Document qmvLzGdKOzGvKOr1EQd6RY9DE

IRONMENT portance is ent of the onCHD." he effect' etate in a uced tin1 -one of a period' of the vn> I >f the 21 Si will* a yeao. O cted that he vin> I sure' *o 10 PI'"' ; as hid' ha'JU^ rds^P /.r Other Important and Widely Used Chemicals 805 physical examinations failed to reseal any chronic effects from long-term expo sures to vinyl acetate at the time-weight ed levels of from 5 to 10 ppm. No eye or upper respiratory irritation was noted below 10 ppm but were definite at 21 ppm. The present threshold limit value for vinyl acetate is 10 ppm. TOXICOLOGY OF VINYI PHI fMlPg The earliest studies on vinyl chloride were limited to acute exposures. These observations led to its consideration as a surgical anesthetic. About 20-25 years ago. during the earlier work exposures, the chief concern was to keep workroom atmospheric concentrations below the explosive limit (3Vi% or about 30,000 ppm); men commonly worked at expo sure levels of 3000 - 4000 ppm (near the narcosis level), and it was not at all un usual to have men leave the work place for relief and fresh air outside. Generally, these studies showed vinyl chloride to be low in acute toxicity , to be anesthetic in action and to have little capacity' to cause li'er injury from exposures of a few hours, Mastromateo et at.33 and Lester et a/*7 reported on acute exposures of ani mals and humans. They reported very lit tle effect until exposure concentrations approached 10,000 ppm, when humans reported dizziness after 5 minutes' expo sure. Torkelson et at.TM conducted animal studies to determine chronic toxicity to J'sessthe hazards to humans. Vinyl chlo ride was found to have a slight capacity to utise liver and kidney injury on repeated exposures. Male and female rats showed microyathologic changes after repeated -hour exposures at 500 ppm for 4,5 months. Repeated 7-hour exposures at -W ppm for 6 months resulted in microPJthologic changes in the livers of rabbits statistically significant increases in Ue average weight of the livers of male and female rats but no detectable changes in dogs and guinea pigs. Repeat ed 7-hour exposures at 100 ppm resulted in slight increases in the average weight of rat livers; the other species were not affected. All species studied tolerated repeated daily 7-hour exposures to 50 ppm for 6 months with no detectable in jury. Repeated daily 1-hour exposures at 200 and 100 ppm of vinyl chloride were with out effect; longer exposures caused a slight increase in liver weight. The standard for evaluating regular daily 7-8-hour exposures may be de fined as the concentration below which practically all analytic results must fall. The value of 100 ppm was suggested as the standard for vinyl chloride, with a time-weighted average for all exposures not to exceed 50 ppm (Torkelson, et at.TM). Lester et alV differed with the conclu sions of Torkelson et at.TM and recom mended 500 ppm as a time-weighted average exposure, Because of these conflicting reports, the TLV Committee of the ACGIH* in 1963 chose to change their TLV from 500 ppm as a maximal time-weighted average for industrial exposure to 500 ppm as a ceiling value. Harris and Adam80 studied workers engaged in the polymerization of vinyl chloride, reporting 2 cases in which auto clave cleaners in the vinyl chloride poly merization process were scraping the walls of the autoclave to remove the polyvinyl chloride with considerable hand/skin contact. Acroosteolysis was reported to have occurred in 2 workers. Of the 588 polyvinyl chloride workers in this plant, including 150 autoclave cleaners, 2 cases were identified based on x-rays of the hands of these workers. The terminal phalanges of the hands, the patella and the phalanges of the feet were involved. Two other workers, also autoclave cleaners, demonstrated early JUL 2 - 1SB4 806 Part Four: The Chemical Occupational Environment changes accompanied by Raynaud's phe nomenon. Wilson et alM studied 31 cases of occu pational acroosteolysis of the hands of workers engaged in vinyl chloride poly merization processes, and most of these had worked as cleaners of vessel walls and other equipment in the polymer process. The acroosteolysis was local ized to the distal phalanges of hands and frequently was associated with Raynaud symptoms. They reported the disorder to have resulted from a combination of phys ical insult, chemical insult and personal idiosyncrasy and were unable to name specific causes. Prevalence was reported to be less than 3% among employees per forming similar work, and no cases were found in workmen processing the poly mer or manufacturing commercial resins. More than 100 workers handled the fin ished resin; those who processed it into plastic products did