The incidence of childhood leukemia in industrialized countries rose significantly from 1975 through 2004, and the reasons for the increase are not understood. Drs. Patricia Buffler and Catherine Metayer from the University of California at Berkeley are investigating how exposure to benzene, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and other Superfund chemicals may affect a child's risk of contracting leukemia. In a case-control study of nearly 400 children from 0-7 years old, the researchers found that detection of PCBs in the home was associated with a 2-fold increase in risk for acute lymphocytic leukemia (ALL).

To determine exposure, Drs. Buffler and Metayer collaborated with Dr. Mary H. Ward and Joanne Colt from the Division of Cancer Epidemiology and Genetics, National Cancer Institute, to measure the concentrations of persistent organochlorines chemicals (some of which were commonly used as pesticides) in carpet dust samples from the child's home. Using a specialized vacuum, the researchers collected carpet dust samples from the room where a child spent the most time before being diagnosed with ALL. The study participants included 184 ALL cases 0-7 years of age, from 35 different counties in northern and central California, and 212 control children matched to cases by birth date, sex, race, and Hispanic ethnicity. Researchers found that the detection of any PCB-related chemicals in the dust conferred a two-fold increased risk of ALL. Compared with those in the lowest quartile of total PCBs, the highest quartile was associated with about a three-fold risk, and the positive trend was significant. These findings suggest that PCBs, which are considered probably human carcinogens and which cause perturbations of the immune system, may represent a previously unrecognized risk factor for childhood leukemia.