Over 100,000 cancer cases could be caused by chemical contaminants in US tap water, finds study
A combination of chemical pollutants in drinking water in the US could result in more than 100,000 cancer cases, according to an assessment by the Environmental Working Group (EWG).
Drinking water contains a complex mixture of contaminants, and yet government agencies currently assess the health hazards of tap water pollutants one by one.
The research team explains that in the real world people are exposed to combinations of chemicals. Hence, it is vital that agencies and policymakers assess health impacts by looking at the combined effects of multiple pollutants.
Accordingly, EWG, a non-profit organization, calculated the combined health impact of carcinogens in 48,363 community water systems in the US.
The findings state that "cumulative risk analysis of contaminant occurrence in US drinking water" indicates that overall, "tap water exposure to the carcinogenic chemicals analyzed in the study corresponds to 105,887 estimated lifetime cancer cases".
For approximately 279 million people served by community water systems, or 86% of the US population, this number of cases is equivalent to "four-lifetime cancer cases per 10,000 people."
"EWG calculated state and nationwide cancer risks due to mixtures of drinking contaminants because these chemical pollutants do not occur alone. They are almost always in mixtures with other water contaminants," Sydney Evans, the lead author of the paper and a science analyst at EWG, tells MEA WorldWide (MEAWW).
"When risks from individual contaminants are added up, then over a lifetime, more than 100,000 cancer cases in the US could be attributable to mixtures of drinking water contaminants," Evans adds.
The majority of the estimated cancer risk is due to contamination with arsenic, disinfection byproducts, and radioactive elements such as uranium and radium, shows the analysis, published in Heliyon. Estimated cancer risks due to disinfection byproducts and arsenic account for 87% of the total number of cases.
According to Evans, a significant implication of the study is that estimated cancer risk is present at levels currently allowed in drinking water. Accordingly, based on the latest science, water that meets legal standards may still pose health risks.
"Currently, water contaminants are assessed and regulated one at a time, but mixtures of a large number of contaminants are present in tap water. Accurately predicting health outcomes from mixtures of contaminants and subsequently protecting public health requires a cumulative risk assessment. This study is the first step in that direction," says Evans.
While a cumulative approach is common in assessing the health impacts of exposure to air pollutants, it has not been applied to a national dataset of drinking water contaminants, until now.
The study was conducted in all 50 US states with the comprehensive national water quality dataset that EWG has collected and compiled over the years, presented in its tap water database.
For the cancer risk assessment, EWG analyzed data from 2010 to 2017 and the occurrence for 22 carcinogenic contaminants using health-based benchmark levels from health agencies such as the US Environmental Protection Agency, and the California EPA/Office of Environmental Health Hazard Assessment (OEHHA).
As defined by the US government agencies, the calculated cancer risk applies to a "statistical lifetime or approximately 70 years". The study does not include water quality information for approximately 13.5 million American households that rely on private wells for their drinking water.
The analysis shows that systems with the highest risk tend to be small, groundwater systems, that serve smaller communities. These communities often lack the resources, funding, and infrastructure to effectively manage water contamination and provide safe drinking water to their residents, says the team, adding that arsenic — a potent carcinogen — is typically found in groundwater.
However, large surface water systems contribute a significant share of the overall risk due to the higher population served and the consistent presence of disinfection byproducts.
"On the other hand, large surface water systems show consistently elevated risk due to the presence of disinfection byproducts, which are a result of required disinfection. Because these systems serve a large proportion of the population, this risk results in a large proportion of the estimated cancer cases," Evans shares.
According to Dr. Olga Naidenko, EWG's vice president for science investigations, while the vast majority of community water systems meet legal standards, yet the latest research shows that contaminants present in the water at those concentrations — perfectly legal — can still harm human health.
"We need to prioritize source water protection, to make sure that these contaminants don't get into the drinking water supplies, to begin with," says Naidenko.
Since water quality varies significantly between systems for individuals, EWG recommends first determining what contaminants are present in local drinking water by checking local water quality reports or using the EWG tap water database.
"Water can be filtered at the tap using the water filter most appropriate for the individual. EWG publishes a water filter guide to help consumers choose the water filter that works best for their water and their budget," says Evans.
"Ultimately, community, state, and national-level measures need to be taken to establish health-based limits based on the latest science and to protect source water to prevent contamination in the first place," Evans adds.