%5BJohn D. Spengler%2C John F. McCarthy%2C Jonathan M. S%28BookFi.org%29+Sach+Chinh.837-860

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POLYCHLORINATED

BIPHENYLSDonna J. Vorhees, Sc.D.Menzie-Cura & Associates, Inc.

Chelmsford, Massachusetts

Polychlorinated biphenyls (PCBs) were valued historically for their thermal stability,chemical inertness, low flammability, low vapor pressure at ambient temperature, andresistance to microbial degradation (de Voogt and Brinkman 1989). These properties madethem excellent dielectric fluids in transformers and capacitors as well as for other applica-

tions. Today, these same properties make PCBs problematic contaminants that persist andbioaccumulate in the environment.

PCBs were manufactured in the United States from 1929 to 1977 as commercial mix-tures called Aroclors. Similar commercial mixtures produced elsewhere in the worldinclude Clophens (Germany), Kanechlors (Japan), Phenoclors (France), Fenclors (Italy),and Soval (Russia). PCB production peaked in the United States in 1970 prior to use andmanufacturing restrictions implemented in the late 1970s. Despite these restrictions, PCBspersist in air, water, soil, sediment, and biota.

Because PCB mixtures are generally hydrophobic and not volatile, they partition to soilsand sediments more than air or water. PCBs can bioaccumulate in fish and higher-trophic-levelorganisms that are consumed by people. In fact, the diet is generally regarded as the mainsource of human exposure. Exposure to PCBs in indoor air might be second only to dietaryexposure given the substantial amount of time people spend indoors (Robinson and Thomas1991), although the specific congener mixtures in air would differ from congener mixturesin food. Individuals working in PCB-using industries (e.g., transformer repair) commonlyexperience the highest indoor exposures; however, this chapter focuses on nonindustrialindoor environments.

36.1 WHAT ARE PCBs?

Aroclors and other commercial mixtures of PCBs were produced by chlorinating moltenbiphenyl with anhydrous chlorine in the presence of a catalyst. The biphenyl molecule canaccommodate between one and ten chlorine substitutions, resulting in 209 possible congeners(Fig. 36.1). PCB congeners with the same number of chlorines are isomers referred to col-

CHAPTER 36

36.1

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lectively as homolog groups. Commercial mixtures are composed of different but overlap-ping congener mixtures. Four-digit numbers assigned to Aroclors reflect the chemical com-position of these mixtures. The first two numbers indicate the 12 carbon atoms in the biphenylring, and the last two numbers denote the weight percentage of chlorine. For example, Aroclor1242 contains 42 percent chlorine by weight. Aroclor 1016, with 41 percent chlorine byweight, is an exception to this nomenclature. It contains almost the same amount of chlorineas Aroclor 1242, but with a lower proportion of high-molecular-weight congeners. Aroclor1016 was developed as an alternative to Aroclor 1242 after concern arose about the environ-mental persistence of the heavier congeners (de Voogt and Brinkman 1989).

36.2 PCBs IN THE ENVIRONMENT

Mixtures and congeners with high chlorine content tend to adhere to soils, sediments, andorganic materials. Fish and other organisms bioaccumulate PCBs, particularly congenerswith high chlorine content that are resistant to metabolism and elimination (Oliver andNiimi 1988, Schwartz and Stalling 1987, Lake et al. 1995). The major destructive pathwayfor PCBs is biologically mediated reductive dechlorination under anaerobic conditions toless chlorinated congeners, followed by slow anaerobic and/or aerobic biodegradation(Brown and Wagner 1990, Lake et al. 1992, Lang 1992). These processes are slow, andPCBs persist in the environment for many years as complex mixtures.

Aroclor mixtures and individual congeners with low chlorine content tend to be morevolatile and soluble than those with high chlorine content. Therefore, they can be dispersed

to remote locations such as the Arctic (Tanabe et al. 1983, Gregor and Gummer 1989) andcan impact indoor air (MacLeod 1981, Oatman and Roy 1986, Vorhees et al. 1997, Curradoand Harrad 1998). PCBs exist in the air in both the gas and particle phases. Recent workdemonstrates that PCB gas/particle partitioning in air is governed primarily by PCB vaporpressures and total suspended particulate levels (Baker and Eisenreich 1990, Duinker andBouchertall 1989, Ligocki and Pankow 1989, Foreman and Bidleman 1987).

Figure 36.2 depicts PCB congener patterns in various environmental media collectedfrom the New Bedford Harbor region of Massachusetts. These patterns illustrate howheavier congeners partition to soil and dust while lighter congeners partition to air andwater. Brown and Wagner (1990) concluded that the New Bedford Harbor sediment con-gener pattern depicted in Fig. 36.2 reflects some microbial dechlorination, because the pat-

tern is shifted toward a lower-molecular-weight congener mixture than the Aroclorshistorically released to the harbor.

Only about half of the 209 congeners have been quantified in environmental samples,and even fewer are prevalent in these samples (McFarland and Clarke 1989). Congener

36.2 INDOOR POLLUTANTS

FIGURE 36.1 Structure of polychlorinated biphenyl

compounds.



POLYCHLORINATED BIPHENYLS


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POLYCHLORINATED BIPHENYLS 36.3

Indoor Air

12

10

8

6

4

2

0

Weight%

810

1

5/17

18

31

33

45

49

37

74

86

90

101

97

138

151

149

146

105

138

183

177

107

156

180

184

188

/203

195

194

206

PCB Congener Number

House Dust

12

10

8

6

4

2

0

Weight%

810

15/17

18

31

33

45

49

37

74

86

90

101

97

138

151

149

146

105

138

183

177

107

156

180

184

188/203

195

194

204

PCB Congener Number

Sediment

12

10

8

6

4

2

0

Weight%

PCB Congener Number

1 2 3 4 5 6 7 8 9 10 1112 13 1415 16 17 18 19 20 2122 2324 25 26 2728 29 30 31 32 3334 3536 3738 39 4041 42 43 44 45 4647 4849 50 51 5253 5455 56 5758 59 60

FIGURE 36.2 Example PCB congener patterns from environmental media collected near

New Bedford Harbor, Massachusetts.





