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The Risks of Waterborne Disease
It is easy to take for granted the safety of modern municipal drinking water, but prior to widespread filtration and chlorination, contaminated drinking water presented a significant public health risk. The microscopic waterborne agents of cholera, typhoid fever, dysentery and hepatitis A killed thousands of U.S. residents annually before disinfection methods were employed routinely, starting about a century ago. Although these pathogens are defeated regularly now by technologies such as chlorination, they should be thought of as ever-ready to “stage a come-back” given conditions of inadequate or no disinfection.
Illnesses Associated with Waterborne Pathogens
Worldwide, about 1.2 billion people lack access to safe drinking water, and twice that many lack adequate sanitation. As a result, the World Health Organization estimates that 3.4 million people, mostly children, die every year from water-related diseases (WHO, 2002a). In the U.S., outbreaks are commonly associated with contaminated groundwater which has not been properly disinfected. In addition, contamination of the distribution system can occur with water main breaks or other emergency situations (CDC, 2002).
Drinking water pathogens may be divided into three general categories: bacteria, viruses and parasitic protozoa. Bacteria and viruses contaminate both surface and groundwater, whereas parasitic protozoa appear predominantly in surface water. The purpose of disinfection is to kill or inactivate microorganisms so that they cannot reproduce and infect human hosts. Bacteria and viruses are well-controlled by normal chlorination, in contrast to parasitic protozoa, which demand more sophisticated control measures. For that reason, parasitic protozoan infections may be more common than bacterial or viral infections in areas where some degree of disinfection is achieved.
Bacteria are microorganisms often composed of single cells shaped like rods, spheres or spiral structures. Prior to widespread chlorination of drinking water, bacteria like Vibrio cholerae, Salmonella typhii and several species of Shigella routinely inflicted serious diseases such as cholera, typhoid fever and bacillary dysentery, respectively. As recently as 2000, a drinking water outbreak of E. coli in Walkerton, Ontario sickened 2,300 residents and killed seven when operators failed to properly disinfect the municipal water supply. While developed nations have largely conquered water-borne bacterial pathogens through the use of chlorine and other disinfectants, the developing world still grapples with these public health enemies.
Viruses are infectious agents that can reproduce only within living host cells. Shaped like rods, spheres or filaments, viruses are so small that they pass through filters that retain bacteria. Enteric viruses, such as hepatitis A, Norwalk virus and rotavirus are excreted in the feces of infected individuals and may contaminate water intended for drinking. Enteric viruses infect the gastrointestinal or respiratory tracts, and are capable of causing a wide range of illness, including diarrhea, fever, hepatitis, paralysis, meningitis and heart disease (American Water Works Association, 1999).
Protozoan parasites are single-celled microorganisms that feed on bacteria found in multicellular organisms, such as animals and humans. Several species of protozoan parasites are transmitted through water in dormant, resistant forms, known as cysts and oocysts. According to the World Health Organization, Cryptosporidium parvum oocysts and Giardia lamblia cysts are introduced to waters all over the world by fecal pollution. The same durable form that permits them to persist in surface waters makes these microorganisms resistant to normal drinking water chlorination (WHO, 2002b). Water systems that filter raw water may successfully remove protozoan parasites.
An emerging pathogen is one that gains attention because it is one of the following:
* a newly recognized disease-causing organism
* a known organism that starts to cause disease
* an organism whose transmission has increased
Source: Guerrant, 1997
Cryptosporidium is an emerging parasitic protozoan pathogen because its transmission has increased dramatically over the past two decades. Evidence suggests it is newly spread in increasingly popular day-care centers and possibly in widely distributed water supplies, public pools and institutions such as hospitals and extended-care facilities for the elderly. Recognized in humans largely since 1982 and the start of the AIDS epidemic, Cryptosporidium is able to cause potentially life-threatening disease in the growing number of immunocompromised patients. Cryptosporidium was the cause of the largest reported drinking water outbreak in U.S. history, affecting over 400,000 people in Milwaukee in April, 1993. More than 100 deaths are attributed to this outbreak. Cryptosporidium remains a major threat to the U.S. water supply (Ibid.).
The EPA is developing new drinking water regulations to reduce Cryptosporidium and other resistant parasitic pathogens. Key provisions of the Long Term 2 Enhanced Surface Water Treatment Rule include source water monitoring for Cryptosporidium; inactivation by all unfiltered systems; and additional treatment for filtered systems based on source water Cryptosporidium concentrations. EPA will provide a range of treatment options to achieve the inactivation requirements. Systems with high concentrations of Cryptosporidium in their source water may adopt alternative disinfection methods (e.g., ozone, UV, or chlorine dioxide). However, most water systems are expected to meet EPA requirements while continuing to use chlorination. Regardless of the primary disinfection method used, water systems must continue to maintain residual levels of chlorine-based disinfectants in their distribution systems.
Giardia lamblia, discovered approximately 20 years ago, is another emerging waterborne pathogen. This parasitic microorganism can be transmitted to humans through drinking water that might otherwise be considered pristine. In the past, remote water sources that were not affected by human activity were thought to be pure, warranting minimal treatment. However, it is known now that all warm-blooded animals may carry Giardia and that beaver are prime vectors for its transmission to water supplies.
