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Vurderingsstrategier i forbindelse med håndtering af forurenede sedimenter
"Evaluation strategies for management of contaminated sediment" is a
literature survey on seabed materials and harbour sludge with particular focus on their
disposal by means of dredging and dumping.
Selected management approaches used in Denmark, our neighbouring countries and other
countries of interest is presented. The methodologies implements the international
conventions and agreements on the topic, which Denmark also is a party to. Various quality
criteria used for metals and organic micropollutants in these countries are presented.
There has been two principle approaches to the development of criteria quality for the
assessment of contaminants in sediment. One rests on the evaluation of the substance
content in comparison with pristine sediment: the background concentration approach. The
other is based on information on the known toxicity in water or sediment of the individual
substances. For three examples (tributyltin, copper and benz(a)pyrene) dramatic
differences are not seen between the the background based and the toxicological sediment
quality criteria. However, for tributyltin the few publicised values cover a large
interval.
A number of possible criteria which may be included in a future revised strategy for
sediment management in Denmark, are discussed. It is assessed that the use of acceptable
load criteria for dumping grounds should only be used after consideration of acceptable
total loads to the environment, substances on "black lists" or with "no
emission targets" are difficult to cope with in a strategy without the introduction
of "lower limits of concern". Calculation of the toxicity of the mixture of
substances in the sediment may be based on "predicted no-effect concentration"
(PNEC) or existing sediment quality criteria (SQC). Examples show that (non-dredged)
harbour sludge generally contained concentrations of contaminants above the PNCE or SQC.
The consequences of using a background value approach or a toxicity based example
criteria value approach are estimated for the annual Danish sediment dredging scenario.
Values for three examples (tributyltin, copper and benz(a)pyrene) are developed. The
disposal options are defined as dumping at sea, controlled disposal in coastal or sea
environment and disposal on-shore.
The selected criteria were taken from the literature and was as such not the target of
an assessment. They are provided to to give an image of the consequences in a realistic
criteria level. An example of the consequences of using existing Norwegian criteria is
provided. The overall conclusion is that the content of tributyltin is the limiting
factor.
With a strategy based on backgorund values it is estimated that approx. 65,000
tonnes/year can be disposed at sea (in addition large volumes of sand from navigation
channels off the Westcoast of Jutland, which is not included in the estimate). In disposal
facilities at sea or in coastal zone some 740,000 tonnes/year must be placed and on land
approx. 20,000 tonnes/year.
With a strategy based on toxicity it is estimated that approx. 65,000 tonnes/year can
be disposed at sea (in addition large volumes of sand from navigation channels off the
Westcoast of Jutland, which is not included in the estimate). In the selected criteria
there is only on order of magnitude to the criteria and no sediment falls in this range,
thus no material can be placed in disposal facilities at sea or in the coastal zone.
Approx. 770,000 tonnes/year must be placed on land.
In the report a number of issues ragarding treatment and disposal facilities are
raised, in addition to revised sampling and analysis programmes, which should be included
in the revision of the sediment
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