Document 6wYEnOrj7R65no80R0dvMaej9

Cancer Induction Following Single ai Multiple Exposures to a Constant Amount of Vinyl Chloride Monomer by Robert M. Hehir,* Bernard P. McNamara,1** Joseph McLaughlin, Jr.,* Donald A. Willigan,* George Bierbower* and Jerry F. Hardistyt Vinyl chloride monomer (VCM), already identified u a human animal carcinogen, was elected aa a model agent to explore an area of concern for lingle and intermittent low level exposure. In traditional cancer bioasay, animal* are repeatedly exposed over their lifespan to a dose of suspected chemical. In the current studies rats and mice were exposed in an inhalation chamber to single one-hour doses of VCM ranging from 50 to 50,000 ppm. A second group was given 10 one-hour exposures to 500 ppm or 100 one-hour exposures to 50 ppm of the same chemical. All animals were then observed for the remainder of their lives, generally 18-24 months. Moribund animals were euthanized, and survivors were sacrificed on schedule and their tissues examined for pathological changes. Specifically, the oncogenic study demonstrated dose related effects for single one-hour exposure of VCM at high levels, i.e., 5,000 and 50,000 ppm. These concentrations increased the incidence of pulmonary adenomas and carcinomas in mice. Repeated exposure of A/J mice to the same chemical at 500 ppm * 10 one-hour exposures also increased the incidence of pulmonary adenomas and carcinomas which are considered highly significant (p - 0.001) when compared to match controls. At the lower dose of 50 ppm x 100 one-hour exposure, no significant increase in tumors was observed. Rats exposed to identical concentrations of VCM failed to elicit a tumorigenic response. Introduction In the last decade there have been concerted efforts by industry and the Federal government to identify carcinogenic substances in the workplace. However, carcinogens are not limited to occupa tional exposures. Many of these same chemicals are also used in the formulation of household products. Therefore, consumers in all walks of life may be exposed to suspect chemicals in their homes without *U.S. Consumer Product Safety Commission, Westwood Tow ers Bailding, Room 738, 5401 West Blvd., Washington, D.C. 20207. tU.S. Army Chemical Systems Laboratories, Edgewood. Md. 21040. tDonald A. Willigan, Inc., Bound Brook, NJ. 08805. Deceased. their knowledge. This type of consumer usually brief and at very low levels. T chemical may be modified in the proce: facturing the consumer product, i.e., as of polymerization of vinyl chloride (VC nyl chloride) (PVC), or trace quanti unreacted monomer may be present in which may be leached out under norma of use. There are other situations when cal like VC is used because it is chemical example as a propellant, and as an gaseous chemical it could become a pote problem. While regulatory bodies try to est exposure levels and industry attempt.1 exposures in the production facilitie control measures would be of practical October 1981 625159 cancer bioassays involve daily exposures to the test chemical over the animal's lifetime. There were no comparable studies on short-term exposure to a carcinogen like VC followed by a lifetime monitor ing for toxicological symptoms with complete histopathological examination at death. Therefore, our approach was to explore what happens to laboratory animals following brief or intermittent exposure to a known carcinogen like VC. Vinyl chloride appeared to be the ideal chemical to use in these experiments because of its widespread use in industrial and consumer products. Furthermore, the relationship for inducing unique pathological lesions, i.e., angiosarcoma of the liver