There is a distinct pattern to the emergence of new pathogens. First, there is a general recognition of the effects of the pathogen in highly susceptible populations such as children, cancer patients and the immuno-compromised. Next, practitioners begin to recognize the disease and its causative agent in their own patients, with varied accuracy. At this point, some may doubt the proposed agent is the causative agent, or insist that the disease is restricted to certain types of patients. Finally, a single or series of large outbreaks result in improved attention to preventive efforts. From the 1960’s to the 1980’s this sequence of events culminated in the recognition of Giardia lamblia as a cause of gastroenteritis (Lindquist, 1999).
The treatment and distribution of water for safe use is one of the greatest achievements of the twentieth century. Before cities began routinely treating drinking water with chlorine (starting with Chicago and Jersey City in 1908), cholera, typhoid fever, dysentery and hepatitis A killed thousands of U.S. residents annually. Drinking water chlorination and filtration have helped to virtually eliminate these diseases in the U.S. and other developed countries.
Meeting the goal of clean, safe drinking water requires a multi-barrier approach that includes: protecting source water from contamination, appropriately treating raw water, and ensuring safe distribution of treated water to consumers’ taps.
During the treatment process, chlorine is added to drinking water as elemental chlorine (chlorine gas), sodium hypochlorite solution or dry calcium hypochlorite. When applied to water, each of these forms “free chlorine,” which destroys pathogenic (disease-causing) organisms.
Almost all U.S. systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. In addition to controlling disease-causing organisms, chlorination offers a number of benefits including:
* Reduces many disagreeable tastes and odors;
* Eliminates slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks;
* Removes chemical compounds that have unpleasant tastes and hinder disinfection; and
* Helps remove iron and manganese from raw water.
As importantly, only chlorine-based chemicals provide “residual disinfectant” levels that prevent microbial re-growth and help protect treated water throughout the distribution system.
The Risks of Waterborne Disease
Where adequate water treatment is not readily available, the impact on public health can be devastating. Worldwide, about 1.2 billion people lack access to safe drinking water, and twice that many lack adequate sanitation. As a result, the World Health Organization estimates that 3.4 million people, mostly children, die every year from water-related diseases.
Even where water treatment is widely practiced, constant vigilance is required to guard against waterborne disease outbreaks. Well-known pathogens such as E. coli are easily controlled with chlorination, but can cause deadly outbreaks given conditions of inadequate or no disinfection. A striking example occurred in May 2000 in the Canadian town of Walkerton, Ontario. Seven people died and more than 2,300 became ill after E. coli and other bacteria infected the town’s water supply. A report published by the Ontario Ministry of the Attorney General concludes that, even after the well was contaminated, the Walkerton disaster could have been prevented if the required chlorine residuals had been maintained.
Some emerging pathogens such as Cryptosporidium are resistant to chlorination and can appear even in high quality water supplies. Cryptosporidium was the cause of the largest reported drinking water outbreak in U.S. history, affecting over 400,000 people in Milwaukee in April 1993. More than 100 deaths are attributed to this outbreak. New regulations from the U.S. Environmental Protection Agency (EPA) will require water systems to monitor Cryptosporidium and adopt a range of treatment options based on source water Cryptosporidium concentrations. Most water systems are expected to meet EPA requirements while continuing to use chlorination.
The Challenge of Disinfection Byproducts
While protecting against microbial contamination is the top priority, water systems must also control disinfection byproducts (DBPs), chemical compounds formed unintentionally when chlorine and other disinfectants react with natural organic matter in water. In the early 1970s, EPA scientists first determined that drinking water chlorination could form a group of byproducts known as trihalomethanes (THMs), including chloroform. EPA set the first regulatory limits for THMs in 1979. While the available evidence does not prove that DBPs in drinking water cause adverse health effects in humans, high levels of these chemicals are certainly undesirable. Cost-effective methods to reduce DBP formation are available and should be adopted where possible. However, a report by the International Programme on Chemical Safety (IPCS 2000) strongly cautions:
The health risks from these byproducts at the levels at which they occur in drinking water are extremely small in comparison with the risks associated with inadequate disinfection. Thus, it is important that disinfection not be compromised in attempting to control such byproducts.
Recent EPA regulations have further limited THMs and other DBPs in drinking water. Most water systems are meeting these new standards by controlling the amount of natural organic material prior to disinfection.
Chlorine and Water System Security
The prospect of a terrorist attack has forced all water systems, large and small, to re-evaluate and upgrade existing security measures. Since September 11th, 2001, water system managers have taken unprecedented steps to protect against possible attacks such as chemical or biological contamination of the water supply, disruption of water treatment or distribution, and intentional release of treatment chemicals.
With passage of the Public Health Security and Bioterrorism Response Act of 2002, Congress required community water systems to assess their vulnerability to a terrorist attack and other intentional acts. As part of these vulnerability assessments, systems assess the transportation, storage and use of treatment chemicals. These chemicals are both critical assets (necessary for delivering safe water) and potential vulnerabilities (may pose significant hazards, if released). Water systems using elemental chlorine, in particular, must determine whether existing protection systems are adequate. If not, they must consider additional measures to reduce the likelihood of an attack or to mitigate the potential consequences.
