Antimony in drinking-water
Background document for development of WHO Guidelines for Drinking-water Quality
Although there is some evidence for the carcinogenicity of certain antimony compounds by inhalation, there are no data to indicate carcinogenicity by the oral route. IARC has concluded that there is inadequate evidence for the carcinogenicity of ATO in humans but sufficient evidence in experimental animals and that there is only limited evidence for the carcinogenicity of antimony trisulfide in experimental animals. ATO was assigned to Group 2B and antimony trisulfide to Group 3 (IARC, 1989).
Antimony trioxide, due to its low bioavailability, is genotoxic only in some in vitro tests, but not in vivo, whereas soluble antimony(III) salts exert genotoxic effects in vitro and in vivo.
The most common source of antimony in drinking-water appears to be dissolution from metal plumbing and fittings. The form of antimony in drinking-water is a key determinant of its toxicity, and it would appear that antimony leached from antimony-containing materials would be in the form of the antimony(V) oxo-anion, which is the less toxic form. It is therefore critical that the study selected for guideline derivation be a drinking-water study.
The suggested NOAEL (Lynch et al., 1999) in the subchronic drinking-water study in rats conducted by Poon et al. (1998) was 6.0 mg/kg of body weight per day based on decreased body weight gain and reduced food and water intake. A TDI of 6 µg/kg of body weight can be determined by applying an uncertainty factor of 1000 (100 for intra- and interspecies variation and 10 for the use of a subchronic study). A guideline value of 20 µg/litre (rounded figure) can be derived from this TDI by assuming a 60-kg adult drinking 2 litres of water per day and allocating 10% of the TDI to drinking-water. It should be noted that this value could be highly conservative because of the nature of the end-points and the large uncertainty factor; further data could result in a lower uncertainty factor.
There are adequate analytical methods for antimony in drinking-water with detection limits below the guideline value. As the most common source of antimony in drinking-water appears to be dissolution from metal plumbing and fittings, control of antimony from such sources would be by product control. At one time, antimony was suggested as a possible replacement for lead in solders, but there is no evidence that this has occurred. Antimony is not removed from water by conventional treatment processes (EUREAU, 1994). Control would therefore be by source selection or dilution.
The possibility of co-exposure of consumers to arsenic and antimony in drinking-water would necessitate an assessment of the local geological conditions on a case-by-case basis. If both elements were found to be present, case-specific risk evaluations for possible additivity and synergistic effects would need to be performed.