Current Trends Update: Styrene, Dioxin, and 1,3-Butadiene in the Workplace

The National Institute for Occupational Safety and Health (NIOSH) periodically issues documents to transmit new information or to update existing information on specific chemical substances found in the workplace. Three such documents that were recently issued are summarized below. Each is available for distribution as indicated.

Styrene: In December 1983, NIOSH published Criteria for a Recommended Standard--Occupational Exposure to Styrene.* Styrene--also known as vinylbenzene or phenylethylene--is an aromatic organic compound with the chemical formula C((6))H((5))CH = CH((2)). It is a commercially important compound used in such products as reinforced plastics, packaging materials, insulation, pipes, automotive components, carpet backcoatings, synthetic rubber, and wall panels. In 1981, 6.6 million pounds of styrene were produced in the United States. NIOSH estimates that at least 30,000 U.S. workers in 1,000 plants are potentially exposed to styrene on a full-time basis, while more than 300,000 workers in over 20,000 facilities are potentially exposed to compounds containing styrene.

The current Occupational Safety and Health Administration (OSHA) standard for occupational exposure to styrene consists of a time-weighted average (TWA) concentration of 100 parts per million (ppm) for an 8-hour day, a ceiling concentration of 200 ppm, and a maximum peak of 600 ppm for no more than 5 minutes in any 3 hours. NIOSH now recommends that worker exposure to styrene not exceed 50 ppm as a TWA concentration for an up-to-10-hour workshift in a 40-hour workweek. This recommendation is based on effects on the central nervous system (CNS) observed among experimental subjects and workers exposed to styrene at TWA concentrations of about 100 ppm. A few investigators have also reported these effects at concentrations less than 100 ppm. The most frequently reported effects of exposure to styrene were subjective symptoms, such as fatique, dizziness, headache, nausea, poor memory, and drowsiness. These symptoms have been substantiated experimentally in human subjects and in clinical studies of workers who demonstrated slower reaction times and impaired balance following exposure to styrene. Abnormal electroencephalograms have also been noted. To prevent CNS depression and irritation of the eyes, nose, skin, and respiratory tract, NIOSH further recommends that exposures not exceed 100 ppm determined as a ceiling concentration by a 15-minute sample.

These limits for exposure to styrene are upper boundaries, and employers should make every effort to maintain exposure concentrations as low as possible. The criteria document presents specific recommendations for medical surveillance and recordkeeping, work practices, and engineering controls to prevent or greatly reduce the health risk to exposed workers. Although the evidence is not strong, exposure to styrene has been implicated in other adverse health effects, such as peripheral neuropathy, abnormal pulmonary function, liver toxicity, teratogenicity, and carcinogenicity. These health effects should be investigated further, and if they are related to styrene exposure, they will provide evidence for considering a reduction in the NIOSH-recommended standard for occupational exposure to styrene.

Order Document No. PB-84-148295 from the National Technical Information Service, Springfield, Virginia 22161. Cost: $22.00 paper, $4.50 microfiche.

Dioxin: On January 23, 1984, NIOSH released Current Intelligence Bulletin #40: 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD, "Dioxin").** TCDD occurs as a contaminant in such materials as 2,4,5-trichlorophenol (TCP), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2-(2,4,5-trichlorophenoxy) propionic acid (silvex). Occupational exposure may occur through contact with these materials or from past contamination of worksites. Currently, no occupational standard exists for exposure to TCDD.

NIOSH recommends that TCDD be regarded as a potential occupational carcinogen, that occupational exposure to TCDD be controlled to the fullest extent feasible, and that decontamination measures be used for TCDD-contaminated work environments. These recommendations are based on studies that demonstrate the carcinogenicity of TCDD in rats and mice. In other animal studies over a wide range of exposure concentrations, TCDD caused teratogenesis, immunologic dysfunction, and effects on hematologic function. Studies of humans exposed to TCDD-contaminated materials indicate that TCDD may be the cause of chloracne, metabolic disorders (porphyria), and other systemic problems and that TCDD may have a potential to cause cancer.

Copies are available without charge from NIOSH Publications, 4676 Columbia Parkway, Cincinnati, Ohio 45226.

1,3-Butadiene: On February 9, 1984, NIOSH released Current Intelligence Bulletin #41: 1,3-Butadiene. 1,3-butadiene is a colorless, noncorrosive, flammable gas. It is produced as a coproduct in the manufacture of ethylene and by dehydrogenation of n-butene and n-butane. In the United States, it is used mainly in the production of styrene-butadiene rubber and polybutadiene rubber for the tire industry. Other uses include copolymer latexes for carpet backing and paper coating, as well as resins and polymers for pipes and automobile and appliance parts. It is also used as an intermediate in the production of such chemicals as fungicides. NIOSH estimates that, currently, about 65,000 workers are potentially exposed to 1,3-butadiene. The present OSHA standard for occupational exposure is 1,000 ppm (2,200 mg/M((3))) determined as an 8-hour TWA concentration.

NIOSH recommends that 1,3-butadiene be regarded as a potential occupational carcinogen and teratogen and as a possible reproductive hazard. These recommendations are based on long-term animal studies that demonstrate carcinogenicity, teratogenicity, and adverse effects on the testes and ovaries. Although the excess risk of cancer to workers exposed to specific airborne concentrations of 1,3-butadiene has not yet been determined, the probability of developing cancer would be decreased by reducing exposure.

Appropriate engineering and work-practice controls should be used; producers and users of 1,3-butadiene should disseminate this information to their workers and customers; and professional and trade associations and unions should inform their members of the potential hazards of working with 1,3-butadiene. In addition, NIOSH recommends that the present OSHA standard for exposure to 1,3-butadiene be reexamined.

Copies are available without charge from NIOSH Publications, 4676 Columbia Parkway, Cincinnati, Ohio 45226. Reported by Div of Standards Development and Technology Transfer, National Institute for Occupational Safety and Health, CDC. *The development of criteria documents is a NIOSH responsibility mandated by the Occupational Safety and Health Act of 1970. These documents are used to recommend standards for promulgation by the Department of Labor. **NIOSH issues Current Intelligence Bulletins (CIB) to disseminate new scientific information about occupational hazards. A CIB may draw attention to a hazard previously unrecognized or may report new data suggesting that a known hazard is either more or less dangerous than was previously thought.

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