What are Disinfection Byproducts?
To protect drinking water from disease-causing organisms, or pathogens, water suppliers often add a disinfectant, such as chlorine, to drinking water. However, disinfection practices can be complicated because certain microbial pathogens, such as Cryptosporidium, are highly resistant to traditional disinfection practices. Also, disinfectants themselves can react with naturally-occurring materials in the water to form byproducts, which may pose health risks.
Disinfection byproducts are formed when disinfectants used in water treatment plants react with bromide and/or natural organic matter (i.e., decaying vegetation) present in the source water. Different disinfectants produce different types or amounts of disinfection byproducts. Disinfection byproducts for which regulations have been established have been identified in drinking water, including trihalomethanes, haloacetic acids, bromate, and chlorite.
A major challenge for water suppliers is how to control and limit the risks from pathogens and disinfection byproducts. It is important to provide protection from pathogens while simultaneously minimizing health risks to the population from disinfection byproducts.
Community and Non-Community, Non-Transient water systems that treat water with a chemical disinfectant for primary or residual treatment must monitor for and are subject to regulations for disinfection byproducts.
What is the Maximum Contaminant Level (MCL) for Disinfection Byproducts?
The Environmental Protection Agency (EPA) has established the following standards for Disinfection Byproducts in drinking water:
- Bromate: 10 ppb (micrograms per liter, µg/L)
- Chlorite: 1 ppm (milligrams per liter, mg/L)
- Haloacetic acids (HAA5): 60 ppb (micrograms per liter, µg/L)
- Total Trihalomethanes (TTHMs): 80 ppb (micrograms per liter, µg/L)
What are the Health Effects of Disinfection Byproducts?
- Bromate: Increased risk of cancer
- Chlorite: Some infants and young children who drink water containing chlorite in excess of the MCL could experience nervous system effects. Similar effects may occur in fetuses of pregnant women who drink water containing chlorite in excess of the MCL. Some people may experience anemia.
- Haloacetic acids (HAA5): Increased risk of cancer
- Total Trihalomethanes (TTHMs): Liver, kidney, or central nervous system problems and increased risk of cancer
How are Disinfection Byproducts removed from Drinking Water?
Water systems that use surface water or ground water under the direct influence of surface water and use conventional filtration treatment are required to remove specified percentages of organic materials that may react with disinfectants to form disinfection byproducts, prior to disinfection. Other control strategies include modification of disinfection practices in a manner that still provides adequate protection against pathogens.