Lead and Cadmium Loadings to the Great Lakes from Precipitation

Abstract

We present the first analysis of precipitation chemistry data from the Great Lakes Atmospheric Deposition (GLAD) network of wet-only precipitation samplers. Lake loadings were calculated from 1- or 2-yr (1982–1983) volume-weighted mean ion concentrations and 30-yr mean annual precipitation amounts, using an objective analysis method to interpolate measurements to a 40 × 40 km square grid over the Great Lakes region. The results show that atmospheric loadings of Cd, Pb, and other cations to the Great Lakes are in many cases considerably smaller than those estimated from the bulk precipitation measurements of the early 1970s. For Pb, some portion of the differences can be accounted for by the decrease in emissions that resulted from reductions in the Pb content of gasoline. Valid dry deposition in the bulk samplers also accounts for a portion of the differences. However, for the most extreme differences, contamination of the bulk collectors by resuspended local surface dust is likely to be a major cause. Good agreement was noted between the precipitation-only loadings derived from the GLAD data and those recently given by Strachan and Eisenreich (1987).