Drinking-water analysis turns up even more toxic compounds
The chronic presence of genotoxic compounds at low levels in U.S. drinking water presents conflicting goals for some water utilities.
For the first time, researchers have published a study that quantifies the levels of iodo-acid disinfection byproducts (DBPs) in drinking water and that includes a toxicity analysis for each compound. In a collaborative study, analytical chemists, analytical biologists, engineers, and toxicologists analyzed water samples from 22 U.S. cities and 1 Canadian city. The findings could present a conflict for water utilities seeking the best technique for disinfecting drinking water, the authors note.
|Six-year occurrence study finds relatively low levels of highly toxic byproducts in U.S. drinking water.|
Susan Richardson, with the U.S. EPA’s National Exposure Research Laboratory, and Michael Plewa of the College of Agricultural, Consumer, and Environmental Studies at the University of Illinois Urbana−Champaign were interested in growing evidence showing that the formation of iodinated DBPs in drinking water may be higher when utilities use chloramines, rather than chlorine, ozone, or chlorine dioxide, as a disinfectant. Many U.S. utilities have switched from chlorine to chloramines to meet EPA Stage 1 and Stage 2 DBP rules designed to reduce DBP formation, Richardson says.
DBPs are created when the compounds used for disinfecting drinking water react with natural organic matter, bromide, or iodide. Research shows that iodoacetic acid is highly cytotoxic and more genotoxic in mammalian cells than bromoacetic acid, which is the most genotoxic of the haloacetic acids (HAAs) regulated in the U.S. Iodoacetic acid also has been shown to cause developmental abnormalities in mouse embryos.
In new research published in ES&T (10.1021/es801169k), Plewa, Richardson, and colleagues set out to develop an analytical method to quantify five iodo-acids in drinking water, measure the concentrations of iodo-acids in several water samples treated with chloramination as a disinfectant, and investigate the mammalian cell toxicity of seven synthesized iodo-acids and six iodo-trihalomethanes (iodo-THMs). The researchers found that five iodo-acids and two iodo-THMs were present in the water samples. The levels for these same chemicals were highest at treatment plants with relatively short free-chlorine contact times and were lowest at a chlorine-only plant with long free-chlorine contact times. Of the 13 compounds measured, 7 were genotoxic, they report. In general, compounds that contain an iodo-group have enhanced cytotoxicity and genotoxicity as compared with their brominated and chlorinated analogs.
“Iodo-acid DBPs are going to become very important in the near future,” Plewa predicts. “Fifty percent of the U.S. population lives within 50 miles of a coast.” The paper notes that urban areas with high levels of iodide in their source waters, including many coastal cities, had higher levels of the iodo-acids. This is likely due to the intrusion of seawater into natural source waters, Plewa says. “As people draw down water sources to meet population growth, more and more seawater gets into the water source,” he says. Other U.S. regions also have high iodide levels as a result of salt deposits left from ancient seas.
The collaborators say that they built on a nationwide DBP occurrence study (Environ. Sci. Technol. 2006, 40, 7175−7185) in which iodo-acids were identified for the first time as DBPs in drinking water disinfected with chloramines. The results also support research published in 1999 detailing just how iodo-organic compounds form during disinfection of iodide-containing natural waters. Urs von Gunten, a chemist at the Swiss Federal Institute of Aquatic Science and Technology (Eawag) and coauthor of the 1999 ES&T paper (33, 4040−4045), says he marvels at how far the researchers have come. “In our paper we developed the basic knowledge of the kinetics of this process,” he says. “But at that point, no one was talking about other iodo-organic compounds and the toxicity” of these DBPs, von Gunten says.
The paper includes a simple engineering solution for water utilities, Plewa adds. Once you know the relative toxicity and occurrence of these DBPs, “you can sit down and then you can modify your approach, so you can produce very good water . . . that is less toxic and includes fewer DBPs,” he says.
