Removal of indigenous compounds to determine maximum capacities for adsorption of phenanthrene by sediments

The maximum amounts of phenanthrene that can be adsorbed in both the slowly desorbing domain and the very slowly desorbing domain of two sediments were determined. To this end, native compounds were removed by mild solvent extraction, heating, or extraction by Tenax. Maximum capacities for adsorption of phenanthrene in the very slowly desorbing domain after removal of native compounds by heating the sediments at 300 degrees C for 24 h were comparable to those after extraction with Tenax at 60 degrees C for 13 days. Mild solvent extraction resulted in lower capacities due to incomplete removal of native compounds. For the slowly desorbing domain, heating the sediment or performing mild solvent resulted in maximum capacities for adsorption exceeding those obtained after non-invasive extraction with Tenax. That was taken to indicate alterations of the sorbent by the solvent or high temperature resulting in an overestimation of the maximum capacities for adsorption. It is concluded that for the determination of maximum capacities of adsorption in the very slowly desorbing domain, removal of native compounds by heating at 300 degrees C for 24 h is reliable and practical. However, for the determination of maximum adsorption capacities of the slowly desorbing domain, native compounds have to be removed by a non-invasive technique such as extraction by Tenax.