for high exposure levels in animal and man was already established by Viola et al. (1) Maltoni (2) and Creech et al. (.3). Quite apart from the need to establish a bench mark for acute short-term intermittent exposures to a carcinogen, such as vinyl chloride, was the question of "threshold effects" or "safety factor" for low level exposures. In setting up our experiments we were mindful of the many factors that could have an impact on the study design. Some of the more important factors are that (1) the substance may not reach a susceptible cell; (2) the substance may make noncarcinogenic biochemical combina tion with the cell; (3) the "initiated" lesion may not receive adequate "promotion"; (4) host factors may be unfavorable to carcinogenesis; (5) biochemical repair of the DNA lesion may occur; (6) morpholog ical regression of tumorigenic proliferation may occur; (7) carcinogenic cells may be destroyed by the body's immune system. These items need to be addressed in any conventional cancer bioassay but are even more critical in searching for noncarcinogenic exposure levels. Experimental Conditions Two strains of rats, Fischer 344 (Charles River Laboratory, Wilmington, Mass.) and SpragueDawley/Wistar (Chemical Systems Lab, Edgewood, Md.), and two strains of mice, A/J (Jackson Lab, Bar Harbor, Maine) and ICR (Charles River Labo ratory) were treated in single or multiple intermit tent inhalation exposures to VC. The chambers were Rochester type, stainless steel, 1000 liter, constructed to provide laminar air flow and insure uniform exposures to VC to test animals. Chamber concentrations were established by proportioning the amounts of VC being dispersed with the air flow through the chamber. Airflow 64 in the chamber at all times when 0] the exhaust gas completely filtere particulate filter) before discharge t ment. The concentration of gas in chamber was monitored by usinj Packard 5830A gas chromatograph flame ionization detector. Exposure Procedures for VC Cancer Studies Male and female rats and Fischer mice were totally exposed for 1 hr t( and 50,000 ppm VC. Fischer rats equally divided by sex received ten 1 to 500 ppm VC (1 hr/day, 5 days/wk i 100 1-hr exposures to 50 ppm (1 hr/c for 20 weeks). Male and female pari Dawley/Wistar) rats (obtained from V< ical Division, Edgewood Arsenal, I reproduction study were also maint served for 24 months post exposun ppm VC 1 hr per day, 5 days per wee (49 exposures). Following exposure, all animals wi until the chamber concentration w; ppm VC. Animals of the same sex wt in stainless steel cages with a maxim 5 rats in each compartment and place holding area. Mice were similarly treat cages were used and the number of partment was limited to two. The observed twice daily for general healt es, alertness, activity or mortalitj were weighed weekly for the first exposure and monthly thereafter, schedules for the studies described al in Tables 1-3. No blood chemistries studies were performed. Pathology Gross and Light Microscopy. A and microscropic examination was most control and exposed animals were sacrificed. Autolysis precluded tion in a few cases. All rodents were to be serially sac and 24 months post exposure. How span of the mice forced some change times of sacrifice and termination of ments. For single exposure the plan month sacrifice were replaced by 18 nv Environmental Health 625160 Species Fischer 344 rat ICR mouse Rat Mouse i>ex Dose, ppm AM M 50 3/4/75 500 3/11/75 5000 3/18/75 50000 3/25/75 F 50 500 5000 50000 M 50 3/4/75 500 3/11/75 5000 3/18/75 50000 3/25/75 F 50 500 5000 50000 M Neg/Cont. F Neg/Cont. M Neg/Cont. F Neg/Cont. PM 3/4/75 3/11/75 3/18/75 3/25/75 3/4/75 