Disinfection by-products
Disinfection by-products (DBPs) form when organic and mineral materials in water react with chemical treatment agents when disinfecting water.[1][2]
For example, chlorinated disinfectants introduced into the water to destroy pathogenic microbes and form a residual chlorine component such that drinking water may reach the consumer tap safe from microbial contamination, may react with naturally present fulvic and humic acids to produce a range of DBPs including trihalomethanes, haloacetic acids and many others. Residual chlorine may also react further within the distribution network if it comes into contact with organic material accumulated there e.g. as biofilms. In addition to being highly influenced by the types of organic and inorganic matter in the source water, the different species and concentrations of DBPs vary according to e.g. chlorine dosing at the drinking water disinfection stage, the time since dosing, temperature, pH of the water [3]. The proposed interim standard for total thrihalomethanes in drinking water is 0.1PPM.
Swimming pools have been found to contain very high levels of trihalomethanes. In freshwater chlorine pools concentrations of trihalomethanes (mainly chloroform) of up to 0.43PPM have been measured. Salt pools generate higher levels of trihalomethanes (mainly bromoform) than freshwater chlorine pools with levels measured of close to 1.3PPM.[4].
Ozone reacts with bromide (oxidization) to create hypohalous acids, aldehydes and carboxylic acids.[5]. Ozone is not as common due to the high costs. Data on its DBPs is not sufficiently researched.
Table of Content
Occurrence
DBPs are present in most drinking water supplies that have been subject to chlorination, chloramination or ozonation. Many hundreds of DBPs exist in treated drinking water and while the exact figure is not known, at least 600 have been identified. The low levels of many of these DBPs, coupled with the analytical costs in testing water samples for them, means that in practice only a handful of DBPs are actually monitored.
Health effects
Exposure to DBPs in drinking water has been associated through epidemiological studies with cancers, adverse birth outcomes and some birth defects. The exact putative agent remains unknown, however, in the epidemiological studies since the number of DBPs in a water sample are high and exposure surrogates such as monitoring data of a specific by-product (often total trihalomethanes) are used in lieue of more detailed exposure assessment. The World Health Organization has stated that "the risk of death from pathogens is at least 100 to 1000 times greater than the risk of cancer from disinfection by-products (DBPs) {and} the risk of illness from pathogens is at least 10 000 to 1 million times greater than the risk of cancer from DBPs [6].
That being said, in countries where life expectancy exceeds 70 years, some disinfection byproducts may be harmful. The EPA has set Maximum Contaminant Levels (MCLs) for Bromate, Chlorate, Haloacetic Acid and Total Trihalomethanes (TTMs) drinking water standards [7].
Resources
This article has been taken from Wikipedia. To read the article in full, CLICK HERE
References
- ^ "What's in your Water?: Disinfectants Create Toxic By-products". ACES News. College of Agricultural, Consumer and Environmental Sciences - University of Illinois at Urbana-Champaign. 2009-03-31. http://www.aces.uiuc.edu/news/stories/news4724.html. Retrieved 2009-03-31.
- ^ Richardson, D.; Plewa, J.; Wagner, D.; Schoeny, R.; Demarini, M. (Nov 2007). "Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research". Mutation research 636 (1-3): 178–242. doi:10.1016/j.mrrev.2007.09.001. ISSN 0027-5107. PMID 17980649. edit
- ^ Koivusalo, M. and Vartiainen, T. (1997) Drinking water chlorination by-products and cancer. Rev Environ Health, 12, 81-90
- ^ Beech, JA et al. (1980) Nitrates, Chlorates and Trihalomethanes in Swimming Pool Water. Am. J. Public Health, 70 (1), 79-82
- ^ http://www.who.int/water_sanitation_health/dwq/gdwq0506_8.pdf
- ^ http://www.who.int/water_sanitation_health/dwq/S04.pdf
- ^ http://www.epa.gov/safewater/contaminants/index.html#dbps
