Toxicology and carcinogenesis studies of a-methylbenzyl alcohol (greater than 99% pure), a cosmetic ingredient and food flavoring agent, were conducted by administering the chemical in corn oil by gavage to groups of F344/N rats and B6C3F1 mice of each sex for 16 days, 13 weeks, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, mouse lymphoma cells, and Chinese hamster ovary (CHO) cells. a-Methylbenzyl alcohol was nominated for study by the National Cancer Institute because of the potential for widespread human exposure.
Sixteen-day and thirteen-week studies
The doses used in the 16-day studies for rats and mice ranged between 125 and 2,000 mg/kg. Six of 10 rats and all mice dosed at 2,000 mg/kg died. In addition, because 7/9 mice dosed at 1,000 mg/kg died, the doses selected for the 13-week studies for mice (47-750 mg/kg) were half those used for rats (93-1,500 mg/kg).
In the 13-week studies, deaths of 1/10 male and 3/10 female rats dosed at 1,500 mg/kg were compound related; none of the mice died. Body weight gain was reduced in rats at 1,500 mg/kg; there were no significant histopathologic lesions in either rats or mice. The only compound-related effects were ataxia, labored breathing, and lethargy for up to 30 minutes after dosing in rats and mice given the two highest doses and increases in liver weight to body weight ratios for male rats given the three highest doses and for female rats at all doses.
Based on the pattern of mortality and the effects on body weight gain in the short-term studies, doses of 375 and 750 mg/kg a-methylbenzyl alcohol were administered in corn oil by gavage, 5 days per week for 103 weeks, to groups of 50 rats and 50 mice of each sex.
Significant reduction in body weight gain commenced at weeks 20-30 in high dose male and female rats, and body weights were 20%-30% below those of vehicle controls at study termination. In the low dose groups, body weight reduction occurred only in male rats during the last 10 weeks of the study. After 80 weeks, 60% of the high dose rats and 80%-100% of the low dose and vehicle control rats were alive; thereafter, the number of deaths in the chemically exposed groups increased sharply so that, at the end of 2 years, final survival for vehicle control, low dose, and high dose rats was 35/50; 8/50; and 1/50 for males and 34/50, 25/50, and 11/50 for females. There were a large number of gavage accidents in these studies (1, 9, and 8 for male rats and 1, 4, and 14 for female rats), but these accidents did not contribute to the increase in mortality after week 80, as all but 4 of these occurred earlier.
Mortality in the last quarter of the study was thought to be due to the effects of cumulative toxicity of a-methylbenzyl alcohol on a renal excretory system already compromised by aging. Renal nephropathy that commonly occurs during aging was found in all groups of rats, but the severity was greater in male rats dosed with a-methylbenzyl alcohol. In addition, a collection of nonneoplastic lesions (parathyroid hyperplasia, calcification of the heart and glandular stomach, and fibrous osteodystrophy of bone) was found in the dosed male rats; these lesions were probably secondary to mineral imbalance arising from renal dysfunction.
Since survival was poor in low and high dose male and high dose female rats, the sensitivity of the study for detecting a carcinogenic effect in these groups was reduced. Despite this limitation, there were dose-related increases in the incidences of renal tubular cell adenomas or adenocarcinomas (combined) in male rats (vehicle control, 0/50; low dose, 2/50; high dose, 5/50). In addition, transitional cell papillomas of the urinary bladder were observed in one high dose male and two high dose female rats.
In mice, a reduction in body weight gain was apparent in the high dose groups of males and females. Final survival rates in mice were similar among groups (male: 39/49; 40/50; 28/50; female: 41/50; 41/50; 38/50). No neoplastic or nonneoplastic lesions were attributed to a-methylbenzyl alcohol administration in mice of either sex.
a-Methylbenzyl alcohol was not mutagenic in S. typhimurium strains TA98, TA100, TA1535, or TA1537 when tested in the presence or absence of exogenous metabolic activation. a-Methylbenzyl alcohol produced a positive response without activation in the mouse L5178Y/TK+/- lymphoma assay for induction of trifluorothymidine resistance; it was not tested with activation. In cytogenetic tests with CHO cells, a-methylbenzyl alcohol induced chromosomal aberrations in the presence, but not the absence, of metabolic activation; no induction of sister chromatid exchanges was observed in CHO cells after exposure to a-methylbenzyl alcohol.
Under the conditions of these 2-year gavage studies, there was some evidence of carcinogenic activity of a-methylbenzyl alcohol for male F344/N rats, as shown by increased incidences of renal tubular cell adenomas and adenomas or adenocarcinomas (combined). There was no evidence of carcinogenic activity for female F344/N rats administered 375 or 750 mg/kg. Renal toxicity characterized by severe nephropathy and related secondary lesions was observed in the dosed rats, and excessive mortality occurred during the last quarter of the studies. Poor survival reduced the sensitivity of the studies for detecting the presence of a carcinogenic response both in chemically exposed groups of male rats and in the high dose group of female rats. There was no evidence of carcinogenic activity of a-methylbenzyl alcohol for male or female B6C3F1 mice administered 375 or 750 mg/kg for 2 years.