Disinfecting drinking water with chloramines, a chlorine-ammonia mix that is used to treat roughly a third of the drinking water in the United States, may have the unintended consequence of producing toxins, a new study suggests.
Although chlorine remains the most widely used disinfectant in the United States, the popularity of chloramine has been growing, in part due to the perception that it is safer because it has fewer byproducts. Chlorine creates potentially harmful byproducts when it reacts with other compounds normally present in drinking water systems. Most scientists blame disinfection byproducts for a link between water disinfection and risk of bladder cancer or miscarriages in humans, but they don't know which of an estimated 2000 byproducts are the culprits. Far fewer byproducts result from chloramine and other chlorine alternatives currently in use, but concern remains because the handful of byproducts regulated by the Environmental Protection Agency (EPA) are the most common but not necessarily the most toxic.
When a 2002 EPA drinking water survey found another potentially hazardous type of compound--so-called iodinated byproducts--in drinking water from a Texas utility using exclusively chloramine, the discovery came "as a complete surprise," says Susan Richardson, an EPA chemist who headed the survey. Now she, toxicologist Michael Plewa of the University of Illinois, Urbana-Champaign, and colleagues have identified five of the iodinated byproducts. One of these, iodoacetic acid (IA), is the most toxic to mammalian cells of any disinfection byproduct ever tested, they reported online on 17 August in Environmental Science & Technology. The findings suggest that the switch from chlorine to chloramine could be bad for people's health, Plewa says.
But others aren't so sure. Even if some of the iodinated byproducts are significantly more toxic than those that are currently regulated, they're probably too rare to harm people, says EPA environmental engineer Stig Regli in Washington, D.C. Chemist Stuart Krasner of the Metropolitan Water District of Southern California in La Verne adds that the rarity of iodinated byproducts also means that they're unlikely to be responsible for the bladder cancer risk.
Plewa counters that the amounts of iodinated byproducts in U.S. drinking water are virtually unknown, making it impossible to assess the risk they pose. Richardson is currently working on a project to chart those levels.