Synthetic organics and heavy metals
Pollution is clearly a major concern in the management of SACs, but
problems posed are considerably more complex than those which arise in relation to other
human activities. Activities such as fishing are relatively clear-cut in terms of origin,
effects and potential for control. By contrast pollution may be difficult to analyse on
all these counts, and can pose major problems for effective management, because:
- The origin of pollution may not be a known point source, with a limited distribution,
but may have uncertain origins and be diffuse over a wide area.
- A pollutant may affect the CFT community in situ, or it may affect the pelagic larval
phase whilst in the water column, possibly in a different location. In either case little
is known of the sensitivity of CFT species to concentrations of specific pollutants, and
even less of synergistic effects.
- Pollutants may build up in organisms and through the food chain, so that concentrations
in the water or sediment may be of little direct relevance.
- Most pollution will arise outside the SAC, limiting management options.
The following pollutants will be considered - sewage (and other organic
based effluents with the same basic effects), oil, synthetic organic compounds, and heavy
Sewage and other organic-based effluents present several environmental
- They contain inorganic plant nutrients, and induce potentially serious impacts which are
considered below under eutrophication.
- They add dissolved and particulate material to the water which will reduce light
penetration and deposit sediment onto the substratum.
- Perhaps most importantly, they utilise the dissolved oxygen in the water.
The majority of CFT biotopes occur on open coasts in areas of vigorous
water movement, and either in or close to waters of considerable depth. They are not
generally near sources of discharge of organic pollutants, such as sewage, and even if
they were, they would be considered as Higher Natural Dispersion Areas, and
therefore apparently at little risk. The only exceptions are the limited CFT biotopes in
sheltered semi-enclosed situations such as in the Scottish sea lochs and south western
rias. These would be exposed to risk of depletion of dissolved oxygen if there was a
substantial organic input, and because of their scarcity, have a high conservation value.
Past experience in Scandinavian fjords and bays has shown this to be a real threat. The
choice of SACs is based upon the existing quality of environment, which means that they
are not currently in an area receiving excess organic input. Any proposed change in
effluent treatment or discharge regimes, or new source of organic input (e.g. intensive
fish farming) would be a management concern, and must be evaluated in the context of the
water dispersion patterns within the SAC. Fortunately all such proposals will (it is to be
hoped) be subject to strict consent conditions.
Another important form of organic pollution is oil, and in contrast to
the above, serious oil pollution incidents are quite unpredictable. For the purposes of
SAC management, the treatment of oil pollution can present conflicts of interests for
different biotopes, and the optimal measures for CFT biotopes cannot be pursued in
isolation. Untreated oil is not a risk, since it is concentrated mainly at the surface,
and the CFT biotopes are protected by their depth. If oil is treated by dispersant the
resulting emulsion will penetrate down the water column, especially under the influence of
turbulence. However, the target response of the Marine Pollution Control Unit is to spray
offshore when spraying is required, and spraying inshore should be a last resort. An oil
spill contingency plan is an integral part of every SAC management programme, but it will
concentrate on vulnerable (or valuable) components of the system - marine birds and
mammals, soft intertidal sediments, aquaculture developments, and amenity sites. CFTs will
inevitably, and realistically, come low on the list of considerations.
Synthetic organics and heavy metals
Synthetic organic compounds include pesticides, PCBs and TBT
antifouling. Heavy metals include cadmium, lead, and mercury. All are known to have toxic
effects in low concentrations, with larval stages being particularly sensitive, and to be
capable of high levels of bioaccumulation. Because of this bioaccumulation they often
affect higher trophic levels most severely, and become a serious consideration in any
species used for human consumption. If there are any suspected point sources within or
near the area of the SAC, then they will have to be a feature of management plans. Their
potential impact upon the dispersive larval stages means that there influence cannot be
ignored beyond the boundaries of SACs, since they may affect recruitment to the