An Italian in the 1700's first noted the ill effects of Hg on miners. Predators and large fish have the highest concentrations of Hg. Mierle had a slide that showed a Hg decline after a chlor-alkali plant closed 16 years ago. This indicates that a reduced usage of Hg will, after many years, reduce the Hg concentration in the environment. Today, primary emissions from volcanoes are less than the secondary re-emissions of previous anthropogenic pollution.
Many scientists do a poor job of extrapolating their data.
Pollution varies so much that scientists should not extrapolate from a single source. For example, a scientist should not measure one municipal incinerator in December and then extrapolate the results to all incinerators for all months. No technology can reduce elemental Hg emissions, but if the Hg form is changed to HgCl, then the pollutant can be scrubbed. This may be an approach for the future. The ARET lists the pollutants that each Canadian reporting company is putting into the environment each year.