Water Technology - Jan 2012

CONTAMINANT OF THE MONTH www watertechonline com 27 Trihalomethanes THMs remove them after formation Some of these include Chloramine for combined chlorine residual chlorine dioxide and ozone followed by chloramine WT Water treatment The Environmental Protection Agency EPA considers that THMs are best managed by using treatment techniques that reduce the formation of THMs rather than to What it is Trihalomethanes THMs are formed along with numerous other disinfection byproducts when chlorine reacts with organic matter in water chlorination THMs were regulated primarily as indicators of the bulk of disinfection byproducts that are not readily measurable so that reductions of formation of THMs and also haloacetic acids HAAs would simultaneously reduce the formation of other unregulated DBPs THMs and HAAs may account for about half of the total organic halogen product mass They consist of four chemicals Chloroform bromodichloromethane dibromochloromethane and bromoform some mixed iodinated THMs are also formed at very low levels when iodide ion is present in the water Chloroform is the most prevalent THM in water systems Brominated THMs are formed from bromide ion in water whereby the bromide is first oxidized to HOBr or OBr by chlorine and then competes effectively with chlorine in the halogenation processes Occurrence In the presence of free chlorine residuals THMs continue to form during water distribution to consumers While drinking water consumption is the principal source of THM exposure to the general population showers are another way people can be exposed because the THMs are VOCs and somewhat hydrophobic Frequent swimmers especially in indoor pools that have been chlorinated can also receive substantial exposure to THMs from inhalation dermal contact and some ingestion of water while swimming Health effects The International Agency for Research on Cancer IARC classifies chloroform and bromodicloromethane as Group 2B possibly carcinogenic to humans and bromoform and dibromomethane as Group 3 not classifiable as to carcinogenicity to humans The World Health Organization has calculated Tolerable Daily Intakes TDIs with safety factors similar to reference doses RfDs for chloroform bromoform and dichlorobromomethane Circle 211