Exposure data Hydrochloric acid is one of the most widely used industrial chemicals. It is used in pickling and cleaning steel and other metals, in the production of many inorganic and organic chemicals, in food processing, in cleaning industrial equipment, in extraction of metals and for numerous other purposes. Hydrochloric acid may occur in workroom air as a gas or mist. The mean concentration of hydrochloric acid during pickling, electroplating and other acid treatment of metals has been reported to range from 0.1 to 12 mg/m3. Mean levels exceeding 1 mg/m3 may also occur in the manufacture of sodium sulfite, calcium chloride and hydrochloric acid, in offset printing shops, in zirconium and hafnium extraction, and during some textile processing and laboratory work. Hydrochloric acid levels in ambient air usually do not exceed 0.01 mg/m3. Human carcinogenicity data: One US study of steel-pickling workers showed an excess risk for cancer of the lung in workers exposed primarily to hydrochloric acid. An increased risk for laryngeal cancer was observed in the same cohort; however, no analysis was performed of workers exposed to hydrochloric acid. None of three US industry-based case-control studies suggested an association between exposure to hydrogen chloride and cancers of the lung, brain of kidney. In on Canadian population-based case-control study, an increased risk for oat-cell carcinoma was suggested in workers exposed to hydrochloride acid; however, no excess risk was observed for other histological types of lung cancer. Animal carcinogenicity data: In one lifetime study in male rats exposed by inhalation at one dose level, hydrogen chloride did not produce a treatment-related increase in the incidence of tumours. Hydrogen chloride was tested at one dose level in combination with formaldehyde by inhalation exposure in the same long-term experiment in male rats. Hydrogen chloride did not influence the nasal carcinogenicity of formaldehyde when mixed with it upon entry into the inhalation chamber. When the two compounds were premixed before entry into the inhalation chamber, an increased incidence of nasal tumours was observed over that seen in animals treated with the combination mixed on entry or with formaldehyde alone. Other relevant data: In single studies, hydrochloric acid induced mutation and chromosomal aberrations in mammalian cells; it also induced chromosomal aberrations in insects and in plants. Hydro- chloric acid did not induce mutations in bacteria. Evaluation: There is inadequate evidence for the carcinogenicity in humans of hydrochloric acid. There is inadequate evidence for the carcinogenicity in experimental animals of hydrochloric acid. Overall evaluation Hydrochloric acid is not classifiable as to its carcinogenicity to humans (Group 3).