CHAPTER 36

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS (PCBs) Richard Lawuyi and Merv Fingas Emergencies Science Division, Environment Canada, Environmental Technology Centre, River Road, Ottawa, Ontario

36.1

OVERVIEW OF PRODUCT AND INDUSTRIAL USES Even though polychlorinated biphenyls (PCBs) are no longer imported into Canada or manufactured in many parts of the globe, large quantities are still being used in transformers or kept in storage facilities for future disposal. First developed and synthesized in 1881 and introduced commercially in 1929, PCBs were manufactured in response to the North American electrical industry’s urgent need for a more stable and effective transformer and capacitor fluid. Unfortunately, their chemical and physical stability have also led to widespread and persistent environmental contamination. As a result, the further import and use of PCBs were banned in Canada in 1977. Because efficient and cheap destruction technologies were lacking in the late 1970s and early 1980s, containment was the obvious effective means of control. PCBs and PCBcontaminated materials were kept in temporary warehouses and special storage facilities. In Canada, as of December 1993, there were 11,505 tons (net weight) of askarel (commercial PCB mixtures used for transformers) still in use in transformers and capacitors, 15,247 tons (gross weight) of waste askarel and askarel equipment, 2,161 tons (net weight) of in-use PCB-contaminated mineral oil, 3,787 tons (net weight) of waste PCB-contaminated mineral oil, and 107,991 tons (gross weight) of other PCB waste, including soil, fluorescent lamp ballasts, and drained equipment (Environment Canada, 1995). There were more than 150 spills and fires involving PCBs in 1999, some of which could have been prevented. Of these, 41 could be considered major. PCBs enter the environment through leaks in piping systems, tanks, and storage containers and during routine disposals, manufacturing, and fires. The danger with PCB fires is the formation of more toxic substances such as polychlorinated dibenzodioxins and polychlorinated dibenzofurans. Two case histories of incidents involving PCBs will be outlined.

36.1

36.2

CHAPTER THIRTY-SIX

36.2

INTRODUCTION The introduction of PCBs for use in electric transformers and capacitors in 1929 represented a major breakthrough in the history and technology of dielectric fluids (Durfee et al., 1976). Essentially, PCBs were used as a fire safety measure by virtue of their good dielectric characteristics, chemical and physical stability, and inertness. Unfortunately, these qualities have also contributed to their persistence and bioaccumulation in the environment (Jensen, 1986; Holmes et al., 1967; Risebrough et al., 1969). As a group, PCBs may contain from 1 to 10 chlorine atoms attached to the biphenyl rings in 209 different ways or 209 congeners. As the number of chlorine atoms increases, so does the degree of bioaccumulation and persistence. Pure PCBs are white crystalline solids, but PCBs are often liquid because of impurities. Because of the need for this dielectric fluid to transfer heat, PCBs were often diluted with chlorinated benzenes to yield askarels, which are less viscous (Durfee et al., 1976; Miller, 1982). While PCBs are no longer manufactured, they continue to be released into the environment.

36.2.1

Spill Profile

PCBs have become identified in the public mind as one of the most hazardous compounds on earth. One possible reason for this is that they are ubiquitous and man-made, and aside from two incidents in Japan (Yusho and Yucheng), not much is known about the long-term effects of low-level exposure on humans. Of all the various toxic effects demonstrated in animals, only one or two have been clearly identified in humans. Because of several government and industry initiatives and increased public awareness, the frequency of PCB spills has decreased dramatically. While the Canadian government banned further production and import of PCBs into Canada in 1977, there are still large quantities of PCBs in Canada. As of December 1993, there were 11,505 tons (net weight) of askarel still in use in transformers and capacitors; 15,247 tons (gross weight) of waste askarel and askarel equipment, 2,161 tons (net weight) of in-use PCB-contaminated mineral oil; 3,787 tons (net weight) of waste PCB-contaminated mineral oil; and 107,991 tons (gross weight) of other PCB waste, including soil, fluorescent lamp ballasts, and drained equipment (Environment Canada, 1995). There were about 41 major PCB spills in 1999, some of which could have been prevented (Environment Canada, 2000). The annual spill frequency of PCBs from 1992 to 1995 is shown in Fig. 36.1. Minor spills are not included in the figure. Most spills occur at stationary situations, from leaking pipes, transformers, and capacitors, and during retrofitting. Such electrical equipment may occasionally fail, resulting in fluid release. Spills can also occur as a result of accidental damage from vehicle accidents and human error (Environment Canada, 2000). Some spills have also been reported during normal maintenance of large tranformers and other equipment involving dielectric fluid such as retrofilling, bushing repair, and topping up.Yet others occur through unlawful disposal. As shown in Table 36.1, PCBs are ranked as fifth on Environment Canada’s priority list of hazardous chemicals (Fingas et al., 1991). The primary objective of the list was to determine the minimum number of hazardous chemicals that were most frequently spilled. The list was developed by a simple ranking of reported spill frequency; supply volumes; historical spill volumes; and toxicity data, stability, accumulation, and persistence.

