and tinfoil. Large amounts of tin can accumulate in foods
in contact with tin plate unless these are lacquered or coat-
ed with resin [4]. The acute toxicity of inorganic tin is
manifested as gastric irritation, nausea, vomiting, and
abdominal discomfort. Inorganic tin salts are poorly
absorbed by the gastrointestinal tract and rapidly excreted.
Nevertheless, there are several reports of gastric irritation
and vomiting in humans consuming canned foods or bev-
erages, particularly sour fruit products packaged in tinplate
cans and containing high levels of tin [5]. High concentra-
tions of tin bring serious interference to the metabolism of
zinc [6].
From published data, there appears to be a small
amount of evidence suggesting that consumption of food or
beverages containing tin at concentrations at or below 200
ppm has caused adverse gastrointestinal effects in an
unknown but possibly small proportion of those exposed
[7]. On the other hand, when the contamination reaches this
level the organoleptic properties of the food can be serious-
ly affected [8].
The Joint Expert Committee on Food Additives of the
Food and Agriculture Organization and the World Health
Organization (JECFA) has recommended a Provisional
Tolerable Weekly Intake (PTWI) for tin of 14 mg/kg body
weight/week to protect against the risk of any chronic
(long-term) effects [9]. This PTWI is equivalent to 120
mg/day for a 60 kg person.
According to the Food and Agriculture Organization of
the UN/World Health Organization (FAO/WHO) the maxi-
mum limit for tin in canned foods is 250 mg/kg [10]. The
EU legislation (EC No. 1881/2006) [11] suggests a maxi-
mum limit of 200 mg/kg for inorganic tin in canned foods,
of 100 mg/kg for canned beverages, and of 50 mg/kg for
canned liquid foods for young children.
Most foods contain very low concentrations of tin, usu-
ally below 10 mg/kg, although canned foods may contain
higher concentrations as a result of the slow dissolution of
the tin coating used on the inside of some food cans to pro-
tect the steel body of the can from corrosion.
Many factors influence the amount of tin that is taken
up by canned foods from the internal coating of the can.
These include: the type and composition of the product
itself (including the acidity, the presence of organic acids
and pigments and certain ions such as nitrate); the type of
can (including the quality and thickness of the tin coating,
the amount of the tin coating that is exposed to the can con-
tents, and the presence or absence of a layer of lacquer over
the tin plate); the canning procedure (including the amount
of air in the container at sealing and the internal vacuum
and 'headspace' between the fill level of the product and the
lid), and storage (time from canning and temperature dur-
ing storage) [12].
Under normal circumstances the shelf life of canned
foods is set so that the tin content of the food remains well
below the legal limit throughout the product's shelf life.
However, under certain circumstances tin dissolution can
accelerate, causing unacceptably high tin concentrations in
the food within its shelf life [13].