Greater risk of bladder cancer linked to arsenic-laden well water in New England

Why has bladder cancer been 20% more common in Maine, New Hampshire, and Vermont than in the rest of the United States? Researchers have now discovered that its increased risk in northern New England is associated with drinking the water from private wells—water that can have low to moderate levels of arsenic.

“Arsenic is an established cause of bladder cancer, largely based on observations from earlier studies in highly exposed populations. However, emerging evidence suggests that low to moderate levels of exposure may also increase risk,” said the study’s senior author Debra Silverman, ScD, Chief of the Occupational and Environmental Epidemiology Branch at the National Cancer Institute (NCI), in Bethesda, MD.

The study, which was published online May 2, 2016 in the Journal of the National Cancer Institute, was led by NCI researchers along with colleagues at the Geisel School of Medicine at Dartmouth, in Hanover, NH, and with the Departments of Health in the affected states.

Bladder cancer mortality rates have been elevated in northern New England for at least five decades and have included both sexes, which suggests a shared environmental factor could be the cause, the researchers noted. So, they first examined such factors as smoking, occupation, French/Canadian ancestry, eating shellfish and fiddlehead greens, and using wood-burning stoves.

“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 said. “This suggests that neither risk factor explains the excess occurrence of bladder cancer in northern New England.”

None of the other factors explained an increased risk of bladder cancer either. However, experts had recently recognized that a high proportion of this population used private wells for drinking water.

“Because of the region’s geology, well water in northern New England often contains low-to-moderate levels of arsenic” released naturally from the earth, the researchers wrote in their study. “Additionally, extensive use of arsenical pesticides from the 1920s to 1960s on blueberry, apple, and potato crops was a man-made source of arsenic in the region.”

To explore this possibility, the researchers interviewed 1,213 northern New Englanders newly diagnosed with bladder cancer as well as 1,418 people without bladder cancer who lived in the same areas. Researchers asked the participants about smoking, occupation, water consumption, and other bladder cancer risk factors.

Results showed that consumption of water from private wells—and especially water from dug wells (as opposed to drilled wells) during the years when arsenical pesticides were widely used—was associated with bladder cancer, which could explain the increased incidence among people of New England, the researchers concluded.

Of the people who drank water from private wells, those who drank the most had almost twice the risk of those who drank the least. This association was even stronger if the water was from dug wells, the researchers found.

The likelihood of exposure to arsenic from dug wells has diminished in recent years after the Environmental Protection Agency (EPA) banned arsenic-based pesticides in the 1980s. Also, dug well use is much less common now than in the first half of the 20th century. However, exposure to arsenic in drinking water from private wells drilled deeply into fractured bedrock is still a potential public health concern.

“There are effective interventions to lower arsenic concentrations in water,” Dr. Silverman said. “New England has active public health education campaigns instructing residents to test their water supply and to install and maintain filters if levels are above the EPA threshold.”

Regardless, arsenic in drinking water is still not as dangerous as other factors, Dr. Silverman noted. “Smoking remains the most common and strongest risk factor for bladder cancer, and therefore smoking cessation is the best method for reducing bladder cancer risk,” she advised.