36.3

PHYSICAL AND CHEMICAL PROPERTIES AND GUIDELINES Polychlorinated biphenyls (PCBs) are light, straw-colored liquids with the usual chlorinated aromatic odors. The trichlorinated biphenyls are mobile liquids, while the pentachlorinated

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.3

FIGURE 36.1 Annual spill frequency of PCBs (1992–1995).

biphenyls are viscous. The most commonly used are the trichlorobiphenyls, containing 42% chlorine, and the pentachlorobiphenyls, containing 54% chlorine Two hundred and nine possible isomers can be obtained by substituting chlorine for the hydrogen on the aromatic rings. From 40 to 70 different chlorinated derivatives can be present in the higher-chlorinated commercial mixtures. For instance, arochlor 1254 contains 69 different PCB molecules differing in number and position of chlorine atoms, as well as

TABLE 36.1 Priority List Ranking of PCBs

Chemical

Ranking

Spill number

Spill volume

Supply volume

Ammonia Chlorine Tetraethyl lead Styrene PCBs Sulfuric acid Sodium cyanide Hydrochloric acid Potassium chloride Pentachlorophenol Phenol Zinc sulfate Phosphorus Toluene

1 2 3 4 5 6 7 8 9 10 11 12 13 14

107 36 4 24 334 155 3 123 31 19 10 3 16 13

470 120 72 5,000 89 13,000 83 3300 12,000 110 14 68 46 110

3,700 1,700 26 630 — 3,700 12 170 — 1.5 68 1,500 68 430

36.4

CHAPTER THIRTY-SIX

CIX

x + y = 10 CIy FIGURE 36.2 Chemical structure of PCB.

other compounds such as chlorinated naphthalenes, dioxins, and dibenzofurans. PCBs are very stable, persistent, thermoplastic, and nonflammable. The chemical structure of PCBs is shown in Figure 36.2. Molecular formula: C12H10-XClX Molecular weight: Varies with number of chlorine atoms UN number: Each congener has a number Aroclor 1242 1248 1254 1260 1262 1268

(42% (48% (54% (60% (62% (68%

Cl) Cl) Cl) Cl) Cl) Cl)

CAS no.

RTECS no.

53469-21-9 12672-29-6 11097-69-1 11096-82-5 37324-23-5 11100-14-4

1356000 1358000 1360000 1362000 1364000 1366000

Synonyms and trade names (RTECS On-Line, 2000): Askarels PCBs Chlorodiphenyls Aroclors Kanechlors Pyranol Pyroclor Phenochlor Pyralene Clophen Elaol Santotherm Fenchlor Apirolio Sovol Grades and purities: PCBs are usually manufactured as mixtures of aroclors, chlorobenzenes, and oxygen-scavenging additives. Different aroclors are characterized by the composition of the isomer groups they contain. Other impurities are chlorinated naphthalenes, dibenzofurans, and dioxins.

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.3.1

Physical Data (NRC, 1979; WHO, 1976):

PCB isomer group

Physical state

Vapor pressure

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid / liquid Solid

1.1 Pa at 25⬚C 0.24 0.054 0.012 2.6 ⫻ 10⫺3 5.8 ⫻ 10⫺4 1.3 ⫻ 10⫺4 2.8 ⫻ 10⫺5 6.3 ⫻ 10⫺6 1.4 ⫻ 10⫺6

PCB isomer group

Melting point (⬚C)

Boiling point (⬚C)

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

25 to 77.9 24.4 to 149 28 to 87 47 to 180 76.5 to 124 77 to 150 122.4 to 149 159 to 162 182.8 to 206 305.9

285 312 337 360 381 400 417 432 445 456

PCB isomer group

Specific gravity

Viscosity (mPa.s)

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

1.1 1.3 1.4 1.5 1.5 1.6 1.7 1.7 1.8 1.8

20 28 56 200 1.5 ⫻ 103 2.9 ⫻ 104 ⬎106 ⬎106 ⬎106 ⬎106

PCB isomer group

Molecular weight

Water solubility

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

188.7 (g / mol) 223.1 257.5 292.0 326.4 360.9 395.3 429.8 464.2 498.7

4.0 (g / m3 @ 25⬚C) 1.6 0.65 0.26 0.099 0.038 0.014 5.5 ⫻ 10⫺3 2.0 ⫻ 10⫺3 7.6 ⫻ 10⫺4

36.5

36.6

CHAPTER THIRTY-SIX

PCB isomer group

LOG Kow

Bioconcentration factor (fish)

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

4.7 5.1 5.5 5.9 6.3 6.7 7.1 7.5 7.9 8.3

2,500 6,300 1.6 ⫻ 104 4.0 ⫻ 104 1.0 ⫻ 105 2.5 ⫻ 105 6.3 ⫻ 105 1.6 ⫻ 106 4.0 ⫻ 106 1.0 ⫻ 107

PCB isomer group

Evaporation rate (g / m2
h @ 25⬚C) (approximately)

Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

0.25 0.065 0.017 4.2 ⫻ 10⫺3 1.0 ⫻ 10⫺3 2.5 ⫻ 10⫺4 6.2 ⫻ 10⫺5 1.5 ⫻ 10⫺5 3.5 ⫻ 10⫺6 8.5 ⫻ 10⫺7

Average Composition of Some Aroclors. Aroclors are essentially mixtures of different isomer groups. Some composition data are shown in Tables 36.2 to 36.5. Askarels. Askarels are mixtures of many isomer groups of PCBs and chlorobenzenes and may also contain phenoxypropene oxide or diepoxide. They are mainly used as transformer oils and are of many types, namely, A, B, C, D, E, F, and G. Physical properties of some askarels are shown in Tables 36.6 and 36.7.

