2.1 General characteristics
PCBs are a group of synthetic aromatic compounds which contain a varying number of chlorine atoms substituted on a biphenyl molecule (Figure 1). In theory, there are 209 possible PCB isomers and congeners (Table 1). It is unlikely that all of them will be formed in the chlorination process; nevertheless, commercially produced PCBs (e.g., Aroclors) are a complex mixture of chlorobiphenyls (Table 2).
Several industrialised countries produced PCBs, which were marketed under various trade names (Table 3). By far, most of the available information in the literature is on Aroclors. These PCB preparations were produced in North America by Monsanto Corporation; no PCBs have been produced in North America since 1977, although some are still being produced in Europe (Hutzinger et al., 1974; McDonald and Tourangeau, 1986). All Aroclor formulations are characterised by a four digit number. The first two digits indicate the type of molecule (e.g., 12 indicates a biphenyl molecule), whereas the last two digits give the percent of chlorine by weight substituted on the molecule. For instance, Aroclor 1242 (abbreviated as A1242 or A-1242 in the text to follow) is a mixture of chlorinated biphenyls containing 42% of chlorine by weight. The product Aroclor 1016, which is also a mixture of chlorinated biphenyls, is an exception to this rule (see Tables 2 and 5 below). There exist other Aroclor products such as Aroclor 5442 which are mixtures of chlorinated terphenyls, but may contain chlorinated biphenyls as well (Hutzinger et al., 1974).
Most individual chlorobiphenyls are solids at room temperature, whereas the commercial mixtures are mobile oils (e.g., A-1221, A-1232, A-1242, and A-1248), viscous fluids (e.g., A-1254), or sticky resins (e.g., A-1260 and A-1262) (Hutzinger et al., 1974). The outstanding characteristics of PCBs are their (i) thermal stability, (ii) resistance to oxidation, acids, bases, and other chemical agents, and (iii) excellent dielectric properties. Other important properties of PCBs from an environmental point of view relate to their solubility and volatility.
FIGURE
1
STRUCTURE AND NOMENCLATURE OF POLYCHLORINATED
BIPHENYLS
|
TABLE 1 Systematic (IUPAC)
Numbering of Polychlorinated Biphenyl Compounds |
|||||||
|
No. |
Structure |
No. |
Structure |
No. |
Structure |
No. |
Structure |
|
Monochlorobiphenyls |
51 |
2,2',4,6' |
105 |
2,3,3',4,4' |
159 |
2,3,3',4,5,5' | |
|
1 |
2 |
52 |
2,2',5,5' |
106 |
2,3,3',4,5 |
160 |
2,3,3',4,5,6 |
|
2 |
3 |
53 |
2,2',5,6' |
