Early Response of the Canine Respiratory Tract Following Long-Term Exposure to a Sulfur(IV) Aerosol at Low Concentration. I. Rationale, Design, Methodology, and Summary

Abstract

The present study was designed to investigate the effect of chronic inhalation of a low concentration of airborne sulfur(IV) on mammalian lungs. Eight beagle dogs were continuously exposed in whole-body chambers for 290 d to a respirable S(IV) aerosol with a mass median aerodynamic diameter of 0.6 µm (geometric standard deviation about 2) at a concentration of 0.3 mg m⁻³, equivalent to a sulfur dioxide concentration of 0.6 mg m⁻³. Three dogs served as sentinels.

To establish baseline data for lung parameters, the dogs were first housed in the chambers for 400 d under clean air conditions. Biochemical and cellular parameters in the lung lavage fluids were evaluated repeatedly for each dog. During exposure, each lung parameter was again measured repeatedly for each dog and the values obtained were compared with the baseline values. Thus each individual served as its own control. Parameters of respiratory lung function and lung morphology were only evaluated at the end of the study The three sentinal dogs were used as controls for these parameters.

The most pronounced effects-were seen in the increased permeability of the alveolar membrane for proteins, in macrophage function like release of Iysosomal components, and in the decline in bacterial defense capacity as indicated by a reduced phagocytic capacity and a decreased formation of oxygen radicals. Macrophage-mediated particle clearance from the lung periphery was enhanced. In addition, there seemed to be some early indications of allergic and immunological reactions to the sulfur(IV) aerosol, reflected in an increase in eosinophils and lymphocytes.

Postmortem morphologic examination of the respiratory system revealed hyperplastic changes in the nasal cavity and disturbance of ciliated cell development in the trachea. Morphometric analysis indicated early peripheral airspace enlargement, resulting in a significant decrease in the surface area available for gas exchange in the exposed lungs. The lungs also showed a tendency to impairment in the membrane diffusing capacity.

The results show that chronic exposure to a sulfur(IV) aerosol at a low dose can initiate pathophysiological and pathobiochemical pathways in the lungs, thus indicating a potential health hazard.