Tin

(endorsed 2011)

Guideline

No guideline value is considered necessary for tin in drinking water, as concentrations are likely to be considerably lower than the level that can cause health effects.

General description

Tin is mainly used for plating. Tin coatings are used in the manufacture of food containers and in food processing equipment. Tin is also used in alloys such as solders, bronzes and pewters. Inorganic tin compounds are used as pigments in the ceramic and textile industries. Organic tin compounds are used as biocides (see Fact Sheet on organotins).

The concentration of tin in rivers, estuaries and oceans is generally less than 0.000005 mg/L (5 ng/L), but in some instances has been measured up to 0.002 mg/L. The use of organotin biocides can produce significantly higher concentrations in environmental waters. Levels of <0.042–0.3 mg/L were found in 37 different bottled mineral waters. A mean range of 0.001–0.002 mg/L (maximum 0.030 mg/L) was found in a survey of water supplies in the United States; values greater than 0.002 mg/L are exceptional (WHO 2004, IPCS 2005).

Food, and particularly canned food, is the major source of human exposure to tin. Intake from this source can vary widely and estimates range from 0.1 mg per day up to 100 mg per day, with a median of 0.2 mg per day.

Typical values in Australian drinking water

Australian drinking water supplies have not been routinely monitored for tin. Based on measurements made overseas, it is likely that concentrations would be extremely low.

Treatment of drinking water

Treatment of drinking water to reduce the concentration of inorganic tin is unlikely to be required.

Measurement

The concentration of tin in drinking water can be determined using graphite furnace atomic absorption spectroscopy (APHA Method 3500-Sn part B 1992). The limit of determination is 0.01 mg/L.

Health considerations

Tin is thought to be an essential element in animals. It is not known whether it is essential for humans.

Tin, or tin salts, are poorly absorbed from the gastrointestinal tract. Most studies indicate that less than 5% is absorbed. Highest concentrations of tin occur in the bone, kidney and liver. Biological half-lives range from 1 to 4 months, and tin is excreted primarily via the kidneys and bile.

Extensive reviews and summaries of the human and animal toxicity data for tin are available (JECFA 2000, WHO 2004, IPCS 2005, ATSDR 2005).

There is no evidence of adverse effects in humans associated with long-term exposure to tin. The main effects, due to consumption of canned food with high tin concentrations (over 150 mg/kg), are gastric irritation resulting in vomiting, diarrhoea, fatigue and headache.

In animals, long-term ingestion studies over 2 years using rats and mice reported no significant adverse effects.

Inorganic tin in the form of stannous chloride was found not to be mutagenic in tests with bacteria; however, in mammalian cells in vitro, inorganic tin has induced DNA and chromosomal aberrations.

Derivation of guideline

The low toxicity of tin and inorganic tin compounds is due largely to low absorption, low tissue accumulation and rapid excretion. A guideline value of approximately 0.7 mg/L could be derived from a 2-year feeding study with rats (WHO 1982), but this value is approximately three orders of magnitude higher than tin concentrations in drinking water. Therefore, the presence of tin in drinking water does not represent a hazard to human health and the establishment of a guideline value is not deemed necessary.

References

APHA Method 3500-Sn Part B (1992). Tin: Atomic Absorption Spectrometric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.

ATSDR (Agency for Toxic Substances and Disease Registry) (2005). Toxicological Profile for Tin and Tin Compounds. ATSDR, US Department Of Health and Human Services Public Health Service. PB2006-100006

IPCS (International Programme on Chemical Safety) (2005). Concise International Chemical Assessment Document 65. Tin and Inorganic Tin Compounds. IPCS, World Health Organization Geneva, Switzerland.

JECFA (Joint Expert Committee on Food Additives) (2000). Who Food Additives Series 46:Tin (Addendum). JECFA, World Health Organization.

WHO (World Health Organization) (2004). Inorganic Tin in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality. WHO, Geneva, Switzerland. WHO/SDE/WSH/03.04/115.