<p> The adverse effects of air pollution on human life is of serious concern for today&rsquo;s society. Two population groups that are especially vulnerable to air pollution are pregnant women and their growing fetuses, and the focus of this thesis is to study the effects of air pollution on these populations. In order to address the methodological limitations in prior research, we quantify the impact of air pollution on various adverse pregnancy outcomes, utilizing machine learning and novel causal inference methods. Specifically, we utilize two semi-parametric, double robust, asymptotically efficient substitution estimators to estimate the causal attributable risk of various pregnancy outcomes of interest. Model fitting via machine learning algorithms helps to avoid reliance on misspecified parametric models and thereby improve both the robustness and precision of our estimates, ensuring meaningful statistical inference. Under assumptions, the causal attributable risk that we estimate translates to the absolute change in adverse pregnancy outcome risk that would be observed under a hypothetical intervention to change pollution levels, relative to currently observed levels. The estimated causal attributable risk provides a quantitative estimate of a quantity with more immediate public health and policy relevance.</p><p>

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Freshwater teleost fish often experience natural and anthropogenic conditions that result in fluctuating energy availability, therefore the ability to acquire, transform and use energy is essential for the survival of these fish. Polychlorinated biphenyls (PCB's) are recognized as physiological sources of stress to fish as they incite defense mechanisms that are generally costly in terms of metabolic resources. Over time, such responses may decrease individual performance and possibly fitness by changes in foraging, migration and escape behaviors, and the population in terms of reproductive capacity due to the alterations in energy allocation following an exposure. The main goal of this study was to determine if a sublethal exposure to PCB-126 affects the energy budget of the fish and can therefore be responsible for functional deficiencies associated with their locomotion. Fish were injected low (100 mug/kg) and high (400 mug/kg) concentrations of PCB-126 and swimming performance parameters including critical swimming speed, metabolic rate and recovery ratios were evaluated. EROD activity was also measured in the liver as an indication of PCB-126 intoxication while blood and white muscle tissue metabolites were analyzed to quantify the physiological disturbance levels associated with this exposure. A significant decrease was observed in the swimming performance of rainbow trout for the low and high PCB-126 treatments as well as an impaired recovery with increasing level of PCB exposure following exhaustive exercise. This study also showed the occurrence of physiological disturbance by a reduction in the hepatosomatic and spleen somatic indices and elevation of plasma cortisol and glucose levels, as well as white muscle reductions in glucose and glycogen indicating higher metabolic costs during recovery and muscle restoration for PCB-exposed fish. Overall, this research provides insights into the sublethal effects of toxic organic compounds on fish.

Cyanobacteria produce toxic compounds with the hepatotoxic microcystins being the most commonly encountered in freshwater. Microcystins are produced by several cyanobacterial genera and show large spatial and temporal variation in aquatic ecosystems as both toxigenic and non-toxigenic strains may co-exist and reach bloom levels. The regulation of microcystin production, the ecological or physiological role(s) of microcystins, and the factors that specifically promote toxic cyanobacterial blooms are not yet well understood. The first part of this thesis tested the role of light intensity in regulating the production and composition of microcystin congeners using laboratory culture experiments. The second part, using field observations and a lake enclosure experiment, examined the effects of physical, chemical and biological variables on microcystin concentrations and the growth of toxigenic cyanobacteria in a shallow, mesotrophic lake. Throughout, chemical and molecular based methods were utilized along with traditional culture and limnological methods in order to measure microcystin production and the presence of toxigenic cyanobacteria. Light intensity had a significant effect on microcystin concentrations and congener composition. However, there were no clear advantages of either toxigenic or non-toxigenic strains in terms of their ability to grow, compete for light resources, or dominate in a mixed-culture setting. The response of each strain of Microcystis aeruginosa was unique such that generalizations could not be made between toxigenic and non-toxigenic strains in terms of their competitive ability in nature; microcystin production did not appear to impair the competitive ability of toxigenic strains. In field studies of a shallow mesotrophic lake over two years, the number of microcystin gene copy numbers (mcyD) did not correlate well with microcystin concentrations. Both within the lake and across a nutrient gradient established in in situ enclosures, the best predictor of the presence of toxigenic strains was the actual biomass of potentially toxigenic genera (mainly Anabaena and Microcystis ), rather than any particular chemical or physical variable such as light. However, both environmental and biological variables were significant in predicting actual microcystin concentrations. The combination of molecular, chemical, and taxonomic data appears necessary to understand and predict toxic cyanobacterial blooms.