3/11/75 3/18/75 3/25/75 90 90 85 90 90 100 95 88 90 90 90 90 90 90 90 90 92 79 82 88 Table Z. Exposure schedule for animals exposed repeatedly to VC. Species Exposure periods. Sex Dose, ppm days Exposure dates From To Exposure group size t Start End St Fischer rat Mi mouse Fischer rat Mi mouse M 50 100 500 10 F 50 100 500 10 M 50 100 500 10 F 50 100 500 10 M Neg. 100(c)* Control KXc) F Neg. 100(c) Control 10(e) M Neg. KXXc) Control 10(c) F Neg. KXXc) Control 10(c) 8/27/75 7/7/75 8/27/75 7/7/75 7/7/75 8/27/75 7/7/75 8/27/75 -- -- -- -- -- -- -- 1/26/76 7/28/75 1/26/76 7/18/75 7/18/75 1/26/76 7/18/75 1/26/76 90 86 2 90 90 ) 90 87 2 90 90 1 90 87 1 90 90 90 88 1 90 90 50 50 2 50 50 ) 50 47 2 50 50 1 40 39 1 50 50 50 50 1 50 50 (c) denotes control for corresponding dose above. Table 3. VC multigeneration study, F parents.* Group I II III Compound Air VC VC Dose* Control Low dose (50 ppm) High dose (500 ppm) Number of males 25 25 25 Numbe Sprague-Dawley/Wstar rats. "Exposure to 50 or 500 PPM of VC 1 hr/day, 5 daya/week for 10 weeks (49 exposures) before mating. October 1981 625161 -1 -- -- -- - , . -? --- x4S&Siicr.Z----. in liLHJtr uie iliuu nice vs<u> at &\j iiiuuiua rauier than 24 months. The change was made in consider ation of the risk of animal loss through death and possible cannibalism. Tissues examined were lung, trachea, heart, liver, stomach, small intestines, spleen, kidney, bladder, bone marrow (sternum), adrenals, pancreas, duodenum, brain, eye, zymbal gland, ear, nose, muscle and bone (femur). Electron Microscopic Studies. Groups of five male and five female Fisher (344) rats from each of the single 1-hr exposure studies (50, 500, 5000 and 50,000 ppm) with equal numbers of their corres ponding control groups were sacrificed at 8, 16, 24 months. Groups of five male and five female Fischer (344) rats from the multiple 1-hr exposure studies at 50 and 500 ppm VC along with equal numbers of control animals were sacrificed at 16 and 24 months. Results Toxicity During Exposure Rats and mice exposed for 1 hr to concentrations of VC ranging from 50 to 50,000 ppm or for repeat ed exposures, i.e., 50 ppm or 500 ppm, produced no remarkable signs of toxicity with the exception of mice at the 50,000 ppm level. At 50,000 ppm VC 50% of the male mice exhibited hyperventilation at 45 minutes together with twitching and possible ataxia. Female mice became hyperactive after 40 min exposure, and respiratory difficulty and ataxia was observed in approximately 25% of the female mice after 55 min. Upon removal from the test atmosphere, all animals recovered to normal appearance within 24 hr. After exposure there were no consistent or dose-related differences between control and exposed (single or multiple) mice or rats in death rate, toxic signs or change in body weight. or repeatedly to VC at the higher dc 500, 5000 or 50,000 ppm. Histological Examination of Mice: Single Exposure Changes ascribable to vinyl chloric ent primarily in the lungs with th pulmonary adenomas and pneumoniti was evident in all animal groups w posed to VC at 500 ppm and above. The development of bronchio-alveincreased with exposure to higher VC. Tables 4 and 5 summarize the si) logical changes observed in ICR mi' months following single exposure to of VC. Mice were more susceptible than monitis following exposure to VC. T ever was not incremental with do incidence of pneumonitis, adenoma ; in ICR mice following single exposur in Table 6. No correlation was obse the incidence of pneumonitis and pneumonitis and carcinoma. However, more prone to the induction of pneun ularly at 50,000 ppm, i.e., 34% M \ 5000 ppm and below, male and femal equally sensitive. There