45
Strontium [Sr, 38]
45.1 INTRODUCTION
Strontium (Sr) is a metal of group 2 in the periodic table of elements and has a silver
appearance, before rapid oxidation, after which it turns into a yellowish color. It is
relatively common in the Earth’s crust, in contents within the range of 260–730 mg/kg.
It is likely to concentrate in mafic rocks (140–460 mg/kg) and calcareous sediments
(460–600  mg/kg). It reveals lithophilic properties, similar to Ca, with which it is
often associated, and does not occur as the free element. It may be accumulated near
S deposits. During weathering, Sr is easily mobile and then absorbed by clay minerals and organic matter (OM). Its contents of some coal may be elevated and vary
within <300–>1000 mg/kg. Fly ash contains, on average, 720 mg/kg of Sr.
Strontium oxidation state is +2 only. It forms several minerals, of which are mainly
strontianite, SrCO 3 , and celestite, SrSO 4 . Celestite occurs much more frequently in sedimentary deposits and is mining from these deposits. Strontianite, however, is more useful
mineral. There are four naturally occurring isotopes: 84 Sr, 86 Sr, 87 Sr, and 88 Sr. During the
nuclear weapon testing, 90 Sr, with a half-life of 28.78 years, and 89 Sr, with a half-live of 50
days, are released to the atmosphere. The isotope 90 Sr is of a real environmental concern.
Global Sr production (rounded), excluding the United States, in 2010 was 420,000 t,
of which 200,000 t was produced in China, Spain—180,000, and Mexico—30,000
(USGS 2011). Strontium was previously used for television tubes. Now, its consumption is mainly in ceramics and glass manufacture. It has also been broadly applied
in pyrotechnics.
Because Sr is very similar to Ca, it is incorporated in the bones, as well as its four
stable isotopes. The amounts of Sr isotopes vary between geographical locations;
thus, its amounts in the bone can help to determine the region it came from.
45.2 SOILS
Worldwide background mean levels of Sr in soils are estimated to be 130–240 mg/kg.
However, its much higher contents are relatively common (Table 45.1). The contents
of Sr are highly controlled by parent rocks and climate. The highest Sr contents are
in heavy loamy soils, especially developed in hot and dry climates (Table 45.1).
In some heavy loamy soils, and in soils from industrial regions, Sr content may be
above 1000 mg/kg. The range of Sr mean contents in soils of various countries are
presented as follows (in mg/kg): China, 26–150; Japan, 32–130; Sweden, 112–258; the
United States (California), 236–246 (Kabata-Pendias 2011). Soils of the remote region
in Spitsbergen, Norway, contain Sr within the range of 0.09–19.7 mg/kg (Gulińska et al.
2003).
Strontium is concentrated mainly in residual soil fractions. It is slightly mobile
and associated mainly with Fe and Mn oxides. It is moderately mobile in soils, and
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