Disinfection is crucial to water system security, providing the “front line” of defense against biological contamination. However, conventional treatment barriers in no way guarantee safety from biological attacks. Additional research and funding are needed to improve prevention, detection and responses to potential threats.
The Future of Chlorine Disinfection
Despite a range of new challenges, drinking water chlorination will remain a cornerstone of waterborne disease prevention. Chlorine’s wide array of benefits cannot be provided by any other single disinfectant. While alternative disinfectants (including chlorine dioxide, ozone, and ultraviolet radiation) are available, all disinfection methods have unique benefits, limitations, and costs. Water system managers must consider these factors, and design a disinfection approach to match each system’s characteristics and source water quality.
In addition, world leaders increasingly recognize safe drinking water as a critical building block of sustainable development. Chlorination can provide cost-effective disinfection for remote rural villages and large cities alike, helping to bring safe water to those in need.
Chlorination and Public Health
Of all the advancements made possible through science and technology, the treatment and distribution of water for safe use is truly one of the greatest. Abundant, clean water is essential for good public health. Humans cannot survive without water; in fact, our bodies are 67% water! Both the U.S. Centers for Disease Control and Prevention and the National Academy of Engineering cite water treatment as one of the most significant advancements of the last century.
Disinfection, a chemical process whose objective is to control disease-causing microorganisms by killing or inactivating them, is unquestionably the most important step in drinking water treatment. By far, the most common method of disinfection in North America is chlorination.
Prior to 1908, no U.S. municipal water systems chemically disinfected water. Consequently, waterborne diseases exacted a heavy toll in illness and death. Without chlorination or other disinfection processes, consumers are at great risk of contracting waterborne diseases. Figure 1-1 shows the decline in the death rate due to typhoid fever following the introduction of chlorine to U.S. municipal drinking water systems in 1908. As more cities adopted water chlorination, U.S. death rates due to cholera and hepatitis A also declined dramatically. Worldwide, significant strides in public health and the quality of life are directly linked to the adoption of drinking water chlorination. Recognizing this success, Life magazine (1997) declared, “The filtration of drinking water plus the use of chlorine is probably the most significant public health advancement of the millennium.”
The timeline at the bottom of these pages highlights important developments in the history of drinking water chlorination.
Providing Safe Drinking Water: A Multi-Barrier Approach
Meeting the goal of clean, safe drinking water requires a multibarrier approach that includes protecting raw source water from contamination, appropriately treating raw water, and ensuring safe distribution of treated water to consumers’ taps.
Source Water Protection
Source water includes any surface water (rivers and lakes) or groundwater used as a raw water supply. Every drop of rain and melted flake of snow that does not re-enter the atmosphere after falling to the ground wends its way, by the constant pull of gravity, into the vast interconnected system of Earth’s ground- and surface waters. Precipitation ultimately collects into geographic regions known as watersheds or catchment basins, the shapes of which are determined by an area’s topography.
Increasingly, communities are implementing watershed management plans to protect source water from contamination and ecological disruption. For example, stream buffers may be established as natural boundaries between streams and existing areas of development. In addition, land use planning may be employed to minimize the total area of impervious surfaces such as roads and walkways, which prevent water from soaking into the ground. Reservoirs may be protected from contamination by disinfecting wastewater effluents, prohibiting septic system discharges and even controlling beaver activity (Beaver feces are potential sources of the harmful protozoan parasites Giardia lamblia and Cryptosporidium parvum.) Similarly, the Safe Drinking Water Act requires well head protection programs of water systems using groundwater sources. In such programs, the surface region above an aquifer is protected from contaminants that may infiltrate groundwater. Because source water quality affects the kind of treatment needed, watershed management planning is a sustainable, cost-effective step in providing safe drinking water.
Every day, approximately 170,000 (U.S. EPA, 2002) public water systems treat and convey billions of gallons of water through approximately 880,000 miles (Kirmeyer, 1994) of distribution system piping to U.S. homes, farms and businesses. Broadly speaking, water is treated to render it suitable for human use and consumption. While the primary goal is to produce a biologically (disinfected) and chemically safe product, other objectives also must be met, including: no objectionable taste or odor; low levels of color and turbidity (cloudiness); and chemical stability (non-corrosive and non-scaling). Individual facilities customize treatment to address the particular natural and manmade contamination characteristic of their raw water. Surface water usually presents a greater treatment challenge than groundwater, which is naturally filtered as it percolates through sediments. Surface water is laden with organic and mineral particulate matter, and may harbor protozoan parasites such as Cryptosporidium parvum and Giardia lamblia. The graphic on the following page illustrates and describes the four main steps in a water treatment plant employing chlorine disinfection.
In storage and distribution, drinking water must be kept safe from microbial contamination. Frequently, slippery films of bacteria, known as biofilms, develop on the inside walls of pipes and storage containers. Among disinfection techniques, chlorination is unique in that a pre-determined chlorine concentration may be designed to remain in treated water as a measure of protection against harmful microbes encountered after leaving the treatment facility.
In the event of a significant intrusion of pathogens resulting, for example, from a broken water main, the level of the average “chlorine residual” will be insufficient to disinfect contaminated water. In such cases, it is the monitoring of the sudden drop in the chlorine residual that provides the critical indication to water system operators that there is a source of contamination in the system.
