Current Intelligence Bulletin 7: Polychlorinated (PCBs)


November 3, 1975
DHHS (NIOSH) Publication Number 78-127

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.


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

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.

Tradenames for Known PCB Containing Products
Tradename Tradename Owner
Aroclor Monsanto Company
St. Louis, MO
Chlorextol Allis-Chalmers
Milwaukee, WI
Clophen Farbenfabricken Bayer GmbH
Dykanol Federal Pacific Electric Co.
Newark, NJ
Fenclor Caffaro S.P.A.
Inerteen Westinghouse Electric Corp.
Pittsburgh, PA
Kanechlor Kanegafuchi Chemical Industry Co., Ltd.
Noflamol Wagner Electric Corporation
Newark, NJ
Phenoclor Prodelec
Pyralene Prodelec
Pyranol General Electric Co.
Schenectady, NY
Santotherm Mitsubishi-Monsanto
Therminol* Monsanto Co.
St. Louis, MO

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.

Description of PCB Mixtures
Approximate Chlorine
21% 42% 42% 54% 60% 42% 48% 53
11 <0.1 <0.1 <0.1
51 1 1 <0.1
32 20 16 0.5 17 3
4 57 49 1 60 33 5
2 21 25 21 23 44 27
<0.5 1 8 48 12 0.6 16 55
<0.1 1 23 38 5 13
<0.1 6 41

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)

PCB Manufacture and Sales Monsanto Industrial Chemicals Company 1965 Through 1975
1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 (1st quarter) 1975
U.S. Production 60480 65849 75309 82854 76389 85054 34994 38600 42178 40466 8532
Domestic Sales 51796 59078 62466 65116 67194 73061 34301 26408 37742 34406 7986
U.S. Export Sales 4234 6852 8124 11231 10624 13651 6388 8346 5395 1538
Domestic Sales by Category
Heat Transfer 1237 1766 2262 2529 3050 3958 3060 752
Hydraulics/Lubricants 4616 4258 4643 5765 8039 7403 1552 0
Misc. Industrial 1841 1779 1426 1283 1079 1627 1155 0
Transformer 8657 8910 11071 11585 12105 13828 11134 >25656 37742 34406 7986
Capacitor 23749 28884 29703 29550 25022 26708 14141
Plasticizer Applications 11696 13481 13361 14404 16460 19537 3259 0
Petroleum Additives 1439 0
Domestic Sales by PCB Grade
Aroclor 1221 369 528 442 136 507 1476 2215 171 35 57 10
Aroclor 1232 7 16 25 90 273 260 171 0 0 0 0
Aroclor 1242 31533 39557 43055 44853 45491 48588 21981 728 6200 6207 2201
Aroclor 1248 5565 5015 4704 4894 5650 4073 213 807 0 0 0
Aroclor 1254 7737 7035 6696 8891 9822 12421 4661 3495 7979 6185 2115
Aroclor 1260 5831 5875 6417 5252 4439 4890 1725 305 0 0 0
Aroclor 1262 558 768 840 720 712 1023 1 0 0 0 0
Aroclor 1268 196 284 287 280 300 330 0 0 0 0 0
Aroclor 1016 0 0 0 0 0 0 3334 20902 23531 21955 3660