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Outdoor Air

12

10

8

6

4

2

0

Weight%

810

1

5/17

18

31

33

45

49

37

74

86

90

101

97

138

151

149

146

105

138

183

177

107

156

180

184

188

/203

195

194

206

PCB Congener Number

Yard Soil

12

10

8

6

4

2

0

Weight%

810

15/17

18

31

33

45

49

37

74

86

90

101

97

138

151

149

146

105

138

183

177

107

156

180

184

188/203

195

194

204

PCB Congener Number

Drinking Water

25

20

15

10

5

0

Weight%

PCB Congener Number

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 3031 32 33 34 35 36 37 38 3940 41 42 43 44 45 46 47 4849 50 51 52 53 54 55 56 57 58 59

FIGURE 36.2 Example PCB congener patterns from environmental media collected near

New Bedford Harbor, Massachusetts. (Continued)





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patterns in environmental samples differ from Aroclors because individual congeners dif-fer in properties that affect partitioning, persistence, and bioaccumulation (Schwartz andStalling 1987, Lang 1992). In addition, PCB congeners in environmental samples mightoriginate from multiple Aroclor sources.

Historically, analytic methods and toxicological studies focused on commercial mix-tures, such as Aroclors. PCBs were quantified by matching congener patterns found in sam-ples to the most similar Aroclor pattern and reporting total PCBs. This approach is notappropriate given how mixtures change following release to the environment. Advances inanalytic chemistry during the 1980s allow identification and quantification of individualcongeners (Erickson 1997). Animal toxicological studies in the United States continue toemploy Aroclors (Brunner et al. 1996). However, in evaluating the carcinogenic potencyof PCBs, the U.S. Environmental Protection Agency (USEPA) interprets and uses studyresults after considering their applicability to congener mixtures as they exist in the envi-ronment (USEPA 1996, Cogliano 1998).

36.3 HISTORIC USES OF PCBs THAT COULD

IMPACT INDOOR AIR QUALITY

PCBs were used extensively around the world in many products. In the United States,Aroclor 1242 was used predominantly, followed by Aroclors 1016, 1254, and 1260.Table 36.1 summarizes PCB-containing products and each Aroclors percent of total U.S.production from 1957 to 1977. PCBs were used primarily as dielectric fluids in transform-ers and capacitors. They were also used in hydraulic systems, heat-transfer systems, lubri-cating oils, cutting oils, wax extenders, paints (as plasticizers), wood product coatings(to reduce flammability), carbonless copy paper, adhesives, sealants, and plastics as inksolvent/carriers (Hutzinger et al. 1974; Pomerantz et al. 1978; USEPA 1994, 1999a).


TABLE 36.1 Historic Uses of PCBs

Percent of

U.S. production

Aroclor Product (19571977)

1016 Capacitors 13

1221 Capacitors, gas transmission turbines, rubbers, adhesives 11232 Hydraulic fluids, rubbers, adhesives 1

1242 Capacitors, transformers, heat transfer, hydraulic fluids,

gas-transmission turbines, rubbers, carbonless copy paper,

adhesives, wax extenders 52

1248 Hydraulic fluids, vacuum pumps, rubbers,

synthetic resins, adhesives 7

1254 Capacitors, transformers, hydraulic fluids, vacuum pumps,

rubbers, synthetic resins, adhesives, wax extenders, dedusting

agents, inks, cutting oils, pesticide extenders, sealants and

caulking compounds 16

1260 Transformers, hydraulic fluids, synthetic resins, dedusting agents 111262 Synthetic resins 1

1268 Rubbers, synthetic resins, wax extenders 1

Source: IARC (1978); Brown (1994).





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Although PCBs are no longer used in these products, they persist in soil, sediment,biota, and old PCB-containing products such as transformers, capacitors, and paints (Welsh1995). Cycling of previously released PCBs among environmental media (e.g., soil andsediment) represents the major source of PCBs in the atmosphere (ATSDR 1999, Murphy

et al. 1985). Old PCB-containing products can also be sources if PCBs are released due toa leak, fire, or improper handling and disposal.

PCBs persist inside some public buildings, offices, and residences in old electricalappliances, fluorescent lights, paint, and building materials (USEPA 1994). Fluorescentlights and capacitors have long been recognized as potential sources of PCBs in indoor air(Staiff et al. 1970, USEPA 1979). In a public building complex, PCBs in indoor air wereattributed to ceiling tiles (Todd 1987). A 1981 study demonstrated PCB exposure insidehomes possibly due to electrical appliances (MacLeod 1981). Oatman and Roy (1986) mea-sured PCBs in the indoor air of public buildings with and without transformers. PCB-con-taining sealants and caulking materials also can impact indoor air quality (Benthe et al.1992; Balfanz et al. 1993a, 1993b; Williams et al. 1980). PCBs in the indoor air of a

Massachusetts school were attributed to joint caulking, wood fiber ceiling material, andpaint (Leung 1996).

36.4 HEALTH EFFECTS OF PCBs

Human exposure to PCBs elicits concern because of their wide range of possible cancer andnoncancer effects. The health effects associated with PCBs have been reviewed extensively(Kimbrough and Jensen 1989, Silberhorn et al. 1990, Safe 1994, Swanson et al. 1995,Longnecker et al. 1997, Rice 1997, Jacobson and Jacobson 1997, Cogliano 1998, Geisy andKannan 1998, ATSDR 1999, Brouwer et al. 1999, NRC 1999). This section provides abrief summary of this large and growing literature, emphasizing evidence of effects inhuman populations.

In occupational studies where people are generally exposed to higher PCB concentra-tions than the general population, PCB mixtures have been associated with chloracne,diverse hepatic effects, pulmonary function decrease, decrease in birthweight in children ofoccupationally exposed mothers, eye irritation, and cancer (Safe 1994).

Exposure to low-level background PCB concentrations may have subtle effects on neuro-logic development and immune function (Lawton et al. 1985, Smith 1984, Svensson et al.1994, Weisglas-Kuperus et al. 1995, Jacobson and Jacobson 1997), and, in susceptible

groups, thyroid function (Koopman-Esseboom et al. 1994). Laboratory assays suggest thatsome PCB congeners exhibit endocrine disrupting potential (Soto et al. 1995, Birnbaum1994, Brouwer et al. 1999). Members of a National Institute of Environmental HealthSciences (NIEHS) workshop recently concluded that some PCB effects demonstrated inexperimental animals can be induced at tissue concentrations near body burdens present inhuman populations exposed to background concentrations in industrialized nations (Brouweret al. 1999).

