More nitrosamines in drinking water
Two nitrosamines, considered to be potential carcinogens, have been detected in drinking water for the first time.
Researchers have detected two new nitrosamines in drinking water. The results, published today on ES&T’s Research ASAP website (DOI: 10.1021/es061332s), point to the need for alternative methods for measuring potentially carcinogenic drinking-water disinfection byproducts (DBPs).
In regulating DBPs, the U.S. EPA has concentrated on trihalomethanes (THMs), which have been associated with an increased risk of bladder cancer, although they are unlikely to be the direct cause. But researchers and water regulators have expected to find nitrosamines—nonhalogenated DBPs that can be 100–10,000-fold more carcinogenic than THMs—in drinking water treated with chloramines.
By using chloramination to reduce THMs, “you provide a nitrogen source, [so] you have the possibility of increasing nitrosamines,” says Steve Hrudey, a coauthor of the new research and an engineer and associate dean of the school of public health at the University of Alberta (Canada). The best known of these nitrosamines is N-nitrososodimethylamine (NDMA), but researchers have recognized that they need to search out other known and unknown forms of nitrosamines to determine whether they too are problematic.
The University of Alberta team, led by Xingfang Li, tracked water from a Canadian treatment plant and distribution system. They drew samples at the plant and then from three points downstream. The researchers detected four nitrosamines—NDMA, N-nitrososopyrrolidine (NPyr), N-nitrosopiperidine (NPip), and N-nitrososodiphenylamine (NDPhA)—by LC/MS/MS. The levels increased the farther the water traveled into the system, indicating that the nitrosamines kept forming faster than they degraded in the pipelines, possibly in the presence of excess chloramine. This report is the first to find NPip and NDPhA in a drinking-water system; levels were 33–117 nanograms per liter (ng/L) and 0 to almost 2 ng/L, respectively. NPyr levels were 18–75 ng/L; NDMA started at 0 but was measured at 108 ng/L downstream. These levels are considered quite high.
LC/MS/MS analyzes samples at a much lower temperature than more commonly used methods, such as GC/MS or GC/MS/MS, which can miss NDPhA. That nitrosamine is thermally labile, and Li and colleagues have developed a “milder technique, which doesn’t tend to destroy compounds” that are sensitive to higher temperatures, says Susan Richardson, an EPA chemist who specializes in DBPs.
Richardson points out that EPA will likely require utilities to measure only six nitrosamines (the EPA method includes seven), not including the two newly detected ones. Most utilities use GC/MS. “I think it’s important to broaden that,” Richardson says. She also underscores the quality-assurance methods used by Li’s team, including isotopically labeled standards, which could account for changes in the samples’ matrices, and the ability to analyze fragments in the samples that are important indicators of nitrosamines.
The method is “interesting” and “novel” even if detecting these two nitrosamines is not particularly surprising, says Stuart Krasner, a chemist for the Metropolitan Water District of Southern California. Krasner notes that the water treatment plant studied had abnormally high levels of nitrosamines. “I think it would be useful to evaluate their method in more typical waters with regard to NDMA” and other nitrosamines, he comments, to see whether NDPhA is present in other waters.
Krasner says he would also like to see the sensitivity of the method improved for N-nitrososodiethylamine (known as NDEA), a nitrosamine that has a California notification level of 10 ng/L. “There isn’t one method that can get all analytes,” he says. “We really need complementary methods.” With GC/MS, water utilities can measure NPip but have yet to find it, he emphasizes.
Richard Bull, an independent consultant and toxicologist who has worked for EPA, Washington State University, and Battelle, says that NPip and NDPhA are about 100 and 1000 times less potent, respectively, than NDMA. Because this system is so atypical in its NDMA levels, this single study “doesn’t imply a broad risk, and the concentrations are generally much lower in other chloraminated [systems]. I don’t think that this one study necessarily raises big alarms,” Bull says. Still, he emphasizes, nitrosamines are generally more carcinogenic than THMs, although NDPhA has the same potency as THMs do.
“We’re looking at the easy stuff—that’s chemistry that’s already known,” Bull says, indicating the potential for a broader problem. “We really don’t know [what] novel nitrosamines are there. [This work is] an alert that maybe somebody should get more serious about the potential occurrence of more ubiquitous secondary amines in even pristine water sources.”
