Characterization of Unregulated Disinfection By-Products (DBPs) in Chloraminated Water and Estimation of Associated Health Risks
Water disinfectants are added to inactivate microorganisms during the drinking water treatment process. But they also have the potential to react with natural organic matter (NOM) and form disinfection by-products (DBPs) that could be both cytotoxic and genotoxic. Four species of Trihalomethanes (THM4) and five species of haloacetic acids (HAA5) are the only two halogenated organic DBP classes regulated by US Environmental Protection Agency (USEPA). Chloramine is used more and more widely in drinking water utilities as a secondary disinfectant since it can significantly reduce the formation of regulated DBPs. However, chloramination could produce more unregulated DBPs formation than chlorination according to some previous studies. To make it worse, many unregulated DBPs, which generally occur at very low concentration levels in drinking water, are proven to be more toxic than regulated DBPs by many orders of magnitude. Therefore, the investigation of unregulated DBP formation in chloraminated water samples and the associated health risks are warranted. In this study, a liquid-liquid-extraction/gas chromatography-electron capture detector (LLE/GC-ECD) method for haloacetamides (HAMs) was revised and validated. The method showed good accuracy and precision for 7 HAM species, but not for monochloroacetamide and monobromoacetamide. Together with haloacetamides, a total of 49 DBPs were measured in three batches of chloraminated reverse osmosis concentrates with increasing chlorine contact times. Results showed that samples treated with preformed monochloramine were associated with the least DBP formation for the majority of DBPs measured. Samples with a longer free chlorine contact time had increasing DBP formation. A reproductive and developmental health risk analysis was also performed in the study using the USEPA relative potency factor (RPF) approach. The illustrative health risk analysis was conducted on a subset of DBPs, the 17 DBPs with validated no-observed-adverse-effects-levels (NOAELs) obtained from animal studies. The estimated health risks associated with these 17 DBPs were highest in the chloraminated samples with longest chlorine contact time. The results of the study could provide helpful information for water utilities about DBPs formation in chloraminated water samples and the choice of chloramination options.
- Environmental health