A ground water humic material has been isolated using XAD-8 adsorption chromatography (Thurman and Malcolm, 1981). Partitioning studies for DDT, hexachlorobenzene (HCB), and bis(2-ethylhexyl)phthalate (BEHP) and soil column studies for HCB and anthracene have been completed. Partition coefficients for DDT, HCB and BEHP are 10('5.99), 10('4.64) and 10('3.66), respectively. A linear relationship between log solubility (mole fraction) and log partition coefficient (Kp) exists where: log Kp = -0.91 log S (mole fraction) -3.34 (R = 0.9984). These values are in agreement with those determined for soil sediments for compounds whose water solubilities are in the range of 1 (mu)g-l('-1), but are lower by an order of magnitude for compounds whose water solubilities are on the order of 500 (mu)g-l('-1) (Karickhoff, 1979). The classical contaminant retardation equation was modified to account for mediated transport by dissolved organic carbon (DOC). Soil column experiments exhibited mediated transport of HCB and anthracene by the humic material and provided strong evidence that the compounds move as an irreversible humic/organic complex. The implications and magnitude of this mediation of organic transport by ground water humics is discussed. The existence of such a complex may account for the enhanced migration of certain trace level organics in ground water
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