Chlorine was discovered in 1774 by chemist Karl Scheele; first used for disinfection in 1850, and used to disinfect London’s water supply during its infamous cholera epidemic.
In the early 1900s, chlorine was widely used as a disinfectant, revolutionising water purification and reducing incidences of water-borne diseases across the Western World.
As a result, global chlorination and/or filtration of drinking water has been hailed as a major public health achievement of the 20th Century.
World Health Organization guidelines state: “Infectious diseases caused by pathogenic bacteria, viruses, protozoa, and helminths, are the most common and widespread health risk associated with drinking-water.”
In 1974, it was discovered the acids derived from water and chlorine react with organic matter creating many water disinfectant by-products, including including chloroform, and bromodichloromethane.
This led to research on other chemicals formed when chlorine is added to water, and to the health effects of these chemicals. More than 600 water by-products have been identified in chlorinated tap water.
Humans are exposed to these by-products through drinking-water and oral, dermal/skin and inhalational contact with chlorinated water. For populations who take hot baths/showers, the inhalation and dermal absorption in the bath/shower accounts for more exposure to by-products than drinking-water.
The International Agency for Research classifies chloroform and bromodichloromethane as “possible human carcinogens”. This comes from data extrapolated from research on animals that may or may not be relevant to human cancer.
WHO recognises the right of all people to an adequate supply of safe drinking water, and so had developed guidelines.
The chloroform guideline value was developed from a study showing hepatotoxity in beagle dogs ingesting chloroform-laced toothpaste for 7.5 yrs, The bromodichloromethane guideline value was developed based on observed increases in kidney tumours in male mice.
Today, with improvements in water disinfection technologies such as ozone, ultraviolet and anolyte, we have the option of choosing which water disinfectant we prefer, knowing what carcinogenic by-product properties we may be exposed to in the long term.
Ka Kite e Kia Manuia,