Environmental Engineering Reference
In-Depth Information
chemical and ecological models have their own parameter errors (from measurements
or used data), which distort the model picture within a range shown by the area
between the dashed lines in Figure 11.14.
Many uncertainty studies emphasize the difference between variability and uncer-
tainty in the risk assessment (Jager et al. , 2001; Verdonck et al. , 2005). It is a basic
dilemma of environmental management how variabilities, e.g., meteorological and cli-
matic parameters, heterogeneities in the environment in time and space, or interspecies
and intraspecies variabilities should be handled. It is generally agreed that the main dif-
ference between uncertainty and variability is that uncertainty can be further reduced
by information, improved models and methods, whereas variability cannot (EUFRAM,
2005). What can be done is that the assessor can harmonize the scale of variability
with the resolution of the assessment method/model in order to reduce uncertainty
in mapping reality and obtain a more and more detailed picture on environmental
variabilities.
Uncertainty analysis deals with identifying and studying uncertain points of a
model and characterizing the impact of uncertainty on the model's result. Uncertainty
analyses use expert judgment, or measured data for the validation of the model.
The following items represent the greatest uncertainty in risk assessment and risk
management of hazardous chemicals :
-
Exposure and characteristics of the chemical substances such as emitted amount,
emission type and rate, chemicals structure of the substance, purity and impurities,
water solubility, volatility, octanol-water partitioning, degradability, biodegrad-
ability measured or calculated from primary data of uncertain quality;
-
Environmental characteristics such as geological, geochemical, hydrogeological
properties, temperature, pH, redox potential, bulk density, humidity, flow rate,
solid content, organic matter content are rather uncertain due to the environment's
high variability. Uncertainty assessment and validation of the data are generally
required;
-
Environmental transport and fate of chemicals summarize the uncertainties caused
by both the chemical substance and the environment. Uncertainties lie in the physi-
cal and chemical form of the contaminant depending on temperature, humidity and
redox potential, partition between environmental phases (air-water, solid-water),
photodegradation, hydrolysis, biodegradation in the environment, interaction
with other contaminants, and interaction with living organisms. Partition in the
soil, for example, depends on the actual physical and chemical form of the con-
taminant (ionic, oxidized, reduced, built into molecular grid, etc.) as well as on
the properties and composition of the matrix (soil texture, organic matter content,
humidity, pH and redox potential). Bioavailability and uptake of a contaminant
is determined by a large number of circumstances such as physical and chemical
form, concentration and binding of the chemical substance, environmental param-
eters (temperature, pH, redox potential and humidity), the organisms' type, age,
and sex, their dermal and membrane properties, and their inherited transport,
elimination and accumulation mechanisms;
-
Hazard and real risk of the contaminant, its hazardous properties, adverse eco-
logical and human health effects can be determined in silico, in vitro or in vivo.
All these models have their uncertainties and errors and the extrapolation from
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