Animal studies suggest that some PCB Aroclor mixtures may cause skin irritations,reproductive and developmental effects, immunologic effects, liver damage, and cancer(ATSDR 1999, WHO 1993).

Challenges in Assessing Exposure to PCBs in Health Studies

With few exceptions, epidemiologic and animal studies focus on total PCBs or Aroclorsrather than specific congeners, despite the fact that PCBs are present in the environment as






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complex mixtures of congeners that differ from the original Aroclor mixtures. The toxicityof PCB mixtures depends on the type of congeners in the mixture and the number and posi-tion of chlorine atoms on each congener. PCB congener metabolites may also exert toxiceffects (Soto et al. 1995).

Individual congeners have been associated with dioxinlike effects, neurotoxic effects,estrogenic and antiestrogenic activity, interference with thyroid hormone homeostasis, andenzyme induction. Recognizing that risk assessments based on total PCBs may notaddress dioxinlike toxicity, USEPA advocates use of a toxic equivalency quotient (TEQ)approach to evaluate possible dioxinlike toxicity of PCB mixtures. However, several inves-tigators note that this approach does not account for PCB toxicity by other mechanisms(Safe 1994, Wolff et al. 1997). Therefore, Wolff et al. (1997) propose congener groupingsaccording to these different mechanisms for use in future epidemiologic studies. Hansen(1998) provides a detailed description of why such groupings are important to improveunderstanding of the toxicity of complex PCB mixtures.

Some studies of PCB toxicity may be confounded by other contaminants. In many stud-

ies, the polychlorinated dibenzofuran (PCDF) content of PCB test materials is not pro-vided, so its contribution to PCB-induced toxic effects is not known (Safe 1994). Inepidemiologic investigations, PCB concentrations in environmental media (i.e., food, soil,and water) might be correlated with PCDF, polychlorinated dibenzodioxin (PCDD), andmethyl mercury concentrations, which could potentially confound analyses.

Health Effects of PCBs Following Accidental Dietary Exposures

In 1968 and 1979, two Asian communities were accidentally exposed to PCBs, PCDFs,polychlorinated terphenyls (PCTs), and polychlorinated quaterphenyls (PCQs) in contam-inated rice oil (Schecter 1994). Exposed individuals developed chloracne, pigmentation ofskin and nails, swelling of limbs, jaundice, paresthesias, headache, dizziness, alteredimmunoglobulin levels, and increased incidence of lung and liver cancer. Yu et al. (1997)detected increased mortality from chronic liver disease and cirrhosis 13 years after thepoisoning incident in Taiwan and recommended additional study of the young cohort.Offspring of exposed adults were born with low body weight and exhibit slight learningdeficits and hyperactivity (Rogan et al. 1988, Chen et al. 1992, Guo et al. 1995).

In both incidents, people were primarily exposed to PCBs. However, laboratorystudies exposing rodents to simulated rice oil PCBs or reconstituted PCB and PCDFmixtures resembling the distribution of these compounds in Yusho patients show that

PCDFs were more potent than the PCBs. Safe (1994) concluded that this evidence, com-bined with the observation that some poisoning victims had serum PCB levels similarto those of industrial workers who did not exhibit adverse effects, suggests that PCDFsare the major etiologic agent in these incidents (Safe 1994).

Cancer

Human Evidence. Epidemiologic data from occupational cohorts provide mixed evi-dence of PCB carcinogenicity. In at least one of nine occupational cohorts, there was a pos-itive association between PCB exposure and the following cancer sites: rectum, liver,

biliary, pancreas, skin, prostate, kidney, brain, and the lymphatic system (Longnecker et al.1997). However, PCBs do not appear to cause consistent increases in one or more cancersin the occupational setting, except possibly kidney cancer (Longnecker et al. 1997).

Rothman et al. (1997) detected a strong dose-response relationship between PCBexposure and non-Hodgkins lymphoma in a case-control study of a nonoccupational






8/24

population. PCBs can suppress the immune system, and immunosuppression is a riskfactor for non-Hodgkins lymphoma, although only severe changes in immune functionhave been linked with this cancer (Rothman et al. 1997). The authors caution that thisfinding should be considered hypothesis-generating rather than conclusive evidence of

an association.Several epidemiologic studies examined the possible association between PCB expo-

sure and breast cancer (Krieger et al. 1994, Hunter et al. 1997, Hoyer et al. 1998, Moysichet al. 1998, Kimbrough et al. 1999). Longnecker et al. (1997) and Laden and Hunter (1998)conclude that these investigations generally do not support an association between breastcancer and PCBs.

U.S. Environmental Protection Agency Classification. USEPA concluded that there isinadequate evidence of carcinogenicity in human populations (USEPA 1999b, Bertazziet al. 1987, Brown 1987, Sinks et al. 1992). Therefore, it classified PCBs as probablehuman carcinogens (group B2) based on animal toxicity data. PCBs generally test negative

for genotoxic activity (ATSDR 1999). However, initiation-promotion studies for severalcommercial mixtures and congeners show tumor-promoting activity in the lung and liverand begin to reveal significant contributors to cancer induction (Silberhorn et al. 1990).

A 1996 study found liver tumors in female rats exposed to Aroclors 1260, 1254, 1242,and 1016, and in male rats exposed to 1260 (Brunner et al. 1996, Mayes et al. 1998). Earlierstudies detected statistically significant incidences of liver tumors in rats ingesting Aroclor1260 or Clophen A60 (Kimbrough et al. 1975, Norback and Weltman 1985, Schaeffer etal. 1984). Congeners present in the four Aroclor mixtures tested by Brunner et al. (1996)span the range of congeners most often found in environmental mixtures, although they arenot identical to any particular mixture found in the environment. PCBs suppressed tumorsin mammary glands of Sprague-Dawley rats, and enhanced tumor formation in the thyroidgland of the males and the liver of both sexes, but primarily in the liver of females (Mayeset al. 1998).

Some PCB congeners persist in the body, remaining biologically active after exposureceases (Anderson et al. 1991). In one study, rats exposed to a persistent mixture (Aroclor1260) developed more tumors than did rats exposed to a less persistent mixture (Aroclor 1016)(Brunner et al. 1996). To explore the possible effect of persistence, some rats were dosed forone year, then allowed to live one more year without exposure before being sacrificed.Brunner et al. (1996) found that one-half lifetime (i.e., 52 weeks) exposure to Aroclor 1260resulted in more than one half the tumor incidence associated with lifetime (i.e., 104 weeks)exposure. Consequently, there may be greater than proportional effects from less-than-

lifetime exposures to persistent mixtures (Cogliano 1998).Mayes et al. (1998) recommend that PCB risk assessment distinguish among differentPCB mixtures because they differ in tumor-inducing potency. In fact, current USEPA guid-ance for PCB risk assessment requires that such a distinction be made (USEPA 1999b).