TABLE 36.2 Composition of Aroclors

PCB isomer group

1221

1232

1016

1242

1248

Biphenyl Monochlorobiphenyl Dichlorobiphenyl Trichlorobiphenyl Tetrachlorobiphenyl Pentachlorobiphenyl Hexachlorobiphenyl Heptachlorobiphenyl Octachlorobiphenyl Nonachlorobiphenyl Decachlorobiphenyl

10 50 35 4 1

26 29 24 15

2 19 57 22

3 13 28 30 22 4

2 18 40 36 4

1254

11 49 34 6

1260

12 38 41 8 1

36.7

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

TABLE 36.3 Physical Properties of Some Aroclors

Property

1016

Appearance Physical state at 25⬚C, 1 atm Distillation range (⬚C) Pour point (⬚C) Vapor pressure at 25⬚C (Pa) Viscosity at 25⬚C (mPa.s) (Saybolt Universal s) Specific gravity at 25⬚C (approx.) Fluid density at 25⬚C (kg / m3)

Clear, mobile oil Liquid 323–356 ⫺14 0.10 45 200

1242

1248

1254

1260

Clear, mobile oil Liquid

Clear, mobile oil Liquid

Light yellow, viscous liquid Liquid

Light yellow, soft sticky resin Solid

325–366 ⫺19 0.091

340–375 ⫺7 0.023

365–390 10 6.7 ⫻ 10⫺3

385–420 31 6.4 ⫻10⫺4

69 270

280 1.0 ⫻ 103

2.0 ⫻ 103 6.7 ⫻ 103

1.9 ⫻ 105 6.0 ⫻ 105

1.4

1.4

1.5

1.6

1,383

1,445

1,539

1,621

1.4 1,370 at 20⬚C

Immediate Concerns Hazard: Readily absorbed into the body by all routes of exposure. May cause irritation to nose, throat, and lungs. Humans: May produce irritation to nose, throat, and lungs. Inhalation may result in all symptoms of long-term exposure. Skin absorption may produce a rash after a few days of exposure. Environment: Environmentally hazardous substance. Very persistent substance. Will bioaccumulate and biomagnify in the food chain. Protection: Wear self-contained breathing apparatus (SCBA) and appropriate clothing impermeable to PCBs.

TABLE 36.4 Physical Properties of Some Aroclors

Property

1242

1248

1254

1260

Average molecular weight (g / mol) Solubility in water at 25⬚C (g / m3) Log Kow Bioconcentration factor

261 0.75 4.5 to 5.8 1.6 ⫻ 103– 3.2 ⫻ 104 0.029 5.8 ⬎35 ⬎500 ⫻ 109

297 0.32 5.8 to 6.3 3.2 ⫻ 104– 1.0 ⫻105 8.3 ⫻ 10⫺3 5.6 ⬎35 ⬎500 ⫻ 109

327 0.14 6.1 to 6.8 6.3 ⫻ 104– 3.2 ⫻ 105 2.7 ⫻ 10⫺3 5.0 ⬎35 ⬎500 ⫻ 109

375 0.035 6.3 to 7.5 1.0 ⫻ 105– 1.6 ⫻ 106 2.9 ⫻ 10⫺4 4.3 ⬎35 ⬎500 ⫻ 109

⬍0.1

⬍0.1

⬍0.1

⬍0.1

Evaporation rate at 25⬚C (g / m2 / h) Dielectric constant at 25⬚C Dielectric strength (kV) Volume resistivity at 100⬚C, 500 V D.C. (ohm-cm) Power factor at 100⬚C (%)

36.8

CHAPTER THIRTY-SIX

TABLE 36.5 Other Physical Properties of Some Aroclors

Property

1242

Flash point (COC) (⬚C) Fire point (COC) (⬚C) Refractive index at 20⬚C Coefficient of thermal expansion (cm3 / cm3 / ⬚C) Maximum moisture content (ppm)

36.3.2

1248

1254

1260

176 to 180

193 to 196

⬎boiling point

⬎boiling point

⬎boiling point ⬎boiling point

⬎boiling point ⬎boiling point

1.628 0.00068 (25 to 65⬚C) 50

1.631 0.00070 (25 to 65⬚C) 50

1.640 0.00066 (25 to 65⬚C) 50

1.648 0.00067 (20 to 100⬚C) 50

Countermeasures

Spills on land: Clean up PCB spills immediately to prevent further contamination. Restrict persons not wearing protective equipment from spill area. Ventilate the area of spill or leak. Absorb liquids in vermiculate, dry sand, earth, or a similar material and deposit in sealed containers. A temporary holding area would consist of a truck box, a dumpster with impermeable lining, or an area on the ground with soil berms or dykes with appropriate impermeable lining. Store in a cool, well-ventilated area away from strong oxidizers. Spills on water: Spills on water require immediate action to minimize widespread contamination. PCBs less dense than water, such as PCB-contaminated oils, will float on the water surface and require usual oil-recovery techniques while those that are heavier will sink rapidly in water and will require dredging of sediments.

36.4

36.4.1

INDUSTRIAL ASPECTS AND PRODUCTION IN THE UNITED STATES, CANADA, AND WORLDWIDE Manufacture of Polychlorinated Biphenyls

PCBs are no longer manufactured anywhere in the world, but large quantities still remain in transformers and in storage in contaminated form. In Canada, the import of PCBs was prohibited in 1977. The following are highlights of the national inventory as of December 1993 (Environment Canada, 1995). TABLE 36.6 Physical Properties of Some Askarels

Property

Type A

Average molecular weight Water solubility at 25⬚C (g / m3) Evaporation rate at 25⬚C (g / m2 / h) Dielectric constant at 100⬚C, 1 kHz Dielectric breakdown voltage, min. (kV) Resistivity at 100⬚C (ohm-cm)

258.6 0.016 7.8 ⫻ 10⫺5 3.7–4.0 35 100 ⫻ 10⫺9

Type B

3.8–4.3 35 100 ⫻ 10⫺9

Type C

Type D

4.4–4.9 35 100 ⫻ 10⫺9

263.4 0.056 4.8 ⫻ 10⫺4 4.3–4.6 35 100 ⫻ 10⫺9

36.9

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

TABLE 36.7 Physical Properties of Some Askarels

Property

A

B

C

D

Physical state at 25⬚C, 1 atm Pour point, max. (⬚C) Vapor pressure at 25⬚C (Pa) Kinematic viscosity at 37.8⬚C (Saybolt universal s) Absolute viscocity at 25⬚C (mPa.s) Specific gravity at 15.5⬚C Density at 25⬚C (kg / m3) Fire point (COC) ⬚C

