- Recent history of PCBs (Baird,
1999; O'Shea, 1999)
- More than 1 million metric tons produced since the late 1950s
- First discovered as environmental contaminant in late 1960s
- The manufacture of PCBs in most industrialized nations ended in the
1970s/80s after recognition of threats posed to human health and environment
- Production halted in North America in 1977
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- Wide variety of industrial applications
(Baird, 1999; O'Shea, 1999; & GPA)
- Used as dielectrics, coolants, and lubricants in transformers
- Heat transfer systems
- Plastics
Most PCBs have yet to reach the environment because they are still bound
up in the their original use, e.g. transformers etc..As such, it is
projected that the quantity of PCBs in the environment will increase
as the industrial applications age.
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- Chemical properties
- Fire resistant
- Low volatility
- Relatively stable and persistent
- Almost entirely insoluble in water but soluble in lipids
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- PCBs and the environment (see
GPA; O'Shea, 1999)
- Released into environment from old electrical devices and the improper
disposal or incineration of PCBs and waste containing PCBs
- Found globally
- Readily picked up in marine food webs because they are adsorbed on
sediment and other organic matter
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- PCBs and marine mammals
Numerous studies, in a variety of species, have documented the following:
- Age-related effects in females: The concentration of PCBs increases
until sexual maturity and then decreases during the reproductively active
years, with the lowest PCB concentrations found in reproductively active
females. This has been noted in Pinniped and Odontocete species (Tanabe
et al., 1994; Lee et al., 1996; Cockcroft et al., 1989; Cockroft et
al., 1990)
- Transfer of PCBs from mother to offspring during development and
through lactation: There is a large range in the literature regarding
the percentage of PCB load passed from mom to offspring. Suggestions
of 80% PCB transfer to offspring have been made for some Pinnipeds and
Odontocetes, while only 14% was found to be transferred in a mysticete
species (Cockcroft et al, 1989; Aguilar and Borrell, 1994a; Lee et al,
1996).
- Higher PCB concentrations in males than in females: Following
from the last two points, studies involving Pinniped, Odontocete, and
Mysticete species all document higher PCB concentrations in adult males
as compared to adult females (Helle et al., 1976; Tanabe et al., 1986;
Subramanian et al., 1988; Cockcroft et al., 1990; Borrell, 1993; Daelemans
et al., 1993; Aguilar and Borrell, 1994b; Beck et al., 1994; Norstrom
et al., 1998).
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- Potential toxic effects based
on other species (GPA)
At this point, scientists do not yet specifically how PCBs will impact
marine mammals. The following are toxic effects based on laboratory
studies.
- After receiving low levels of PCBs for twelve months, rats, mice,
monkeys and quail showed neural changes, and monkeys showed impaired
or abnormal neuromotor function.
- Reproductive problems related to PCB levels found in minks (embryo
toxicity), birds (eggshell thinning), and turtles (hormone disrupting
effects on sex determination).
- Immune system problems, specifically imparied immune response to infections,
are reported for perinatal exposure to PCBs.
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