Current Intelligence Bulletin 7: Polychlorinated (PCBs)

R. J. William Lloyd, Sc.D.; Roscoe M. Moore, Jr., D.V.M.;
Barbara S. Woolf, M.S.; and Harvey P. Stein, Ph.D.

Reports of adverse health effects in humans and the demonstration of carcinogenic effects in certain animal species have led to the reexamination of the distribution of polychlorinated biphenyls (PCBs) in the environment and the potential health effects of human exposure.

Because the industrial environment represents the major source of potentially high exposures to PCBs, the National Institute for Occupational Safety and Health (NIOSH) has gathered pertinent information on the manufacture, uses, and reported deleterious effects of polychlorinated biphenyls and is advising the occupational health community of these hazards.

Background

Polychlorinated biphenyls (PCBs) describe a group, of synthetic chlorinated organic compounds having the following structure:

where each of the ten Z’s can represent either a hydrogen or a chlorine atom. There are 209 different chlorinated biphenyls and they are collectively referred to as PCBs although many are not actually polychlorinated. Approximately half of these compounds have been synthesized and characterized.

Mixtures of polychlorinated biphenyls are important industrial products. The most common tradenames for these mixtures are Aroclor,^* Inerteen,^** Kanechlor,^*** and Pyranol.^† known tradenames for PCB-containing products are listed in Table 1. PCB-containing dielectrics (electrical insulators) are generally referred to as “askarels” in the electrical industry.

Table 1. — Tradenames for Known PCB Containing Products.

Table 1 Note:
* Therminol products now formulated in the U.S. do not contain PCBs. [return to table]

Mixtures of polychlorinated biphenyls are very resistant to degradation, are thermally stable, and resistant to oxidation, acids, bases, and other chemical agents. They are soluble in most of the common organic solvents and lipids, but only slightly soluble in water, glycerol, and glycols. PCBs are good electrical insulators. Although most individual polychlorinated bipheynyls are solids at room temperatures, the mixtures vary in consistency from mobile oils to viscous liquids or sticky resins.

PCBs are generally prepared industrially by the chlorination of biphenyl with anhydrous chlorine in the presence of iron filings or a ferric chloride catalyst. Trace quantities of chlorinated naphthalenes and chlorinated dibenzofurans have been reported in some commercial samples of PCBs and it has been suggested that the presence of these impurities may be of toxicological significance.^1-3

Commercial PCBs are generally mixtures of many different chlorinated biphenyls, as shown in Table 2, manufactured to meet operational specifications (such as dielectric constant, flash point, fire point, density, percent chlorine, and color); these commercial mixtures may vary chemically from batch to batch.

Table 2. – Description of PCB Mixtures.

Table 2 Notes: It must be emphasized that these are approximate compositions of the PCB mixtures and that a particular product may vary in chemical composition from batch to batch.

* Weight-weight percent. None detected = less than 0.01%. Source of component compositions: Monsanto Company, quoted in Hutzinger, O., et al., op. cit., p. 23 [return to table]

† Percent. Source of component compositions: , A., PCB Newsletter, No. 3, July 1971, quoted in Hutzinger, O., et al., op. cit., p. 23 [return to table]

‡ Percent. Source of component compositions: , N., et al., op. cit., p. 1637 [return to table]

PCBs have found wide use in industry and have been manufactured in the United States since 1929. The major domestic manufacturer, Monsanto Company, produces PCBs at Sauget, Illinois and reports manufacturing 40 million pounds of PCBs in the United States during 1974 (down from 85 million pounds in 1970).⁴ Monsanto’s domestic production and sales of PCBs by grade and category from 1957 through the first quarter of 1975 are shown in Table 3.

Table 3 — PCB Manufacture and Sales Monsanto Industrial Chemicals Company
1965 Through 1975
(Thousands of Pounds)

* Used Primarily in capacitors[return to table]
** Used Primarily in transformers[return to table]

(1) Production figures and Plasticizer Applications figures unavailable during year indicated.[return to table]
(2) U.S. Export Sales figures unavailable during year indicated.[return to table] Source: Monsanto Industrial Chemicals Company, St. Louis, Missouri, September, 1975.

Uses

PCBs are employed in capacitors and transformers because they combine: dielectric properties with chemical stability and fire resistance. Approximately twice as many pounds of PCBs are used in the manufacture of capacitors as in the manufacture of transformers.

Prior to the environmental concern surrounding the persistence and ubiquitousness of PCBs,⁵ they were more widely used in industry as fluids for heat transfer systems, hydraulic systems, gas turbines, and vacuum pumps, as fire retardants, and as plasticizers in adhesives, textiles, surface coatings, sealants, printing, and carbonless copy paper.

