BUTYLTIN COMPOUNDS IN SEVERN SOUND, LAKE HURON, CANADA

Severn Sound is a heavily used recreational and boating area in the so utheast corner of Georgian Bay, Lake Huron, Canada. Because of the con cern over the possible release of tributyltin species (TBT) from antif ouling paints on boat hulls and marinas, surveys were carried out in 1 989 and 1992 to determine the presence of this species and its degrada tion products dibutyltin (DBT) and monobutyltin (MBT) in this area. Ma ny fish (pike and young-of-the-year spottail shiners) and sediment sam ples collected in 1989 contained detectable levels of TBT. A maximum c oncentration of TBT was recorded in northern pike in the spring to be 240 ng Sn g-1. Maximum levels occurred in marinas during the beginning of the boating season and significantly reduced during the summer and early autumn, although the maximum value of TBT in sediment (392 ng S n g-1) was observed in the summer of 1989. The seasonal variation of T BT levels was further substantiated in the subsequent 1992 study, in w hich sediments from three areas in a marina were sampled at monthly in tervals from May to October. TBT levels were much higher in May and th en generally decreased with time. Mussels (Elliptio complanta) caged i n the marina for three months also contained TBT. DBT was frequently d etected in the sediments but less frequently in fish and mussels. MBT was generally below detection limits. Plants (macrophytes and cladopho ra) contained very small amounts of butyltin compounds.