An Index of the Ecological Impacts of Water Toxics Emitted to Freshwater Ecosystems

ABSTRACT

We describe a composite freshwater Aquatic Toxicity Index (ATI) for chronic toxicity conditions that can be easily computed for a broad range of chemicals. The ATI expresses the potential toxic impact of chemicals on the ecosystem, scaling the potency of each chemical with respect to a reference compound (1,4 dichlorobenzene). It is based on a simple stochastic process model and a few inherent properties of each chemical, such as chronic toxicity, adsorption coefficient to sediments, and Henry's Law constant. Our goal is to provide a simple compartmental model for obtaining a rough quantitative assessment of the life-cycle environmental impact of life-cycle emissions inventory data.

To illustrate the potential of our approach we compare the ATI index, for a small set of chemicals, with comparable measures of freshwater aquatic ecotoxicity potential and freshwater sediment ecotoxicity potential obtained by others using the European-based impact assessment tool USES-LCA, which is based on a more elaborate fate and transport model. The rank correlation between the ATI and USES-LCA indices is greater than 0.85, showing surprisingly good agreement given the simple nature of our model. More analysis of the differences between ATI and the results of other models is needed, but these results suggest that our model may be useful for priority setting and meta-modeling applications.

Key Words:

• life-cycle impact assessment
• water toxics
• chronic toxicity
• ecotoxicity potential.

ACKNOWLEDGMENTS

We are grateful to Patricia Harrigan and Charles Tamulonis at the USEPA Office of Science and Technology for providing us with additional toxicity data. We also thank David Pennington and two anonymous reviewers for their helpful comments on this article.