Antimony in drinking-water
Background document for development of WHO Guidelines for Drinking-water Quality
|Compound||CAS No.||Molecular formula|
|Antimony trioxide (ATO)||1309-64-4||Sb2O3|
|Potassium antimony tartrate (APT)||28300-74-5||KSbOC4H4O6|
|Sodium antimony tartrate (AST)||34521-09-0||NaSbOC4H4O6|
2 Physicochemical properties (Wiberg, 1985; HSDB, 1990)
|Melting point (°C)||630.5||655||100||–|
|Boiling point (°C)||1635||1425||–||–|
|Density at 20 °C (g/cm3)||6.691||–||2.6||–|
|Vapour pressure at 886 °C (kPa)||0.133||–||–||–|
|Water solubility (mg/litre)||insoluble||0.0171||readily soluble||readily soluble|
3 Organoleptic properties
APT is odourless and has a sweet metallic taste (Hawley, 1981). ATO is both odourless and tasteless. 4 Major uses
Elemental antimony is an inflexible metal and therefore has few technical uses. However, it forms very hard and technically interesting alloys with copper, lead and tin.
ATO as a technical product or in technical processes can serve as a flame retardant, as a turbidifier in white enamel and as an initiator or additive in the production of polyethylene terephthalate.
Soluble pentavalent antimony (antimony(V)) compounds (sodium stibogluconate, stibosamine) are used as specific therapeutics against different forms of leishmaniasis and are physiologically tolerated more than trivalent antimony (antimony(III)) compounds (Winship, 1987).
APT (tartar emetic) has been used to induce vomiting in poisoning cases, and antimony compounds such as piperazine antimony tartrate were used as drugs against bilharzia.
5 Environmental fate
The emission of antimony into the human environment appears to be exclusively the result of human activity. Most emitted antimony is in the form of ATO, which is released as a result of coal burning or with fly ash when antimony-containing ores are smelted (Nriagu & Pacyna, 1988). Approximately 6400 tonnes of antimony are transported annually to oceans (Bowen, 1979).
The chemical behaviour of antimony is as complex as that of arsenic, its neighbour in the periodic table (Wiberg, 1985). It is speculated that antimony could be a natural co-contaminant with arsenic in some drinking-waters (Gebel, 1999b). Soluble forms of antimony (and arsenic) tend to be quite mobile in water, whereas less soluble species are adsorbed onto clay or soil particles and sediments, where they are mainly bound to extractable iron and aluminium (Crecelius et al., 1975). Although few data address the speciation of antimony in water, those that are available together with thermodynamic predictions indicate that the most favoured form in water will be the pentavalent oxo-anion, Sb(OH6)- (Mohammad et al., 1990; Cotton et al., 1999).