Water treatment transforms raw surface and groundwater into safe drinking water. Water treatment involves two types of processes: physical removal of solids (mainly mineral and organic particulate matter) and chemical disinfection (killing/inactivating microorganisms). Treatment practices vary from system to system, but there are four generally accepted basic techniques.
Alum (an aluminum sulfate) or other metal salts are added to raw water to aggregate particles into masses that settle more readily than individual particles.
Coagulated particles fall, by gravity, through water in a settling tank and accumulate at the bottom of the tank, clearing the water of much of the solid debris.
Water from the sedimentation tank is forced through sand, gravel, coal, or activated charcoal to remove solid particles not previously removed by sedimentation.
Chlorine is added to filtered water to destroy harmful microorganisms. An additional amount, known as a “chlorine residual” is applied to protect treated water from re-contamination as it travels throughout the distribution system.
Source: Illustration by Bremmer and Goris Communications.
Chlorine: The Disinfectant of Choice
Chlorine is added to drinking water to destroy pathogenic (disease-causing) organisms. It can be applied in several forms: elemental chlorine (chlorine gas), sodium hypochlorite solution (bleach) and dry calcium hypochlorite.
When applied to water, each of these forms “free chlorine” (see Sidebar: How Chlorine Kills Pathogens). One pound of elemental chlorine provides approximately as much free available chlorine as one gallon of sodium hypochlorite (12.5% solution) or approximately 1.5 pounds of calcium hypochlorite (65% strength). While any of these forms of chlorine can effectively disinfect drinking water, each has distinct advantages and limitations for particular applications.
Almost all water systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. Table 2-1 shows the percentage of drinking water systems using each of these methods.
The Benefits of Chlorine
Chlorine disinfectants can reduce the level of many disease-causing microorganisms in drinking water to almost immeasurable levels.
Taste and Odor Control
Chlorine disinfectants reduce many disagreeable tastes and odors. Chlorine oxidizes many naturally occurring substances such as foul-smelling algae secretions, sulfides and odors from decaying vegetation.
Biological Growth Control
Chlorine disinfectants eliminate slime bacteria, molds and algae that commonly grow in water supply reservoirs, on the walls of water mains and in storage tanks.
Chlorine disinfectants destroy hydrogen sulfide (which has a rotten egg odor) and remove ammonia and other nitrogenous compounds that have unpleasant tastes and hinder disinfection. They also help to remove iron and manganese from raw water.
How Chlorine Kills Pathogens
How does chlorine carry out its well-known role of making water safe? Upon adding chlorine to water, two chemical species, known together as “free chlorine,” are formed. These species, hypochlorous acid (HOCl, electrically neutral) and hypochlorite ion (OCl-, electrically negative), behave very differently. Hypochlorous acid is not only more reactive than the hypochlorite ion, but is also a stronger disinfectant and oxidant.
The ratio of hypochlorous acid to hypochlorite ion in water is determined by the pH. At low pH (higher acidity), hypochlorous acid dominates while at high pH hypochlorite ion dominates. Thus, the speed and efficacy of chlorine disinfection against pathogens may be affected by the pH of the water being treated. Fortunately, bacteria and viruses are relatively easy targets of chlorination over a wide range of pH. However, treatment operators of surface water systems treating raw water contaminated by the parasitic protozoan Giardia may take advantage of the pH-hypochlorous acid relationship and adjust the pH to be effective against Giardia, which is much more resistant to chlorination than either viruses or bacteria.
Another reason for maintaining a predominance of hypochlorous acid during treatment has to do with the fact that pathogen surfaces carry a natural negative electrical charge. These surfaces are more readily penetrated by the uncharged, electrically neutral hypochlorous acid than the negatively charged hypochlorite ion. Moving through slime coatings, cell walls and resistant shells of waterborne microorganisms, hypochlorous acid effectively destroys these pathogens. Water is made microbiologically safe as pathogens either die or are rendered incapable of reproducing.
Detractors Continue to Challenge Chlorination as a Safe Water Solution for Developing Nations - Chlorine Div
Former PAHO official, Fred Reiff, recounts his experiences battling chlorine misinformation during the Latin American cholera epidemic of the 1990s.
Despite data supporting chlorine's highly beneficial impact on clean water supplies and public health, claims persist that the potential risks of chlorination outweigh the public health value of water disinfection. To me this is comparable to watching the third sequel of a grade Z science fiction movie about a monster that won't die. A case in point is a Greenpeace report currently posted on the organization's website asserting that DBP concerns had no bearing on the spread of disease during the 1991 cholera epidemic that began in Peru and was propagated to almost all countries of Latin America. From personal experience I can confirm that these claims are utter nonsense. I am concerned that such disinformation and half truths might be accepted as fact, resulting in otherwise avoidable disease, suffering, death, and economic impact on the poor people of developing countries.
