Industrial And Domestic Effluent Discharge
Industrialised and urbanised estuaries and coastlines receive effluent discharges which
contain conservative contaminants, i.e. those with a long half-life, are likely to
bioaccumulate (remain within the food-chain) and thus have a toxic effect (Clark, 1997).
Such contaminants include heavy metals, both essential (e.g. copper, zinc) and toxic (e.g.
mercury, cadmium), radionucleides and synthetic organic compounds (e.g. dieldrin and
polychlorinated biphenyls). The lethal and sub-lethal effects of these pollutants vary
according to the state and availability of the compound and the characteristics and
organisms of the receiving systems. Some effects may be lethal, by removing individuals
and species and thus leaving pollution tolerant and opportunistic species. Other effects
may be sub-lethal, in affecting the functioning of organisms such as the reproduction,
physiology, genetics and health, which will ultimately reduce the fitness for survival
Sheltered, low-energy areas such as intertidal mudflats in enclosed bays or estuaries
will be most susceptible to these pollutants as dispersion is low and the finer substrata
in these areas will act as a sink (e.g. McLusky, 1982; Nedwell, 1997; Ahn et al, 1995;
Somerfield et al, 1994). The pollutants will then enter the food chain and be
accumulated by predators, as shown by the seasonal loading of heavy metals in tissues of
wading birds in the Wash (Parslow, 1973). However, the industrialisation and urbanisation
of these areas results in them receiving complex mixtures of pollutants. For example,
intertidal areas in Southampton Water (Coughlan, 1979) and the Tees (Langslow, 1981) had
reduced benthic communities through contamination by phenols, oil effluent, sulphides and
In contrast to the low-energy areas, the higher-energy sedimentary biotopes are less
likely to receive and/or retain these contaminants. The coarser sediments of exposed
intertidal sandflats and the hydrodynamic characteristics, including high dispersion, at
subtidal sandbanks dictates that there are few cases of severe pollution in these areas.
However, chemical pollution of intertidal sands can occur and will remove elements of the
fauna, for example effluent from a pharmaceutical plant created a degraded community in
intertidal sands near Montrose (SEPA East, unpublished).