Zirconium [Zr, 40]
369
Rainwaters collected in Sweden, during 1999, contained Zr at an average value
of 0.024 μg/L within the range of 0.01–0.04 μg/L. Its wet deposition has been estimated to be 0.25 g/ha/yr (Eriksson 2001a).
The median Zr concentration in bottled waters of the EU countries is 0.015 μg/L
and is higher than in tap waters, estimated to be 0.009 μg/L (Birke et al. 2010).
Zirconium in stream sediments is likely to accumulate, up to about 2433 mg/kg,
with median values within the range of 256–818  mg/kg (Reimann and de Caritat
1998).
56.4 AIR
The average Zr concentration in air collected in urban areas is about 3  ng/m 3 ,
and its contents from air of contaminated regions vary between 0.7 and 27 ng/m 3
(Table 56.1).
56.5 PLANTS
Although most soils contain relatively high amounts of Zr, its availability to plants,
presumably in anionic form, Zr(OH) 5
, is greatly limited. Its availability is controlled
by its chemical species, and the easiest taken up are Zr–organic ligands.
Zirconium contents are usually higher in roots than in tops of plants (especially of
legumes). Higher accumulation of Zr in roots than in tops is confirmed in the experiment with tomato plants, which contain Zr at levels 0.56 and 7.96 mg/kg in aerial
parts and roots, respectively (Vera Tome et al. 2003). However, when aerial dust is
enriched in Zr, it may be easily absorbed by plant tops. Increased Zr level in mosses,
at an average value of 0.35 mg/kg, indicates its sources from dust and rainwater
(Berg and Steinnes 1997).
Zirconium contents of food plants vary from 0.005 to 2.5 mg/kg, being lowest
in cereal grains and highest in peanuts and beans. Winter wheat and barley grains
grown in Sweden contain Zr at the mean values of 0.008 and 0.013, respectively
(Eriksson 2001a). Some herbages, especially legumes, trees, and shrubs, may
concentrate more Zr than other plants. Plants grown along highways in Germany
contain Zr within the range of 0.07–0.92  mg/kg, being highest in dandelion
(Djingova et al. 2003).
Although the toxic effects of Zr on plants, and especially on root growth, are
observed, its stimulating effects on growth and protein synthesis of some microorganisms are also reported (Ferrand et al. 2006).
56.6 HUMANS
The total amount of Zr in the human body is 1 mg, of which 0.01 mg/L is in the
blood, <0.1  mg/kg in the bone, and average 0.1  mg/kg in other tissues (Emsley
2011). Most of ingested Zr passes through the gut, without being adsorbed, and that
which is adsorbed tends to accumulate slightly more in the skeleton than in tissue.
Zirconium has no known biological role or toxicity and is biocompatible and is used
for surgical implants and prosthetic devices.