Gold [Au, 79]

Gold, a chemical element of the group 11 in the periodic table of elements, is one of the metals of the so-called group noble metals. Gold was one of the first metals to be recognized by humans, and due to its chemical and physical properties, it became very important throughout the human civilization. The global balance of the gold accumulation in sewage streams is estimated at 360 t/yr. Sewage sludge may be a major source of gold when applied to soils. Increased levels of gold in some sewage sludge are as follows: 500–3000 in the United States and 500–4500 in Germany. Gold is easily phytoavailable, and when it enters the root vascular systems, it is easily transported to the tops. In reducing media, however, gold precipitates on a cell surface, and thus inhibits membrane permeability. Gold demonstrates excellent biocompatibility within the human body, hence the number of direct applications of gold, as a medical material.