Feature Article November 20, 2003
LAND O' LAKES NewsWeb HomePollution - What is it
We can't hope to understand or to deal with pollution if we think of it as a great cloud of bad stuff. A specific thing -- usually a chemical -- causes each impact of pollution. Recently announced findings of a study of the disappearance of lake trout from Lake Ontario are a clear example.
Lake Ontario had millions of lake trout in the 1930's, the population collapsed in the 1940's and they were all gone by 1960. Commercial over fishing and increasing sea lampreys were pointed to as causes. They certainly had their effects but it turns out they were not the final effect that eliminated Lake Ontario's lake trout.
A fifteen-year study by a U.S. Environmental Protection Agency scientist shows that dioxin was the final cause that wiped out the Lake Ontario lake trout. Dioxin is an unwanted by-product of processes that use chlorine in the pulp and paper industry and similar processes that use chlorine in the chemical industry. A large chemical industry in Niagara Falls N.Y. produces dioxins that entered Lake Ontario.
By studying the lake sediments, the study showed that dioxins in Lake Ontario peaked around 1940 at about 30 parts per trillion parts of water. This is an extremely low concentration but newly hatched lake trout start dying at this concentration. At 100 parts per trillion, all the new hatchlings die. Measuring concentrations of dioxins in the tissue of adult lake trout does not reveal the problem; they can tolerate 1000 parts per trillion before it kills them. But during the worst period of dioxin pollution from 1948 to 1976, dioxin killed every newly hatched lake trout in Lake Ontario. The adults could live but they could not reproduce. The population disappeared.
Tighter controls on dioxin production and release have reduced the concentration to about 5 parts per trillion but even this concentration is suspected of causing deformities in the newly hatched fish. Lake trout hatchlings turn out to be more sensitive to dioxins than any other animals.
Pollution by dioxins is exceptionally specific for lake trout and even without the lampreys and the over fishing, probably would have destroyed the Lake Ontario lake trout population simply by killing all the young hatched.
