Environmental Engineering Reference
In-Depth Information
use of such a basic protection level and the corresponding value for this protection
level obviously fall into the category of a policy decision.
With regard to site-specific Ecological Risk Assessment, there are good argu-
ments for linking ecological protection limits to land use. In other words: to link the
level of acceptable damage of the soil ecosystem to the 'ecological relevance' of the
corresponding land use. The reasoning behind this is that from a political viewpoint
a small disturbance of the soil ecosystem in a nature reserve can be worse than a
huge disturbance of the soil ecosystem at an industrial park (assuming that at least
some basic growth of trees and plants is possible at the industrial park).
The land uses 'Nature' and 'Agriculture' have a status apart. Some continents
(e.g., Antarctica) and countries (e.g., Australia, Canada, etc.) are still endowed with
a pristine or almost pristine environment. For some, to allow any contamination to
develop while dismantling human installations and remediating a contaminated site
located in such an area is perceived as a step which, over time, will inevitably lead to
the general degradation of those environments. Thus some countries have adopted
policies aiming at a full remediation of those sites (e.g., Quebec Soil Protection
and Contaminated Sites Rehabilitation Policy, Canada), independently of any poten-
tially acceptable ecological risks levels. Still, application of this principle must be
balanced with the appraisal of the threat to the ecosystem resulting from the tech-
niques used to remediate the site. If the excavation of slightly contaminated soils
found around rare mature trees in a park may result in the dying of the trees or, next
to a salmon spawning site in a river triggers a devastating erosion process, it may be
ecologically sounder to drop the remediation altogether.
Next to Nature reserves, Agriculture is the land use that is most dependent on
good functioning of the soil ecosystem. Arable farming and horticulture strongly
depend on a good Ecological Health, especially. Contaminated land could result in
a yield reduction or even make the growth of proper agricultural crops impossible.
One good reason to protect the soil quality in agricultural areas is that the soil qual-
ity impacts the amount and quality of the food that is produced. Poor quality soil
produces small amounts of poor quality food. Contaminants present in the soil or
pesticides applied during the growth season may be absorbed in, or adsorbed on the
food. On the other hand, the intensive use of the soil during agricultural practices
also threatens the soil ecosystem, for example, by using pesticides and by tillage.
During the last few decades the relationship of farmers to the soil ecosystem has
come under pressure. Today, a general belief in the need for more sustainable agri-
cultural practice is gaining popularity in all developed countries, worldwide (see
Section 13.8.3 ). Although politically debatable, the ecological relevance of land
use decreases in this order: Nature, Agriculture, Residential areas (the relevance
depending to a large extent on the unsealed surface area, for example gardens and
other green areas), Infrastructural work and Industrial areas.
13.7.4 Secondary Poisoning and Food Web Approach
Secondary poisoning refers to a chain of feeding relationships, where each organ-
ism higher in the food chain is exposed to contaminants (mainly contaminants with
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