Antagonists have been crucial in the characterization of nicotine's pharmacology. Initial evidence for the existence of central nicotinic receptors was based on the fact that nicotine produced a number of behavioral effects that were antagonized by ganglionic blockers that crossed the blood-brain barrier, such as mecamylamine and pempidine. Although the mechanism of action of these compounds has been studied extensively in the periphery, little is known about their mechanisms of action in the brain. These compounds are thought to be noncompetitive antagonists due to the fact that they do not compete for agonist binding to brain homogenate in vitro. However, pharmacological evidence in support of noncompetitive antagonism is lacking. Dose-response curves for nicotine were determined in the presence of various doses of pempidine for depression of spontaneous activity and antinociception in mice. Pempidine was found to shift the dose-response curves for these effects of nicotine in a manner consistent with noncompetitive antagonism. A number of mecamylamine analogs were investigated for antagonism of these central effects of nicotine as well. These studies revealed that the N-, 2-, and 3-methyls were crucial for optimal efficacy and potency and suggests that these compounds possess a specific mechanism of action, possibly involving a receptor. Furthermore, the structure-activity relationships for the mecamylamine analogs were found to be different than that previously reported for the agonists, suggesting that they do not act at the same site. The binding of [3H]-L-nicotine and [3H]-pempidine was studied in vitro to mouse brain homogenate and in situ to rat brain slices. The in situ binding of [3H]-L-nicotine to rat brain slices was quantitated autoradiographically to discrete brain areas in the presence and absence of 1, 10 and 100 µM nicotine and pempidine. Pempidine did not effectively displace [3H]-L-nicotine binding. The studies with [3H]-pempidine failed to demonstrate saturable binding. The evaluation of the antagonism of nicotine by mecamylamine and pempidine presented in this thesis supports a noncompetitive action of these compounds in the brain. The shift in the dose-response curves for nicotine, the structure-activity relationship for mecamylamine analogs and the binding studies are consistent with this hypothesis. The noncompetitive nature of these compounds suggests that they do not compete for the binding site of the agonist, and that endogenous nicotinic antagonists may exist in the brain.

