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ERRORS IN APPLYING LOW IONIC-STRENGTH ACTIVITY COEFFICIENT ALGORITHMS TO HIGHER IONIC-STRENGTH AQUATIC MEDIA
Citation:
Loux, N T. AND J W. Washington. ERRORS IN APPLYING LOW IONIC-STRENGTH ACTIVITY COEFFICIENT ALGORITHMS TO HIGHER IONIC-STRENGTH AQUATIC MEDIA. Presented at 223rd American Chemical Society National Meeting, Orlando, FL, April 7-11, 2002.
Impact/Purpose:
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
Description:
The toxicological and regulatory communities are currently exploring the use of the free-ion-activity (FIA) model both alone and in conjunction with the biotic ligand model (BLM) as a means of reducing uncertainties in current methods for assessing metals bioavailability from aquatic media. While most practitioners would support the desirability of this objective, several technical questions remain to be addressed in achieving this goal.
The free ion activity (aMez+) of an ion in solution is composed of the product of the concentration of the ion ([Mez+]) times the respective activity coefficient (gMez+); i.e., aMez+ = [Mez+]gMez+. The activity coefficient represents the excess free energies associated with the interactions of the host ion with other ions and/or water molecules in solution. In sufficiently dilute salt solutions, gMez+ equals 1.