Clear, mobile oil Liquid ⫺32 2.5 ⫻ 10⫺4 54 31 1.564 1563 ⬎boiling point

Clear, mobile oil Liquid ⫺44

Clear, mobile oil Liquid ⫺30

43

53

Clear, mobile oil Liquid ⫺30 1.5 ⫻ 10⫺3 59 33 1.523 1524 ⬎boiling point

Appearance

1.566

1.419

⬎boiling point

⬎boiling point

• There were 11,505 tons of askarel in use, 9,649 tons of which were in transformers, 1,697 • • • • •

36.5

tons in capacitors, and 159 tons in other equipment. There were 15,247 tons of waste askarel and askarel equipment, 6,131 tons of which were in transformers, 2,576 tons in bulk storage, and 125 tons in other equipment. There were 2,161 tons of in-use PCB-contaminated mineral oil, 2,083 tons of which were in transformers and 77 tons in other equipment. There were 3,787 tons of waste PCB-contaminated mineral oil, 418 tons of which were in transformers, 3,364 tons in bulk storage, and 5 tons in other equipment. There were 107,991 tons of other PCB wastes, consisting of 95,718 tons of soil, 6,328 tons of fluorescent lamp ballasts, 1,581 tons of drained equipment, and 4,364 tons of other wastes. In the United States, more than 340,000 tons of PCBs were in service in over 900 million pieces of equipment in the mid-1970s.

CHEMISTRY There are two main reactions of PCBs that significantly affect the environment. These are the stripping off of the chlorine atom / atoms by sodium metal to produce biphenyl and sodium chloride (Fig. 36.3) and the formation of polychlorinated dibenzofurans and polychlorinated dibenzodiozins at elevated temperatures, such as during fires (Fig. 36.4).

CI

Na +

2 NaCl

CI

PCBs

Biphenyl

FIGURE 36.3 Formation of biphenyl and sodium chloride.

36.10

CHAPTER THIRTY-SIX

Cl

CI

Fire CI

and

O Cl

Dibenzofurans O

Cl

O Dibenzodioxins

Cl

FIGURE 36.4 Formation of dibenzofurans and dibenzodioxins.

36.6 36.6.1

ENVIRONMENTAL FATE AND EFFECTS Environmental Fate and Transport

The predominating factors in terms of the environmental fate of a chemical when spilled are its physicochemical properties as well as the location of the spill and weather conditions in the area. PCBs are transported by air, water, insects, fish, birds, and humans and are deposited by rain, snow, and dry fallout. Polychlorinated biphenyls have been detected in all corners of the globe and in almost every medium, including soil, air, sediment, water, human milk, fish, seagulls, meat, and even polar bears. While very low concentrations of PCBs have been found in the air and water, extremely high levels have been reported in soils, sediments, and aquatic biota. This is not surprising given the persistence of these chemicals and the various forms of transport involved. The ultimate sink for PCB spills is the sediments. Various types of models have been used to predict the environmental long-term fate of spilled chemicals. In fate and transport studies, the following types of chemical releases are possible: volatilization, run-off, leaching to groundwater, and fugitive dust emissions. Volatilization. Even though the vapor pressure of PCBs is very low, small amounts of spilled PCBs will slowly evaporate into the overlying air (evaporation rate is about 4.8 ⫻ 10⫺4 to 7.8 ⫻ 10⫺5 g / m2 / h) (NRC, 1979). This can happen for spills on both water and soils. Calculations of average mass losses through evaporation could be computed for many spills. As for PCB mixtures that contain chlorobenzenes and mineral oils, the lighter components consisting mainly of chlorobenzenes and mineral oils will evaporate first, leaving behind the thicker PCBs. The evaporation rate is dependent on the wind speed and temperature. However, the net result of volatilization is the removal or transference of PCBs from one environmental compartment to another without any net loss from the environment. Runoffs. In the case of spills that occur near coastlines or water bodies, PCBs can be transported to receiving surface waters by runoff of surface soil from the spill site. The amount of runoff will depend on the properties of the surface soil, the location, the slope or proximity to the shoreline, and the nature of vegetation. The mass of PCBs that is lost from a site has been roughly estimated from the average concentration in surface soil, the amount of runoff, and soil erosion.

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.11

Leaching to Groundwater. Because PCBs are highly adsorptive and relatively immiscible in soil, small spills (about 1 to 2 L) are not likely to leach into groundwater. As for larger spills, it is possible that the PCBs will migrate through the soil to shallow groundwater. Soil penetration is enhanced by rainfall that infiltrates through the soil downward to the water table. Some leaching can also occur through water movement as a result of partitioning of PCBs, but this is not considered to be a major mechanism, as the partitioning coefficient of PCBs to water is very low. Fugitive Dust Emissions. Fine dust contaminated with PCBs can be stirred up at spill and station sites during heavy construction and high winds. Because particles of smaller sizes travel much farther than those of larger sizes, it is not surprising to find PCBs in the Arctic as well as the Antarctic. PCB dust emissions are transported by air, water, human, animals, fish, birds, and microorganisms. Precipitation from air can also occur by rain, snow, vapor condensation, and dry fallout. 36.6.2