was an increase in bronchic nomas with exposure to higher doses condition manifests itself more frequ< i.e., at 50,000 ppm: 51% M vs. 18% continued at the 5000 ppm: 22% M vs. and females were equally susceptibh 500 ppm and below. The upper res (nasal turbinates) and trachea reveal changes specifically attributable to \ Table 4. Histological examination of ICR mice at 8 and 18 months following a single (1-hr) exposure to vinyl chi Vinyl chloride concentration, ppm Histological changes attributable to vinyl chloride Induction of pulmonary adenomas Progression to car- 50,000* 6,000* 500* 50 0 (control) 45/137 (33.3%) 24/143 (16.8%) 18/139 (12.9%) 14/139(10.1%) 12/120 (10.0%) 3/137 (2.2%) 1/143 (0.7%) 1/139 (0.7%) 0/139 (0%) 0/120 (0%) 'Pneumonitis was evident in all animal groups which were exposed to VCM at doses of 500 ppm or more. 66 Environmental Health 625162 500 ppm, 10 days, 1 hr. Changes ascribable to VC were apparent in the lung only, primarily the induction of pulmonary adenomas. Bronchio-alveolar adenomas were induced in the test group with approximately equal frequency in males and females, i-e., 73.7% M vs. 75.6% F, respectively. The in crease in incidence as shown in Table 7 for the test group over that of the controls was substantial, by trots, p/w or 6.6'vo; ouu ppm, 22/lbt> oi animals scheduled for evaluation (sun monary adenomas were observed as months post exposure in 60% of males ai at 20 months, 75% of animals were affe< The incidence of pneumonitis, adenon cinoma in A/J mice following multiple e VC is presented in Table 8. Pneumoni' served more frequently in the control a Table 5. Overall summary: incidence of nonneoplastic changes and histologically proven neoplasms within the live* ICR Swiss mice exposed to vinyl chloride in tingle inhalation exposures. Tissue/response 0 M (62P F (77)* Incidence of response for various vinyl chloride concns 50.000 ppm 5.000 ppm 500 ppm M (74)* F (82)* M (76P F (82)* M (72)* F (75)* M (8 Liver (number evaluated) Hepatic cell necrosis 50 75 63 78 68 76 67 72 64 2 10 3 5 5 7 4 6 2 Hepatic cell vacuolation (lipidosis) 2 11 4 2 12 3 5 1 Hepatic cell hypertrophy 1 28 8 4 13 1 Hepatic cell hyperplasia 44 Angiectasia Sinusoidal reticulosis Hepatic cell adenoma Hepatic cell carcinoma Hemangioma 2 2 14 5 11 4 161 9 1 2 2 Hemangiosarcoma 1 ..ling (number evaluated) SO 70 61 76 65 78 66 73 71 Pneumonitis 1 6 21 10 13 17 19 15 4 Bronchio-alveolar adenoma 4 8 31 14 14 10 8 10 8 Bronchio-alveolar carcinoma 121 1 'Numbers in parentheses denote animals per group. Total includes animals from scheduled sacrificed (8 and montt spontaneous deaths. Table 6. Single inhalation exposure of ICR mice to vinyl chloride monomer. VcoCncenx* pTo>psmure Group Lung tissue: incidence of response/number evaluated' Pneumonitis Adenoms Card 0 (control) 50,000 5,000 500 50 Male Female Combined (M F) Male Female Combined (M + F) Male Female Combined (M + F) Male Female Combined (M + F) Male Female Combined (M + F) 1/50 (2**> 6/70 (9%) 7/120 (6%) 21*1 (34%) 10/76 (13%) 31/137 (23%) 13/65 (25%) 17/78 (22%) 30/143 (21%) 19*6 (29%) 15/73 (21%) 34/139 (24%) 4/71 (6%) 7*8 (10%) 11/139 (8%) 4/50 (8%) 8/70 (11%) 12/120 (10%) 31*1 (51%) 14/76 (18%) 45/137 (33%) 14*5 (22%) 10/78 (13%) 24/143 (17%) 8*6 (12%) 10/73 (14%) 18/139 (13%) 8/71 (11%) 6*8 (9%) 14/139 (10%) 0*0 0/70 0/120 1*1 2/76 3/137 1/65 0/78 1/143 0*6 1/73 1/139 0/71 0/68 0/139 Total includes animals from scheduled sacrifice (8. 16. 20 months period) and spontaneous deaths. October 1981 oat: tu tiiuoc uuaci vcu m me Millie exposing study. 