3 - International Joint Commission

esult of analytical artifacts.
The concentrations of toxic chemicals in particulates in Lake Superior
are given in Table 4. The benthic nepheloid layer has been described by
Baker et al. (1985) and Baker and Eisenreich (1989). Rossmann (1986)
reported that in 1983, particulate arsenic concentrations were significantly
higher in the eastern region than in the central region. The 1977 data
discussed above cannot be compared with the 1983 data because of sample
contaminations and the of use different analytical procedures. Rossmann and
Barres (1988) compared the 1983 results of metal particulate concentrations
for Lake Superior with similar studies on the other Great Lakes done between
1980 and 1985. Generally, the mean concentrations of lead, mercury,
cadmium and arsenic in particulates of Lake Superior were significantly less,
or not significantly different from concentrations in the other Great Lakes.
The exception was the concentration of particulate cadmium which was
significantly higher in Lake Superior than in Lake Michigan.
There are limited data on toxic organic chemicals in suspended solids,
other than those for PCBs. Most concentrations were measured in whole
water samples (Table 4). Baker et al. ( 1985) reported DDE concentrations in
suspended solids from the nepheloid layer of western Lake Superior in 1983
as being from 0.005 to 0.024 ppt. They also found that the concentrations
of particulate-associated PCBs in the benthic nepheloid layer were not that
different from those in thepilimnion. In 1980, the range of PCB concentrations
in suspended solids was 30 to 2,770 ppb (ng/g) (Capel and Eisenreich,
1985). Capel and Eisenreich pointed out that the fraction associated with
particulates versus the dissolved phase changed with time and with depth.
By 1986, the particulate-associated PCB concentration had dropped
dramatically to 33 +/- 16 ppb (ng/@ (Baker and Eisenreich, 1989).
Concentrations of some PCBs and PAHs in Lake Superior were greater in
suspended solids collected by sediment traps than when collected by
centrifugation (Baker and Eisenreich, 1988). This was thought to be related
to biological processes. They found that the flux rates of PCBs to the bottom
waters of Lake Superior were up to two orders of magnitude higher than the
net accumulation rates of PCBs in the bottom sediments, implying high
benthic organism recycling rates. Particulate concentrations of total PCBs
could thus be higher than those found in surflcial sediments. When Lake
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