Dioxinlike PCB Congeners. Several congeners appear to have 2,3,7,8-tetrachlorodibenzo-p-dioxinlike activity (Safe 1994). Strong evidence points to a common aryl hydrocarbon(Ah)-receptor signal transduction pathway mechanism of action. A toxic equivalency (TEQ)approach has been developed to represent the fractional toxicity of PCB congeners relative toTCDD for congeners exhibiting the following characteristics:

Structurally similar to PCDDs and PCDFs Bind to the Ah receptor

Elicit dioxin-specific biochemical and toxic responses

Persistent and accumulate in the food chain (Van den Berg et al. 1998).






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Immune System Effects

Svensson et al. (1994) and Weisglas-Kuperus et al. (1995) found that PCB exposure canresult in alteration of lymphocyte subtypes, but these changes were detected in populations

where dioxins or fatty acids from fish might confound the PCB-lymphocyte relationship.PCB exposure was associated with the frequency of infectious illness in the first 4 monthsof life in a Wisconsin cohort (Smith 1984), but not in a Dutch cohort of breastfed infants inthe first 18 months of life (Weisglas-Kuperus et al. 1995).

Endocrine System Effects

The National Research Council (NRC) reviewed (1999) the potential endocrine-disruptingeffects of PCBs and other hormonally active compounds. Specifically, the NRC summa-rized evidence of reproductive, immunotoxic, estrogenic, and carcinogenic effects related

to disruption of endocrine function.PCB congeners may be estrogenic (Soto et al. 1995, Li and Hansen 1995) or antiestro-

genic (Moore et al. 1997). Exposure to PCBs is associated with decreased thyroid hormonelevels (Koopman-Esseboom et al. 1994, Desaulniers et al. 1997). In mothers and their chil-dren from Rotterdam, background PCB exposures were associated with lower maternal T3and T4 levels and higher infant TSH levels (Koopman-Esseboom et al. 1994). However,hormone levels were within normal limits and observed associations might be due to diox-ins, which were highly correlated with PCB concentrations (Longnecker et al. 1997).Morse et al. (1996) found that orally administered doses of Aroclor 1254 were associatedwith decreases in fetal, neonatal, and weanling plasma total thyroxine and brain T4 con-centrations, possibly due to selective accumulation of a hydroxylated PCB metabolite in

fetal plasma and brain.Some adverse effects may be thyroid-mediated. Haddow et al. (1999) found that undiag-

nosed hypothyroidism in pregnant women may adversely affect their fetuses, possibly byimpaired neuropsychological development. In addition, in utero exposure to PCBs has beenlinked to reduced serum concentrations of thyroid hormones (Koopman-Esseboom et al.1994). Goldey et al. (1995) prenatally exposed rats to Aroclor 1254, causing a reduction in cir-culating thyroid hormones that might have resulted in observed hearing deficits. This evidencecollectively suggests that prenatal PCB exposure could cause adverse effects via thyrotoxicity.

Dermatologic EffectsRelatively high occupational exposures have been associated with chloracne and other skinabnormalities (Meigs et al. 1954, Fischbein et al. 1982). Consistency among studies leaveslittle doubt that PCBs cause chloracne (Longnecker et al. 1997).

36.5 U.S. ENVIRONMENTAL PROTECTION

AGENCY TOXICITY CRITERIA FOR PCBs

Carcinogenic Effects

USEPA recommends a tiered approach to assess cancer risk associated with exposure toPCBs (USEPA 1999b). Studies to date suggest that more highly chlorinated, less volatile






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congeners are associated with greater cancer risk. These congeners tend to persist in theenvironment in soils and sediment and bioaccumulate in biota. If congener data are notavailable, the exposure pathway can be used to indicate how the potency of a mixture mighthave changed following release to the environment. For example, more volatile, less chlo-

rinated congeners are more likely to be metabolized and eliminated than are highly chlori-nated congeners that persist in environmental media and bioaccumulate in biota.

Therefore, a higher cancer slope factor [upper-bound estimate 2.0 per (mgkg)/day,central estimate 1.0 per (mgkg)/day] is used to evaluate risk from exposure to highlychlorinated congeners or exposure via pathways that tend to involve highly chlorinatedcongeners. This higher slope factor is used for (1) food-chain exposure; (2) sediment or soilingestion; (3) dust or aerosol inhalation; (4) dermal exposure, if an absorption factor hasbeen applied; (5) presence of dioxinlike, tumor-promoting, or persistent congeners; and (6)early-life exposure (all pathways and mixtures).

A lower cancer slope factor [upper-bound estimate 0.4 per (mgkg)/day, centralestimate 0.3 per (mgkg)/day] is used for more volatile PCB congener mixtures that are

less persistent. This lower slope factor is used for (1) ingestion of water-soluble congeners,(2) inhalation of evaporated congeners, and (3) dermal exposure, if no absorption factor hasbeen applied.

If congener or isomer analyses verify that congeners with more than four chlorinescomprise less than 0.5 percent of total PCBs, USEPA (1999b) recommends use of aneven lower cancer slope factor [upper-bound estimate 0.07 per (mgkg)/day, centralestimate 0.04 per (mgkg)/day].

Cogliano (1998) states that bioaccumulated PCBs appear to be more toxic than Aroclors(Aulerich et al. 1986, Hornshaw et al. 1983) and more persistent in the body (Hovinga etal. 1992). However, cancer studies to date use Aroclor mixtures as test materials; therefore,Cogliano (1998) recommends conducting a cancer study comparing commercial and bioac-cumulated PCB mixtures.

With congener data, the slope factor approach can be supplemented by analysis ofdioxin TEQs to evaluate dioxinlike toxicity. USEPA recommends that risks from dioxin-like congeners should be added to risks from the rest of the mixture estimated using anappropriate PCB cancer slope factor. However, because PCB test materials used in the1996 cancer study contain some amount of dioxinlike congeners as well as PCDDs andPCDFs (Mayes et al. 1998), adding these risks together could be overly conservative if thePCB carcinogenicity is due, at least in part, to the dioxinlike congener content.

