Disinfection by-product

Disinfection by-products (DBPs) result from reactions between organic and inorganic matter in water with chemical treatment agents during the water disinfection process.^[1]

Chlorination disinfection by-products

Chlorinated disinfection agents such as chlorine, chlorine dioxide, and chloramine, are strong oxidising agents introduced into water in order to destroy pathogenic microbes, to oxidise taste/odour-forming compounds, and to form a disinfectant residual so as water may reach the consumer tap safe from microbial contamination. These disinfectants may react with naturally present fulvic and humic acids, amino acids, and other natural organic matter, as well as iodide and bromide ions, to produce a range of DBPs such as the trihalomethanes (THMs), haloacetic acids (HAAs), and chlorite (which are regulated in the US), and so-called "emerging" DBPs such as halonitromethanes, haloamides, halofuranones, iodo-acids, iodo-THMs, nitrosamines, and others. ^[1]

Chloramine has become a popular disinfectant in the US, and it has been found to produce N-nitrosodimethylamine (NDMA), which is a possible human carcinogen, as well as highly genotoxic iodinated DBPs, such as iodoacetic acid, when iodide is present in source waters.^[1][2]

Residual chlorine (and other disinfectants) may also react further within the distribution network —both by further reactions with dissolved natural organic matter and with biofilms present in the pipes. 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 the type of disinfectant used, the dose of disinfectant, the concentration of natural organic matter and bromide/iodide, the time since dosing, temperature, and pH of the water.^[3]

Swimming pools using chlorine have been found to contain trihalomethanes, although generally they are below current EU standard for drinking water (100 micrograms per litre).^[4] Concentrations of trihalomethanes (mainly chloroform) of up to 0.43 ppm have been measured.^[5] In addition, trichloramine has been detected in the air above swimming pools^[6], and it is suspected in the increased asthma observed in elite swimmers. Trichloramine is formed by the reaction of urea (from urine and sweat) with chlorine and gives the indoor swimming pool its distinctive odor. Salt-water pools generate higher levels of trihalomethanes (mainly bromoform) than freshwater chlorine pools with levels measured of close to 1.3 ppm.

By-products from non-chlorinated disinfectants

Several powerful oxidising agents are used in disinfecting and treating drinking water, and many of these also cause the formation of DBPs. Ozone, for example, produces ketones, carboxylic acids, and aldehydes, including formaldehyde. Bromide in source waters can be converted by ozoneinto bromate, a potent carcinogen that is regulated in the United States, as well as other brominated DBPs.^[1]

As regulations are tightened on established DBPs such as THMs and HAAs, drinking water treatment plant may switch to alternative disinfection methods. This change will alter the distribution of classes of DBP's.^[1]

Occurrence

DBPs are present in most drinking water supplies that have been subject to chlorination, chloramination, ozonation, or treatment with chlorine dioxide. Many hundreds of DBPs exist in treated drinking water and at least 600 have been identified.^[1][7]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. Increasingly it is recognised that the genotoxicities and cytotoxicities of many of the DBPs not subject to regulatory monitoring, (particularly iodinated, nitrogenous DBPs) are comparatively much higher than those DBPs commonly monitored in the developed world (THMs and HAAs).^[1][2][8]

Health effects

Epidemiological studies have looked at the associations between exposure to DBPs in drinking water with cancers, adverse birth outcomes and birth defects. Meta-analyses and pooled analyses of these studies have demonstrated consistent associations for bladder cancer^[9][10] and for babies being born small for gestational age,^[11] but not for congenital anomalies (birth defects).^[12] Early-term miscarriages have also been reported in some studies.^[13][14]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 lieu 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".^[15]

Regulation and monitoring

The United States Environmental Protection Agency has set Maximum Contaminant Levels (MCLs) for bromate, chlorite, haloacetic acids and total trihalomethanes (TTHMs).^[16] In Europe, the level of TTHMs has been set at 100 micrograms per litre, and the level for bromate to 10 micrograms per litre, under the Drinking Water Directive.^[17] No guideline values have been set for HAAs in Europe. The World Health Organization has established guidelines for several DBPs, including bromate, bromodichloromethane, chlorate, chlorite, chloroacetic acid, chloroform, cyanogen chloride, dibromoacetonitrile, dibromochloromethane, dichloroacetic acid, dichloroacetonitrile, NDMA, and trichloroacetic acid.^[18]

