Pipe scales release hazardous metals into drinking water
Mobilization of mineral deposits within the distribution system can contaminate treated water before it reaches the tap.
Mineral deposits inside drinking-water pipes can contain high levels of hazardous metals, including arsenic, cadmium, and mercury, and the metals can contaminate tap water when they are disturbed, according to new research published in ES&T (DOI: 10.1021/es0702488v). But current water-quality regulations miss such disturbances, because they call for monitoring at the treatment plant before the water enters the distribution system pipes.
U.S. EPA corrosion chemist Michael Schock and colleagues analyzed lead pipe scales from 26 water systems and found unexpectedly high accumulations of many hazardous metals. The scales had arsenic concentrations as high as 426 parts per million (ppm), mercury as high as 2 ppm, barium as high as 2900 ppm, vanadium as much as 20,000 ppm, and cadmium up to 308 ppm. Mobilization of these scales would cause drinking water at the tap to exceed federal water-quality limits. At the time of sampling, almost none of the utilities were in violation of water-quality regulations. In a few cases, lead and copper, the only inorganic contaminants currently monitored at the tap, exceeded regulatory standards.
"Our work shows that when corrosion impacts water quality, it isn't just about the metal that makes up the pipe. Other metals can be mobilized as well," says Schock.
The research is important, says engineer Vernon Snoeyink at the University of Illinois, because "it should open people's eyes to what may be lurking in the water distribution system. Schock's results could be the tip of the iceberg," he adds.
In recent years, corrosion within the distribution system has been blamed for high lead levels in Washington, D.C., drinking water; high levels of arsenic, lead, and antimony in Park City, Utah, drinking water; and high levels of radon in water from systems in Iowa, Minnesota, and Florida. Apart from Washington, D.C., at the time of the contamination, all of these systems met water safety standards.
It is impossible to say how common or significant such disturbances are, because contamination that occurs within the distribution system isn't monitored, according to Rich Valentine, a University of Iowa engineer whose ongoing work is generating similar results.
Contamination from water systems can be extreme, says former Utah Department of Environmental Quality chemist Larry Scanlan, who investigated consumer complaints in Park City, Utah, in 2000. After determining that the source of contamination lay within the distribution system, Scanlan and colleagues sampled drinking water at a fire hydrant and found that after 10 minutes of flushing, the drinking-water lead levels were 1370 ppb and rising, arsenic was 151 ppb and rising, and antimony was 27 ppb and rising. At the time, the water at the treatment plant met regulatory standards.
In Park City, changes in the flow rate caused the contamination, says Scanlan. Similar changes can occur during high-demand periods, for instance in the morning as households wake up or in the evening when people come home from work. Abrupt changes in water chemistry as a result of a water treatment change can also release contaminants into the distribution system, according to Schock. These changes can potentially cause undetected, long-term intermittent exposure to contaminants in tap water.
"It is clear that consumers are sometimes drinking water containing levels of contaminants that are orders of magnitude higher than those detected in water leaving the treatment plant," says environmental engineer Marc Edwards of Polytechnic Institute and State University.
EPA could take action on this issue as part of the ongoing review of the Total Coliform Rule. An issue paper (PDF: 785KB) by consulting firms HDR Engineering and Environomics indicates that the problem is significant. EPA's Office of Water did not respond to ES&T queries for this story.
The experts contacted by ES&T have differing opinions about options for proceeding on this issue. Some say that contaminants should be monitored at the treatment plant and within the distribution system. Others say that with more research it should be possible to determine which water systems are vulnerable to such problems and then to focus attention there. All agree that the problem is real and currently ignored by water regulators.
