Scientific and engineering improvement of environmental risk management - Environmental Deterioration and Contamination: Problems and their Management - page 418

have a conceptual, modeling or parameter origin. Variability as a phenomenon causes
similar problems as uncertainty. Therefore it has been included in the summary list,
even if it differs from uncertainty as it cannot be reduced by scientific and engineering
tools. Its inclusion is justifiable because large-scale environmental heterogeneity results
in high uncertainty in both models and parameters.
Contaminant transport, fate, and the effects and interactions among each other
(mixtures), with environmental matrices (clay minerals, humus) and the living part
of the environment (microorganisms, roots, skin, cell membranes) greatly increase
uncertainties in the real environment. In addition to the spatial and time-related vari-
ations, uncertainty and variability are further increased by geological, geochemical,
hydrogeological, hydrological, soil structural and textural heterogeneities and dynamic
processes. Latter include contaminant distribution, non-equilibrium partitioning,
chemical transformation, ageing, biological transformation, accumulation, etc.

- Identification of the contaminants is highly uncertain in contaminated land, espe-

cially in abandoned sites, brownfields and illegal hazardous waste disposal sites.
Chemical models do not fit to the objective of identifying all risky components
because the assessment plan using only chemical analytical tools cannot take into
account all possible and unknown contaminants. Many of them are uncommon,
unexpected or originally not present, but formed as transformation products from
one of the original contaminants and would not be included in the analytical
program. Uncertainty can be reduced by a tiered assessment using an integrated
chemical and ecotoxicological screening in an iterative way. This means that one
should identify the chemicals which cause the adverse effects;

- Source location of the identified contaminants may be highly uncertain, even in

the case when satisfactory historical information is available. Identifying the loca-
tion of the source can be done by in situ screening and assessment and by the
inverse application of transport modeling. If the source is not a point source but
a diffuse one, one faces spatial and time-related uncertainties, and interpolation
and extrapolation uncertainties when mapping the diffuse pollution;

- Characterization of the real environment combines the uncertainties of the concep-

tual model with the errors of sampling, sample handling and preparation, sample
analysis and tests. In addition to multiple uncertainties, the variability of the same
environment (spatial heterogeneities, meteorological, seasonal and time-related
variations) may corrupt the results of site characterization;

- Transport and fate of contaminants from the source through transport routes to

the target environmental compartments and the receptors are mainly accompanied
by uncertainties in association with the above mentioned multiple interactions.
Contaminants may interact with other contaminants and establish new chemical
forms, and additive, synergic or antagonistic effects may occur. Heterogeneous
distribution, partition, volatilization, sorption and desorption, dissolution and
precipitation, uptake and release of a contaminant or the components of a con-
taminating mixture are highly influenced by environmental parameters and the
environmental matrix. Uncertainties are enlarged by the heterogeneities and vari-
ability of the environment. Biological interactions, i.e., interactions between the
contaminants and the living part of the environment are significant and depend
on the genetic, metabolic, physiological and behavioral characteristics of the