Using high performance computing and visualization to enhance risk assessment methodology: case study with perchlorate

Site-specific risk assessments commonly result in large amounts of information that needs to be processed for a wide, often non-scientific, audience consisting of risk managers, regulators, and other decision makers. For this work we combined a series of models into a large virtual representation of the study system. By using a location-based approach, we were able to arrive at a more accurate determination of risk compared to just a maximum-dose approach. Caddo Lake at Longhom Army Ammunition Plant was used to study the impacts of perchlorate (C104') on thyroid hormone secretion in the channel catfish (Ictalurus punctatus). Two hypothetical contaminant plumes were modeled accounting for groundwater upwelling into the lake and effluent discharge near the surface. Results were compared between environmental systems and the three dosing techniques; maximum dose, time-lapsed maximum dose, and location-based dose. Perchlorate tissue concentrations for liver, kidney, gill, skin, muscle, GI tract, and thyroid, as well as thyroid hormone levels and secretion rates were simulated. We have shown that a standard maximum dose approach vastly overestimates exposure for individuals and populations. By simulating large numbers of individuals we are able to achieve low probability extreme events, thereby limiting the need for uncertainty factors. Through the use of commercially available graphics software Maya®, we were able to generate 3- dimensional visualizations of our study site, PBTK model, thyroid hormone secretion, catfish movement, and contaminant plumes, further aiding in data comprehension. This is the first study to generate a 3-dimensional PBTK with commercially available software, as well as use grid computing and 3-d visualization for risk assessment.