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NEWS Cholera epidemic -traced to risk misValclAla tio  • Cancer fear led to halting of chlorination ® Uncertainties in balancing risks Washington A DECISION by Peruvian officials not to chlorinate much of the country's drinking water, which was based on studies by the US Environmental Protection A enc ( A showmg t at e c onne may cre- ate a slight cancer risk, is being blamed for , the devastating cholera epidemic that is ', now sweeping Peru and a dozen other , countries in South and Central America. Since the first incidents of cholera were identified in January, more than 300,000 new cases have been reported, mostly in Peru. Statistics released earlier this month by the Pan American Health Organization (PAHO) show that the epidemic has claimed 3,516 lives. PAHO officials be- lieve that the bacteria first arrived with a Chinese freighter, which released its ap- parently contaminated bilge water into the harbour at Lima, Peru. The bacteria quickly made their way to the shellfish and fish, probably reaching humans first in the form of ceviche, a raw seafood dish popular in Peru. But once the disease appeared in humans, it quickly moved into the water supply, infecting many times as many people as might have otherwise been ex- posed by person-to-person contact. US and international health officials last week blamed Peruvian water officials for a gross miscalculation in not chlorinat- ing the entire water supply. Although Peru has good water-filtration technology and pumps safe water into the drinking water system, old pipes and open unchlorinated wells appear to have allowed the cholera bacteria to enter the water supply after filtration. Chlorine is a disinfectant and could have protected the water supply even if it were exposed to bacteria. Yet chlorine can also react with by- products of organic decay in the water to create several suspected carcinogens, including chloroform. A class of these chlorine-based compounds, called trihalo- methanes (THMs), are currently regulated by EPA, which requires that their concen- tration in major water systems be less than one part per billion (p.p.b.). EPA studies in the 1970s found that a 100-p.p.b. level poses a cancer risk of about I in 10,000. Since then, EPA has wrestled with the question of how to balance the cancer risk of chlorination with the microbial risk of no disinfection at all (chlorine altema- tives, such as ozone gas, are expensive and may have even more serious health ef- fects). Current US regulations set a 100- p.p.b. limit for THM chemicals, although one study suggests that even that level may cause 700 extra cases of cancer each year in the United States. Yet most epide- miologists agree that a relatively small risk ofcancer is preferable to the possibil- ity of a microbial epidemic. During the 1980s local water officials, citing the EPA studies of chlorine's can- cer potential, decided to stop chlorinating many of Lima's wells. This has now raised serious questions about both EPA's risk assessment and the way it has been com- municated to the rest of the world. Given the uncertainties of risk assessment and the difficulties in balancing microbial and cancer risks, researchers ask whether EPA should have given more emphasis to the disaster potential of not disinfecting water supplies. Even if EPA was sending mixed sig- nals, Peru appears to have heard only what it wanted to hear. Frederic Reiff, PAHO's regional director for water quality, says the decisions may have been based more on the practical and economic difficulties of chlorination than on analysis of the risks. The EPA studies "were one of a number of excuses they used to not chlo- rinate their water," he says. Robert Clark, director of the EPA Drinking Water Re- search Division, adds, "They knew the dangers. I think that they were simply using the EPA position, so they could turn around and point the finger at us and say, ' Well, they told us not to. "' This sobering case of risk assessment gone wrong is forcing US and interna- tional health officials to come to grips with the flaws in what most agree is a haphaz- ard process of balancing real and theoreti- cal public health risks. At a risk assess- ment meeting at the National Academy of Sciences in Washington last week, re- searchers and health organizations urged US officials to reexamine their analysis of chlorine's cancer risk in the light of the South American epidemic. "Chlorination and disinfection of the watersupplies are the pubic health success story of the century," said Carol Henry, director of the International Life Sciences Institute's (ILSI) Risk Science Institute. "To start altering this in some way has very grave and immediate consequences. I don't think we've looked at this with any rational or reasoned approach." Next August, ILSI will convene an international conference to discuss the problems of balancing chemical and mi- crobial risks in watersupplies. Meanwhile, the EPA, which had promised to update its chlorination standards by this year, is still wrestling with the basics: in the absence of a viable alternative to chlorination, the agency is reluctant to reduce the amount of permissible chlorine levels and risk a Peru-like epidemic. EPA officials say that they need more research to estimate chlorine's real-world risk. New regula- tions are not expected before the middle of the decade. -- - Ghrlstopher Anderson N4TURE • Vnt 3Fd •')R NnVFMRFR 19Q1 trr