107 |
2,3,3',4',5 |
161 |
2,3,3',4,5',6 |
|
3 |
4 |
54 |
2,2',6,6' |
108 |
2,3,3',4,5' |
162 |
2,3,3',4',5,5' |
|
Dichlorobiphenyls |
55 |
2,3,3',4 |
109 |
2,3,3',4,6 |
163 |
2,3,3',4',5,6 | |
|
4 |
2,2' |
56 |
2,3,3',4' |
110 |
2,3,3',4',6 |
164 |
2,3,3',4',5',6 |
|
5 |
2,3 |
57 |
2,3,3',5 |
111 |
2,3,3',5,5' |
165 |
2,3,3',5,5',6 |
|
6 |
2,3' |
58 |
2,3,3',5' |
112 |
2,3,3',5,6 |
166 |
2,3,4,4',5,6 |
|
7 |
2,4 |
59 |
2,3,3',6 |
113 |
2,3,3',5',6 |
167 |
2,3',4,4',5,5' |
|
8 |
2,4' |
60 |
2,3,4,4' |
114 |
2,3,4,4',5 |
168 |
2,3',4,4',5',6 |
|
9 |
2,5 |
61 |
2,3,4,5 |
115 |
2,3,4,4',6 |
169 |
3,3',4,4',5,5' |
|
10 |
2,6 |
62 |
2,3,4,6 |
116 |
2,3,4,5,6 |
Heptachlorobiphenyls |
|
|
11 |
3,3' |
63 |
2,3,4',5 |
117 |
2,3,4',5,6 |
170 |
2,2',3,3',4,4',5 |
|
12 |
3,4 |
64 |
2,3,4',6 |
118 |
2,3',4,4',5 |
171 |
2,2',3,3',4,4',6 |
|
13 |
3,4' |
65 |
2,3,5,6 |
119 |
2,3',4,4',6 |
172 |
2,2',3,3',4,5,5' |
|
14 |
3,5 |
66 |
2,3',4,4' |
120 |
2,3',4,5,5' |
173 |
2,2',3,3',4,5,6 |
|
15 |
4,4' |
67 |
2,3',4,5 |
121 |
2,3',4,5',6 |
174 |
2,2',3,3',4,5,6' |
|
Trichlorobiphenyls |
68 |
2,3',4,5' |
122 |
2',3,3',4,5 |
175 |
2,2'3,3',4,5',6 | |
|
16 |
2,2',3 |
69 |
2,3',4,6 |
123 |
2',3,4,4',5 |
176 |
2,2',3,3',4,6,6' |
|
17 |
2,2',4 |
70 |
2,3',4',5 |
124 |
2',3,4,5,5' |
177 |
2,2',3,3',4',5,6 |
|
18 |
2,2',5 |
71 |
2,3',4',6 |
125 |
2',3,4,5,6' |
178 |
2,2',3,3',5,5',6 |
|
19 |
2,2',6 |
72 |
2,3',5,5' |
126 |
3,3',4,4',5 |
179 |
2,2',3,3',5,6,6' |
|
20 |
2,3,3' |
73 |
2,3',5',6 |
127 |
3,3',4,5,5' |
180 |
2,2',3,4,4',5,5' |
|
21 |
2,3,4 |
74 |
2,4,4',5 |
Hexachlorobiphenyls |
181 |
2,2',3,4,4'5,6 | |
|
22 |
2,3,4' |
75 |
2,4,4',6 |
128 |
2,2',3,3',4,4' |
182 |
2,2',3,4,4',5,6' |
|
23 |
2,3,5 |
76 |
2',3,4,5 |
129 |
2,2',3,3',4,5 |
183 |
2,2',3,4,4',5',6 |
|
24 |
2,3,6 |
77 |
3,3',4,4' |
130 |
2,2',3,3',4,5' |
184 |
2,2',3,4,4',6,6' |
|
25 |
2,3',4 |
78 |
3,3',4,5 |
131 |
2,2',3,3',4,6 |
185 |
2,2',3,4,5,5',6 |
|
26 |
2,3',5 |
79 |
3,3',4,5' |
132 |
2,2',3,3',4,6' |
186 |
2,2',3,4,5,6,6' |
|
27 |
2,3',6 |
80 |
3,3',5,5' |
133 |
2,2',3,3',5,5' |
187 |
2,2',3,4',5,5',6 |
|
28 |
2,4,4' |
81 |
3,4,4',5 |
134 |
2,2',3,3',5,6 |
188 |
2,2',3,4',5,6,6' |
|
29 |
2,4,5 |
Pentachlorobiphenyls |
135 |
2,2',3,3',5,6' |
189 |
2,3,3',4,4',5,5' | |
|
30 |
2,4,6 |
82 |
2,2',3,3',4 |
136 |
2,2',3,3',6,6' |
190 |
2,3,3',4,4',5,6 |
|
31 |
2,4',5 |
83 |
2,2',3,3',5 |
137 |
2,2',3,4,4',5 |
191 |
2,3,3',4,4',5',6 |
|
32 |
2,4',6 |
84 |
2,2',3,3',6 |
138 |
2,2',3,4,4',5' |
192 |
2,3,3',4,5,5',6 |
|
33 |
2',3,4 |
85 |
