Net Atmospheric Inputs of PCBs to the Ice Cover on Lake Huron

This report describes the first measurements of the net atmospheric deposition of PCBs to the ice cover of a body of water. The net deposition of PCBs includes the wet, dry, and vapor deposition, less any evaporation. The measurements were made on ice cores collected from the frozen surface of Lake Huron late in the ice seasons of 1978 and 1979. Intrusions of lake water into the accumulated deposition layer of ice and snow were not encountered in these studies. Such intrusions, however, have complicated other attempts to use this method. Possible reasons for not encountering them in this study are discussed. For Saginaw Bay, a net deposition rate of 2.0 gm/km²/mo of PCBs to the ice was found for the winters of 1977–1978 and 1978–1979. Upon ice break-up and thaw in the spring, all of the PCBs accumulated on the ice are likely to enter the bay. For inner Saginaw Bay, this would have been 8 kg in March 1978 and 6.5 kg in March 1979.