See more from this Session: Dissolved Organic Matter (DOM): Fate and Role In Soil and Environmental Processes
Monday, October 17, 2011: 1:45 PM
Henry Gonzalez Convention Center, Room 210A, Concourse Level
Batch equilibration method is usually used for deriving Kd (and Koc) of hydrophobic organic compounds (HOCs) in soils and sediments, where centrifugation is typically used to separate the solid and aqueous phases. However, centrifugation does not exclude DOM from the aqueous phase. Presence of DOM in the aqueous phase artificially increases the aqueous phase concentration (Cw) due to sorption of HOCs to the DOM phase, leading to an artificially depressed Kd. We have employed solid-phase microextraction (SPME) as a selective method to measure the freely dissolved aqueous concentration (Cfree) to estimate the true Kd and Koc for a wide range of HOCs. In each experiment, we compared the SPME measurement against the conventional approach for the same sediment or soil. Paired comparisons consistently showed that Kd for strongly hydrophobic compounds was grossly underestimated for the standard batch method, with underestimation often up to an order of magnitude. Therefore, many Kd or Koc values of HOCs in the literature may be significantly underestimated and should be revised by correcting for the artifact due to DOM.