Case study 2: Seal Marsh
Assessment of likely significant
Expansion of an existing organic chemical manufacturing
plant which will discharge directly into the mouth
of an estuary. The effluent will contain increased
quantities of copper (5 mg.l-)1
and phthalates - principally DNBP (20 mg.l-1),
but lower concentrations of other phthalates may
also be present.
Instead of the current short outfall, it is proposed
to build a longer outfall to discharge closer to
the mouth of the estuary where greater mixing is
available. Extensive salt marshes are present in
the estuary on the opposite side to the chemical
works, and Spartina (which recently established
itself at a number of sites on the intertidal flats)
is now expanding in area, leading to locally increased
sediment accumulation rates. The outer estuary is
used by breeding seals.
The site is designated for Annex I habitat (estuary)
and Annex II species (common seal).
The conservation objectives for the site include
maintaining the habitat conditions that will maintain
seal population and maintaining biodiversity of
the upper salt marsh. It is accepted that the area
colonised by Spartina will increase, and
so sediment accumulation rates within the estuary
are also likely to increase. The conservation objectives
emphasise the importance of protecting salt marsh
creeks as nursery areas for fish.
To demonstrate the use of this guidance manual
for an amendment to an existing consent (i.e. to
be considered as a new plan or project) with an
effluent containing toxic substances in a situation
of greater complexity where background water quality
is less good and where there are several interest
features to consider.
Assessment of likely significant
The expansion of an existing chemical factory would
already have gone through the planning process and
the conservation and environment agencies would
have been consulted at that stage. The organic chemical
industry is a prescribed process under IPC, so a
variation to an IPC authorisation will be the mechanism
for considering effects on the SAC interest features.
The IPC authorisation will cover the release of
effluent to air, water and land, requiring that
BATNEEC be applied and so effects of atmospheric
discharges, as well as any solid waste disposal
on the site, will be considered as well as aquatic
discharges. In this case, the principal components
of this discharge are toxic aquatic discharges,
having direct effects on the interest features.
Formal standards exist for one of the principal
polluting substances (copper), but only for water;
not in the sediment. No standards are available
for any phthalates.
The revised outfall discharge point would be below
MLWS, the mixing zone would not impinge upon the
shoreline and the outfall will be suitable to achieve
the design guidance for initial dilution. Discharge
conditions will also need to take account of other
EC Directive requirements, international obligations
Step I: Are the interest features sensitive to
any hazard arising from this process?
Seal Marsh is designated as an estuary. The vulnerable
features of interest are the salt marsh and the
Step II: Is there a mechanism by which the consented
discharge is likely to affect the designated features
of the site?
As with the previous example, the discharge is
directly into the site.
Step III: Is the potential scale of any effect
likely to be deemed significant?
Table 4.1 of the guidance manual lists 16 principal
activities and the mechanisms by which water quality
might be affected. With applications to vary discharges,
it is important to determine what the changes will
mean for polluting substances in the discharge.
The information for prescribed substances will be
contained in the application for variation. For
many polluting substances, there will be a profile
in the appendices of the guidance manual describing
the behaviour of that substance, or group of substances,
in the environment and the effects on groups of
aquatic organisms. This information can be used
to determine whether a mechanism exists which links
the discharge and the designated features, and also
to indicate whether the mechanism is likely to operate
in this situation.
For the situation in Seal Marsh, the polluting
substances are copper and phthalates (DNBP and the
designated features are a saltmarsh (with its associated
fauna of invertebrates and fish) and seal colony.
The profiles for the polluting substances are in
the Appendix of the guidance manual.
Both copper and phthalates should be regarded as
persistent. Bioaccumulation can be a problem for
copper but does not appear to be an issue for phthalates.
When copper in solution comes into contact with
the sediment, it may bind. Similarly, it will also
be adsorbed onto suspended solids. Suspended sediment
which has come into contact with the outfall plume
is likely to contain elevated levels of copper,
which could be deposited on the saltmarsh, potentially
damaging biota. Copper is known to be toxic to vertebrates,
invertebrates and algae and higher plants. Limited
information is provided in the manual about standards
for metals in sediments but this route of exposure
would need to be considered for all potentially
Biomagnification of copper is not thought to be
a problem, and seals are more likely to have lower
tissue levels of copper than invertebrates and fish.
