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Last Edited: 3/18/2008

Childhood cancer incidence rates and hazardous air pollutants in California: an exploratory analysis
Written: Apr 2003


Hazardous air pollutants (HAPs) are compounds that have been shown to cause cancer or other adverse health effects in laboratory animal or occupational health studies.  We analyzed population-based childhood cancer incidence rates in California from 1988 to 1994 by HAPs exposure scores for all census tracts in the state.

We calculated the HAPs exposure scores by combining cancer potency factors with modeled outdoor concentrations, obtained from the United States Environmental Protection Agency, for each census tract.  We evaluated the relationship between exposure scores for 25 potentially carcinogenic HAPs emitted from all sources combined with childhood cancer rates.  We also analyzed exposure scores based on HAPs emissions from mobile, area and point sources separately.

There were 7,143 newly diagnosed cases of childhood cancer in California during the study period, of which 6,989 (97.8%) could be assigned to a census tract and were included in the analysis.  Age, race/ethnicity, and sex adjusted rate ratios (RR) were estimated via Poisson regression.  There was little evidence for elevated rate ratios for childhood cancer in general, or for the gliomas specifically, among children living in areas ranked high for exposure to combined, mobile or area source pollutants.  An elevated rate ratio was found for childhood leukemia in the tracts ranked highest for exposure to the combined group of 25 HAPs (RR=1.21, 95% confidence interval=1.03-1.42), and also in tracts ranked highest for exposure to HAPs emitted primarily from point sources (RR=1.32, 95% confidence interval=1.11-1.57).  Rate ratios were also significantly elevated for all childhood cancer sites combined in tracts ranked highest for exposure to HAPs emitted from point sources (RR=1.13, 95% confidence interval=1.03-1.23).  In each of these cases there was a significant trend with increasing exposure level.

The finding of increased rates of childhood leukemia in census tracts with high exposure scores for hazardous air pollutants is suggestive of an association, but further studies with more comprehensive exposure assessment and individual-level exposure data are important for elucidating this association.

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Suggested Citation

  • Reynolds P, Von Behren J, Gunier R, Goldberg DE, Hertz A, Harnly M, Smith DF.  Childhood cancer incidence rates and hazardous air pollutants in California: an exploratory analysis.  Environmental Health Perspectives, 111(4):663-668, April 2003.