Rainfall samples were collected in Chicago, Illinois, and on Beaver Island, Michigan, and analyzed for polychlorinated biphenyls (PCBs). The precipitation weighted mean concentration of 35 samples of rain was 111 mg/l. (111 parts per trillion). This would result in the deposition of 4800 kg/yr of PCBs to the Lake from precipitation. Presently available evidence on other sources of PCBs to the Lake indicates that precipitation is now the major source of PCBs to the Lake. The future PCB problems in the Lakes will then be determined mainly by the magnitude of atmospheric inputs to the Lake. The concentrations of PCBs in rainfall were found to be as high on Beaver Island as in Chicago. Results obtained from the simultaneous sampling of air and precipitation indicate that PCBs are present in the atmosphere as vapor as well as being present on particulates. This result raises doubts as to the validity of results for the dry deposition of PCBs obtained from the use of collectors covered with mineral oil or other non-polar liquid. PCB concentrations in the parts per billion range obtained from gas samples from a vented sanitary landfill, indicate that PCB containing materials incorporated into landfills may be an important source of PCBs to the atmosphere.

"Grant no. R803915." "July 1978." Includes bibliographical references (pages 24-27).