Published: Feb. 28, 2000

The results of a new study conducted in the rapidly expanding Denver metropolitan area indicates children living near heavily traveled streets or highways are at significantly greater risk of developing cancer, including childhood leukemia.

The researchers found a correlation between high volumes of traffic on streets or highways near homes where incidences of childhood cancer previously had been documented. The study was authored by Robert Pearson of Denver’s Radian International, University of Colorado at Boulder electrical engineering Professor Howard Wachtel and Kristie Ebi of the Electric Power Research Institute in Palo Alto.

The study was published in the February 2000 issue of the Journal of the Air and Waste Management Association.

"What we are seeing is that children who live near high-traffic streets have an increased risk for childhood cancer," said Pearson, also an adjunct professor of urban planning at CU-Denver. "What we have not yet been able to pin down is the specific cause-and-effect relationship."

The new study showed that homes adjacent to street corridors carrying 20,000 or more vehicles per day had roughly a six-fold increase in risk for children contracting cancer, including childhood leukemia, said Wachtel.

Motor vehicles are a significant source of air-pollution emissions, including benzene and other organic compounds, said Pearson. Occupational exposure to elevated concentrations of benzene is a known cause of leukemia in adults.

A 1989 Study by University of North Carolina researchers David Savitz and Lisa Feingold linked heavily trafficked Denver streets to confirmed cases of childhood cancers on the specific streets, said Wachtel. But the effect of heavy traffic on nearby thoroughfares was not taken into account, leaving the study open to criticism.

But the new study takes into account the neighboring traffic in several ways, including adjustments for the distance between the highest-traffic streets and homes up to 1,500 feet away. This allowed the researchers to consider the typical pattern of dispersion and decay of drifting vehicle emissions as they migrated from the traffic corridors outward to homes under study.

For example, a house used as a control in the study or a house with a confirmed case of childhood cancer might be located in a quiet cul-de-sac. But if it also is only a few hundred feet from an interstate highway, the volume of highway traffic weighed heavily in assessing the traffic-exhaust exposure for that dwelling, Wachtel said.

The authors also speculated that children living near heavily trafficked streets could be exposed to benzene and other carcinogens via inhalation or exposure to soil where vehicle-emission chemicals may be deposited.

A study in Stockholm several years ago in which researchers looked at nitrogen dioxide pollution from vehicles and cancer rates of nearby residents found a correlation, although not as strong as the one in the new Denver study, said Pearson. Another study in Great Britain showed a correlation between childhood cancer and the proximity of children’s homes to steel mills, factories and high-traffic streets, he said.

Savitz, a former professor at the CU Health Sciences Center, had previously worked with Wachtel, CU-Boulder Professor Frank Barnes and several other researchers on a 1988 study that linked Denver childhood cancers to high current-capacity power lines common along high-density traffic corridors. But that research and subsequent studies around the world failed to pinpoint a specific cause-and-effect relationship between the electromagnetic fields generated by the power lines and cancer.

For their study, Pearson, Wachtel and Ebi obtained street-traffic densities for 1979 and 1990 from the Colorado Department of Transportation and the Denver Regional Council of Governments. The years 1979 and 1990 were closest to the period of exposure addressed in the 1988 power line-cancer study from which the specific cases and locations of childhood cancer were drawn for the new study.

Interestingly, children living in homes close to both high-traffic corridors and high current-capacity power lines show more elevated risks for cancer than children living only in high-density traffic areas, Wachtel said.

"It’s possible that benzene and other organic compounds from vehicle exhaust may initiate cancer in children while EMF’s may act to promote such cancers," he said. "We need to design some well thought-out follow-up studies, since there is still a lot we don’t understand about the associations involving cancer, high-density traffic and EMFs."