This is the VOA Special English ENVIRONMENT REPORT.
Scientists say they have evidence that the world’s biggest freshwater lake system is cleaning itself of pollutants. North America’s Great Lakes hold about twenty percent of the world’s fresh surface water. Pollution has been a problem there for years. Yet scientists now say large amounts of chemical pollutants are disappearing from the water’s surface. A team of Canadian and American scientists reported the unusual finding.
The five Great Lakes are named Superior, Michigan, Huron, Erie and Ontario. They extend from the middle western state of Minnesota to the eastern state of New York. Only Lake Michigan lies completely within the United States. The United States and Canada share the other four lakes. They also form part of the border between the two countries. A treaty signed in Nineteen-Oh-Nine provides for control of the lakes by the two countries.
The Great Lakes form the most important inland waterway in North America. The five lakes and their waterways are important to the economies of the United States and Canada.
In the new study, the scientists measured levels of several harmful chemicals that have washed into the lakes. They include chemicals to kill insects and polychlorinated biphenyls, or P-C-Bs. P-C-Bs are chemicals used in industry. The United States and Canada have banned P-C-Bs because of their links to cancer. Yet they still are used in some developing countries.
The study found that Lake Ontario alone released almost two metric tons of P-C-Bs between Nineteen-Ninety-Two and Nineteen-Ninety-Six. The five lakes decreased their combined levels of P-C-Bs by about ten metric tons during the period. Levels of one banned chemical dropped more than four metric tons.
The scientists believe the chemicals were released into the atmosphere. Keith Puckett of Canada’s environment agency worked on the project. He said the lakes are like huge lungs that have been breathing in pollutants for the past fifty years. Mister Puckett says now it is as if the lakes are starting to breathe out again.
Mister Puckett adds that air pollution near the Great Lakes remains a threat. He called for increased efforts to control pollution from power production centers, factories, vehicles and other causes.
This VOA Special English ENVIRONMENT REPORT was written by George Grow.