There is a vast amount of information in the open
literature on the fate, behaviour, toxicity and
bioaccumulation of PCBs in the aquatic environment
. This profile only presents an outline of the data
available, and the reader is directed to more extensive
reviews such as US EPA (1984), CCME (1992) and WHO
(1993) for a more detailed explanation of the data
and reported values.
Entry into the marine environment
Polychlorinated biphenyls (PCBs) are mixtures of
aromatic chemicals, manufactured by the chlorination
of biphenyl in the presence of a suitable catalyst.
The empirical formula for PCBs is C12H10-nCln
where n may be any value from 1 to 10. PCBs with
5 or more chlorine atoms per molecule are referred
to as 'higher chlorobiphenyls' and are relatively more persistent in the
environment that 'lower
chlorobiphenyls' which have four or fewer chlorine atoms.
Individual PCBs (commonly referred to as congeners,
e.g. PCB 153) vary widely in their physical and
chemical properties, according to the degree and
position of chlorination. Most PCBs are slightly
soluble in water and the solubility decreases with
chorine content. Estimates of PCB solubility range
from 2.7 to 15,000 µg l-1
PCBs have been widely used in industrial applications
in view of their excellent thermal stability, strong
resistance to both acid and base hydrolysis, general
inertness, solubility in organic solvents, excellent
dielectric properties, resistance to oxidation and
reduction and nonflammability (CCME 1992).
PCBs can be considered to be among the most ubiquitous
and resistant pollutants in the global ecosystem.
The principal route of PCB transport to the marine
environment is from waste streams to receiving waters,
downstream movement by means of solution and re-adsorption
onto particles and by the transport of the sediment
itself, until eventually reaching estuaries and
coastal waters. The marine environment appears to
be the ultimate and major sink for PCBs (CCME 1992).
Recorded levels in the marine
WHO (1993) stated that in the oceans, levels of
0.05 - 0.6 ng l-1 have been found.
Monitoring data for sediments and biota from the
National Rivers Authority and the National Monitoring
Programme Survey of the Quality of UK Coastal Waters
are presented in Appendix D and indicate some elevated
levels in certain estuaries.
Fate and behaviour in the marine
In the aquatic environment, PCBs are usually found
in much higher concentrations in sediments than
in the overlying water. PCBs have a high affinity
for suspended solids, especially those higher in
organic carbon. This is supported by their low water
solubility and high octanol/water partition coefficients
(calculated Log Kow values range from 3.76 for biphenyl
to 8.26 for decachlorobiphenyl) (CCME 1992).
PCBs, with the exception of some lower-chlorinated
compounds, have low volatility and are soluble in
organic solvents, particularly hydrocarbons. Temperatures
in excess of 1,000 °C
are required for their complete combustion.
Sorption to sediments is the predominate mechanism
removing PCBs from the water column.
Individual PCBs vary widely in their susceptibility
to biodegradation. PCBs with three or fewer chlorine
atoms per molecule can be biodegraded by many organisms,
whereas these with 5 or more chlorines are resistant
to biodegradation and biotransformation. In general,
PCB congeners have a low solubility in water, and
high octanol-water partition coefficients, bioaccumulation
potential, and resistance to biodegradation. The
physical and chemical properties of PCBs cause their
removal from water by sorption to suspended particles
and bottom sediments (CCME 1992).
Effects on the marine environment
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of PCBs to marine organisms has not been carried
out for the purposes of this profile. The information
provided in this section is taken from existing
review documents (WHO 1993). The most sensitive
groups of organisms have been identified.
With regard to direct toxicity, WHO (1993) reported
that results had been extremely variable with no
consistent relationship between percentage chlorination
or environmental conditions and toxicity. Over 96
hours, under static conditions, LC50 values have
ranged between 12 µg l-1
to >10 mg l-1 for various aquatic
invertebrate species. Flow-through studies showed
increased toxicity. WHO (1993) reported a similar
variation for PCB mixtures for fish with 96 hour
LC50s varying between 0.008 and >100 mg l-1.
Long-term tests have shown that acute exposure,
particularly in static conditions, considerably
underestimates the toxicity of PCBs.
WHO (1993) also reported that for birds fed PCBs
in their diet, there was evidence of egg-shell thinning,
while for sea mammals, there was evidence that PCBs
reduce their reproductive capacity. The main effect
is on the implantation of the embryo but there can
be physical changes to the female reproductive tract.
Consequently, PCBs have been identified as an endocrine
disrupting group of substances.
Accumulation of PCBs in sediments poses a potential
hazard to sediment-dwelling organisms. Environment
Canada has recently issued interim marine sediment
quality guidelines and these include a guideline
of 21.5 µg kg-1 (dry weight)
of total PCBs above which effects on sediment-dwelling
organisms may occur.
The main concern over PCBs is their high bioaccumulation
PCBs are soluble in the lipids of biological systems
and therefore tend to be bioaccumulated in fatty
tissues (especially the higher chlorobiphenyls).
BCFs of 200,000 and greater have been reported for
fathead minnows Pimephales promelas (Duke
1971 and Neely 1977) and pink shrimp (Klien and
Weisgerber 1976) and up to 1,000,000 in other organisms.
Relatively low concentrations of PCBs in the aquatic
environment can result in the accumulation of relatively
high PCB levels in biota.
WHO (1993) quoted experimentally determined BCFs
in various aquatic species, ranging from 200 to
70,000 or more. In the open ocean, there is bioaccumulation
of PCBs in higher trophic levels with an increased
proportion of higher chlorinated biphenyls in high-ranking
The presence of high concentrations of PCBs or
their residues in marine mammals have been suggested
as the cause of (or contributing towards) pathological
changes and reproductive failures in Baltic seals
(Helle et al 1976), sealions, seals and beluga
whales (Addison 1989); immunity suppression (and
hence the possibility of being more susceptible
to disease) in harbour porpoises (Kuiken et al
1994) and seals (Reijnders 1986; Swart et
al, 1994); changes in the development stability
of the Baltic grey seal (Zakharov and Yablokox 1990);
and premature pupping in California sea lions (Delong
et al 1973).
Potential effects on interest
features of European marine sites
Potential effects include:
- toxicity of PCBs to invertebrates and fish in
the water column;
- accumulation in sediments and potential hazard
to sediment-dwelling organisms at concentrations
greater than 21.5 µg kg-1
(dry weight) of total PCBs;
- bioaccumulation of PCBs in fish, birds and Annex
II sea mammals with known sublethal toxicological
- endocrine disruption in birds and sea mammals
posing a hazard to populations of these animals.