3 - International Joint Commission

Lakes Ontario and Huron (Thomas, 1972: 1973). Concurrently, high
concentrations of mercury were discovered in Lake St. Clair fish (Fimreite et
al., 1971) at levels which resulted in a ban on commercial fishing in the lake
in 1970. The source of mercury to Lake St. Clair was upstream chlor-alkali
plants on the St. Clair River. In 1971, the Michigan Public Health Department
issued a consumption advisory because of PCBs in lake trout and
salmon in Lake Michigan. Soon after, in 1974, mirex was discovered in fish
in the Bay of Quinte, Lake Ontario. In late 1979, chlorinated dioxins were
detected in herring gull eggs from colonies in Saginaw Bay, Michigan. In
1982, toxaphene was first detected in fish from Lake Superior. Subsequent
sampling showed that most of these chemicals were present throughout the
Great Lakes system. Also, analyses of Great Lakes media for metals, such as
lead and cadmium, showed that these were also ubiquitous contaminants.
Thus, the scientific and public awareness of the level of toxic chemical
pollution of the Great Lakes developed over approximately 25 years. The
period of greatest public concern was around 1980 and was related to the
discovery of 2, 3, 7, 8-tetrachloro-dibenzo-(p)-dioxin, in herring gull eggs.
Another major event occurred in 1985 when there was a perchloroethylene
spill into the St. Clair River.
Chemical analyses of radiodated sediment coreshowed that contamination
of the Great Lakes began only after World War 11, concurrently with
the expansion in urban and industrial development. PAHs were detected in
lake sediments deposited at the turn of the century. Some chlorinated
organics such as PCBs and chlorinated benzenes (CBs) were produced before
the war. However, peak inputs of these chemicals and chlorinated pesticides
took place much later in the 1950s, 1960s and early 1970s. During the
1970s. it became apparent that bottom sediments were contaminated with
organochlorine pesticides and PCBs.
1.4 SAMPLING AND ANALYSIS
The chemicals discussed in this report are those traditionally analyzed
for in most media. However, recent attempts to calculate mass balances for
the Great Lakes have shown that the data bases are quite inadequate, with
the possible exception of PCBs (Strachan and Eisenreich, 1988). Since about
1979, concentrations of hydrophobic chemicals have been measured in
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