Destruction and Degradation

Abiotic Degradation. Incineration is the most common method of destroying PCBs. This method is carefully regulated to ensure that PCBs are completely destroyed since incomplete destruction can lead to more toxic products such as polychlorinated dibenzofurans and dioxins, which are often detected during fires, use, or aging of askarels. The destruction efficiency for incinerators has been specified as 99.9999% for emissions of all PCBs. This efficiency can be achieved with high heat, long residence time, and various pollution control systems. High efficiency boilers have also been approved for combustion of PCBs (Hunt et al., 1984). Abiotic nonthermal methods include chemical processes such as reaction with molten sodium, sodium naphthalide, sodium salt in amine, catalytic dechlorination, wet air oxidation, ozonation, and physical methods including adsorption, microwave plasma, and photolysis. Photolysis is another possible route of environmental breakdown of PCBs. The process appears to occur by C–Cl bond cleavage to produce biphenyl-free radical species, which then abstract hydrogens. Photolytic degradation depends on the degree of chlorination, position of chlorine substitution in the ring, and the solvent used for the PCB dissolution. For example, while the half-life of monochlorobiphenyl ranges from 0.62 to 1.4 days, that of pentachlorobiphenyl is over 67 days. It has been shown that the photolysis of the o-chlorine is probably due to steric hindrance to the preferred excited state geometry. Therefore, the more highly chlorinated commercial PCBs often photolyze preferentially in environmental samples. Bunce et al. (1978) reported that in shallow waters, at least one chlorine atom from highly chlorinated PCBs is photolyzed annually. Biodegradation. The only form of biodegradation is microbial degradation and this includes different bacteria methods, activated sludge, and trickling filters. Microbial degradation has been shown to depend on the degree and position of chlorination (Moolenaar, 1983). For example, the half-life of monochloro biphenyls has been shown to be about 2 to 3 days and over 3,000 days for the pentachloro biphenyls. The smaller the number of chlorine atoms, the higher the efficiency of degradation (Moolenaar, 1983). The substitution of chlorine also affects the extent of dechlorination; it has been reported that ortho substitution markedly decreases the rate of degradation. Typical end products found were hydroxychlorinated biphenyls and chlorobenzoic acid. 36.6.3

Bioaccumulation, Bioconcentration, and Biomagnification

Bioaccumulation. The hydrophobic and lipophilic nature of PCBs is a strong indication of their tendency to partition into the fatty tissues of animals. Their stability or persistence is an additional factor that contributes to their accumulation since they cannot be readily

36.12

CHAPTER THIRTY-SIX

degraded by enzymes. It has also been shown that species with high lipid contents tend to accumulate relatively large concentrations of PCBs. PCBs exhibit bioaccumulation tendencies very similar to DDT and some chlorinated pesticides, and the higher the degree of chlorination, the more readily it will be accumulated (Hansen et al., 1983). Other factors that affect the bioaccumulation of PCBs are: 1. 2. 3. 4. 5. 6. 7.

Duration of exposure Temperature Solubility Species age Concentration of PCBs Adsorption Lipid content

Bioconcentration. Uptake of PCBs from surrounding water and sediments has been demonstrated for many aquatic animals, such as young oysters, clams, and worms. Biomagnification. Several authors have reported that PCB concentration in the components of the food web shows a stepwise increase at each trophic level (NRC, 1979). PCBs are accumulated by lipid-water partitioning via the food chain. It is possible that there are different PCB-uptake mechanisms at different trophic levels.

36.7 36.7.1

BEHAVIOR Behavior and Environmental Fate during a Spill

There are no known natural sources of PCBs. Sources are mainly anthropogenic. PCBs were prepared commercially by the chlorination of biphenyl with anhydrous chlorine in the presence of catalysts, followed by some purification. Usually, the longer the purification step, the more chlorine substitution takes place on the rings. ‘‘Behavior’’ includes all the visible characteristics displayed by a chemical. PCB is a viscous to mobile, colorless to brown liquid that slowly spreads when spilled, depending on the ambient temperature and exact formulation. Indoor spills usually occur in small quantities on concrete, and the vapor will adsorb onto walls, carpeting, drapery, and metal objects. All forms of exposure should be avoided and the airborne concentration carefully monitored. On the other hand, outdoor spills can range from a few drops from transformers to full trailer tanks and can take place on either land or water. From an environmental impact standpoint, the four most important physical properties of PCBs are very low water solubility and vapor pressure, high octanol / water partition coefficients, and stability or persistence (NRC, 1979). The five mechanisms by which PCBs can be transported in the soil are as a dissolved material in the water; by sorption; as an emulsion with water; as an immiscible oily liquid phase; and as a discrete fluid. PCB fluids are generally insoluble in water and, when spilled on the soil, usually settle first as a pool on the ground surface before infiltration and downward movement through multilayered soil, water, and soil gases. The liquid fills the pores at the soil surface and begins to penetrate downward. Some of the lighter components will evaporate. The downward transport of oils and immiscible liquids has been extensively reviewed (Greenkorn, 1983). The following are the different stages of PCB fluid penetration through the soil:

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.13

1. 2. 3. 4.

