"The main reason for undertaking this study was that we know much more about the causes of adult cancers than we do of the causes of childhood cancers," said Julia Heck, Ph.D., M.P.H., assistant researcher in the Department of Epidemiology at the University of California, Los Angeles School of Public Health. "We studied pregnancy exposures because the fetus is likely to be more vulnerable to environmental factors during that time, and we also know that certain childhood cancers originate in utero."
Heck and her colleagues identified 3,590 children from the California Cancer Registry born between 1998 and 2007 who could be linked to a California birth certificate. Children were five years of age or younger at diagnosis. Researchers selected controls at random from 80,224 children listed on California birth rolls. They used the California Line Source Dispersion Modeling Version 4 (CALINE4) to generate estimates of local traffic exposure at the mother's home during each trimester of pregnancy and during the child's first year of life. Estimates were based on local traffic emissions of gasoline vehicles and diesel trucks within a 1,500-meter radius buffer and included traffic volumes, roadway geometry, vehicle emission rates and meteorology.
Each interquartile range increase in exposure to traffic-related pollution was associated with an increased risk for developing acute lymphoblastic leukemia (4 percent), retinoblastoma (14 percent for all cases of the disease; 11 percent for retinoblastoma affecting just one eye and 19 percent for retinoblastoma affecting both eyes) and germ cell tumors (17 percent).
Because CALINE4 estimates were highly correlated across trimesters and during the first year of life, the researchers were not able to determine the most important period in terms of exposure.
"This is the first study that's ever been reported on air pollution as it relates to rarer pediatric cancers, so it needs to be replicated in other states or in other countries," Heck said. "It would be interesting to determine if there are specific pollutants like benzene or polycyclic aromatic hydrocarbons that are driving these associations."