A.R.D. Stebbing . R.I. Willows
vi. EQSs can be based on 'annual average' concentrations or 'maximum allowable concentrations'. They may thus allow transient concentrations that are toxic, while
the annual average concentration remains less than that permitted by an EQS.
vii The extrapolation factor used varies between nations, and there seems to be agreed
protocol for their specification. In the UK it is arbitrarily determined (Wharfe
and Tinsley 1995), and adjusted in the light of experience, rather than having a
basis in scientific understanding. It is intended to account for uncertainties and
lack of knowledge in extrapolating between species, from acute short term exposure to chronic long term exposure, from one environment ecosystem to another. Extrapolation factors may vary between ranges of 1-5, where confidence
is greatest that effects in the field may be avoided, to 200-1000 for persistent
new chemicals, where the toxicological database is sparse. Some use larger ex'irapolation factors account for possible synergistic effects between contaminants.
Derived in this way, EQSs for listed contaminants provide the means by which
statutory limits of environmental contamination are determined and controlled,
providing the standards to which the regulatory authorities operate in order to
prevent pollution. However, chemical EQSs have led to a waste of monitoring effort, measuring inconsequential contaminants (i) in the wrong place (x) and in the
wrong compartment (n) (see Section 8.3.2).
8.3.4
A Resource of Economic Value
The marine environment has a capacity to assimilate wastes and effluents by their
dilution, dispersion and degradation, such that they are reduced to harmless concentrations, are transformed into less toxic species, or utilized and recycled by the
ecosystem. This capacity is an environmental service of considerable economic
value. Globally such services are approximately valued at $1.28 tr p.a., which is 7.1%
of the global Gross National Product p.a. (using data from Costanza et al. 1997).
When the basic ecotoxicological and economic variables are considered together
(Fig. 8.3), it is clear that a number of factors bear on the management of the rates
of contaminant inputs to the system. A low level ofloading by nutrient -rich organic
wastes (Fig. 8.3a) promotes primary and enhanced heterotrophic production. Increasing nutrient inputs can cause eutrophication. Primary production has increased in the German Bight by 3-4 times since 1962 (Radach et al. 1990). In stratified waters eutrophication and the consequential phytoplankton blooms can lead
to hypoxia. The system becomes overloaded at the point at which hypoxia and metabolic by-products have an adverse effect on productivity, although community and
other ecosystem changes may occur earlier. Where such events are severe, mortalities of benthic and pelagic organisms occur. The stages of marine eutrophication
and its harmful consequences are considered by Gray (1996) and will not be considered further to give greater consideration to toxic contaminants and their control.
With non-degradable toxic contaminants such as metals (Fig. 8.3b), resistance
to low concentrations may incur a physiological cost, but typically there is a threshold concentration at which toxic effects occur in an individual organism (Willows 1994), or may occur in a population or community (Warwick and Clarke 1992).
vi. EQSs can be based on 'annual average' concentrations or 'maximum allowable concentrations'. They may thus allow transient concentrations that are toxic, while
the annual average concentration remains less than that permitted by an EQS.
vii The extrapolation factor used varies between nations, and there seems to be agreed
protocol for their specification. In the UK it is arbitrarily determined (Wharfe
and Tinsley 1995), and adjusted in the light of experience, rather than having a
basis in scientific understanding. It is intended to account for uncertainties and
lack of knowledge in extrapolating between species, from acute short term exposure to chronic long term exposure, from one environment ecosystem to another. Extrapolation factors may vary between ranges of 1-5, where confidence
is greatest that effects in the field may be avoided, to 200-1000 for persistent
new chemicals, where the toxicological database is sparse. Some use larger ex'irapolation factors account for possible synergistic effects between contaminants.
Derived in this way, EQSs for listed contaminants provide the means by which
statutory limits of environmental contamination are determined and controlled,
providing the standards to which the regulatory authorities operate in order to
prevent pollution. However, chemical EQSs have led to a waste of monitoring effort, measuring inconsequential contaminants (i) in the wrong place (x) and in the
wrong compartment (n) (see Section 8.3.2).
8.3.4
A Resource of Economic Value
The marine environment has a capacity to assimilate wastes and effluents by their
dilution, dispersion and degradation, such that they are reduced to harmless concentrations, are transformed into less toxic species, or utilized and recycled by the
ecosystem. This capacity is an environmental service of considerable economic
value. Globally such services are approximately valued at $1.28 tr p.a., which is 7.1%
of the global Gross National Product p.a. (using data from Costanza et al. 1997).
When the basic ecotoxicological and economic variables are considered together
(Fig. 8.3), it is clear that a number of factors bear on the management of the rates
of contaminant inputs to the system. A low level ofloading by nutrient -rich organic
wastes (Fig. 8.3a) promotes primary and enhanced heterotrophic production. Increasing nutrient inputs can cause eutrophication. Primary production has increased in the German Bight by 3-4 times since 1962 (Radach et al. 1990). In stratified waters eutrophication and the consequential phytoplankton blooms can lead
to hypoxia. The system becomes overloaded at the point at which hypoxia and metabolic by-products have an adverse effect on productivity, although community and
other ecosystem changes may occur earlier. Where such events are severe, mortalities of benthic and pelagic organisms occur. The stages of marine eutrophication
and its harmful consequences are considered by Gray (1996) and will not be considered further to give greater consideration to toxic contaminants and their control.
With non-degradable toxic contaminants such as metals (Fig. 8.3b), resistance
to low concentrations may incur a physiological cost, but typically there is a threshold concentration at which toxic effects occur in an individual organism (Willows 1994), or may occur in a population or community (Warwick and Clarke 1992).