Noncarcinogenic Effects

Table 36.3 lists reference doses (RfDs) for PCBs. USEPA defines RfDs as estimates (withuncertainty spanning perhaps an order of magnitude) of a daily exposure to the human pop-ulation (including sensitive subgroups) that is likely to be without appreciable risk ofadverse effects. RfDs are compared to estimates of average daily dose to determine whethernoncancer effects are likely to occur. RfDs assume that a concentration or dose thresholdexists, below which no adverse effects are expected.

USEPA last revised the RfDs in Table 36.3 in November 1996. The RfD for Aroclor1016 is based on studies of perinatal toxicity and long-term neurobehavioral effects ininfant monkeys. In this study, decreased birthweight and possible neurologic impairment

were observed among infants born to exposed monkeys. The Aroclor 1254 RfD also isbased on a study of monkeys. Preliminary analysis of reproduction and histopathology datasuggest that effects on female reproductive function may occur at doses as low as 0.005(mgkg)/day and the RfD is derived from this value.






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TABLE

36.3

U.S.EnvironmentalProtectionAgencyReferenceDoses(R

fDs)forPCBs

ChronicoralRfD,

Targ

etorganor

Uncerta

inty

CASnumber

Compound

(mgkg)/day

Studytype

criticaleffect

modifying

factors

1336-36-3

Polychlorinatedbiphen

yls

*

12674-11-2

Aroclor1016

7.0031025

M

onkeyreproductive

Reducedbirthweights

100

bioassay

11104-28-2

Aroclor1221

NA

11141-16-5

Aroclor1232

NA

53469-21-9

Aroclor1242

NA

12672-29-6

Aroclor1248

NA

11097-69-1

Aroclor1254

2.0031025

M

onkeyclinicaland

Ocularexudate;inflamed

300

immunologic

andprominent

studies

Meibomianglands;

distortedgrowthof

finger-andtoenails;

decreasedantibody

responsetosheep

erythrocytes

11096-82-5

Aroclor1260

NA

*App

ropriateAroclormixtureRfDisusedtoevaluatenoncancerrisk.

Not

available.

Sour

ce:

U.S.EPAIntegratedRiskInform

ationSystemDatabase,1999.

36.13





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Both RfDs were revised in 1996, but the PCB toxicity literature continues to grow. Theyare both based on animal studies rather than human studies, primarily because it is notpossible to specify the type of PCB mixture, pattern of exposure, and route of exposure inmost human studies.

36.6 INDOOR AIR PCB CONCENTRATIONS

Table 36.4 summarizes indoor air concentrations of PCBs reported in the literature foroffices, homes, and laboratories. Outdoor air concentrations were provided where thesemeasurements were collected simultaneously. Indoor air concentrations typically exceedoutdoor air concentrations by at least a factor of 10. Except for indoor environments withknown PCB sources, measurements in the mid- to late 1990s (Vorhees et al. 1997) arelower than measurements made in the early to mid-1980s (MacLeod 1981, Oatman and

Roy 1986). Comparison of these numbers is complicated by the differing laboratory ana-lytic and PCB quantification techniques used. However, the difference might reflect a gen-eral decline since the mid-1980s as the number of possible PCB sources decreases.

PCB concentrations as high as 580 ng/m3 have been measured in the indoor air of homesnot identified as being affected by any local PCB source (MacLeod 1981). Much higherPCB concentrations have been measured in buildings with known PCB sources. For exam-ple, Balfanz et al. (1993a, 1993b) measured indoor air levels as high as 7500 ng/m3 in build-ings with PCB-containing permanently elastic sealant composed of about 40% PCBs byweight. Fromme et al. (1996) measured PCB concentrations as high as 7360 ng/m 3 inschool community rooms with PCB-containing caulking compound.

Offices, Schools, and Laboratories

Canadian Laboratories. Williams et al. (1980) measured PCB concentrations in a labo-ratory in Ottawa where PCBs contaminated sample blanks. Air samples as well as caulk-ing material samples were analyzed to isolate the source of PCBs in sample blanks. Indoorair samples were collected on Florisil and a filter using MDA Accuhaler, model 808, per-sonal sampling pumps at rates from 1 to 2 L/min. PCBs were quantified using gas chro-matography with electron-capture detection.

Concentrations in the laboratory ranged from 120 to 320 ng/m3. Levels elsewhere in the

laboratory building ranged from 21 to 294 ng/m3

. Chromatograms for indoor air samplesresembled Aroclor 1254. The caulking material contained 28 to 36% PCBs, also exhibitingan Aroclor 1254 congener pattern. The PCBs contaminating sample blanks were attributedto this caulking material.

North Carolina Office Buildings and Laboratories. MacLeod (1981) measured PCBconcentrations in an industrial research facility, an academic laboratory building, and ashopping complex. Outdoor air concentrations were measured outside two laboratorybuildings when indoor and outdoor air temperatures were similar. All laboratories andoffices contained fluorescent lights.

Indoor air samples were collected on polyurethane foam plugs (PUFs, 0.022 g/m3 den-

sity), using the low-volume mine safety appliance (MSA) portable pump model S and theDu Pont constant-flow sampling pump model P4000A. Sampling rates ranged from 2.5 to4.0 L/min for 8- to 16-h sampling periods. Outdoor air samples also were collected onPUFs, using a Bendix hurricane pump to collect at rates of 100-500 L/min. Samplers were






15/24

TABLE36.4

PCBConcentrationsMeasuredinIndoorAir*

IndoorAir

OutdoorAir

Mean

Mean

(standarddeviation),


Loc

ation

ng/m3

Range,ng/m3

ng/m3

Ra

nge,ng/m3

Ref.

LaboratoryinOttawa,Canada

withPCB-containingcaulking

Laboratory

265

68

120320

Williamsetal.(19

80)

Basement

108

81

44294

Floor1

63

37

21124

Floor2

72

30

26128

Floor3

96

48

41200

NorthCarolina

MacLeod(1981)

Laboratories

200240

418

Laboratoryoffices

80110

Shoppingcomplexoffice

44

Homes

Kitchen

NA

150580

4

Livingro

om

39

Bedroom

170

Basement

120

Library

400

Garage

64

Minnesota

OatmanandRoy(1986)

Buildingsw

ithtransformers

460

220

Offices

192881

Laboratory

498

355628

OatmanandRoy(1986

)

36.15





16/24

TABLE36.4

PCBConcentrationsMeasuredinIndoorAir(Continued)

IndoorAir

OutdoorAir

Mean

Mean



Loc

ation

ng/m3

Range,ng/m3

ng/m3

Ra

nge,ng/m3

Ref.

