Ammonium perchlorate has been used as an oxidizer in solid propellants, rockets, missiles, fireworks, and some munitions. Recent advances in analytical capabilities have brought national attention to the potential for distribution of perchlorate in surface and ground water in many states throughout the Western United States. The perchlorate anion is extremely water-soluble and environmentally stable, resulting in rapid movement through groundwater and surface water. Perchlorate disrupts normal thyroid function in exposed organisms. In contrast to the wealth of human health data available for perchlorate, little data exist on the potential ecological effects of environmental perchlorate contamination.

The focus of this project was to expand the knowledge base for environmental perchlorate contamination issues using field and laboratory studies designed to characterize and quantify ecological risks associated with distribution and movement of perchlorate in ecosystems. The principal objective of this research was to examine the impact of environmental exposures of perchlorate on fish, amphibians, and mammals at the Longhorn Army Ammunition Plant.

Ecological receptors deemed to be at risk from exposure to perchlorate were identified through a number of inter-related sub-projects including analytical, terrestrial, and aquatic toxicology as well as ecological modeling. Important routes of exposure and potential food web-related exposure pathways were determined. Sensitive markers of perchlorate-related toxicity were used to assess ecological impacts of perchlorate exposure. Movement of perchlorate within abiotic and biotic components of the ecosystem was assessed with ecological modeling. Long-term risks to exposed populations were evaluated using individual-based population models driven by inputs specific to perchlorate and the site-specific abiotic conditions.

Perchlorate was found to readily accumulate in plant tissues, but it was only toxic to earthworms at very high concentrations. Perchlorate did inhibit amphibian metamorphosis and alter fish thyroid histology. Fish accumulated perchlorate in response to concentrations found in water, but perchlorate did not affect reproduction at environmentally relevant concentrations. Perchlorate could not be detected in nor did it cause deleterious effects in raccoons inhabiting a contaminated site. Finally, environmental transport and food chain models were developed for contaminated sites.

This research program was designed to identify perchlorate-related ecological risks and to develop perchlorate-specific models of exposure and toxicity useful for assessment of other contaminated sites. Models of exposure and toxicity may also be useful for evaluation of remediation techniques. Results of this research project will likely be used to help establish regulatory standards and cleanup criteria for perchlorate. (Project Completed - 2003)