ACRYLONITRILE Explanation This compound has not been previously reviewed by the Joint FAO/WHO Expert Committee on Food Additives. Acrylonitrile (synonums: 2-propenenitrile, cyanoethylene, vinyl cyanide) is a clear, colourless and highly flammable liquid that has an unpleasant and irritating odour. It has the following chemical formula: H C = C - C = N H H The major use of acrylonitrile is a monomer in synthetic rubber and plastics that may be used for food containers. The compounds is also used in many countries as a fumigant for grain and as a fluocculant in waste and water treatment plants. BIOLOGICAL DATA BIOCHEMICAL ASPECTS Absorption, distribution and excretion Single oral doses of 0.1 or 10 mg/kg of 14C-acrylonitrile given to male albino rats were 95% absorbed while 5% was excreted in the feces. Depending on the dose, 34.2% or 66.7% of the radiolabeled dose, respectively, was excreted in the urine over a period of 72 hours. Total recovery of the administered radioactivity was between 82 and 104% (Young et al., 1977). The study of body burden (% of dose not excreted at the end of the different time intervals) and of plasma concentration after oral or intravenous administration of 14C-acrylonitrile, revealed a biphasic disappearance of the radioactivity. This indicates a pharmacokinetic two-compartment model for elimination. The half-life values of alpha- and beta-phases, calculated by linear regression analysis of plasma concentration curves, ranged from 3.5 to 5.8 hours and 55 to 70 hours, respectively (Young et al., 1977). Seventeen percent of an intravenous dose of 1 mg of acrylonitrile per kg body weight was excreted in the bile but most of this radioactivity was reabsorbed through the enterohepatic circulation (Young et al., 1977). Freshour & Melcher (1983) observed a biphasic elimination after oral administration of 30 mg of acrylonitrile per kg body weight to rats (half-life of terminal phase 85-120 minutes) but a first-order elimination pattern was found after intravenous administration. Tissue distribution of radioactivity after single oral or intravenous dosing of rats with 14C-acrylonitrile demonstrated high levels in stomach, skin and erythrocytes regardless of route of administration. The retention of radioactivity in the stomach wall after intravenous administration indicates that the high concentration of acrylonitrile in this site after oral dosing was not entirely due to poor absorption (Young et al., 1977). The accumulation of radioactivity in blood was mainly due to covalent binding of acrylonitrile to macromolecules and lipids in the erythrocytes (Ahmed & Patel, 1979). Whole-body autoradiography after oral or intravenous administration of 14C-acrylonitrile to rats or monkeys showed similar distribution patterns. High levels of activity were present in the blood and excretory pathways (bile, intestinal contents and urine) with liver, kidney, lung and adrenal cortex accumulating appreciable label. Stomach and hair follicles showed constant uptake of label. Radioactivity was still present in rats, seven days after administration. In fetuses, exposed in utero, only the eye lens accumulated label higher than that observed in the maternal blood. Monkeys displayed a more pronounced activity in the liver than rats (Sandberg & Slanina, 1980). Biotransformation Two metabolites were identified in urine of rats exposed to 30 mg/kg of acrylonitrile by gastric intubation as thiocyanate and N-acetyl-S (2-cyanoethyl)cysteine. A third was tentatively identified as 4-acetyl-3-carboxy-5-cyanotetrahydro-1,4-2H-thiazine (Langvardt et al., 1980). Acrylonitrile was not detected in the urine of these rats. However, Houthuijs et al. (1982) have reported the excretion of unchanged acrylonitrile in factory workers and proposed monitoring urinary acrylonitrile as a measure of exposure. Cyanoethanol and cyanoacetic acid were detected by gas chromatography in the urines of rats injected i.p. with acrylonitrile (Lambotte-Vandepaer et al., 1981). In bile of rats exposed to acrylonitrile orally, 4 metabolites were isolated. The two biliary metabolites were glutathione conjugates of acrylonitrile (Ghanayem & Ahmed, 1982). Using 14C-label on different parts of the molecule, Kopecky et al. (1980) showed two metabolic pathways of acrylonitrile metabolism, when administered to rats. The minor pathway, through glycidonitrile and glycolaldehyde cyanohydrin, produced cyanide and subsequently thiocyanate. The major metabolites were derived from glutathione conjugation. These pathways were confirmed in vitro with rat liver microsomes. The cyanide formation being dependent on a cytochrome P-450-dependent mixed function oxidase system (Abreu & Ahmed, 1980). Duverger-van Bogaert, et al. (1981) isolated four metabolites: cyanoacetic acid, cyanoethanol, acetic acid and glycolaldehyde from rat liver homogenates after incubation with acrylonitrile. Isolated rat hepatocytes were incubated with acrylonitrile. The major glutathione-adduct formed was identified as S-(2-cyanoethyl) glutathione. S-(2-cyanoethyl)-cysteine was the major adduct found in radiolabeled protein. 