UCLA researchers say they’ve discovered a link between exposure to traffic-related air pollution and several childhood cancers.

New research from the University of California, Los Angeles, says that a child’s exposure to high levels of traffic pollution in the womb and during the first year of life increases the child’s risk of developing three rare types of cancer.

Researchers from UCLA’s Fielding School of Public Health say that repeated exposure to air pollution caused by fuel-burning engines may increase a child’s risk of the following cancers:

  • acute lymphoblastic leukemia (ALL): this type of blood and bone marrow cancer is characterized by an excess of lymphoblasts, immature cells that typically turn into white blood cells
  • germ-cell tumors: germ cells mature into sperm or egg cells, so these cancers affect the testicles, ovaries, and other reproductive organs.
  • retinoblastoma: a malignant tumor of the eye’s retina. Researchers say children affected by air pollution have a higher rate of bilateral retinoblastoma, or tumors in both eyes.

“Much less is known about exposure to pollution and childhood cancer than adult cancer,” lead researcher Julia Heck of UCLA’s epidemiology department and Jonsson Comprehensive Cancer Center said in a press release. “Our innovation in this study was looking at other, more rare types of childhood cancer, such as retinoblastoma, and their possible connection to traffic-related air pollution.”

Because these cancers are so rare, Heck cautioned that her team’s findings need to be replicated in future studies to prove a definitive link.

This research is part of an ongoing realization of the effects of air pollution on developing fetuses and young children. Earlier this month, researchers from Dartmouth College found that traffic pollution is as harmful for kids as second-hand smoke and can raise a child’s risk of developing asthma.

The UCLA researchers used data from 3,950 children born in California between 1998 and 2007 who were enrolled in the California Cancer Registry.

Using a technique called unconditional logistic regression, cancer risk was determined by estimating pollution exposure around a child’s home. Pollution exposure was calculated using the number of gasoline and diesel vehicles within a 1,500-meter radius, traffic volumes in the area, roadway geometry, vehicle emission rates, and weather data.

Researchers say that no particular period in a fetus or child’s early development stands out as the highest risk, making it difficult to determine if a single period of exposure to air pollution, such as during the first trimester of pregnancy, was more significant than the others.