Why am I qualified to respond? From 1981 through most of 1995, I was an official in the Pan American Health Organization/World Health Organization (PAHO) in a position that offered a very unique vantage point. During this period I was responsible for disseminating the WHO drinking water quality guidelines and fomenting the adoption or updating of national drinking water quality standards. I also was responsible for managing the United Nations Global Environmental Monitoring Programs for Water (for the Americas), the development and promulgation of environmental interventions in disaster preparedness and relief, and the development of appropriate technology for treatment of both potable and waste water. I also served on PAHO's management task force that was formed for the prevention and control of cholera. This level of involvement provided many opportunities for both overall and close-up monitoring of the status of water supply disinfection and its effectiveness as a public health measure in prevention and control of waterborne diseases in all Latin American and the Caribbean countries before, during, and after the introduction of cholera in Peru in 1991.
For many years prior to the cholera outbreak, PAHO had been promoting the disinfection of community water distribution systems and other delivery systems for water for human consumption. Primarily through its Center for Sanitary Engineering and Environmental Science (CEPIS) in Lima, Peru, PAHO collaborated in pilot and demonstration projects for virtually all disinfection methodologies in various countries to ascertain their relative disinfection efficiency, cost effectiveness, and practicality for various cultural and economic situations. Some of them worked well and others were failures. Everything considered, chlorination was almost always found to the most reliable and cost effective.
Until the cholera outbreak erupted in Peru in January-February of 1991, the acute and deadly diarrheal disease had not been prevalent in the Americas since the early 1900's. Immediately upon verification of its presence, PAHO began organizing workshops to inform the appropriate officials of the countries of Latin America (and later Caribbean countries) of the seriousness of this disease and its potential to become an epidemic. We shared the most effective and advanced technologies to detect the pathogen, how to diagnose and treat the disease, the tried and proven methodologies that have been used to prevent cholera, public education strategies, and the epidemiological efforts and methodologies to track and understand the propagation of the disease.
Simultaneously, PAHO headquarters directed each of the PAHO Country Offices to advise health and water agencies to take measures to continuously chlorinate all water distribution and delivery systems. For the population not connected to public water systems, special programs were developed to promote the disinfection of water at the household level. In addition, treatment of the waste products of cholera victims with lime was recommended before its discharge to the sewer systems or the environment, and a list of all preventive measures to be taken by officials and individuals were provided to all appropriate officials. Chlorination was recommended, not only because all of the countries were familiar with this technology, but also because chlorine products were readily available and chlorination was the least costly of the disinfection methodologies. And, most importantly, chlorine is very effective in killing or inactivating Vibrio cholerae, the pathogen of this disease as well as pathogens associated with almost all other waterborne diseases.
Shortly after this directive was issued, I was surprised to learn that some local PAHO officials were encountering pockets of resistance to chlorination from a number of health officials, both in Peru and in other countries. I was specifically told that the reason was their concern for chlorination by-products, especially trihalomethanes. This concern had its origin in press releases and published scientific studies widely disseminated by environmental agencies in the developed countries. I traveled to Peru and other countries and personally met with the health officials and even heads of water agencies who expressed their concern directly to me; some even believed that they might be subjected to a lawsuit if they chlorinated or raised the level of chlorine in their water supplies. I also met other concerned health officials in various cholera workshops and symposiums sponsored by PAHO. Most surprising of all was the discovery that even officials in small towns were aware of disinfection by-products and their alleged negative health effects. It was pointed out to all that when the cholera pathogen is present in a water supply, the risk of contracting the disease is immediate, and that a resulting epidemic could cause thousands of deaths. In contrast, the hypothetical health risk posed by trihalomethanes in levels in excess of those recommended by WHO (and EPA) was one extra death per 100,000 persons exposed for a period of 70 years. Unfortunately, some of these well-meaning, but ill-informed officials had to experience the immense proportional difference in risk before accepting this reality.
Debates over the relative significance of the drinking water pathway for cholera in comparison to other pathways also impeded the rapid implementation of drinking water chlorination. Routes that can be taken by cholera include food, beverage, and ice that have been processed or prepared with contaminated water, unhygienic food handlers, produce that is eaten raw but which has been irrigated with cholera contaminated water, filter feeding shellfish harvested in sewage contaminated water, and casual person-to-person contact. Both practical experience and studies have proven that even if cholera is initially introduced through a pathway other than drinking water, the waterborne pathway will soon be activated unless drinking water is disinfected continuously with an adequate level of disinfectant and measures are taken to prevent recontamination before its consumption. A cholera contaminated distribution system is without doubt the most efficient way to transmit this disease.
It should be noted that throughout the first four years of this epidemic the countries with the highest percentage of continuously and adequately chlorinated water systems had no secondary transmission of cholera, even though the disease was introduced into these countries. Also countries that quickly implemented chlorination were able to bring the epidemic under control. There was also an obvious inverse correlation between the percentage of the population receiving chlorinated water and the incidence of new cases of cholera. In one country with excellent long-term epidemiological surveillance in place, it was found that after implementation of measures to prevent cholera, there was also a significant reduction in typhoid fever and infectious hepatitis.
Conversely, those countries that were not able (for whatever reason) to implement chlorination of water supplies on a timely basis, suffered recurring annual epidemics until a sufficient percentage of the population had developed immunity, preventing further epidemic propagation of the disease. Typically there were a number of reasons for delay in implementing widespread chlorination of drinking water supplies. However, no obstacle was harder to overcome than the incorrect perception of risks posed by disinfection by-products relative to the very real and deadly threat of cholera.
