Nose-Only Inhalation System Using the Fluidized-Bed Generation System for Coexposures to Carbon Black and Formaldehyde

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Abstract
The purpose of this research was to develop a nose-only inhalation toxicology system for exposing animals to carbon black and formaldehyde—both individually and in combination. This study discusses the modifications necessary to use a fluidized-bed generator to generate carbon black in the concentration range of 0.5–20 mg/m3 with a mass median aerodynamic diameter of approximately 2.5 μm. The specific recommendations involve changing the size and placement of the delivery and overflow tubes as well as installing a motorized ball valve to automate delivery of premixed bed material and carbon black to the generator. The inhalation chamber was modified from a previously published design. By using a cyclone preclassifier to remove the nonrespirable fraction of the aerosol and a laminar flow element to reduce inlet vortic-ity, it was possible to obtain a uniform chamber concentration with less than ±25% overall variation. The formaldehyde generation system produced stable concentrations in the range of 0.5–20 ppm with a variability of less than ±10%. Combined carbon black and formaldehyde generation resulted in less than 0.3% by weight of formaldehyde being bound to the carbon black particles based on both theoretical considerations and actual measurement.