DCEG researchers investigate a number of water contaminants that are thought to be associated with cancer risk. These include naturally-occurring substances, like arsenic, fertilizer by-products like nitrate, as well as compounds formed when chlorine to disinfect water comes into contact with organic material in water.
Ingestion of high levels of arsenic is an accepted cause of bladder cancer, but risk at lower levels is uncertain. Large populations are needed to adequately characterize cancer risk from lower levels of this relatively common exposure. The OEEB recently conducted the New England Bladder Cancer Study, a population-based case-control study in Maine, New Hampshire, and Vermont, to identify risk factors that might explain the persistent high rates in these states, to evaluate exposure to arsenic at low to moderate levels, and to evaluate possible gene-exposure interactions. Exposure to arsenic and other drinking water contaminants (i.e., DBP and nitrates) was assessed based on drinking water samples taken at current and former homes, monitoring data obtained from public water utilities, and a GIS-based predictive model based on geologic characteristics at the wells when measurements were missing. Urine and toenail clippings were collected from study subjects and arsenic concentrations in these biologic samples were measured for comparison with environmental levels and to help inform our exposure assessment.
Chlorine interacts with organic materials in water to form a mixture of disinfection byproducts (DBPs). Although concentrations are quite low, there is concern that some chemicals in the mixture may increase cancer risk. A DCEG 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. Recent studies indicate that dermal and inhalation exposures to trihalomethanes (THM), a major component of DBP in treated water, can be significant. With collaborators in Spain, we evaluated DBP in relation to bladder cancer risk in the Spanish Bladder Cancer Study, considering exposure via ingestion, showering/bathing, and swimming in pools. THM exposure estimates revealed an overall two-fold excess of bladder cancer among individuals with estimated household levels above 49 mg/L and the association was modified by polymorphisms in DBP metabolizing enzymes. We have assessed exposure to DBP in the New England Bladder Cancer Study and are now evaluating bladder cancer risk by route of DBP exposure and interactions with genes involved in pathways that activate or detoxify DBP.
For more information, contact Laura Beane Freeman.
Contamination of drinking water by nitrate is a growing problem in many agricultural areas of the country. Ingested nitrate can lead to the endogenous formation of N-nitroso compounds (NOC), which are potent animal carcinogens. Population-based case-control studies in Iowa and Nebraska evaluated community-supplied drinking water nitrate levels and cancers of the stomach, esophagus, bladder, brain, colon, rectum, pancreas, and kidney. Increased risks of colon, kidney, and stomach cancer were observed among those with higher ingestion of water nitrate and higher meat intake compared with low intakes of both, a dietary pattern that results in increased NOC formation. With collaborators at University of Minnesota and University of Iowa, we are evaluating nitrate ingestion in relation to a number of cancer sites in the Iowa Women’s Health Study. Thyroid cancer risk was increased among women with higher average nitrate levels in public water supplies and with higher dietary nitrate intake. 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, nitrogen inputs, and other factors, we are estimating private well nitrate levels for the Agricultural Health Study cohort.
For more information, contact Mary Ward.