not demonstrate findings of acroosteolysis. In 1970 and 1971, the Institute of Envi ronmental and Industrial Health at The University of Michigan'3 conducted a comprehensive study of acroosteolysis in workers producing and compounding vinyl and polyvinyl chloride. The epide miologic population represented more than 5000 workers in 32 plants. Thirtyone cases were discovered, of which 25 had a definite diagnosis; there were 16 suspicious diagnoses of acroosteolysis clearly associated with hand cleaning of the polymerizers. Dodson and co-workers'4 determined that work practices rather than any spe cific agent or combination of agents ap peared to relate to the occurrence of the disease. These investigators thought the disease to be of systemic rather than lo Flg. 31-2. --A worker entering a polyvinyl chloride reactor vessel to clean out caked polymer adhering to the inner surfaces. Dur ing the polymerization reaction, sludge from the slurry has a tendency to form a crust on the impeller mechanism as well as the tank inner surfaces. The caked polymer is periodi cally hand-chipped by workers inside the tank, and this is the operation that subjected workers to the highest concentrations of vinyl chloride. Current practice requires that flexi ble ducts be used for purging with clean air before the worker enters In addition, work ers in this operation must be provided with positive-pressure air-supplied respirators preferably the hood type. Demand-type respi rators have been used, but may not offer the same protection as the continuousflow type of hood respirator. (Courtesy of Maurice N, Johnson, M.D., B. F. Goodrich Company, Akron, Ohio. Photographer- H. Groskinski.) calized nature, but were unable to define the etioiogic agent or portal of entry, sug tion* revealed vinyl chloride concentra gesting some idiosyncratic "sensitization tions in the reactor before ventilation 1,1 of susceptibility." An industrial hygiene be about 3000 ppm. After aeration of d" survey of this epidemiologic investiga- containers, the vinyl chloride concendJ SL 071280 I Other Important and Widely Used Chemicals 807 H' -% Let Fig. 31-3.-The solid, caked polymer must be removed by chisels, hammers and hand picks, Neither workers nor management may be aware of the hazard involved when a spark is generated by steel on steel. It is not uncom mon to open a pocket ot the cake lining the vessel. The pocket may contain liquid vinyl chloride monomer. It is very possible that the lower explosive limit for vinyl chloride mo nomer (33,000 ppm) can be reached during the chipping with steel on steel. Reactor ves sels have exploded, leaving nothing but a crater in the ground where the plant once stood Reactor chipping or cleaning tools should be of the nonsparking type. To mini mize worker entry, some companies use highpressure water guns to remove the caked polymer These water guns may operate from WO to 13,000 pounds of pressure per square inch This in itself may produce a serious aiety hazard. Some attempts in the United Stales to remove the caked slurry have uti- ted closed solvent cleaning systems in "hich solvents such as tetrahydrofuran are j^ed To date, such solvent cleaning systems *ve been relatively unsuccessful. Recently ompleted production systems using 30,0008 on reactor vessels have been utilizing tion inside the reactors during scraping was found to be under 100 ppm and usually around 50 ppm. It was found that scraping released some unpolymer ized vinyl chloride so that levels of6001000 i>i>m were /ownrf close to the hands during these operations.* Other possible constituents of the scrapings of the reac tor vessels were thought to be polymer ized resins, unreacted catalysts, additives and, of course, the polymerized vinyl chloride. No serious disability had been reported in any of the above-mentioned cases but a few men had been partially disabled because of hand soreness, with some restriction in manual activity. With proper protective equipment and careful hygienic measures, all these cases are preventable. Vinyl chloride, although thought to be relatively nontoxic and even innocuous, typified by the 1973 threshold limit value of 500 ppm and known mainly as a narcotizing substance when inhaled in high concentrations, re cently has caused alarm in occupational health practitioners. Conjunctivitis, cor neal burns and dermatitis have been seen, and high concentrations and pro longed exposures cause headaches, dizzi ness and some irritation of the upper res piratory tract. With extreme exposures, narcosis may occur, and it has been appar ent from the acroosteolysis reports men tioned that preventive measures were undertaken lightly. *Onr italics, implying the potentially high worker respiratory