50ppm, 100 days, 1 hr. Again changes attribut able to VC were apparent in the lung only, primari ly pulmonary adenomas. However, the incidence in the induction of adenomas and progression to carci noma are considered only marginal and not statisti cally significant. Comparatively, the potential for development of pulmonary adenomas as shown in Table 7 was great er in A/J mice following multiple exposures at 500 ppm than at 50 ppm, i.e., incidence at 500 ppm, 74.7%; at 50 ppm, 44.1%, despite an equivalent total dose of5000 ppm VC. Also, pulmonary adenomas were induced earliest (8 months) following multiple exposures at 500 ppm. It is also of interest that the Table 7. Histological examination of A/J mice at 8. 16 and 20 months following multiple (1-hr) exposures to vinyl chloride monomer. Number of exposures and concentration ofVCM Histological changes attributable to vinyl chloride monomer Induction of Progression pulmonary adenomas to carcinoma 0 (controls) 10 x 500 ppm* 0 (controls) 100 x 50 ppmb 31/90 (34.4%) 124/166 (74.7%) 29/84 (34.5%) 65/158 (44.1%) 3/90 (3.3%) 22/166 (13.3%) 2/84 (2.4%) 7/158 (4.4%) "Highly significant difference in the number of pulmonary adenomas (p-0.001) observed at the 500 ppm * 10 hr exposure level versus control by Z test. hNo significant difference for pulmonary adenomas Ip < 0.14) and carcinomas (p - 0.19) observed at the lower multiple exposure level. ppm. o4.4vc; at ou ppm, d^.o-ye. Table 9 provides an overall sumn dence of histologically proven neop in both strains of mice, i.e., ICR an< single and multiple exposures to Vt tic and nonneoplastic changes obser and/or lungs of A/J mice following sures to VC at 50 and 500 ppm are s 10 and 11. Although other neoplast plastic changes occurred variously i organs and tissues, the response s sporadically or was shared by all tes ing controls. Relationship by inciden to test exposure was not evident, morphologic deviations were not ui mally observed in aging A/J mice mi standard laboratory conditions. Electron Microscopic Result In general, these studies indicate to vinyl chloride increased organelle t as loss of volume control (bleb fori creased lysosomal activity in the live alterations progressively decreased a exposure increased. Hepatocellular carcinoma was se Fischer rat which had received 10 e. ppm. Lymphosarcoma was noted Fischer rat which had received a sin 500 ppm. Since these were indivi< since no cancers were seen at 5C lymphosarcoma and the hepatocell are not likely related to vinyl chlori Table 8. Multiple inhalation exposure of A/J mice to vinyl chloride monomer. VC Exposure Frequency concn, ppm Group Lung Ussue: incidence of response/number Pneumonitis Adenoma 10 x 1 10 x 1 100 x 1 100 x 1 0 Hale 0/43 (0%) 15/43 (35%) Female 2/47 (4%) 16/47 (34%) Combined (M + F) 2/90 (2%) 31/90 (34%) 500 Male 0/76 (0%) 56/76 (74%) Female 090 (0%) 68/90 (76%) Combined (M + F) 0/166 (0%) 124/166 (75%) 0 Hale 5/39 (13%) 11/39 (28%) Female 3/45 (7%) 18/45 (40%) Combined (M + F) 8/84 (10%) 29/84 (35%) 50 Male 4/77 (5%) 27/77 (35%) Female 5/81 (6%) 38/81 (47%) Combined (M + F) 9/158 (6%) 65/158 (41%) "Total includes animals from scheduled sacrifice (S, 16, 20 months period) end spontaneous deaths. 68 Environmental Healt 625164 XJJJS-'-i--*' " A. ' JJawley/ w istar) were divided into three groups with equal numbers of males and females. These specific-pathogen-free, random bred animals were obtained from the Animal Resources Branch at Edgewood Arsenal. The rats were 12 weeks old when initially exposed to VC. One hundred rats were exposed as described and the remaining 50 were carried as unexposed controls. The parental generations of S-DAV rats were maintained 24 months post exposure for carcinogenic evaluation. A complete gross and microscopic pathological examination