Environmental Engineering Reference
In-Depth Information
concentration in the bioavailable fraction is assumed, it seems fair to increase the
acceptable concentration for this specific site by a factor of two, that is, to com-
pare measured concentrations with an ecologically based Soil Quality Standard of
200 mg/kg dry weight .
In spite of decades of research, however, the concrete application of bioavail-
ability assessment procedures, certainly with regard to Soil Quality Standards,
has so far been limited. The reason for this is that bioavailability is a highly
site-specific process. Several countries have implemented practical guidelines for
correcting Soil Quality Standards for bioavailability (Carlon and Swartjes 2007 ).
In the Netherlands, for example, soil type correction relationships are used for this
purpose on the basis of the organic matter content (organic contaminants), and the
organic matter and clay contents (metals) (Ministry of VROM 2008 ). Although the
use of these relationships for the bioavailability correction of Soil Quality Standards
lacks a strong scientific foundation, it is believed that these corrections are better
than totally ignoring bioavailability. Further research is on its way concerning the
application of different mechanistic models to tackle the problem (e.g., Koster et al.
2006 ).
In Hodson et al. ( Chapter 16 of this topic), the principles of bioavailability are
described in detail.
13.5.4 Endpoints
One important aspect in Ecological Risk Assessment is the definition of criteria
for assessing the ecological state of the soil ( Soil Ecological Health ). For this pur-
pose, relevant endpoints for testing must be selected, generally a protection target
at a lower trophic level than the soil ecosystem. These endpoints play a role in the
empirical derivation of the relationship between soil concentrations and Ecological
Health (or with ecological effects) such as, for example, for the derivation of Species
Sensitivity Distributions (SSDs), see Chapter 14 by Posthuma and Suter, this topic.
Effects are often related to, in ascending order of gravity, no-effect levels (No
Observed Effect Concentration, NOEC), lowest observed effects (Lowest Observed
Effect Concentration, LOEC), all kind of effects (Effect Concentration, EC), haz-
ardous effects (Hazardous Concentration, HC), or death (Lethal Concentration,
LC). Decision-makers may select an appropriate protection level in terms of a
specific percentage that apply to one of the endpoints, for example, Hazardous
Concentration for x% of the organisms (HCx) at which x% of the organisms are
hampered (Posthuma et al. 2002 ).
The selection of endpoints is also an important issue in site-specific Ecological
Risk Assessment. In these applications, a predescribed acceptable level of protection
of the appropriate endpoint must be defined. Since the range in which the physical
and chemical factors vary is strongly dependent on climate, soil type, soil conditions
and land use, it seems fair that the requirements for specific soil ecosystems should
differ by countries and regions. Often, endpoints are related to a single species such
as activity, reproduction rate, and mortality related to one type of organism. It is also
generally recognized that a healthy microbial population in soil is an indication that
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