M2 - Methods for Human and Ecological Risk AssessmentChino 2 10:30 am - Noon
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| Chair(s): Randy Ryti
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M2.1 Spatially Identifying Data Gaps Using Geographical Information Systems. W.R.* Alsop, K.E. Ausanka, J.H. Samuelian; AMEC Earth & Environmental bill.alsop@amec.com
Abstract: In many hazardous waste site investigations, soil samples are collected in different phases over a long period of time, by different methodologies, different contractors, and in some cases, with differing sampling objectives. Typically, a biased soil sampling strategy is employed where more soil samples are collected in areas that are suspected to contain higher concentrations of chemicals of potential concern, or additional (or fewer) samples are collected in different areas based upon their current or presumed future use. Different sampling strategies may also be employed to characterize potential exposures to human or ecological receptors. This paper will look at different ways of combining such disparate data sets using geographical information systems (GIS) to visually identify areas within the site that need additional analytical data to (1) to minimize the uncertainty and properly assess the nature and extent of potential soil impacts, (2) to adequately characterize potential sources, and (3) to develop representative exposure point concentrations. Examples will be presented consisting of multiple spatial data sets for several compounds collected at different times with differing data quality objectives. In addition, the GIS approach can be used to identify areas within the site boundary but not necessarily associated with known (or suspected) source area(s) that have not been adequately characterized but still represent part of the exposure area for a given receptor.
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M2.2 Does the Exposure Point Concentration Software ProUCL Provide a “Reasonable and Representative” Estimate for Human and Ecological Risk Assessments? . J.H.* Samuelian, W.R. Alsop; AMEC Earth & Environmental john.samuelian@amec.com
Abstract: USEPA developed the ProUCL software (version 3; USEPA, 2004) to support their 2002 guidance for deriving Exposure Point Concentrations (USEPA, 2002). This software allows the investigator to determine which of several distributions best fits the available data. This paper will compare a number of different approaches (including ProUCL) for calculating the upper confidence limits (UCLs) of the mean chemical concentration that are used as inputs in risk assessments. Several of the central assumptions to applying any of the ProUCL calculation methods (e.g., that random sampling was performed, that the samples were derived from a single - or at least similar - distribution) may not be achievable at many waste sites. In order to test the robustness of these tools, we developed a hypothetical “true” dataset of an unspecified recalcitrant chemical for a site encompassing a total area of approximately 2,000 by 2,000 ft (about 37 hectares), which is consistent with a medium to large Superfund site undergoing remedial investigation and an ecological or human health risk assessment. The site will then be “sampled” following (1) a commonly applied biased stratified random sampling scheme and (2) an unbiased fully random sampling scheme. In both cases, bootstrap methods will be used to develop the distribution of potential means and UCLs. These results will then be compared to the results estimated using the sampling results with the ProUCL software to determine whether the exposure point concentrations estimated using ProUCL are reasonable and representative when the underlying assumptions have not been met.
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M2.3 Balancing the Risk of Bubonic Plague with the Ecological Significance of the Black-tailed Prairie Dog and the Mandates of the Endangered Species Act . M.A.* Nascarella, C.B. Pepper, S.M. Presley; Texas Tech University and Texas Commission on Environmental Quality marc.nascarella@ttu.edu
Abstract: Initially documented during the Lewis and Clark expedition, prairie dog’s were once among the most numerous mammals on the North American prairie. Increased urbanization, declining habitat, rodent population control measures and disease have recently contributed to the decline of this once abundant animal. The reduction of prairie dog populations has led to the proposal of the black-tailed prairie dog (BTPD) as a candidate for listing under the Endangered Species Act (ESA). Despite anthropogenic stress exerted on this animal, the most significant factor contributing to the decline of prairie dog populations may be the disease sylvatic plague. As an extremely sensitive host for the plague bacterium, epizootics periodically extirpate entire prairie dog colonies. Often regarded only as a disease of historical significance to humans, the plague bacterium has been identified in BTPD’s in the Texas Panhandle as recently as May 2004. This has underscored the controversy surrounding the BTPD and the need to balance the inherent risk of plague transmission to humans with the legal and scientific underpinnings of listing the BTPD under the ESA. Of immediate concern is the risk of an epizootic occurring in a BTPD colony in an urban center where there is an increased risk of disease transmission to humans. However, an additional concern is the risk of a prairie dog population decline that is followed by the listing of the BTPD as an endangered species. This later scenario would result in the economic burden of enforcement costs, conservation programs, and land use restrictions that would be indirectly engaged under the mandates of the ESA. This presentation will examine the ecological interaction of the BTPD and the plague and provide a conceptual framework for evaluating the risk of zoonotic disease transmission in BTPD colonies. Proposed solutions for reducing the risk of human disease as well as strategies for keeping the BTPD off of the ESA list will be discussed.
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M2.4 Should Ecological and Human Health Risk Assessments be Based on Similar Endpoints? . B.A. Williams, J.A. Nedoff, L.J. Kennedy; Kennedy/Jenks Consultants, Portland, Oregon, and Kennedy/Jenks Consultants, San Francisco, CA. billwilliams@kennedyjenks.com
Abstract: The goal of a Human Health Risk Assessment (HHRA) is to estimate the potential risk to humans by exposure to contaminants. While a focus of the HHRA is protection of the maximally exposed individual, an Ecological Risk Assessment (ERA) is designed to protect communities and populations of wildlife species. Under FIFRA and TSCA, ERAs are designed to characterize chemical-specific risks including potential adverse effects to local populations and communities of plants and animals (e.g., reductions in populations of fish-eating birds, or reductions in survival, reproduction, or species diversity of indigenous benthic communities). HHRA has been of paramount interest in risk assessments at most sites, but ERA has become an increasingly more important element of the risk assessment process for CERCLA sites and for other environmental assessments. While it has been generally accepted that a fundamental principle of the HHRA is to focus on individuals, this concept has often been inappropriately extended to the ERA, where the focus should be at the population level, consistent with wildlife management practices. With the focus on populations, ecological risk characterization must address the relative impact of numerous other complex parameters such as disease, predator-prey interactions, etc. When ecological risks are not presented in the context of the exposed wildlife populations, unrealistic risk estimates may result that drive poor risk management decisions. In this paper we present comparisons of selected risk drivers at sites where both HHRA and ERA were conducted.
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