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Trace Elements in Abiotic and Biotic Environments
Au concentrations in tissues. Au toxicity leads to necrosis and wilting, due to the loss
of turgidity in leaves.
Gold content in lichens is also a good indicator for elevated Au levels in the surroundings. Its contents in lichens from the vicinity of the Au mine in New Zealand
vary between 224 and 7450 mg/kg (Williams et al. vide Kabata-Pendias 2011).
18.6 HUMANS
Gold content in the human body (70 kg) is estimated at less than 0.2 mg, of which
in the blood, 1–40 μg/L; in the bone, 16; and in the liver, 0.4 μg/kg (Emsley 2011).
It is not known to perform any essential functions in humans. Metallic gold (Au°) is
arguably considered to be the least corrosive and most biologically inert of all metals. Human exposure to Au° is relatively common. However, it does not mean that
Au° has been shown to be completely inert in mammals. Metallic Au can be gradually dissolved by thiol-containing molecules, such as cysteine, penicillamine, and
glutathione to yield gold complexes (Sun et al. 2011).
Gold demonstrates excellent biocompatibility within the human body (the main
reason for its use as a dental alloy), hence the number of direct applications of Au,
as a medical material. Gold also possesses a high degree of resistance to bacterial
colonization, which makes it the material of choice for implants, which are at risk
of infection.
Injectable Au thiolate drugs such as aurothiomalate, aurothioglucose, and aurothiopropanol sulfonate, and the oral drug auranofin, are widely used for the treatment of difficult cases of rheumatoid arthritis (Sadler and Guo 1998). In recent times,
injectable Au has been proven to help reduce the pain and swelling of rheumatoid
arthritis and tuberculosis.
It is important to draw a distinction between the properties of Au in its bulk
form, and properties exhibited when it is present in the form of tiny nanoparticles
(NPs). At the nanoscale, the properties of gold can be markedly different. Colloidal
Au preparations (suspensions of AuNPs) in water are intensely red colored and can
be made with tightly controlled particle sizes, up to a few tens of nanometers, by
the reduction of Au chloride with citrate or ascorbate ions. Colloidal Au is used in
research applications in medicine, biology, and materials science. The technique of
immunogold labeling exploits the ability of the Au particles to adsorb protein molecules onto their surfaces.
Many new nanogold-based biomedical products are being developed for drug
delivery, cancer therapy, diagnostic devices, and biosensing. AuNPs are widely used
in consumer products, including cosmetics, food packaging, beverages, toothpaste,
automobiles, and lubricants. With this increase in consumer products containing
AuNPs, the potential for worker exposure to AuNPs will also increase. There are
limited data on the in vivo toxicology of AuNPs, meaning that the absorption, distribution, metabolism, and excretion of AuNPs remain unclear (Sun et al. 2011a).
The high accumulation of AuNPs in the kidneys suggest that the kidneys are
the major accumulation site for metal NPs. There is a difference in the pattern of
nanoparticle distribution between male and female kidneys (Sun et al. 2011a).