Colloid characterization and colloidal phase partitioning of polycyclic aromatic hydrocarbons in two creosote-contaminated aquifers in Denmark

Colloidal matter inherent in the subsurface may provide a favorable phase for contaminant partitioning and furthermore act as agents for facilitated contaminant transport. The objectives of the present study were to determine the abundance and properties of intrinsically mobile colloids in the anoxic groundwater from two creosote-contaminated aquifers and to determine the in situ distribution of polycyclic aromatic hydrocarbo- ns (PAHs) between the dissolved phase and two colloidal fractions. The experimental procedure comprising field sampling of bulk groundwater and a sequential laboratory fractionation scheme consisting of a centrifuga- tion and an ultrafiltration step was designed and performed to maintain groundwater chemical and physical integrity. The colloids were identified as clay minerals, Fe-oxides, Fe-sulfides, and quartz particles containing significant amounts of organic carbon. The PAH partitioning to the coarse (>100 nm) colloid fraction (log Koc) was linearly correlated with the corresponding PAH octanol-water partitioning coefficient (log Kow), indicating a hydrophobic partitioning. The Koc values agreed with literature information of PAH sorption to soil organic matter.