Preparation of Radiolabeled Materials for Studies of Deposition of Fibers in the Human Respiratory Tract

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Abstract
Inhalation of elongated or fibrous materials such as asbestos has been long associated with high risks of pulmonary toxicity. There is much interest in the adverse health effects of inhaled particles with this shape because they occur in many natural and manufactured materials. One of the reasons for the toxic potential is thought to be the aerodynamic behavior of the long, thin particles which enables them to deposit in the distal parts of the respiratory tract to a greater extent than the more compact (e.g. spherical) particles of equal mass. The knowledge about the deposition of fibers in the human respiratory tract is based entirely on indirect evidence. In order to study under controlled conditions the deposition of elongated particles in live human subjects, it would be necessary to have a non-toxic material whose lung deposition could be monitored by a non-invasive method. This article describes the preparation of radiolabeled elongated particles of two acids whose sodium salts - cromolyn and nedocromil - have been used for aerosol therapy with minimum side-effects. Therefore, these substances are unlikely to exhibit any acute or chronic pulmonary toxicity in humans. We show that the radiolabel distribution among the different aerodynamic particle sizes follows the same pattern as the aerodynamic distribution of the bulk of the material. Therefore, monitoring of the deposition of the label by an external detector should reflect the mass distribution of the elongated particles in the human respiratory tract.