Sorption of hydrophobic pollutants on natural sediments

The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The sorption isotherms were linear over a broad range of aqueous phase pollutant concentrations. The linear partition coefficients (Kp) were relatively independent of sediment concentrations and ionic strength in the suspensions. The Kp ś were directly related to organic carbon content for given particle size isolates in the different sediments. On an organic carbon basis (Koc = Kp/fraction) organic carbon), the sand fraction (> 50 μm particle size) was a considerably less effective sorbent (50–90% reduction in Koc) than the fines fraction (> 50 μm particles). Differences in sorption within the silt and clay fractions were largely related to differences in organic carbon content. Reasonable estimates of Kocś can be made from octanol/water distribution coefficients, which are widely catalogued or easily measured in the laboratory.