Indium [In, 49]
143
20.4 AIR
Indium concentrations in the atmosphere of remote areas vary between 0.05 and
78 pg/m 3 , with the lowest in Antarctica. Air of urban/industrial area contains much
higher In amounts, up to 1200 ng/m 3 (Table 20.1). The main anthropogenic source
of In in air is from waste and coal combustions. Its natural sources are mainly from
volcanic emissions, which are clearly proofed by its variable contents in various layers of the ice cores (Matsumoto and Hinkley 2001).
Indium content of moss (Pleurozium schreberi) has decreased significantly from
110 μg/kg in 1975 to 13 μg/kg in 2000 (Rühling and Tyler 2004). This clearly indicates that the In emissions have decreased during that period.
20.5 PLANTS
Although In is readily available to plants, its accumulation is not observed.
Physiological effects of increased In levels in plants is associated with In-induced
toxicity in roots, which occur in plants grown in culture solution, with its contents
within 1–2 mg/kg. A few data on In in plants are reported by Fergusson (vide KabataPendias 2011) as follows (in μg/kg FW): beets, 80–300; vegetables, 30–710; fruit
tree leaves, 0.64–1.8; tomato leaves, 0.64–1.8. Mean content of In in cereal grains
sampled in Sweden contain <5 μg/kg (Eriksson 2001a).
Plants grown in soils amended with sewage sludge may contain much
higher amounts of In, up to 300 μg/kg in beets. Also, elevated In contents (up
to 2100 μg/kg FW) was reported for unwashed grass from industrial regions
(Kabata-Pendias 2011).
20.6 HUMANS
Indium content in human body is about 0.4 mg (Emsley 2011). It is not known to have
any biochemical functions. Ionic In is nephrotoxic, and may cause various damages.
It may resemble Hg functions. At extremely high doses, ionic In causes focal necrosis in the liver (Castronovo and Wagner 1971).
Human exposure to In compounds may occur in the semiconductor industry, during the manufacture (sawing, grinding, or polishing) of semiconductor wafers, or
during the maintenance of the production equipment. It may also be a result of In
isotope utilization for organ scanning, and for the treatment of tumors. Radioactive
111 In (in very small amounts on a chemical basis) is used as a radiotracer to nuclear
medicine tests.
Hydrated In oxide causes damage to those organs that contain phagocytic cells,
which clear the insoluble particles from the blood after intravenous injection.
Focal necrosis was found in the liver, the spleen, and the bone marrow. Damage
was also found in the thymus and lymph nodes. At its extremely high doses, convoluted tubules of the kidney may be damaged. Hydrated In oxide caused extensive