By Rich Anderson, Urban Water Council and Jeff Sloan, Chlorine Chemistry Council
December 3, 2001

A Mixture of Bleach to Disinfect Common Surfaces Directions assume use of 5.25% by weight sodium hypochlorite solution (normal household laundry bleach). Dilutions of bleach lose effectiveness after 24 hours, requiring new solutions to be made daily as needed.

Lynn (MA) Mayor Patrick J. McManus and Trenton (NJ) Mayor Douglas H. Palmer presented findings concerning water system security at the Mayors Emergency, Safety and Security Summit in Washington, DC last month. Since then, the Urban Water Council has received numerous requests for more information on how water systems are protected from bio-agents such as anthrax. Mayor McManus explained at the Summit that bio-agent attacks on the water supply are important, but are not top priority because the vast majority of water systems employ disinfectants that are very effective at destroying such agents.

Serious concerns have arisen regarding our nations preparedness for bioterrorism attacks in the wake of the September 11, 2001 terrorist attacks. Confirmed cases of anthrax fuel this concern and local government is fully engaged in discussion as to how to prepare for and respond to various forms of bioterrorism. Nearly all known biological warfare agents are intended for aerosol application. While many could potentially be applied to drinking water supplies, the US EPA and other experts believe that a biological or chemical attack on U.S. water supplies is relatively unlikely, partly because current water treatment practices would minimize their impacts.

Chlorine disinfectants join other inorganic and organic disinfectants on the front line of defense against bio-agents. Chlorine is effective against bacteria, parasites and viruses. The U.S. Centers for Disease Control and Prevention (CDC), in a Weekly Report (April 21, 2001) has recommended priorities for addressing biological terrorism. Chlorine has been shown to inactivate seventeen of the nineteen biological agents in the CDCs two highest priority categories. Some of these agents, including Salmonella, E. coli, and Vibrio cholerae, are known to be inactivated by normal drinking water treatment. For others, the available data show chlorines efficacy for disinfecting contaminated surfaces, such as those upon which Bacillus anthracis (anthrax) has been found.

A History of Protecting Drinking Water

Along with filtration of raw water, chlorination was cited by Life magazine (Fall 1997) as "...probably the most significant public health advance of the millennium," and is responsible for the virtual elimination of serious waterborne diseases such as cholera, typhoid, dysentery and hepatitis A in the United States.

Water supply reservoirs are probably an unlikely target of bioterrorism for several reasons. Most biological agents added to a reservoir, in addition to being greatly diluted, would be inactivated by chlorine disinfection at water treatment facilities. Because of the high efficiency of chlorination disinfection, it is thought that the quantity of a bio-agent required to contaminate a municipal water supply is orders of magnitude greater than the quantity required for a deadly atmospheric release. Such large amounts would be hard to produce and easy to detect, (see Schonfeld, E., Oct. 5, 2001, Committing bioterrorism isnt as easy as it sounds., available at http://www.business2.com/articles/web/o,1653,17605\2,00.html. As pointed out by mayors McManus and Palmer, large water systems may be more vulnerable to physical disruption of equipment than to bio-agent contamination.

EPA Recommends Using Chlorinated Solutions to Disinfect Contaminated Areas The Johns Hopkins Center for Civilian Biodefense Studies has advised the Conference of Mayors in recent teleconference forums that the most likely route for a large-scale bioterrorism attack is by aerosol spray distribution. The two agents capable of the greatest potential for mass casualties and civil disruption by aerosol distribution are anthrax and smallpox, (report available on-line at http://www.hopkins-biodefense.org/. In the event of an aerosol spray attack of a bio-agent, common household bleach will take on a new role of critical importance as a biological agent disinfectant. Surfaces of all types contacted with the biological agent would have to be sanitized. Familiar, widely available and inexpensive, chlorine bleach can be diluted with water to specified concentrations for specific disinfection applications.

Surfaces contacted by letters and packages suspected of being tainted with biological agents should be decontaminated with a bleach solution following a crime scene investigation. For example, the USEPA Region IV office recently prepared a "Fact Sheet for Clean Up of a US Postal Service Facility" in response to the discovery of anthrax spores in a Boca Raton post office. Based on the recommended EPA procedures, pouring 1.5 cups of household laundry bleach into a 1 gallon container of water and adding water up to the 1 gallon mark will make a solution of sufficient strength to inactivate anthrax spores on surfaces. The solution must be applied to contaminated surfaces for 5 minutes before rinsing.

Maximizing Public Health Protection

While chlorine disinfection of water supplies is a proven public health protection measure, scientists have long known that chlorine and other disinfectants used in drinking water can react with organic material to create disinfection byproducts (DBPs). Concerns about potential human health risks have lead regulatory bodies in Europe and North America to regulate some DBP concentrations in treated drinking water. Although these potential risks warrant serious attention, the World Health Organization (WHO) notes "the risks to health from DBPs are extremely small in comparison with inadequate disinfection." Similarly, the American Academy of Microbiology has recommended, "the health risks posed by microbial pathogens should be placed as the highest priority in water treatment to protect public health."

There is a range of water supply treatment and disinfection methods available, and in use today in the United States. Some of these other methods include ultra-violet radiation, ozonation, and use of bromine instead of chlorine for disinfection. Each of these methods should be considered for a particular system based on their unique strengths and weaknesses. Over 98 percent of drinking water systems employ chlorine-based disinfectants for primary treatment. Regardless of the primary treatment method, it is common practice to ensure that treated water contains at least a small amount of chlorine (referred to as chlorine residual) to prevent recontamination in the distribution system between the treatment plant and the citizens tap in the household.