Acting EPA Inspector General Bill Roderick issued a May 15 report citing "several uncertainties associated with key variables in the analysis" that could affect the agency´s conclusion that the Clean Air Mercury Rule would not result in mercury hot spots.

Roderick cites gaps in available data and science for mercury emission estimates, limitations in modeling for mercury deposition, uncertainty over how mercury reacts in the atmosphere, and uncertainty over how mercury changes to a more toxic form in bodies of water.

Many environmentalists and health advocates have criticized the agency´s cap-and-trade program. However, the agency has stated that more stringent reductions would not be practical given existing technology and has expressed confidence that hot spots would not be a problem.