Falling arsenic levels in drinking water linked to lower death rates

Access to clean water may seem simple enough. You turn on a faucet, fill a cup with clean water, and never think twice about what else might flow from it. In many villages in Bangladesh, that trust has been misplaced because groundwater bears a silent danger.

Arsenic, a natural element that is tasteless and odorless, has entered shallow wells over the decades, exposing millions of people to unsafe levels of consumption. A new 20-year follow-up study of nearly 11,000 adults shows that when exposure declines, so does mortality from cancer and cardiovascular diseases, and that the risk of death may decrease by fifty percent.

The study published in the Journal of the American Medical Association represents one of the clearest longer-term studies to document that reducing arsenic in drinking water leads to improved survival. The study also gives us a lesson that is relevant to so many regions that extend beyond Bangladesh. Arsenic in groundwater affects communities all over the world, even in places you would not expect. Millions of people in the United States depend on private wells, which are rarely tested, and many of these private wells likely have arsenic.

These findings come with a sense of hope and responsibility. You realize that even after long-term exposure, once you have access to safe wells, your risk decreases. That kind of impact demonstrates what patient public health work can accomplish over time.

Arsenic is naturally occurring in groundwater, and because you cannot taste or smell it, it can go undetected into your home. Chronic exposure causes skin lesions, certain cancers, and cardiovascular disease. In Bangladesh, which saw the rapid establishment of shallow tube wells during the late 20th century, about 50 million individuals were exposed to elevated concentrations (>10 micrograms/liter) as defined by World Health Organization guidelines.

Residents of Araihazar, a district located approximately 25 km east of Dhaka, have been tracked by the Health Effects of Arsenic Longitudinal Study since the start of the century. Researchers initially tested nearly 6,000 wells in the study area and discovered arsenic concentrations from less than 1 microgram/liter to levels hundreds of times higher. Households were often unaware they were consuming high levels of arsenic in drinking water trusted by their families.

From 2000 to 2002, the research team recruited nearly 12,000 adults who met study criteria, being a regular user (minimum of three years) of the same well. Each adult passed an interview, had a physical exam completed, and supplied a urine sample to be examined, a more direct reflection of actual arsenic exposure.

Public health workers began their efforts shortly after the study started, attaching a metal plate to each well designating whether it was in compliance with the national standard (50 micrograms/liter). Local educators instructed families to obtain water from nearby well(s) if they had access to an alternative, even if that well was further from the home, particularly if the original well was marked as unsafe. In communities with high risk, government teams drilled deeper wells for community access (and lower arsenic exposure). Many families installed new wells when they discovered the toxicity of their water.

These actions changed exposure and made a real difference. From 2000 to 2018, the mean concentration of arsenic in wells decreased from 102 micrograms per liter to 32 micrograms per liter. Urinary arsenic levels declined by about fifty percent. Because most of the participants provided multiple urine samples during the follow-up period, the research team was able to track the reduction in exposure for these individual subjects over time.

Despite this average decline, not all participants followed the same trend. Researchers categorized participants into four exposure patterns based on whether urinary arsenic levels were persistently high, persistently low, or changed from high to low or vice versa. Over 1/3 of participants shifted from high exposure to low exposure during the study, and nearly half of the participants were always low. The remaining participants, a much smaller group, shifted from low to high exposure.

What was observed about health risk, however, was perhaps more enlightening. Of the 1,401 participants who died during the 20-year study period due to chronic disease (e.g., 730 deaths due to cardiovascular disease; 256 deaths due to cancer), the research team compared the time trends of urinary arsenic levels and the cause of death. Specifically, they established that for approximately every 197 microgram per gram of creatinine decrease in urinary arsenic levels, there was a 22% reduction in chronic disease mortality, a 23% reduction in mortality due to heart disease, and a 20% reduction in cancer mortality.

Participants who exhibited a high representational change over the study period experienced the most favorable findings. In comparison to individuals with continuous high-level arsenic exposure, individuals who decreased their arsenic exposure had a 54 percent lower risk of death from chronic disease, a 49 percent reduced risk of cancer death, and a 57 percent decreased risk of death from cardiovascular diseases. Individuals who remained with low arsenic exposure had comparable outcomes. Individuals who experienced increased arsenic exposures over time exhibited inflated r

Columbia University's Lex van Geen, a co-lead author of the study, described the findings succinctly. "We demonstrate what happens when chronic exposure to arsenic is interrupted,” he said, “You are stopping deaths from continued exposure and preventing deaths due to past exposure."

The exposure story parallels the opportunity story. Individuals who transitioned to reduced arsenic exposure tended to have greater education and household resources. To rule out the influence of advantages on the health benefits, the investigators paired individuals from the high-to-low exposure group with individuals who maintained extended high arsenic exposure with similar education or resources.

After matching over 1,700 pairs from the high-exposure and low-exposure groups, the change to a safer water source did not result in changes in the risk of chronic disease.

For co-principal investigator Joseph Graziano of the Mailman School of Public Health at Columbia University, the outcomes had emotional resonance. "After seeing how much our work will directly decrease deaths due to cancer and heart disease, I felt the impact of our work will go far beyond the impact we can see in our study," he said. Graziano further mentioned that the study reflected the decades of effort and persistence with science was a reminder that meaningful public health progress always tends to be incremental.

To expand public access to a safe water supply, the researchers collaborated with the Bangladeshi government to make the testing results more available and accessible. They are currently piloting a free mobile application named NOLKUP, developed from over six million well tests.

The application allows members of the public to look up a well, see its arsenic level, and access safer water alternatives, along with the ability for public health planners to pinpoint areas within neighborhoods where communities have yet to have access to deep wells with low arsenic exposure.

The research team believes that the study will motivate governments to act even more rapidly on arsenic "hot spots," including evidence for a potential protective policy, according to co-author Kazi Matin Ahmed of the University of Dhaka.

The study indicates that much of the damage from long-term exposure to arsenic can be mitigated by switching to reduced exposure sources of water supply. For public policy purposes, it shows that public health monitoring directed to well testing, well labeling, deep community wells, and continued monitoring of the arsenic levels can also decrease the mortality from chronic disease.

The base impact of the findings can apply in any area where aquifers are utilized for water supply (e.g., the largest use of the groundwater in the U.S. is for domestic use, and individual wells are still unmonitored). Families utilizing unregulated wells can have regular testing performed and filtration systems for improved health risks.

For global health researchers, this study sets a new precedent for how to measure the compound effect of an environmental exposure over decades. The researchers are calling for continued support to ensure stable funding to sustain long-term scientific studies. The message for communities living with arsenic exposure today is optimism. Clean water can provide you with a lifespan even when highly exposed.

Research findings are available online in the journal JAMA.

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