Nitrosamine Carcinogens Also Swim in Chlorinated Pools

02/25/2010
Departments: Chemical & Environmental Engineering

When epidemiological studies suggested that an increased risk of bladder cancer accompanied the use of chlorinated water for drinking and, most recently, swimming, Bill Mitch, associate professor of environmental engineering, was intrigued. Currently, only a handful of chlorine disinfection byproducts (chemicals formed when chlorine is used to treat water) are regulated and none of these exhibit strong bladder cancer specificity or potency. While there are hundreds more chemicals to investigate, Mitch believes chemical compounds called nitrosamines may be the culprit.

These compounds are highly carcinogenic to bladder tissue. Their presence in chlorinated waters, however, has only recently been discovered and studied by researchers, such as Mitch, who has investigated their formation in chlorinated drinking water sources as well as treated waste water effluents. Their presence in swimming pools would further suggest their possible link to bladder cancer incidences.

While currently unregulated, the EPA lists the concentration of NDMA (a form of nitrosamine) required to result in a one in one million lifetime cancer risk at 0.7 ng/L, which is comparable to the concentration of a grain of salt dissolved in a large swimming pool.
 
They can be formed when organic nitrogen reacts with chloramines, which are commonly used for water treatment, but in the case of swimming pools, are typically formed when free chlorine reacts with organic substances, such as urine and sweat in the presence of nitrite.
 
Mitch’s research team collected water samples at 27 different pools, including hot tubs, indoor pools, an indoor/outdoor pool, outdoor pools, and outdoor sea lion, whale, and penguin aquaria. Their work was reported in the February 15, 2008, issue of Environmental Science & Technology and showed clear concentration differences between pool types, with nitrosamine concentrations in indoor pools and hot tubs exceeding that of outdoor pools and by as much as 500 times that which poses a one in one million lifetime cancer risk.
 
“Because a significant difference in concentration exists between pool types,” says Mitch “an epidemiological study that exploits these differences could illuminate the role of nitrosamines in the incidence of bladder cancer.”
 
Growing interest in utilizing waters impacted by wastewater effluents—high in organic nitrogen—to meet drinking water demands has brought the issue of nitrosamine formation to the forefront. While the EPA has yet to set a regulatory maximum contaminant level, monitoring is now required.
 
“Right now, we’re looking at ways we can tweak the chloramination process,” says Mitch. UV light can destroy nitrosamines and, in combination with chorine, can be a very effective water treatment method, but expensive. “Sometimes just alternating where you inject chloramines reagents can reduce the formation, hopefully to the point where you no longer need UV light.”