MedicalResearch.com Interview with:
Dr. Debra Silverman
Dr. Debra Silverman Sc.D
Branch Chief and Senior Investigator in the Occupational and Environmental Epidemiology Branch, Division of Cancer Epidemiology & Genetics
National Cancer Institute
MedicalResearch.com: What is the background for this study? What are the main findings?
Dr. Silverman: We know that bladder cancer mortality rates have been elevated in northern New England for at least five decades. Incidence patterns in Maine, New Hampshire and Vermont are similar—about 20% higher than those for the United States overall. Elevated rates have been observed in both men and women, suggesting the role of a shared environmental etiologic factor.
A unique feature of northern New England is that a high proportion of the population uses private wells as their primary source of drinking water. The well water may contain low-to-moderate levels of arsenic. There are two possible sources of this arsenic contamination:
- Naturally occurring arsenic from geological sources (released from rock deep in the earth)
- Leaching of arsenic-based pesticides used on food crops many years ago. From the 1920s through the 1960s there was extensive agricultural use of arsenic-based pesticides. These compounds were used on food crops such as blueberries, apples and potatoes. Residue from the treatments may have leached into the ground water.
Intake of water containing high levels of arsenic is an established cause of bladder cancer, largely based on studies conducted in highly exposed populations. However, emerging evidence suggests that low-to-moderate levels of exposure may also increase bladder cancer risk.
To explore possible reasons for the excess incidence of bladder cancer in northern New England, we conducted a large, comprehensive population-based case-control study in Maine, New Hampshire and Vermont. We examined the role of known and suspected bladder cancer risk factors, with a focus on private well water consumption and arsenic levels in drinking water.
The major cause of bladder cancer is cigarette smoking. Some occupational exposures (e.g., exposure to metalworking fluids such as that experienced by metalworkers and some types of machine operators) are also associated with elevated risk. However, smoking and occupational exposures do not appear to explain the New England bladder cancer excess.
This study was funded and carried out by researchers in the NCI Division of Cancer Epidemiology and Genetics in collaboration with the Geisel School of Medicine at Dartmouth, the Departments of Health for Maine, New Hampshire, and Vermont, and the US Geological Survey.
We reported that heavy consumption of drinking water from private dug wells (which are shallow—less than 50 feet deep—and susceptible to contamination from manmade sources than drilled wells), established prior to 1960 (when arsenic-based pesticides were widely used), may have contributed to the longstanding bladder cancer excess in northern New England.
We saw that cumulative arsenic exposure from all water sources showed an increasing risk with increasing exposure (exposure-response relationship). Among the highest exposed participants, risk was twice that of the lowest exposure group. (Cumulative arsenic exposure is a measure of the average daily arsenic intake by number of days of arsenic exposure.)