Disinfection by-products (DBPs) are a major group of water contaminants and their role in causing adverse health outcomes, including adverse pregnancy outcomes, endocrine disruption, respiratory related adverse health outcomes and cancer has been subject to extensive epidemiological and toxicological research and review. Determination of safe exposure to DBPs, particularly within drinking water supplies, has been a topic of extensive debate, with a wide range of acceptable levels set across the industrialized world. The focus of the research in this thesis was on two of the main health outcomes associated with DBP exposure, namely adverse pregnancy outcomes and asthma related symptoms. To assess adverse pregnancy outcomes in Perth, an extensive classification quantification of the major DBPs in Perth drinking water was conducted. A registrybased prevalence study was carried out to assess birth defects in relation to high, medium and low DBP areas (defined by the water sampling and analysis). It was found that women living in high THM areas are 22% (odds ratio (OR) 1.22, 95% confidence interval (95% CI) 1.01-1.48) more likely of having a baby with any birth defect. High exposure was also strongly associated with an increased risk of having a baby with a cardiovascular defect (62% increased risk). Low birth weight and prematurity were also assessed; however these outcomes were not associated with an increased risk through an increase in exposure. Following on from this analysis, a population risk assessment model was developed for DBPs in high exposure environments. This involved a three step process: (i) Firstly a questionnaire-based validation and reliability study was used to assess water consumption patterns of a population of pregnant women in Perth. (ii) Secondly a prediction model for teratogenic burden of DBPs in Perth was developed, related to the exposure patterns of the population of pregnant women involved in the validation and reliability study. (iii) Finally, combining the information collected in (i) and (ii), along with the regression slope estimates for birth weight from the prevalence study (defined in Section 2.2.1), a dose-response model for THMs and birth weight was developed. Predictive simulations for birth weights at given THM levels were then conducted. It was estimated that pregnant women in Perth are exposed to between 0.3 – 4.10 μg/day ingested TTHM, and of this, the more toxic brominated forms accounted for between 0.27 – 3.69 μg/day. Based on a dose-response model used, birthweights calculated for the ‘hypothetical’ exposures ranged from 3403.2g for the highest exposure to 3503.5g in the lowest exposure, which is a difference of over 100g. Although the resulting reduction in birth weight is not extreme, there is still a significant reduction in birth weight present as exposure to TTHMs increases. This is the first doseresponse model to be developed to assess an adverse pregnancy outcome based on pregnant women exposure data, and will be a useful tool for assessing varying exposures throughout not only Australia but also throughout the industrialised world, where DBP exposure is highly prevalent.
|Qualification||Doctor of Philosophy|
|Publication status||Unpublished - 2008|