The purpose of water disinfection is to destroy or inactivate waterborne pathogens. A number of toxic disinfection byproducts (DBPs) can be formed from chlorination, ozonation and other disinfection processes that are widely used. For example, the major DBPs resulting from water chlorination are trihalomethanes (THMs) and haloacetic acids (HAAs) that are present in finished drinking water in concentrations ranging from 10-50 mg/L. Many other DBPs, e.g., chlorinated phenols, haloacetonitriles, haloketones and haloaldehydes, are detected at lower levels. A strong mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), is a DBP resulting from water chlorination and is found at low (ng/L) levels in finished water. Results of toxicologic and epidemiologic studies regarding adverse health effects associated with long term exposure to DBPs are suggestive but not conclusive. To minimize exposure and comply with regulations, research is addressing the mechanisms that form DBPs and controls that can lower their concentrations in finished water (see below).
Current research in this area is evaluating the use of a new secondary disinfectant formulation utilizing hydrogen peroxide and silver to (1) determine the efficacy of the formulation in providing long term residual disinfection, including the control of coliform bacteria, bacterial regrowth and slime/biofilm control, and (2) identify and quantify disinfection byproducts resulting from interactions with conventional chlorine-based and oxidant-based disinfectants. The research encompasses laboratory studies and field demonstrations that together will evaluate the efficacy of the proposed alternative disinfectant in a range of source waters and utility system characteristics. The proposed secondary disinfectant is one of the few non-chlorine based disinfectants that can provide long term residual disinfection in drinking water systems.
Most exposure assessment activities have focused on trihalomethanes that result from chlorination of water. We have recently evaluated evaporative losses, finding that as much of 50% of the assumed ingestion dose is lost by volatilization.
We have also quantified partition coefficients of blood, urine, water and milk, providing information necessary to estimate risks to nursing infants as well as to understand results of biological monitoring.
Research is also underway to characterize exposures to disinfection byproducts that are found in foods.