inhalation. automatic high-pressure water cleaning guns and solvent systems to minimize or eliminate the need for worker entry into reactor ves sels. Older reactor vessels, which contain cooling vanes of heat exchangers, compli cate the cleaning process and high-pressure water guns and solvent systems cannot be used in these tanks. (Courtesy of Maurice N. Johnson, M.D., B F. Goodrich Company. Akron. Ohio Photographer-H. Grpskinski.) SL 071281 808 Part Four: The Chemical Occupational Environment Because of the report of acroosteolysis in humans, ViolaM attempted to produce the disease in animals. He exposed rats 4 hours per day, 5 days per week to 30,000 ppm (3%) vinyl chloride vapor. In his first report on the results of 12 months' exposure, he described metaplastic changes in the bones, which he consid ered similar to human acroosteolysis. He made no mention of having observed cancer in these animals until the Tenth International Cancer Congress in May, 1970. In the abstracts of this meeting, and subsequently in May, 1971, Viola et ti/.sl reported tumors of the skin, lungs and bones occurring first after 10 months' exposure, appearing to be the earliest and only publication in which carcino genic activity had been ascribed to vinyl chloride. Observing workers of a PVC-producing plant (Germany), Marsteller et al.3* found esophageal varicosities, splenomegaly and nonspecific liver damage. These observations, together with the abovementioned reports on "subclinical liver damage" initiated an investigation of the pathology of these changes. Radiologic, biochemical and enzymatic tests, liver scanning, laparoscopy and liv er needle biopsy were used in 20 workers (ages 30-56 years) of a PVC-producing plant; length of work exposure was 1V* -- 21 years. There was a total of 120 workers in volved in the production of PVC; 45 of them had been examined at the Depart ment of Dermatology, some because of manifest skin changes, but many were given a preventive examination. In most of these 45 workers, the examination re sulted in a clinical and/or biochemical suspicion of liver damage. Until May, 1973, it was possible to per form laparoscopy in 20 of these 45 work ers suspected of having liver damage. The prevalence of liver damage in work ers exposed m the PVC-producing plants could not be evaluated on this basis only In 13 ot 20 cases, the liver was found to be enlarged. Two patients had pain on abdominal palpation in the right upper quadrant; hyperlipidemia had been diug. nosed in 1967 (after 6 years ot exposure I in another patient, together with ' h\er damage." There was a history of jaundice in onh 1 patient in 1955, before the onset of ex posure; in 1968, a diagnosis of chronic liver dysfunction had been established There was no history of alcohol ism. Sple nomegaly was found in 7 of 20 cases (range 1.5-5 cm). Bilirubin (total) ex ceeded the upper normal limit of I mg/100 ml in 3 cases (range 1.1-1.7 mg/100 ml). The bromsulphalein test wax abnormal (5% after 45 minutes in 19 cases [range 6.1-21.5]). SGOT exceeded the upper normal limit of 12 mU/ml in 17 cases; in 14 cases, SGPT was elexated (range 15-30). An increased level of al kaline phosphatase was found in 2 pa tients (48 mU/ml). Hypothrombocythemia (less than 150 x Kf/mm1) was found in 19 of 20 patients, at least initially, in 12, the initial level was lower than 100 x lCP/mnF. Acroosteolysis was present in 4 patients. BSR, CBC, glycemia, uri nalysis, LDH, cholinesterase, acid phos phatase, iron and copper serum levels, proteinemia and electrophoretic separa tion of serum proteins, cholesterol, betalipoproteins, triglycerides and plasmatic coagulation factors were not found to be abnormal. In 3 cases, varicose esophageal veins (and in 2 cases also of the gastric fundus) were visualized. Laparoscopy showed the following changes: capsular fibrosis in 15 cases, reorganization of the liver architecture in 8 cases, splenomegaly in 7 cases, portal hypertension in 2 cases and hepatomega ly in 4 cases. The histologic changes encompassed the following: centrilobular collagen OTHE trausf 5 case 9 eas cases the P1 tal fil cases cases few : Th tolog of a 1 findii saint weig time plan livei sign the teol Ir pol> fied for Ker the gio: con the res jol see CO' mu sur wo Cr re wl It al p! ill in Ci P I >NMENT us only, ound to oain on t upper ;n diagposure) 1 "liver a in only et of ex chronic Wished, m. Sple0 cases tal) ex it of 1 LI-1.7 test was s in 19 cce ml levated el of aln 2 parocythers found iallv; in han 100 present nia, uriid plios1 levels, separaol, betalasmatic nd to be al vein' fundus' tllowinc 5 case-*, chire in i. porta! tomeca- Other Important and Widely Used Chemicals 809 transformation of the walls of sinusoids in 5 cases, focal