Spill occurs. Soil penetration begins. Spill pool is dissipated. Saturated plug continues to move downward, leaving behind a constant residual saturation in the soil. 5. Saturated slug is exhausted as residual saturation and downward movement stop. 6. Light PCB oils form a pancake and float on the water table. 7. Heavy PCB oils sink into the water table. Extensive soil and water sampling is necessary to determine the nature and extent of contamination when a spill occurs (NRC, 1979). Soil sampling should always be directed first at determining the presence of PCBs. Several quick tests are now available. Once the qualitative results are known, the quantitative measurements can be made. Water table contamination after a PCB spill can also be determined based on knowledge of the elapsed time, stratigraphy of the soil, permeability coefficient, and penetration depth. The area of the spill pool will increase with time and depth of soil penetration for a given location. Soil penetration also depends on how long the spill pool has been at the location. The maximum soil penetration generally occurs where the spill originates. When spilled on water, PCB fluids are less dense than water (density of water ⫽ 1,000 kg / m3; average density of PCBs ⫽ 1,500 kg / m3), such as contaminated mineral oils, will float and assume a round or pancake shape (NRC, 1979). This will subsequently be broken down into globules due to turbulence or the action of waves. On the other hand, PCB fluids heavier than water will sink and adhere to the sediments, where they will be taken up by aquatic organisms. Some of the PCB fluids that float, even though not very volatile, will evaporate into the atmosphere, depending on the wind speed, temperature, atmospheric stability, and type of fluid. When human exposures are likely, protective respiratory equipment should be used. Table 36.8 shows the distribution and fate of an Aroclor 1248 spill after 30 days (NCR, 1979). It is interesting to note that most askarels spilled on land end up in the soil, while the bulk of askarels spilled on water will eventually be adsorbed onto the sediments.

36.7.2

Fires

Because PCB molecules have two benzene rings or 12 carbon atoms as well as some chlorine atoms, they will burn at high temperatures when ignited. The main danger from a PCB fire is not the PCB itself, but the formation of extremely toxic byproducts of combustion, such as polychlorinated dibenzodioxins, polychlorinated dibenzofurans, and hydrogen chloride gas, which often produce immediate respiratory effect. The formation of dioxins and furans

TABLE 36.8 Distribution of Spilled Aroclor 1248, 30 days after Spill

Medium

% PCB remaining (land spill)

% PCB remaining (water spill)

Air Soil Water Bottom sediment Groundwater

0.005 96.3 0.001 0.001 0.003

0.4 0.04 0.4 90.1 0

36.14

CHAPTER THIRTY-SIX

from thermal degradation of PCBs has been reviewed (Choudhry and Hutzinger, 1983; Erickson et al., 1984). Dioxins are frequently formed during thermal breakdown as a result of molecular rearrangement of chlorinated organic compounds during incineration. The actual formation of dioxins takes place after flue gases, fly ash, and other byproducts have begun to cool down and condense at about 300⬚C. Incomplete combustion of PCBs usually produces furans. Its synthesis often takes place during the postcombustion phase. Generally, PCDDs in soot from fires involving PCBs range from nondetectable to 19 ppm. There are three theories about the presence of dioxins and furans after a PCB fire (Choudry and Hutzinger, 1983). 1. Dioxins and furans are present all along and are able to survive the thermal stress. 2. Dioxins and furans are formed as a result of thermal breakdown and molecular rearrangement of the starting materials to form precursors very similar to dioxins and furans, such as chlorinated phenols, polychlorinated biphenyls, and chlorinated benzenes. 3. Dioxins and furans are formed from precursors that bear no resemblance to these products. For example, burning different nonprecursor substances such as cellulose, lignin, chlorinated plastics, hydrogen chloride gas, and other petroleum products has produced dioxins.

36.8 36.8.1

HUMAN AND ENVIRONMENTAL TOXICITY Chronic Toxic Effects on Humans

PCBs are suspected human carcinogens (IARC, 1994). They are moderately toxic for shortterm exposure by ingestion and skin exposure. There are no reported deaths of humans as a result of a single ingestion. However, experiments in animals suggest that an ingestion of 6 to 10 fluid oz would cause death to a healthy 150-lb adult. Much lower dose levels for chronic exposures have been found to cause various toxic effects that are very similar to those of polychlorinated dibenzofurans and other halogenated aryl hydrocarbons and include the following symptoms:

• • • • • • •

Chloracne, blackheads, and skin lesions in many laboratory animals and humans Immunotoxic effects A wasting syndrome Reproductive and fetal toxicity Carcinogenesis and fetal toxicity Porphyria and hepatotoxicity The induction of various drug-metabolizing enzymes

Other effects include unusual eye discharge by all routes, liver damage and digestive disturbance, burning feeling in the eyes, nose, and face, dry throat, lung and throat irritation, nausea, and dizziness (Kimbrough, 1974). The toxicity of PCBs depends not only on the degree of chlorination but also on the types of isomer. For example, PCBs devoid of orthosubstitution but heavily substituted at the meta and para positions can assume a planar conformation that can interact with the same receptor as TCDD. Examples of these isomers are: 3,3⬘,4,4⬘-tetrachlorobiphenyl; 3,3⬘,4,4⬘,5pentachlorobiphenyl; and 3,3⬘,4,4⬘,5,5⬘-hexachlorobiphenyl (NIOSH, 1977). The Yusho and Yucheng incidents in Japan have provided much of the information on the effects of PCBs on humans (WHO, 1976; NIOSH, 1977; Gaffey, 1983a, b). Some health effects on workers exposed to PCBs are outlined in Table 36.9. Environmental standards and criteria for PCBs are given in Table 36.10.

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.15

TABLE 36.9 Health Effects on Workers Exposed to PCBs

36.8.2

Duration (years)

Environmental level (mg / m3)

Blood level (ppb)

Effects

Not known 0.33–0.66 1–20 2.5 2.5–18 1.17 2–23 Up to 15

10 5–7 0.2–1.6 – 0.013–0.27 0.1 0.32–1.44 –

– – 370 820 36–286 — ⬎200 7–300

Unbearable irritation Chloracne Chloracne, hyperpigmentation, liver disease Chloracne Irritation, liver disease Chloracne, liver disease Chloracne, liver disease Chloracne, elevated triglycerides

Chronic Toxic Effects on Animals

Animals respond in a variety of different ways to the same chemical. Toxicity studies on PCBs are very difficult for the following reasons:

• • • •

PCBs are extremely heterogeneous, each formulation consisting of several isomers. No two formulations are identical. Samples of the same formulation may be different. The composition of the same sample often changes when exposed to the environment (NRC, 1979). Some effects on animals are given in Table 36.11.