Despite the presence of the genotoxic compounds, the researchers say that they aren’t worried about the safety of any treated drinking water in the U.S. They note that if the plants studied had used only chlorine they would likely have exceeded the EPA standard for THMs and HAAs. Plewa notes that this raises competing issues for water utilities—how can they meet current EPA standards and produce drinking water free of potentially hazardous byproducts while simultaneously keeping it hygienically safe?
It is rather to teach a man fishing than to give him fish.
The deadly bacteria can linger in biological treatment ponds and elsewhere—but how far can pathogenic strains of legionellae travel in air? New research in ES&T revisits the debate.
An outbreak in Norway of legionellosis, or Legionnaires’ disease, killed 10 people and made more than 50 people sick in 2005. An epidemiological study pegged the source of the infectious Legionella bacteria to an air scrubber at a wood-processing plant, about 10 kilometers away from where the outbreak took place. The facility also houses aeration ponds that are known to harbor all sorts of microbes, some of which may be pathogenic—including strains of Legionella bacteria.
Now, research published in ES&T (DOI 10.1021/es800306m ) revisits the debate over how far Legionella can travel. New modeling and measurements taken at the site confirm that the bacteria can travel by air at least 200 meters downwind of the ponds; however, some controversy still exists.
In 2006, lead author Janet-Martha Blatny of the Norwegian Defence Research Establishment , with co-workers from the company Borregaard, the Norwegian Institute of Public Health, and life sciences company Telelab AS, modeled the wood-processing plant’s air space, using computational fluid dynamics and weather data. They looked at wind flow and other factors to figure out exactly where to place air monitors at various heights and locations around the buildings to capture Legionella aloft.
The researchers found that they could accurately predict the airborne path of aerosolized Legionella within the plant’s footprint, and their monitors captured several different species, depending on weather conditions and each monitor’s height. They also found that the bugs traveled 200 meters downwind, in this case remaining within the compound, where workers might inhale the bacteria.
But Blatny and colleagues needed to determine whether the captured bacteria were viable and infectious. They used real-time polymerase chain reaction and other techniques to examine the bugs. But the serotype of Legionella pneumophila trapped by the monitors turned out not to be the type most likely to cause infections.
Legionellae are ubiquitous in surface waters and are sometimes even found in groundwater. But the most likely sources of human exposure are cooling towers and water distribution systems (including showers and air conditioners), in addition to treatment ponds for industrial sites. The disease is passed not from person to person but only through direct inhalation of viable cells from the environment. Thousands of people get sick from legionellae every year, but those most susceptible tend to be elderly or immune-compromised patients.
None of the sources of the bug can be ruled out, says Jeroen den Boer, a legionellosis specialist at the Regional Public Health Laboratory Kennemerland (The Netherlands). But other research has placed Legionella bugs too far from their source, he says, including the epidemiological studies of the outbreak in Norway. “The way to prove that this person got Legionella from that facility is the way that Janet did it in her article: through air sampling,” den Boer states. “If you have an outbreak, you should look in the vicinity of the thing” that is suspected to be the source.
Lloyd Larsen, a microbiologist at the U.S. Army’s Life Sciences Test Facility at Dugway Proving Ground, says that although the researchers were successful in designing a sampling regime that could capture Legionella, they did not sufficiently validate their model. The experiment failed “to demonstrate the outside limits,” he explains, by sampling beyond the predicted legionellae boundaries.
The monitoring techniques the team used are not groundbreaking, comments Torbjörn Tjärnhage of the Swedish Defence Research Agency. However, the way the researchers put together known technology and modeling yielded useful results, he says, and confirms that air transport is possible. More studies are needed, he adds, particularly in different industries that use such treatment ponds. The team also needs to compare the airborne strains with those present in the ponds, Tjärnhage comments.
The new research “would be far more convincing if [DNA comparisons] would have been included,” den Boer agrees, and he questions whether the researchers tested correctly for various strains that they caught in their air monitors.
However, den Boer says he “was happy to read” the results, which could bolster the idea that airborne Legionella stays relatively close to home. “It is an old discussion which we had in the 1980s and 1990s,” he comments. “Legionella is a bacteria that needs water,” and that’s hard to find kilometers away from its source.