Influence of desorption and contact time on sediment-water distribution of spiked polychlorinated biphenyls and polycyclic aromatic hydrocarbons: relation with in situ distribution.

The long-term sediment-water distribution of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), spiked to Lake Ketelmeer (The Netherlands) sediment, was studied using a gas-purge technique. Contact times varied from 2 to 1,461 d for the PCBs and from 5 to 100 d for the PAHs. Purge-induced desorption experiments lasted 300 to > 4,000 h. The initial distribution coefficients that were observed during the first part of the experiment were close to literature values for distribution after short contact times. The distribution coefficients increased during the purge-induced desorption experiments. The final distribution coefficients that were observed during the last part of the experiment were one to two orders of magnitude higher than the initial values and were close to distribution coefficients reported earlier for in situ PCBs and PAHs present in a field-contaminated sediment for years to decades. The change in distribution coefficients during a gas-purge experiment may resemble the long-term change in a field sediment. Final distribution coefficients seem to be a more relevant measure for the distribution coefficients of hydrophobic organic chemicals in aged field sediments than values obtained after short contact times.