Strontium sulphate

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not sensitising)

Additional information:

Toxicological relevance of the counterion “sulfate”

The registrant is of the opinion that the toxicity of strontium sulfate is driven by the strontium moiety and that the sulfate anion does not contribute to the overall toxicity of the substance strontium sulfate to any relevant extent, for the following reasons:

Sulfate anions are abundantly present in the human body in which they play an important role for the ionic balance in body fluids. Sulfate is required for the biosynthesis of 3′-phosphoadenosine-5′-phosphosulfate (PAPS) which in turn is needed for the biosynthesis of many important sulfur-containing compounds, such as chondroitin sulfate and cerebroside sulfate. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) concludes that the few available studies in experimental animals do not raise any concern about the toxicity of the sulphate ion in sodium sulphate. Sodium sulphate is also used clinically as a laxative. In clinical trials in humans using 2-4 single oral doses of up to 4500 mg sodium sulphate decahydrate per person (9000 – 18000 mg per person), only occasional loose stools were reported. These doses correspond to 2700 - 5400 mg sulphate ion per person. High bolus dose intake of sulphate ion may lead to gastrointestinal discomfort in some individuals. No further adverse effects were reported (JECFA 2000, 2002). This position was adopted by the European Food Safety Authority (EFSA 2004) without alteration.

Based on the above information, one can therefore safely assume that the sulfate anion in strontium sulfate does not contribute to the overall toxicity of strontium, sulfate. It is concluded that only the effect of “strontium” is further considered in the human health hazard assessment of strontium sulfate.

Read across from SrCl₂to SrSO₄: The toxicity of strontium substances such as strontium sulfate can reasonably assumed to be determined by the availability of strontium ions in solution. As a first surrogate for bioavailability, the water solubility of a test substance may be used. Strontium chloride is highly water soluble with ~538 g/L at pH ~ 7, whereas strontium sulfate is moderately soluble (~125 mg/L at pH ~ 6.5). Hence, any read across from strontium chloride to strontium sulfate is inherently very conservative.

Justification for selection of skin sensitisation endpoint:
reliable GLP guideline study with the structural analogue strontium chloride hexahydrate available

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

Justification for selection of respiratory sensitisation endpoint:
During long-year industrial practice no cases of hypersensitivity were documented till now by workers exposed exclusively to strontium sulfate. Thus, no classification as respiratory sensitiser according to Regulation (EC) 1272/2008 is required.

Justification for classification or non-classification

Sensitisation:

The reference Allen (1997) is considered as the key study on skin sensitization. In this study, the test material, Strontium chloride-6-hydrate extra pure, produced a 0 % (0/10) sensitisation rate and was classified as a non-sensitiser to guinea pig skin. According to the criteria specified by Directive 67/548/EEC and subsequent regulations and Regulation (EC) No 1272/2008 and subsequent regulations, the test item does not require classification as skin sensitizer.

 

Respiratory sensitisation:

During long-year industrial practice no cases of hypersensitivity were observed till now by workers exposed exclusively to strontium sulfate. Thus, no classification as respiratory sensitiser according to regulation (EC) 1272/2008 is required.