Perlite toxicology and epidemiology – a review

Abstract

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.

• Applications
• epidemiology
• mining
• occupational exposure
• perlite
• processing
• toxicity

Acknowledgements

We appreciate the insightful comments of Dr. Mark J. Utell (University of Rochester School of Medicine and Dentistry, Rochester, New York, NY) on an earlier draft of this article. We also appreciate the assistance of Bill Mihalopoulos in providing copies of some of the unpublished studies referenced in this article and Michalis Stefanakis for providing the Bania et al. reference and for useful comments on perlite production technology. It is also appropriate to acknowledge the constructive comments of the anonymous reviewers of this manuscript in draft. Their comments were useful and improved the quality of this work. The conclusions are those of the authors and do not necessarily represent the views of S&B Minerals or subsidiary companies.

Notes

¹Parting is separation along a structural plane in minerals. In the case of onionskin parting, the mineral fractures along rounded “shells” that resemble onion skin peels.

²This is the rock or soil overlying the mineral deposit.

³This is the overall range among all grades, not the range for any particular grade.

⁴A pack-year is equivalent to smoking one pack of cigarettes per day for 1 year. This is a conventional measure used in epidemiological studies of the amount a person has smoked over a long period.

⁵Wynder (1987) wrote “The important point to note, however, is that the closer the risk of some association comes to unity (i.e. an SMR of 100), the more likely it is that choice of the comparison standard, bias, confounding, or inappropriate analysis may explain it and the greater the need for thorough understanding of the underlying biological mechanisms”.

⁶We were unable to find published data on occupational or ambient exposures to mining dusts at Milos. There is evidence that occupational exposures to nuisance dusts have decreased over the years in some countries (see e.g. Creely et al., 2007), but no data for Milos.

⁷International Classification of Diseases, 9th revision.

⁸We could not find data specific to Milos, but according to the UNCTAD Handbook of Statistics, the average length of stay of tourists in Greece in 2007 was 5.37 d (see http://www.nationsencyclopedia.com/WorldStats/UNCTAD-average-length-stay-visitors.html).