Preliminary risk assessment of the Mexican Spotted Owl under a spatially-weighted foraging regime at the Los Alamos National Laboratory

Abstract

The Record of Decision on the Dual Axis Radiographic Hydrodynamic Test Facility at the Los Alamos National Laboratory requires that the Department of Energy takes special precautions to protect the Mexican Spotted Owl (Strix occidentalis lucida). In order to do so, risk to the owl presented by radiological and nonradiological contaminants must be estimated. A preliminary risk assessment on the Mexican Spotted Owl in two Ecological Exposure Units (EEUs) was performed using a modified Environmental Protection Agency Quotient method, the FORTRAN model ECORSK4, and a geographic information system. Estimated doses to the owl under a spatially-weighted foraging regime were compared against toxicological reference doses generating hazard indices (HIs) and hazard quotients (HQs) for three risk source types. The average HI was 0.20 for EEU-21 and 0.0015 for EEU-40. Under the risk parameter assumptions made, hazard quotient results indicated no unacceptable risk to the owl, including a measure of cumulative effects from multiple contaminants that assumes a linear additive toxicity type. An HI of 1.0 was used as the evaluative criteria for determining the acceptability of risk. This value was exceeded (1.06) in only one of 200 simulated potential nest sites. Cesium-137, Ni, {sup 239}Pu, Al and {sup 234}U we`re among the constituents with the highest partial HQs. Improving model realism by weighting simulated owl foraging based on distance from potential nest sites decreased the estimated risk by 72% (0.5 HI units) for EEU-21 and by 97.6% (6.3E-02 HI units) for EEU-40. Information on risk by specific geographical location was generated, which can be used to manage contaminated areas, owl habitat, facility siting, and/or facility operations in order to maintain risk from contaminants at acceptably low levels.