Beginning in 1971, Monsanto voluntarily restricted its domestic sales of PCBs to closed system dielectric applications in capacitors and transformers.⁶ current domestic applications of PCBs include use in investment casting processes, as heat exchange fluids, and as hydraulic fluids. Imports of PCBs have been estimated to exceed 375,000 pounds for 1974. Reclaimed PCBs also are reported to be available.⁷

More than 95% of all power capacitors contain PCBs. Among their applications are use on electric utility lines, in air conditioners, and in the ballast of fluorescent lamp fixtures. PCBs are employed for safety, reliability, and long life, as well as to achieve size compatibility with equipment and instalation requirements. However, non-PCB power capacitors are being manufactured (e.g., General Electric’s Econol line and Sprague’s Eccol line) which may serve as alternatives.^{8, ‡}

PCBs are employed in transformers at locations where their proximity to people and/or property demand a fire resistant dielectric. Approximately 5% of transformers are PCB filled and each of the transformers so filled contains between 40 and 500 gallons of PCBs (about 235 gallons is average). Possible alternatives to PCB filled transformers may include dry transformers (which are larger) as well as transformers filled with silicone fluids or other materials under evaluation. ^8,9

Chlorinated terphenyls, as well as PCBs, are used in some formulations of wax for investment casting processes.⁸ The chemical structure of chlorinated terphenyls resembles that of PCBs. Chlorinated terphenyls have been reported to have toxicological effects similar to those of PCBs.¹⁰

Approximately 330,000 pounds of chlorinated terphenyls were imported into the United States during 1974¹¹ and 125,532 pounds during 1973.¹²

Toxicity

PCBs are poorly metabolized and tend to accumulate in animal tissues, including humans.^13-17 The accumulation particularly in tissues and organs rich in lipids, appears to be higher in the case of penta and more highly chlorinated biphenyls. ¹⁸

Studies have revealed PCBs in human fat tissue and blood plasma. PCBs, in amounts greater than 2 parts per million, were reported in 198 of 637 (31%) samples of human fat tissue taken from the general population of 18 states and the District of Columbia.¹⁴ residues ranging up to 29 parts per billion have also been found in 43% of 616 plasma samples collected from volunteers in a southeastern U.S. county.¹⁵

Human

The known toxic effects of PCBs in humans include an acnelike skin eruption (chloracne), pigmentation of the skin and nails, excessive eye discharge, swelling of eyelids, and distinctive hair follicles.¹⁹

For a number of years, chloracne of the face and neck has been reported among workers exposed to chlorinated hydrocarbons. Workers exposed to PCBs in the process of insulating cables,²⁰ in the production of condensers²¹ and in the manufacture of chlorobiphenyls²² have reported these skin lesions along with systemic effects such as digestive disturbances, edema of the face and hands, burning of the eyes, impotence, and hematuria. ^16,22

The toxic effects of PCBs in humans are further illustrated by a 1968 outbreak of poisoning in Japan that involved over 1,000 people who ingested PCB contaminated rice bran oil for a period of several months. The contamination of the oil (estimated 1,500 to 2,000 ppm) occurred when heat transfer pipes immersed in the oil during processing developed pin-sized holes. The clinical aspects of the poisoning included chloracne, brown pigmentation of the skin and nails, distictive hair follicles, increased eye discharge, swelling of eyelids, transient visual disturbance, and systemic gastrointestinal symptoms with jaundice.¹⁹ In some patients, symptoms persisted three years after PCB exposure was discontinued. Infants born to poisoned mothers had decreased birth weights, and showed skin discoloration due to PCB placental passage. Two stillbirths to PCB exposed women were also reported. ²³

Animal

The toxic effects of PCBs in animals have been studied extensively. Reports of malignant, nonmalignant, and reproductive effects are shown in Tables 4, 5, and 6

Table 4. – Malignant Pathologic Effects Induced by PCBs in Animals.

Table 5. – Nonmalignant Pathologic Effects Induced by PCBs in Animals.

Table 6. – Reproductive Effects of PCBs in Animals.

Occupational Exposure

It is estimated that 12,000 people are occupationally exposed to polychlorinated biphenyls. The majority of these exposures are in capacitor production and in investment casting processes.

Permissible Occupational Exposure

The current Occupational Safety and Health Administration, Department of Labor standards for chlorinated biphenyls are 1 mg/cubic meter for 42% chlorine mixtures and .5 mg/cubic meter for 54% chlorine mixtures. These are based on the Threshold Limit Values (TLV) established by the American Conference of Governmental Industrial Hygienists.³⁵

August 20, 1976

Dear Colleague:

In a June 24, 1976 letter, Mobil Oil Corporation advised the National Institute for Occupational Safety and Health (NIOSH) of a possible association between occupational exposure to polychlorinated biphenyls (PCBs) and cancer in humans. Mobil Oil reported preliminary results of an epidemiologic analysis based on medical records of employees exposed to PCBs at their Paulsboro, New Jersey plant. This study was conducted by Professor Anita K. Bahn (School of Medicine, University of Pennsylvania) and is being reported by Dr. Bahn in a letter to the editor of the New England Journal of Medicine, August 19, 1976.

