Evaluation of subchronic chemical exposure and risks related to regulated disinfection by-products in drinking water distribution systems




Carabin, Anne

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The practice of disinfecting potable water is widely accepted as a way of reducing the risk of waterborne infections. This practice, however, may also result in the formation of numerous compounds known as disinfection by-products (DBPs). Among the DBPs produced by chlorination of organic matter, trihalomethanes (THM4) and haloacetic acids (HAA5) are the most prevalent families in terms of occurrence and concentration. Toxicological and epidemiological studies, reviews and meta-analysis have investigated associations between those DBPs levels/exposure and carcinogenic effects and adverse reproductive effects with different findings. The occurrence of THM4 and HAA5 is determined based on regulatory quarterly sampling for many utilities where DBPs levels fluctuate along the year and more specifically during warmer months. Hence, there is a need to investigate how this variability during warmer months can impact DBPs subchronic exposure and the associated risks. To answer to this knowledge gap, this dissertation aims to highlight the importance of taking higher seasonal concentrations into account in regulatory frameworks. It also seeks to investigate subchronic exposure and risks, as well as evaluating alternative techniques for preventing the emergence of such peaks in the warm summer months. The dissertation begins with a literature overview of DBPs health effects and a perspective paper that recommends re-examining some critical aspects of DBP risk assessment mostly related to subchronic exposure. Secondly, using an extensive dataset covering those warmer months of high variability, spatial and temporal variability of regulated DBPs were investigated in a middle-sized municipality. In order to assist stakeholders in limiting concentration peaks in the network, a model as well as an alternative technique, known as incremental differential UV-VIS, were evaluated for the first time throughout a distribution network. Furthermore, investigations were conducted to determine how this variability would affect exposure estimates and TCM subchronic risks when sampling is performed on a weekly or monthly basis. Disinfecting water is an essential public health measure, and since many people are exposed to DBPs, there is a strong need for the intra-seasonally spatial and temporal variability to be incorporated into DBP risk assessments, even if some relative health risks are small.



Disinfection by-products, Drinking water, Subchronic exposure and risks