2-cyanoethylene oxide accumulated in the cell suspension. Cyanide appeared to be completely converted to thiocyanate (Geiger et al., 1983). Effects on enzymes and other biochemical parameters Oral or i.p. administration of 40 or 100 mg/kg body weight of acrylonitrile to mice caused inhibition of cytochrome oxidase in liver and brain. At the highest dose, the enzyme inhibition persisted until death. On the basis of identifiation of cyanide in these organs, the authors postulated that this metabolite is responsible for the observed effect (Nerudova et al., 1981). Male rats were exposed intraperitoneally to 33 mg/kg body weight of acrylonitrile for 3 days. Treatment resulted in a 20% decrease in liver microsomal cytochrome P-450 activity. This decrease was confirmed by a reduction in benzo(a)pyrene metabolism by liver microsomes. Corticosterone and prolactin levels in the serum of these animals were markedly reduced whereas FSH-levels doubled (Nilsen et al., 1980). Four hours after i.p. injection of acrylonitrile (30 mg/kg) in hamsters glutathione levels in liver and brain were reduced. Twenty-four hours after injection liver and kidney weights were increased as were brain and kidney GSH-levels. Brain succinate dehydrogenase and cytochrome oxidase levels were decreased as were liver and kidney ethoxycoumarin deethylase and liver cytochrome P-450 (Zitting et al., 1981). Although a one-time i.v. injection of acrylonitrile in rats depleted liver, adrenal gland and brain of glutathione (GSH), a 21-day exposure in drinking water at concentrations of 0, 20, 100 and 500 ppm caused increased GSH levels in the liver (Szabo et al., 1977). Vainio and Makinen (1977) demonstrated species specificity in the GSH-depletion in liver comparing rats, hamsters and mice. The mouse was most sensitive to one-time oral or intraperitoneal administration and the rat the most resistant. Irreversible covalent binding of acrylonitrile to rat liver microsomal proteins in vitro was reported by Duverger-van Bogaert (1982a). This observation was confirmed in vivo after i.p. injection of acrylonitrile to rats (Peter & Bolt, 1981). Incubation of rat liver microsomes with acrylonitrile also resulted in irreversible binding to DNA, RNA or polynucleotides (Peter et al., 1983a). TOXICOLOGICAL STUDIES Special study on reproduction Rat A three-generation reproduction study was performed on 20 rats/dose consuming 0, 100 or 500 ppm of acrylonitrile in the drinking water for 100 days before the first mating and throughout the experiment, including during lactation. Two litters were produced in each generation and the offspring of the second litter were used to produce the next generation. In the first generation parental toxicity signs were apparent at the 500 ppm level in the form of decreased food-water consumption and body weights. In both litters of the first generation, a greater number of pups died in the 500 ppm group. These deaths may have been a result of acrylonitrile's toxicity to the dams, since pups fostered by untreated dams had normal survival. The only adverse effect observed in pups that survived treatment was a decrease in body weight in the 500 ppm group in all litters. There was a suggestion of tumorigenic activity in the females of the F1b generation that were sacrificed after weaning of their second litter. An increase was observed in astrocytomas in the brain (4 tumors out of 17 necropsied) in the 500 ppm group and Zymbal gland tumors (2 out of 19 and 4 out of 17 in the 100 and 500 ppm groups, respectively) while no tumors were reported in the controls. No other histopathological adverse findings were described (Beliles et al., 1980). Special study on species specificity of fetotoxicity Mouse One single i.p. injection of 32 mg/kg body weight of acrylonitrile in groups of 11-13 pregnant mice of the inbred AB Jena-Halle strain on day 5, 7 or 9 of gestation caused an increase in post-implantation loss of fetuses. No significant embryotoxic effect was observed in DBA or C57B1 mice even after repeated applications from day 1-14 or day 7-14 of gestation (Scheufler, 1980). Special studies on teratogenicity Hamster Groups of 5 or 6 (12 for control) pregnant hamsters were treated intraperitoneally with a single dose of physiological saline or 4.8, 10.1, 24.9, 65.3 or 80.1 mg/kg body weight of acrylonitrile on day 8 of gestation. Additional groups were pre- and post-treated with the known cyanide antagonist sodium thiosulfate to investigate the role of cyanide involvement in the teratogenic effects observed. The hamsters were sacrificed on day 14 of gestation and fetuses were recovered by caesarian section. Implantation and resorption sites were recorded, and fetuses were examined under a dissecting microscope for skeletal malformations. After fixation in Bouin's solution, the fetuses were re-examined to confirm the observed abnormalities. Maternal toxicity was observed at 80.1 mg/kg of acrylonitrile in the form of respiratory distress, salivation and convulsions. At this dose level, the number of resorptions was increased and 7 out of 51 live fetuses had an encephalocele (0/135 in controls). Treatment with 1.275 g/kg of sodium thiosulfate intraperitoneally, protected dams and fetuses of toxic effects of acrylonitrile at this dose. However, at higher dose levels of acrylonitrile (100 mg/kg) with sodium thiosulfate, teratogenic effects were observed in the absence of maternal toxicity. At 120 mg/kg of acrylonitrile, this dose of sodium thiosulfate failed to protect the dams from maternal toxicity (Willhite et al., 1981a). The same authors studied the changes caused by 80.1 mg/kg of acrylonitrile administered intraperitoneally to pregnant hamsters on day 8 of gestation. Early embryos (10 hours after acrylonitrile administration) and term fetuses (sacrificed on day 14 of gestation) were studied histopathologically after hematoxylin-eosin staining. Signs of acute mesodermal damage were noted 10 hours after dosage including reduced cell number, shrinkage of cytoplasm, and enlarged extracellular spaces. The affected embryos were smaller and were delayed in their development. The treated embryos showed a shortening of the neural folds and failure of the neural tube to close. The 14-day old fetuses showed cranioschisis occulta with encephalocele, and axial lordotic malformations (Willhite et al., 1981b). Rat Between 29 and 39 pregnant rats were given 10, 25 or 65 mg/kg body weight of acrylonitrile in water by gastric intubation on days 6-15 of gestation. A group of 43 control animals received an equal volume of water (2 mg/kg body weight) by gavage. On day 21 of gestation, the dams were sacrificed