| Popis: |
Tributyltin is effective at controlling fouling organisms on vessels' hulls when used as an additive in marine paints. Its effectiveness is due to its extreme toxicity to fouling organisms after it is released from the paint. Unfortunately, it is also toxic to some nontarget organisms at concentrations approaching one part per trillion. After leaching from the hull of a vessel, the rates of degradation and transport from the water column have important implications for estuarine ecosystems, but the processes involved in these removal mechanisms are poorly understood. Using radiolabeled tributyltin, in a 13 m3 mesocosm, the processes of degradation and transport were monitored. The total removal rate was found to be 6 to 20% per day. The primary mechanisms consisted of: biodegradation (40%): transport to the sediment (35%); and transport to the atmosphere (25%) . Biodegradation proceeded primarily through the process of debutylation to dibutyltin, which in turn degraded to monobutyltin. In addition to this degradation sequence, the data suggested that a degradation pathway from tributyltin directly to monobutyltin may have been important. Transport to the sediment was accelerated by adsorption to suspended particles. The distribution coefficients between suspended particles and water (in units of [μg/kg]/[μg/L]) were found to be; (60 ± 30) (10)3 for tributyltin; (30 ± 20) (10)3 for dibutyltin; and (2.9 ± 0.5) (10)3 for monobutyltin. Tributyltin also accumulated in the surface layer of the water column, implying that transport to the atmosphere may have been an important removal process. A concentration as high as of 1.7 ± 0.3 μg/L was found. This value was 3 times the concentration measured in the underlying water column. |
