THMs

trihalomethanes

• methane with 3 halogens
  • e.g., chloroform (CHCl3) and dibromochloromethane (CHBr2CI)
• formed by the reaction of chlorine with humic substances
  

humic substances

degradation-resistant materials formed during the decomposition of vegetation
three components have operational definitions

humin - residue not extracted w/ strong base
humic acids - precipitate in acidified extract
fulvic acids - do not precipitate in acidified extract

high-molecular weight, polyelectrolytic macromolecules

MW fulvic acids lOO's
MW humic acids & humin lO,OOO's

carbon skeleton w/ large number of functional groups

most functional groups contain oxygen
important chelator for metals
Gelbstoffe- yellow stuff (iron colored organics in water)

elemental composition C_45-55% 0_30-45% N_1-5% S_0-l%

formation of THMs associated with chlorination

chlorination of drinking water introduced in 1908
successful prevention of infectious diseases
associated production of THMs - micropollutants

epidemiological studies in populations with chlorinated drinking water

descriptive studies suggest increased cancer risk bladder, stomach, large intestines, & rectum analytical studies show moderate increase in risk bladder & colon cancer populations with long exposure to chlorinated drinking water but causal relationship has not yet been determined.