VERTICAL-DISTRIBUTION OF BUTYLTIN RESIDUES IN SEDIMENTS OF BRITISH-COLUMBIA HARBORS

Vertical distributions of tributyltin (TBT) and its degradation produc ts di-and monobutyltin have been measured in five sediment cores colle cted in harbours and marinas of southern British Columbia, Canada. Des pite restrictions on the use of organotin-based marine antifouling pai nts imposed in Canada in 1989, concentrations of butyltin compounds in coastal marine sediments remain high. The highest concentration of TB T, 520 ng g(-1) TBT-Sn, was recorded in a core collected from a small marina near Sidney, Vancouver Island. Similar levels of TBT were also recorded in a core collected in inner Vancouver Harbour, indicating th at commercial shipping continues to be a significant source of butylti n contaminants to British Columbia's marine environment. Vertical prof iles of butyltins differed according to location. The marina core show ed the maximum in TBT concentration at 8 cm depth, indicating clearly that the retail ban on organotin-based paints to craft less than 25 m in length has successfully reduced the flux of TBT to surface sediment s. However, no such trend was visible in harbour cores, with the highe st concentrations of TBT in superficial sediments. The presence of TBT throughout the sediment cores implies that it must be considered a pe rsistent contaminant. Applying a simple regression model to one core, for which an approximate chronology is known, suggests a half-life for the first order degradation of TBT of about 8.7 years. This is a slow er rate of degradation than any previously reported, and may be due to inhibition of microbial action in cold waters.