Toxicological evaluation and limit values for Methyl-tertiary-butyl ether (MTBE), Formaldehyde, Glutaraldehyde, Furfural

4. Toxicity, animal data

single exposure

For rat and dog, LC₅₀-values of 175 ppm and 370 ppm (700 and 1480 mg/m³) for 6 hours exposure have been reported. For mice, an LC_Lo of 370 ppm (1480 mg/m³) for 6 hours exposure has been reported. (RTECS 1995).

In two short-term studies, groups of six adult male rats were exposed by inhalation to furfural.

In the first study (Mishra et al. 1991) rats were exposed at 95 ppm (370 mg/m³) in a single exposure of 1 hour, or at 38 ppm (150 mg/m³) for 1 hour/day, 5 days/week for 7, 15 or 30 days.

In the second study (Gupta et al. 1991) rats were exposed at up to about 220 ppm in single exposures of 1 hour, or at 40 ppm (155 mg/m³) for 1 hour/day, 5 days/week for 7, 15 or 30 days. Six rats were in the control group.

In both studies, furfural exposed animals showed yellowish discoloration of fur, severe irritation of eyes and nose, lachrymation, perinasal and perioral wetness, and mild nasal bleeding. Respiratory difficulty was observed in some animals.

In the first study, the single exposure to 95 ppm resulted in moderate congestion and perivascular oedema in the lungs, these changes were more pronounced after repeated exposure. Changes in some enzyme activities in the lung were observed.

In the second study, an LC₅₀ of 189 ppm was found. Changes in some enzyme activities in the lung were observed.

single exposure

The oral LD₅₀-values in various species indicate that the relative decreasing order of acute oral toxicity of furfural is rat > mouse > guinea pig > rabbit, dog. Oral LD₅₀-values reported are in the range from 65-149 mg/kg in the rat, 333-400 mg/kg in the mouse, 540 mg/kg in the guinea pig, 800 mg/kg in the rabbit, and 950 mg/kg in the dog. (JECFA 1993, Brabec 1994, RTECS 1995).

Rats and mice (5 animals of each sex per group) were administered furfural in corn oil daily by gavage, 5 days/week for 12 doses over 16 days at dose levels of 0, 15, 30, 120, or 240 mg/kg/day for rats and 0, 25, 50, 100, 200, or 400 mg/kg/day for mice.

In rats, low survival rates and laboured breathing were reported at the highest dose level. Animals that received 120 mg/kg were slightly inactive. No compound-related lesions were observed at necropsy.

In mice, no compound-related lesions were noted at necropsy.

(NTP 1990).

Dermal contact

No data have been found.

Syrian golden hamsters (10 animals of each sex per group) were exposed to furfural vapour at concentrations of 0, 77, 448, or 2165 mg/m³ for 6 hours/day, 5 days/week for 13 weeks. At the highest exposure level, the main findings were mild growth retardation, irritation of the eyes and nose, and hyperplastic atrophy of the nasal epithelium. At 448 mg/m³, some mild nasal epithelial degeneration was observed. (Feron et al. 1979 - quoted from JECFA 1993).

Syrian golden hamsters (18 animals of each sex) were exposed to furfural at concentrations of 400 ppm (1550 mg/m³) for 7 hours/day, 5 days/week for 9 weeks, then 300 ppm (1280 mg/m³) during weeks 10-20, and then 250 ppm (970 mg/m³) during weeks 21-52.

Furfural exposure caused yellowish discoloration of the fur, irritation of the nasal mucosa, growth retardation, atrophy and downward growth of sensory cells of the olfactory epithelium, degenerative changes in Bowman's glands, and the occurrence of cyst-like structures in the lamina propria beneath the olfactory epithelium. There was neither evidence of recovery of the nasal changes after a period of six months nor any progression of the lesions. There were no changes in other parts of the respiratory tract or outside the airway system that could be ascribed to furfural. (Feron & Kruysse 1978).

In oral subchronic studies, dose levels of furfural above 50 mg/kg/d were primarily associated with hepatic effects. Mice appeared to be more resistant than rats to the effects of orally administered furfural.

