Arsenic-Contaminated Well Water Boosts Bladder Cancer Risk
by Roxanne Nelson, originally posted on May 5, 2016
Drinking water derived from private wells, particularly those dating back to the early part of the twentieth century, could be related to high rates of bladder cancer in several New England states.
In fact, the incidence rates of bladder cancer in Maine, New Hampshire, and Vermont are about 20% higher than rates in the rest of the United States.
The water in many of these older wells, which are not maintained by municipalities and therefore not subject to federal regulations, contain low to moderate levels of arsenic, report Debra Silverman, ScD, from the National Cancer Institute in Bethesda, Maryland, and her colleagues.
A high proportion of the population uses private wells for their drinking water, which is a “unique” feature of this particular region.
“Arsenic is an established cause of bladder cancer, largely based on observations from earlier studies in highly exposed populations,” said Dr Silverman in a statement. “However, emerging evidence suggests that low to moderate levels of exposure may also increase risk.”
The results were published online May 2 in the Journal of the National Cancer Institute.
Mortality rates related to bladder cancer have been high in northern New England for more than 50 years and are not explained by traditional risk factors for the disease, which include smoking and occupational exposures.
Arsenic contamination in the well water in northern New England comes from two possible sources, the researchers explain. It can naturally be released into water from rock deep beneath the surface of the earth, or it can be manmade and come from pesticide residue. Arsenic-based pesticides were used extensively on crops such as blueberries, apples, and potatoes in this region from the 1920s through to the 1950s.
Although previous studies have shown that the consumption of water containing high concentrations of arsenic increases the risk for bladder cancer, the effect of exposure to low to moderate levels has been unclear.
Possible Link to Arsenic
Dr Silverman and her colleagues conducted a population-based case–control study of arsenic levels in private wells in Maine, New Hampshire, and Vermont. The team compared 1213 patients with newly diagnosed bladder cancer with 1418 control subjects who resided in the same geographic area.
They looked at known and suspected bladder cancer risk factors, including smoking, occupation, ancestry, use of wood-burning stoves, and consumption of various foods. In addition, arsenic concentrations were estimated from water samples taken from current and previous homes.
Overall, the risk for bladder cancer increased with increasing water intake (P trend = .003), and for people with a history of using a private well, this trend was significant trend (P trend = .01).
If private wells were shallow dug wells, which are more vulnerable to contamination from manmade sources of arsenic, there was a trend toward an increased risk for bladder cancer (P trend = .002). However, if private wells were deeper drilled wells, this trend was not evident (P trend = .48).
If the wells were dug prior to 1960, when the arsenic-based pesticides were widely used in this region, the risk for bladder cancer was twice as high in heavy water consumers (>2.2 L/day) as in light water consumers (<1.1 L/day; P trend = .01).
“Although smoking and employment in high-risk occupations both showed their expected associations with bladder cancer risk in this population, they were similar to those found in other populations,” Dr Silverman reported. “This suggests that neither risk factor explains the excess occurrence of bladder cancer in northern New England.”
The most important limitation of the study is the ability to precisely measure arsenic exposure, the researchers note. This hampered the ability to detect an effect of average arsenic concentration in the study population and the ability to accurately quantify the contribution of arsenic exposure to the high rates of bladder cancer seen in this geographic location.
The team points out that the likelihood of exposure to arsenic from well water has declined in recent years because arsenic-based pesticides are no longer used in agriculture, and dug wells are much less common now.
However, arsenic in drinking water from wells drilled deep into fractured bedrock remains a public health concern.
This study was funded by the intramural program of the National Institutes of Health and the National Cancer Institute. The authors have disclosed no relevant financial relationships.