Buildingsw

ithout

transformers

230

110

Offices

78384

Schools

114303

OfficebuildinginGermany

withPCB-containingsealant

440

355

1250(maximum)

Bentheetal.(1992

)

OfficebuildingsinGermany

Balfanzetal.

withPCB-containingsealant

120

0

407500

(1993a,1993b)

Communityro

omsofschools

andchildcarecenters

inGermanywith

PCB-containin

gsealant

114

7360(maximum)

Frommeetal.(1996)

PublicbuildingsinIndiana

6490

1.5

Wallaceetal.(199

6)

HomesinMas

sachusetts

Vorheesetal(1997)

NearSup

erfundsite

181.8

7.961

4.94.6

0

.453

(n18)

14miawayfrom

101.8

5.251

0.63.3

0.18.2

Superfundsite(n

16)

*Blankcells()indicatestatisticnotavailable.

Geometric

meangeometricstandarddeviation.

36.16





17/24

positioned 1 to 2 m above the floor. All laboratory analyses of PUF extracts wereconducted using a Tracor 222 gas chromatograph equipped with a 63Ni electron-capturedetector. PCB concentrations were reported as Aroclors 1242 and 1254.

Average laboratory indoor air concentrations exceeded outdoor air concentrations by a

factor of 5. Laboratory indoor air concentrations ranged from 200 to 240 ng/m3, higher thanthose in the laboratory offices (80 to 110 ng/m3). PCB concentrations in the shopping cen-ter office were lower, with a mean of 44 ng/m3.

Minnesota Office Buildings and Schools. Oatman and Roy (1986) provided backgroundconcentrations of PCBs in five state-owned office buildings and two elementary schools in1984. All buildings used fluorescent lighting. All samples were collected on PUFs, using aBendix high-volume pump to collect at rates of 570 to 590 L/min. Samplers were posi-tioned 0.75 m above the floor. Both PUFs and filters were extracted for analysis with aVarian 3700 gas chromatograph equipped with a 63Ni electron-capture detector. PCB con-centrations were reported as Aroclors 1242 and 1254.

The average PCB concentration in buildings with transformers exceeded the concentra-tion in buildings without transformers by a factor of2 (460 and 230 ng/m3, respectively).Overall, concentrations were slightly higher than those measured by MacLeod (1981).

German Office Buildings. Benthe et al. (1992) measured indoor air PCB concentrationsin an office building where a PCB-containing sealant was used to join fabricated concreteelements. Samples were collected on Florisil at a sampling rate of 2.5 L/min. Analyses wereconducted with a Varian gas chromatograph 3500 equipped with an electron capture detec-tor. Indoor air concentrations in 45 rooms ranged from non-detected values to 1200 ng/m3.Nearly all of these concentrations were contributed by the most volatile congeners.

Balfanz et al. (1993a, 1993b) measured PCB concentrations in more than 100 buildingsin Germany with PCB-containing permanently elastic materials. These products were usedmainly in buildings constructed from fabricated concrete. Some buildings also containedparticleboard ceiling panels with PCB-containing coatings.

Samples were collected on polyurethane foam plugs and glass fiber filters at a samplingrate of about 50 L/min. Both PUFs and filters were extracted for analysis with a Hewlett-Packard model 5890 gas chromatograph equipped with an electron capture detector. About80 percent of PCBs passed the filter and adsorbed onto the PUFs.

Concentrations were reported for six PCB congeners: IUPAC (International Union ofPure and Applied Chemistry) numbers 28, 52, 101, 153, 138, and 180. Detected concen-trations for the sum of these congeners ranged from 40 to 7500 ng/m3 (Balfanz 1993a,

1993b). The more volatile the PCB commercial mixture contained in the sealant, the higherthe measured indoor air PCB concentration.

German Schools and Childcare Centers. Fromme et al. (1996) collected indoor air sam-ples in German schools and childcare centers to determine any impacts from PCB-contain-ing elastic sealants. Average PCB concentrations in 308 community rooms of schoolsexceeded concentrations in 102 childcare centers by about a factor of 4 (geometric meansof 230 and 48 ng/m3, respectively. About 15 percent of schools and 3 percent of childcarecenters had concentrations greater than 300 ng/m3, and 5 percent of schools had concen-trations greater than 3000 ng/m3, the level warranting intervention under German law.

Indiana University Offices and Laboratories. Wallace et al. (1996) collected indoor airsamples from a number of public buildings on the Indiana University campus from 1987 to1995. One high-volume and two low-volume sampling techniques were used over thisperiod. Two techniques employed PUFs, while one low-volume technique involved a






18/24

diffusion denuder. All samples were analyzed with a Hewlett-Packard model 5890 gaschromatograph with an electron-capture detector.

Outdoor air PCB concentrations ranged from 1 to 2 ng/m3. Indoor air PCB concentra-tions sometimes exceeded outdoor air concentrations by a factor of 100. Indoor air PCB

concentrations were highly correlated with building construction date. The highest con-centrations were detected in the oldest buildings constructed prior to the ban on manufac-ture and use of PCBs. Capacitors might be the source of PCBs measured in this study.However, other sources (e.g., PCB-containing caulks and sealants) could not be ruled out.

Residences

North Carolina Residences. In addition to laboratory and office measurements,MacLeod (1981) measured PCB concentrations in nine private residences, using the samesampling and analytic methods. PCB concentrations were reported as Aroclors 1242 and1254. Outdoor air concentrations were measured outside one home when indoor and out-door air temperatures were similar.

Indoor air concentrations ranged from 39 to 580 ng/m3. The air outside one home con-tained 4-ng/m3 PCBs while indoor air collected on the same day contained 310 ng/m3, a fac-tor of10 higher than the outdoor air. Four of the nine homes sampled had pre-1972fluorescent lighting fixtures in their kitchens, but there was no correlation between lightingand PCB concentrations. MacLeod (1981) postulated that electrical appliances might be thesource of PCBs detected in this study.