of all tissues was performed on each control and exposed animal. Particular emphasis examined by electron microscopic techn Neoplastic and nonneoplastic lesions we: in approximately equal frequency in con parent generation of Sprague-DawleyA exposed to 50 ppm or 500 ppm of VC, 1 five days per week for 10 weeks (49 exj The only lesions that occurred in high' cy in the exposed animals than in contro eosinophilic cellular alterations presente areas. The appearance of these foci was the dosage of VC. The nature of these le. interest but as yet are controversial, inference can be drawn. Table 9. Summary of incidence of histologically proven neoplasms observed within tissues of mice at various inten single or multiple exposures to vinyl chloride monomer. Inhalation exposure Exposure concentration. ppm Number of neoplasms observed (scheduled sacrifice) 8 months 16 18 20 months months months Totals Single (1 hr) Multiple (1 hr) 50.000 5.000 500 50 0 (control) 500 x 10 0 (control) 50 x 100 0 (control) 5 3 1 0 0 12 0 4 1 24 18 29 16 14 22 2 16 5 70 38 63 27 29 21 30 16 14 104 40 83 33 MCR strain used in single (1 hr) exposure studies; and AAJ mice used in the multiple (1 hr) exposure studies. Table 10. Overall summary: incidence of nonneoplastic changes and histologically proven neoplasma within the mice exposed to vinyl chloride in multiple inhalation exposures. Tissue/response Incidence of response Control (0 ppm), 100 x 1 Vinyl chloride, 50 p( 100 x 1 M (39)* F (47)* M (81)* I Lung (number evaluated) 39 45 77 Edema 2 Congestion 41 1 Focal hemorrhage Pneumonitis 22 534 Bronchio-alveolar hyperplasia 3 Osseous metaplasia Bronchio-alveolar adenoma 11 18 27 Bronchio-alveolar carcinoma 2 3 Reticulum cell sarcoma 13 18 30 'Numbers in parentheses denote animals per group. Total includes animals from scheduled sacrifice (8, 16, 20 montl spontaneous deaths. October 1981 625165 ui iv iidu uccii ueoeiiueu u> i iti'iuus uivesuguturs like Maltoni (2,5) and Lee et al. (6) to coincide with dose and length of exposure implies that the total dosage (concentration x exposure time) may be an important factor in the carcinogenicity of VC. There fore, the inhaled dose was approximated by the Haber (7) concept. In its simplest form this concept states that the dosage, Ct is the product of C (concentration in miliigrams/cubic meters) and t (time in minutes). The total concentration can also be expressed in parts per million (ppm) and the approximation oi total inhaled dost useful, as is, for comparative purpos In his experiments Maltoni (5, 10 and mice as shown in Table 12 to a sei VC ranging from 50 to 10,000 ppm 1 days per week for 52 weeks. The res questionable carcinogenic effect at 5> dosage of 52,000 ppm-hr after 135 we er experiment (BT3), Sprague-Dawled in a similar fashion to BT1 but for: show after 86 weeks a negative ca Table 11. Overall summary: incidence of nonneoplaatic change! and histologically proven neoplasms within th of A/J mice exposed to vinyl chloride in multiple inhalation exposures. Tissue/response Incidence of response Control (0 ppm), 10 x 1 Vinyl chloride, 50 10 x 1 M (46P F (48)* M (78)* Liver (number evaluated) Hepatic cell necrosis Lymphoid cell infiltrate Hepatic cell lipidosis Neutrophil infiltrate Bile duct hyperplasia Granulomatous fod Sinusoidal reticulosis Hepatocyst Amyloidosis Angiectasia Hepatic cell adenoma Cholangiocarrinoma 45 48 46 1 2 2 1 1 78 6 1 2 1 1 _I 11 6 Lung (number evaluated) 43 47 Edema Pneumonitis 2 Bronchio-alveolar hyperplasia 2 1 Bronchio-alveolar adenoma 15 16 Bronchio-alveolar carcinoma _3 13 76 56 12 17 22 68 `Numbers in parentheses denote animals per group. Total includes animals from scheduled sacrifice (8, 16, 20 m spontaneous deaths. Test BT1 BT3 BT6 BT7 BT4 70 Table 12. Maltoni vinyl chloride atudlea.