Abstract
Recently, increases in the incidence of respiratory diseases which may be connected with air pollution have developed into a serious social problem.
The purpose of the present study is to estimate experimentally whether low concentrations of SO2 similar to levels actually recorded in the atmosphere in Japan have injurious effects on the respiratory system.
The d-d strain mice were continuously exposed to low concentration (0.05, 0.15, 0.23ppm) of SO2 for periods of 6 weeks or 3 months, using a specially constructed exposure chamber coupled with a standard gas generator with a built-in Teflon tube.
Histopathological studies were conducted through light microscopic observation.
Following results were obtained:
1) Increase in mean body weight of each SO2 exposure group was no different than that of the control group.
2) There was no death in the control group. Three of the ninety six mice belonging to the SO2 exposure groups died, but there was no difference of mortality among each group.
3) Incidence of the changes such as goblet cell-like formation in the epithelia in the nasal respiratory region (80%) and slight irregularity in arrangement or decrease of olfactory hairlets (44%) were higher among the SO2 exposure groups than the control.
4) The trachea, the bronchi and the alveoli did not show any significant changes in both the control group and the SO2 exposure groups.
5) Incidence of bronchitis and pneumonia was not significantly different between the control and the SO2 exposure groups, but the seriousness of the pneumonia was greater in the groups exposed to SO2.
6) There was no significant correlation between goblet cell-like formation in the nasal respiratory region and changes in the bronchus and the alveolus.
The results above mentioned can be summarized as follows:
Continuous exposure to low concentrations of SO2 produces significant pathological changes i. e. slight goblet cell-like formation in nasal respiratory regions, but changes occuring in the lower respiratory tract and alveolus were of little significance.
It is considered that the changes found in nasal respiratory regions are a reactive feature to the irritative effect of SO2 or H2SO3.