Residences Near the New Bedford Harbor Superfund Site. Vorhees et al. (1997) ana-

lyzed PCB concentrations and congener patterns in indoor and outdoor air in homes sur-rounding the New Bedford Harbor Superfund site during dredging of highly contaminatedharbor sediments. PCBs volatilize from harbor sediments or waters, exposing residents liv-ing in nearby neighborhoods. The study was conducted while the most highly contaminatedsediments (hot spot sediments) were dredged and piped to a confined disposal facility(CDF) along the western shoreline of the harbor about 1.5 km south of dredging activity(Fig. 36.3). The study assessed PCB levels in residential indoor air during disturbance ofthese highly contaminated harbor sediments. PCBs are ubiquitous in the environment(Eisenreich et al. 1981; Gregor and Gummer 1989; Hoff et al. 1992a, 1992b). Therefore,samples were collected concurrently in an appropriate comparison neighborhood removedfrom the harbor to discern the portion of contamination attributable to harbor proximity.

Indoor and outdoor air samples were collected for 34 homes between April 1994 andApril 1995 on days when harbor dredging was scheduled (Fig. 36.3). These homes wererecruited from five neighborhoods: three harbor neighborhoods (Acushnet, Fairhaven, andNew Bedford hot spot) immediately downwind of the hot spot and CDF (based on pre-vailing winds during fair weather when warm temperatures induce the greatest amount ofvolatilization from sediments and water) and two comparison neighborhoods (Dartmouthand New Bedford downtown). On each sampling day, two homes were sampled: one har-bor neighborhood home and one comparison neighborhood home. Because higher PCBconcentrations have been measured historically in urban areas than in rural areas(Eisenreich et al. 1981), rural Dartmouth homes were paired with rural Acushnet andFairhaven homes and urban New Bedford downtown homes were paired with urban New

Bedford hot spot neighborhood homes. Outdoor air samples were collected concurrentlyfrom a central site in each neighborhood (Fig. 36.3).

All samples were collected on quartz fiber filters followed by PUFs. Indoor air samplingrates ranged from 5 to 10 L/min, while outdoor airflow rates ranged from 190 to 230 L/min.






19/24

All analyses were conducted with a Hewlett-Packard 5890 series II gas chromatograph,

using a 63Ni electron-capture detector.

Indoor Air and Outdoor Air PCB Concentrations. On each sampling day, 24-h indoorand outdoor air samples were collected simultaneously and analyzed for 65 PCB congeners


FIGURE 36.3 Residential indoor air and outdoor air sampling locations (Vorhees et al. 1997).





20/24

to evaluate the relative importance of the harbor and indoor sources for human inhalationexposure. Outdoor air concentrations were highest in neighborhoods closest to the harbor (0.4to 53 ng/m3) and contained slightly higher proportions of volatile PCB congeners comparedto outdoor air concentrations from comparison neighborhoods (0.1 to 8.2 ng/m3). Indoor air

concentrations in homes near the most contaminated part of the harbor (7.9 to 61 ng/m3) wereslightly higher than concentrations in homes distant from this area (5.2 to 51 ng/m3).

In all neighborhoods, indoor air concentrations exceeded corresponding outdoor airconcentrations (mean ratio 32), suggesting the importance of indoor PCB sources evennear a highly contaminated waste site. Figure 36.4a and b depicts daily indoor and corre-sponding outdoor air PCB concentrations for all harbor and comparison homes, respec-tively. With few exceptions, indoor air concentrations exceed outdoor air concentrations,regardless of neighborhood. In winter, these ratios increase, probably because colder out-door temperatures reduce PCB volatilization from outdoor sources, while indoor tempera-tures remain relatively constant throughout the year. Indoor air PCB concentrations werenot found to be significantly correlated with outdoor air PCB concentrations, regardless of

neighborhood. Indoor air and outdoor air PCB concentrations in harbor neighborhoodsoften exceed concentrations in comparison neighborhoods.

PCB Concentrations and Congener Patterns on Filters. Filters were analyzed for a sub-set of indoor and outdoor air samples collected over the range of ambient temperatures thatoccurred during the study. The results of this filter analysis were used to assess the congenerpattern and PCB mass fraction retained on filters under different sampling conditions. Filtersare expected to collect the particulate-phase PCBs while gas-phase PCBs adsorb to the PUF.However, separation of the gas- and particulate-phase PCBs is hindered by the samplingprocedures used in this study and most others (high-volume air sampling using a filter andsolid adsorbent). Previous studies in which PCBs were quantified on both filters and PUFsfrom the type of high-volume air sampler used in this study demonstrate that nearly all thePCB mass ends up in the PUF (Ligocki and Pankow 1989, Manchester-Neesvig and Andren1989, Foreman and Bidleman 1990), where the rate of particulate-phase PCB loss fromfilters is primarily a function of sampler flow rate and ambient temperature.

In this study, sampling condition differences in indoor and outdoor environments couldresult in different congener patterns and masses on filters. The indoor sampler flow rate islower and subject to more constant indoor temperatures relative to outdoor temperatures.Gas/particle concentration ratios for PCBs rise with temperature (Manchester-Neesvig andAndren 1989); therefore winter air filters may contain more PCBs than do filters collectedin summer.

On average, indoor air filters (n

12) contained 6 percent of the PCB mass found oncorresponding PUFs, while outdoor air filters (n 12) contained only 1 percent. No obvi-ous pattern difference was observed between indoor and outdoor air pairs, regardless ofoutdoor temperature during sampling. As other investigators have detected (Foreman andBidleman 1990, Hoff 1992a, Duinker and Bouchertall 1989, Burdick and Bidleman 1981),all indoor and outdoor air filter congener patterns consistently show a higher proportion ofmore highly chlorinated congeners than PUF congener patterns.

Influences on Indoor Air PCB Concentration. Although indoor air PCB concentrationsappear to be affected by neighborhood location, other factors may influence indoor PCBlevels. These factors include the number of potential indoor PCB sources present during

sampling and past or present occupational exposure to PCBs of residents. Residents wereasked to provide their occupational histories and the number of potential PCB sources intheir homes so that the relationship between these factors and indoor air PCB concentrationcould be explored.