Rats and mice (10 animals of each sex per group) were administered furfural in corn oil daily by gavage, 5 days/week for 13 weeks at dose levels of 0, 11, 22, 45, 90, or 180 mg/kg/day for rats and 0, 75, 150, 300, 600, or 1200 mg/kg/day for mice.

Low survival rates were reported at the highest dose level in rats and the two highest dose levels in mice.

In rats, absolute and relative liver and kidney weights were significantly increased in male rats in the two highest dose levels. The incidences of cytoplasmic vacuolisation of hepatocytes were increased in male rats at all dose levels. There were no compound-related histological lesions in the kidney of male rats.

In mice, a significant increase in relative liver weight was observed in females that received 75, 150, or 300 mg/kg/d and in males that received 300 mg/kg/d. Centrilobular coagulative necrosis of hepatocytes was seen in the liver of 8/10 males and 2/10 females that received 1200 mg/kg, 9/10 males that received 600 mg/kg, 1/10 males that received 300 or 150 mg/kg. Inflammation in the liver was also present when necrosis occurred.

(NTP 1990).

Male rats were fed furfural at a level of 20 ml/kg in the diet (ca. 175 mg/kg/day) for 7 days, 30 ml/kg diet for 7 more days, 40 ml/kg diet (ca. 350 mg/kg/day) from day 15 to 90, and then 40 ml/kg for 5 days/week for a further 30 days. Hepatic cirrhosis was observed in treated animals, and the fibrotic changes were more prominent in animals killed at 120 days than in those killed after 90 days. (Shimizu & Kanisawa 1986 - quoted from IARC 1995 and JECFA 1993).

No data have been found.

No data have been found.

Furfural exhibits an inconsistent pattern of genotoxic activity, being generally negative in bacterial assays but positive in some mammalian cells in vitro.

Furfural did not induce umu c' gene expression in Salmonella typhimurium TA1535/pSK1002 (IARC 1995). Furfural was reported to be mutagenic to Salmonella typhimurium TA100 in the presence and absence of metabolit activation in one study ((Zdzienicka et al. 1978 - quoted from IARC 1995, JECFA 1993 and NTP 1990), but this result was not confirmed in three subsequent studies, which gave equivocal or negative results (IARC 1995). Furfural was reported to be non-mutagenic in Salmonella typhimurium strains G46, TA100, TA1535, C3076, TA1537, D3052, TA1538 and TA98 and in Eschericia coli strains WP2 and WP2 uvrA with a concentration gradient protocol (IARC 1995).

Injection, but not feeding, of furfural to adult Drosophila melanogaster induced sex-linked recessive lethal mutation but not heritable reciprocal translocations (Woodruff et al. 1985 - quoted from IARC 1995, JECFA 1993 and NTP 1990).

Furfural induced gene mutation in mouse lymphoma cells in the absence of metabolic activation (McGregor et al. 1988 - quoted from IARC 1995, JECFA 1993 and NTP 1990).

In in vitro tests, furfural induced sister chromatid exchanges in Chinese hamster ovary cells both with and without exogenous metabolic activation (NTP 1990) and in human lymphocytes without exogenous metabolic activation (Gomez-Arroyo & Souza 1985 - quoted from IARC 1995, JECFA 1993 and from NTP 1990).

In in vivo tests, furfural did not induce sister chromatid exchanges in bone-marrow cells of B6C3F1 male mice injected intraperitoneally with single doses of furfural at doses of 50, 100 or 200 mg/kg b.w. (NTP 1990).

In in vitro tests, furfural induced chromosomal aberrations in Chinese hamster ovary cells both with and without exogenous metabolic activation (NTP 1990, Stich et al. 1981 - quoted from IARC 1995, JECFA 1993 and from NTP 1990) and in Chinese hamster V79 lung cells without exogenous metabolic activation (Nishi et al. 1989 - quoted from IARC 1995).

In in vivo tests, furfural did not induce chromosomal aberrations in bone-marrow cells of B6C3F1 male mice injected intraperitoneally with single doses of furfural at doses of 50, 100 or 200 mg/kg b.w. (NTP 1990).

