THE OCCURRENCE, DISTRIBUTION AND SOURCES OF DDT IN THE ST-LAWRENCE-RIVER, QUEBEC (CANADA)

Water and suspended sediment samples were collected in the St. Lawrenc e River and analyzed for DDT and its metabolites at different periods of the year. DDT parent compounds were present in almost all the sampl es. The likely sources and their contributions were found to be: Great Lakes (32%), tributaries (33%), atmospheric deposition (4%) and the d iffuse load from leaching and erosion processes (31%). o,p'-DDT is mor e persistent than p,p'-DDT in the St. Lawrence River basin. p,p'-DDT s eems to be degraded faster in the bottom sediment than in soils.