Long‐term inhalation study with Wistar rats and four cadmium compounds

Abstract

In a previous long‐term inhalation study it was shown that by continuous exposure (23 hours per day, 7 days per week) to CdCl₂ for one and a half years primary lung tumors were induced in male Wistar rats at Cd concentrations between 12.5 and 50 μg/m³. In these new extended experiments the carcinogenic result with CdCl₂ was also verified for female rats and for either the water soluble aerosol Cd sulfate (CdSO₄) or the insoluble compounds Cd sulfide (CdS) and Cd oxide (CdO) as dust and fume. The same types of primary lung tumors were determined histopathologically as in the previous study: benign and malignant adenomas, squamous cell carcinomas and combined forms. The lung tumor rates were rather high for all Cd compounds. At the Cd aerosol concentrations of 90 μg/m³ or more, the tumor rates decreased due to shorter inhalation periods for the water insoluble compounds. For these groups the inhalation times had to be reduced because of increased toxicity (lethality). But even if the inhalation periods lasted only for 6 months and for 40 hours per week primary lung tumors were found. In contrast, at lower Cd concentration (30 μg/m³) additional zinc oxide (ZnO) aerosol showed complete antagonism towards the lung carcinogenic potency of Cd in rats.