Inorganic mercury is the term used to refer to mercuric ion (HgII). Inorganic mercury is highly toxic but not very mobile. Inorganic mercury in sediments, soils and food sources does not pass easily into biological tissues. However, once inside of the tissue, inorganic mercury is very difficult to remove. Inorganic mercury accumulates in tissues when a more mobile form of mercury such as elemental mercury vapor, methylmercury or ethylmercury enters the tissue and breaks down into inorganic mercury. In biological tissues, most organic forms of mercury will eventually break down into inorganic mercury.