19 August 2008 19:30 [Source: ICB]
The use of chlorine has helped provide potable water and has improved public health for many years. Now, its credibility is under attack after several health scares
"FILTHY WATER cannot be washed," says a West African proverb. But for the past 100 years, chlorine has been used to do just that - killing off fatal waterborne diseases and providing clean drinking water to millions of people around the globe. However, in recent years the image of chlorine as a miracle worker has been tainted as skeptics have linked the chemical to increased rates of cancer and a greater risk of miscarriage in pregnant women.
Chemists began experimenting with chlorine and chlorine compounds in the 18th century. British physician John Snow was one of the first people to use chlorine for water disinfection in 1850, when he attempted to disinfect the Broad Street Pump water supply in Soho, London after an outbreak of cholera. In 1897, pathologist Sims Woodhead used a bleach solution to temporarily sterilize drinking water in Maidstone, Kent, UK following a typhoid outbreak. Continuous chlorination of drinking water began in the UK in the early years of the 20th century, and its success in reducing typhoid deaths led to its adoption in Jersey City, New Jersey, US, in 1908.
Chlorine was, however, difficult to handle and its application was often unreliable. The Wallace & Tiernan Company - now part of Siemens Water Technologies - helped solve this problem in 1913 with the invention of the chlorinator - a chlorine gas feeder.
Adoption of water chlorination by other cities and towns across the US soon followed and resulted in the virtual elimination of waterborne diseases such as cholera, typhoid, dysentery and hepatitis A. Before the introduction of chlorination in drinking water, typhoid fever killed about 25 out of 100,000 people in the US every year.
Today, chlorine is added to drinking water as chlorine gas, sodium hypochlorite solution or dry calcium hypochlorite. In addition to controllingdisease-causing organisms, chlorination is used to reduce disagreeable tastes and odors, eliminate slime, mold and algae, and to help remove iron and manganese from raw water.
A LIFE SAVER, BUT WITH QUESTIONS
Life magazine declared in 1997 that "the filtration of drinking water plus the use of chlorine is probably the most significant public health advancement of the millennium." But during the past 30 years, scientists have highlighted that chlorine reacts with organic matter naturally present in water, such as decaying leaves, forming potentially dangerous disinfection by-products (DBPs). The most common of these are trihalomethanes (THMs), which include chloroform, and haloacetic acids.
Water authorities monitor the concentration of these compounds, but the World Health Organization (WHO) believes that the "risks to health from DBPs are extremely small in comparison with inadequate disinfection." Nonetheless, some environmentalists, health campaigners and scientists continue to register their concerns about the potential link between these substances and increasing rates of cancers, including bladder and breast cancer. One study showed a higher risk of bladder and possibly colon cancer in people who drank chlorinated water for 35 years or more.
High levels of THMs may also endanger pregnancies - a California study found that pregnant women who drank large amounts of tap water with high levels had an increased risk of miscarriage. And earlier this year, researchers led by Professor Jouni Jaakkola from the University of Birmingham, UK, said pregnant women could expose their unborn children to a greater risk of holes in the heart, cleft palates and anencephalus, which results in the absence of a major portion of the brain, skull, and scalp, if they were exposed to high levels of THMs.
To reduce these compounds, some water treatment facilities have started to substitute chloramines for chlorine as a secondary disinfectant, while other systems now reduce DBP formation by more effectively removing organic matter in source water prior to disinfection
Some plants have even begun to move away from using chlorine altogether, adopting alternatives such as ozone and chlorine dioxide for primary disinfection. European chlorine trade group Euro Chlor agrees that ozonation does not produce THMs and is a very effective disinfectant.
However, it says that because it breaks down quickly, ozone cannot be used to maintain disinfection in the distribution system and small amounts of chlorine or other disinfectants still must be added. It adds that retrofitting treatment plants is expensive.
"Chlorine has the major advantage of ensuring clean water right up to the tap, whereas the action of other disinfectants, such as ozone, ultraviolet light and ultrafiltration, is only temporary," a Euro Chlor spokesman says.
Some health officials claim that negative publicity is scaremongering and could be deadly, in particular for communities in developing countries where waterborne diseases are still common. They blamed the 1991 cholera epidemic in Peru on the fact the disinfection of water supplies with chlorine was discontinued because of fears over the safety of this method. International environmental pressure group Greenpeace, on the other hand, argued that the causes of the disease were the "inadequate management of human excreta resulting in fecal contamination of water supplies, lack of the necessities for proper personal hygiene, and lack of education in personal hygiene."
Former Pan American Health Organization (PAHO)/WHO official Fred Reiff ridiculed Greenpeace's claim, saying 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 was one extra death per 100,000 persons exposed for a period of 70 years."
Reiff says that the results of water treatment during the cholera epidemic in Peru and the surrounding region prove the importance of water chlorination. "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," he states. "Also, countries that quickly implemented chlorination were able to bring the epidemic under control. Conversely, those countries that were not able to implement chlorination of water supplies on a timely basis suffered recurring annual epidemics until a sufficient percentage of the population had developed immunity."
Canadian authorities came to a similar conclusion after E. coli and other bacteria infected the water supply in Walkerton, Ontario, in May 2000, causing the deaths of seven and more than 2,300 to fall ill. A report published by the Ontario Ministry of the Attorney General concluded that even after the well was contaminated, the disaster could have been prevented if the required chlorine residuals had been maintained.
There is no doubt that chlorination has saved an inestimable number of lives, and most experts remain unconvinced that chlorine's array of benefits can be provided by alternative disinfectants.
Moreover, as world leaders increasingly recognize safe drinking water as a key criteria of sustainable development, governments and organizations like the WHO are keen to encourage the adoption of water chlorination as a simple, cost-effective solution for remote rural villages and large cities alike. Water chlorination will, therefore, for the foreseeable future at least, remain a cornerstone of waterborne-disease prevention. However, the growing negative publicity surrounding this method of "cleaning" water suggests that chlorine will have to fight hard to prove its worth to remain the leader of the pack for another 100 years.
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