* Species Results (carcinogenesis), ppm-hr RATS RATS RATS RATS MICE Questionable at 52,000 Negative at 17,000 Questionable at 85,000 Poeitive at 170,000; 850,000; 2,000,000; 3,000,000 Positive at 24,600.000 Negative at 52,000 and 260,000 Questionable at 520,000 Poaitive at 2,600,000; 6,200,000; 10,400,000 Positive at 30,000; 150,000; 300,000; 600,000; 1,500,000 Environmental Health 625166 'Ullg mu -jmj)t%um.r^-l.T~ experiment BT7, Wistar rats treated with VC at doses ranging from 50 to 10,000 ppm, for 4 hr daily, 5 days/week for 52 weeks in the same manner as described above show positive carcinogenic affects at total dosage of 2,600,000 ppm-hr. The author suggests from comparison of the experimental data obtained with two different strains of rats (BT1/BT3), Sprague-Dawley and (BT7) Wistar, that the strain seems to be a factor in neoplastic response. Based upon neoplastic lesions observed, the Wistar strain was less responsive than Sprague-Dawley. Exper iment BT4 with Swiss mice, involving exposure to VC at 50 to 10,000 ppm, 4 hr per day, 5 days per week for 30 weeks produced carcinogenic effects with a total dosage Ct of 30,000 to 3,600,000 ppm-hr. In the studies of Viola, Bigotti and Caputo (1), tumors were seen in rats which had been exposed to 30,000 ppm VC, 4 hr/day, 5 days/week, for 12 months. The total dose (Cf) of VC was 28,800,000 ppm-hr. In the studies of Caputo, Viola and Bigotti (), rats and rabbits were exposed to VC for 4 hr/day, 5 days/week for 12 months at six dose levels. The exposure to 50 ppm VC or total dose of 48,000 ppm-hr produced no tumors. Carcinogenic effects were observed at total dosage of 320,000 ppm-hr and above for rats and at 7,800,000 ppm-hr for rabbits. Keplinger et al. (3) exposed rats, hamsters and mice to VC. Only the data on mice were sufficiently complete for examination of total dose effect. Total dosage of 56,000 ppm-hr and above produced tu mors in mice. The final report on the rats and hamsters is still unavailable for evaluation. Lee et al. (5) exposed mice and rats to three levels of VC: 50, 250 and 1000 ppm, 5 hr/day, 5 days/week for up to 12 months. All tests with a total dose of 48,000 ppm-hr and below were essentially carcinogenic effect in rats may not app< total dose (Cf) of VC exceeds 50,000 p single exposure study with ICR mice w at 50 and 500 ppm-hr, borderline at 5 but did produce neoplastic lesions in 50,000 ppm-hr. The A/J mice exposed doses of VC, i.e., 50 ppm x 100 days x ppm x 10 days x 1 hr for a total cumule VC of 5000 ppm-hr show a significant i response, but only at the higher dose ! In our studies Fischer rats expose* dosage of 50, 500, 5000, and 50,000 ppm showed no chemically induced tumor res ther did the Sprague-Dawley/Wstar rat exposed to 500 ppm VC 1 hr/ day, 5 da 10 weeks (total dosage 24,500 ppm-hr). Table 13 summarizes various investi results, including our own, on vinyl ch tests with ICR mice, single exposure ti an increased frequency of adenomas at t of 5000 ppm-hr and above. For A/J mic exposures to 50 and 500 ppm VC for a t of 5000 ppm-hr shows a similar dose re tern for adenomas. In general, in ter dosage Cf, carcinogenic effects are seer mice strains at Cf levels of 5000 to 50,C Thus total dosage for carcinogenicity it general agreement with Lee et aL (6) (78, and Maltoni (5) (between 30,000 and 150,< and other investigators. There is no doubt that risk is related exposure and hence total dose. In oui much attention has been focused on cancer associated with total dosage of \ er, the multiple exposure experiment at ppm dose