CH2=CH-CH=Ch2
CH2=CH-CH=CH2
February 9, 1984
Current Intelligence Bulletins are prepared by the staff of the Division of Standards Development and Technology Transfer, NIOSH, (Robert A. Taft Laboratories, 4676 Columbia Parkway, Cincinnati, Ohio, 45226) and are distributed to representatives of organized labor, industry, public health agencies, academic institutions, and public interest groups as well as to those federal agencies, such as the Department of Labor, which have responsibilities for protecting the health of workers. It is our intention that anyone with the need to know should have ready access to the information contained in these documents; we welcome suggestions concerning their content, style, and distribution.
It is recommended that 1,3-butadiene be regarded as a potential occupational carcinogen, teratogen, and as a possible reproductive hazard. Consequently, appropriate engineering and work practice controls should be used to reduce worker exposure. These recommendations are based on long-term animal studies which demonstrated carcinogenicity, teratogenicity and adverse effects upon the testes and ovaries.
On the basis of this information, it is recommended that producers and users of 1,3-butadiene disseminate this information to their workers and customers and that professional and trade associations and unions inform their members of the potential hazards of working with 1,3-butadiene.
It is also recommended that the present Occupational Safety and Health Administration (OSHA) standard of 1,000 ppm for exposure to 1,3-butadiene be reexamined. The excess risk of cancer to workers exposed to specific airborne concentrations of 1,3-butadiene has not yet been determined, but the probability of developing cancer would be decreased by reducing exposure.
[signature] J. Donald Millar, M.D., D.T.P.H. (Lond.) Assistant Surgeon General Director, National Institute for Occupational Safety and Health Centers for Disease Control |
The offspring of pregnant rats exposed to 1,3-butadiene at 8,000 ppm had major skeletal defects. In addition, fetal toxicity was observed when pregnant dams were exposed at 200 ppm, 1,000 ppm, and 8,000 ppm.
Epidemiological studies of workers employed in facilities producing styrene-butadiene rubber indicated an increased, but not statistically significant, risk of mortality from neoplasms of the lymphatic and hematopoietic tissues and from leukemia.
Based on these data, the National Institute for Occupational Safety and Health (NIOSH) recommends that 1,3-butadiene be regarded as a potential occupational carcinogen and teratogen and as a possible reproductive hazard.
1,3-Butadiene is a colorless, noncorrosive, flammable gas. It is slightly soluble in water, more soluble in methanol and ethanol, and readily soluble in common organic solvents such as cyclohexane. Additional chemical and physical properties are listed in Table 1.
Chemical Identity: | 1,3-Butadiene |
CAS Registry No.: | 106-99-0 |
Synonyms: | Biethylene, bivinyl, butadiene, buta-1,3-diene, alpha-gamma-butadiene, divinyl, erythrene, NCI-C50602, pyrrolylene, vinylethylene |
Molecular Weight: | 54.10 |
Molecular Formula: | C4H6 |
Structural Formula: | CH 2:CHCH:CH 2 |
Boiling point | -4,41°C (at 760 mmHg) |
Freezing point: | -108.9°C |
Heat of vaporization, J/g (cal/g), 25°C | 389 (93) |
Explosive limits, vol % butadiene in air | lower - 2.0 upper - 11.5 |
Vapor pressure | 2 atm at 15.3°C
5 atm at 47.0°C |
Recognition (Odor) Threshold | 1.3 ppm |
Production, Use, and Potential for Occupational Exposure
In the United States (U.S.), approximately 78% (3,240 million pounds) of all 1,3-butadiene is produced as a coproduct in the manufacture of ethylene, and 22% (910 million pounds) is produced by dehydrogenation of n-butene and n-butane.4
Styrene-butadiene rubber (SBR) and polybutadiene rubber (BR) account for the two largest uses of 1,3-butadiene in the U.S., approximately 2,880 million pounds (primarily in the tire industry); polychloroprene (neoprene) rubber production ranks third, 320 million pounds. Other uses are in styrene-butadiene copolymer latexes used as carpet backing and paper coating materials; in acrylonitrile-butadiene-styrene (ABS) resins used to make high impact resistant pipes and parts for automobiles and appliances; and in the production of nitrile rubber, adiponitrile/hexamethylenediamine for nylon, polybutadiene polymers, thermoplastic elastomers, and methyl methacrylate-butadiene-styrene and nitrile resins. As an intermediate, 1,3-butadiene is used in the production of various chemicals such as 1,4-hexadiene, 1,5-cyclooctadiene, and fungicides such as tetrahydrophthalic anhydride.4 Approximately 65,000 workers (Table 2) are potentially exposed to 1,3-butadiene as estimated from data compiled from the National Institute for Occupational Safety and Health (NIOSH) National Occupational Hazard Survey (NOHS).5
SIC* Code | Description | Workers Potentially Exposed |
26 | Paper and allied products | 1,221 |
28 | Chemical and allied products | 44,980 |
29 | Petroleum and coal products | 84 |
30 | Rubber and plastics products, NEC | 9,086 |
33 | Primary metal industries | 55 |
34 | Fabricated metal products | 96 |
35 | Machinery, except electrical | 1,210 |
36 | Electrical equipment and supplies | 121 |
37 | Transportation equipment | 145 |
38 | Instruments and related products | 175 |
39 | Miscellaneous manufacturing industries | 2,244 |
73 | Miscellaneous business services | 5,339 |
80 | Medical and other health services | 493 |
Health Hazard Evaluation surveys conducted by NIOSH at six facilities indicated that exposures to 1,3-butadiene in those facilities were significantly below the OSHA standard of 1,000 ppm. The range of reported exposures was 0.06 ppm to 39 ppm. The types of facilities surveyed included those which manufactured helmets and visors, synthetic rubber, rubber tires and tubes, automotive weather stripping, braided hoses, and plastic components for aircraft.6-11
