CONTAMINANT DEPOSITION AND REMOBILIZATION ON THE TUG HILL PLATEAU

A half meter core of fine fluvial sands deposited by the North Branch of the Salmon River records a complex history of organic contaminant deposition and remobilization in a remote area of the Tug Hill Plateau. Lead-210 and Cesium-137 activity profiles suggest that the bottom 10 cms of core are greater than ~100 years old. However, man-made organic compounds including PCBs, DDE, and HCB were found in this interval, prior to their widespread commerical production and use.

Radionuclide activity increases gradually from the bottom of the core to the 24-26 cm interval where several major changes occur. 210-Pb and 137-Cs activities become highly variable, major and trace element concentrations change, and sediment porosity increases. Substantial reworking of the sediments is thought to have occurred during 1965 when 59 cm of rain fell between September and November on the Tug Hill Plateau.

The concentration of PCBs (maxiumum - 98.5 ng/g, dry wt.) is significantly higher than would be expected in sediment from a remote area without local sources. Congener profiles are comprised almost entirely of higher chlorinated congeners and are nearly identical to those from a similar core taken 50 km away near Oswego. The presence of elevated concentrations of PCBs in century old sediments and similar congener compositions over a broad area suggest regional processes of enhanced contaminant deposition, perhaps related to abundant lake-effect precipitation downwind of Lake Ontario.