Direct anthropogenic sources such as coal combustion, however, still release large amounts of inorganic mercury into the atmosphere, either as gaseous elemental mercury (GEM; Hg °) or as divalent gaseous mercury species (Hg2 +)(3). (pnas.org)
As a side effect of their normal metabolic processes, sulfate - reducing bacteria convert inorganic mercury into the organic compound methylmercury. (eos.org)
That's because scientists still don't know precisely how inorganic mercury transforms into toxic methylmercury. (sciencemag.org)