Furfural reacted with calf thymus DNA in vitro, primarily at AT base pairs, leading to destabilisation of the secondary structure of DNA and to single-strand breaks (Shahabuddin 1991).

4.5 Carcinogenic effects

Rats

Rats (F344/N, 50 animals of each sex per group) were administered furfural in corn oil daily by gavage, 5 days/week for 103 weeks at dose levels of 0, 30 (low), or 60 (high) mg/kg/day. (NTP 1990).

The main non-neoplastic findings were an increased incidence of hepatic centrilobular necrosis in males (3/50, 9/50, 12/50 in controls, low- and high-dose groups, respectively).

No compound-related neoplastic or lesions preneoplastic were observed at any site in female rats. Cholangiocarcinomas were present in two high-dose males rats, and a similar lesion, biliary dysplasia with fibrosis considered to be an early stage in the development of cholangiocarcinoma, was present in two additional high dose male rats. Cholangiocarcinomas are uncommon neoplasms in F344/N rats and have been observed in only 3/2145 corn oil vehicle control male rats in previous NTP 2-year studies.

The NTP conclusions were that there was some evidence of carcinogenicity in male rats, based on the rarity of the biliary pathology. There was no evidence of carcinogenicity in female rats.

Mice

Mice (B6C3F1, 50 animals of each sex per group) were administered furfural in corn oil daily by gavage, 5 days/week for 103 weeks at dose levels of 0, 50 (low), 100 (mid), or 175 (high) mg/kg/day. (NTP 1990).

The main non-neoplastic findings were minimal multifocal chronic inflammation and pigmentation along or immediately below the serosal surface of the liver (pigmentation: 0/50, 0/50, 8/49, 18/50 and 0/50, 0/50, 0/50, 11/50 in controls, low-, mid- and high-dose males and females, respectively; chronic inflammation: 0/50, 0/50, 8/49, 18/50 and 0/50, 0/50, 1/50, 8/50 in controls, low-, mid- and high-dose females, respectively).

Hepatocellular adenomas (both sexes) and carcinomas (males only) occurred with significant positive trends in dosed mice and were significantly increased in high dose groups (175 mg/kg/day).

Forestomach hyperplasia was observed at increased incidences in female mice. Forestomach squamous cell papillomas occurred with at significant positive trend in female mice.

Renal cortical adenomas occurred in 1/49 mid dose and 1/50 high dose males, and a renal cortical carcinoma was seen in 1/50 low dose males.

The NTP conclusions were that there was clear evidence of carcinogenicity in male mice, based on the incidence of hepatocellular adenomas and carcinomas. There was some evidence of carcinogenicity in female mice based on the increased incidence of hepatocellular adenomas.

Samples of mouse liver neoplasms from the NTP-study (NTP 1990) were assessed for transforming gene activity. Liver neoplasms from mice exposed to furfural exhibited a pattern of oncogene activation involving multiple ras alleles, mutations in multiple codons of the same ras allele, and activation of non-ras transforming genes. In contrast, a more restricted pattern of oncogene activation was found in spontaneously occurring liver neoplasms in mice. Of 17 spontaneous liver neoplasms from mice, 15 contained H-ras activated by point mutations in codon 61. The authors concluded that furfural has a direct genotoxic effect in mouse liver.

According to the authors, these novel mutations in ras genes could have resulted from direct genotoxic effects of furfural. The absence of cytotoxic lesions in the liver, based on histopathological examination after 90 days of administration of furfural at the carcinogenic dose argues in favour of direct genotoxic mechanisms. (Reynolds et al., 1987).

Hamsters

Syrian golden hamsters exposed to 0 or 250/400 ppm furfural vapour, 7 hours/day, 5 days/week for 52 weeks. Simultaneously, a proportion of the animals were given either intratracheal instillations of benzo[a]pyrene (BP) or subcutaneous injections of diethylnitrosamine (DENA). There was no evidence of furfural possessing carcinogenic activity. The carcinogenic effect of BP or DENA on the respiratory tract did not appear to be influenced by furfural exposure. For further details, see part 4.2. (Feron & Kruysse 1978).

IARC

Based mainly on the NTP-studies, IARC has concluded that there is limited evidence in experimental animals for the carcinogenicity of furfural.