10/01/2023
Contamination of the Haw River, North Carolina with 1,4-Dioxane
What happened?
In mid-September, 2023, the chemical 1,4-dioxane was detected in receiving and treated water at the Burlington and Pittsboro water treatment plants. These facilities draw water from the Haw River. All told, the Haw River provides drinking water to one million people in towns spanning Greensboro to Cary. The source of the contamination is believed to be a chemical company in Burlington (1).
The Burlington water treatment plant recorded a discharge of nearly 500 ug/L (ppb) dioxane on September 14. Dioxane concentrations ranging from approximately 1 to 7 ug/L were reported 12 days later at various locations in Pittsboro (2).
What is 1,4-dioxane?
1,4-dioxane, often simply called dioxane, occurs primarily as a colorless liquid. It is used commercially as a solvent in inks, glues, and other products (3). It is also used as a stabilizer in the transport of some other chemicals. Dioxane also has been detected in some deodorants, perfumes, shampoos, toothpastes, and other personal care products (4). This chemical is water soluble and, as a result, has contaminated water supplies throughout the United States. It has a low propensity to bind to soil and can contaminate groundwater by percolating through soil along with water in which it is dissolved (3).
What are the adverse health effects associated with exposure to 1,4-dioxane?
Dioxane has low toxicity (LD50 = 5,170 mg/kg in rats). Toxicity due to acute toxicity is primarily associated with irritation at sensitive points of contact (eyes, throat, etc.) (5).
Prolonged exposure to high concentrations of dioxane has resulted in nasal, liver and kidney cancer in rodents (6). The development of cancer appears to be secondary to damage to these tissues. No increases in cancer mortality were observed in epidemiological studies of workers exposed to dioxane. Dioxane is classified by the US EPA as a probable carcinogen, based on evidence of carcinogenicity in rodent models but not in humans.
Am I at risk of adverse health effects by drinking contaminated Haw River water?
The highest measured concentration of dioxane reported on September 26 in Pittsboro (~7 ug/L) can be used as an estimate of exposure to dioxane. Assuming that an individual drinks 2 liters of water per day (~2 quarts) and weighs 70 kg (~150 pounds). Then, the daily exposure to dioxane would be 0.2 ug/kg/day.
Modeling done by the US EPA predicts that drinking water containing dioxane at a concentration of 0.67 ug/L could result in one excess cancer in a population of one million people (7). Using the same assumptions as above (a 150-pound individual drinking 2 liters of water per day), the dose of dioxane responsible for a 1 in a million increase in cancer is 0.02 ug/kg/day.
The risk of cancer from drinking water containing 7 ug/L dioxane is low but significant. There are assumptions in this assessment that result in an overestimate of the cancer risk from drinking Haw River water.
1) EPA’s estimate of cancer risk is based upon lifetime exposure to dioxane.
2) The model used by EPA assumes that any exposure to dioxane causes cancer, the model estimated the magnitude of the risk. Since dioxane appears to cause cancer in tissues that have been damaged from high exposure, this assumption may be false.
What actions can be taken to minimize the risk of adverse health outcomes from drinking dioxane-contaminated water?
1) Reduce consumption of contaminated water. Use bottled water to make coffee, tea, soup, etc. You shouldn’t be overly concerned about using tap water to wash vegetables, shower, etc. Exposures from these sources will be minimal.
2) Install an under-the-counter reverse osmosis unit to effectively remove dioxane and other contaminants from your drinking water. Remember to provide maintenance to these units as recommended by the company.
3) Monitor concentrations of dioxane measured in your municipality. Levels will likely drop rapidly as will the risk from drinking the water.
References
(1) Apollo Chemical is suspected source of 1,4-dioxane pollution in Haw River (wral.com)
(2) For the second time in two months, Burlington discharged toxic 1,4-Dioxane into Haw River, Pittsboro's drinking water supply | NC Newsline
(3) 1,4-Dioxane - Wikipedia
(4) 1,4-Dioxane in Cosmetics: A Manufacturing Byproduct | FDA
(5) Surprenant K. S. (2000). "Dioxane". Dioxane in Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a08_545. ISBN 978-3527306732
(6) 1-4-dioxane.pdf (epa.gov)
(7) Technical Fact Sheet – 1,4-Dioxane (epa.gov)
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