Occurrence in food
Tin is very scarce in the earth's crust, but it may occur in some places as rich mineral deposits. The main mode of tin occurrence in nature is tin oxide (SnO). In addition, it can be contained in many complex sulphide minerals which contain iron, silver, copper and antimony, among others.
Tin is a fairly inefficient metal and it is very resistant to rusting. For this reason, various tin coatings are widely used to coat metals. Tin-coated metal cans are the main source of human exposure to inorganic tin compounds. Tin coating is used on both the outer and inner surfaces of the can. Tin also acts as an antioxidant, making it important for the colour retention of certain pale vegetables or fruits (e.g. white asparagus and pineapple). In the case of highly acidic foods, a varnish coating, in addition to the tin coating, can also be applied to the inner surface of the can, which effectively prevents tin dissolution in the food. In addition to its pH, the dissolution of tin is also affected by the presence of corrosion accelerators such as nitrates and the oxygen content in the can, as well as the processing temperatures of the can.
In addition to coating cans, tin can also be used to coat kitchen utensils. Inorganic tin compounds are also present in food additives approved for use (E512, tin chloride).
Adverse health effects
Little information is available on the health effects of inorganic tin compounds, whereas organotin compounds are considered to be by far the most harmful. However, some individuals who have eaten a lot of canned food have reported stomach symptoms due to the effect of tin migrating from the can to the food.
JECFA, the World Health Organization's (WHO) Scientific Committee under the Food and Agriculture Organization (FAO) has set a tolerable weekly intake of 14 mg/kg (human weight) / week for tin and has estimated the acute effects to be 150 mg/kg for canned beverages and 250 mg/kg for other canned foods.
Maximum levels in food
EU regulation ((EU) 2023/915 as amended) sets maximum levels for inorganic tin compounds in canned beverages and in other canned foods as well as in canned baby foods and processed cereal-based foods for infants and young children, canned infant formulae and follow-on formulae, and canned special dietary foods for infants.
In 2013, the Council of Europe set a special release limit (SRL) for tin of 100 mg/kg to approach the release limits set out in Regulation (EC) No 1881/2006. The amount of tin present in food contact materials is not regulated separately.