Behavior of [14C]-4-nitrophenol and [14C]-3,4-dichloroaniline in laboratory sediment-water systems: Part 2. Desorption experiments and identification of sorptive fraction

Both [14C]-4-nitrophenol (4-NP) and [14C]-3,4-dichloroaniline (3,4-DCA) were applied to laboratory sediment-water systems; these were a sandy sediment (SED-M), and a sediment with high clay/silt and organic carbon content (SED-J). After sorption periods of 2 d (assay I) and 28 d (assay II) the water phases were replaced by fresh sample water. About 20/10% (3.9/3.9% of total applied 4-NP in SED-M/SED-J) and 40/15% (8.5/6.2%; 3,4-DCA) of the sediment-associated radioactivity were initially (1 d of incubation) desorbed in assay I. The corresponding data of assay II amounted to 2/1% (0.9/0.7%; 4-NP) and 3/2% (1.7/1.4%; 3,4-DCA). No parent compounds were detected in the fresh-water phases. The radioactivity released in assay I was readsorbed to the respective sediment. Remobilization distinctly reflected the preceding sorption process, and that regarding sediment properties and chemical features of 3,4-DCA and 4-NP. Fractionation of the nonextractable residues of 3,4-DCA in SED-J revealed that the xenobiotic was mainly attached to the insoluble humin fraction (55.8/53.8% after 7/28 d of incubation). Only minor amounts were associated with fulvic (14.3/12.7%) and humic acids (5.3/6.1%). Experiments using a clay fraction of SED-J (< 0.063 μm; SED-J-C) and bentonite (CM) demonstrated that 3,4-DCA was primarily bound to the organic matter of SED-J-C. Concerning sorption of 3,4-DCA, both SED-J and SED-J-C behaved very alike; in contrast, CM showed a strikingly different pattern. Regarding “outdoor” situations, it may be concluded that 4-NP is not translocated very far from the site of contamination, whereas 3,4-DCA shows considerable mobility.