Graduation date: 2006

Fecundity, defined as the biologic capacity for reproduction, is measured operationally as time-to-pregnancy (TTP) among non-contracepting couples. While most couples conceive naturally within six menstrual cycles of trying, 10-24% of couples take longer than six cycles. Fecundity impairments are associated with long-term adverse health consequences including insulin resistance and gynecologic cancers, can cause substantial psychological and economic hardship, and cost over $5 billion annually in the U.S. Therefore, identifying risk factors for subfecundity in order to increase the chances of natural conception among pregnancy planners is an important public health goal. Environmental and psychosocial risk factors are understudied in relation to reproductive health. The goal of this dissertation is to examine the independent associations between exposure to tetrachloroethylene, perceived stress, and cigarette smoking and fecundability, the per cycle probability of conception. In study one, we used data from a retrospective cohort study of Cape Cod women who were exposed to tetrachloroethylene-contaminated drinking water in the 1960s-1980s to examine the relation between tetrachloroethylene exposure and fertility. We found that women with the highest modeled tetrachloroethylene exposure around the time of the pregnancy attempt had increased risk of TTP>12 months compared with unexposed women. Cumulative exposure, however, was not associated with elevated risk of TTP>12 months. Studies two and three used data from Pregnancy Study Online (PRESTO), a preconception cohort study of pregnancy planners from North America. In study two, we found that perceived stress levels in women, but not their male partners, were associated with lower fecundability, with little evidence of mediation by measured behavioral factors. In study three, we found that male current active smoking was associated with lower fecundability. In women, current smoking was only associated with reduced fecundability among women who smoked with high intensity and/or long duration. Passive smoking was not substantially associated with fecundability in either partner, but women exposed in utero to high intensity smoking had lower fecundability than unexposed women. Overall, we observed weak associations between tetrachloroethylene exposure, perceived stress, and active smoking and fertility among pregnancy planners. These findings indicate that environmental and psychosocial factors may play a role in the etiology of infertility. In addition, given that these exposures are common and modifiable, they may be important targets for public health interventions.

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This work focused on using a microbubble dispersion to deliver hydrogen and carbon dioxide to anaerobic consortia to stimulate their ability to reductively dehalogenate tetrachloroethylene all the way to ethene and ethane. A continuous flow system, consisting of six anaerobic soil column bioreactors, inoculated with sediments from Virginia Tech's Duck Pond, was used for this study. Two columns received microbubbles containing hydrogen and carbon dioxide, two received sodium propionate, and two were not fed a substrate. A 30 micromolar PCE solution was delivered to the consortia at 3 ml/min. Microbubbles containing a mixture of 90% hydrogen and 10% carbon dioxide were effectively produced in a closed spinning disk generator, and were acceptable for delivering the gases to the columns. After the biodegradation study was completed, the microbubbles were found to have a pH of 4.4, due to the carbon dioxide. Microbubbles amended with NaOH to 0.01 molar yielded pH neutral microbubbles with improved stability. Methane was measured in all six columns throughout the experiment, verifying that methanogens were present. Methane levels were highest in the propionate columns, showing the the methanogens there were more active. Methane levels in the microbubble columns were similar to those in the control columns. Propionate and acetate were not detected in the columns where propionate was fed, showing that proton reducers and acetoclastic methanogens were both active. Recovery of PCE and the degradation products was almost 90% in the microbubble and control columns where most of the PCE was recovered in the effluent. The predominant product in both systems was TCE, although some ethene was detected in all four columns. The control consortia produced TCE averaging about five micromolar while the microbubble columns averaged about two micromolar TCE. One of the components of the microbubbles probably caused the lowered amounts of PCE reduction. That some ethene was seen in the microbubble columns suggests different conditions can be found to stimulate the further reduction of PCE with hydrogen and carbon dioxide microbubbles. The product recovery in the propionate columns was about 64%. Over half of the injected PCE was dechlorinated to ethene and ethane. / Ph. D.

For this study, we revisited whether the common iron Fe mineral, magnetite Fe3O4 (s), can reduce tetrachloroethylene (PCE) and trichloroethylene (TCE) as discrepancies exist in the literature regarding rates and extent of reduction. We measured PCE and TCE reduction in batch reactors as a function of magnetite stoichiometry (x = Fe2+/Fe3+ ratio), solids loading, pH, and Fe(II) concentration. Our results show that magnetite reacts only slowly with TCE (t1/2 = 7.6 years) and is not reactive with PCE over 150 days. The addition of aqueous Fe(II) to magnetite suspensions, however, results in slow, but measurable PCE and TCE reduction under some conditions. The solubility of ferrous hydroxide, Fe(OH)2(s), appears to play an important role in whether magnetite reduces PCE and TCE. In addition, we found that Fe(OH)2(s) reduces PCE and TCE at high Fe(II) concentrations as well. At certain conditions degradation of the PCE and TCE is enhanced by an unexplored synergistic response from magnetite and ferrous hydroxide iron phases. Our work suggests that measuring dissolved Fe(II) concentration and pH may be used as indicators to predict whether PCE and TCE will be abiotically degraded by groundwater aquifer solids containing magnetite.

Tetrachloroethene (PCE) is a major groundwater contaminant that often persists as dense, nonaqueous phase liquids (DNAPLs) in subsurface environments. Dissolved-phase PCE plumes emanate from DNAPL source zones, which act as continuous sources of contamination for decades. Removal of DNAPL source zones is crucial to achieve lasting remedy of contaminated aquifers. This research explored the contributions of the microbial reductive dechlorination process (i.e., anaerobic bioremediation) to PCE-DNAPL source zone remediation, either in isolation or as a polishing step for the removal of residual DNAPL remaining after application of surfactant enhanced aquifer remediation (SEAR), an emerging physical-chemical source zone treatment. Specific objectives of this research were to: (1) evaluate the ability of microorganisms to dechlorinate in the presence of PCE-DNAPL and at high dissolved-phase PCE concentrations expected near/in DNAPL source zones, (2) assess the distribution and activity of key dechlorinating populations during bioenhanced PCE-DNAPL dissolution in continuous-flow column experiments, (3) determine the influence of Tween 80, a biodegradable surfactant commonly used in SEAR, on the microbial reductive dechlorination process, (4) design and optimize quantitative real-time PCR (qPCR) protocols to detect and enumerate key dechlorinating populations (e.g., Geobacter lovleyi, Sulfurospirillum multivorans), and (5) explore the effects of oxygen on Dehalococcoides viability and biomarker quantification. This research demonstrated that microbial dechlorinating activity within DNAPL source zones promotes bioenhanced dissolution although many dechlorinating isolates cannot tolerate saturated PCE concentrations. Application of newly designed qPCR protocols established a direct link between dissolution enhancement and the distribution of relevant dechlorinating populations in the vicinity of PCE-DNAPL. The limited and reversible impact of Tween 80 on key dechlorinators supported the feasibility of a treatment train approach of SEAR followed by microbial reductive dechlorination to remediate PCE-DNAPL source zones. Finally, experiments with oxygen-exposed, Dehalococcoides-containing cultures suggested limitations of using Dehalococcoides DNA and RNA biomarkers for monitoring bioremediation at field sites. These findings advance the scientific understanding of the microbial reductive dechlorination process and are relevant to environmental remediation practitioners. The advantages and current shortcomings of PCE-DNAPL source zone bioremediation, as well as recommendations for future research, are discussed.

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