Orthophosphoric acid

Carcinogenicity

Description of key information

No regulatory studies are available however the following documents discuss the possibility of phosphoric acid mist being carcinogenic via the inhalation route:
- IARC (1992). International Agency for Research on Cancer. Occupational exposure to mists and vapours from strong inorganic acids; and other industrial chemicals. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, volume 54. http://monographs.iarc.fr/ENG/Monographs/vol54/mono54.pdf
- IARC (2012). International Agency for Research on Cancer. Chemical agents and related occupations. A review of human carcinogens. Mists from strong inorganic acids. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, volume 100F. http://monographs.iarc.fr/ENG/Monographs/vol100F/mono100F-33.pdf
A full assessment of the available data has been performed and the conclusions are summarised under 'conclusions for classification or non-classification'. 

Justification for classification or non-classification

Conclusion on classification and labelling

In accordance with Regulation EC No.1272/2010 (EU CLP) phosphoric acid does not meet the criteria for classification as “carcinogenic to humans” for the following reasons:

1.     There are no human studies on phosphoric acid that establish a causal relationship between exposure and the development of cancer. As such, a classification as Category 1A is not warranted.

2.     There are no animal experiments that show evidence of phosphoric acid being a carcinogen. Therefore, a classification as Category 1B is not supported by the dataset.

3.     There are no supporting data that would constitute ‘limited evidence’ of carcinogenicity for phosphoric acid. None of the studies report a positive association between exposure to phosphoric acid and cancer due to the lack of phosphoric acid specific data. For the reasons details above a causal interpretation based on acidity and alleged similarities to sulphuric acid does not appear credible and therefore Category 2 is not considered appropriate.

It is not advised to apply a ‘precautionary’ approach to classification based on the proposed classification for sulphuric acid since there is no proven mode-of-action or threshold for the proposed effects and it is not scientifically proven that any substance capable of causing respiratory irritation (due to low pH) is also a carcinogen. Furthermore, it would not be advisable to propose an animal study to investigate the mode of action. The OECD guideline for long-term carcinogenicity (OECD TG 451) focusses on exposure via the oral route, the guideline states that carcinogenicity studies via the inhalation route must be designed on a case-by-case basis. As reported in the OECD guideline for sub-chronic inhalation (OECD TG 413) it is possible to perform repeated-dose inhalation testing on dilutions of corrosive substances but it is stated that ‘when exposing animals to these materials the targeted concentrations should be low enough to not cause marked pain and distress ’. Given that the hypothesized mode of action for phosphoric acid mist induced lung cancer revolves around the irritation effects it would be meaningless to perform a study to investigate dilutions of phosphoric acid that did not induce irritation. In addition, testing at higher concentrations would cause significant pain and distress to the test animals and a test protocol detailing such a method is unlikely to be acceptable to regulating authorities. 

There is no regulatory requirement to perform animal testing to assess the risk and therefore no testing is proposed in accordance with the Regulation (EC) No 1272/2008 (EU CLP) and Regulation (EC) No 1907/2006 (REACH).

Please see attached report for further analysis.