Emerging toxics from drinking-water treatment
A survey of drinking-water utilities across the U.S. has revealed the occurrence of new disinfection byproducts.
Alternative methods to disinfect water without chlorine have created a whole new suite of byproducts that might affect human health. A study on U.S. drinking-water treatment systems in regions with compromised source waters documents 28 new disinfection byproducts (DBPs). The results are published today on ES&T’s Research ASAP website (DOI: 10.1021/es060353j).
First author Stuart Krasner of the Metropolitan Water District of Southern California and researchers at the University of North Carolina, Chapel Hill, and the U.S. EPA tracked the occurrence of emerging DBPs. Many of the substances they found were not included when EPA designed DBP regulations for drinking-water utilities, which took effect earlier this year.
The group selected 12 water treatment plants representing a variety of possible treatment technologies and local conditions. Where possible, they chose utilities that use different methods to treat the same water and examined input and output waters. After synthesizing standards for many of the new DBPs and optimizing analytical methods, the team documented several trends.
Their main conclusion was that source waters high in total organic carbon or bromide (or both) tend to lead to potential problems with the finished water in sometimes unexpected ways. Bromide-laden waters treated with pre-ozonation had an increased level of trihalonitromethanes, for example.
David Reckhow of the University of Massachusetts, Amherst, says he found the results to contain some surprises. Initial presentations of the data at scientific conferences “raised everyone’s awareness of iodinated compounds,” he notes.
One utility that produced a lot of iodinated compounds used chloramine for treatment, with little to no free chlorine. In addition, the utility’s source water started out with levels of iodide that were higher than those usually observed, Reckhow says. “That treatment scenario had not really been tested before,” he comments.
Reckhow also noted the researchers’ conclusions about the mutagen MX, a chlorinated furanone, which was found at levels “higher than we’ve typically seen,” he says. The discrepancy is likely due to the limited analytical work done in the past at isolated locations and laboratories. “I think the methods are improving,” he comments.
Work done by Urs von Gunten of the Swiss Federal Institute of Aquatic Science and Technology (Eawag) further elucidated the chemistry that gives rise to iodinated DBPs from chloramines, says Philip Singer of the University of North Carolina, Chapel Hill.
Singer, who assisted in selecting sites used in the EPA study, says that the research identifies areas of concern. “This work needs to be followed up with a comprehensive survey to see how widespread the occurrence of these DBPs is on a truly nationwide basis,” he says, in addition to “a study of the underlying chemistry that contributes to the formation of these DBPs.”
Some of the new DBPs are already under investigation, which is an expensive process, says Eva Nieminski, a water-treatment-plant specialist at the Utah Department of Environmental Quality. She notes that the work is of excellent quality and valuable but agrees that it is limited in its scope. “Picking the utilities with compromised, poor-quality water sources helped in understanding the kinetics of the formation of these byproducts but yielded much higher concentrations of emerging DBPs than might be average,” Nieminski warns. Any conclusions about the new DBPs’ significance require a nationwide study of their occurrence in treatments of both high- and low-quality source waters, she says.
Still, “they explored something that we really did not systematically explore before,” says Yuefeng Xie, who is an environmental engineer at Pennsylvania State University and codirector of the university’s Small Public Water Systems Technology Assistance Center. He says the study did a good job in identifying and attempting to quantify emerging DBPs. “From a health professional’s point of view, we identified the problem here. How does this risk compare to other risks?” Xie asks rhetorically. More importantly, he says, “How are we going to remove these DBPs?”