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

1957 Through 1964
1957 Through 1964
1957 1958 1959 1960 1961 1962 1963 1964
U.S. Production (1) (1) (1) 37919 36515 38353 44734 50833
Domestic Sales 32299 26061 31310 35214 37538 38043 38132 44869
U.S. Export Sales (2) (2) (2) (2) (2) (2) 3647 4096
Domestic Sales by Category
Heat Transfer 157 582 929
Hydraulics/Lubricants 1612 1549 2685 2523 4110 3915 3945 4374
Miscellaneous Industrial 704 755 1569 1559 2114 1681 1528 1692
Transformer 12955 5719 5984 7921 6281 7984 7290 7997
Capacitor 17028 14099 16499 16967 15935 15382 15606 19540
Plasticizer Applications (1) 3939 4573 6244 9098 8924 9181 10337
Petroleum Aditives
Domestic Sales by PCB Grade
Aroclor 1221 23 16 254 103 94 140 361 596
Aroclor 1232 196 113 240 155 241 224 13 13
Aroclor 1242 18222 10444 13598 18196 19827 20654 18510 23571
Aroclor 1248 1779 2559 3384 2827 4023 3463 5013 5238
Aroclor 1254 4461 6691 6754 6088 6294 6325 5911 6280
Aroclor 1260 7587 5982 6619 7330 6540 6595 7626 8535
Aroclor 1262 31 184 359 326 361 432 414 446
Aroclor 1268 72 102 189 158 210 284 190
Aroclor 1016

(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.


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


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


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


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.

Malignant Pathologic Effects Induced by PCBs in Animals
PCB Mixture Treatment Animal Effects
Kanechlor 50024
Kanechlor 400
Kanechlor 300
500 ppm, 250 ppm
and 100 ppm in
diet for 32 weeks
Mice Liver weight increased with percent
chlorine and dosage Kanechlor 400 and 500 produced liver cell hypertrophy. 500 ppm of Kanechlor 500 produced hyperplastic noduels in 7 of 12 mice and hepatocellular carcinomas in 5 of 12 mice No nodules or carcinomas in controls
Aroclor 125425 300 ppm in diet
for 6 & 11 months
Mice Increased liver weight. Adenofibrosis in all mice fed for 11 months. Nine of 22 mice fed for 11 months had hepatomas. One of 24 mice fed for 6 months had a hepatoma. No hepatomas in control mice.
Aroclor 126026 100 ppm in diet
for 21 months
Rats Hepatocellular alteration in 182 of 184 rats fed PCBs and in 28 of 173 control rats. Neoplastic nodules in 144 of 184 PCB fed rats and none in control rats. Hepatocellular carcinomas in 26 of 184 rats fed PCBs and in 1 of 173 control rats.

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

Nonmalignant Pathologic Effects Induced by PCBs in Animals
PCB Mixture Animal Route of
Acute Effects
42% Chlorine27
Aroclor 124228
Aroclor 1254
Guinea pigs
Guinea pigs
Subcutaneous Skin application
Fatty degeneration and central
atrophy of the liver. Aroclor 1242 produced no ill effects on basis of mortality, growth, pathology, organ enlargement, liver function, or hematological changes. Aroclor 1254 produced no harmful effects regarding growth or mortality, but did produce enlarged livers with microscopic evidence of hepatic cellular injury.
Aroclor 124829 Monkeys Feeding Weight loss, hair loss, mouth and eyelid edema, acneform lesions, decreased hemoglobin and hematocrit, severe gastric mucosal ulceration and extreme hypertrophy of the liver.
Chronic Effects
Aroclor 125430
Aroclor 1260
Rats Feeding Hypertrophy of the liver cells, a brown pigment in the Kupffer cells, lipid accumulation in the cytoplasm of hepatocytes and adenofibrosis.

Table 6. – Reproductive Effects of PCBs in Animals.

Reproductive Effects of PCBs in Animals
PCB Mixture Animal Route of
Aroclor 124231
Aroclor 1254
Chickens Feeding Aroclor 1242 and 1254 reduced egg production and hatchability and caused thin eggshells. Aroclor 1260 produced no harmful effects.
Aroclor 125432 Mallards
Feeding No adverse effects.
Aroclor 125433 Pheasant Feeding Reduced egg production and hatchability.
Aroclor 125434 Mink Feeding Severely affected reproduction.
Aroclor 124829 Female
Feeding Reduced ability to become pregnant. Pregnancies produced small infants with PCBs in tissues.

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,
John F. Finklea, M.D.


* 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]


  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.
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