A review of the chronic toxicity, carcinogenicity, and possible mechanisms of action of inorganic acid mists in animals

A Putative Adverse Outcome Pathway Relevant to Carcinogenicity Induced by Sulfuric Acid in Strong Inorganic Acid Mists

Based on epidemiological studies, an International Agency for Research on Cancer Working Group determined that strong inorganic acid mists containing sulfuric acid are carcinogenic to human even though, sulfuric acid, per se, is not. Accumulative studies indicate that there is a link between chronic occupational exposure to sulfuric acid mists and an increased risk of laryngeal cancer. Unintended, acute exposure to sulfuric acid mists can cause corrosive damage to target tissues depending on the route of exposure. This review compares the toxicity and carcinogenicity of sulfuric acid mists compared to other strong inorganic acid mists. It also examines the routes and duration of exposure (short-term, prolonged, and long-term). In vivo evidence does not support or refute the carcinogenicity of sulfuric inorganic mists even though its co-carcinogenic or promoting potential has been considered. On the basis of existing evidence on sulfuric acid mist toxicity, we suggested a putative adverse outcome pathway (AOP) relevant to carcinogenicity caused by mists containing sulfuric acid. A possible key factor involved in sulfuric acid mist carcinogenesis is the genotoxic effects of low pH since it can increase instability in chromosomes and DNA. A putative AOP for sulfuric acid mist carcinogenicity would help generate better risk assessments and more accurate predictions regarding the risk of developing cancer due to prolonged exposure. Establishing an AOP would also be useful for future studies examining the carcinogenicity of other strong inorganic mists.

Responses in the respiratory tract of rats following exposure to sulphuric acid aerosols for 5 or 28 days

Sulphuric acid mists have been classified by the International Agency for Research on Cancer as being carcinogenic to humans based on epidemiological findings of respiratory tract tumours. To determine if early changes in the respiratory tract following exposure to sulphuric acid (H(2)SO(4)) aerosols are consistent with the possible development of tumours after extended periods of exposure, groups of female rats were exposed to respirable aerosols of H(2)SO(4) at target concentrations of 0, 0.2, 1.0 or 5.0 mg m(-3) for 6 h per day for either 5 days or for 5 days a week over a 28-day period. Additional groups exposed to 0 or 5.0 mg m(-3) over the 28-day period were retained after exposure for 4 or 8 weeks to assess recovery. Histopathological examinations and quantitative cell proliferation measurements were conducted on the nasal passages, larynx and lung. Achieved concentrations were 0.3, 1.38 and 5.52 mg m(-3) H(2)SO(4). Histological and cell proliferative changes were confined to the larynx and no effects were seen in the nasal passages or lungs. At the two highest concentrations, squamous metaplasia accompanied by significant cell proliferation was apparent after 5 and 28 days of exposure and there was a reduction in the severity of the pathological changes following the recovery periods. No effects were seen at 0.3 mg m(-3) after 5 days of exposure and only minimal metaplastic change was seen after 28 days in a few animals and was not accompanied by cell proliferation. The toxicological relevance of these findings is discussed.

Lung cancer near an industrial site in Lithuania with major emissions of airway irritants

To assess the relation between air pollution with airway irritants, including sulfuric acid and lung cancer, a case-control study was performed near an industry producing sulfuric acid and fertilizers in Kedainiai county, central Lithuania. The county had the highest lung cancer rates of the country among men. Between 1967 and 1973, the levels of sulfuric acid exceeded 500 microg/m(3) within 2 km of the industry and 100 microg/m(3) more than 5 km away. A total of 277 men who were diagnosed as having lung cancer during 1981-1991 in Kedainiai county were included as well as 1,108 population controls. Information on residential history since 1960, smoking habits, occupations and workplaces during lifetime was obtained from questionnaires mailed to next-of-kin. The relative risk of lung cancer associated with living within approximately 5 km from the plant was 1.02 (95% CI: 0.76-1.38) compared to those who had never lived in this area. No relation with distance or duration of residence was observed. Furthermore, workers at the plant did not have an increased lung cancer risk. The relative risk of lung cancer associated with smoking was 21.2 (95% CI: 7.51; 60.1) for current smokers and 14.0 (95% CI: 4.88; 40.3) for exsmokers. The duration of smoking, a low age at start and amount of cigarettes smoked daily were positively associated with lung cancer risk. Smoking levels appeared more pronounced among study controls than in the rest of the country. Our study could not confirm earlier evidence of an association between exposure to airway irritants, such as sulfuric acid and lung cancer. Smoking is the major determinant of the risk of lung cancer in men in Kedainiai county. It is probable that higher smoking rates constitute the main reason for the increased lung cancer risk among men in this area.