and examined for implantation sites, resorptions and fetal abnormalities. Additional rats (30/group) were exposed to 0, 40 or 80 ppm of acrylonitrile by inhalation for 6 hr/day during the same period. As determined by acrylonitrile blood levels, the 80 ppm inhalation dose was equivalent to a 23 mg/kg oral dose. The dams receiving 65 mg/kg body weight of acrylonitrile showed signs of maternal toxicity in the form of hyperexcitability, excessive salivation, thickening of the non-glandular portion of the stomach, decreased weight gain, food consumption and increased water consumption as well as increased absolute and relative liver weights. In the 65 mg/kg gavage group, 4 pregnancies did not develop to term but all fetuses were resorbed. However, in the remaining successful pregnancies there was no indication of early fetal death (litter sizes and resorptions were comparable to controls). Fetal body weight and crown-rump length were depressed in this dose group. An increase in short-tailed fetuses and missing vertebrae was described for the 65 mg/kg group as well as a few minor skeletal aberrations. In the animals exposed to acrylonitrile by inhalation, these changes did not reach statistical significance (Murray et al., 1976 and Murray et al., 1978). Chicken Acrylonitrile in saline was injected into the air space or the yolk sac of 3 day old incubated chicken eggs at concentrations of 0, 0.01, 0,1, 1 and 10 umol/egg. Embryos were examined for viability and malformations after 14 days of incubation. Embryotoxicity was observed in 100% and 44% in the two highest dose groups, respectively. No signs of teratogenicity were reported (Kankaanpaa et al., 1979). Special study on teratogeniticy of the metabolite sodium cyanide Hamster Pregnant hamsters were dosed with concentrations of 0.12- 0.13 mmol/kg/hr (141-153 mg/kg/day) of sodium cyanide by implantation of osmotic minipumps from day 6-9 of gestation. Fetuses were examined on day 11 of gestation. Maternal toxicity was noted in 4 to 7 dams receiving 150 mg/kg/day in the form of ataxia. Five of 7 litters in this group had 3 or more malformed fetuses whereas 2 litters were completely resorbed. Malformations noted were exencephaly, encephaloceles, hydropericardium, and limb and tail defects (Doherty et al., 1981). Special studies on the mechanism of acrylonitrile toxicity Antidotes to cyanide poisoning were reported to protect rabbits against the acute toxicity of acrylonitrile. The use of sodium thiosulfate prevented the death of 3 out of 4 rabbits exposed to 75 mg/kg of acrylonitrile intravenously and delayed toxicity symptoms and death after 100 mg/kg. Animals were dying in spite of reduced blood cyanide levels. Similar results were obtained with rats and guinea pigs (Hashimoto & Kanai, 1965). In addition, these authors pretreated rabbits with L-cysteine 3 minutes before dosing with acrylonitrile. Cysteine caused a large decrease in the levels of acrylonitrile and cyanide in the blood and protected the animals from poisoning (Hashimoto & Kanai, 1965). Similar results were noted with guinea pigs, rats and mice. Groups of 10 male rats were treated with 144 mg/kg of acrylonitrile, 15.6 mg/kg of KCN or 12.75 mg/kg of acetone cyanohydrin (1.5 × LD50) subcutaneously. Half of the groups were pretreated with 30 mg/kg of sodium nitrite. Sodium nitrite effectively protected rats from the lethal effects of KCN but had no effect on survival rate or survival time of acrylonitrile (Magos, 1962). Rats poisoned with lethal doses of acrylonitrile were protected by cyanide antidotes only after oral administration of acrylonitrile (150 mg/kg). After inhalation or i.p. administration of arylonitrile cyanide antidotes were not protective. Cysteine prevented the lethal effect of 100 mg/kg acrylonitrile i.p. even when given 2 hours after the acrylonitrile dose (Appel et al., 1981). A single dose of 60 mg/kg of acrylonitrile administered orally or subcutaneously to rats caused gastrointestinal bleeding 3 hours after treatment. This effect was enhanced after pretreatment with the cytochrome P-450 inducing compounds phenobarbital or Aroclor 1254 and reduced after inhibition of this enzyme with CoC12 or SKF 525A. The authors concluded that metabolic activation of acrylonitrile is a prerequisite for the toxic effect on the stomach (Ghanayem & Ahmed, 1983). Special studies on mutagenicity Bacterial Mutagenic potential of acrylonitrile was tested in four tryptophan-dependent Escherichia coli WP2 strains at concentrations of 75 and 150 umol/plate, using a plate-incorporation assay. Doses above 150 umol/plate were cytotoxic. Acrylonitrile had a weak mutagenic effect that was not enhanced by Aroclor 1254-induced rat liver S-9 microsomal fraction. The use of the fluctuation test confirmed the mutagenicity of acrylonitrile in these strains at concentrations 20-40 fold lower than the plate-incorporation test (Venitt et al., 1977). Acrylonitrile showed weak mutagenic activity in Salmonella typhimurium strains TA 1535 and TA 1538 after activation with Aroclor 1254-induced mouse liver S-9. Cells were exposed to acrylonitrile by spotting on a lawn of bacteria, by liquid suspension or under vapor. In the last test method, concentrations as low as 57 ppm for 4 hours caused a statistically significant increase in revertants (Milvy & Wolff, 1977). In a modification of the Ames test using a gradient plate of the test compound, acrylonitrile was listed as positive in a mutagenesis screening test with 10 strains of Salmonella typhimurium and Escherichia coli (McMahon et al., 1979). Aroclor 1254-induced rat liver S-9 was necessary for expression of mutagenic activity of acrylonitrile when exposing the base-pair substitution sensitive strains TA 1538, TA 1535, TA 1530 and TA 1950 to acrylonitrile vapor for 1 hr in a closed environment causing concentrations of about 200 ug/plate. The frameshift-sensitive