Benzylmagnesium chloride

Carcinogenicity

Description of key information

Studies presented in section 7.7 of this dossier regard tetrahydrofuran (CAS 109-99-9, EINECS 203-726-8) that is the stabilizing additive of benzylmanesium chloride in concentrations specified in section 1.2.
The carcinogenicity of tetrahydrofuran was investigated during two-year inhalation study by National Toxicological Program (1998). Groups of 50 male and 50 female of rats and mice were exposed to 0 (control chamber), 200, 600 and 1800 ppm. No clinical findings related to tetrahydrofuran exposure were observed in male or female rats. The incidences of kidney adenoma was increased in 600 and 1800 male rats exposed to tetrahydrofuran and two carcinomas were observed in male rats exposed to 1800 ppm. Under the conditions of these studies, there is some evidence of carcinogenic activity of tetrahydrofuran in male F344/N rats due to increased incidences of renal tubule adenoma or carcinoma (combined). there was no evidence of carcinogenic activity for F344/N female rats. No clinical findings related to test material exposure were reported for female mice. However, male mice exposed to 1800 ppm were in a state of narcosis during and up to one hour after exposure. The incidences of hepatocellular neoplasm (adenoma or carcinoma) in female mice exposed to 1800 ppm were significantly greater than that of the chamber control and the trend was positive along all exposure groups. Under the condition of this study, there was clear evidence of carcinogenic activity of tetrahydrofuran in female B6C3F1 mice based on increased incidences of hepatocellular neoplasms at the 1800 ppm exposure concentration. There was no evidence of carcinogenic activity in B6C3F1 male mice.

Justification for classification or non-classification

At the present time, no data about carcinogenicity endpoint are available for the substance as described in section 1.2. For this reason, some scientific evidence of toxicity under repeated administration of tetrahydrofuran (stabilizer additive of benzylmagnesium chloride) were assessed.

In conclusion, based on studies about tetrahydrofuran carcinogenicity on rodents, it is not possible to establish with certainity the mode of action of the substance, and therefore the aethiology of the tumors. In rats, studies about tumors in kidney of males rats demonstate that two possible mode of action are involved: alfa2u-globulin nephropathy and chronic progressive nephropathy.

However, reviews of carcinogenicity findings against the criteria used to determine the mechanisms involved in both mode of action (alfa-2u-g and CPN) do not permit to conclude that there is sufficient evidence about mechanisms involved in the aethiology of the tumors. Therefore, it is not possible to conclude that chronic progressive nephropathy or alfa2u-g nephropathy are mechanism involved in tumor findings in male kidney rats. As a consequence, it is not possible to exclude that possibile mechanims responsible for tumors in rats could account also for humans.

Likewise, for mice, some mechanistic data suggest that tetrahydrofuran may induce cell proliferation and lead to a promotion in the growth of pre-initiated cells. However, key precursor events linked to observed cell proliferation have not been identified and the available data are insufficient to establish a mode of action for the tetrahydrofuran liver tumore induction. Thus, liver tumors observed in female mice are considered relevant to the assessment of the carcinogenic potential of tetrahydrofuran to humans.

Based on these evidences, mechanisms that could account also for humans could not be excluded; therefore, tetrahydrofuran is classified as Carc. 2, H351, Suspected of causing cancer under CLP regulation and Carc. Cat. 3; R40, Limited evidence of a carcinogenic effect under DSD directive.

The classification as Carc. 2, H351 under CLP (and Carc. Cat. 3, R40 under DSD) is therefore adopted also for the substance benzylmagnesium chloride as characterized in section 1.2, taking into account that, in a mixture-like approach, the generic concentration limit is 1% (w/w).

Additional information

At the present time, no data about carcinogenicity endpoint are available for the substance as described in section 1.2. For this reason, some scientific evidence of toxicity under repeated administration of tetrahydrofuran (stabilizer additive of benzylmagnesium chloride) were assessed.

In the 2 -year NTP (1998) carcinogenicity study, groups of 50 male and 50 female rats and mice were exposed through inhalation to tetrahydrofuran at levels of 0 (control chamber), 200, 600 and 1800 ppm.

Rats.

Mean body weights and survival of male and female rats exposed to test material were similar to those of the chamber control; however, increased mortality was observed in all group of male rats during last 55 days of the study. No clinical findings related to tetrahydrofuran exposure were observed in male or female rats. The incidences of kidney adenoma was increased in 600 and 1800 male rats exposed to tetrahydrofuran and two carcinomas were observed in male rats exposed to 1800 ppm. The overall rate of incidence of adenoma and carcinoma exceeded the historical range for chamber controls in 2 -year NTP inhalation studies. Furthermore, since chronic progressive nephropathy incidence or severity in male rats seem not to be affected by tetrahydrofuran exposure concentration, it suggests that observed neoplasms are not due to nephropathy, but to test material exposure. Under the conditions of these studies, there is some evidence of carcinogenic activity of tetrahydrofuran in male F344/N rats due to increased incidences of renal tubule adenoma or carcinoma (combined). there was no evidence of carcinogenic activity for F344/N female rats.

Mice.

