3 - International Joint Commission

of the lake has been more severe than the northern end. One of its main
tributaries is Fox River which empties into Green Bay. The bay is about 8%
of the surface area of the lake but it has about one third of the lake’s
watershed (Harris et aL, 1987). There has been concern about water quality
in Green Bay since the 1920s.
2.2.1 Water and Suspended Solids
Published data on chemical concentrations in Lake Michigan water are
shown in Table 6. Historical data on total lead concentrations in Lake
Michigan waters were reviewed by Rossmann (1984). The values for both
total and dissolved lead as determined by Rossmann in 1981 are much less
than many of the historical levels measured in the 1960s and 1970s because
of sample contamination problems. Rossmann’s mean values of 260 ppt total
lead and 150 ppt of dissolved lead (n = 11) are considered the most accurate.
Earlier measurements of total lead had ranged up to 170 ppb with a mean of
18 ppb (n = 30) in 1976 (Wisconsin Electric Power Company and Wisconsin
Michigan Power Company, 1977, as cited in Rossmann, 1984). Reported
historical mean mercury values were as high as 4.3 pph (Rossmann, 1984)
but these earlier values are now considered to be invalid. All of the cadmium
measured by Rossmann in 1981 at 11 sites was in the dissolved phase.
Earlier mean cadmium values as high as 2,800 ppt (n = 42) in 1974 are now
considered to be erroneous. Owen and Meyers (1984) reported total cadmium
concentrations in the mid-lake subsurface in the late 1970s were 70 ppt and
nearshore subsurface as 80 ppt. In southern Lake Michigan, the mean
concentration of total cadmium was 26.6 ppt with a range of 12.0 to 45.6 ppt
(Lum, 1987). These values are similar to Rossmann’s (Table 6). Rossmann
considered historic arsenic concentrations to be valid for comparison with
recent results. Values of just over 1,000 to 2,000 ppt were measured in the
mid to late 1970s and compared to Rossmann’s whole water mean value in
1981 of 790 ppt. Much higher values for mean total arsenic were reported
prior to 1970 (up to 40 ppb in 1969) but these were almost certainly
analytical artifacts.
There is little published information available on organochlorines in
Lake Michigan water (Table 6). From 1968 to 1970, total DDT values were
reported as 3 to 151 ppt (Sonzogni and Simmons, 1981). Open water
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