Written by Joyce Smith, BS. Over 100,000 lifetime cancer cases could be due to carcinogenic chemicals in United States drinking water according to a cumulative risk analysis done between 2010 and 2017.
Today’s drinking water contains complex mixtures of contaminants, yet government agencies currently assess the health hazards of pollutants in drinking water one by one. For the last 30 years, researchers and health agencies have been requesting a transition from assessing chemical contaminants one at a time to an aggregate and cumulative assessment 1. This cumulative approach is used by the Environmental Protection Agency (2018a) 2 to assess the health impacts of exposure to air pollutants but has never before been applied to a national dataset of drinking water contaminants.
The Environmental Working Group (EWG), founded in 1992, is a nonprofit, non-partisan organization that empowers people to live healthier lives in a healthier environment and drives consumer choice, civic action, and corporate accountability through research, advocacy and education. In a recent study by EWG, lead author Sydney Evans 3 estimates that more than 100,000 cancer cases could stem from contaminants in tap water. Thus Evans et al 3, using a model that builds on a cumulative cancer risk assessment of water contaminants in the state of California 4, offers deeper insight into the quality of our national drinking water. This study, utilizing a comprehensive nationwide dataset for contaminants present in community water systems in the U.S., analyzed water quality profiles for 48,363 community water systems. Excluded from the study was water quality information for approximately 13.5 million American households (approximately 14% of the U.S. population) that obtain their drinking water from private wells. Ranges of accumulated risk, categorized as 10 6 (lowest risk), 10 5, or 10 4 correspond to contaminant concentrations that, following a lifetime of exposure, would cause one cancer case in a population of one million, 100,000 or 10,000 people, respectively. As defined by U.S. government agencies, the calculated cancer risk applies to a statistical lifetime, or approximately 70 years.
Findings revealed that 71% of the population served by public water systems rely on surface water and 29% rely on ground water for their drinking water. Overall, groundwater systems had the widest range of cumulative risk, from the lowest risk of 10 6 or less to the highest risk of greater than 10 3. Surface water systems, which serve the largest populations, contributed the greatest number of cancer cases at every risk level. A population of 229 million people are served by combined ground and surface water systems that collectively had the highest cumulative lifetime cancer risks of 10 3 and 10 4.
There was also a significant correlation between water quality and quantity 5 (P=0.001). Greater water quality challenges are faced by western states in the US (lower rainfall and greater water shortage) where decreased precipitation concentrates contaminants in ground water and forces people to use ground water with higher concentrations of arsenic and radioactive chemicals, as evidenced in 41% of sampled wells that had drinking water concentrations of 1 ug/L or more of arsenic. Arizona had the highest levels while New York New York had medium levels, and North Carolina, with its abundant rainfall, had the lowest levels of ground water pollution. In contrast to high groundwater contamination with arsenic, surface water systems had significantly higher levels of trihalomethanes and other disinfection byproducts, which, by law, must use disinfection to kill pathogenic microorganisms (p<0.001)
This study failed to address private wells and their health risks as well as non-monitored contaminants or contaminants for which no benchmarks are available. Mixtures of carcinogenic contaminants in water might act synergistically to produce a greater toxic effect and cancer risk than implicated in the study. Finally, subpopulations or age groups such as infants and children with potentially heightened susceptibility to contaminants were not accounted for.
Most of the increased cancer risk is due to contamination with arsenic, disinfection byproducts and radioactive elements such as uranium and radium. Water systems with the highest risk tend to serve smaller communities that rely on groundwater. These communities often need improved infrastructure and resources to provide safe drinking water to their residents. However, large surface water systems contribute a significant share of the overall risk due to the greater population served and the consistent presence of disinfection byproducts.
Source: Evans, Sydney, Chris Campbell, and Olga V. Naidenko. “Cumulative risk analysis of carcinogenic contaminants in United States drinking water.” Heliyon 5, no. 9 (2019): e02314.
© 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/).
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Posted February 17, 2020.
Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.
References:
- EPA. Framework for Cumulative Risk Assessment. 2003; https://www.epa.gov/risk/framework-cumulative-risk-assessment. Accessed February 13, 2020.
- EPA. Technical Support Document EPA’s 2014 National Air Toxics Assessment. 2014; https://www.epa.gov/sites/production/files/2018-09/documents/2014_nata_technical_support_document.pdf. Accessed February 13, 2020.
- Evans S, Campbell C, Naidenko OV. Cumulative risk analysis of carcinogenic contaminants in United States drinking water. Heliyon. 2019;5(9):e02314.
- Stoiber T, Temkin A, Andrews D, Campbell C, Naidenko OV. Applying a cumulative risk framework to drinking water assessment: a commentary. Environmental Health. 2019;18(1):37.
- Ascott, M.J., Stuart, M.E., Gooddy, D.C., Marchant, B.P., Talbot, J.C., Surridge, B.W.J.,Polyad, D.A., 2019. Provenance of drinking water revealed through compliance sampling. Environ. Sci.: Process. Impact. 21, 1052–1064