To reduce the spread of cholera in areas of abject poverty where household were not connected to water distribution systems PAHO worked in concert with the U.S. Centers for Disease Control and Prevention (CDC) and the University of North Carolina to develop, test, and microbiologically and epidemiologically monitor the results of a methodology to purify the available water at the household level. The end result was chlorination of the household water in containers that were specifically designed to preclude subsequent contamination during storage and use. The annual cost of this intervention was found to be less than $2.00 per family, the major cost being the container. The annual cost of the calcium hypochlorite was less than fifty cents per family. Not only did this prove effective for Latin America but it also led to global health organizations adopting this or similar programs as a viable interim health measure for developing countries in Africa and Asia.
Since the cholera outbreak of 1991, many nations have embraced what is known as the "Precautionary Principle", a protocol acknowledging that uncertainty is inherent in managing emerging risks. The thrust of public health management in the principle is to take steps to reduce potential harm, even when uncertainties remain. Yet a true precautionary approach also means that you do not do away with a proven health intervention. This concept was clearly stated by Dr. Carlyle Macedo, Director of PAHO in his address to the 1992 International Conference on the Safety of Water Disinfection, Balancing the Chemical & Microbiological Risks sponsored by the International Life Sciences Institute.
"In developing countries, the primary public health concern for water supplies should remain preventing them from becoming an efficient vehicle for the widespread transmission of enteric diseases. This concern should not be overshadowed in any way in our efforts to also address the tertiary concern of minimizing the relatively small risk stemming from disinfection by-products…
The high incidence of diseases that are related to water supply and sanitation are primarily a reflection of the social and economic inequities and marginalization that unfortunately still exist in our hemisphere. Basically the people that suffer the most from these diseases have so few economic resources that all but the simplest and least expensive of interventions to reduce their risk of exposure to the many waterborne pathogens are beyond their means. Under such circumstances the disinfection of drinking water with chlorine at the household level, is usually the most viable and cost-effective public health intervention available. To cause these people to abandon chlorination is not only unwise, but cruel, if the alternative is beyond their economic and technical means. Unless there is a simple alternative at an affordable cost, these people should not be frightened away from chlorinating their water. This will only increase their suffering and decrease their life expectancy."
To protect public health, particularly in developing regions, applying the precautionary principle requires use of practical, affordable technologies and a realistic balancing of known and uncertain risks.
Fred M. Reiff, an engineer, is a former official of the Pan American Health Organization/World Health Organization. He retired from that organization in 1995 but continues to serve as an independent international consultant.
Balancing the risks of waterborne pathogens and disinfection byproducts (DBPs) is an evolving challenge for the modern water treatment professional. Widespread disinfection of drinking water, approximately a century old, is regarded as a major public health victory over typhoid fever, cholera and other waterborne diseases. Only in the past 30 years has science demonstrated a potential "downside" to mass water treatment: the formation of DBPs, families of unwanted compounds resulting from the chemical reaction of disinfectants with the organic matter in natural waters. Increasingly, scientists and regulators are addressing the complex presence of DBPs in treated water. Some of these compounds have been regulated. Now, new research demonstrates that with only an incomplete knowledge of the universe of DBPs and their potential hazards, current regulations may have unintended consequences.
The U.S. Environmental Protection Agency (EPA), through its 1998 Stage 1 Disinfectants and Disinfection Byproducts Rule, attempts to manage DBP risk from chlorinated drinking water by regulating two families of DBPs-trihalomethanes (THMs) and haloacetic acids (HAAs). To reduce the presence of these compounds substantially, many water treatment facilities have begun to substitute chloramines for chlorine as a secondary disinfectant. Some systems are also adopting alternatives such as ozone and chlorine dioxide for primary disinfection, although chlorine remains the most popular choice by far. Employing a different tactic, other systems choose to reduce DBP formation by more effectively removing organic matter in source water prior to disinfection. Unfortunately, there is no "one size fits all" solution to managing DBP levels. Facilities must consider the natural chemistry and quality of their source water and their available resources, and plan accordingly.
But there is complicating news: A 2002 nationwide EPA study demonstrates that certain unregulated DBPs are present in drinking water in concentrations on par with those that are regulated. And while alternative disinfectants reduce the presence of THMs and HAAs relative to chlorination, alternate disinfectants can produce higher levels of unregulated DBPs. For example, chloramination of natural waters containing high levels of bromine results in iodinated (iodine-containing) DBPs, one of which is more toxic to cells of mammals than any DBP ever identified.
Disinfection Byproducts: Many and Varied
Hundreds of DBPs have been reported in the scientific literature since EPA scientists first found low levels of chloroform in chlorinated drinking water in 1974. Thirty years later, EPA estimates that less than half of all chlorinated DBPs have been identified. Most of the successfully characterized DBPs are easily extracted from water using analytical techniques; those more difficult to extract remain a challenge to identify. Although substantial progress has been made in investigating chlorinated HAAs and THMs, the body of knowledge on the large number of DBPs resulting from alternative disinfectants is meager. EPA is attempting to characterize all chemicals formed during water treatment so that it can minimize public exposure to the most potentially hazardous DBPs while still maintaining microbiologically safe, healthful drinking water.
