Introduction to Ecological Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 607

human life, resilience and recovery are sometimes described as Ecosystem Services
in and of themselves. In general, both qualifications are used for the ecosystem as
a whole, since the huge diversity of organisms offers different kinds of possibilities
for resilience and recovery. However, it also can be applied to a specific species or
Ecosystem Service. It should be noted that since the mobility of soil organisms is
much less than that of aquatic organisms, recovery times in soil are generally much
longer than in an aquatic environment.
One important aspect of Ecological Risk Assessment, although difficult to assess,
is the timeframe during which an ecosystem can be impacted by a specific soil
contamination, while resilience and recovery are working to restore the ecosystem
(Eijsackers 2004 ). In other words: up to what level of contamination and for what
time span of exposure is ecological damage reversible?
Another important factor in Ecological Risk Assessment is the time span needed
for returning to the previous position. Periods for restoration differ to a large extent
among species. In general, the time spans for total recovery of vegetation and most
microorganisms may require years to decades, while for larger animals this might
take decades to centuries.
13.7.2 Adaptation
Adaptation is the ability of a community of organisms to improve its resistance to a
threat such as soil contamination. Adaptation can either relate to the behaviour of the
organisms (reducing exposure) or to the genetically controlled higher resistance of
specific organisms (reduced effects or no effects). Adaptation can be regarded on an
individual scale or from the perspective of a group of organisms. Individual organ-
isms, specifically larger organisms, may learn to deal with soil contamination, but it
is not expected that this significantly mitigates the corresponding adverse effects.
Adaptation from a population perspective is much more promising. It is well
known from the medical use of antibiotics, for example, that there is a part of
the bacterial population that is insensitive, and will survive and produce descen-
dants that form a largely insensitive population. Madsen et al. ( 1992 ), for example,
showed that at a forested site in the northeastern United States, metabolic adaptation
to the presence of PAHs was evident; radio labeled naphthalene and phenanthrene
were converted to 14 CO 2 in core material from inside but not outside a plume of
groundwater contamination.
Pollution-Induced Community Tolerance (PICT) is a tool to assess the adaptation
capability. The concept of PICT covers the issue of causality better than classi-
cal ecological community response parameters such as species densities or species
diversity indices (Boivin et al. 2002 ). Moreover, PICT relates to a more relevant
level of ecological organization, namely, the community.
There is not much known about the power of ecosystems to create 'inert pop-
ulations', not to mention 'an inert ecosystem', that can stand up against exposure
to contaminants in soil or groundwater. Posthuma et al. ( 1992 ) found that the cad-
mium excretion efficiency of Orchesella cincta (L.) (Collembola) populations were