activation of Kupffer cells in 9 cases, fatty infiltration (focal) in 14 cases, increased collagen deposition in the portal spaces and portal fibrosis, sep tal fibrosis or intralobular fibrosis in 17 cases, isolated cellular necrosis in a few cases and a low degree of cholestasis in a few instances. The biochemical changes and the his tologic abnormalities were, in most cases, of a low or moderate degree. The similar findings in many cases, all exposed to the same toxic environment, gave more weight to the above-mentioned observa tions. In workers at FVC-prodncing plants, thrombocytopenia, chronic toxic liver damage, with splenomegaly and signs of portal hypertension in some of the cases, are more frequent than acroos- feolysis. In January, 1974, a manufacturer of polyvinyl chloride and copolymers noti fied its employees, the National Institute for Occupational Safety and Health, the Kentucky State Department of Labor and the public that 3 workers had died of an giosarcoma of the liver. These cases had a common denominator --employment in the manufacture of polyvinyl chloride resins. This report by Creech and Johnson" has resulted in an enlarged 'cope of knowledge and eventually un covered a total of 14 known angiosarco mas connected with vinyl chloride expo sures, all within a few months, from other work places. Two case reports were described by Creech and Johnson. One of these was reported as: Patient One, a 36-year-old white male, was hospitalized January 5, 1970, becau se of tarry stools. Occupation al Hbtory: The patient had been em ployed from November, 1955, until his illness, except for two la;, offs of 9 months m 1958and 6 months in 1959, as a chemi cal helper and operator in the Louisville Plant of a chemical company in the manu facture of polyvinyl chloride resins. Pres ent Illness: At the time of admission, the patient had no complaints except passage of tarry stools. Past history was negative except for an operation for hemorrhoids 4 years earlier. Physical examination showed pallor and black stool on rectal examination. Liver and spleen were not palpable. Although an upper GI series was interpreted as normal, a tentative diagnosis of bleeding duodenal ulcer was made. On diet and medication, the patient had no recurrence of overt bleeding until May 1,1970, 4 months later, wdien he was readmitted for tarry stools. Again, he was found to have marked pallor and tarry stool on rectal examination. At this time, the liver was demonstrably enlarged and the spleen was palpable. Blood chemis try studies ("SMA/12") were not signifi cantly abnormal; total bilirubin, alkaline phosphatase. LDH and SCOT were only slightly elevated. GI series showed only anterior displacement of the stomach, but barium swallow suggested esophageal varices. Intravenous pyelogram was normal; barium enema was normal ex cept for displacement of the splenic flex ure by an enlarged spleen. Liver scan on May 4, 1970 was interpreted as being compatible with a large lesion in the left lobe of the liver, extending into the right lobe. The report of pathologic findings was "liver, biopsy of, angiosarcoma (malig nant hemangioendothelioma)." The pa tient succumbed to the liver tumor on September 27, 1971, 14 months postoperatively, despite cobalt therapy and interarterial infusions of 5 FU. The authors refer to Viola et al.,** who had reported in 1971 the oncogenic prop erties based on experimental use of mon omer vinyl chloride. Viola and co-work ers performed experiments with pure vinyl chloride on 3-month-old male (albino) rats exposed to vinyl chloride SL 071283 9 810 Part Four; The Chemical Occupational Environment vapors for 4 hours a day, 5 days a week for 12 months. The animals were kept in air tight cages in which a constant flow of air containing 3% (equal to 30,000 ppm) of vinyl chloride was passed through. They described the lesions found in the experi mental animals and demonstrated that almost all of the animals developed tu mors of the skin and lungs, skin tumors most frequently accounting for 65-70%. Maltoni** presented his results of un published experiments with vinyl chlo ride in February, 1974, at a U. S. Depart ment of Labor hearing in Washington, D, C. He has observed liver cancer in rats exposed 4 hours a day, 5 days a week to 250 ppm of vinyl chloride for up to 12 months. An investigation under the aus pices of the Manufacturing Chemists' Association43 reported the development of angiosarcoma in mice after 7 months of exposure to 50 ppm 7 hours a day, 5 days a week. Mancuso32 testified that although the focus now is on the experimental cancer- causing effect, it is very important to note that other pathologic changes occur in the brain (degeneration of the nerve cells --cerebellum), severe chronic hepa titis (as well as cirrhosis), interstitial pneumonia and damage to the kidneys. Further, the skin tumors frequently de veloped near the ear and submaxillary or the same areas as the salivary glands. It was postulated by the investigators that vinyl chloride may enter the salivary gland system. If this is confirmed subse quently, it will raise the question wheth er tumors of the parotid gland can also occur (as has been demonstrated in the rubber industry). (At this writing there have been 31 cases of angiosarcoma of the liver reported associated with vinyl chloride exposures.) Investigators ob serving and conducting epidemiologic studies of vinyl chloride monomer work ers must be aware of other unusual or unique pathologic findings, such as lar yngopharyngeal involvement. These cases have been noted in plants in differ ent locations in the United States and as yet have not been officially reported; however, they reinforce the need to cor relate pathologic changes in other organ systems with chronic work exposure. Analytic Methods Four methods are available for envi ronmental monitoring of air for the pres ence of vinyl chloride; combustion-con ductivity, gas chromatography, infrared spectrophotometry and flame ionization spectrophotometry. Gas chromatography is very specific but requires about 10 minutes per sample. Flame ionization detectors have no specificity --respond ing to all carbon-carbon or carbon-hydrogen bonds-but are portable and the measurement is instantaneous. Infrared analyzers are very specific, respond quickly and are portable. All these tech niques have adequate sensitivity, detect ing concentrations of 1 ppm or less. Worker monitoring is achieved through the use of absorption tubes filled with activated carbon, and the absorbed chlor inated hydrocarbons are determined by gas chromatography. Most environmental monitoring has been with combustion-conductivity ana lyzers. These analyzers are used for con tinuous monitoring with excellent re sults. NIOSH recommends the gas chro matographic method with known sensi tivity of 1 ppm. Medical and Hygienic Controls The National Institute for Occupation al Safety and Health33 published detailed medical and hygienic recommendations for the manufacture and processing of polymer from vinyl chloride on March 11,1974; "Consultants from industry who worked with NIOSH proposed that the SL 071284 SNT tiontiled :ions g of arch Other Important and Widely Used Chemicals 811 recommended standard contain the concept of an allowable `working level' for vinyl chloride gas in the atmosphere, which they identified as a time-weighted average of 50 ppm. They recommended that where workers were exposed to con centrations in excess of this level they should wear air-supplied respirators. This concept of an allowable `working level' might seem justifiable in that Pro fessor Maltoni1 found no liver tumors at 50 ppm, but there is the possibility that tumors might have been produced if a larger number of animals had been ex posed at that concentration. Based on theoretical considerations, there is proba bly no threshold for carcinogenesis al though it is possible that with very low concentrations, the latency period might be extended beyond the life expectancy. In view of these considerations and NIOSH's inability to describe a safe ex posure level as required in section 20(a) (3) of the Occupational Safety and Health Act, the concept of a threshold limit for vinyl chloride gas in the atmosphere was rejected. "Consequently, the recommendations are such that where any employee is ex posed to measurable concentrations of vinyl chloride, as determined by the rec ommended sampling and analytical method, he shall wear an air-supplied respirator. This recommendation is based on some preliminary information that the standard chemical cartridge respirators are inefficient in protecting against vinyl chloride. NIOSH is implementing a study to evaluate the degree of protection afforded by different types of respirators using vinyl chloride as the test gas. As information becomes available, it will be forwarded to OSHA as recommendations for alternative respirator usage. The em ployer is also required to develop a Con trol Plan to reduce airborne concentra tions of vinyl chloride to levels not de tectable by the recommended method." Similar recommendations have been made for other toxic substances by the ACGIH: "Recommendations for worker exposure by all routes should be reduced to a minimum in the light of the warning of the potency of the substances to in duce tumors in animals. `Reduced to a minimum' means extraordinary care shall be taken both in manufacture and in han dling so that worker exposure by all routes is