Shellfish waters monitoring
What are shellfish waters?
Shellfish waters are areas designated by the
Scottish Government where water quality must be protected or
improved to protect shellfish growth and contribute to the quality
of shellfish for human consumption. Sites are designated in
accordance with the European Union Shellfish Growing Waters
Directive (79/923/EEC) which was updated and replaced in 2006
(2006/113/EC). There are currently 78 designated shellfish growing
waters in Scotland; a full list is available here 
(45kb).
What are we required to
monitor?
The directive sets imperative and guideline
standards to be achieved for each parameter monitored, as well as
minimum sampling frequency and the reference methods of analysis.
Imperative standards are those which the directive requires to be
met, while guideline standards are those which member states must
“endeavour to respect”.
The frequency of monitoring can be reduced if
there is evidence that there is no risk of failing the standards.
If the water quality standards are not met, the directive requires
that measures are taken to ensure compliance within six years of
the site being designated.
Table 1: Shellfish waters imperative and
guideline standards
| Parameter |
Guideline
standard |
Imperative
standard |
| pH |
|
7–9 |
| Temperature |
A discharge affecting shellfish waters must not
cause a 2C increase compared to waters not affected. |
|
| Colour |
|
A discharge affecting shellfish waters must not
cause an increase of 10 Hazen units in filtered waters compared to
waters not affected. |
| Suspended solids |
|
A discharge affecting shellfish waters must not
cause a 30% increase compared to waters not affected. |
| Salinity |
12-38 ppth |
< 40 ppthA discharge affecting shellfish waters
must not cause a 10% increase compared to waters not
affected. |
| Dissolved oxygen |
> 80% |
> 70% (average value)
if < 70%, repeat
if < 60%, there must be no harmful effects on shellfish
colonies
|
| Petroleum hydrocarbons |
|
Must not produce a visible film on water surface or a
deposit on the shellfish, nor have harmful effects on the
shellfish. |
| Organohalogenated substances |
Concentrations in shellfish flesh must be limited so that
it contributes to the high quality of shellfish
products. |
Concentrations in shellfish water or flesh must not
exceed a level which gives rise to harmful effects on the shellfish
and larvae. |
| Metals |
Concentrations in shellfish flesh must be limited so that
it contributes to the high quality of shellfish
products. |
Concentrations in shellfish water or flesh must not
exceed a level which gives rise to harmful effects on the shellfish
and larvae. |
| Faecal coliforms |
< 300/100ml in the shellfish flesh and intervalvular
liquid. |
|
| Substances affecting the taste of the
shellfish |
|
Concentration lower than that liable to impair the
taste of the shellfish. |
| Saxitoxin (produced by dinoflagellates) |
|
|
Shellfish waters are monitored according to
the directive requirements unless there is sufficient evidence to
show that there is no risk of failing the standards. In practice
this means that the frequency of chemical monitoring has stopped or
has been reduced at the majority of sites as water quality is
generally good in these areas. However faecal coliforms in
shellfish flesh is monitored at the majority of sites. Sites
are exceed this guideline standard more than any other
parameter because the mussels accumulate bacteria from water as
they filter it to feed. The Food Standards Agency (Scotland)
monitor Escherichia. coli in shellfish flesh from
commercial sites who send their product to market. This data is
used to assess compliance with the shellfish waters coliform
standard where the site is in a designated water. Food Standards
Agency Class A is equivalent to the shellfish waters guideline
standard.
What are the
results?
All sites passed the imperative standards in
2008 showing that water quality in these areas is good however 30
of the 71 monitored sites failed the coliform guideline standard in
shellfish flesh. Studies have shown that there is no link
between coliform concentrations in waters and shellfish flesh at
this low concentration because the mussels concentrate bacteria
from the water. SEPA aims to improve compliance with the coliform
standard by reducing inputs of human and animal waste. Sources of
human waste are being reduced by investment in sewage treatment
however sources of domestic and wild animal waste are difficult to
identify and manage.
2008 SEPA and SFA faecal
coliforms in mussel flesh map
Click
here to
view map
(153kb).