Tanners may be exposed to chromium, sulfuric acid, leather dust, and H2S. Tanning uses either vegetable or chromium (III) solutions. In the past, tanning was done with the more toxic chromium (VI). [ILO Encyclo: Tanning and Leather Finishing] Other potential exposures include: nitrosamines, chromate pigments, benzidine-based dyes, formaldehyde, and aromatic organic solvents. [Stern, FB. Mortality of chrome leather tannery workers and chemical exposures in tanneries. [Scand J Work Environ Health. 1987 Apr;13(2):108-17] Calcium oxide is a dehairing agent. Hydrogen sulfide can evolve if acid reacts with sodium sulfide, also used for dehairing. Ammonia is generated from ammonium buffering salts and protein putrefaction. Various biocides are used. [Hills B, Fajen J. Leather Manufacturing. In: Zenz C, ed. Occupational Medicine: Principles and Practical Applications, 2nd Ed. Chicago: Year Book Medical Publishers, 1988:1036-1039.] Leather tanning and processing is not classifiable as to carcinogenicity to humans. [IARC] Leather production includes hide preparation, tanning, and finishing. Preparation chemicals include DDT, zinc chloride, formaldehyde, mineral oils, arsenious anhydride, and phenols. Tanning chemicals include calcium hydroxide, sodium sulfide, sulfuric acid, formic acid, hydrogen sulfide, aniline-based dyes, and solvents (dichloromethane, benzene, ethanol, tetrachloroethane, trichloroethylene). Finishing chemicals include formaldehyde, aniline, nitrocellulose, and resins. [PMID 16586406] The three Swedish plants studied opened in 1860, 1897, and 1906 and closed in the late 1980s to early 1990s. Potential carcinogens were used: chromium, chlorophenols, aniline dyes, formaldehyde, methyl mercury, arsenic, benzene, and chlorinated solvents. Arsenic sulfides were used until 1950, methyl mercury (fungicide) until 1960, chlorophenols (fungicide) until 1980, and benzidine dyes until 1980. Toluene was contaminated with benzene until the 1960s.[PMID 15961622] The three steps in leather processing are: 1. "Preparation of hides (curing, soaking and hair removal liming) and pre-tanning stage (bating and pickling) in a special shed (called beam house)." 2. "Tanning stage (tanning, sammying and shaving)." 3. "Post-tanning or finishing stage (drying, fat liquoring and finishing)." [PMID 21938525] See the agent "Leather dust."