36.8.3

Estimated Dietary Intake of PCBs in Canada

Most meat and dairy products contain some amount of PCBs. Major exposure routes are contaminated water, vegetation, and feed. Dietary intake of PCBs from various food sources is given in Table 36.12.

TABLE 36.10 Environmental Standards and Criteria for PCBs Environmental medium

Region

Concentration

Notes / comments

Air–ambient Water–ambient Water–ambient Water–recreation Water–drinking Sediments Soil Solid waste Fish Food (TDI)a

Ontario Great Lakes–IJC U.S. EPA Quebec Nova Scotia Canada Saskatchewan Canada Canada Canada

35 ng / m3 (1 Y average) 1 ng / L 0.79 to 0.79 ⫻ 10⫺3 ng / L 0.1 ␮g / L 3 ␮g / L 1 mg / kg ⬍5 mg / kg ⱖ50 mg / kg 2 mg / kg 1 ␮g / kg / d

Air quality criteria Aquatic life Human health Standard recommendation Maximum concentration Disposal (marine) Cleanup PCB wastes Health Canada Estimated tolerance

a

⫽ tolerable daily intake.

36.16

CHAPTER THIRTY-SIX

TABLE 36.11 Chronic Toxic Effects on Animals

Test (chronic feeding) Aquatic species Terrestrial species

Teratogenicity Mutagenicity

Oncogenicity

Effects Threshold effects in egg hatchability of vertebrates and invertebrates at levels of 2–5 ␮g / L. Embryo toxicity evident at 50 ␮g / L. Mice: Some liver changes with exposure to high chlorine-containing products, 300–500 ␮g / g. Rats: Some liver changes, minimal reproductive effects, 100–500 ␮g / g. Monkeys: Yusho symptoms, altered reproductive cycles, hyperplastic gastritis and ulceration, 2.5–5 ␮g / g. Chickens: Some morphologic deformity, reproduction decline, subcutaneous edema, 20–50 ␮g / g. Mink: Dose response relationship in growth and reproduction, 10 ␮g / g. Pelicans: Some hepatocellular changes, 100 ␮g. Dogs: Reduced growth, some liver changes, 100 ␮g. Wildfowl: Some reproduction changes, varies with species, 50–200 ␮g / g. Effects seen in avian species, 50–200 ␮g / g. Chromosomal abnormalities: negative Dominant lethal mutations: negative Ames test: 1221, tetrachloro biphenyl significantly mutagenic. Highly chlorinated compounds produced tumors in rats and mice, relationship with PCBs not always clear.

Source: NIOSH, 1977; NRC, 1979.

36.9

SURVEY OF PAST SPILLS, LESSONS LEARNED, AND COUNTERMEASURES APPLIED The two worst-case histories of a PCB spill and a fire are presented here. These exemplify some aspects of the behavior and environmental fate of PCBs as described in the previous sections. A number of small spills of PCBs and askarels have been described in Garrett (1983).

TABLE 36.12 Dietary Intake of PCBs

Foodsource

Food intake (g / person / day)

PCBs intake (␮g / person / day)

Dairy Meat Poultry Eggs Fish Total

32.8 48 3.6 34 20 138.4

6.6 9.6 1.8 3.4 40 61.4

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.9.1

36.17

PCB Spill in Regina, Saskatchewan

In the summer of 1976, an estimated 6,800 to 21,000 L of a transformer oil formulation (Inerteen 70-30) containing PCBs (Aroclor 1254), trichloro, and tetrachlorobenzenes were spilled when an underground pipe broke at the Federal Pioneer Limited manufacturing plant in Regina, Saskatchewan (Haug and Atwater, 1992; NRCC, 1980). The spill site was located on a major aquifer that supplies drinking water to the city. There was also the potential for contamination of future water supply wells and another aquifer close to the site. Methods were sought to determine the extent of the spill and its surface and subsurface distribution. Detailed test drilling and sampling identified the following major hydrostratigraphic units: a thin surface fill, Regina clay, Condie silt, the till zone, the interglacial silt, and the Regina aquifer system. The permanent water table is situated below the Condie silt and the sandy glacial till. It was reported that an active perched groundwater had developed within the thin fill layer beneath the floor of the plant. The spread and extensive contamination of the PCBs were the result of the lateral flow of the groundwater. It was also found that PCBs had moved downwards through fractures in the Regina clay and the upper part of the Condie silt. It has been suggested that the potential for transport as a dissolved phase in the groundwater may be the mechanism for the migration of the PCBs downward to the aquifer or laterally to the surrounding sites. Shallow sumps and deep wells were dug to dewater the site. The effectiveness was measured by a network of piezometers. The extent of groundwater contamination was also determined. The concentration of PCBs in the water collected from sumps on the site ranged from 1 to 500 ppm. High concentrations of approximately 5,000 ppm were detected in some cases. Soil containing over 50 ppm of PCBs was excavated and transported to a nearby storage facility. The remedial measures to contain and mitigate the effects of the spill consisted of constructing a cutoff wall extending down through the clay to the silt on the spill site to contain the spill, installing a thick seal over the entire surface, and practicing active dewatering to prevent further downward migration of PCBs since one of the driving forces is the downward movement of moisture through the clay. It has been suggested that the contamination of the deeper wells may have been due to the fact that the PCBs were dissolved in mineral oil. The PCBs moved downward through fractures in the Regina clay and in the upper part of the Condie silt. It was also mentioned that the possible existence of fracture connections to the Regina aquifer and the transport in the dissolved phase may have allowed not only downward migration but also lateral off-site flow. A large amount of the PCBs found at great depths could have moved as discrete fluid.