Gathering Data Through the Nationwide Disinfection By-product (DBP) Occurrence Study
The Nationwide Disinfection By-product Occurrence Study was undertaken by EPA to characterize and quantify DBPs formed throughout the United States. Drinking water across the country was sampled. To limit the number of compounds analyzed to a manageable quantity, EPA experts were asked to prioritize, by potential toxicity, over 500 DBPs reported in the literature. The result is a list of approximately 50 priority compounds. EPA's goal is to conduct a complete assessment of DBPs formed by different treatments in various regions of the nation.
An important result of the EPA study is the development of information about DBPs from increasingly popular alternative disinfectants. The table below outlines the significant prioritized DBPs associated with each alternative disinfection technique:
Levels of many of the prioritized DBPs resulting from the treatments listed above are higher than levels of THMs and HAAs resulting from chlorination. These study results have implications for utilities considering replacing chlorination with alternative disinfection methods to meet EPA's DBP regulations. A facility treating source water containing naturally elevated bromine levels, for example, might consider avoiding chloramine treatment.
Understanding the Big Picture
Widespread drinking water treatment remains today no less a public health triumph than it was a century ago. A safe, abundant water supply that virtually eliminates waterborne disease frees a society to pursue greater goals. The immeasurable value of safe water to human life is reflected in the United Nations Millennium Goal to "halve, by 2015, the proportion of people without sustainable access to safe drinking water and basic sanitation."
Today's water treatment professionals are faced with a growing database of complex information on DBPs. Their challenge will be to map out the optimum course for managing these compounds, taking into consideration the unique characteristics of their source water and keeping in mind the first priority--eliminating waterborne pathogens.
In a campaign timed to coincide with October 2007, Breast Cancer Awareness Month, a web-based company claims that its PINK water filter products reduce women’s breast cancer risk by removing chlorine from water. The company’s claims are not supported by facts. The U.S. Environmental Protection Agency (EPA) has determined that chlorine levels meeting current drinking water regulations do not pose any known or expected health risks. No U.S. government health agency considers chlorine to be a potential carcinogen.
The company supports its claim by citing a small 1992 study that examined breast cancer and women’s exposures to the banned substances — DDT/DDE and PCBs. These compounds are not related to water chlorination. Additionally, since the 1970s, their production has been prohibited. This 1992 study cited by the water filter company was followed by several larger studies probing a potential link between breast cancer and these substances. After four years reviewing all the relevant studies, the National Academy of Sciences, one of the premier scientific organizations in the U.S., concluded in 1999 that research does not support an association between DDT/DDE and PCBs and breast cancer.
But back to chlorinated water…Chlorine is added to drinking water to help protect public health by destroying disease-causing bacteria, viruses and parasites. Before cities began treating drinking water with chlorine — starting with Chicago and Jersey City almost a century ago — cholera, typhoid fever, hepatitis A and dysentery killed thousands of U.S. residents annually. Today, the vast majority of U.S. water systems that disinfect their water use some type of chlorine-based process, either alone or in combination with other disinfectants. Only chlorine-based disinfectants provide “residual disinfectant” levels that help protect treated water as it journeys from the treatment plant to the tap.
EPA regulates chlorine levels in drinking water to pose no risk of adverse health effects. Not to the breast or to any other organ of the human body.
The Water Quality Association, which represents manufacturers of home water treatment products, states in its Code of Ethics that statements “which deceptively disparage publicly or privately supplied water…. shall not be used.”
Breast cancer is an emotional, devastating and potentially life-threatening illness. Baseless claims as to its causes can only serve to confuse and frustrate the public.
A family of elements
The Halogens are a family of five naturally-occurring chemical elements represented in one of the vertical columns of the Periodic Table of the Elements. Chemical elements are the basic building blocks of matter: substances that cannot be broken down into simpler forms by ordinary chemical means. The Halogen family consists of the elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At).
Each of nature’s chemical elements is made of atoms comprising a positively charged nucleus surrounded by concentric shells of negatively charged electrons. In the Periodic Table of the Elements, vertical columns contain elements whose atoms have the same number of electrons in their outermost electron shells. All of the members of the Halogen family, for example, contain seven outermost electrons. In the world of chemistry, seven outermost electrons is a highly unstable configuration, while eight is extremely stable. As a result, the Halogen elements are always “swiping” electrons from other atoms—a process known as oxidation—to achieve a “stable octet.” This electron swiping forms a chemical bond between Halogens and other elements, resulting in chemical compounds. Because of their reactive nature—a consequence of their “pursuit” of a stable outer electron shell—the Halogens are always found in nature chemically bonded.
Not one chemistry
The members of the Halogen family are known for their tendency to form salts. Table salt, sodium chloride, is an example of a familiar Halogen salt. Sodium chloride is found in natural geologic deposits of salt minerals left over from the slow evaporation of ancient seawater (see photo to the right). The mineral name for table salt is halite. Calcium chloride, applied to roads in winter to help melt ice and snow for public safety, is another example of a common, useful salt.