2,2',3,4,4' |
139 |
2,2',3,4,4',6 |
193 |
2,3,3',4',5,5',6 |
|
34 |
2',3,5 |
86 |
2,2',3,4,5 |
140 |
2,2',3,4,4',6' |
Octachlorobiphenyls |
|
|
35 |
3,3',4 |
87 |
2,2',3,4,5' |
141 |
2,2',3,4,5,5' |
194 |
2,2',3,3',4,4',5,5' |
|
36 |
3,3',5 |
88 |
2,2',3,4,6 |
142 |
2,2',3,4,5,6 |
195 |
2,2',3,3',4,4',5,6 |
|
37 |
3,4,4' |
89 |
2,2',3,4,6 |
143 |
2,2',3,4,5,6' |
196 |
2,2',3,3',4,4',5',6 |
|
38 |
3,4,5 |
90 |
2,2',3,4',5 |
144 |
2,2',3,4,5',6 |
197 |
2,2',3,3',4,4',6,6' |
|
39 |
3,4',5 |
91 |
2,2',3,4',6 |
145 |
2,2',3,4,6,6' |
198 |
2,2',3,3',4,5,5',6 |
|
Tetrachlorobiphenyls |
92 |
2,2',3,5,5' |
146 |
2,2',3,4',5,5' |
199 |
2,2'3,3',4,5,6,6' | |
|
40 |
2,2',3,3' |
93 |
2,2',3,5,6 |
147 |
2,2',3,4',5,6 |
200 |
2,2',3,3',4,5',6,6' |
|
41 |
2,2',3,4 |
94 |
2,2',3,5,6' |
148 |
2,2',3,4',5,6' |
201 |
2,2',3,3',4',5,5',6 |
|
42 |
2,2',3,4' |
95 |
2,2',3,5',6 |
149 |
2,2',3,4',5',6 |
202 |
2,2',3,3',5,5',6,6' |
|
43 |
2,2',3,5 |
96 |
2,2',3,6,6' |
150 |
2,2',3,4',6,6' |
203 |
2,2',3,4,4',5,5',6 |
|
44 |
2,2',3,5' |
97 |
2,2',3',4,5 |
151 |
2,2',3,5,5',6 |
204 |
2,2',3,4,4',5,6,6' |
|
45 |
2,2',3,6 |
98 |
2,2',3',4,6 |
152 |
2,2',3,5,6,6' |
205 |
2,3,3',4,4',5,5',6' |
|
46 |
2,2',3,6' |
99 |
2,2',4,4',5 |
153 |
2,2',4,4',5,5' |
Nonachlorobiphenyls |
|
|
47 |
2,2',4,4' |
100 |
2,2',4,4',6 |
154 |
2,2',4,4',5,6 |
206 |
2,2',3,3',4,4',5,5',6 |
|
48 |
2,2',4,5 |
101 |
2,2',4,5,5' |
155 |
2,2',4,4',6,6' |
207 |
2,2',3,3',4,4',5,6,6' |
|
49 |
2,2',4,5' |
102 |
2,2',4,5,6' |
156 |
2,3,3',4,4',5 |
208 |
2,2',3,3',4,5,5',6,6' |
|
50 |
2,2',4,6 |
103 |
2,2',4,5',6 |
157 |
2,3,3',4,4',5' |
Decachlorobiphenyls |
|
|
104 |
2,2',4,6,6' |
158 |
2,3,3',4,4',6 |
209 |
2,2',3,3',4,4',5,5',6,6' |
||
TABLE 2 Approximate molecular composition of Aroclor mixtures (U.S.EPA, 1980) |
|||||||
PCB Formulation Chlorobiphenyl |
A-1016 |
A-1221 |
A-1232 |
A-1242 |
A-1248 |
A-1254 |
A-1260 |
--- % --- |
|||||||
Biphenyl |
trace |
11.0 |
6.0 |
- |
- |
- |
- |
Monochlorobiphenyl |
1.0 |
51.0 |
26.0 |
1.0 |
- |
- |
- |
Dichlorobiphenyl |
20.0 |
32.0 |
29.0 |
17.0 |
1.0 |
- |
- |
Trichlorobiphenyl |
57.0 |
4.0 |
24.0 |
40.0 |
23.0 |
- |
- |
Tetrachlorobiphenyl |
21.0 |
2.0 |
15.0 |
32.0 |
50.0 |
16.0 |
- |
Pentachlorobiphenyl |
1.0 |
0.5 |
0.5 |
10.0 |
20.0 |
60.0 |
12.0 |
Hexachlorobiphenyl |
trace |
- |
- |
0.5 |
1.0 |
23.0 |
46.0 |
Heptachlorobiphenyl |
- |
- |
- |
- |
- |
1.0 |
36.0 |
Octachlorobiphenyl |
- |
- |
- |
- |
- |
- |
6.0 |
Nonachlorobiphenyl |
- |
- |
- |
- |
- |
- |
- |
Decachlorobiphenyl |
- |
- |
- |
- |
- |