Arecoline and nicotine are two psychoactive cholinergic alkaloids. Arecoline is primarily a muscarinic agonist while nicotine, at low doses, is a nicotinic agonist. The experiments in this dissertation investigated two major areas: (1) the role of different factors in the development of tolerance to the behavioral effects of arecoline and nicotine, and (2) the possible mechanism and site of action of the discriminative stimulus (DS) effects of arecoline and nicotine. The role of dispositional and physiological factors comfiared to behavioral factors in the development of tolerance to the effects of arecoline and nicotine on operant behavior was assessed in Experiments I and II, respectively. In part one of Experiment I, rats were trained to respond (M1 a variable-interval 15 second (VI-15) schedule for milk reinforcement. Dose-effect relationships were assessed prior to and during chronic arecoline (1.74 mg/kg/day) treatment. After 21 days Of arecoline administration prior to the session, the dose-effect relationship for total responses was not shifted. However, the dose-effect relationship for total reinforcements was shifted to the right. In part two of Experiment I, rats were trained to respond on a fixed-ratio 20 (FR-ZG) schedule for milk reinforcement. Dose-effect relationships were assessed prior to and during chronic arecoline (0.87 mg/kg/day) administration. One group of rats received daily injections of arecoline prior to the seSsion and a second group received arecoline injections after the session. Daily administration of arecoline resulted in a greater shift to the right of the dose-effect relationship in the pre-session group compared to the post-session group. These data demonstrate the importance cflf behavioral factors in the development of tolerance to arecoline. In Experiment II, rats were trained to respond on a VI-15 second schedule of milk reinforcement. Dose-effect relationships were determined prior to and during chronic nicotine (2.28 mg/kg/day) administration. One group of rats received daily injections Of nicotine prior to the session, another group received nicotine injections after the session. After 36 days of chronic treatment, similar degrees of tolerance were observed in both groups, however the group receiving post-session nicotine developed tolerance at a faster rate. The data suggested that 21 complex interaction of nicotine and the experimental environment affected the rate of tolerance development. Experiment III characterized the DS effect of arecoline. Using a two-lever operant paradigm, rats were trained to discriminate arecoline from saline on a VI-12 second schedule of milk reinforcement. Rats could learn to discriminate 1.74 mg/kg arecoline from saline, but not 0.58 mg/kg from saline. Agonist and antagonist studies demonStrated that the DS effect of arecoline is mediated through central muscarinic receptors. In Experiment IV, the ability of physostigmine to interact fiith the DS effect of nicotine (1.14 mg/kg) and arecoline (1.74 mg/kg) was assessed. Physostigmine (0.125 mg/kg) pretreatment shifted the dose-effect relationship for arecoline to the left but did not affect that of nicotine. Physostigmine (0.25 mg/kg) almost completely generalized to the DS effect of arecoline but not to the DS effect of nicotine. These data suggest an interaction of endogenous acetylcholine with muscarinic receptors but not with nicotinic receptors. In Experiment V, the ability hf arecoline and nicotine injected directly into the dorsal hippocampus (DH) and mesencephalic reticular formation (MRF) to generalize to the DS effect of peripherally administered arecoline (1.74 mg/kg) and nicotine (1.14 mg/kg) was assessed; Nicotine injected into these sites generalized in a dose-related manner to nicotine. The MRF was slightly more sensitive than the DH. Arecoline injected into either site did not generalize to the DS effect of, peripherally administered arecoline. However, a decrease in response rates was observed.

The access of drugs to variofis sites of action in the body is impeded by a succession of membranes. Likewise, the removal of a drug or foreign substance from the body is similarly dependent on the ability of the substance under consideration to permeate biological barriers. A con-committant problem generally arises concerning the overall time course of drug action: that of drug storage through binding or similar processes. Schanker (196h) however, has stated that "Although the mechanisms of localization and those of membrane transfer are in many respects different problems, there are some instances in which they are inseparable parts of the same problem." Examples include phenomena whereby the binding of a substance to the cell membrane is required for transport (Rosenberg and Wilbrandt, 1955; Peters; 1960; Lacko and Burger, 1961; Schwartz and Matsui, 1967; Stein, 1967). From a functional standpoint, body membranes may be classified in three major categories (Schanker, 1962b); membranes several cell layers thick such as skin, those one cell layer thick such as the brush border epithelium of the intestine, and membranes less than one cell in thickness such as the cell membrane itself or the membranes of organelles (e.g. mitochondria). Thus, except for the barriers associated with subcellular structures, the cell membrane 6 (or plasma membrane as it is often called) may be considered the fundamental unit of body membranes in general.

