Mercury methylation is a process by which Hg bio-accumulates in ecosystems. The methylation index is a parameter correlated with methylmercury (MeHg) concentration in water bodies based on sulfur-reducing bacteria (SRB), particulate organic carbon (POC), sediment oxidation-reduction potential and mobile mercury concentration. The Michaelis–Menten equation for MeHg leads to an alternate comparison, in terms of , the MeHg saturation constant; , the half-saturation methylation constant; and , total sedimentary mercury. In Graph 2, river POC is estimated as 56 M/L, estuarine POC is estimated as 6 M/L, and seawater is estimated as 0.3 M/L. Graph 3 also displays the limit of MeHg formation in the system as mobile mercury concentration increases.