The ACGIH included 1,3-butadiene in their Notice of Intended Changes for the 1983-84 Threshold Limit Values, based upon reported animal carcinogenicity data. The Intended Change identified 1,3-butadiene as an industrial substance suspect of carcinogenic potential for man. No numerical TLV® was assigned.14
Acute -- Inhalation exposure studies with 1,3-butadiene have shown the lethal concentration for 50 percent (LC50) of the mice and rats tested to be 122,000 ppm and 129,000 ppm, respectively,15 an LC100 of 250,000 ppm was reported for rabbits exposed to 1,3-butadiene.16 Toxic effects of exposure in the animals progressed from light anesthesia, to running movements and tremors, to deep anesthesia and death.
Subchronic -- Except for moderately increased salivation at 4,000 and 8,000 ppm concentrations, exposure of rats on a daily basis for 3 months at 1,3-butadiene concentrations of 1,000, 2,000, 4,000, or 8,000 ppm produced no effects in the animals related to the exposures.16 Rats and guinea pigs exposed daily for 8 months at a 6,700 ppm concentration of 1,3-butadiene experienced a slightly reduced body-weight gain compared to controls. No significant effects were noted in animals exposed at concentrations of 600 or 2,300 ppm.17
Chronic -- In a chronic inhalation study, rats exposed for two years, 6 hours per day, 5 days per week at 1,3-butadiene concentrations of 1,000 or 8,000 ppm developed tumors at multiple sites. Occurrences of mammary fibroadenomas/carcinomas, thyroid follicular cell adenomas, and uterine stromal sarcomas in female rats exposed at both concentrations were statistically significant when compared with the controls. Male rats had significant increases in the incidence of testicular Leydig cell adenomas at 1,000 ppm and 8,000 ppm exposures and for pancreatic exocrine tumors at 8,000 ppm when compared with the controls.18
Mice exposed at 1,3-butadiene concentrations of 625 or 1,250 ppm, 6 hours per day, 5 days per week for 61 weeks developed cancer at multiple sites. A statistically significant increase of tumors in exposed male and female mice compared to the controls included hemangiosarcomas of the heart, malignant lymphomas, papillomas of, the stomach, and alveolar/bronchiolar adenomas and carcinomas of the lungs. Exposed female mice also had a statistically significant increase of granulomatous tumors of the ovary at exposures of 625 and 1,250 ppm and mammary gland carcinomas at a concentration of 1,250 ppm when compared with the controls. In addition, 1,3-butadiene was associated with the induction and early onset of non-neoplastic changes in both sexes of mice. These non-neoplastic changes included atrophy of the ovaries, testes, and nasal olfactory epithelium; hyperplasia and metaplasia of the respiratory epithelium; and liver necrosis.19
Teratogenicity and Reproductive Effects -- An inhalation study of pregnant Sprague-Dawley rats exposed at 200, 1,000, or 8,000 ppm of 1,3-butadiene for 6 hours per day on days 6-15 of gestation produced dose-related maternal and fetal toxicity when compared to an unexposed group of controls. Depressed body weight gain among dams was observed at all concentrations, and fetal growth was significantly retarded among rats exposed at the 8,000 ppm. Fetal deaths, though not statistically significant, were higher for all exposed groups, and at 8,000 ppm, a statistically significant increase in major skeletal abnormalities was recorded (skull, spine, sternum, long bones and ribs).20
Mutagenicity -- 1,3-Butadiene was not found to be a direct-acting mutagen, but in the presence of a liver microsomal activating system, it was transformed into mutagenic metabolites.21
Occupational exposure at 2,000, 4,000 or 8,000 ppm concentrations of 1,3-butadiene is reported to cause irritation of the skin, eyes, nose, and throat. Coughing, drowsiness, and fatigue have also been reported at higher, but not specified, exposure concentrations. These physiological responses dissipated upon removal of the workers from the area where 1,3-butadiene had accumulated.17,22,23 Dermatitis and frostbite may result from exposure to liquid and evaporating 1,3-butadiene.24
Epidemiology Studies
A retrospective cohort study was conducted at two SBR production facilities in the U.S. The combined cohorts consisted of 2,756 white males who had an average length of employment of approximately 10 years. No historical exposure data were available. Environmental sampling conducted at the time of the study characterized the most likely chemical exposures to be 1,3-butadiene, styrene, and benzene. Average exposure concentrations of 1,3-butadiene in the two facilities were 1.24 ppm (range, 0.11-4.17 ppm) and 13.5 ppm (range, 0.34-174 ppm). No statistically significant excesses in total or cause-specific mortality were observed for the total worker populations of either facility. However, a subgroup of workers from one cohort had a non-statistically significant excess mortality for cause-specific categories of the lymphatic and hematopoietic tissues.25
Eight facilities that produced SBR in the U.S. and Canada provided data for another retrospective study.26 The study covered a period of 36 years and included a total worker population of 13,920 black and white males. No significant excesses in cause-specific mortality were observed; however, some cancers (digestive system, kidney, lymph nodes, and larynx) occurred at a higher rate in white males compared with the general population, and the black male population had a non-statistically significant elevated risk of arteriosclerotic disease. The small number of workers in the cohorts from the 8 facilities studied and the relatively short latency periods of workers exposed inhibited the capability to identify statistically significant increases in risk of mortality or cause-specific disease. Also, environmental data were insufficient to characterize and quantify the workers' chemical exposures.
