Carcinogenicity Mutagenicity Studies

The toxicity and carcinogenicity of sodium hypochlorite has been examined extensively. Both published and unpublished studies have repeatedly demonstrated this ingredient's safety, and failed to raise any significant questions regarding acute toxicity or carcinogenicity. A number of studies that examine sodium hypochlorite's carcinogenic and mutagenic potential have been investigated by both in vitro and in vivo methods.

One of the most common worldwide uses of chlorine and chlorine containing compounds (including sodium hypochlorite) is as a disinfectant for drinking water. This use has led a number of investigators to examine the carcinogenicity of chlorinated water.

Hasegawa et al. [30] examined the effects on rats of a 104-week administration of sodium hypochlorite in drinking water at levels of 0.05-0.2%. No significant increase in incidence of any tumors was observed, leading the investigators to conclude that sodium hypochlorite showed no carcinogenic potential.

Kurokawa examined the carcinogenicity of long-term exposure to sodium hypochlorite in both rats and mice [31]. The rats were given a 104-week administration of sodium hypochlorite in drinking water at levels of 0.05-0.2%, whereas the mice underwent a 103-week administration of sodium hypochlorite in drinking water at levels of 0.05-0.1%. The authors also concluded that sodium hypochlorite was not carcinogenic in rats and mice.

Robinson et al. [32] examined hyperplasia in mouse skin after dermal exposure to sodium hypochlorite, hypochlorous acid, and to the hypochlorite ion. The stated goal of this study was to examine the potential for these compounds to promote skin cancer. The study consisted of exposing the skin of SENCAR mice to concentrations of 0.001-0.1% of various chlorine compounds. All of these compounds resulted in some degree of hyperplasia. The author's decision to use the ability of sodium hypochlorite, and its derivatives, to induce hyperplasia (thickening of the skin) as an indicator of the substance's tumor promoting capacity was based upon the 'excellent correlation' between the hyperplasiogenic activity and tumor promotion among phorbol esters. However, the author admits that this correlation does not hold true for compounds of chemical classes other than phorbol esters. Given that the correlation between skin hyperplasia and tumor promotion appears to be limited to phorbol esters, and that sodium hypochlorite is unrelated to this compound, one questions the selection of this assay as a valid indicator of sodium hypochlorite's possible carcinogenicity. One cannot conclude any positive information concerning carcinogenicity with an assay of this dubious nature.

In another study using an assay of dubious relevance, Meier examined the effect of interperitoneally administered sodium hypochlorite and its derivatives on the production of sperm-head abnormalities in mice [33]. In this study, three different in vivo tests designed to look for chromosomal damage were used to examine various disinfectant chemicals. In one of these tests, the sperm-head abnormality assay, hypochlorite ions were detected in only one of three sample groups, and were not found for other sodium hypochlorite derivatives. Further, three different assays showed no indication of mutagenic activity. Additionally, the author admits that the meaning of a positive result in this assay was the subject of scientific debate. Therefore, a weak positive result to interperitoneally administered hypochlorite ions in an unproven assay for mutagenic activity has little bearing on the safety of sodium hypochlorite for topical use.

Amuchina (now Alcavis) commissioned two in vitro studies to examine the possible mutagenic potential of its 'Amuchina - Electrolytic Chloroxidizer,' a sodium hypochlorite disinfectant/antiseptic.

One study by Pirovano [34] was conducted using one of the most widely used of all tests for mutagenesis, the Ames assay. This assay measures the influence of a chemical compound on the spontaneous mutation rate of Salmonella typhimurium. In this test, mutagenic compounds showed an increase in the rate of mutations over the background or control rate. Amuchina's sodium hypochlorite solution did not increase the mutation rate, therefore, it can be concluded that it does not have mutagenic potential in tests that are often difficult when the chemical is an antimicrobial.

Pirovano [35] also conducted a second study. This study was similar to the first, but used the yeast Saccharomyces cerevisiae in place of S. typhimurium as an indicator organism. Again, Amuchina's solution did not show an increase in the mutation rate, and did not show mutagenic potential.

In sum, many studies with sodium hypochlorite have not found any demonstrated mutagenic or carcinogenic potential. Two long-term feeding studies in rats and one in mice showed no increase in the rate of tumor formation. In two standard in vitro assays, sodium hypochlorite did not show any mutagenic potential.

The study design of some authors' work discussed above strains the concept of a toxicity profile in that a rather obscure measurement of toxicity, let alone a means to examine chromosomal abnormalities, was used. Similarly, grouping chemicals other than known carcinogens like phorbal esters together for testing based on an unproven correlation between hyperplasia induction and development of skin cancer must be discounted as well-intentioned, but not reasonable.

More conventional tests for mutagenic potential show that sodium hypochlorite is not mutagenic. The carcinogenicity and mutagenic potential in vitro and in vivo have been studied as well as its toxicity using several methods of exposure, and the possible development of blood levels after topical use.

In summary, in all these studies, no adverse toxicological effects were found with sodium hypochlorite. Therefore, based on these studies as well as toxicological information accumulated during the long history of use of sodium hypochlorite, it should be considered non-carcinogenic, non-mutagenic, and essentially non-toxic for its proposed use, at use concentrations.

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