[en] Improved control devices, advances in fuel stack measurements and ambient sampling techniques have clarified some of the issues associated with the release of trace substance emissions into the atmosphere, particularly mercury emissions, from electric utilities. It has been determined that mercury emissions to the atmosphere from all sources globally, including utilities, has an approximate lifetime of 1-2 years before deposition, but 30 -70 per cent of mercury emissions are deposited locally within hours to days. Recent and continual field studies are being conducted to determine how much mercury is actually emitted from background sources and how this mercury enters general atmospheric circulations. The issue of how much mercury deposits locally versus being transported regionally or globally is also under study along with how mercury enters the food chain for fish in lakes and ultimately the consumer. Current health effects studies have indicated that there are slight differences in some of the earlier estimates of mercury's health effects. More studies are underway to help determine the degree of health threat to U.S. consumers of fish and to determine if mercury emissions are carried beyond U.S. borders to global dispersion. Some studies have also indicated a net reduction of mercury in clouds