By analyzing drinking-water samples from U.S. treatment plants, a multi-institute research team has identified some unexpected by-products of disinfection processes. The data indicate compounds that toxicologists should target for further study, the researchers say.
Reactions between disinfection chemicals, such as chlorine and ozone, and natural organic matter in water create a wide variety of by-products. Primarily through laboratory studies, researchers have identified more than 500 of these disinfection by-products.
The Environmental Protection Agency regulates a handful of the by-products, including trihalomethanes (THMs), that have been shown to be toxic to animals and are prevalent in U.S. water systems.
For the new study, the team tested water from 12 treatment plants for the 50 unregulated by-products that EPA scientists ranked as most likely to cause cancer. To increase the likelihood of finding these by-products, Stuart W. Krasner of the Metropolitan Water District of Southern California in La Verne, Susan D. Richardson of EPA’s National Exposure Research Laboratory in Athens, Ga., and their colleagues chose plants that had large amounts of natural organic matter, bromide, and iodide in their incoming water.
“We wanted to get an idea of the worst-case scenario,” says Richardson.
For comparison, the researchers measured the concentrations of regulated disinfection by-products.
Among the unregulated compounds that the researchers found in the water were iodine-containing versions of THMs. The median amount of these by-products was 400 parts per trillion, which was lower than the 31 parts per billion (ppb) of regulated THMs. The researchers noted that the plant with the highest concentration of iodinated THMs, 19 ppb, used only chloramines to treat the water.
Some plants are switching from chlorine to chloramines because they reduce the production of the regulated THMs.
In an upcoming Environmental Science & Technology, the researchers also report finding 28 disinfection byproducts not previously detected. These include iodine-containing acids such as iodoacetic acid. Other work has linked iodoacetic acid to birth defects in mice.
Toxicity studies are now under way for the iodoacids, iodinated THMs, and other compounds that the researchers found. The results of those tests and further measurements of the chemicals’ concentrations in drinking water will indicate whether attempts to decrease effects of regulated by-products may have introduced problems caused by emerging ones, says Krasner.
“If you disinfect water, you are going to have by-products,” he notes. “The more we understand, the more we can get efficient disinfection and minimize as many by-products as we can.”
“It’s a milestone paper,” comments Paul Westerhoff, an environmental engineer at Arizona State University in Tempe. “It’s the most up-to-date view of the occurrence of emerging disinfection by-products.”
Says environmental engineer David A. Reckhow of the University of Massachusetts at Amherst, “They found a number of interesting compounds that surprised many of us.” What’s needed, he says, is a better understanding of the human-health impacts of these compounds and their prevalence in U.S. drinking waters.