Due to their enormous reactivity, the Halogen elements can form many types of compounds in addition to salts. One of the tenets of chemistry is that the properties of compounds are entirely independent of the properties of their constituent elements (for example, water, H2O, is very different from hydrogen or oxygen). While the Halogen elements share similar properties (their chemical tendency to swipe electrons, for example, makes them all good oxidizers), the physical, chemical and even biological properties and the toxicities of halogen-containing compounds can vary greatly. It is not possible, therefore, to make general statements about the characteristics of all halogen-containing compounds.
With their wide diversity, many halogen-containing compounds are used to make thousands of everyday products. Halogen compounds also may be useful in intermediate steps in manufacturing processes, and absent in the final product.
Are all halogens the same?
No, although they have some similar properties. The Halogen family of chemical elements, including fluorine, chlorine, bromine, iodine and astatine, are grouped together in the Periodic Table of the Elements based upon their electronic structure. Because of this electron configuration, all of the Halogen elements are quite reactive and form compounds by gaining an electron from other chemical elements. However, there are significant differences among the Halogen elements. For example, at room temperature fluorine and chlorine are gases, bromine is a liquid and iodine and astatine are solids. Astatine, naturally radioactive, is much rarer than the other Halogens.
The properties of chemical elements are unrelated to the properties of the compounds in which they occur. It is not possible to make broad statements about the chemical, physical or biological properties of the wide variety of halogen-containing compounds.
Do halogens occur in nature?
Yes. Halogens occur naturally combined with other elements in compounds in plants, animals, rocks, minerals and soils of all types. Fluoride is bound with other elements in bone; iodide, an essential component of human thyroid hormones, is found in seawater and marine life. Bromide is also present in seawater, and in the human body. The U.S. Geologic Survey estimates the Dead Sea, actually a lake more than eight times saltier than ocean water, contains one billion tons of bromine. The long-prized brilliant Tyrian purple of ancient times was available because a little snail in the Mediterranean had the ability to take bromide from the sea and bind it to indigo, forming dibromoindigo—Tyrian purple.
More than 2,000 naturally occurring “organochlorine” compounds—chlorine-containing organic compounds—have been identified in living organisms. Sodium chloride literally keeps our bodies from drying up, moves our muscles, makes our meals matter, and attacks germs to help keep us healthy.
What are some common products made from halogens?
From Fluorine: Many man-made fluorochemicals have been developed over the years. At the top of a very long list: the inorganic fluorides used in drinking water and dental products; one out of every five active pharmaceutical products is fluorinated, and the synthetic blood substitutes and inhalation drug delivery systems use fluorocarbons. Industrial and household refrigeration and air conditioning industries use low-toxicity, nonflammable, and energy-efficient fluorocarbon fluids. Fluoropolymers and fluoroelastomers are used widely in homes, buildings, automobiles, aerospace applications, and wherever high-quality thermal, flame, electrical, chemical, and solvent resistance and low oxygen and moisture permeability are needed. Other low-molecular-weight perfluoroalkyl-based materials provide oil-, water-, and soil-repellent surface properties for textile, fiber, and paper coatings; and similar materials are used as surfactants to stabilize aqueous fire-fighting foams. Fluorocarbons are used as fire extinguishants in aerospace and other critical areas. Modern high-energy-density lithium-ion batteries used in handheld electronic devices rely on LiPF6. The manufacture of silicon chips relies on the wet and dry etch processes utilizing materials such as ultra-high-purity HF and NF3.1
From Chlorine: Public health relies on chlorine-based disinfectants to help purify drinking water, sanitize swimming pools, and kill pathogens in our homes using household bleach. From helping provide one of the most basic human needs—clean drinking water—to contributing to the production of high-tech first-responder equipment, sustainable building materials, food protection chemicals, computer microprocessor chips and 93 percent of prescription pharmaceuticals, chlorine chemistry is essential to everyday life in America. Among its many uses, chlorine chemistry is instrumental in producing high-purity silicon which is needed to make the tiny integrated circuit “chips” that are at the heart of modern electronics. Solar panels, which generate greenhouse gas-free electricity directly from sunlight, are also made using high-purity silicon. And fiber optic cable, also manufactured with high-purity silicon, is currently in great demand as the communications industry competes to deliver integrated voice, data and Internet services to consumers. The on-line Chlorine Tree demonstrates the many products of chlorine chemistry.
From Bromine: Bromine’s main uses are in producing flame retardants, drilling fluids, agrochemicals, water purification compounds, dyes, medicines and photography chemicals. Brominated flame retardants, such as tetrabromobisphenol A, decabromodiphenyl ether, and vinyl bromide, represent retardants of growing importance. The bromide salts of calcium, sodium, and zinc form dense solutions in water that are used as drilling fluids.
From Iodine: Iodine is an essential micronutrient for humans. Table salt is iodized to help prevent goiter and mental retardation. Potassium iodide is used to help reduce the dose of radiation to the thyroid gland in treating victims of radiation poisoning. Iodine is used in halogen lamps and in ink pigments. Tincture of iodine is used as a topical antiseptic to kill bacteria. Silver iodide is used in the preparation of some photographic films.
From Astatine: Astatine, a rare radioactive chemical element with an extremely short half-life, decays to isotopes of lead. Researchers are investigating the use of astatine for the treatment of human tumors.