|Abstract or Summary
- There are many links between exposure to environmental pollution and risks to human health. While advances in the fields of toxicology, exposure science, and environmental chemistry have shown light on many of these links, many more research challenges remain. One major challenge is how to accurately characterize the toxicity of a mixture of chemical pollutants. There is evidence to suggest that assuming the toxicities of chemicals in a mixture are additive is an oversimplification. Additionally, there are many chemicals that are commonly found in the environment or that are potentially toxic, but that remain under-studied. All of these caveats apply to polycyclic aromatic hydrocarbons (PAHs). Another challenge is how to best quantify an individual’s exposure to environmental pollutants. Traditionally this is done using a combination of self-reported exposure information from questionnaires, extrapolation of data from stationary monitors to the exposures of mobile individuals, and occasionally data from personal monitors. Passive sampling is an effective tool for measuring the fraction of chemical pollutants people are exposed to in the environment. The work presented in this dissertation uses passive sampling to measure PAH contamination in air, water, and the personal environment, and to predict PAH concentrations in crayfish. It also estimates carcinogenic human health risks associated with exposure to this PAH contamination. Shellfish contamination data is needed for use in consumption advisories. However, existing methods of measuring this contamination are often prohibitively time and resource-intensive. It has been observed that passive samplers, coupled with predictive models, can accurately estimate PAH contamination in shellfish. In Chapter 2 we further validated the ability of passive water samplers and predictive models to predict PAH contamination in the resident signal crayfish, Pacifastacus leniusculus. This work was conducted within and outside of the Portland Harbor Superfund Megasite. We estimated PAH concentrations in crayfish from PAH concentrations measured by passive samplers in water, using a simple linear regression model that included 34 PAHs. The model predicted PAH concentrations in crayfish within an average factor of 2.4 of PAH concentrations that were measured in crayfish. Additionally, we observed substantially higher PAH levels, and carcinogenic PAH levels, in crayfish visceral tissue than in crayfish tails. This indicated that eating only the tail of a crayfish would drastically reduce a consumer’s cancer risk compared to eating the whole crayfish. We also demonstrated the importance of appropriately characterizing the toxicity of chemical mixtures. For instance, benzo[c]fluorene was identified as the main contributor to carcinogenic potency in crayfish tissues. However, this PAH is not traditionally included in analyses of environmental samples. Additionally, we saw strikingly similar profiles of carcinogenic PAHs in crayfish tissues collected in this Superfund site in 2003 and 2013. This demonstrated that there are chemical mixtures that commonly occur at this Superfund site. Knowing this could enable researchers to drastically reduce the number of chemical mixtures to prioritize for toxicological study. Natural gas extraction (NGE) activity has expanded rapidly in the U.S. in recent years. This rapid expansion has been met with minimal study of potential environmental or health effects, leading to concern among scientists and the public. In Chapters 3 and 4 we present two studies assessing the impact of NGE on environmental PAH levels, in a community heavily affected by the recent natural gas boom. In Chapter 3 we used passive air samplers to assess how proximity to the nearest active NGE well affected PAH concentrations in ambient air. In this study we saw decreasing PAH concentrations, as well as carcinogenic PAH concentrations, as air samplers moved farther from active NGE wells. We also saw predominantly petrogenic signatures of PAH mixtures measured closer to NGE wells. This suggested that measured PAH mixtures were impacted by fugitive emissions of PAHs during NGE, and that this impact was stronger closer to active NGE wells. In Chapter 4, we more thoroughly assessed spatial patterns of PAH concentrations in air using passive air samplers, at sites with and without active NGE wells. In this study we observed higher PAH concentrations in air at sites with NGE wells than at sites without. Again, we saw more petrogenic PAH mixtures at sites with active NGE wells than at sites without wells. This gave us further evidence that PAH mixtures in air near NGE wells are affected by direct releases from the earth during NGE. In this study we also assessed the impact of NGE on the personal PAH exposure of people living and working in this community. We did this using a novel personal passive sampler, the silicone wristband. PAH concentrations measured in wristbands demonstrated that living or working closer to an active NGE well was associated with increased PAH exposure. However, all carcinogenic PAH concentrations measured in air in both NGE studies were below the U.S. EPA’s acceptable threshold. Thus, even the highest carcinogenic PAH concentrations measured in air closest to NGE wells would not be expected to increase lifetime cancer risk of people living or working nearby above background risk levels. The work presented in this dissertation further validates the ability of passive samplers to predict PAH contamination in crayfish, provides evidence for PAH emissions coming from NGE, and comments on the estimated health risks associated with exposure to these PAH mixtures. Taken together these findings help solve the current challenges in environmental toxicology research, and provide ideas for solving the remaining challenges facing this field.
- There are many links between exposure to environmental pollution and risks to human health. While advances in the fields of toxicology