Impact/Purpose:

The primary objectives of this research task are to measure the magnitude and kinetics of organic contaminant sorption and transport in soils and sediments, to apply and compare the utility of bicontinuum and distributed parameter models for describing contaminant release from soils and sediments, and to use the measured and estimated sorption/desorption kinetic descriptors developed for assessing long-term contaminant release from soils and sediments. Miscible displacement techniques with soil and sediment columns (with some supporting batch equilibration treatments) will be used in these studies, with analyses by high performance liquid chromatography (HPLC)and gas chromatography (GC). Liquid scintillation counting will be used to quantify 14C-labelled HOCs and the 3H2O used as a conservative tracer to characterize column hydrodynamics.

Description:

Although simple modeling approaches have been adequate for describing the symmetric, sigmoidal breakthrough curves (BTCs) generated in some simple solute transport systems, they have been inadequate for describing the asymmetric (chromatographic fronting and tailing) BTCs often observed in miscible displacement studies using hydrophobic organic compounds (HOCs) and natural sorbents, such as soils and sediments. While sorption isotherm nonlinearity and nonsingularity, solute transport related phenomena (hydrodynamic dispersion, axial diffusion, and mobile-immobile water effects) may contribute to BTC asymmetry in solute transport studies, carefully designed studies have indicated that when these phenomena are accounted for, there often remains significant nonideality during solute transport. This nonideality is attributable to nonequilibrium in the sorption-desorption process. Research has shown that the sorption of HOCs occurs in two stages, an initial rapid sorption phase (usually less than an hour) followed by a slower sorption phase that can last for several months, or even years, for very high Kp solute-sorbent combinations. Hence, the popularity of various "two-step" or "two-domain" conceptualizations and mathematical models for describing sorption. More recently, distributed parameter models have been used effectively to describe contaminant desorption from soils and sediments characterized by long contaminant-sorbent contact times.

Record Details:

Record Type:PROJECT

Start Date:10/01/2000

Completion Date:09/30/2001

OMB Category:Other

Record ID: 56175

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Project Information:

Progress :Recruitment of a technician was halted due to the hiring freeze.

JOURNAL

Bouchard, D.C. 1999. Sorption of vinclozolin and atrazine on four geosorbents. Pesticide Sci., 55:1095-1102.

Bouchard, D.C. Effects of methanol-water mixed solvent systems on HOC sorption. Submitted to: Environmental Science & Technology.

Bouchard, D.C. Cosolvent effects on phenanthrene sorption-desorption on a fresh-water sediment. Submitted to: Environmental Toxicology and Chemistry.

ABSTRACT

Bouchard, D.C. Cosolvent effects on organic chemical partitioning to sediment organic carbon. Abstract presented at: SETAC Organic Soil Contaminants Conference, September 2-5, 2001, Copenhagen, Denmark.



Relevance :The sorption phenomenon directly determines contaminant concentrations in the aqueous and vapor phases and therefore is an important process in determining a contaminant's environmental fate. Sorption process elucidation and measurements can enhance the accuracy of multimedia modeling efforts (such as TMDLs) required for the exposure and risk assessments needed for developing scientifically defensible regulations (GPRA Goals 2.2, 8.1.1). Specific ORD Strategic Research areas with sorption contributions include endocrine disruptors, PBT's, pesticides, and research to improve ecosystem risk assessment.

Clients :OW, OPPTS, Regional Offices, State EPDs and any other users of sorption data and multimedia models.

Project IDs:

ID Code :5553

Project type :OMIS