Carcinogenicity study with sodium dichromate in rats

Solutions of sodium dichromate were administered to Sprague Dawley rats by intratracheal instillations over a period of 30 months. Dosage was 0.01, 0.05 or 0.25 mg/kg, five times a week, or 0.05, 0.25 or 1.25 mg/kg once a week. Each group consisted of 40 male and 40 female rats. Groups left untreated or given saline served as negative controls. The highest chromate dose proved to be within the range of the maximum tolerable amount. The main determinant of effect was the concentration of chromate instilled, not the total dose per week. Non-neoplastic pulmonary lesions, which occurred predominantly in the highest dose group, were fibrotic regions containing residual distorted bronchiolar lumens or cellular inflammatory foci containing alveolar macrophages, proliferated epithelium and chronic inflammatory thickening of alveolar septa. Fourteen rats given 1.25 mg/kg sodium dichromate had a total of 20 lung tumours (12 benign, 8 malignant). One rat given 0.25 mg/kg once a week had a malignant tumour. Tumours were generally small and were non-fatal. A comparable solution of calcium chromate, which was tested at the two highest dose levels, had virtually the same effect. The positive controls, benzo(a)pyrene and dimethylcarbamyl chloride, induced a high rate of fatal malignant tumours in the respiratory tract.