ACUTE AND SUBACUTE INHALATION TOXICITY OF GERMANIUM DIOXIDE IN RATS

Two acute (4 hr) and one subacute (4 wk) inhalation toxicity studies o n germanium dioxide (purity greater than or equal to 99%, mean particl e size 1.7-2.6 mu m) were conducted in young adult Wistar rats. In the acute studies, exposure of two groups of five rats of each sex to max imum attainable concentrations of either 3.10 g amorphous or 1.42 g he xagonal germanium dioxide/m(3) for 4 hr was not lethal. In the subacut e study, four groups of five rats of each sex were exposed to 0, 16, 7 2 and 309 mg hexagonal germanium dioxide/m(3) for 6 hr/day, 5 days/wk during 4 wk. Two additional groups of 5 rats per sex, exposed either t o 0 or to 309 mg/m(3), were kept for a 33-day post-exposure period. At the end of the treatment period, changes were observed only in rats o f the high concentration group: these changes were decreased body weig ht gain (both sexes), decreases in haematocrit (females) and thrombocy te count (both sexes), and increases in neutrophil count (both sexes) and white blood cell count (females). On clinical chemistry evaluation , decreased fasting blood glucose (females), decreased total protein c oncentration (both sexes), increased plasma alanine aminotransferase a nd aspartate aminotransferase activities (females), increased plasma u rea nitrogen (males) and increased plasma bilirubin level (females) we re observed. In addition, urinary volume was elevated, and urine densi ty and pH were lowered in both sexes. Relative weights of kidneys, spl een, heart and lungs were higher than in controls. Microscopic examina tion revealed effects on renal tubular epithelium. Effects on growth, kidneys, and liver were still present at the end of the 33-day recover y period. It was concluded that the 4-hr LC(50) value of amorphous ger manium dioxide was greater than 3.10 g/m(3) and that of the hexagonal form greater than 1.42 g/m(3). The no-adverse-effect-level in the 4-wk study using hexagonal germanium dioxide was 72 mg/m(3).