Tin is a trace element that is required in bone formation. It has the atomic symbol Sn, atomic number 50, and atomic weight 118.71. (PubChem). Experimental studies over the last decade have suggested an association between thymus immune and homeostatic function and exogenous tin. It has been hypothesized that the thymus gland synthesizes and secretes one or more tin bearing factors that enhance immune defenses against malignancy and retard the gradual loss of immune capacity with senescence. (3). Physiologically, it exists as an ion in the body. Inorganic tin salts are poorly absorbed and rapidly excreted in the faeces; as a result they have a low toxicity. Only about 5 per cent is absorbed from the gastrointestinal tract, widely distributed in the body, then excreted by the kidney. Some tin is deposited in lung and bone. Some tin salts can cause renal necrosis after parenteral doses. Mutagenic studies on metallic tin and its compounds have been negative. Long-term animal carcinogenic studies have shown fewer malignant tumors in animals exposed to tin than in controls. Human volunteers developed mild signs of toxicity with tin, given in fruit juices, at a concentration of 1400 mg per litre. The WHO 1973 permissible limit for tin in tinned food is 250 micrograms per kg. The adult daily intake of tin was about 17 mg per day in 1940, but it has now decreased to about 3.5 mg, due to improvements in technique of tinning with enamel overcoat and crimped lids to minimize exposure to tin and lead solder. (4).
belongs to the class of inorganic compounds known as homogeneous post-transition metal compounds. These are inorganic compounds containing only metal atoms,with the largest atom being a post-transition metal atom.
Organotin compounds produce neurotoxic and immunotoxic effects. Organotins may directly activate glial cells contributing to neuronal cell degeneration by local release of pro-inflammatory cytokines, tumor necrosis factor-α, and/or interleukins. They may also induce apoptosis by direct action on neuronal cells. Organotin compounds stimulate the neuronal release of and/or decrease of neuronal cell uptake of neurotransmitters in brain tissue, including aspartate, GABA, glutamate, norepinephrine, and serotonin. This may be either a contributing factor to or result of the neuronal cell loss. The immunotoxic effects of organotins are characterized by thymic atrophy caused by the suppression of proliferation of immature thymocytes and apoptosis of mature thymocytes. Organotin compounds are believed to exert these effects by suppressing DNA and protein synthesis, inducing the expression of genes involved in apoptosis (such as nur77), and disrupting the regulation of intracellular calcium levels, giving rise to the uncontrolled production of reactive oxygen species, release of cytochrome c to the cytosol, and the proteolytic and nucleolytic cascade of apoptosis. The suppression of proliferation of immature thymocytes further results in the suppression of T-cell-mediated immune responses. Organotins are also endocrine disruptors and are believed to contribute to obesity by inappropriate receptor activation, leading to adipocyte differentiation. Inorganic tin triggers eryptosis, contributing to tin-induced anemia. (6, 1, 2)
Metabolism
Though tin metal is very poorly absorbed, tin compounds may be absorbed via oral, inhalation, or dermal routes, with organotin compounds being much more readily absorbed than inorganic tin compounds. Tin may enter the bloodstream and bind to hemoglobin, where it is distributed and accumulates mainly in the kidney, liver, lung, and bone. Organotin compounds may undergo dealkylation, hydroxylation, dearylation, and oxidation catalyzed by cytochrome P-450 enzymes in the liver. The alkyl products of dealkylation are conjugated with glutathione and further metabolized to mercapturic acid derivatives. Tin and its metabolites are excreted mainly in the urine and feces. (6)
No indication of carcinogenicity to humans (not listed by IARC).
Uses/Sources
Tin is found in many alloys, such as brass, bronze, and pewter, as well as soldering materials. Tin metal is also used to line cans for food, beverages, and aerosols. Inorganic tin compounds are used in toothpaste, perfumes, soaps, food additives and dyes. Organotin compounds are used to make plastics, food packages, plastic pipes, pesticides, paints, and pest repellents. (5, 7)
Minimum Risk Level
Not Available
Health Effects
Metallic tin is not very toxic due to its poor gastrointestinal absorption. However, ingestion of large amounts of inorganic tin compounds can cause stomachache, anemia, and liver and kidney problems. Breathing or swallowing, or skin contact with organotins, can interfere with the way the brain and nervous system work, causing death in severe cases. Organic tin compounds may also damage the immune and reproductive system. (5, 6)
Symptoms
Inorganic or organic tin compounds placed on the skin or in the eyes can produce skin and eye irritation. (6)
