Date of Award

Fall 1998

Document Type

Thesis

Degree Name

Master of Science in Environmental Science - (M.S.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

Lisa Axe

Second Advisor

Trevor Tyson

Third Advisor

Daniel Watts

Abstract

An ecological risk assessment process requires a modeling tool that can adapt to changing environmental conditions. Computer simulation tools are a useful means to develop an ecological risk assessment, because if properly used they can provide an organized framework to evaluate multiple data sources, complex problems and hypotheses. An evaluation was completed of the University of Tennessee CHEMS-1 model that ranks and scores contaminant toxicity and exposure potential. Tantalum posed less of a hazard than hexavalent chromium to the terrestrial and aquatic animals. Although, results indicated that the vanadium compounds, in particular vanadium pentoxide, presented the greatest hazard, with hexavalent chromium following. A significant limitation of this model is that only two animals are used to assess ecosystem toxicity. Furthermore, due to multiple toxicity data and therefore uncertainty, many hazard values overlapped. Overall, the model is qualitative and cursory at best, and is not recommended as a tool for ecological risk assessment.

In the RESRAD-ECORISK model, a transport model is linked to the ecological risk model for soil contamination. This model is limited to five receptors: American robin, mallard, white-tailed deer, white-footed mouse, and the eastern cottontail. (A code problem currently being addressed by the developers prevented risk assessment of the mallard.) Risks are categorized into four groups ranging from potential to an extreme adverse risk. The code also includes a sensitivity analysis. Applying this model revealed risks posed to receptors were found to be greatest for the American robin, where all metals resulted in extreme adverse effect risk characterization. While extreme risks were found for the eastern cottontail and white-footed mouse from exposure to vanadium, moderately high risks were observed from exposure to Cr(VI). On the other hand, the White-tailed deer received the least amount of risk from these contaminants, where all risk resulted as "potential". Based on vanadium and chromium (VI) surrogates, tantalum and molybdenum, respectively, contaminated soil presented a limited risk to the deer, while tantalum contaminated soil posed a greater risk to the rabbit and mouse than molybdenum contamination.

The third model, the Columbia River Comprehensive Impact Assessment (CRCIA), included the most comprehensive ecological habitat of the models evaluated. Risk in this model is divided into two categories; a site requires further assessment when a potential risk exists, which was the case for terrestrial and aquatic plants when exposed to any contaminants. Overall risks posed by the metals followed the order of Cr> V > Ta > Mo. Only three (of the twenty) terrestrial animals were at risk; the muskrat and raccoon were at potential risk from vanadium and tantalum, and the American coot was at risk from hexavalent chromium. Therefore, because of the multiple receptors at potential risk, CRCIA protocol would deem further assessment of the contaminated site applying stochastic risk assessment methods.

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