Partitioning of 2,2',4,4'-tetrachlorobiphenyl by the dissolved organic matter in oxic and anoxic porewaters

Until recently, the dissolved organic matter(DOM) of pore waters was an overlooked pool of organic matter important to the fate and transport of hydrophobic organic chemicals (HOCs). The aqueous solubility enhancement and the porewater DOM partition coefficient (K-PWDOM) Of 2,2',4,4'-tetrachlorobiphenyl (TeCB) were compared in samples of anoxic porewater and that same porewater after aeration. Aeration of anoxic porewater increased TeCB partitioning by porewater DOM. Despite a decrease in DOM concentration (coagulated by precipitated iron(III) oxidized during porewater aeration), oxic (aerated) porewaters had greater solubility enhancement and up to an order of magnitude larger K-PWDOM than anoxic (unaltered) porewaters. Anoxic porewaters with no detectable dissolved oxygen and 45 mg/L dissolved iron(II) had the smallest TeCB solubility enhancement and K-PWDOM Using experimentally determined K-PWDOM values, a three-phase equilibrium-partitioning model predicts the following: (1) the distribution of HOC freely dissolved and associated with porewater DOM will change when anoxic sediments are aerated; (2) HOC mobility will increase with anoxic sediment aeration because HOC concentration in the aquatic phase will increase; and (3) HOC bioavailability will be less in anoxic porewaters as compared to oxic systems because a smaller concentration of HOC will be freely dissolved.