Butyltin concentrations in sediments and blue mussels (Mytilus edulis) of the southern Gulf of St. Lawrence, Canada

Profiles of the butyltins tributyltin (TBT) and dibutyltin (DBT) in sedimen ts were obtained in 1996 from four sites frequented by commercial and/or re creational ships in the southern Gulf of St. Lawrence: Summerside (Prince E dward Island, FED, Pictou (Nova Scotia, NS), Miramichi (New Brunswick NB), Shediac (NB) and one reference site: Cardigan (PEI). Sediments from Shediac and Summerside were the most contaminated with both TBT and DBT shaving in the surficial sediments levels reaching 83.4 ng Sn g(-1) (d.w.) for Shedia c. Seasonal monitoring of levels of TBT and DBT in wild blue mussels, Mytil us edulis, was also conducted at these same sites in 1995 and 1996 with the addition of a second reference site in 1996 Richibucto (NB). Mussels from all sites, except Richibucto, were contaminated by TBT at levels ranging fr om 7 ng Sn g(-1) (d.w.) in Cardigan to 426 ng Sn g(-1) (d.w.) in Summerside in 1995 and from below the detection limit in Richibucto to 671 ng Sn g(-1 ) (d.w.) in Summerside in 1996. DBT was also present in most samples at con centrations reaching 161 ng Sn g(-1) (d.w.) in 1995 and 378 ng Sn g(-1) (d. w.) in 1996 in samples from Summerside. The highest levels correspond to mo derately high contamination with the potential of causing deleterious effec ts in biota. In most sampling sites, no clear relationship could be establi shed between butyltin concentrations found in sediment and in mussels. Our results suggest that inputs of TBT from June to September, at least in the southern Gulf of St. Lawrence, are still well above expected levels after e ight years of TBT-paint regulation. The main source would appear to be plea sure boating activities with a lower but chronic contribution from the comm ercial fleet.