| Abstract
| - Sediments contaminated with organotin compounds (OTs),in particular triorganotins (TOTs), are abundant in areaswith high shipping activities. To assess the possibleremobilization of these highly toxic compounds from suchsediments, a profound understanding of their sorption/desorption behavior is necessary. In this work the extentand reversibility of sorption of OTs to sediments has beeninvestigated using contaminated freshwater harborsediments and two certified OT containing marine sediments.Experiments conducted with perdeuterated OTs showedthat sorption of OTs to sediments is a fast and reversibleprocess involving primarily particulate organic matter(POM) constituents as sorbents. The organic carbon-normalized sediment−water distribution ratios (Doc, expressedin L/kgoc) determined in the laboratory were consistentwith in-situ Docs obtained from OT concentrations measuredin sediment and pore water samples from two datedsediment cores. For both butyl- and phenyltin compoundsthe log Doc values were in the range of 4.7−6.1, andthe following sequence was observed: Doc (tri-OT) ≥ Doc (di-OT) ≥ Doc (mono-OT). However, the differences weremuch less pronounced than would have been expectedfor hydrophobic partitioning of the corresponding compoundsinto POM. These results support our hypothesis fromearlier work with dissolved humic acids that OT sorptionto sediments occurs primarily by reversible formationof (innerspere) complexes between the tin atom andcarboxylate and phenolate ligands present in POM. Becauseof the high Doc values (i.e. log Doc ≥ 4) the diffusion ofOTs from deeper sediments to the surface will be ratherslow, and thus a major release from undisturbed sedimentsis not expected. However, because OTs readily desorb,any resuspension of contaminated sediments (e.g., by thetide, storms or dredging activities) will lead to enhancedOT concentrations in the overlaying water column.Furthermore, in contrast to polycyclic aromatic hydrocarbons(PAH) where large fractions may be tightly bound (in)tosoot or other carbonaceous materials, OTs will be morereadily bioavailable due to the fast and reversible sorption/desorption behavior.
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