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(057) Partitioning of 1,2-dichlorobenzene to soil size fractions containing different types and amounts of organic matter.
Choate, LaDonna*,1, Ranville, James2, Chen, Chen-Peng3, Thorn, Kevin1, Bunge, Annette3, Macalady, Donald2, 1 U.S Geological Survey, Denver, Colorado, USA2 Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado, USA3 Department of Chemical Engineering, Colorado School of Mines, Golden, Colorado, USA
ABSTRACT- A variety of chemicals are added to soil by different segments of society. One of the most important chemical processes occurring in soil is sorption, since many compounds have low water solubility, and are not degradable so they are persistent in the environment. The organic carbon content of soils has been shown by several studies to be the factor that principally controls the sorption of hydrophobic organic compounds (Pignatello & Xing, 1996; LeBoeuf & Weber, 1999). This research examined the relative importance of carbon content and organic matter functionality to soil sorption of 1,2-dichlorobenzene. Two soils were investigated a clay loam and a silty-clay loam, and two dispersion methods were used. The importance of organic matter functionality, determined by 13C NMR cp/mas (nuclear magnetic resonance spectroscopy cross polarization/magic angle spin), was studied by performing sorption experiments of 1,2-dichlorobenzene to the size fractions at the extremes (2000-500 and 25-0.6 micrometer). The possibility of sorption onto mineral phases was also considered by investigating the effect of clays and specific surface area (SSA). Variation in composition of organic matter in soil affected the sorption of 1,2-dicholorbenzene, which is reflected in the statistically significant difference in the Kd and Koc values for the two fractions of the clay loam and is also observed in the isotherms and Koc values for the sonicated silty-clay loam fractions. The organic matter, in the size fraction extremes (2000-500 and 25-0.6 micrometer), of the aggregated silty-clay loam is more homogeneous and these fractions have statistically similar values for the Kd and Koc. This is because aggregation tends to distribute the organic matter through the size fractions. The implication of this work to risk assessment through dermal contact with contaminated soil is discussed.
Key words: sorption, soil organic matter
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