Ecological Risk Assessment of Diffuse and Local Soil Contamination Using Species Sensitivity Distributions - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 629

specific (sometimes large) areas as compared to water contamination. The “slow-
ness” of soil can be considered an extra motive for applying the Precautionary
Principle (UNESCO 2005 ) in soil protection.
14.2.2 Protecting Living Soil - Handling Diverse
Stressor Responses
When - as a consequence of protection goals - policy makers decide that soil protec-
tion should be of local, regional, national or international importance, soil protection
frameworks and associated tools are needed. The same holds for Risk Management
and remediation of soils that have been contaminated by past human activities or by
natural causes, like metal ore deposits that reach into the upper soil.
Given a policy decision to protect and manage soils, the issue of soil diver-
sity arises. Soils can be contaminated with vast numbers of contaminants and
mixtures. They differ vastly in physico-chemical properties (dry to wet, acid to
alkaline, sandy to clayey, low to high organic content, et cetera). They can have
vastly different contamination histories. They contain a vast variety of biotic species
assemblages, the compositions of which reflect the cumulative influences of climate,
soil composition, biogeography and evolution. As a result, we ask:
How can we appraise, protect and manage vital soil systems when facing the threats from
contaminants in this context of vast diversity and variability?
This chapter suggests an operational way to answer that question. That way is:
Model the ecological risks of contaminants, or contaminants mixtures, over a range of
concentrations from very low to very high.
Although risk modeling includes an array of empirical statistical modeling
approaches and mathematical simulations, such as models of organism bioenerget-
ics, population demographics, food web transfers, and ecosystem energetics, this
chapter is mostly restricted to sensitivity distributions , distributions of observed
sensitivities of species or of ecosystem functions.
Sensitivity distributions have been adopted (or are being discussed) in various
environmental regulations worldwide, including chemicals regulation, water quality
assessment, and the assessment of plant protection products. See, as examples, the
technical guidance documents related to Stephan et al. ( 1985 ), OECD ( 1992 ), U.S.
EPA ( 1995 ), EU ( 1997 ), EU (2000), and EU (2003). Amore detailed overview of the
implementation of sensitivity distributions in environmental regulations is presented
in Posthuma et al. ( 2002b ).
14.2.3 Field Effects of Soil Contamination in a Pollution Gradient
The use of the basic concept of sensitivity distributions in Risk Assessment is not at
variance with observed field effects of contaminant exposure; field effects along
pollution gradients clearly show that species indeed differ in their responses to