PCBs are synthetic chemical compounds which have been used widely in industrial applications. Because their hazardous nature has only recently been understood, PCBs have been routinely disposed of over the years without any precautions being taken. As a result, large volumes of PCBs have been introduced into the environment through open burning or incomplete incineration; by vaporisation from paints, coatings and plastics; by direct entry or leakage into sewers and streams; by dumping in non-secure landfill sites and municipal disposal facilities; and by other routes (e.g., ocean dumping). Despite regulations, some PCBs have been illegally dumped through ignorance, through negligence, or wilfully. Accidental spills and leaks, while of local significance, have been relatively minor sources of PCB contamination of the global environment (CCREM, 1986). The following sections outline levels found in the environment.
4.1 Waters
PCBs are only slightly soluble, resulting in low dissolved levels in water. Using 1975 to 1983 water quality data obtained from the National Water Quality Data Bank (NAQUADAT), Strachan (1988) noted a wide regional disparity in the number of those samples in which quantifiable amounts of PCBs were measured (0 to 35% based on detection limits of 0.009 to 0.02 µg/L). In samples with positive results, the mean concentration of total PCBs was found to range from 0.015 (in the Atlantic region) to 0.04 µg/L (in the Provinces of Quebec and Ontario). None of the water samples from western Canada contained PCBs at quantifiable levels, despite their appearance in areas other than those reported in NAQUADAT.
In British Columbia, PCBs have not been detected in the vast majority of freshwater samples collected (Garrett, 1983; SEAM, 1989). However, detectable levels were observed in the McLeese Lake area (up to 0.2 µg/L in Cuisson Lake in December 1976), in Coldstream Creek (<0.2 to 5 µg/L in June 1979) in the Okanagan, and in Lime Creek (0.1 to 4.8 µg/L in March 1980) near the Amax Kitsault Mine. These high levels were attributed to accidental spillage or disposal of PCB-containing materials (Garrett, 1983).
PCB levels ranging from <0.0002 to 0.09 µg/L have been measured in marine and estuarine waters (Garrett, 1983). Maximum residues seldom exceed 0.002 µg/L and may fall below 0.0002 µg/L in offshore marine areas; however, unfiltered water samples containing particulate matter often bear much higher residues (Moore and Ramamoorthy, 1984). No data are available for marine waters off the British Columbia coast.
4.2 Sediments and soils
Unless indicated otherwise, the PCB concentrations in sediments in the following discussion are expressed on a dry weight basis.
Sediments are the primary sink for PCBs. The concentrations of PCBs in sediment depend upon the characteristics of the sediments and their proximity to the source. Frank et al. (1981) reported sediment residues of 0.010-0.020 µg/g in Lake Michigan near Chicago, Milwaukee, and Green Bay; by contrast the whole lake average was 0.0097 µg/g. In the vicinity of waste outfalls, residues may range from 2 to > 500 µg/g (Elder et al., 1981). The mean and 95% confidence limits, respectively, for the Niagara River sediment at Niagara-on-the-Lake were 0.580 and ±0.103 µg/g; somewhat lower levels were detected in the Ontario portion of the St. Lawrence River (mean concentration of 0.179 µg/g) and in the Atlantic Region (mean concentration of 0.247 µg/g) (Strachan, 1988).
In British Columbia, total PCB concentrations in freshwater sediments are generally below the detection limits (0.02 and 0.01 µg/g) (SEAM, 1989; Swain and Walton, 1988 and 1990). However, elevated levels of PCBs have been measured in sediments off certain industrial facilities; e.g., up to 1.0 µg/g was measured in sediments adjacent to the Belkin Paperboard paper recycling plant in Burnaby (Garrett, 1983).
Inshore marine areas of industrial zones are often highly contaminated. PCB levels in sediments of the Southern California Bight (Los Angeles) generally exceeded 1.0 µg/g and in some areas reached 10 µg/g (Young and Heeson, 1978). In British Columbia, PCB concentrations in marine sediments have been measured up to (a) 16.8 µg/g off the Bayshore Inn in Coal Harbour, (b) 17 µg/g in the vicinity of Burrard Yarrow Shipyards in Burrard Inlet, (c) 6.9 µg/g under the Granville Street Bridge in the False Creek area of Vancouver, and (d) 3.6 µg/g in Victoria's Inner Harbour (Garrett, 1983).
More recently, Goyette and Boyd (1989) found that mean PCB concentration in sediments from Vancouver Harbour (based on 1985/86 data) ranged from < 0.02 µg/g to 0.90 µg/g. The maximum concentration (0.90 µg/g) was recorded for the site at Burrard Yarrow on the north shore. Overall mean level for the Vancouver Inner Harbour (44 sites) was 0.17 ± 0.20 µg/g. Sediment PCB concentration in Port Moody Arm in 1985/86 (13 sites) averaged 0.06 µg/g (range, 0.02 - 0.18 µg/g), and in 1987 (33 sites) the average was 0.13 µg/g (range, 0.03 to 0.32 µg/g).
Offshore sediments such as those in the Mediterranean and Baltic seas, usually contain much lower residues of PCBs (<0.005 µg/g) (Basturk et al., 1980).
PCBs do not generally occur in soil environments, except when spills, industrial releases, atmospheric transport, or application of sewage occur. Carey and Gowen (1976) reported that agricultural soils in the U.S. rarely contain detectable levels of PCBs; although PCBs were frequently detected in soils from urban areas, concentrations were <1.0 µg/g. In a study on Ontario soils, Weber et al. (1983) reported a range of 0.007 to 0.025 µg/g with a mean value of 0.013 µg/g PCBs for ten sites.
