# Presentation: 817914

## Ecological Impact/Transport and Transformation ofPerchlorate

- Mr. Cornell Long, USAF
- Dr. Ron Porter, USAF
- Dr. Mark Sprenger, USEPA
- Dr. Clarence Callahan, USEPA

## Introduction

- Background
- Fate and Transport of perchlorate
- Historical Studies
- Potential ecological receptors
- Observed Effects
- Proposed Activities and EPA Framework
- Discussion

## Background

- Perchlorate salts have low volatility, but high solubility
- Solubility leads to high mobility in aqueous systems
- Surface water
- Groundwater
- Mobility and persistence may pose a threat to ecological receptors

## Slide 4

## Exposure Model

## Fate and Transport(Transport and Transformation)

- What happens to perchlorate in the environment?
- Physical characteristics
- Attenuation processes
- What are the data gaps?

## Physical Characteristics

- Vapor Pressure--no values found in literature
- Volatilization not expected to be predominant pathway
- Density--1.95 g/mL
- Will sink in water
- Concentrated solutions also more dense than water

## Physical Characteristics

- Solubility--20.2 g/100g solution
- Dissolution expected and perchlorate ion will predominate in solution
- Potential for potassium salt to precipitate--function of ion concentrations
- Standard potential--reduction for Cl from +7 oxidation state to -1
- All values positive which indicates the reaction is thermodynamically favored

## Physical Characteristics

- Standard potential
- ClO4**-** + 4H2            4H2O + Cl**-**
- Little evidence that reaction occurs spontaneously
- Reduction rate negligible at room temperature
- Conclusion:  Perchlorate is kinetically stable (most stable oxo-compound of chlorine)

## Mobility of Perchlorate

## Attenuation Processes

- Dilution
- Precipitation
- Biological or chemical reduction
- Adsorption
- Ion-exchange

## Attenuation Processes

- Dilution--concentrations expected to be significantly lower away from the source
- However, function of the inert binder may influence source area concentrations
- Precipitation
- Potassium less soluble, could lead to subsurface precipitation; long-term source area, near source area, and far source area re-dissolution

## Mobility of Perchlorate

## Attenuation Processes

- Biological or chemical reduction
- Perchlorate reduction can occur at metal surfaces under acidic pH; however, inhibition by competing anions a problem
- Sorption
- Perchlorate absorbs weakly to most soil minerals (NO3- and Cl- more favorable)
- Minimal impact inhibiting mobility

## Summary

- Perchlorate is very soluble
- Very stable at low concentrations
- Very inert ion
- Some potential for precipation in subsurface
- Reduction and sorption occurs to a lesser extent

## Data GapsGeneral

- Binder Effects
- Binder chemical degradation rates?
- Leachability from binder?
- Concentration of binder + other contaminants?
- Role of reduction and interaction of Cl04 with subsurface soils

## Data GapsSite-Specific

- Soil properties
- Hydrology
- Infiltrating groundwater
- Characterization of leachates produced from source and near source soils

## Contact

- Cornell Long
- Det 1, HSC/OEMH
- 2402 E Drive
- Brooks AFB, TX 78235-5114
- 210-536-6121     Fax 1130
- cornell.long@guardian.brooks.af.mil