kept below the limit of sensitivi ty of the analytic method of determining the exposure concentration."3 surve The following recommendations are directed primarily at medical screening to detect liver disease and/or hepatic tumor. They should be considered in the context of routine health screening for any general employee health problems, including nonhepatic health conditions potentially related to vinyl chloride monomer exposure. Routine health screening should include at the time of initial employment the recording of past medical history and the performance both of a general physical examination and certain basic laboratory procedures (e.g., complete blood count, urinalysis, chest x-ray); provisions should also be made for routine periodic health follow up examinations. Employees covered by the following specific recommendations shall encom pass all persons engaged in vinyl chlo ride monomer production and polymeri zation, including personnel peripherally involved, such as in clerical and manage ment assignments. The recommenda tions shall be applied both as a pre-em ployment requirement and as part of a periodic health follow-up. Screening pri ority should be given to current employ ees with prolonged and close potential exposure to vinyl chloride monomer, whether in present or past work settings. SL 071285 812 Part Four: The Chemical Occupational Environment 1. At the time of initial employment, or orF^nstitution of screening, a physical examination shall be performed with specific attention to detecting enlarge ment of liver or spleen by abdominal palpation. At the time of initial employment, or on institution of screening and annually thereafter, a medical history check list shall be completed by the employee. This list shall include questions concern ing alcohol intake: past history of hepati tis; past exposure to potential hepatotoxic agents, including dmgs and chemicals; past history of blood transfusions; and past history of hospitalizations. The com pleted medical check list shall be re viewed by a physician and should be act ed on as medically indicated for each in dividual employee. 3. At the time of initial employment, or on institution of screening, a serum spec imen shall be obtained for screening with respect to the following 5 biochemical determinations of liver function: total bil irubin, alkaline phosphatase, serum glu tamic oxaloacetic transaminase (SGOT), serum glutamic pyruvic transaminase (SGPT) and gamma glutamyl transpepti dase (GGTP, if test is available). Additional tests that may optionally be considered for use in screening include lactic dehydrogenase (LDH), serum pro tein determinations, serum protein elec trophoresis and platelet count. Labora tory analysis shall be performed in lab oratories accredited by the College of American Pathologists or licensed in ac cordance with the provisions of the Clini cal Laboratories Improvement Act of 1967. 4, If the results of laboratory screening are normal, screening shall be repeated on an annual basis. If the person being screened has been employed directly in vinyl chloride monomer production or polymerization for 10 years or longer, screening shall be repeated every 6 months. 5. If one or more liver function tests are abnormal, serum testing shall be re peated as soon as possible, preferably within 2-4 weeks. If no abnormalities are present on rescreening, testing should be repeated in 3 months. 6. If abnormalities persist on rescreen ing, the employee shall be removed from contact with vinyl chloride monomer operations and an individualized medical work-up shall be instituted. Suggested as initial steps in the medical work-up are a complete physical examination and vari ous special procedures, such as hepatitis B antigen determination and liver scan ning. If liver function abnormalities are de termined to be unrelated to liver disease (e.g., elevated alkaline phosphatase in a young, physically active man or elevated bilirubin in Gilbert's syndrome) or to be transient (e.g., due to recent hepatitis or recent alcohol intake), the employee may be permitted to return to vinyl chloriderelated employment, subject to individ ual medical evaluation. 