strains TA 98 and TA 1978 and the basic-pair substitution sensitive strain TA 100 were only weakly reverted (De Meester et al., 1978). Negative results were found with the strains TA 1975z, TA 1532, TA 1537 and his G 46. Pre-treatment of Wistar rats or NMRI mice with Aroclor 1254 or 3-methyl-cholanthrene caused the liver S-9 to be more effective in activating acrylonitrile's mutagenicity than phenobarbital- or acrylonitrile induction. The S-9 mix prepared from mice was more effective than that from rats. Uninduced Beagle dog liver S-9 was also capable of activating acrylonitrile (De Meester et al., 1979). The addition of trichloroacetonitrile, a radical scavenger, abolished the mutagenic activity of acrylonitrile (at a concentration of 14 umol/plate and preincubated with S-9 mixture) to Salmonella typhimurium TA 1530 indicating a role of radical formation in the mutagenic action of acrylonitrile (Duverger van Bogaert et al., 1982b). Acrylonitrile was reported to be mutagenic to Salmonella typhimurium TA 1535 after activation by Aroclor 1254-induced hamster liver S-9 causing 49 revertants/plate at 100 ug and 131 revertants/plate at 1000 ug per plate (Lijinski & Andrews, 1980). Drosophila The occurrence of sex-linked recessive lethal mutations in Drosophila melanogaster was studied by Benes and Shram (1969) following injection of 0.2 ul of an 0.1% acrylonitrile solution in the abdomen of male flies. The results were inconclusive. Mammalian Dosages of 0, 7, 14 or 21 mg/kg body weight of acrylonitrile (5 times per week) were given orally or intraperitoneally to groups of 6 male mice for periods of 4, 15 or 30 days. No chromosomal aberrations were noted in the bone marrow 6 hours after the last administration of acrylonitrile. The chemical also was found to be negative when Sprague-Dawley rats were exposed orally to 40 mg/kg body weight of acrylonitrile for 16 days (Rabello-Gay & Ahmed, 1980). Male mice were injected intraperitoneally with a single dose of 20 or 30 mg/kg of acrylonitrile. Chromosome aberrations were examined in bone marrow cells at 6, 18, 24, 48 and 72 hrs after administration, and micronuclei in polychromatic erythrocytes at 24, 30 and 48 hrs. Both tests yielded negative results. In addition, a dominant lethal test was performed by mating each male with groups of 3 females immediately after injection, and at days 7, 14, 21 and 28. The females were sacrificed and dissected 17 days after the start of mating. Reproductive performance of the experimental animals was comparative to controls as were testicular weights (Leonard et al., 1981). Syngeneic Balb/c mice were inoculated with 2-4 × 106 Balb/3T3 cells immediately prior to subcutaneous injection of acrylonitrile. After 3-4 hr of exposure, cells were recovered for estimation of transformation rate. Acrylonitrile was reported to have a weak positive response (Barnett & Ward, 1979). Primary hamster embryo cells were cultured in the presence of 0, 12, 25, 50 and 100 ug/ml of acrylonitrile. At 50 and 100 ug/ml exposure, these celles produced foci of morphologically transformed cells. When similar cells were pretreated with Simian adenovirus (SA7) and subsequently treated with acrylonitrile, the viral transformation was enhanced. When 3H-thymidine labeled hamster embryo cells were treated with acrylonitrile, cellular DNA, subjected to alkaline sucrose gradients, exhibited a sedimentation pattern reminiscent of that observed for chemical carcinogens (Parent & Casto, 1979). Acrylonitrile did not produce sister chromatid exchanges in Chinese hamster ovary cells in culture but a significant increase was produced when these cells were co-cultured with freshly isolated rat hepatocytes indicating that a reactive metabolite of acrylonitrile was transported from the hepatocytes to the CHO cells (Brat & Williams, 1982). Concentrations of 5 × 10-4M of acrylonitrile, pretreated with rat liver S-9 mixture, caused a significant increase in sister chromatid exchanges as well as increased 3H-tymidine uptake in cultured human lymphocytes (Perocco et al., 1982). Special studies on mutagenicity of acrylonitrile metabolites Urine (0.1 ml per plate) from mice or rats treated with a single i.p. dose of acrylonitrile (30 mg/kg) was mutagenic in Salmonella typhimurium TA 1530. When assayed in the presence of mouse liver S-9 mixture, this activity was decreased and pretreatment of the test animals with phenobarbital abolished the direct mutagenicity of the urines of acrylonitrile-treated rats and reduced that observed in the urine of mice (Lambotte-Vandepaer et al., 1980). The mutagenicity of rat urines was also reduced by pretreatment of the animals with inhibitors of alcohol dehydrogenase and mixed-function oxidases or with a radical trapping agent. The authors postulated that a radical species or an epoxide formed in the metabolic pathway of acrylonitrile could be the metabolites responsible for the mutagenicity of these urines (Lambotte-Vandepaer et al., 1981). These same enzyme inhibitors depress the activation by rat liver S-9 of acrylonitrile's mutagenicity with Salmonella typhimurium TA 1530 as the tester strain (Duverger-van Bogaert, 1981). Glutathione enhanced that S-9-mediated mutagenicity of acrylonitrile suggesting a role of GSH in the formation of mutagenic metabolites of acrylonitrile. However, the adduct between acrylonitrile and GSH was not mutagenic (Duverger-van Bogaert et al., 1982c), The bile from adult male rats collected for 6 hours after an i.p. injection of 45 mg/kg body weight of acrylonitrile, was not mutagenic to Salmonella typhimurium TA 1538 while mutagenic metabolites from other test compounds were excreted in the bile (Connor et al., 1979). The known metabolite of acrylonitrile, glycidonitrile, was reported to induce strand breaks in SV40 phage DNA in vitro, whereas acrylonitrile did not (Peter et al., 1983b). Mutagenic activity of