Safety evaluation of butylated hydroxyanisole from the perspective of effects on forestomach and oesophageal squamous epithelium.

Butylated hydroxyanisole (BHA) induces tumours of the squamous epithelium of the forestomach of rodents, but not at other sites. Although humans do not have squamous epithelium in their stomach the likelihood that BHA will induce tumours of the squamous epithelium of the oesophagus needs to be considered. Studies in several species indicate that the forestomach epithelium is very responsive to hyperplastic and neoplastic change induced by BHA, but the oesophageal epithelium is not responsive. The lack of effect in the oesophagus is likely to be due to the fact that the rapid speed of transit through the oesophagus limits the exposure time of the oesophageal mucosa to the food contents. Conversely, as the rodent's forestomach has storage function, exposure of the squamous epithelium of the forestomach would be continuous. The fact that the no-observed-effect level for hyperplasia of the oesophageal mucosa is several hundred times the acceptable daily intake for BHA supports the view that BHA would not be a human carcinogen at food additive levels of use.

Long-term toxicity of hexachlorobenzene in the rat and the effect of dietary vitamin A.

The toxicological effects of analytical-grade hexachlorobenzene (HCB) were examined in two chronic studies. Study I was an in utero exposure carcinogenicity feeding experiment in which Sprague-Dawley rats, in groups of 40 males and 40 females except where noted, were fed from weaning on diets containing 0.0 (64 M/64 F), 0.32, 1.6, 8.0 or 40.0 (66 M/66 F) ppm HCB. After 3 months on test, the F0 rats were bred and 50 pups (F1) of each sex were randomly selected from every group. From weaning, when the F0 animals were killed, the F1 animals were fed their parents' diet for the rest of their life (130 wk). There were no treatment-related effects on growth, feed consumption, haematological parameters or survival in either generation. Increased heart and liver weights were found in the 8.0 and 40 ppm F0 males. HCB had no effect on fertility but pup viability was significantly reduced in the 40 ppm group. Histopathological changes in the F1 generation included significant linear trends in the incidence of parathyroid adenomas and phaeochromocytomas in both sexes, neoplastic liver nodules in females, centrilobular basophilic chromogenesis of the liver in both sexes, peliosis of the liver in females, peribiliary lymphocytosis of the liver in males and chronic nephrosis of the kidney in males. In Study II, the toxicological effects of HCB were examined as a consequence of varying the dietary levels of vitamin A. In this single generation lifetime (119 wk) feeding study, groups of 50 weanling Sprague-Dawley male rats were randomly assigned to each of the following dietary groups: control, control + 40 ppm HCB, 1/10 the vitamin A content of the control diet, 1/10 vitamin A + 40 ppm HCB, 10 times the vitamin A content of the control diet and 10 times vitamin A + 40 ppm HCB. After 25 and 49 wk on test, five animals from each group were killed and subjected to haematological and histological examinations. All other aspects of evaluation were similar to those for the F1 generation in Study I. No consistent differences were observed in the haematological parameters and there were no significant differences in the incidence of pathological lesions between the test groups. The animals in the 1/10 vitamin A groups, with or without HCB, had significantly lower body weights and poorer survival than did their corresponding control (normal vitamin A) groups.

Monochlorodiisobutylene vapor: acute and 9-day inhalation studies in Fischer-344 rats and B6C3F1 mice.

Acute and 9-day repeated exposures to monochlorodiisobutylene (CDIB) were conducted in male and female Fischer-344 rats and B6C3F1 mice. The 4-hr LC50 values for these animals ranged between 1400 and 2100 ppm. Animals in the 9-day study were exposed at a mean concentration of 478, 97, or 25 ppm of CDIB for 6 hr per day. Treatment-related effects differed between species in this study. Body weight change was decreased in rats. Morphologic changes in the kidneys with accompanying polyuria and hematuria/hemoglobinuria were observed in male rats. The only effect observed at 25 ppm was a low incidence of hematuria/hemoglobinuria in male rats. Mice appeared unaffected by exposure to CDIB at levels as high as 478 ppm.

Monitoring animal health during chronic toxicity studies.

Adequate and appropriate appraisal of the health of the animals in toxicity studies is required to differentiate between toxic manifestations attributable to the test material and non-treatment-related disease. The appraisal will help to ensure that each animal remains on test for as long as reasonably possible and that useful tissue samples are obtained from each animal. Attainment of this objective requires highly motivated personnel who have undergone a specific and continuous training program. The establishment of protocols and procedures for daily and weekly monitoring of the animals, and an efficient and relevant system for data collection, recording, and storage is also required. Various laboratory and clinical procedures are described which may be used either on a routine basis or as diagnostic tools. By following the described procedures it has been possible to reduce the loss of animal tissues due to autolysis to less than 1% during chronic feeding studies.