N-nitrosamines are considered as a group of emerging disinfection byproducts (DBPs) with potential carcinogenicity at ng/L level. The presence of nitrosamines in drinking water is most commonly associated with chloramination of amine-based precursors. This research investigates the potential of amine-based pharmaceuticals and personal care products (PPCPs) as nitrosamine precursors under practical drinking water disinfection conditions, as well as some critical factors that may affect the nitrosamine formation via PPCPs.
All of the twenty selected PPCPs were able to form the corresponding nitrosamines upon chloramine disinfection, and eight of them rendered molar conversions higher than 1 % under practical disinfection conditions. Ranitidine had the highest N-nitrosodimethylamine (NDMA) molar conversion among the tested PPCPs.
A three-parameter kinetic model was proposed to describe and predict the NDMA formation from pharmaceuticals during chloramination in various water matrices. The model accurately reflected all three significant characteristics of the NDMA formation curve, including an initial lag phase, followed by a fast increase in NDMA formation, and eventually reaching a plateau.
In lab-grade water, the NDMA formation from pharmaceuticals was affected by the Cl2:NH4-N mass ratio, pH, and prechlorination. The NDMA formation increased with the Cl2:NH4-N mass ratio, indicating an enhancement effect of dichloramine. The pH affected both the ultimate NDMA conversion and the reaction rate. The reaction rate is mainly determined by the level of non-protonated amine species, and it increased consistently with increasing pH. The ultimate NDMA conversion is limited by the level of dichloramine, and the maximum NDMA formation occurred in the pH range of 7 to 8. The application of prechlorination may increase or reduce the NDMA conversion, depending on the chlorine reactivity towards the amine group and its surrounding structures.
Water matrix components can slow down the initial NDMA formation from selected pharmaceuticals most likely due to the formation of natural organic matter (NOM)-pharmaceutical complexes, while they had less impact on the ultimate NDMA molar conversion. The application of prechlorination may enhance the initial reaction by destroying the NOM-pharmaceutical complexes, but prolonged prechlorination may further inhibit the NDMA formation due to the binding between pharmaceuticals and NOM breakdown products.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/35995 |
| Date | 13 August 2013 |
| Creators | Shen, Ruqiao |
| Contributors | Andrews, Susan |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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