Residential exposure to traffic in California and childhood cancer

Background: Motor vehicle emissions are a major source of air pollution in California. Past studies have suggested that traffic-related exposures can increase the risk of childhood cancer, particularly leukemia. Methods: From California's statewide, population-based cancer registry, we identified cancers diagnosed in children younger than 5 years of age between 1988 and 1997. We matched these cases to California birth certificates. For each case, we randomly selected 2 control birth certificates, matched by birth date and sex. For each mother's residential address at the time of her child's birth, we calculated road density by summing the length of all roads within a 500-foot radius of the residence. Traffic density was based on road lengths and vehicle traffic counts for highways and major roads. Results: The distributions of road and traffic density values were very similar for the 4369 cases and 8730 matched control subjects. For all cancer sites combined, the odds ratio (OR) for the highest road density exposure category, compared with the lowest, was 0.87 (95% confidence interval [CI] = 0.75-1.00). For all sites combined and for leukemia, the ORs were also below 1.0 for the highest traffic density exposure category (0.92 for both). For central nervous system tumors, the OR was 1.22 (CI = 0.87-1.70). Conclusions: In a large study with good power, we found no increased cancer risk among offspring of mothers living in high traffic density areas for all cancer sites or leukemia.