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T8 PM Measurement/ Estimation of Environmentally Relevant Physico-Chemical Properties
(LOD-1117-846240) Interpretations of detailed phase distribution measurements and their implication for fate and risk assessment.
Lodge, K1, Danso, D1, Egyepong, E1, 1 University of Minnesota Duluth, Duluth, Minnesota, USA
ABSTRACT- The measurement of physical-chemical properties is beset by many difficulties; a detailed description of those associated with basic laboratory and reporting procedures for the water solubilities and octanol-water distribution coefficients of DDT and DDE have been given by Pontolillo & Eganhouse (USGS, Water-Resources Investigations Report 01-4201, 2001). These difficulties make the selection of "reliable" data difficult. However, we believe that there may also be physical phenomena present in the system under test that make the use of single phase-distribution coefficient inappropriate as an accurate descriptor of the system. That is, the coefficient depends upon the concentration of the chemical because of association in the phases. For ionizing compounds, this is not new; for example, these phenomena were reviewed by Leo & coworkers (Chem Rev. 71(6), p525-616, 1971). However, we are investigating the possibility that association may be significant for non-ionizing compounds, such as benzene, toluene, ethylbenzene and p-xylene distributed between water and octanol, and water and air. We were led to study these "simple" systems after having measured octanol-water distribution coefficients for a series of acylate esters as a function of concentration. These data can be interpreted in terms of association in the octanol phase (Edelbach & Lodge, Phys. Chem. Chem. Phys., 2, p.1763-1771, 2000). Later attempts to measure the octanol-water distribution coefficients for dioxin and p,p'-DDT brought us to a "back-to-basics" approach (Lodge et al., unpublished work, 1995). Detailed measurements of octanol-water distribution coefficients for toluene may be interpreted in terms of association in both the aqueous and octanol phases; supporting evidence is also found in our data for p-xylene and ethylbenzene. We will describe a new method for the measurement of fugacities of these compounds in the air-water system. These data may also be interpreted by invoking association in the aqueous phase.
Key words: distribution, phase, association, aromatics
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