A Review of the Chronic Toxicity, Carcinogenicity, and Possible Mechanisms of Action of Inorganic Acid Mists in Animals

Abstract

Occupational exposure to inorganic acid mists containing sulfuric acid has been associated with increased laryngeal cancer. The primary objective of this review was to compile the literature regarding chronic toxicity and carcinogenicity of inorganic acid mists in laboratory animals. Several chronic toxicity studies had exposures of 1 year or longer. Whereas numbers of animals were limited, no evidence of neoplastic or preneoplastic lesions was reported. Two studies evaluated the carcinogenicity of inorganic acid mists in rats; however, one was limited by a short duration of exposure and the other did not achieve a maximum tolerated dose. A large lifetime study in hamsters evaluated the carcinogenicity of 100 mg/M3 sulfuric acid mist, as well as its ability to act as a promoter or co-carcinogen for benzo(a)pyrene. No evidence of carcinogenic potential was shown. Although an increase in papillomas was noted in the benzo(a)pyrene + H2SO4 group, the co-carcinogenic or promoting potential was considered equivocal. Thus, no evidence from experimental animals strongly supports or refutes the induction of cancer by inorganic acid mists. A possible mechanism that could be associated with inorganic acid mist carcinogenicity relates to the genetic consequences of lowering the pH. Reduced pH can induce chromosomal aberrations, enhance depurination, and deamination of cytidine in DNA. This mechanism has not been evaluated in tissues of the respiratory tract.

Effect of organic compounds on nanoparticle formation in diluted diesel exhaust

“…Sulfuric acid seems to be a relevant compound for human health effects in volatile nanoparticles. Inhalation of acid aerosols in laboratory animal studies causes genotoxic damage in cells (Soskolne et al, 1984;Swenberg and Beauchamp, 1997). Kilgour et al (2002) showed cell proliferation of the respiratory tract in rats due to exposure to sulfuric acid.…”

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

“…Others have concluded that there is insufficient evidence to show a causal relationship between exposure to sulphuric acid mist and an excess of laryngeal cancer. It has been hypothesized that reduced pH resulting from exposure to acid mists may represent or contribute to any potential mechanism for cancer induction because it is known that acid pH causes genotoxic damage in cells and can affect also the toxicity of a number of chemicals (Soskolne et al, 1984;Swenberg and Beauchamp, 1997). There is limited information of relevance in earlier inhalation studies in experimental animals to support the hypothesis that sulphuric acid might be carcinogenic.…”

“…Although the short-term effects of sulphuric acid may either subside or progress, depending on a number of exposure-and duration-related factors, there are no adequate long-term studies investigating either the carcinogenicity of acid mists or potential mechanisms to help evaluate the biological plausibility of the association between respiratory tract cancer and occupational exposure to acid mists that forms the basis of the IARC classification (Swenberg and Beauchamp, 1997). In view of the limitations of the currently available experimental data to address the latter relationship, the study described here was designed to investigate the early response of the rat respiratory tract following exposure for either 5 or 28 days to sulphuric acid aerosols at target concentrations of 0.2, 1 and 5 mg m −3 and mass median aerodynamic diameters of 1 µm.…”

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

“…12 An association between occupational exposure to strong inorganic acid mists containing sulfuric acid and the risk increase of laryngeal cancer was seen. However, in many studies exposure to other carcinogens, such as asbestos, nickel, radon progeny and smoking, had not been taken into account.…”

“…11 However, the evidence from experimental animals regarding the carcinogenicity of inorganic acid mists is not conclusive. 12 Sulfuric acid is an abundant ambient air pollutant derived from manufacturing processes and from atmospheric oxidation of SO 2 , which is a primary effluent of fossil fuel combustion. In addition, sulfur trioxide gas hydrolyzes in the air or in mucous membranes to sulfuric acid.…”