Chlorine is the anti-hero of disinfected drinking water. A pathogen-killer with that fresh swimming pool scent, the green gas has kicked cholera and e. coli to the curb in most developed nations. In recent years however, chlorine’s “dark side” – a tendency to increase the rate of bladder cancer and miscarriages – has prompted water treatment facilities to shun the chemical and turn to alternative disinfectants.
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The results of this switch have proved toxic in some cities, such as in Washington D.C., where the use of chloramine, the ammonia diluted version of chlorine, allowed lead to leach from city pipes into the drinking water. Chlorine, with its oxidizing powers that could coat lead pipes with a less soluble compound, would never have let that happen to our nation’s capital.
It would have just quietly waited for the remnants of WWI ammunition to take the blame or perhaps chromium-6. While there is no danger from the recovered WWI artifacts, chromium-6 is currently under review.
EPA Administrator Lisa Jackson met in late December with senators from several states to announce a detection plan for testing chromium-6 contamination in the nation’s drinking water and likely revise drinking water regulations accordingly.
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Today, it is not clear whether the risks of sticking with chlorine, or the costs associated with techniques that can minimize its bad behavior, outweigh the slough of new problems that are arising from chlorine’s abandonment and the use of alternative treatments, caution environmental engineers from the United States and Switzerland in the Jan 7, issue of Science.
“Recognition of these unexpected consequences of the shift away from chlorine disinfection raises new challenges with respect to the operation of drinking-water and wastewater treatment plants,” the authors warn.
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Chlorine stops microbes in their tracks. Microbes tend to thrive in water that is rich in organic matter. When chlorine mixes with organic matter, it gets funky with its bad self and produces toxic disinfection by-products. So basically, the more organic matter in the source of drinking water the more likely our hero is to take nasty liberties in the act of killing bad bugs.
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One solution is enhanced coagulation and activated carbon filtration of the organic matter prior to letting chlorine loose to do its job – yes that’s as expensive as it sounds. Which is why most utilities worldwide -- according to the authors David Sedlak of U.C. Berkeley and Urs von Gunten of the Swiss Federal Institute for Environmental Science and Technology (EAWAG) in Switzerland, go for the cheap fix and simply dump ammonia into the mix, then add the chlorine. This cuts down on chlorine’s reactivity levels and reduces the amounts of toxic disinfection by-products, but the result is the lead-leaching chloramine. To fix the lead problem, Washington Aqueduct in 2004 started adding the corrosion inhibitor orthophosphate to drinking water. Today the lead levels are well below the Environmental Protection Agency limits for drinking water.
But Sedlak and von Gunten claim that using chloromine can also result in a different set of toxic by-products, called carcinogenic nitrosamines, when the water contains the presence of synthetic polymers such as water-softening agents. They urge for the development of less costly ways for removing organic matter, and better investigation into the use of alternative disinfectants -- such as ozone, which comes with its own set of bromate by-products, and ultraviolet (UV) light, which has no known by-products and is considered a safe replacement for chlorine.
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But giving up chlorine entirely may stop some of the little known side effects that are working to society’s advantage: namely helping reduce the effects of antibiotics, antimicrobials, beta-blockers, and endocrine-disrupting compounds that are finding their way into the aquatic environment. In surface waters downstream of sewage treatment plants, where wastewater is disinfected with chlorine, synthetic chemicals that have bonded with chlorine electrons undergo photochemical transformation and breakdown into dioxins that accumulate in the sediment – and this is a good thing, the authors argue. Enough they say to maybe make it worth it to keep some chlorine as a residual disinfectant in the future.
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While drinking water standards in the United States are set at the federal level through the EPA, along with a list of acceptable methods for treating contaminated water, states are free to set tougher standards and work with the EPA to enforce these regulations on public water systems. Municipal water supplies base the type of water treatment they use on what works best and is most cost effective for their communities. Depending on how contaminated the source of drinking water is to begin with, generally speaking, the lower the limits on contaminants, the higher the cost of the treatment.
If you want to know more about what’s in your water – check out this latest interactive from the New York Times.
Images: (Top) A glass of clean water at a water treatment plant; photo by Boris Khamitsevich, iStockphotos. (Bottom) Graphic showing water purification processes for drinking water and the results of various techniques; Credit: D.L. Sedlak, Science/AAAS.
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