CONCENTRATIONS AND SOURCES OF PCBS AND ORGANOCHLORINE PESTICIDES IN THE ST-LAWRENCE-RIVER (CANADA) AND ITS TRIBUTARIES

Polychlorinated biphenyls and some organochlorine pesticides were anal yzed in St. Lawrence River water and suspended particulate matter samp les collected in 1991. A Lagrangian approach was used as the sampling method in order to evaluate the relative importance of the major conta minant sources along the River, viz. the Great Lakes, Ottawa River tri butaries and industries. PCBs appear to be the major organochlorine co ntaminant in the River with a mean concentration of ca. 1.00 ng/L. Chl ordane is quite important with a mean concentration of 0.32 ng/L. Howe ver, hexachlorobenzene (HCB) and hexachlorocyclohexanes (BHCs) have mu ch smaller concentrations, 0.01 and 0.06 ng/L respectively. The situat ion for PCBs has improved as their concentrations have decreased sligh tly since the late eighties. BHCs showed a similar trend during the sa me period. In contrast, HCB and chlordane concentrations have remained relatively constant since 1986. Fluxes of each organochlorine compoun d in general tend to increase from Cornwall to Quebec. However, differ ences in behaviour were observed depending on the contaminant. Seasona l trends were also evident. However, in general, the transport of hydr ophobic contaminants is closely linked to the fluxes of suspended part iculate matter. BHC on the other hand being quite hydrophilic behaves differently. Finally, the relative importance of each source varies ac cording to the contaminant.