice, ants, and other kinds of insects," Dr Roberts pointed out. "Other sources at home include the application of herbicides used for weed control on lawns and the application of tick and flea control products to household pets."

Links to Pesticides and Herbicides

In the current paper, Dr Lu and colleagues looked primarily at exposure to indoor pesticide use. They reviewed all observational studies published in PubMed before February 2014 and reviewed reference sections of articles derived from searches. The search yielded 277 studies that met inclusion criteria, and of those, 16 were included in the meta-analysis.

A subgroup analysis that combined studies on acute leukemia showed elevated risks for exposure to both home pesticides (OR, 1.55; 95% CI, 1.38 - 1.75) and indoor insecticides (OR, 1.59; 95% CI, 1.39 - 1.81).

When studies were combined for both leukemia and lymphoma risks, the authors observed a statistically significant association between childhood hematopoietic malignancies and home pesticide exposure during childhood (11 out of 12 data were from indoor insecticides).

A positive but a statistically insignificant association was observed between home pesticide exposure and childhood brain tumors (OR, 1.22; 95% CI, 0.83 - 1.81; I 2 = 23%).

The use of outdoor pesticides, including insecticides, herbicides, and fungicides also showed a statistically significant association between childhood leukemia and exposure to herbicides (OR, 1.26; 95% CI, 1.10 - 1.44, I 2 = 0%), but the association with lymphoma was not statistically significant. There was also no apparent association between herbicide exposure and brain tumors.

When studies on all types of childhood cancers were combined, including neuroblastoma and Wilms' tumor, a statistically significant association with residential herbicide exposure was observed (OR, 1.35; 95% CI, 1.16 - 1.55; I 2 = 23%), but no association was observed between exposure to outdoor pesticides or outdoor insecticides and any types of childhood cancers.

"Overall, the results suggest that cancer risks are related to the type of pesticide and where it was used," write the authors.

The study was supported by the Department of Energy and Environmental Protection, State of Connecticut. The authors have no disclosures.

Pediatrics. Published online September 14, 2015.

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