Hormesis is a nonlinear dose-response characterized by biological responses at low doses that are opposite to those observed at higher doses. Studies and review articles on hormesis are being published at an increasing rate by researchers from diverse disciplines and debate has emerged over the role hormesis in risk assessment. As a result, a survey was conducted to assess toxicologists and risk assessors knowledge and attitudes about the hormesis dose response. Study goals were to: (1) ascertain attitudes towards hormesis and other dose-response models, (2) identify whether acceptance or rejection of hormesis is based on knowledge of hormesis, predisposing values, or demographic characteristics, and (3) evaluate potential for response bias. The survey consisted of 44 questions pre-tested by 25 toxicologists and risk assessors. The survey was distributed via email to the membership of the Society of Toxicology and the Society for Risk Analysis, 9,500 potential respondents. The overall response rate was 17% (n= 1,463) with a completion rate over 87%. Major findings were that 50% of respondents indicated sufficient data exist to support the view hormesis occurs across a wide range of species and endpoints, 59% indicated evaluating potential benefits due to hormesis should be included in risk assessments, and 65% are in favor of modifying hazard assessment protocols to identify the presence of hormesis. Respondent characteristics such as: years of experience, society membership, education, residence, employment (excluding government and pharmaceutical companies), and political, economic or social views had little influence on opinion. One of the largest positive influences was experience with hormesis based on actual research; 79% of subjects who reported observing hormesis commonly in their studies agreed hormesis is broadly generalizable. The influence of non-response bias was evaluated through several internal and external measures. Despite a lower than hoped for response rate, but because of robust external validity measures, it is concluded that respondents’ opinions are likely a reasonable representation of the societies of which they are members. Because this is a baseline survey, a follow-up survey is in order. Future survey design should separately evaluate the science of dose-response from the regulatory approach to risk assessment.

Environmental mercury pollution of the Valley of a Thousand Hills area of KwaZulu-Natal, South Africa, in particular the river system below the Thor Chemicals mercury recycling plant, has been a topic of heated debate for a number of years. Thor Chemicals was established as a mercury recycling plant in the mid-1980' s and it processed mercury waste imported from various countries. A number of factory workers were subsequently exposed to high levels of mercury vapour causing the death of a worker. Upon investigation it was found that in addition to the occupational exposures of workers, mercury waste had been discharged into the river systems of the Valley of a Thousand Hills. During the 1998 South African Parliamentary session, questions were raised regarding the lack of adequate monitoring and research directed at quantifying human health risks in the region. A number of Government departments were accused of apathy and incompetence in adequately addressing the issue. Fish forms an important part of the diet of the local community living in the Valley of a Thousand Hills. Children, in particular, are frequently observed fishing in the rivers, thus placing these individuals at risk should the fish be contaminated with mercury. The aims of this study were: to determine the extent of environmental mercury pollution of the river system downstream from the Thor Chemicals plant, and to quantify the human health risk associated with fish consumption in the region. Samples of streambed sediment, algae, cattle hair, fish and human hair, were obtained from the study area as well as from a control area upstream from the Thor Chemicals plant. These were analysed to determine the concentration of mercury in each sample. Mercury levels in the study group were compared to mercury levels in the control areas.

Marbled salamanders (Ambystoma opacum) have individually variable dorsal pigmentation patterns. But it is unclear whether or not dorsal pigmentation is associated with variables such as body size and sex. In this study, we test the hypothesis that the body size variables and sex are important predictors of the coverage of dorsal body white pigmentation in adult marbled salamanders. We evaluate the degree of sexual dimorphism in several body traits, including the dorsal body white pigmentation, using univariate and multivariate methods, and analyze the sex-related difference in pigmentation asymmetry. The General Linear Model (GLM) predicts a significant main effect of sex and a significant interaction between sex and dorsal body area (DBA), influencing the coverage of dorsal body white pigmentation. The interaction effect is greater in males than in females. We show significant sex-related differences in body size and shape. Eight morphometric traits reveal female-biased sexual size dimorphism, while males display a greater coverage of dorsal white pigmentation than females. Prominent female characteristics, compared to males, include a significantly heavier and longer body with a wider trunk, head, neck, shoulder and waist. These sex-specific differences suggest selection for a larger body size in females because of increased maternal reproductive success associated with larger body size. Additionally, females display greater pigmentation asymmetry than males, suggesting a significant sex-related disparity in asymmetric pigmentation. Potential ecological and developmental implications of the observed dimorphism are discussed. To our knowledge, this is the first study demonstrating an association of dorsal white pigmentation with dorsal body area and sex, including a significantly disproportionate pigmentation asymmetry between sexes, in adult marbled salamanders.