332
Trace Elements in Abiotic and Biotic Environments
period 1990–1995, contained Sn within the range of <0.008–25 mg/kg, depending
on the locations (Berg and Steinnes 1997).
50.5 PLANTS
There are no evidences that Sn is essential to plants, and it is considered as toxic to
both higher plants and fungi. Its mobile species, mainly Sb 2+ and Sn 4+ , are easily
available to plants, and then accumulated in roots.
The common range of Sn in food plants is between <0.04 and <0.1  mg/kg,
whereas in grass it varies from 0.2 to about 2.0 mg/kg. The worldwide Sn concentrations in wheat grains are reported to be within the range of 5.6–7.9 in mg/kg
(Kabata-Pendias 2011). Much lower Sn amounts, 0.01–0.12 mg/kg, are in wheat of
Sweden (Eriksson 2001a). Tin contents in forest plants are variable, up to 0.3 mg/kg
in Lactarius blennius and up to 1.8 mg/kg in Collybia peronata (Tyler 2004).
Plants growing in mineralized or contaminated soils accumulate Sn to high levels. Sugar beets from areas around Sn smelter contain this metal up to 1000 mg/kg,
whereas various vegetables contain up to 2000 mg/kg. Some bacteria are resistant to
Sn excess and may concentrate it up to 7700 mg/kg (Kabata-Pendias 2011).
50.6 HUMANS
Tin content in the human body is 30 mg, of which about 0.4 mg/L is in the blood,
1.4 mg/kg in the bones, and 0.3–2.4 mg/kg in soft tissues (Emsley 2011). Its highest concentrations occurred in the kidney, liver, lung, and bones. In the lungs, Sn
appeared to increase with age.
Human exposure to Sn may occur by inhalation, ingestion, or dermal absorption. Dermal absorption is a significant route of occupational exposure for certain
organotin compounds. Tin ingested in food is poorly absorbed. At most about 1% of
ingested Sn enters the blood. Absorption appears to be related to the chemical form
of the element, with Sn 2+ being 4 times more readily absorbed than Sn 4+ compounds
(2.8% of Sn 2+ compounds and 0.64% of Sn 4+ compounds). Absorbed Sn is rapidly
excreted, but its small amounts may be retained in the kidney, liver, and bones, as
well as in other soft tissues.
Tin does not appear to have any biological role in the body. It affects the metabolism of other metals, such as Cu, Zn, and Fe. Humans chronically exposed to inorganic
Sn (e.g., stannic oxide dust or fumes) manifest a form of pneumoconiosis, known
as stannosis, which involves mainly the lower respiratory system. Gastrointestinal
effects, such as nausea, vomiting, and diarrhea, have been reported, when food is
contaminated with inorganic Sn. However, potential target organs for inorganic Sn
toxicity have not yet been established (ATSDR 2005b).
Organotin compounds are much more toxic than inorganic forms. Triethyland trimethyl-tin (TET and TMT) are dealkylated rapidly to toxic trialkyl derivatives and are metabolized more slowly to less toxic di- and monoderivatives. All
of these and other related compounds, especially TBT, are genotoxic. TET interferes with cellular metabolism by uncoupling oxidative phosphorylation, causing
mitochondrial damage and resulting in cerebral edema, leading to neurotoxicity