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 tw o cross-sections of the St. Lawrence River and at the mouth of four of its tributaries regularly between March and November 1991, and analyz ed for thirteen PCB congeners. Mean total PCB concentrations were simi lar in the St. Lawrence River and its tributaries at 1.33 ng/L. The hi ghest concentrations were observed in the spring with an important fra ction of the contamination in the dissolved phase during the spring sn owmelt must likely due to the accumulation of contaminated snow and at mospheric dry deposition during winter. For the rest of the year, the concentrations are lower and the PCBs are essentially transported by t he suspended particulate matter. The PCB concentrations measured in th e St. Lawrence River system seem to be more a residual signal than due to point sources.