Male Wistar rats were exposed to two types of magnesium sulphate whisk
ers by inhalation for six hours a day, five days a week, for four week
s (sub-chronic study), or for one year (chronic study) to clarify the
biological effects of the whiskers. There were few whiskers detected i
n the rat lungs even at one day after the exposure, suggesting that th
ey are dissolved and eliminated rapidly from the lungs. To measure the
clearance rate of the whiskers from the lungs, an intratracheal insti
llation was performed in golden hamsters. The half life of the whisker
s in the lung was determined as 17.6 minutes by temporally measuring t
he magnesium concentration up to 80 minutes after the instillation. A
histopathological examination indicated a frequent occurrence of adeno
ma and carcinoma in the year after chronic exposure, but it was not si
gnificantly different between exposed and control rats.