NIOSH also recommends that the present OSHA standard of 1,000 ppm TWA for 1,3-butadiene be reexamined based on the health effects in animals exposed at concentrations of 1,3-butadiene at or below the standard. In addition, the excess risk of cancer to workers exposed to specific airborne concentrations of 1,3-butadiene has not yet been determined but the probability of developing cancer would be decreased by reducing exposure. As prudent public health policy, employers should voluntarily assess the conditions under which workers may be exposed to 1,3-butadiene and to the fullest extent possible take all reasonable precautions to reduce exposure.
Guidelines recommended in the Appendix for minimizing worker exposure to 1,3-butadiene are general in nature and should be adapted to specific work situations as required.
Worker exposures should be estimated by 8-hour TWA and short-term (15-minute) exposures calculated from personal or breathing zone samples. Short-term samples should be taken during periods of maximum expected exposure by using all available knowledge of the work areas, procedures, and processes. Area and source measurements may be useful in identifying problem areas, processes, and operations.
A detailed analytical method for 1,3-butadiene is in the NIOSH Manual of Analytical Methods, Second Edition.30
There are four basic methods of limiting worker exposure to 1,3-butadiene, none of which is a simple industrial hygiene or management decision. Careful planning and thought should be used prior to implementation.
Product Substitution
Substitution, when feasible, of an alternative material with a lower potential health risk is an important method for reducing exposure. Extreme care must be used when selecting substitutes. Possible health effects from potential exposure to alternatives for 1,3-butadiene should be fully evaluated prior to selection.
Contaminant Controls
Airborne concentrations of 1,3-butadiene can be most effectively controlled at the source of contamination by enclosure of the operation and use of local exhaust ventilation. Guidelines for selected processes and operations can be found in NIOSH's Recommended Industrial Ventilation Guidelines.31 When a process or operation is being enclosed, a slight vacuum should be used to create negative pressure so that leakage will cause external air to flow into the enclosure and minimize contamination of the workplace. This can be accomplished with a well-designed local exhaust ventilation system that physically encloses the process as much as possible with sufficient capture velocity to keep the contaminant from entering the workplace atmosphere. The design of ventilation systems should take into account the reactive characteristics of 1,3-butadiene.
Ventilation equipment should be checked at least every three months to ensure adequate performance. System effectiveness should also be checked soon after any change in production, process, or control that might result in significant increases in airborne exposure to 1,3-butadiene.
Worker Isolation
If feasible, workers may be isolated from direct contact with the work environment by the use of automated equipment operated from a closed control booth or room. The control room should be maintained at a greater air pressure than that surrounding the process equipment so that air flows out of, rather than into, the room. This type of control will not protect workers who must perform process checks, adjustments, maintenance, assembly-line tasks, and related operations. Therefore, special precautions are often necessary to prevent or limit worker exposure in these situations and frequently involve the use of personal protective equipment.
Personal Protective Equipment Personal protective equipment, which may include goggles, gloves, coveralls, footwear, and respirators, should not be the only means of preventing or minimizing exposure during routine operations. Since 1,3-butadiene is a skin irritant and can produce frostbite, personal protective clothing and equipment should be selected that is appropriate for the potential exposures.
The use of respiratory protection requires that a respiratory protection program be instituted according to the requirements of 29 CFR 1910.13432 and that the respirators have been approved by the Mine Safety and Health Administration (MSHA) and by NIOSH. This program should include training on proper fit testing and use and procedures for respirator maintenance inspection, cleaning and evaluation.
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