4.3 Biota
PCB concentrations in animal tissues in the following sections are on a wet weight basis unless reported otherwise.
4.3.1 Aquatic organisms
PCBs are readily sorbed from water by aquatic organisms; although variable, bio-concentration factors up to 300 000 have been reported for freshwater and marine organisms (Defoe et al., 1978; Scura and Theilacker, 1977).
Johnston et al. (1975) reported PCB levels in fish collected in 1972/73 from the Fraser River. Although concentrations in most species were generally between 0.1 and 0.9 µg/g, certain coarse fish species showed levels in their muscle tissue which were equivalent to or in excess of the Health and Welfare guideline of 2 µg/g. One large-scale sucker contained over 3 µg/g and tissue levels in two northern squawfish approached 2 µg/g. Singleton (1983) reported measurable PCB levels in 11 of 253 fish (muscle tissue) samples collected from the Fraser River in 1980; detectable values (0.3 µg/g) ranged from 0.4 to 0.8 µg/g. Fish muscle tissue analyses carried out in 1988 by Swain and Walton (1989) had PCB levels between 0.003 and 0.26 µg/g (mean concentrations in the fish ranged from 0.02 to 0.06 µg/g),which were lower than those measured in the 1972/73 and 1980 surveys.
PCBs are extremely lipophilic; hence, maximum concentrations in fish are usually associated with fat deposits. The liver is another site of PCB accumulation. Residues are generally lowest in the muscle but are dependent on the fat content of the tissue. Removal of skin and adipose (fatty) tissue significantly decreases the level of PCBs in the trimmed fillet of fish (White et al., 1985; Sanders and Haynes, 1988). Overall, concentrations in fat are a good tool for monitoring PCB contamination and should be measured in conjunction with edible muscle tissue determinations.
PCB levels in fish can vary with season. Three- to seven-fold seasonal differences in PCB residues were noted in perch and roach collected from a bay on the Baltic coast (Edgren et al., 1981). Similarly, residues in whiting from the Medway Estuary (UK) peaked at 0.16 µg/g in April, declining to 0.01 µg/g by October (van den Broek, 1979). Such variability stems from the interplay of nutritional, reproductive, and activity cycles of the fish.
Sewage discharges have been shown to cause a significant increase in PCB levels in the marine environment. McDermott et al. (1975) showed that Dover sole collected near large sewage outfalls in the South California Bight contained much higher PCB concentrations than sole collected away from the outfalls. The median levels in the muscle tissue of the fish collected near three of the larger outfalls ranged from 0.7 to 1.9 µg/g in 1971-72 and 0.6 to 2 µg/g in 1974-75.
In British Columbia, PCB concentration was measured in rainbow trout caught from Okanagan Lake. The mean PCB concentration (on wet weight basis) in the muscle tissues of the fish was 1.57 µg/g (range, 0.37 to 4.06 µg/g) in 1974, 0.03 µg/g (range, 0.1 to 0.4 µg/g) in 1975, 0.50 µg/g (range, < 0.1 to 1.83 µg/g) in 1976, 0.24 µg/g (range, < 0.1 to 0.6 µg/g) in 1988, and 0.27 µg/g (range, 0.13 to 0.37 µg/g) in 1990 (Bryan and Jensen, 1991).
High concentrations of PCBs have been detected in the sediments from Coal Harbour. Crab collected from this area contained a mean concentration of 0.2 µg/g. The same species from False Creek contained PCB levels about 10-fold lower (Garrett, 1983).
Mussels collected under the Burrard and Granville bridges contained very low concentrations (0.014 - 0.017 µg/g) of PCBs. However, mussels collected in Alice Arm near the Kitsault Mine contained relatively high PCB levels (up to 1.7 µg/g). Limited data indicated that water samples collected in this area (Alice Arm) also had elevated PCB levels (0.24 to 4.8 µg PCBs/L) (Garrett, 1983).
4.3.2 Wildlife
Certain wildlife species, particularly fish-eating birds and aquatic mammals, accumulate high levels of PCBs.
Populations of double-crested cormorants (Phalacrocorax auritus ) from Lake Huron are recovering rapidly, presumably due to a decrease in PCBs and other contaminant residues in their eggs. PCB levels between 10.3 and 25.6 µg/g (fresh weight) measured in the eggs of the cormorant population in 1972 were higher than in other Canadian cormorant populations (Weseloh et al., 1983).
Average PCB concentrations of 14.9 and 21.4 µg/g (fresh weight) were measured in Great Blue Heron eggs from the Coquitlam and the University of British Columbia populations in 1977-78. The concentration in heron eggs collected in the Kootenay River area in 1969 ranged from 0.036 to 25.6 µg/g (fresh weight) with a mean value of 13 µg/g. These levels are higher than those that cause embryonic deformities and mortalities in poultry. However, no impacts on heron colonies in British Columbia traceable to PCBs have been observed (Garrett, 1983).
Residues of PCBs in birds are modified by numerous biotic factors including fat content, tissue specificity, sex, and developmental stage. Sexual differences in PCB content are pronounced due to the female's ability to shed a significant portion of the PCB burden into eggs. Also, PCB levels are reduced from egg to fledgling. Residues in the brain appear to be good indicators of PCB stress in birds. Concentrations greater than 300 µg/g of PCB in the brain (fresh weight) were consistently recorded in dead or dying ring-billed gulls (Larus delawarensis ) and ring-necked pheasants (Phasianus colchicus ) poisoned by PCBs (Eisler, 1986).