Chemical Information Review Document for Synthetic and Naturally Mined Gypsum

Gypsum is the dihydrate form of calcium sulfate. The word "gypsum," however, is used to describe different phases of the same material, including anhydrite (calcium sulfate, with no water of crystallization), selenite, calcined gypsum, and plaster of Paris. It forms as evaporites from marine waters and is usually found collectively with other mineral deposits such as quartz, sulfur, and clays. Gypsum is also found in lakes, seawater, and hot springs as deposits from volcanic vapors. It is primarily used to manufacture wallboard and plaster for homes, offices, and commercial buildings; it is the most common natural fibrous mineral found indoors. Other applications of gypsum are as a soil additive, as a food and paint filler, and a component of blackboard chalk, medicines, and toothpaste. Humans may therefore be exposed to gypsum via inhalation, ingestion, skin contact, and eye contact. There is concern over the exposure of individuals to gypsum dust in the workplace and home, and this concern has increased in the aftermath of the World Trade Center (WTC) collapse in September 2001. Patients being examined in clinics include office workers, emergency response workers, constructions workers, and public members exposed to dust from the destruction. Analysis of general area and personal breathing zone air samples show that nonasbestos fibers consist mostly of gypsum, fibrous glass, and cellulose. In air and dusts collected from building materials dispersed from the WTC collapse three months later, gypsum was the most common mineral found in outdoor air samples from lower Manhattan. The majority of studies of gypsum workers, however, have reported no lung fibrosis or pneumoconiosis, except when gypsum was contaminated with silica. Gypsum is very soluble in the body. Aerosols of calcium sulfate fibers were quickly cleared from the lungs of rats and guinea pigs via dissolution. Nonpathological findings of subchronic inhalation studies in rats were dependent on the shape of the gypsum fibers. In a chronic inhalation study, calcined gypsum dust produced only minor effects in the lungs of guinea pigs. In carcinogenicity studies, gypsum was weakly tumorigenic. Gypsum induced abdominal cavity tumors in 5% of rats after intraperitoneal injection, carcinomas of the heart and kidney in hamsters after intratracheal administration, and no lung tumors in guinea pigs following inhalation exposure. None of the long-term studies can be considered adequate tests of chronic toxicity or carcinogenicity by modern standards.