Minor element geochemistry of Lake Michigan ferromanganese nodules

Samples of ferromanganese nodules from several localities in Lake Michigan have been analyzed for their minor element content utilizing neutron activation techniques. The thorium and uranium levels in Lake Michigan nodules exhibit marked dissimilarities with marine nodules. The radium content of these freshwater nodules is substantially higher than the reported marine values. The concentrations of barium in the Lake Michigan nodules appear to be abnormally high. Although barium could be present as minute segregations of the mineral barite, patterns obtained using the electron microprobe suggest it is evently dispersed throughout the nodules. The average arsenic content of these freshwater nodules is at least twice as great as that reported for highly oxidized marine sediments. If all this arsenic is dissolved and released into Green Bay as a result of changing environmental conditions (eutrophication), the concentration in the water of Green Bay would be several times the maximum permissible level for drinking water.