Several types of toxic effect are associated with chemical contaminants in the
Great Lakes. The easiest to understand is lethality. Some compounds, at a
sufficient concentration, are lethal to aquatic life. Several heavy metals, for
example, kill fish by destroying the ability of the gills to extract oxygen from water.
Effluents from certain industrial processes, such as electroplating, once contained
a sufficiently high level of dissolved heavy metals to be lethal to aquatic
organisms. All such discharges are now illegal on the U.S. side of the basin.
A variety of sub-lethal effects are also associated with toxic compounds. At
very low levels, some heavy metals can interfere with kidney function, the
ability of fish to locate prey, and can make organisms more susceptible to
disease. Some organic compounds have similar effects.
Carcinogenesis – the induction of cancer or tumors – is another consequence
of toxic exposure. Numerous fish collected from areas contaminated with
organic pollutants have lesions and tumors.
Perhaps the most insidious consequences of chemical contamination are
those that pass from generation to generation in utero, or through the food
chain from prey to predator. Teratogenic compounds are those that interfere
with the development of young. They can cause birth defects such as crossed
bills in birds, development of extra limbs in amphibians, or developmental
impairments in humans. Chemicals can also bioconcentrate or biomagnify
through the food chain. In the Great Lakes, minute concentrations of PCBs in the water column will concentrate some hundred fold in phytoplankton,
thousands fold in zooplankters and planktivorous fish, hundreds of thousands
fold in piscivorous fish, and up to six million fold herring gulls.
Several types of toxic effect are associated with chemical contaminants in theGreat Lakes. The easiest to understand is lethality. Some compounds, at asufficient concentration, are lethal to aquatic life. Several heavy metals, forexample, kill fish by destroying the ability of the gills to extract oxygen from water.Effluents from certain industrial processes, such as electroplating, once containeda sufficiently high level of dissolved heavy metals to be lethal to aquaticorganisms. All such discharges are now illegal on the U.S. side of the basin.A variety of sub-lethal effects are also associated with toxic compounds. Atvery low levels, some heavy metals can interfere with kidney function, theability of fish to locate prey, and can make organisms more susceptible todisease. Some organic compounds have similar effects.Carcinogenesis – the induction of cancer or tumors – is another consequenceof toxic exposure. Numerous fish collected from areas contaminated withorganic pollutants have lesions and tumors.Perhaps the most insidious consequences of chemical contamination arethose that pass from generation to generation in utero, or through the foodchain from prey to predator. Teratogenic compounds are those that interferewith the development of young. They can cause birth defects such as crossedbills in birds, development of extra limbs in amphibians, or developmentalimpairments in humans. Chemicals can also bioconcentrate or biomagnifythrough the food chain. In the Great Lakes, minute concentrations of PCBs in the water column will concentrate some hundred fold in phytoplankton,thousands fold in zooplankters and planktivorous fish, hundreds of thousandsfold in piscivorous fish, and up to six million fold herring gulls.
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