Bladder cancer incidence and mortality rates in northern New England have significantly exceeded those in the rest of the United States for decades. Investigators honed in on drinking water as a possible explanation because a high proportion of residents of Maine, New Hampshire, and Vermont rely on private wells. The region's geology can also produce low-to-moderate levels of naturally occurring arsenic in groundwater. Moreover, from the 1920s to the 1960s, arsenical pesticides were widely used by farmers in the region, thereby adding man-made arsenic into the environment.
Arsenic is a known cause of bladder cancer, a connection largely based on observations of highly exposed populations. Now, a large population-based case–control study indicates increased risk of bladder cancer in people exposed to low-to-moderate levels of arsenic through drinking water. The association was strongest in heavy water users who relied on shallow dug wells prevalent during the years of arsenic-based pesticide use. Deeper drilled wells predominate in the region today, although water from these still tests positive for arsenic from geologic minerals.
Researchers interviewed 1,213 patients in the three states shortly after they were diagnosed with bladder cancer between 2001 and 2004, as well as 1,418 control subjects. They assessed other potential risk factors, such as tobacco use, occupation, and diet. They also asked detailed questions about water consumption to estimate daily water intake. Historical well-water sampling and statistical modeling yielded estimates of daily and cumulative arsenic consumption. The researchers acknowledged that smoking and occupational hazards contributed to some subjects’ bladder cancer risk, and that their method of measuring arsenical pesticide exposure was crude owing to gaps in historical records. Still, well-water intake was associated with elevated bladder cancer incidence and mortality in the region as a whole.
Although arsenical pesticide use was discontinued in northern New England more than 50 years ago, naturally occurring arsenic in drinking water remains a concern. The authors calculated a doubling of risk of bladder cancer among people who habitually drink large quantities of water (more than 2.2 liters daily) from drilled wells, suggesting a need for further research. —Joan Zolot, PA
Baris D, et al. J Natl Cancer Inst 2016 108 9 djw099