The sediments are identified as the major environmental sink for tributyltin (TBT) in marine and estuarine systems. Observed distribution coefficients between sediments and the overlying water are in the approximate range from 0.2 to 20 1 g-1. Higher values may reflect the presence of antifoulant paint chippings. Equilibrium partition coefficients (K p ) for TBT with natural particulate material from laboratory experiments are reported in the range from 0.1 to 70 1 g-1. The partition coefficient appears to decline with increasing particle concentration and to increase in proportion to organic carbon content, consistent with an organic carbon-water partition coefficient (K oc ) of ~40 1 g-1. Particle-water partitioning of TBT depends on salinity; both increases and decreases of K p with salinity have been observed. The K p is also shown to depend markedly on pH, and variations in this or other aspects of the chemical milieu could explain the varied relations to salinity. Published data indicate that the partitioning of TBT can show a Freundlich dependence on its own concentration, concentration on particles varying as about the two-thirds power of dissolved concentration in one particular case. A simplified exponential model of the uptake of contaminants into bodies of natural sediment is used to demonstrate the likely importance of the uptake and re-release of TBT in terms of its half-life in the sediments and its maximum rate of release to the water column. With rapid sediment exchange, re-release only exceeds a proportion ζμ of the previous input when the dimensionless product of TBT degradation rate and its residence time in the sediments with no degradation exceeds (1-ζμ)/ζμ. Example plots indicate conditions with maximum re-release >20% of the preceding input and half-life in the sediment exceeding 30 d.
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- Particle-Water Partitioning and the Role of Sediments as a Sink and Secondary Source of TBT
J. R. W. Harris
J. J. Cleary
A. O. Valkirs
- Springer Netherlands
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