50
Tin [Sn, 50]
50.1 INTRODUCTION
Tin (Sn), a silvery metal of group 14 in the periodic table of elements, occurs in the
Earth’s crust at an average amount of 2.5 mg/kg. Its contents are slightly elevated in
acidic magmatic rocks, up to 3.6 mg/kg, and in argillaceous sediments, up to 10 mg/kg.
It is easily fixed by organic matter (OM), and thus, its concentration in coal may be
up to 30 mg/kg. Its content may also be increased in several other bioliths.
The oxidation states of Sn are +2 and +4, of which the last one is more common
and reveals amphoteric properties. The most important of few Sn minerals is cassiterite (SnO 2 ). Tin is also associated with other minerals, such as stannite (Cu 2 SnFeS 4 ),
teallite (Cu 3 SnS 4 ), and montesite (PbSn 4 S 3 ).
Global Sn production (rounded), excluding the United States, in 2010 was
2,651,000 t, of which 115,000  t was produced in China, 60,000 t in Indonesia,
38,000 t in Peru, and 16,000 t in Bolivia (USGS 2011). The recovery of Sn through
secondary production, or recycling of Sn scrap, is also its important source. Tin
in combination with other metals forms a wide variety of useful alloys. It is most
commonly alloyed with Cu. Bronze, an alloy of Sn and Cu, has been used in large
quantities since 3000 BC. It is a malleable metal, not easily oxidized in air, and used
to coat other metals to prevent corrosion.
Alloy of Sn–Pb is commonly used soft solder. Because of low Sn toxicity, it is
also used for food packaging, including tin cans. It has a number of organometallic
derivatives of an importance in various manufacturing sectors. It is also used in glass
production, and as polyvinyl chloride (PVC) stabilizers and wood preservatives. It is
a common component of ship paints, which may be of an environmental concern.
Its major use is now estimated as follows: electrical, 28%; cans and containers, 19%;
construction, 13%; transportation, 12%; and other, 28% (USGS 2011).
50.2 SOILS
The average Sn abundance in soils is 2.5 mg/kg, within the range of <0.1–>10.0 mg/kg,
being a bit elevated in heavy loamy and organic soils (Table 50.1). Its contents of
soils from various countries are reported as follows (in mg/kg): China, 2.5–17.7;
Germany, 1.0–5.0; Japan, 2.0–3.1; Sweden, 0.4–8.6; the United States, 1.0–11.0
(Kabata-Pendias 2011). Soils derived from rocks with increased Sn levels or soils
near metal smelter plants may contain increased Sn levels, up to 1000 mg/kg. Soils
of the remote region in Spitzbergen contain Sn <0.41 mg/kg (Gulińska et al. 2003).
The criteria for contaminated land (Dutch List 2013), following Sn concentrations in
soils, are established (in mg/kg) as follows: uncontaminated, 20; medium contaminated, 50; and heavily contaminated: 300. The allowable concentration of Sn in soils
is 50 mg/kg (ATSDR 2002b).
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