Environmental Engineering Reference
In-Depth Information
(failing to consider correlations between parameters). In addition to the model's uncer-
tainties, the applied physico-chemical, biological and toxicological data used by the
models may have their own measurement errors, called parameter uncertainty. This
means that real database models or models calibrated by existing datasets imply the
parameter uncertainty of the dataset used.
Current practice uses 3D models to visualize and better understand complex and
diverse environmental datasets. The models are applied to geospatial data mapping,
conceptual model evolution, communication to stakeholders, or for testing hypotheses.
When applying these models, it is important to recognize that their ability to replicate
the true situation is controlled by the data used to generate the model and the model
algorithms. For the models to be applied correctly the model uncertainty needs to be
identified and, where possible, quantified (Lelliott
et al.,
2009).
Parameter uncertainty
is the uncertainty of numerical values. The values of expo-
sures and effects needed for risk assessment are burdened with different uncertainties
including:
-
Measurement errors
of the physical, chemical analytical, biological and ecological
as well as environmental toxicological test methods;
-
Sample uncertainty
means the representativeness of the dataset, adequate sam-
ple size and range, and proper averaging methodologies. The site-specific risk
assessment procedure may be burdened by extreme sample uncertainty depending
on the heterogeneity of the environment, which is always a significant factor;
-
False data selection
, the lack of adequacy of the selected data or low resolution of
environmental data may lead to parameter errors. The use of default data implies
uncertainty because the environment characterized by default data is an abstrac-
tion, and default environmental parameters are not valid at any concrete point
or area. Maps of a resolution of a kilometer, 100 m or even 10 m are not able
to characterize heterogeneities of meter scale. The dose-response of a rat at high
concentration and short time (acute toxicity tests) is not adequate for modeling
long-term human exposure. The true value of ecotoxicity is between the measured
highest no effect (NOEC) and lowest effect concentrations (LOEC); the distance
between these two measured concentrations can be even an order of magnitude
as shown in Figure 11.13. The figure demonstrates the alternative series of test
results between no observed effect concentration (NOEC) and lowest observed
effect concentration (LOEC). After filling the gap between NOEC and LOEC by
the insertion of new measurement data, the alternative results may be 50, 60 or
90 mg/kg, reading the NOEC values from the dotted graphs (See also Chapter 1
in Volume 2);
-
Uncertainties due to the interactions between contaminants
, the compartments and
phases of the environment as well as the living organisms are significant and show a
wide variety. Transport of the contaminants, mobility and availability of different
physical and chemical forms of the contaminant, covered by the terms bioacces-
sibility, bioavailability and uptake are determining factors in risk assessment and
are responsible for multiple uncertainties;
-
Inadequacy of the models and methodologies
applied to the assessment of the
problem and the risk are frequent sources of uncertainties. It is still a typical
attitude, that managers and regulators accept a method, which is standardized
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