Sorption and Desorption Behavior of Organotin Compounds in Sediment−Pore Water Systems

Abstract

Sediments contaminated with organotin compounds (OTs), in particular triorganotins (TOTs), are abundant in areas with high shipping activities. To assess the possible remobilization of these highly toxic compounds from such sediments, a profound understanding of their sorption/desorption behavior is necessary. In this work the extent and reversibility of sorption of OTs to sediments has been investigated using contaminated freshwater harbor sediments and two certified OT containing marine sediments. Experiments conducted with perdeuterated OTs showed that sorption of OTs to sediments is a fast and reversible process involving primarily particulate organic matter (POM) constituents as sorbents. The organic carbon-normalized sediment-water distribution ratios (DOC, expressed in L/kgOC) determined in the laboratory were consistent with in-situ DOCs obtained from OT concentrations measured in sediment and pore water samples from two dated sediment cores. For both butyl- and phenyltin compounds the log DOC values were in the range of 4.7-6.1, and the following sequence was observed: DOC (tri-OT) > or = DOC (di-OT) > or = DOC (mono-OT). However, the differences were much less pronounced than would have been expected for hydrophobic partitioning of the corresponding compounds into POM. These results support our hypothesis from earlier work with dissolved humic acids that OT sorption to sediments occurs primarily by reversible formation of (innerspere) complexes between the tin atom and carboxylate and phenolate ligands present in POM. Because of the high DOC values (i.e. log DOC > or = 4) the diffusion of OTs from deeper sediments to the surface will be rather slow, and thus a major release from undisturbed sediments is not expected. However, because OTs readily desorb, any resuspension of contaminated sediments (e.g., by the tide, storms or dredging activities) will lead to enhanced OT concentrations in the overlaying water column. Furthermore, in contrastto polycyclic aromatic hydrocarbons (PAH) where large fractions may be tightly bound (in)to soot or other carbonaceous materials, OTs will be more readily bioavailable due to the fast and reversible sorption/desorption behavior.

Organotin compounds in surface sediments from seaports on the Gulf of Gdańsk (southern Baltic coast)

“…These results correspond also to the conclusions presented by e.g. Berg et al (2001), Burton et al (2004), Fent (1996 or Hoch and Schwesig (2004), who suggested that OTs are more likely to bind to fine particles associated with higher organic carbon content, as humic acids readily form complexes with OTs.…”

Butyltin speciation in sediments from Todos os Santos Bay (Bahia, Brazil) by GC-PFPD

“…Fent found from studies in seawater that 95-99% of the total TBT is present in the dissolved phase 2 . Berg et al described the adsorption-desorption behavior of TBT in sediments as a fast and reversible process involving mainly particulate organic matter 26 . In TSB the low availability of particles of organic nature (0.13 to 1.3 mg L -1 ) is a factor that contributes to increasing residence time of these labile compounds in the water phase 25 .…”

Butyltin compounds in a sediment core from the old Tilbury basin, London, UK

“…The binding of organotin species to sediments has been demonstrated to be a reversible process involving particulate organic matter in the sediments and desorption occurs readily. As a consequence, disturbance of contaminated sediments is likely to result in an increase in organotin concentrations in the water column, although if undisturbed contaminated sediments are unlikely to be an input source (Berg et al, 2001). However, laboratory studies have indicated that sediment bound TBT may not be as available as new inputs and that the development of pollution induced community tolerance may result from long-term exposure to contaminated sediments (Dahllof et al, 2001).…”