this metabolite in Salmonella typhimurium tester strains TA 100 and TA 1535 was reported by Cerna et al., (1981). Special study on carcinogenicity Groups of 40 male and 40 female rats were exposed to 0 or 5 mg/kg body weight of acrylonitrile dissolved in olive oil by gastric intubation; the control group was intubated with olive oil, 3 times per week, for 52 weeks. All animals were kept until spontaneous death, at which time they were necropsied and the following tissues were examined microscopically: Zymbal gland, interscapular brown fat, salivary glands, tongue, lungs, liver, kidneys, spleen, stomach, intestines, urinary bladder, brain and grossly recognizable lesions. Body weight and survival were not affected by the administration of acrylonitrile. Although a few gliomas in the brain, mammary tumors, forestomach papillomas and Zymbal gland carcinomas were observed, they appeared evenly distributed among experimental animals and controls (Maltoni et al., 1977). In a parallel study group of 30 male and 30 female Sprague-Dawley rats were exposed to acrylonitrile by inhalation (0.5, 10, 20 and 40 ppm). A moderate increase in mammary tumors (incidence 5/30, 10/30, 7/30, 10/30, 7/30 in females; 1/30, 0/30, 1/30, 4/30, 7/30 in males in order of increasing dosage), Zymbal gland carcinomas, (0/30, 0/30, 1/30, 1/30, 0/30 in females; 0/30, 0/30, 1/30, 0/30, 0/30 in males), forestomach carcinomas (0/30, 1/30, 2/30, 1/30, 0/30 in females; 0/30, 1/30, 2/30, 0/30, 3/30 in males) and brain tumors (9/30, 17/30, 11/30, 14/30, 8/30 in females; 0/30, 1/30, 10/30, 13/30, 12/30 in males) diagnosed as gliomas was reported, but the incidences were such that the significance of these findings is doubtful (Maltoni et al., 1977). Other studies addressing the carcinogenic effect of acrylonitrile are discussed under "long-term toxicity tests" and one under "special study on reproduction". Special study on skin and eye irritation Acrylonitrile was mildly irritant to shaved rabbit abdominal skin at dosages of 1,2 and 3 ml/kg applied to areas of 100, 200 and 300 cm2. The application of 0.05 ml of the compound caused mild conjunctivitis without clouding of the cornea or papillary damage after 1 hr (McOmie, 1949). Special comparative studies on inhalation Four rhesus monkeys and 2 dogs were exposed to an atmosphere containing 56 ppm of acrylonitrile for 4 hrs per day, 5 days per week over a 4-week period. The monkeys did not show overt signs of toxicity, whereas 1 dog died and the other dog had intermittent paralysis of the hind legs (Dudley et al., 1942). From 3-16 rats, guinea pigs, rabbits and cats were exposed to 100 ppm or 153 ppm acrylonitrile, and 2 monkeys to 153 ppm for 8 weeks. At the highest exposure level, severe toxicity was noted with many animals dying prior to completion of the study. Three female rats at the 100 ppm level gave birth to normal pups. The dog was the most sensitive species tested followed by monkey, cat and rabbit. Guinea pig and rat were the least sensitive. Microscopic examination of spleen, kidney, liver, lung, heart, pancreas, lymph nodes, stomach and small and large intestines, showed hemosiderosis in rat spleens, renal irritation in most animals, subacute bronchopneumonia (all species except cat). Cats were the only species that showed signs of liver damage (Dudley et al., 1942). Acute toxicity Animal Route LD50 References (mg/kg) mouse oral 27 Benes & Cerna, 1959 i.p. 46 Paulet & Desnos, 1961 s.c. 35 Benes & Cerna, 1959 rat oral 78 Benes & Cerna, 1959 percut. 148 NIOSH, 1979 i.p. 65-100 Knobloch et al., 1971 s.c. 80-96 Knobloch et al., 1971 Magos, 1962 guinea pig oral 50 NIOSH, 1979 percut. 202 NIOSH, 1979 s.c. 35 NIOSH, 1979 rabbit oral 93 NIOSH, 1979 percut. 250 NIOSH, 1979 i.v. 50-69 Paulet & Desnos, 1961 Hashimoto & Kanai, 1965 Short-term studies Rat Administration of 50 mg/kg of acrylonitrile to rats i.p., once/day for 3 weeks resulted in decreased body weight, leukocytosis, increased weights of liver, kidney and heart. Organ weight changes were confirmed microscopically as parenchymal degeneration of liver and kidney. Damaged neuronal cells of cortex and brainstem were also diagnosed (Knobloch et al., 1971). Intravenous administration of 200 mg/kg of acrylonitrile to female rats resulted in massive bilateral hemorrhagic apoplexy of adrenal glands within 1-2 hours (Szabo et al., 1976a). Female rats were exposed to 0, 0.05% or 0.2% of acrylonitrile in the drinking water for 7, 21 or 60 days. Body weights, water intake and urine output were reduced in all groups. Na+ concentration in plasma and urine were elevated whereas K+ was only elevated in urine, not in plasma. However, 24 hr urinary Na+ and K+ were reduced. Plasma corticosteroids were also depressed. The adrenal zona fasciculata was atrophic after 21 and 60 days (Szabo et al., 1976b). Groups of 4 female rats were exposed to 0, 100 or 500 ppm of acrylonitrile in the drinking water for 21 days. Water consumption decreased significantly in the 500 ppm group. Food consumption was only slightly reduced in both experimental groups. Sorbitol dehydrogenase was elevated in the high-dose group. Relative liver weights were comparable to controls. The livers showed no gross or light-microscopic abnormalities (Silver et al., 1982). Dog Groups of 4 male and 4 female dogs were exposed for 6 months to 0, 100, 200 and 300 ppm of acrylonitrile in the drinking water. Exposure for males was 0, 10, 16 and 17 mg/kg, for females, 0, 8, 17, 18 mg/kg respectively. The two highest doses were highly toxic with increased mortality. Food and water consumption were decreased at 300 ppm in both sexes and at 200 ppm in females. There were also substantial decreases in boy weight at all dose levels. Hematological changes in the higher dose levels were consistent with bronchopneumonia which was chronically present. Chemical studies of blood and urine revealed no