TEMPORAL VARIATION OF PCB CONCENTRATIONS IN THE ST-LAWRENCE-RIVER (CANADA) AND 4 OF ITS TRIBUTARIES

Samples of water and suspended particulate matter were collected at two cross-sections of the St. Lawrence River and at the mouth of four of its tributaries regularly between March and November 1991, and analyzed for thirteen PCB congeners. Mean total PCB concentrations were similar in the St. Lawrence River and its tributaries at 1.33 ng/L. The highest concentrations were observed in the spring with an important fraction of the contamination in the dissolved phase during the spring snowmelt must likely due to the accumulation of contaminated snow and atmospheric dry deposition during winter. For the rest of the year, the concentrations are lower and the PCBs are essentially transported by the suspended particulate matter. The PCB concentrations measured in the St. Lawrence River system seem to be more a residual signal than due to point sources.