No data are available on the toxic effects of DNBP
on mammals, fish or algae; neither have bioaccumulation
studies been undertaken to determine the likely
uptake route of DNBP by seals via fish. However,
indications from bioaccumulation assessments undertaken
for other phthalates do not suggest that this is
a cause for concern.
The phthalate group contains some endocrine-disrupting
chemicals, with potential consequences for the breeding
seal population, as well as possible effects on
marine invertebrates and fish. However, little information
is available about which phthalates are endocrine
disrupters, or the concentrations at which endocrine
For phthalates, there is a potential mechanism
for affecting the seal colony and the saltmarsh
invertebrate and fish fauna. For copper there is
a potential mechanism for affecting saltmarsh fauna
and flora. Given that this is a major industry (regulated
under IPC), there are initial grounds for assuming
that the scale of effect might be significant. For
both DNBP and copper, there is sufficient evidence
to suggest that a significant effect may be likely.
Available information sources should be consulted
for available site-specific information on which
the current water quality status of the site may
There are a number of different sources of copper
in the estuary, largely associated with discharges
in the upper reaches. The background copper concentration
in the outer estuary mid-channel is usually ~3m
gl-1 but during storm events may exceed
5m gl-1. An
EQS of 5m gl-1 (dissolved annual average) exists for copper
in water, but no standards exist for copper in sediment
(although see guideline values from other countries).
Concern has been raised that the current EQS may
not be protective enough for some fauna, but where
levels of organic carbon are elevated, a higher
EQS may be acceptable.
The term phthalates covers a relatively wide group
of chemicals which should be regarded as ubiquitous.
At least some may be adsorbed onto sediments where
they can be concentrated to much higher concentrations
than found in overlying water. DNBP is likely to
be present in both the water column and the sediment.
The conservation agencies may be consulted at this
stage to provide information on whether the features
are in favourable condition. This approach will
be useful in cases as this where the "new plan
or project" is a variation to an existing consent.
This guidance manual can provide no information
on the definition of favourable condition for individual
features but can provide some guidance as to what
aspects of water quality should be considered in
drawing up condition tables for the site sub-feature.
In the current example, the most appropriate response
is that the designated feature is in favourable
condition, but there is concern that water quality
problem may be threatening that condition based
on the knowledge of occasional breaches of the EQS
and uncertainty over effects of the current copper
The conclusion for the situation in Seal Marsh
is that the change to the loading of copper may
have a likely significant effect on the condition
of the saltmarsh. Saltmarsh creeks acting as nursery
areas for crustaceans and fish may potentially be
significantly affected by increased loads and localised
high concentrations of DNBP, which may also have
an effect on the seal population.
Step IV: Internal and external consultation
The conclusions of Steps I to III are subject to
internal (within the competent authority) and external
(with the country conservation agency) consultation
to confirm, or otherwise, the judgement of likely
significance. On the basis of the concentrations
above, a judgement that a significant effect is
likely seems reasonable. The reasons for this are:
- Not enough information available on toxicity
of DNBP or endocrine disruption of mammals to
assess likely significant effect, but a possible
mechanism exists for an effect which would not
be restricted to the immediate outfall location
and may have serious population consequences if
realised. Therefore, precautionary approach is
- Background levels of DNBP (and other phthalates)
are not known.
- Copper is already known to exceed EQS outside
of a 100m mixing zone during storm events and
this risk is increased if loading increases. The
mixing zone would have to be made larger to comply
with EQS under such circumstances and the consequences
of this for the SAC feature would need to be examined.
- The rate of accumulation in sediment is likely
to increase under this scenario. There is a risk
of long-term exposure via this route.
For the situation in Seal Marsh, the conclusion
is upheld through the consultation steps and the
judgement of likely significant effect is confirmed.
An appropriate assessment is therefore required.
The appropriate assessment for this scenario is
likely to require the following:
1. For DNBP:
An assessment (from up-to-date sources
of information) of endocrine disruptor effects
- aquatic mammals
with emphasis on pthalates, possible routes
of exposure and any information on threshold
- Modelling of likely phthalate exposure
for the most sensitive organisms.
- There will be a need to adopt a very precautionary
approach to areas of uncertainty surrounding
this group of pollutants.
2. For copper:
Consideration of the adequacy of the copper
EQS in this case (see Table 5.2).
Modelling of copper mixing zone (where EQS
or other threshold selected will be exceeded)
in relation to occurrence of features of
of current Cu levels in sediment and modelling
of Cu accumulation in sediment over time.