Substances Directive (fresh water)
1. Many human activities, and some natural processes, release
chemicals into watercourses. Some of these substances require
strict control if harm to the environment is to be minimised.
The most harmful, or dangerous, substances are controlled by
the EC Dangerous Substances Directive (76/464/EEC) and the associated
set of Daughter Directives.
2. Substances that
have the potential to cause the most harm to aquatic life due
to their persistence, toxicity or bio-accumulation are known
List 1 Dangerous Substances. The Directive requires that
pollution by these substances is reduced by eliminating their
discharge. Substances which are thought to be harmful, but not
to the same degree as List 1 substances are known as List
2 Dangerous Substances (above),
and discharges of these substances are to be reduced.
3. Every listed dangerous
substance has a concentration limit known as an Environmental
Quality Standard (EQS). The EQS is usually an upper concentration
(the exception being pH which has both upper and lower limits)
and is set for the receiving watercourse and not the discharge
itself. The dangerous substance is not believed to be detrimental
to aquatic life at any concentration below its EQS limit. EQSs
vary for each substance and can be different for fresh, estuarine
or coastal waters (Table 3). It can be an annual average concentration,
a maximum allowable concentration or a percentile concentration.
If the EQS is exceeded at a site then it will not be compliant
with the Dangerous Substances Directive (it will have failed).
The cause of every non-compliance must be fully investigated
and action plans to remedy the situation must be put in place
4. EQSs must not
be exceeded in any controlled watercourse in England and Wales.
Human activities produce the greatest levels of List 1 and List
2 substances, with industrial plants or sewage treatment works
being the major sources. Agency monitoring for EQS compliance,
therefore, is largely carried out downstream of this type of
discharge if there is the possibility that the effluent will
contain dangerous substances. Monitoring at these sites is likely
to represent the 'worst case' for EQS compliance. The Agency
carries out additional background monitoring at the bottom of
major river catchments (known as 'National Network' monitoring).
The downstream monitoring is carried out monthly, while background
monitoring is carried out quarterly. The results are gathered
and reported annually