Bismuth [Bi, 83]
37
decreased to 33 μg/kg in 2000. Increased Bi levels resulted mainly from aerial
pollution. Grass (Agrostis scabra), plots from where Bi pellets were used, contains
elevated Bi amounts, up to 95 μg/kg (Fahey et al. 2008).
Wheat and barley grains contain Bi at the mean values of 3 and 5 μg/kg, respectively (Eriksson 2001a).
6.6 HUMANS
Amount of Bi found in the human body (average 70 kg) is less than 500 μg (Emsley
2011); in the rib bone is 15 μg/kg (Zaichik et al. 2011). Normal concentration of Bi in
the blood is between 1 and 15 μg/L. Distribution of Bi in the organs is either largely
independent of the compound administered or the route of administration: the concentration in the kidneys is always highest and retained for a long time. It is bound to
a Bi metal-binding protein in the kidneys, the synthesis of which can be induced by
the metal itself (Slikkerver and de Wolf 1989).
A number of toxic effects have been attributed to Bi compounds in humans:
nephropathy, encephalopathy, osteoarthropathy, gingivitis, stomatitis, and colitis.
Each of these adverse effects is associated with certain Bi compounds. Bismuth
encephalopathy occurred in France as an epidemic of toxicity and was associated
with the intake of inorganic salts including Bi subnitrate, subcarbonate, and subgallate (Slikkerver and de Wolf 1989).
Bismuth and its salts can cause kidney damage, although the degree of such damage is usually mild. Large doses can be fatal. Due to the low stability in aqueous
solutions of Bi compounds, with +5 oxidation state, Bi with the +3 oxidation state is
regarded as the only relevant Bi species in biological systems. It is seen as the least
toxic metal for humans, and is widely used in medical applications for its good antibacterial properties, mainly because of their low uptake into human cells.
Compounds containing Bi are, therefore, widely used in medical applications.
Bismuth-containing pharmaceuticals, partially in synergy with antibiotics, are
already used or are being considered in the treatment of infections caused by certain
bacteria, especially to eradicate Helicobacter pylori, Pseudomonas aeruginosa, and
others. However, careless use of Bi-containing pharmaceuticals can result in encephalopathy, renal failure, and other adverse effects. Both the benefits and the adverse
effects of Bi are based on the same property of the metal, that is, its strong affinity
to thiols groups of proteins. It is important that the concentration of Bi applied in
medication does not cause an increased accumulation of the metal in the cytoplasm
of human cells (Thomas et al. 2012).
Microbial methylation of Bi by the human gut microbiota resulting in more mobile
and presumably more harmful derivatives has recently been reported. Transformation
of several elements such as Bi, As, Sb, Se, and Te into volatile derivatives by methylation or hydridization plays an important role in the spreading and cycling of these
elements in natural and anthropogenetically modified environment. Because many
of these volatile derivatives are more toxic than their (mostly inorganic) precursors,
these processes may have an impact on human health. A high risk can be expected
from scenarios in which these derivatives are accumulated in closed systems, such as
compartments of all living organisms (Michalke et al. 2008).