abnormalities that were directly associated with acrylonitrile treatment. Non-protein sulfhydryl levels in liver and kidneys were comparable to controls in the 100 ppm group. The higher dose levels had too few numbers surviving for meaningful statistical analysis. Relative kidney weights were increased but these kidneys appeared normal on histopathological examination. The 2 surviving males of the 200 ppm, and the 2 surviving females of the 300 ppm groups had a decreased relative brain weight. The lungs of dogs at the two higher levels showed bronchopneumonia caused by aspirated food particles. In these same groups, focal erosions and ulcerations as well as dilation and thinning of the walls of the esophagus were described. It was believed that acrylonitrile may have caused irritation of the membrane of the throat (Quast et al., 1975). Long-term studies Rat A combined chronic toxicity and carcinogenicity study was performed on rats. Three groups of 100 male and 100 female weanling rats were administered acrylonitrile in distilled water by gastric intubation in dosages of 0, 0.1 and 10 mg/kg body weight, 7 times per week, for 19 months and 1 week. Periodic observations were made of appearance, mortality, growth, tissue masses and food and liquid intake. Ophthalmoscopy was performed at pretest, 6, 12, 18 and 20 months. Comprehensive hematological examinations, clinical chemical tests (SGPT, AP, BUN, glucose) and urinalysis were performed on 10 animals/sex/high-dose and control, routinely and low-dose as required, at 6, 12, 18 and 20 months. All animals were necropsied. Interim sacrifices took place at 6, 8 and 12 months on 10 animals/sex/dose. At interim and terminal sacrifices (20 months), organ weights of brain, pituitary, adrenals, gonads, heart, kidneys and liver were recorded for 10 animals/sex/dose. Tissue samples of 10 animals/sex/dose at each necropsy interval were subjected to comprehensive histopathological examination. The study was terminated at 20 months because of high mortality in the high-dose groups (both sexes). No consistent changes suggesting compound involvement were found in appearance, eye examinations, food consumption, hematological, biochemical and urinary parameters. Mean body weights of the high-dose males were consistently slightly lower than controls. The body weights of the other groups were considered comparable to controls throughout the study. An increase in palpable masses of the head region was noted in high-dose males (incidence 2/100, 3/100, 12/100 for 0, 0.1 and 10 mg/kg, respectively) and palpable masses in both head and mammary regions were reported in high-dose females. The incidences of palpable masses in the head region of females was 7/100, 5/10, 23/100 in order of increasing dosage, and in the mammary region 29/100, 26/100 and 42/100. These findings were confirmed histopathologically by an increased incidence of astrocytomas of the brain (1/99, 2/100, 17/100 for females; 2/100, 0/97, 16/98 for males) and spinal cord, (0/100, 0/95, 1/99 for females; 0/94, 0/93, 1/97 for males), squamous cell carcinomas and papillomas of the Zymbal gland (ear canal) in the high-dose groups (both sexes) and carcinomas of the mammary gland in high-dose females. Incidences of Zymbal gland papillomas were 1/73, 0/84, 6/84 for females; 0/80, 1/80, 8/82 for males, and Zymbal gland carcinomas 0/73, 0/84, 9/84 for females, 1/80, 0/80, 10/82 for males. The incidences of mammary carcinomas in females were 7/101, 6/100, 22/101. In addition, an increase was noted in adeno-carcinomas of the intestines in high-dose males only (6/100, 1/100, 6/100) and squamous cell carcinomas (0/99, 0/97, 18/99 in males) and papillomas (1/99, 4/99, 16/99 in females, 2/99, 6/97, 22/99 in males) in the non-glandular stomach (anonymous, 1980a). A second study with identical protocol was performed on rats with the exception that acrylonitrile was administered in the drinking water, at concentrations of 0, 1 and 100 ppm. The daily intake of acrylonitrile was 0, 0.093 and 7.98 mg/kg for males and 0.146 and 10.69 mg/kg for females. This study was also terminated at 20 months and the findings confirmed the results of the intubation study: increased incidences of astrocytomas of brain (incidences: 0/99, 1/100, 32/97 in females, 2/98, 3/95, 23/97 in males) and spinal cord (0/96, 0/99, 7/98 in females) and of squamous cell carcinomas of the Zymbal gland (0/99, 0/95, 7/98 in females, 1/100, 0/91, 19/93 in males) of high-dose males and females, as well as increased squamous cell carcinomas and papillomas of the non-glandular stomach in the high-dose groups. Incidences in stomach carcinomas were 0/100, 0/99, 0/99 in females, 0/98, 1/98, 4/97 in males and papillomas 1/100, 4/99, 7/99 in females and 3/98, 2/98, 8/97 in males. No increase in tumor incidence in the intestines of males nor the mammary glands in females were reported in this study, however (anonymous, 1980b). In a third study of similar protocol, performed by the same laboratory, rats of a different strain (100 animals/sex/dose, except controls which consisted of 200 animals per sex) were exposed to acrylonitrile in the drinking water at concentrations of 0, 1, 3, 10, 30 and 100 ppm for 2 years. The average daily amount of acrylonitrile ingested for male rats was 0, 0.08, 0.25, 2.49, 8.37 mg/kg and for female rats 0, 0.12, 0.36, 1.25, 3.65 and 10.89 mg/kg. Interim sacrifices were performed at 6, 12 and 18 months (10 animals/sex/dose) and the study was terminated at 23 months for females and at 26 months for males. Early mortality was observed in both the male and female rats exposed to 100 ppm of acrylonitrile. Tumors sites and incidence are as follows: astrocytomas in the brain (1/99, 0/100, 1/100, 2/101, 4/95, 6/100, 23/98 in females; 0/100, 2/100, 2/100, 1/100, 2/100, 10/99, 21/99 in males in order of increasing dosage); squamous cell carcinomas and papillomas