Drinking water: make mine unleaded, says UMR chemist

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On May 10, 2006

The use of monochloramine to disinfect drinking water can cause harmful levels of lead in the water, says a University of Missouri-Rolla chemist. His research will be published in the May 15 issue of the journal Environmental Science and Technology.

With $150,000 in funding from the National Science Foundation, Dr. Jay A. Switzer, the Donald L. Castleman/Foundation for Chemical Research Missouri Professor of Discovery in Chemistry at UMR, studied what happens when water districts switch from using free chlorine to disinfect drinking water to using monochloramine.

In early 2004, officials in Washington, D.C., a city whose water district had recently switched to monochloramine as a disinfectant, discovered abnormally high levels of lead in several homes across the city – some as high as 48,000 parts per billion (ppb). The Environmental Protection Agency stipulates an action limit of 15 ppb of lead for drinking water to be safe.

The rise in lead levels appeared to coincide with the water district’s switch from the use of free chlorine to the use monochloramine to treat the city’s water. This coincidence led researchers to explore its affect on lead in drinking water.

“You have to disinfect drinking water to kill pathogens or to inactivate them and what has traditionally been used is chlorine,” explains Switzer. “In the field they call this free chlorine. Basically they just bubble chlorine through the water and the practice has been very effective.”

Effective, but not necessarily safe. Chlorine reacts with natural organic matter in the water and makes what are called disinfection byproducts. Of these byproducts, chloroform and other trihalomethanes are suspected to be carcinogenic.

In an effort to reduce the carcinogens in drinking water, the EPA began exploring other disinfection options and found several advantages to monochloramine. While it isn’t quite as good a disinfectant as free chlorine, it doesn’t react with the natural organic molecules, so no trihalomethanes are formed. Plus, Switzer says, it lasts longer. “It’s kind of a time-release disinfectant.”

When chlorine is added to water, it produces hypochlorite and hypochlorous acid, which act as disinfectants. Free chlorine is still used in the water treatment plants as a primary disinfectant, but as a secondary or residual disinfectant, many plants bubble ammonia through the water to react with chlorine, which produces monochloramine.

To see if the switch to monochloramine in Washington, D.C., caused the elevated lead levels, Switzer and his research team deposited lead onto an electrochemical quartz crystal microbalance, a sensitive device capable of measuring masses to nanograms in a solution.

“You can deposit lead onto this device and put it into a beaker of simulated drinking water, then add a shot of monochloramine or chlorine and see what happens, then record the mass,” Switzer says.

The researchers found that when monochloramine was added to the water, the lead almost completely dissolved into the water.

Switzer’s team also tested lead deposits with chlorine. “We found that with chlorine, the lead gets coated with a lead dioxide, which passivates the lead and keeps it from dissolving.”

While homes are rarely constructed with lead pipes today, there are still several sources of lead along the path from the water district to a kitchen tap.

The water mains are usually made of plastic or cast iron with a service line running from the main to each home. In a lot of older houses, that service line is lead. Another source is brass alloys in water meters that contain lead. In houses, flow regulators, check valves, water meters and faucets – even lead-free brass faucets – can contain up to 8 percent lead. Even copper pipes in many modern houses are soldered with lead solder.

When water treated with monochloramine passes this lead, the monochloramine dissolves the lead into the water. This could explain the lead increase in Washington, D.C.’s drinking water.

Now, Switzer is studying ways to disinfect water without producing harmful byproducts or leaching lead. One thing they’re experimenting with is the occasional switch back to solely using free chlorine.

“What if you, periodically, just use chlorine to passivate the pipes,” Switzer poses. “We’ll be studying how long that passivity lasts, once the chlorine is introduced to the water supply.”

Switzer will also explore the affects of monochloramine on copper pipes. Many cities whose water districts use the disinfectant are finding pin-hole perforations in their copper piping. Switzer hopes to determine if there is a correlation.

Switzer’s article is co-authored by Vishnu Rajasekharan, postdoctoral associate in the UMR Materials Research Center; Sansanee Boonsalee, Graduate Student; Elizabeth Kulp, Graduate Student; and Eric Bohannan, research assistant professor, in the UMR Materials Research Center.

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On May 10, 2006. Posted in Research