levels with A/J mice for an total exposure to 5000 ppm-hr appears i with the thesis of total dosage. Indeed Authors Viola, Bigotti and Caputo (J) Caputo, Viola and Bigotti (8) Keplinger et al. (9) Lee (ff) Consumer Product Safety Commission (1979) Table 13. Other vinyl chloride studies. Species Results (carcinogenesis), ppm-hr Rats Rats Rabbits Mice (rats and hamsters) Mice ICR mice A/J mice Fischer rats Positive 2S.800.000 Negative at 48.000 Positive at 320,000; 1,280,000; 3,200.000; 6,400.000 Positive at 7.200,000 Positive at 6,000 All tests essentially negative below 78,000 and positive above 78,000 50 and 500, negative 5000. borderline positive 50,000 positive 50. 500, 5000 and 50,000, negative 24,500, eosinophilic lod, no cancers October 1981 625167 4 a ijAvUGJ'-'' basis ol a number ot factors, i.e., metabolism, de toxication, DNA repair or a time for tumor devel opment for low level exposure beyond the animals' lifespan. As is evident from Table 13, the two strains of rats, Fischer (344) and S-D/W, were more resistant to the adverse effects of single and multiple inter mittent exposures of VC. Our studies are in agreement as to the dose-time relationship for carcinogenesis related to the VC exposure. All of the continuous exposure studies considered collectively indicate that there is a life time total dose (CO for VC. However, from our own studies with single or intermittent low level expo sures to VC we believe that concentration may be the most dominant factor in whether or not carci nogenic effects are observed. For single dose stud ies with VC in ICR mice, neoplastic lesions were produced at 5000 ppm. For multiple intermittent exposures studies with A/J mice the critical concen tration for VC was 500 ppm, total dosage 5000 ppm-hr. Approximate carcinogenic Ct levels of VC based on data for mice and rats are Ct = 5,000-50,000 ppm-hr, carcinogenic tendencies; 500,000 Ct > 50,000 ppm-hr, definite carcinogenicity; Ct > 500,000 ppm-hr, high incidence of carcinogenicity. Considerations of Carcinogenicity of VC: Conclusions Cancer seems dependent on total dose of vinyl chloride, especially in life-time exposure studies, but for short-term exposure the concentration may be the most critical factor. There were apparent noncarcinoj. the study. Mice were more sensitive indicator carcinogenic effects of vinyl chloride. REFERENCES 1. Viola, P. L., Biogotti, A., and Caput response to rat skin, lungs and bones ( Cancer Res. 31: 516-622 (1971). 2. Maltoni, C. Communication sent to OSH/ the Proposed. Permanent Standards for O sure to Vinyl Chloride, Occupational S; Administration, U.S. Department of Lai D.C., 1974. 3. Creech, J. L., Jr., and Johnson, M. N. liver in the manufacture of polyvinyl ch Med. 16: 150.151 (1974). 4. National Cancer Institute. Guidelines for say in small rodents. NCI Carcinogenesis Series No. 1, NC1-CC-TR-1, U.S. DHEU 5. Maltoni, C. The value of predictive experii occupational and environmental cardnogpie: vinyl chloride. Ambio. 4: 18-23 (1975) 6. Lee. C. C., Bhandari, J. C,, Winston, J. I Dixon, R. L., and Wooda, J. S. Carom chloride and vinylidene chloride. J. Toxicol 4: 15-30 (1978). 7. Haber, F. Die Chemie im Kriege; Zur Gaskampes. In: Funf Vortrage aus den Julius Springer. Berlin; cited in Prentiss, < McGraw-Hill. New York, 1937. 8. Caputo. A., Viola, P. L., and Bigotti. A vinyl chloride at low concentrations in ra Int. Rea. Commun. 21: 1582 (1974). 9. Keplinger. M. L., Goode, J. W., Gor Calendra, J. C. Interim results of expos sters and mice to vinyl chloride. Ann. N. 219-224 (1975). 10. Maltoni, C.. and Lefemine, G. Carrino vinyl chloride. Ann. N.Y. Acad. Sci. 246: 72 Environmental Health 625168