of the Zymbal gland (ear canal), (carcinomas 0/98, 0/95, 0/94, 1/92, 2/90, 2/94, 7/86 in females, 0/95, 1/94, 0/97, 0/93, 2/88, 5/94, 8/93 in males; papillomas: 0/98, 0/95; 0/94, 1/92, 2/90, 3/94, 1/86 in females, 0/95, 1/94, 1/97, 0/93, 0/88, 2/94, 8/93 in males); squamous cell carcinomas and papillomas of the fore-stomach in males only (combined incidence: 0/99, 0/100, 1/100, 4/97, 4/100, 4/100, 1/100) (anonymous, 1980c). In another study acrylonitrile was administered for 2 years to male and female rats in the drinking water at concentrations of 0, 35, 100 and 300 ppm to groups of 48 animals/sex (80/sex for control). For the first 21 days of the study, the concentrations were 35, 85 and 210 ppm; then the two higher doses were raised to 100 and 300 ppm. The daily intake of acrylonitrile based on water consumption was 0, 3.4, 8.5 and 21.2 mg/kg for males and 0, 4.4, 10.8 and 25.0 mg/kg for females. Periodic observations of appearance, body weights, food and wate consumption, condition of the teeth and palpable masses were reported. At predetermined intervals, blood and urine were collected from 10 rats/sex of control and high dose of hematological and biochemical measurements and urinalysis. Necropsy and gross pathology were performed on all animals that were not lost through autolysis. On death or at termination at 24 months, microscopic examination was performed on a complete set of tissues from the control and high-dose animals and on 23 selected organs or tissues with obvious lesions, from the other exposure groups (Quast et al., 1980a). After 9 months of treatment, the animals of the highest dose groups showed signs of toxicity as indicated by an unthrifty appearance. There was a dose-related decrease in food consumption (except in male rats at the lowest dose level), and a concomitant dose-related decrease in water consumption. Early mortality was observed at the high dose level in males and at all dose levels in females. The reduced water intake was reflected in an increased urinary specific gravity in the 300 ppm groups and the 100 ppm female group. There were decreases reported in white blood cell count, packed cell volume and hemoglobin and increases in blood urea nitrogen in the 300 ppm groups at some of the test points. Increased incidences of astrocytomas in the brain (incidence 1/80, 17/48, 22/48, 24/48 in females, 1/80, 8/47, 19/48, 23/48 in males), were reported for all dose groups in a dose-related fashion, occurring predominantly in the cerebral cortex and the brainstem. Possible pre-neoplastic foci of glial cells were also noted. Tumors in the ear canal (Zumbal gland) were progressively growing ulcerated tumors, causing displacement of the lower jaw and consequent interference with food consumption in some animals. These tumors were observed at increased incidence and severity in the 300 ppm group for both sexes, and all dose groups for the females(1/80, 5/48, 8/48, 18/48 in females, 3/80, 4/47, 3/48, 16/48 in males). Both papillomas and carcinomas were found in the non-glandular portion of the stomach at 100 and 300 ppm, with a progression from hyperplasia and hyperkeratosis, to papilloma and, finally, to carcinoma being apparent (combined tumor incidence 1/80, 1/48, 12/48, 30/48 in females and 0/80, 2/47, 23/48, 39/48 in males). Squamous cell papillomas and carcinomas of the tongue were increased in the high-dose groups of both sexes (0/80, 1/48, 2/48, 12/48 in females, 1/80, 2/47, 4/48, 5/48 in males), and carcinomas of the small intestine were increased in the 100 and 300 ppm female groups (0/80, 1/48, 4/48, 4/48). Mammary gland tumors in females (58/80, 42/48, 42/48, 35/48) were common and were one of the major reasons for animal deaths prior to the end of the study. An apparent decrease in this tumor type in the 300 ppm group could probably be attributed to the early death of animals at this dose level. The early mortality could also be implicated in the reduced incidences of pituitary, thyroid, adrenal, pancreas and uterus tumors (Quast et al., 1980a). A study in which groups of 100 male and 100 female rats were exposed to vapor levels of 0, 20 and 80 ppm of acrylonitrile for 2 years for 6 hours per day, 5 days per week, essentially confirmed the occurrence of tumors in the brain (0/100, 4/100, 16/100 in females, 1/100, 4/99, 15/99 in males) and ear canal (Zymbal gland) (0/100, 0/100, 10/100 in females, 1/100, 3/100, 11/100 in males) in both sexes as well as epithelial tumors of the tongue (1/96, 0/14, 7/89 in males) carcinoma of the small intestines in males (2/99, 2/20, 14/98) and mammary adenocarcinomas in females (9/100, 7/100, 20/100). General toxic effects were also observed in this study in the form of unthrifty appearance, decreased body weight gain, early mortality, increased palpable masses in the ear region (male and female) and in the mammary region (female only) as well as signs of irritation of the respiratory tissues. No consistent compound-related changes were noted in hematological, biochemical parameters and urinalyses (Quast et al., 1980b). OBSERVATIONS IN MAN Acute intoxication Non-fatal intoxication by acrylonitrile was reported in workers who cleaned polymerizers in rubber-manufacturing plants. Exposure was estimated at 16-100 ppm for 20 to 45 minutes. All workers complained to nasal irritation and an oppressive feeling in the upper respiratory passages. Dull headaches, nausea, apprehension and nervous irritability were frequent complaints. In more severe cases anemia and jaundice were diagnosed (Wilson, 1944; Wilson et al., 1948). Similar symptoms of headache, vertigo, nausea and vomiting were reported by a chemist distilling acrylonitrile (Sartorelli, 1966), including tremors, uncoordinated movements and convulsions. Baxter (1979) has summarized the sequence of symptoms of acrylonitrile poisoning in man as follows: irritation of eyes and nose, limb