Date on Master's Thesis/Doctoral Dissertation

5-2012

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Environmental and Occupational Health Sciences

Committee Chair

Tollerud, David John

Author's Keywords

Population exposure; Mercury bioaccumulation; Biomarkers of exposure; Fish tissue mercury; Land cover characteristics; Stream systems

Subject

Mercury--Environmental aspects; Mercury wastes--Environmental aspects; Biochemical markers

Abstract

Human exposure to mercury has been shown to cause a number of adverse health outcomes, predominantly neurological effects. The developing fetus is most susceptible, and even low levels of exposure have been shown to produce nervous system deficits. A systems approach was used to address the problem of human exposure to mercury from the consumption of contaminated fish from local waterways. Two models were developed in order to link environmental levels of mercury with human exposure. The human exposure model characterizes the disposition of mercury in the human body and fetus. The bioaccumulation model tracks the movement of mercury from water column to fish tissue. The two models were combined in order to evaluate the outcome of potential policy scenarios. The human disposition model projects mercury concentrations in common biomarkers of exposure in response to mercury concentrations in fish. The model predicts biomarkers for fish consumption rates representing the mean, 90th, 95th, and 99th percentiles of populations of interest. Water quality and basin characteristics were inputs into the bioaccumulation model and fish tissue mercury the output. Mean average prediction error for calibration sites was 26% and 51 % for evaluation sites. Sensitive parameters influenced the system at several points and included forested and wetlands coverage, and nutrient levels. Less sensitive parameters modified the system at only one point and included the total mercury input and the portion of the basin that is developed. The two models were combined and the impacts of potential policies were analyzed. Evaluated policy scenarios included fish consumption advisories, emissions reductions, and watershed management strategies. Simulations indicated the characteristics of a basin combined with the unique pattern of intake rates of susceptible populations determine the risk associated with fish consumption from a given waterway. Each population had a unique pattern of biomarker response to changes in fish tissue mercury. Bioaccumulation efficiency, a result of basin characteristics, determined the responsiveness of a basin to reductions in loading. Management strategies that lowered bioaccumulation rates lessened ecosystem services to an unacceptable degree. Targeting systems with greater bioaccumulation efficiency for reductions in loading would provide the benefit of reduced contamination and greater services.

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