1 In view of the preliminary results of animal toxicology studies, it is recom mended that no woman who is pregnant or who expects to become pregnant should be employed directly in vinyl chloride monomer operations. [See chapter 30, Lead, by Hernberg, on wom en of reproductive age who are exposed to toxic threshold limits.] In summary, these new regulations state that until exposures to vinyl chlo ride are reduced below detectable levels, employees entering any regulated area shall be provided with and required to wear and use a full-face supplied-air res pirator with a continuous flow or a pres sure-demand type. In addition, employ ees are to be provided with and required to wear clean full-body protective cloth ing and gloves prior to entering the regu lated area. At the Second International Sympo sium on Cancer Detection and Preven- SL 071286 * JMENT i tests be reerably mlities should creend from monier ledical sted as p are a td varipatitis r scan- are de disease Jn a Ited be ititis or ee may iloridemdivid- sults of recomregnant regnant n vinyl [See >n wornexposed ulations iyl chloe levels, (ed area uired to 1-air resr a presemployrequired ve cloth- r^regu- ympoPreven- Otheb Important and Widely Used Chemicals 813 tion, Maltoni* concluded his presenta tion on Occupational Carcinogenesis by stating, "We may diagnose some tumors quite early, but on the basis of 15 years' experience with periodic checks of work ers exposed to high risk, I doubt that peri odic medical examination has a real bear ing in saving people with occupational cancer although detected early, or in pro longing their life span. Thus, my position is in sharp contrast with those who claim to `protect' (!) workers exposed to carci nogenic risk with medical examinations. 1 do believe that the potentialities of medical examinations should be evaluat ed at an international level. In conclu sion, I would like to emphasize the need for a close collaboration among scientists, public health services, workers' unions and industries, to evaluate the risks and to devise preventive measures for avoid ing or minimizing occupational tumors." Grateful acknowledgment is given Dr. H. E. Christensen of the National Insti tute for Occupational Safety and Health for his review and suggestions in the preparation of this chapter. REFERENCES 1. American Conference of Governmental Industrial Hygienists: Proceedings of the 28th Annual Meeting, Pittsburgh, May, 1955. 2. American Conference of Governmental Industrial Hygienists: TLV for Chemical Substances and Physical Agents in the Workroom Environment with Intended Changes for 1963, Cincinnati, Ohio. 3. American Conference of Governmental Industrial Hygienists: TLV for Chemical Substances and Physical Agents in the Workroom Environment with Intended Changes for 1973, p. 41, Cincinnati, Ohio. 4. American Conference of Governmental Industrial Hygienists: TLV for Chemical Substances and Physical Agents in Work room Environment with Intended Changes for 1974, Cincinnati, Ohio. 5. Block, J. B.: Angiosarcoma of the liver fol lowing vinyl chloride exposures, JAMA 229:53,1974, 6. Bourne, H. G., Yee, H. T,, and Seferian, S.; The toxicity of rubber additives, Arch Environ. Health 16:700, 1968. 7. Brieger, H.: Chronic carbon disulfide poisoning, J.Occup. Med. 14.123,1972. 8. Calley, D., et at.: Toxicology of a series of phthalate esters, Chem. Abstr. 64:11749c, 1966. 9. Cook, W. A., et al.: Occupational acroos- teolysis. II. An industrial hygiene study, Arch. Environ. Health 22:74,1971. 10. Cornish, H. H,, Dambrauskas, T., and Beatty, L. D : Oral and inhalation toxicity of 2-N-dibutylaminoethanol, Am. Ind. Hyg, Assoc. J. 30:46,1969. 11. Creech, J. L., Jr., and Johnson, M. N.: Angiosarcoma of liver in the manufacture of polyvinyl chloride, J. Occup. Med 16: 150, 1974. 12. Deece, D. E., and Joyner, R. E.: Vinyl acetate --a study of chronic human expo sure, Am. Ind. Hyg. Assoc. J. 30,449, 1969. 13. Dmman, B. D., et ul.: Occupational acroosteolysis. I. An epidemiological study. Arch. Environ. Health 22:61,1971. 14. Dodson, V. N., et ul.: Occupational acroosteolysis. 111. A clinical study, Arch. Environ. Health 22.83,1971. 15. Eckardt, R. E., and Hindin, R.: The health hazards of plastics, J. Occup. Med. 15: 808,1973. 16. Fox, A. J., Lindars, D. C., and Owen, R.; A survey of occupational cancel in the rub ber and cablemaking industries: Results of a five year analysis 1967-1971, Br. J. Ind. Med. 31.140, 1974, 17. Gerarde, H. W.; Toxicology 6- Biochemis try ofAromatic Hydrocarbons (New York; Elsevier Publishing Company, 1960). 18. Goto, S., Hotta, R., and Suginioto, K,. An Aetiologic Factor Responsible for Retinal Microaneurysm due to Carbon Disulfide, Second International Symposium on Tox icology of Carbon Disulfide, Yugoslavia, Banja Koviljaca, May, 1971, pp, 25 - 28. 19. Hamilton, A.: Introduction to viscose ray on survey in Pennsylvania, Pennsylvania Department of Labor and Industry, Bulle tin No. 46, 1938. 20. Harris, D. K , and Adam, W. G. F.: Acroosteolysis occurring among men engaged in the polymerization of vinyl chloride, Br. Med. J. 3:712,1967. 21. Hemberg, S., Nurminen, M,, and Tolonen, M.: Excess mortality from coronary heart disease in viscose rayon workers exposed to carbon disulfide, Work-Environ.-Health 10.93,1973. SL 071287