Concentrations and sources of PCBs and organochlorine pesticides in the St. Lawrence River (Canada) and its tributaries

Abstract

Polychlorinated biphenyls and some organochlorine pesticides were analyzed in St. Lawrence River water and suspended particulate matter samples collected in 1991. A Lagrangian approach was used as the sampling method in order to evaluate the relative importance of the major contaminant sources along the River, viz. the Great Lakes, Ottawa River, tributaries and industries. PCBs appear to be the major organochlorine contaminant in the River with a mean concentration of ca. 1.00 ng/L. Chlordane is quite important with a mean concentration of 0.32 ng/L. However, hexachlorobenzene (HCB) and hexachlorocyclohexanes (BHCs) have much smaller concentrations, 0.01 and 0.06 ng/L respectively. The situation for PCBs has improved as their concentrations have decreased slightly since the late eighties. BHCs showed a similar trend during the same period. In contrast, HCB and chlordane concentrations have remained relatively constant since 1986. Fluxes of each organochlorine compound in general tend to increase from Cornwall to Québec. However, differences in behaviour were observed depending on the contaminant. Seasonal trends were also evident. However, in general, the transport of hydrophobic contaminants is closely linked to the fluxes of suspended particulate matter. BHC on the other hand being quite hydrophilic behaves differently. Finally, the relative importance of each source varies according to the contaminant.