"Before this study, no one had directly linked atmospheric deposition (mercury emissions) and mercury in fish," says study co-author Vincent St. Louis of the University of Alberta.

The experiment filled a major gap in scientists' understanding of how mercury moves from the atmosphere through forests, soils, lakes and into the fish that people eat.

It's immediate value is that it provides undeniable proof of a direct link, said St. Louis, who specializes in what is called whole-ecosystem experimentation.

He said it should spur policy-makers to enact regulations for more rapid reductions in mercury emissions by industry.