36.9.2

PCB Storage Depot Fire at St-Basile-le-Grand, Quebec

On August 23, 1988, a warehouse containing about 3,800 barrels of PCBs and PCBcontaminated oils (22,400 gallons of askarels in 45-gallon drums) caught fire (Journault et al., 1989; Phaneuf et al., 1995; Emergency Preparedness Canada, 1988). The warehouse is located approximately 50 km east of Montreal on the south shore of the St. Lawrence River at St-Basile-le-Grand, which has a population of 12,000. It took four fire departments and two police forces seven hours to put out the fire. More than 3,800 people were evacuated in the incident. The heat generated by the fire was so great at one point that the roof and walls collapsed and the drums of PCB were exploding. When the fire subsided, a team of scientists from Environment Canada’s Environmental Technology Centre in Ottawa went to the site to determine the extent of contamination. The Quebec Environmental Department, the TAGA 3,000 team of the Ontario Ministry of the Environment, and the TAGA 6,000 research group of the New York State Department of Environmental Conservation were also involved. Contaminant levels in air, water, soil, vegetation, and livestock were measured. The following are some of their findings.

36.18

CHAPTER THIRTY-SIX

1. All the air samples from the schools and residences were below the detection limits (100 mg / m3). 2. The maximum concentration of PCBs detected in the air samples was 11,512 ng / m3. 3. Mostly T4CDF, P5CDF, and H6CDF were found and small quantities of dioxins. The dioxins were generally H6CDD, H7CDD, and O8CDD. 4. Most of the determinations were below the detection limits. One or two samples of PCBs that exceeded the guidelines toxicity equivalents (15 pg / L for surface water; 1 ␮g / kg for soil) were found in the soil and surface waters. 5. None of the positive values for the PCBs and dioxins detected off-site presented any health hazards, since they were well below the guidelines (0.25 ng / 100 cm2). 6. The levels of both dibenzodioxins and dibenzofurans close to the site were as high as several hundreds of ppm. 7. Many oil droplets that vaporized in the fire and particulates were found to contain PCBs and furans two times below the exposure limit. Complete combustion of PCBs produces hydrogen chloride gas and carbon dioxide, while incomplete combustion yields plenty of soot and smoke and far more toxic products such as polychlorinated dibenzofurans (mostly) and polychlorinated dibenzodioxins. This is why incineration of PCBs is strictly regulated. The guideline is 99.9999% combustion. Lessons to Be Learned 1. These incidents demonstrate the cause, mechanisms, remedial measures, and ways to minimize the impact and prepare for similar occurrences in the future. 2. While no lives were lost in these incidents, disasters involving hazardous materials can be very expensive. The St-Basile-le-Grand fire cost over $6.6 million, while costs of the Regina spill are over $5 million. In both cases, regular maintenance and vigilance are all that is needed to prevent such accidents. 3. A sprinkler system could have helped put out the fire at the initial stages, or at least cool down the warehouse structures. A heat- or smoke-activated chemical foam and fire alarm system could also have been installed in storage places. Materials for cleanup, selfcontained breathing apparatus, protective clothing, and portable fire extinguishers should be available on-site. 4. The broken pipe at Federal Pioneer in Regina could have been prevented with an accurate leak detection system. Because the pipe had been reported leaking for some time, the leak could have been detected much earlier. 5. Steps should also be taken to incinerate or otherwise dispose of all PCBs and PCBcontaminated oils that are in storage to avoid fires such as this.

36.10

CONCLUSIONS The human health risks from environmental exposure through the skin and by inhalation have been assessed with occupationally exposed workers as shown in Table 36.9. It has been found that these chronically exposed workers exhibit few adverse effects. One can only conclude that the potential adverse human health effects that can result from accidental exposure and low-level environmental impact are very low. The chronic low-level, long-term impact on the environment is still unclear.

PERSPECTIVES ON SPECIFIC SUBSTANCES: POLYCHLORINATED BIPHENYLS

36.11

36.19

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enport and B. K. Bernard, Report No. LSI-TR-507-1373, NTIS No. PB84-135771 67-96, Office of Toxic Substances, U.S. EPA, Washington, DC. National Institute for Occupational Safety and Health (NIOSH). 1977. Criteria for a Recommended Standard: Occupational Exposure to Polychlorinated Biphenyls (PCBs), U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease Control and National Institute for Occupational Safety and Health DHEW (NIOSH), Publication No. 77-225. National Research Council (NRC). 1979. Polychlorinated Biphenyls, National Academy of Sciences, Washington, DC. National Research Council of Canada (NRCC). 1980. A Case Study of a Spill of Industrial Chemicals— Polychlorinated Biphenyls and Chlorinated Benzenes, Publication No. 17586. Phaneuf, D., J. L. DesGranges, N. Plante, and J. Rodrigue. 1995. ‘‘Contamination of Local Wildlife Following a Fire at a Polychlorinated Biphenyl Warehouse in St-Basile-le-Grand, Quebec, Canada,’’ Archive of Environmental Contamination and Toxicology, vol. 28, pp. 145–153. Risebrough, R. W., P. Reichle, and H. S. Olcott. 1969. Bulletin of Environmental Contamination and Toxicology, vol. 4, p. 192. RTECS On-Line. 2000. Registry of Toxic Effects of Chemical Substances, Department of Health and Human Services, Centers for Disease Control, National Institute for Occupational Safety and Health, Washington, DC. World Health Organization (WHO). 1976. Polychlorinated Biphenyls and Terphenyls, Environmental Health Criteria 2, WHO, Geneva.