Cleaner Technology Projects in Denmark 1997
Sustainability of the Present Environmental Strain with Persistent Chemical Compounds
Bæredygtighed af nuværende miljøbelastning med persistente kemiske stoffer
Arbejdsrapport nr. 52, 1997, Miljøstyrelsen
This project points out a method for assessment of the long time sustainability of the loss of persistent chemical compounds to the environment in Denmark. In this context sustainability is defined in so far as the concentration of these compounds in the environment must not be increased and if necessary they should be reduced. The environment is considered to include the top soil layer (exclusive city areas), ground water, the fresh water environment and the sea environment, which are those parts of the environment that may directly effect humans, plants and animals. Thus, air has not been considered and is in this context only included as a way of transport.
The methodology considerations are grounded in heavy metals. However it may also be used on persistent organic compounds, if knowledge exists that will make it possible to pay attention to the degradation of these compounds that will take place in depots and the environment, or if it is deemed acceptable not to consider this degradation.
The method is based on mass balances, as supplies to and removals from each of the relevant parts of the environment are calculated. Furthermore, transport between the different parts of the environment, and stock building in landfills and residual products used for road construction purposes and the like, are taken into account. With regards to the ground water there is, however, employed a methodology of dividing supplies with the net precipitation.
As part of the methodological considerations, it has been evaluated, which final depots for heavy metals, that exist in the Danish environment. It is estimated that lake and sea sediments should be regarded as final depots. On the contrary, it has been chosen not to regard landfills and soil as final depots, since all known mechanisms for retainment of heavy metals in soil are reversible, and it must be anticipated that heavy metals, given the necessary time, will be washed out by percolating water. With respect to landfills, it was assumed that very few landfills, if any, will continue leachate collection for more than 50-100 years after the landfill operations have stopped. From that time on, leachate will likely be allowed to find its own way into the environment.
The long-term consequences of continued stock building in the topsoil and other depots (including incineration clinkers used for constructions work etc.) was considered. The basic problem in this context is that release and transport of metals will vary considerably depending on geological conditions (e.g. sandy versus clayey soils) and the chemical occurrence of the metal. As an example, significant leaching of metals from incineration clinkers may likely require around 10.000 years or more, whereas complete release of metals from limebased residues from flue gas cleaning may take place in 500-5000 years.
As calculations otherwise would become extremely complex, the choice was made to include the long-term perspective distinguishing between the following two scenarios:
 | The current situation, in which supplies to and removals from each compartment and transport to other compartments was estimated based on existing observations (this situation is not balanced, as stock building may take place in the top soil as well as in landfills/depots). |
| A hypothetical future on the assumption that the current pattern of consumption and disposal of the substance in question could continue forever, leading to the situation that removals and transport to other compartments have increased to a level reflecting a balanced situation for all compartments (output equals input also with respect to landfills and other depots). |
The methodology may be regarded as an overall evaluation based on average considerations. The methodology will provide an overview, but will not be able to cover local worst cases. In reality the methodology is only dealing with the top soil layer, ground water and the sea environment, since it is not possible, based on existing knowledge, to establish reliable calculations for the fresh-water environment.
The methodology has been tested by assessments and calculations for the heavy metal lead. The data fundament available for lead is assessed to be generally adequate except for data addressing the concentration of lead in percolating water and surface run-off. In addition to this, better data should be welcomed considering particle transport of lead in Danish streams, sedimentation of lead in lakes and transport in/out with water movements of the Danish internal marine waters. These data represent significant gabs in the existing knowledge on lead transport in the Danish environment.
The most important data requirements to undertake the assessments and calculations outlined here covers knowledge of:
| Mass flow in the society |
| Mass flow within agriculture |
| Previous assessments of the contribution to the Danish internal marine waters |
The data fundament available for the heavy metals cadmium and copper is deemed to be of almost the same quality as for lead. For nickel, zinc, mercury, chromium and arsenic the available data are partly inadequate.
For other heavy metals as well as for persistent organic compounds, the data fundament available is deemed as being poor. A significant effort with respect to investigations and data collection will be necessary, if the assessments and calculations outlined here should be completed for such compounds.
Author/ institution
Erik Hansen og Carsten Lassen, COWI
This report is subsidised by the National Council for Recycling and Cleaner Technology
ISSN no. 0908-9195
ISBN no. 87-7810-826-8