- |
- |
TABLE 3
|
||
Apirolio |
Dykanol |
Phenoclor (France) |
Aroclor (US, Great Britain) |
Elemex |
Pydraul (US) |
Aroclor B |
Eucarel |
Pyralene (France) |
Asbestol |
Fenclor (Italy) |
Pyranol (US, Canada) |
Askarel |
Hyvol |
Pyroclor (Great Britain) |
Chlorestol |
Inclor |
Saf-t-kuhl |
Chlorinol |
Inerteen (US, Canada) |
Santotherm FR (Japan) |
Chlophen (Germany) |
Kanechlor (Japan) |
Santovec 1 and 2 |
DK Decachlorobiphenyl (Italy) |
Nepolin |
Sovol (USSR) |
Diaclor |
No-flamol |
Therminol FR Series |
2.2 Uses
The major Canadian use of PCBs was in dielectric fluid for industrial electrical equipment (McDonald and Tourangeau, 1986). Other products containing PCBs included:
· -waxes
· -adhesives
· -paints
· -heat exchange fluids
· -de-dusting agents
· -vacuum pump oils
· -caulking compounds
· -hydraulic fluids
· -printing inks
· -cutting oils
· -sealants
· -plasticizers
· -carbonless copying paper
· -specialised lubricants
· -bridge bearing
· -fire retardants
· -cable insulating paper
· -lubricants
· -flame-proofing
Some uses of PCBs classified according to the type of Aroclors are shown in Table 4. PCBs mixed with DDT (Lichtenstein et al., 1969), organophosphorus compounds (Fuhremann and Lichtenstein, 1972), and carbaryl (Plapp, 1972) have been reported to enhance the insecticidal properties of these compounds. Although recommended for incorporation into pesticide formulations, PCBs were apparently never used as pesticides (Hutzinger et al.,1974).
|
TABLE 4
|
||
|
Base material |
Aroclor type |
Purpose and Effect |
|
Polyvinyl chloride |
A-1248, A-1254, |
Secondary plasticizers to increase flame retardance and chemical resistance |
|
Polyvinyl acetate |
A-1221, A-1232, |
Improved quick-track & fibre-tear properties |
|
Polyester resins |
A-1260 |
Stronger fibreglass; reinforced resins & economical fire retardants |
|
Polystyrene |
A-1221 |
Plasticizer |
|
Epoxy resins |
A-1221, A-1248 |
Increased resistance to oxidation & chemical attack; better adhesive properties |
|
Styrene-butadiene co-polymers |
A-1254 |
Better chemical resistance |
|
Neoprene |
A-1268 |
Fire retardant; injection moldings |
|
Crepe rubber |
A-1262 |
Plasticizer in paints |
|
Nitrocellulose lacquers |
A-1262 |
Co-plasticizers |
|
Ethylene vinyl acetate |
A-1254 |
Pressure sensitive adhesives |
|
Chlorinated rubber |
A-1254 |
Enhances resistance, flame retardance, electrical insulation properties |
|
Varnish |
A-1260 |
Improved water & alkali resistance |
|
Wax |
A-1262 |
Improved moisture & flame resistance |