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Trace Elements in Abiotic and Biotic Environments
Rainwater collected in Sweden, during 1999, contained Ta in the range of <0.1–0.4
ng/L, at an average value of 0.2 ng/L (Eriksson 2001b).
The median Ta concentrations in bottled water of the EU countries is <1 ng/L and
is a bit lower than in tap water, estimated to be 1.8 ng/L (Birke et al. 2010).
46.4 AIR
The concentration of Ta is 10–30 pg/m 3 in the atmosphere above Greenland and up to
280 pg/m 3 in air above the United States (Reimann and de Caritat 1998).
Wet deposition of Ta in Sweden is reported to be, on average, 1.5 μg/ha/yr
(Eriksson 2001a).
46.5 PLANTS
There are very limited sources of Ta in plants. Various vegetables contain Ta within
the range of <1–<6 μg/kg, at a mean value of <1 μg/kg (Kabata-Pendias 2011).
In cereal grains from Sweden, Ta amounts vary from 1.1 to 5  μg/kg (Eriksson
2001a).
46.6 HUMANS
Tantalum content in the human body (70 kg) is about 0.2 mg (Emsley 2011). The
pure metal is, to a great degree, inert both in vivo and in vitro. The pure metal and its
oxides possess low solubility and toxicity; however, its halide compounds are more
biologically active. It may be concentrated in hard tissues.
Tantalum has been in clinical use since before 1940, and has found a wide range
of diagnostic and implant applications. In some applications, such as for radiographic
bone markers and cranial closure, Ta may well be the current material of choice;
thus, metallic Ta is a promising biomaterial (Black 1994). It is inert enough to be
used as an implant material for humans.
Tantalum is highly resistant to chemical attack and arouses very little adverse
biological response in both reduced or oxidized forms. It is very biocompatible in a
variety of applications, including bone surgery. Metals coated with Ta and Ta itself
release nothing into extraction media during standardized procedures, and the surface analysis shows low impurity.
There are very little data on Ta toxicity. This probably means that Ta and its
common compounds are relatively innocuous. It is an experimental tumorigenic, or
tumor-causing substance. However, overall systemic industrial poisoning is apparently unknown. Tantalum and its common compounds are not listed as either presumptive or possible human carcinogens, in the United States by the International
Agency for Research on Cancer (IARC 2013). However, some circumstances, following the implantation of Ta in animal tissues, it has caused cancer. Apparently,
the smoothness of the implanted Ta sheet plays a role, with highly polished surfaces
potentially leading to cancer in animals.