Physicochemical and Mineralogical Characterization of Test Materials used in 28-Day and 90-Day Intratracheal Instillation Toxicology Studies in Rats

Abstract

Two recent intratracheal instillation toxicology studies in rats clearly show that a naturally occurring quartz, with occluded crystal surfaces (quartz isolate), produced significantly less inflammatory response than a crushed reference quartz (DQ12). Respirable-size quartz isolate was isolated from bentonite parent rock, without crushing or the use of chemicals, to ensure that the surface properties of the quartz particles were unaltered. The isolation technique utilized gentle mechanical dispersion followed by sedimentation in an aqueous medium. Extensive mineralogical and chemical characterizations were undertaken to define the physicochemical properties of the test materials. The characterizations showed significant, measurable physicochemical differences between the two quartz types. These differences may help to explain the difference in toxicological response associated with these materials. The evaluation methods and resulting data that characterized the chemical and physical properties of the instillation test materials are discussed. The data presented show that such characterizations are essential if meaningful correlations are to be made between test materials and their toxicological profiles.

This study was supported by the Sorptive Minerals Institute, Washington, DC. The authors thank the following individuals and organizations for their help in developing data for this article: Dr. Marc Herpfer, Oil-Dri Corporation, Chicago, who directed surface area measurement using BET and EGME methods; Dr. Vincent Castranova and Dr. Steven Leonard, NIOSH, Morgantown, WV, who conducted the electron spin resonance studies; Dr. Don Eisenhour, AMCOL International, Arlington Heights, IL, who obtained the zeta potential test data; Gary Tomaino, Mineral Technologies, Inc., Easton, PA, who conducted the differential scanning calorimetry and high-temperature x-ray diffraction analysis; Dr. Haydn Murray, Indiana University, Bloomington, IN, who allowed use of his laboratory for developing the separation techniques; and Dr. M. I. Knudson, Southern Clay Products, Gonzales, TX, who provided the initial quartz concentrates used in both rat studies. The authors also thank Dr. John Domanski for his very helpful comments and suggestions.