Under commission from the U.S. EPA, Lakes Environmental developed a method to properly partition elemental mercury, divalent mercury (Hg++), and methyl mercury (MHg). Previously, the mercury soil and waterbody partitioning model in the U.S. EPA Human Health Risk Assessment Protocol would deviate from observed values. After extensive literature reviews and analytical mass balances an updated mercury model was suggested by Lakes Environmental, which was subsequently incorporated into the national risk assessment protocol.