Baselines for judging percent reductions are from 1988 in Canada, and vary for the U.S. challenges.
All challenges address human sources as opposed to naturally occurring sources.
Report by 1997 no use, generation, or release from Ontario sources that enter the Great Lakes of the above. Seek by 2000 a 90 percent reduction in use, generation, or release of alkyl-lead. Seek by 2000 a 90 percent reduction in the release of mercury, or, where warranted, the use of mercury in the Great Lakes Basin. Promote pollution prevention and the sound management of Level II substances. If ongoing long-range sources are confirmed, work within international frameworks to reduce releases of such substances.