21/24

Potential indoor sources were defined as electrical appliances and fluorescent lightsmore than 10 years old. No significant correlation was found between indoor air concen-tration and the number of potential indoor PCB sources reported by residents. The non-significant test result must be considered in light of the fact that electrical appliances and


(a)

(b)

FIGURE 36.4 Comparison of indoor air and outdoor air PCB concentrations for homes located (a) adja-

cent to New Bedford Harbor in Massachusetts and (b) in Dartmouth, Massachusetts, nearly 4 mi away fromNew Bedford Harbor.





22/24

fluorescent lights are the most obvious PCB sources, but do not necessarily represent allpossible indoor sources.

Three residents with occupational exposure lived in harbor neighborhoods. Of the threehomes with residents who were occupationally exposed to PCBs, one resident was cur-

rently employed in a PCB-using industry, one had not worked for 13 years, and the thirdresident had not worked for 30 years. After excluding these three homes, harbor and com-parison indoor air concentrations were still significantly different (p 0.008). This resultsuggests some influence of harbor contamination on indoor air.

PCB Congener Patterns in Indoor Air and Outdoor Air. Volatility decreases and molec-ular weight generally increases with increasing IUPAC congener number. Therefore, it is notsurprising that congener patterns reflect a high proportion of the most volatile congeners.Figure 36.5 compares average congener weight-percent patterns in indoor air and outdoor air.In 30 of 34 homes, congener patterns in indoor air closely resemble the patterns in outdoorair. However, Fig. 36.5 shows a slightly higher proportion of more volatile congeners in out-

door air compared to indoor air. This difference reflects four homes with congener patternsthat include high proportions of less volatile congeners. Indoor air in one home closely resem-bled Aroclor 1254. These heavier patterns may suggest indoor sources.

Importance of Exposure to PCBs in Indoor Air

There are no applicable indoor air quality guidelines for PCBs in private or public build-ings. Occupational limits for PCBs are listed in Table 36.5. Indoor air PCB concentrationsin Table 36.4 do not exceed regulatory limits, except in buildings with known indoor PCBsources. However, occupational limits are applicable to 8-h/day exposure periods for adultsand do not necessarily protect against adverse health effects for commercial and residentialexposure scenarios.

Office and laboratory concentrations ranged from 6 to 7500 ng/m3. Potential cancer riskfor adults associated with these concentrations can be calculated using standard USEPAdefault exposure parameters for the workplace, the average daily inhalation dose equation(USEPA 1989), and the cancer slope factor of 0.4 (mgkg)/day for inhalation exposure(USEPA 1999b). Using this information, potential cancer risk estimates range from 4 107

to 5 104 for this range of indoor air concentrations. Residential concentrations range from5 to 580 ng/m3. Potential cancer risk estimates associated with these concentrations rangefrom 5 107 to 7 105. The non-cancer-hazard quotient for adult residents ranges from

0.07 to 2.3; a hazard quotient of 1 is typically the upper bound that is acceptable to regula-tory authorities. These hazard quotients were estimated using the RfD for Aroclor 1016because this commercial mixture might more closely resemble congener patterns in air thandoes Aroclor 1254.

The highest potential cancer risk estimates (i.e., 5 in 10,000 and 7 in 100,000) andpotential noncancer hazard estimates (i.e., 2.3) represent levels of possible concern tomany federal and state regulatory authorities. However, people are likely to experiencegreater risk from consumption of PCB-contaminated seafood, meats, and dairy products.

36.7 REDUCING EXPOSURE TO PCBs IN

INDOOR AIR

The ubiquitous nature of PCB contamination makes it difficult to reduce exposure. However,indoor air PCB concentrations appear to be declining over time as PCB-containing materials






23/24

FIGURE36.5

ComparisonofindoorairandoutdoorairPCBcongenerpatterns.Errorbarsindicateonestandarddeviation.

68

19

18

15/17

24/27

16

26

31

28

33

2245

52

49

44

37

41

74

70

66

95

60

84

101

99

97

87

136

77/110

151

135

149

118

146

153

105

141

138

187

183

128

167

174

177

171

156

157/201

180

36.23





24/24

are gradually discarded. Despite this trend, some buildings have unacceptably high concen-trations of PCBs in indoor air (Balfanz et al. 1993a, 1993b; Fromme et al. 1996). Indoor airexposure to PCBs can be reduced by properly disposing of old appliances, fluorescent light-ing, and other indoor sources of PCBs. Track-in of PCBs from the outdoor environmentcan be decreased through use of doormats and removal of shoes on entering buildings. PCB-containing building materials are more difficult to identify and remove. Therefore, thesePCB sources might impact indoor air for some time.

ACKNOWLEDGMENTS

Portions of the research described in this section were made possible by grant 5 P42 ES-05947 from the National Institute of Environmental Health Sciences, NIH, with fundingprovided by USEPA and a grant from the Harvard Center for Risk Analysis. Its contentsare the sole responsibility of the author and do not necessarily represent the official viewsof the NIEHS, NIH, or USEPA. The contributions of Alison C. Cullen, Sc.D., Larisa M.Altshul, Jeffrey Silverman, Craig De Ruisseau, Raisa Stolyar, and Thomas Dumyahn aregreatly acknowledged and appreciated.

REFERENCES

Agency for Toxic Substances and Disease Registry (ATSDR). 1999. Toxicological Profile forPolychlorinated Biphenyls (update). Draft for public comment.

American Conference of Governmental Industrial Hygienists (ACGIH). 1999. Guide to OccupationalExposure Values1999. Cincinnati, OH: ACGIH, Inc.


TABLE 36.5 Occupational Regulations and Guidelines for PCB Indoor Air Concentrations

Agency or Chlorodiphenyl Chlorodiphenyl

government Acronym* 42% chlorine, mg/m3 54% chlorine, mg/m3

U.S. Occupational PEL-TWA 1 0.5

Safety and Health

Administration

(OSHA)

U.S. National REL-TWA 0.001 0.001

Institute of

Occupational Safety

and Health (NIOSH)

American Conference TLV-TWA 1 0.5

of Governmental

Industrial Hygienists(ACGIH)

Federal Republic of MAK-TWA 1.1 0.7

Germany (former)

*Key: MAKmaximum concentration values in the workplace; PELpermissible exposure limit; RELrec-

ommended exposure limit; TLVthreshold limit value; TWAtime-weighted average exposure concentration fora conventional 8-h (TLV, PEL) or up to a 10-h (REL) workday and a 40-h workweek.

Source: ACGIH (1999).


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