weakness, labored breathing, dizziness, impaired judgement, cyanosis and nausea, collapse, irregular breathing, convulsions. Case reports have been presented of lethal intoxications of patients after exposure to fumigant mixtures containing acrylonitrile (Davis et al., 1973; Radimer et al., 1974). The latter report implicated acrylonitrile as the causative agent for severe epidermal necrosis resembling burn blisters. Epidemiological studies A retrospective cohort study of 1345 employees with potential exposure to acrylonitrile analysing cancer incidence and mortality from 1956-1976, reported the occurrence of 25 cases of cancer with 20.5 expected. Of these, 8 were respiratory cancer with 4.7 expected. A trend toward increased risks was seen with increased duration and severity of exposure. Twenty cancer deaths were found with 17.4 expected (O'Berg, 1980). The mortality experience of workers exposed to acrylonitrile at two plants in Texas and Alabama was studied with special emphasis on overall cancer rate, cancer of the lung and colon. Total cohorts for this study was 352. The follow-up period was around 15 years. There were no statistically significant differences between observed and expected numbers of death for any of the cause-of-death category examined (Zack, 1980). Comment: Considering the small size of the study cohort and the relatively short period of follow-up, this study is probably too insensitive to detect increased cancer risk. In an analysis of mortality among 327 employees of a rubber chemicals plant who had potential exposure to acrylonitrile, 9 deaths from lung cancer were found versus 5.9 expected based on U.S. mortality rates of white males or 4.7 expected based on mortality rates of other rubber workers in the same area. The excess was greatest among men who worked 5 or more years and who died 15 years after starting work in the plant (Delzell & Monson, 1982). A cohort of 1111 men working with acrylonitrile or acrylic fibers in the UK was analysed for mortality and cancer rates. Exposure occurred between 1950-1968 with a follow-up period until 1978. In the group of men exposed to acrylonitrile for at least one year, the total number of deaths was smaller than expected. An excess of deaths from all cancers was found, arising mainly from cancers of the lung, stomach, colon and brain, but the excess was not statistically significant (Werner & Carter, 1981). Analysis of chromosomes in lymphocyte cultures of 18 workers who had been exposed to vapors containing acrylonitrile for an average of 15.4 years did not show an increase in abnormalities over an age-matched control group of non-exposed workers (Thiess & Fleig, 1978). Comments Orally administered acrylonitrile is rapidly absorbed. The absorbed material is distributed throughout the body with highest concentrations occurring in blood, liver, kidney, lung of adrenal cortex and stomach. Pharmacokinetic studies indicate of two compartment model for elimination, with half-life ranging from 3-5 hr, and 55-70 hr. Excretion of the metabolic products is mainly in the urine. The metabolism involves cytochrome P-450 dependent mixed function oxidase systems, followed by glutathione conjugation. The urinary metabolites identified include thiocyanate, N-acetyl-S(2-cyanoethyl) cysteine and 4-acetyl-3-carboxy-5-cyanotetra- hydro-1,4-2H-thiazine. The major biliary metabolites are glutathione conjugates of acrylonitrile. Acrylonitrile was teratogenic to hamsters and rats. Acrylonitrile was weakly mutagenic in a number of Salmonella typhimurium strains after activation with S-9 mixtures. Urine from rats and mice treated with a single i.p. injection of acrylonitrile was also shown to have mutagenic activity in the Ames test (strain TA 1530). Acrylonitrile, when administered to rats by gastric intubation, or in the drinking water, resulted in statistically significant increases of tumor incidence at multiple sites, including: astrocytomas in brain and spinal cord, squamous cell carcinomas of the Zymbal gland (ear canal gland), carcinomas and papillomas of the non-glandular stomach. These findings were confirmed in other 2-year drinking water and inhalation studies in rats. Inhalation study showed increased incidences of tumors of the brain and Zymbal gland, and in one study tumors of the tongue. The suspicion of carcinogenicity of acrylonitrile has been supported by a number of epidemiological studies of factory workers exposed to acrylonitrile vapors. There is a slight indication of increased lung, stomach, colon and brain tumors. EVALUATION Level causing no toxicological effect Acrylonitrile is considered to be teratogenic in hamsters and rats, and carcinogenic in rats when administered orally and when inhaled. A "no effect" level in experimental animals has not been established. Provisional acceptance Human exposure to acrylonitrile in food as a result of its migration from food contact material should be reduced to the lowest levels which are technologically achievable. REFERENCES ABREU, M.F. & AHMED, A.E. (1980) Metabolism of acrylonitrile to cyanide. In vitro studies. Drug Metab. Dispos. 8: 376-9. AHMED, A.E. & PATEL, K. (1979) Pharmacokinetics, distribution and binding of 1-14C-acrylonitrile in rats. Phamacologist, 21(3): A 131 (Abstract). ANONYMOUS (1980a) A twenty-four month oral toxicity/carcinogenicity study of acrylonitrile administered by intubation to Spartan rats, Project No. 77-1746. Unpublished report by Bio/dynamics, Inc., East Millstone, N.J., submitted to WHO by Monsanto Co., St. Louis, Mo. 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See Also: Toxicological Abbreviations Acrylonitrile (EHC 28, 1983) Acrylonitrile (HSG 1, 1986) Acrylonitrile (ICSC) ACRYLONITRILE (JECFA Evaluation) Acrylonitrile (FAO Meeting Report PL/1965/10/2) Acrylonitrile (CICADS 39, 2002) Acrylonitrile (IARC Summary & Evaluation, Volume 71, 1999)