The study included two cohorts of Mobil employees who were reported to have had varying exposure to Aroclor 1254 (a mixture of PCBs). The cohort of research and development employees was exposed to PCBs between 1949 and 1957 and the cohort of refinery plant employees between 1953 and 1958. The extent of exposure of these workers to other chemicals is not known. The cancer incidence among these workers for the period 1957 through 1975 was determined using Mobil medical records. Because medical records for 37 employees were incomplete, these workers were excluded from this analysis.

Among the 92 workers in these two cohorts for whom adequate medical records were available, eight cancers (in seven workers) were observed between 1957 and 1975. Of these eight cancers, three were malignant melanoma and two were cancer of the pancreas. This is significantly more skin cancer (melanoma) and pancreatic cancer than would be expected in a population of this size (based on the Third National Cancer Survey). The remaining cancers were found at three other sites in two employees; sarcoma of the right thigh and multiple myeloma in one employee, and recto-sigmoid cancer in the other.

NIOSH is unaware of any other published animal or human data which suggest a correlation between exposure to PCBs and skin (melanoma) or pancreatic cancer. However, hepatomas (mice, Aroclor 1254) and hepatocellular carcinomas (mice, Kanechlor 500; rats, Aroclor 1260) have been reported in PCB feeding studies of laboratory animals.

Background information on PCBs has been summarized in the NIOSH Current Intelligence Bulletin on Polychlorinated Biphenyls issued to the occupational health community on November 3, 1975, and subsequently published in the Journal of Occupational Medicine, Volume 18, pages 109-113, February 1976. Since the NIOSH Bulletin was first issued, a number of large firms have introduced products (e.g., butylated monochlorodiphenyl oxide and dimethyl siloxane polymer) claimed to be fire resistant dielectrics which can serve as alternatives to PCBs. In addition, one of the large domestic transformer manufacturers announced that it will cease using PCBs as fire resistant transformer fluids at the end of this year. NIOSH would like to stress that alternatives for PCBs should be thoroughly studied to assess the consequences they may pose to human health.

To aid in evaluating PCBs as a potential occupational health problem, NIOSH would welcome receiving reports of studies regarding the possible association between exposure to PCBs and human cancer.

Your cooperation in this matter is appreciated.

Sincerely yours,
[signature]
John F. Finklea, M.D.
Director

Notes

* Aroclor is a registered trademark of the Monsanto Company. [return to text]

** Inerteen is a registered trademark of the Westinghouse electric Corporation for its brand of PCB containing dielectric fluids. [return to text]

*** Kanechlor is a registered trademark of the Kanegafuchi Chemical Industry Company, Ltd. [return to text]

† Pyranol is a registered trademark of the General Electric Company for its brand of PCB containing dielectric fluids. [return to text]

‡ In December, 1975, The Dow Chemical Company and McGraw Edison Company announced the development of a substitute for PCBs in high voltage capacitors, butylated monochlorodiphenyl oxide. [return to text]

References

1. Hutzinger 0, Safe S, and Zitko V: Chemistry of PCB’s, CRC Press, Cleveland, Ohio, p. 22, 1974.
2. Bowes GW, Mulvihill MJ, Simoneit BRT et al: of chlorinated dibenzofurans in American polychlorinated biphenyls, Nature 256:305, 1975.
3. Curley A, Burse VW, Jennings RW, et al: of Tetrachlorodibenzofuran (TCDF) in Aroclor 1254 and the Urine of Rats Following Dietary Exposure to Aroclor 1254, Bull Environ Contam and Toxicol 14:153-58, 1975.
4. Communication from Monsanto Industrial Chemicals Company, St. Louis, Missouri, September, 1975.
5. Interagency Task Force on PCBs: and the Environment, COM-72-10419, Washington, DC, March 20, 1972.
6. Polychlorinated Biphenyls: Company’s Program of Restricted Sales and Controlled Manufacturing Practices, Monsanto Industrial Chemicals Company, St. Louis, Missouri, October, 1974.
7. Glenn Schweitzer, Office of Toxic Substances, U.S. Environmental Protection Agency, testimony at an August, 1975, Wisconsin hearing, quoted in Toxic Materials News, p. 139, September 15, 1975.
8. Personal communications with representatives of the industry, October 1975.
9. Dow Corning Dielectric Liquids for Power Transformers, Dow Corning Corporation, Midland, Michigan, received September, 1975 (booklet not dated).
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11. Telephone conversation with a representative of the U.S. International Trade Commission, Washington, DC, September, 1975.
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