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Perlite is a generic name for an amorphous volcanic alumina-silicate rock that expands by a factor of 4-20 when rapidly heated to 1400-1800 °F (760-980 °C). Both the ore and the expanded product have extensive and widespread commercial applications. Limited data on the toxicology of perlite in animal studies indicate that the LD₅₀ (oral ingestion) is more than 10 g/kg and, from a chronic inhalation study in guinea pigs and rats, that the NOAEL for the inhalation pathway is 226 mg/m³. Health surveillance studies of workers in US perlite mines and expansion plants (including some workers exposed to levels greater than prevailing occupational exposure limits (OELs) conducted over 20 years indicate that the respiratory health of workers is not adversely affected. Studies in Turkish mines and expanding plants had generally similar results, but are more difficult to interpret because of high smoking rates in these populations. A recent mortality study of permanent residents of the island of Milos (Greece) exposed to various mining dusts (including perlite) resulted in non-significant increases in standard mortality ratios for pneumonia and chronic obstructive pulmonary disease (COPD), whereas a companion morbidity study revealed elevated odds ratios for allergic rhinitis, pneumonia, and COPD when compared to another industrial area of Greece. Residents were exposed to other mining dusts and other possible causes or contributing factors and no ambient monitoring data were presented so it is not possible to use this study for risk calculations of perlite-exposed populations. Perlite is regulated as a "nuisance dust" in most countries.