References

1. ^ ^{a b c d e f g} Richardson, Susan D.; Plewa, Michael J.; Wagner, Elizabeth D.; Schoeny, Rita; DeMarini, David M. (2007). "Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: A review and roadmap for research". Mutation Research/Reviews in Mutation Research 636: 178–242. doi:10.1016/j.mrrev.2007.09.001. 
2. ^ ^{a b} Richardson, Susan D.; Fasano, Francesca; Ellington, J. Jackson; Crumley, F. Gene; Buettner; Evans, John J.; Blount, Benjamin C.; Silva, Lalith K. et al. (2008). "Occurrence and Mammalian Cell Toxicity of Iodinated Disinfection Byproducts in Drinking Water". Environmental Science & Technology 42 (22): 8330–8338. doi:10.1021/es801169k. 
3. ^ Koivusalo,, Meri; Vartiainen,, Terttu (1997). "Drinking Water Chlorination By-Products And Cancer". Reviews on Environmental Health 12 (2): 81–90. doi:10.1515/REVEH.1997.12.2.81. PMID 9273924. 
4. ^ Nieuwenhuijsen, Mark J.; Toledano, Mireille B.; Elliott, Paul (2000). "Uptake of chlorination disinfection by-products; a review and a discussion of its implications for exposure assessment in epidemiological studies". Journal of Exposure Analysis and Environmental Epidemiology 10 (6): 586–99. doi:10.1038/sj.jea.7500139. PMID 11140442. 
5. ^ Beech, J. Alan; Diaz, Raymond; Ordaz, Cesar; Palomeque, Besteiro (January 1980). "Nitrates, Chlorates and Trihalomethanes in Swimming Pool Water". American Journal of Public Health 70 (1): 79–82. doi:10.2105/AJPH.70.1.79. PMC 1619346. PMID 7350831. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1619346. 
6. ^ LaKind, Judy S.; Richardson, Susan D.; Blount, Benjamin C. (2010). "The Good, the Bad, and the Volatile: Can We Have Both Healthy Pools and Healthy People?". Environmental Science & Technology 44: 3205–3210. doi:10.1021/es903241k. 
7. ^ Richardson, Susan D. (2011). "Disinfection By-Products: Formation and Occurrence of Drinking Water". In Nriagu, J.O.. Encyclopedia of Environmental Health. 2. Burlington Elsevier. pp. 110–13. ISBN 9780444522733. 
8. ^ Plewa, Michael J.; Muellner, Mark G.; Richardson, Susan D.; Fasano, Francesca; Buettner, Katherine M.; Woo, Yin-Tak; McKague, A. Bruce; Wagner, Elizabeth D. (2008). "Occurrence, Synthesis, and Mammalian Cell Cytotoxicity and Genotoxicity of Haloacetamides: An Emerging Class of Nitrogenous Drinking Water Disinfection Byproducts". Environmental Science & Technology 42 (3): 955–61. doi:10.1021/es071754h. 
9. ^ Villanueva, C. M.; Cantor, K. P.; Grimalt, J. O.; Malats, N.; Silverman, D.; Tardon, A.; Garcia-Closas, R.; Serra, C. et al. (2006). "Bladder Cancer and Exposure to Water Disinfection By-Products through Ingestion, Bathing, Showering, and Swimming in Pools". American Journal of Epidemiology 165 (2): 148–56. doi:10.1093/aje/kwj364. PMID 17079692. 
10. ^ Costet, N.; Villanueva, C. M.; Jaakkola, J. J. K.; Kogevinas, M.; Cantor, K. P.; King, W. D.; Lynch, C. F.; Nieuwenhuijsen, M. J. et al. (2011). "Water disinfection by-products and bladder cancer: is there a European specificity? A pooled and meta-analysis of European case-control studies". Occupational and Environmental Medicine 68 (5): 379–85. doi:10.1136/oem.2010.062703. PMID 21389011. 
11. ^ Grellier, James; Bennett, James; Patelarou, Evridiki; Smith, Rachel B.; Toledano, Mireille B.; Rushton, Lesley; Briggs, David J.; Nieuwenhuijsen, Mark J. (2010). "Exposure to Disinfection By-products, Fetal Growth, and Prematurity". Epidemiology 21 (3): 300–13. doi:10.1097/EDE.0b013e3181d61ffd. PMID 20375841. 
12. ^ Nieuwenhuijsen, Mark; Martinez, David; Grellier, James; Bennett, James; Best, Nicky; Iszatt, Nina; Vrijheid, Martine; Toledano, Mireille B. (2009). "Chlorination, Disinfection Byproducts in Drinking Water and Congenital Anomalies: Review and Meta-Analyses". Environmental Health Perspectives: 1486–93. doi:10.1289/ehp.0900677. 
13. ^ Waller, Kirsten; Swan, Shanna H.; DeLorenze, Gerald; Hopkins, Barbara (1998). "Trihalomethanes in drinking water and spontaneous abortion". Epidemiology 9: 134–140. doi:10.1097/00001648-199803000-00006. 
14. ^ Savitz, David A.; Singer, Philip C.; Hartmann, Katherine E.; Herring, Amy H.; Weinberg, Howard S.; Makarushka, Christina; Hoffman, Caroline; Chan, Ronna et al. (2005). "Drinking Water Disinfection By-Products and Pregnancy Outcome". Denver, CO: Awwa Research Foundation. http://www.watersanitationhygiene.org/References/EH_KEY_REFERENCES/WATER/Water%20Treatment/Chlorination/Disinfection%20By%20Products%20and%20Pregnancy%20(EPA).pdf. 
15. ^ "Disinfectants and Disinfection By-Products Session Objectives [Water Sanitation Health (WSH)]". World Health Organization (WHO). http://www.who.int/water_sanitation_health/dwq/S04.pdf. 
16. ^ "Drinking Water Contaminants". United States Environmental Protection Agency (EPA). http://water.epa.gov/drink/contaminants/index.cfm. 
17. ^ European Union directive: Directive 1998/83/EC of the European Parliament and of the Council of 3 November 1998 on the quality of water intended for human consumption
18. ^ "Guidelines for Drinking-water Quality [Water Sanitation Health (WSH)]". Geneva: World Health Organization (WHO). 2008. http://www.who.int/water_sanitation_health/dwq/fulltext.pdf.