Survival of male rats exposed to 1800 ppm level was significantly less than that of the chamber control. Survival of female mice of all exposure concentration was similar to chamber control. Mean body weights of males and females exposed to tetrahydrofuran were similar to the chamber control.

No clinical findings related to test material exposure were reported for female mice. However, male mice exposed to 1800 ppm were in a state of narcosis during and up to one hour after exposure.

Regarding neoplastic lesions, the incidences of hepatocellular neoplasm (adenoma or carcinoma) in female mice exposed to 1800 ppm were significantly greater than that of the chamber control and the trend was positive along all exposure groups. In male mice, the incidences of hepatocellular neoplasms in exposed animals were not significantly different than that of the chamber control. Furthermore, male mice exposed to tetrahydrofuran at 1800 level had greater incidences of nonneoplastic lesions of the urogenital tract than those in the chamber control. The inflammatory urogenital tract lesions in 1800 ppm were considered the most likely cause of the deaths observed in this group.

Under the condition of this study, there was clear evidence of carcinogenic activity of tetrahydrofuran in female B6C3F1 mice based on increased incidences of hepatocellular neoplasms at the 1800 ppm exposure concentration. There was no evidence of carcinogenic activity in B6C3F1 male mice.

Results of 2 -year carcinogenicity NTP study

Species	Conc.mg/L	Exposure time(h/day) &duration oftreatment	Observations and Remarks
Rat(Fischer344)	0, 0.6, 1.8, or 5.4 mg/L(0, 200, 600, or 1800 ppm)	6 h/day5 days/week105 weeks	50 males and 50 females per group were exposed toTHF. Survival, body weight, and clinical findings were similar to those of chamber controls (number of survivors in the controls: 12/50, and 5.4 mg/L group:6/50)Males: Positive trend (P=0.037) for combined occurrence of renal tubule epithelial adenoma and carcinoma (relatively uncommon spontaneous renal neoplasms in two-year NTP studies), although pairwise comparisons between control and experimental groupswere not significant. The incidence was as follows: historical control range: 0-4%; current control: 1/50 (2%); 200 ppm: 1/50 (2%); 600 ppm: 4/50 (8%); and 1800 ppm: 5/50 (10%). Tumours in the high-dose group appeared by day 668 (95 weeks), comparedwith day 733 (terminal sacrifice) in the controls. Slightly higher incidence of mammary glandfibroadenoma in high-dose males, but not considered significant: historical incidence: 4.2 ± 3.5%; current controls: 0/50 (0%); 200 ppm: 2/50 (4%); 600 ppm: 3/50 (6%); and 1800 ppm: 4/50 (8%). Higher incidence of testes adenoma in treated rats (but well within the historical control range and not considered significant): historical control: 46-83%; current controls: 23/50 (46%); 200 ppm: 31/50 (62%); 600 ppm: 31/50 (62%); and 1800 ppm: 31/50 (68%). Increased incidence of epithelium hyperplasia in the prostate: current controls: 2/50 (4%); 200 ppm: 1/50 (2%); 600 ppm: 0/50 (0%); and 1800 ppm: 5/50 (10%).Females: Slightly greater incidence of mammary gland fibroadenoma in the high-dose group with a trend marginally significant (P=0.031), but the pairwise comparisons were not: historical control: 16-42%; controls: 23/50 (46%); 200 ppm: 22/50 (44%); 600 ppm: 29/50 (58%); and 1800 ppm: 31/50 (62%). The NTP concluded that THF exhibited some evidence of carcinogenic activity in male rats for renal tubule epithelial adenoma and carcinoma but no evidence of carcinogenic activity in females.
Mouse B6C3F1	0, 0.6, 1.8, or 5.4 mg/L(0, 200,600, or 1800ppm)	6 h/day5 days/week105 weeks50 males and 50 females per group	Survival and lifespan of high-dose males were significantly lower than the survival and lifespan ofcontrols (456 days versus 689 days for controls). Mean body weights of exposed male and female micewere not affected. The highest exposure concentration (1800 ppm) selected for male mice in this study exceeded the MTD (state of narcosisduring and up to 1 h after the exposure periods). High-dose males had significantly greater incidencesof nonneoplastic lesions of the urogenital tract thant hose in the chamber controls. The authors explained this by the inflammatory character of these lesions, which occurred primarily among the animals dying in the first 52 weeks of the study, suggested anascending bacterial infection (due likely to prolonged wetting of the preputial fur).Females:1800 ppm: increased incidence of hepatocellularneoplasms (adenoma and carcinoma) [85% versus34% in controls (significant)], and of multiplehepatocellular neoplasms and liver necrosis. 200 & 600 ppm: increases in the incidences of liverneoplasms observed. They were not statisticallysignificant, but the trend test was positive.Males: no indication of an increase in the incidencesof hepatocellular neoplasms. The incidence of nonneoplasiceffects in males was increased: iliac hyperplasia in the lymph node was 75% in low andmid-dose groups and 100 % in high dose group (0% in controls); hematopoietic cell proliferation in thespleen was increased with exposure (19%; 27%; 30%; 37%), and the incidence of thymus atrophy wasenhanced in the higher exposure groups (6%; 5%;12%; 25%).THF exhibited no evidence of carcinogenic activity in male mice but showed clear evidence of carcinogenicactivity in female mice.