General Environmental Exposures and Cancer

Residential radon exposure and risk of lung cancer in Missouri

There is substantial variation in the annual mean concentration of radon in the same North American homes measured several years apart. These findings call into question the assumption that year-long indoor air radon measurements offer a valid estimate of cumulative radon exposures in homes over a period of 15-20 years, the most biologically meaningful exposure period. All previous studies used detectors that measure current radon in air. In our new case-control study, we carried out both standard year-long air measurements and CR-39 alpha detectors measurements (call surface monitors) which directly measure long-term (20- year and more) cumulative exposure using glass objects in the home. The surface monitors take advantage of the fact that the first long-lived radon progeny, 210-lead (half-life 22 yrs), becomes embedded in glass surfaces in homes. The alpha activity of 210-polonium, a decay product of 210-lead, is measured in glass objects in the home and serves as a long-term retrospective exposure-meter for residential radon. This population-based case-control study of lung cancer was specifically designed to compliment our earlier study by evaluating the effect of cumulative residential radon exposure among Missouri women who were predominantly smokers and former smokers using a control selection technique that minimized the inherent imbalance in smoking frequency between cases and controls. More information, Michael Alavanja

Drinking Water Contaminants and Cancer

Nitrates - Contamination of drinking water with nitrates is a growing problem in many agricultural areas of the country. A Branch study in Nebraska noted an association between measured nitrate levels in community-supplies drinking water and an increased risk of non-Hodgkin's lymphoma. Residential histories from a case-control study of non-Hodgkin's lymphoma in Iowa is being linked with data on nitrate levels in community water systems to further evaluate this finding. Further studies in Iowa are evaluating community-supplied drinking water nitrate levels and cancers of the bladder, brain, colon, rectum, pancreas, and kidney. The population using private wells can have considerably higher exposure to nitrate because private wells are not regulated and they are often located in agricultural areas. Using a geographic information system-based model that incorporates land use, soil characteristics, irrigation practices, and other factors, we are estimating private well nitrate levels for census block groups in the Platte River Valley of Nebraska. The combined public and private supply nitrate estimates will be used in an ecologic study to evaluate drinking water nitrate and cancer incidence patterns.

Chlorination byproducts - Chlorine interacts with organic materials in water to form a mixture of chlorinated chemical byproducts. Although concentrations are quite low, there is concern that some chemicals in the mixture may increase cancer risk. A Branch study of six cancer sites conducted in Iowa found associations of rectal and bladder cancers with long-term (> 40 years) exposure to drinking water high in these unintentional byproducts. The data from additional cancer sites included in the study are under evaluation.

Arsenic - Arsenic in drinking water causes skin cancer, and a growing body of evidence suggests internal cancers, especially cancer of the bladder. A recent study in Utah suggested that the elevated bladder cancer risk of men who had smoked was increased even more by long-term consumption of arsenic in drinking water. We are following up on this observation in a collaboration with Utah researchers who collected information from bladder cancer patients and controls in the early 1980s. A case-control study of bladder cancer in New England is underway to determine if arsenic in drinking water might contribute to persistently high rates of this cancer in that region. More information, Mary Ward, Ken Cantor, Debra Silverman, and Dalsu Baris

Study of Childhood Leukemia and Environmental Pesticide Exposure in California

Childhood leukemia is the most common type of childhood cancer and its etiology is largely unknown. We are collaborating with investigators at University of California at Berkeley and the California Department of Health Services on their ongoing population-based case-control study of childhood leukemia in the San Francisco Bay area and the agricultural Central Valley (35 counties). A substantial proportion of the population in this area is employed in agriculture or lives in close proximity to agricultural fields, making this an ideal study population to evaluate agricultural pesticide exposures and risk of childhood leukemia. Furthermore, a large proportion of the study population is Hispanic. No previous large-scale childhood leukemia studies have targeted Hispanics or agricultural populations. A major aim of our collaboration is to improve the exposure assessment of agricultural and home and garden pesticides by measuring pesticides in house dust samples. We are also measuring other chemical exposures including cotinine, PCBs, and polycyclic aromatic hydrocarbons. In addition to evaluating specific chemical levels in dust and risk of childhood leukemia, we are conducting several methodological studies to evaluate factors associated with residential exposure to pesticides. More information, Mary Ward