Tap water contaminated with a toxic cocktail of chemical pollutants could be responsible for more than 100,000 cancer cases in the US over a lifetime, according to a new study by scientists with the Environmental Working Group (EWG).
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The study, which was recently published in the journal Heliyon, is the first to carry out a cumulative assessment of the cancer risk associated with 22 carcinogenic pollutants in drinking water across the nation.
The majority of the cancer risk is due to radioactive contaminants, by-products of disinfection chemicals and naturally occurring arsenic, says the EWG.
We want people to realize that water that meets legal specifications may still cause health risks based on the latest science. This is a concern nationwide, whether urban or rural, with a small or large [water system].”
Sydney Evans, Lead Author
Contaminated water responsible for many cancers that have environmental causes
According to the American Cancer Society, there were an estimated 1.7 million new cases of cancer in 2018 alone. Assuming a lifetime of 70 years, that would mean many millions of new cases.
The number of cancer cases arising from contaminated water is small compared with the number of cancer cases in the US overall.
However, EWG’s vice-president of science investigations, Olga Naidenko, points out that contaminated water accounts for a high proportion of the cases that are caused by environmental factors.
Although the US ranks highly for water quality because it has mainly eliminated biological contaminants such as the bacterium E. coli, other dangerous pollutants remain a problem.
Health agencies call for a shift towards cumulative assessment
Since the 1990s, health agencies and scientists worldwide have been calling for the assessment of chemical contaminants to change from a framework that focuses on one contaminant at a time to one that is based on aggregate and cumulative assessment.
Cumulative assessments of cancer risk has become the standard approach for evaluating air quality in the US, yet no such approach has ever been applied to a national dataset of drinking water contaminants, whether it be in the US or any other country.
Risk assessments of drinking water have generally been focused on individual water contaminants such as arsenic or nitrate, or on small groups of related chemicals.
Drinking water contains complex mixtures of contaminants, yet government agencies currently assess the health hazards of tap water pollutants one by one. In the real world, people are exposed to combinations of chemicals, so it is important that we start to assess health impacts by looking at the combined effects of multiple pollutants."
Sydney Evans, Lead Author
Assessing cancer risk cumulatively
Now, Evans and team have presented the first application of the cumulative cancer risk framework to a drinking water dataset covering the whole of the US.
The researchers say the approach builds on a recently published cumulative cancer risk assessment of water contaminants in the state of California and “offers a deeper insight into national drinking water quality.”
The new analytical framework calculated the combined health impact of exposure to carcinogens in 48,363 community water systems across the US. The assessment was not applied to water quality data covering the 13.5 million households that depend on private wells for their drinking water.
As defined by US government agencies, the cancer risk that was calculated applies to a statistical lifetime, which is approximately 70 years.
Smaller communities showed the greatest risk
Most of the cancer risk identified was the result of contamination with radioactive elements such as uranium and radium, by-products of disinfection processes and naturally occurring arsenic. The greatest risk identified was for water systems that serve smaller communities and sourced by groundwater.
The problem in small, rural communities has already been well documented; these communities often require better resources and infrastructures if the water provided is going to be safe for residents to drink.
However, the current study highlights that contaminants in large communities also “contribute a significant share of overall cancer risk associated with drinking water,” due to the larger population served by the water systems and the consistent presence of disinfection byproducts.
"The vast majority of community water systems meet legal standards," says Naidenko. "Yet the latest research shows that contaminants present in the water at those concentrations - perfectly legal - can still harm human health."
Furthermore, in some areas, the level of contaminants did exceed health guidelines. In Washington DC, for example, ten contaminants were detected at levels that exceed guidelines and most of them are associated with cancer.
Water protection needs prioritizing
"We need to prioritize source water protection, to make sure that these contaminants don't get into the drinking water supplies to begin with," warns Naidenko.
Evans recommends that people who are concerned about chemicals in their tap water check their own local water report and install a water filter to help reduce exposure to the contaminants.
People would need to select suitable filters that are designed to protect against the specific contaminants detected in the tap water. The EWG maintains a drinking water database for that purpose.
Evans, S., et al. (2019). Cumulative risk analysis of carcinogenic contaminants in United States drinking water. Heliyon 5. heliyon.com/article/e02314.