Thesis (Ph. D.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

published_or_final_version / abstract / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

No description available.

Secular trends in breast cancer incidence in younger women suggest environmental factors, like exposure to environmental chemicals, may play a role in rising incidence. One of the strongest risk factors for developing breast cancer, next to family history, is high mammographic breast density, which is defined as the proportion of fibroglandular breast tissue relative to fat as seen on a mammogram. Phthalates, a ubiquitous endocrine disrupting chemical, have the potential to interfere with endogenous hormones like estrogen and androgens. There is growing evidence from animal and epidemiologic studies indicating distinct periods of heightened susceptibility to endocrine disrupting chemicals throughout the life course, particularly during critical windows of breast development. Exposure to hormonally active environmental chemicals like phthalates may be a modifiable risk factor for breast cancer, therefore reducing or eliminating exposure could have substantial public health benefits. The overarching goal of this dissertation was to assess the relationship between exposure to phthalates during two critical windows of susceptibility, the prenatal and pregnancy periods, and its effect on breast tissue composition in adolescence and adulthood. First, a comprehensive review of epidemiologic studies summarized the body of evidence for the association between phthalate exposure and intermediate markers known to be in the causal pathway of breast cancer risk (age at breast development, menarche, and breast tissue composition). This systematic review of the literature aimed to identify potential patterns of evidence by outcome and timing of exposure. Evidence from this review suggested that phthalate exposure during the prenatal and childhood periods may play a role in altering menarche. Findings for phthalate exposure and age at breast development were inconclusive. There was a considerable lack of epidemiologic data on phthalate exposure and breast tissue composition throughout the life course. Based on one study, there is a potential association between phthalate exposure during pre-puberty and altered breast tissue density in adolescent girls. No study assessed the relationship between phthalate exposure during the prenatal or pregnancy period and subsequent breast tissue composition. Second, an examination for the association between prenatal phthalate exposure and breast tissue composition measured in adolescence (Chapter 3) and the association between phthalate exposure during pregnancy and breast tissue composition measured during or after the postpartum transient period (Chapter 4) aimed to address this major gap identified from the comprehensive review. The empirical chapters of this dissertation used data from an ongoing longitudinal birth cohort study of mothers and their children conducted by the New York City Columbia Center for Children's Environmental Health and the Breast Cancer and the Environment Research Project (CCCEH-BCERP). The CCCEH-BCERP study cohort has prospective data on nine phthalate metabolite concentrations measured during the third trimester of pregnancy and breast tissue composition measured in a subsample of mother-daughter dyads. Notably, we used novel non-invasive methods (optical breast spectroscopy) in this younger cohort of mothers and daughters to objectively measure specific components of the bulk breast composition before mammography screening age. There was significant evidence of altered breast tissue composition in both mothers and daughters. For daughters (n=127, mean age 15.2 ± 1.9 years), prenatal exposures to select low molecular weight (LMW) and high molecular weight (HMW) phthalate metabolites altered overall breast density in opposing directions, which appears to be driven by significant altered percent breast water. There was a significant association between higher prenatal levels of a LMW phthalate metabolite (monobutyl phthalate) and lower levels of overall breast density (adjusted β = -0.32; 95% CI: -0.51, -0.13) and significant association between sum of di(2-ethylhexyl) phthalate (∑DEHP), a HMW phthalate metabolite, and higher levels of overall breast density in girls (adjusted β = 0.20; 95% CI: 0.05, 0.34). For mothers (n=133, mean age 41 ± 5.3 years at follow-up), there was a significant association between two LMW phthalate metabolites and lower levels of percent breast collagen. Additionally, there was a significant inverse relationship between levels of mono-(3-carboxypropyl), a HMW phthalate metabolite, and percent total hemoglobin of the breast (adjusted β =-0.03; 95% CI: -0.06, 0.00, p=0.05). Overall, this dissertation increased our understanding of the impact that exposure to phthalates during critical windows of susceptibility may have on specific components of the breast. Reducing exposure to both HMW and LMW phthalates may have an impact in reducing breast cancer risk, particularly for girls prenatally exposed, as there was stronger evidence of higher overall breast density and percent water from exposure to select HMW phthalates. Future prospective studies should confirm these results as findings might provide an opportunity for modifying potential breast cancer risk.

The objective of this thesis was to assess the environmental fate and transport of chemicals emitted from consumer products through the development and application of modelling tools. The following hypotheses were tested: i) Multimedia fate models can be applied in a multistage assessment process to emerging chemicals when limited knowledge exists to identify the likely environmental fate and to direct further research; ii) the indoor environment acts as a source of anthropogenic substances in consumer products to the outdoor environment; and iii) chemical removal pathways in the indoor environment are important for the fate of organic chemicals in densely populated areas. The thesis shows that a structured chemical fate assessment strategy can and should be applied at early stages of the evaluation of emerging chemicals to assess their fate and to direct further research. Multimedia fate models play a key role in this strategy. The three‐solubility approach is a simple, rapid method that can be used to estimate physical‐chemical properties for use in early stage evaluation (Paper I). Emissions in the indoor environment affect the urban fate of hydrophobic organic chemicals by providing additional removal pathways and prolonging urban chemical residence times compared to outdoor emissions (Paper III). Emissions of BDE 209, DINP and DEHP to Stockholm indoor air were estimated to be 0.1, 3.4 and 290 mg/capita year, respectively (Paper IV). The contribution of emissions indoors to outdoor air pollution varies between substances. For BDE 209, emissions in the indoor environment added 38 % to the mass entering Stockholm city with inflowing air. For Sweden, the indoor environment was estimated to account for 80 % of BDE 209 emissions to outdoor air (Papers II and IV). For the phthalates, outdoor emissions and/or background inflow are the dominant sources to outdoor air pollution in Stockholm and the influence of the indoor environment is limited (Paper IV). / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript</p>

Source: Masters Abstracts International, Volume: 47-06, page: 3476. Adviser: Arnold J. Schecter. Includes bibliographical references.

Organophosphate and phthalate esters are polymer additives that are frequently found in air and dust in indoor environments. This thesis describes the development and application of air sampling and selective mass spectrometric (MS) determination of these two compound groups. It also describes the sampling and screening of these compounds in indoor air and dust from different environments and the development and evaluation of a method for the extraction and determination of these compounds in indoor dust. An air sampling method previously used for air sampling of only organophosphate esters, is here demonstrated to be applicable for simultaneous sampling of both phthalate and organophosphate esters. Selective detection using tandem mass spectrometry (MS/MS) showed good results for simultaneous determination of organophosphate and phthalate esters in air. The high selectivity of this technique was especially advantageous when analyzing dust. Comparison of chemical profiles of the organophosphate ester between indoor environments including daycare centers, offices and private homes differed between the types of locations while the phthalate profiles were rather similar. Comparison of concentration levels of these compounds in multi-storey apartment buildings classified as either high or low risk “sick” buildings could not differentiate the two classes of buildings. Further, the studies also points out some potential sources of organophosphate and phthalate esters in these indoor environments. In general the levels of phthalate esters were consistently higher than the levels of organophosphate esters both in air and in dust. Phthalate and organophosphate esters were also determined in a dust standard reference material; seventeen of the targeted compounds were quantified out of which ten had not previously been reported for this reference material. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Manuscript.</p>

published_or_final_version / Chemistry / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1990.