Risk management of chemicals and contaminated land – from planning to verification - Environmental Deterioration and Contamination: Problems and their Management - page 262

Figure 9.6 Typical risk profiles as functions of time.

which come into contact with the atmosphere will be oxidized, and the resulting sul-
furic acid under wet conditions i.e., when raining, will dissolve and leach toxic metals
from the rock. The same metal-containing sulfide minerals are completely stable and
biologically unavailable under anoxic conditions, e.g., in the river bed sediment.
The fate of the chemicals in the environment can be modeled by generic or
site-specific numerical models and the effects can be calculated using mathematical,
chemical, biological, ecological, etc. models. The models describing the transport, fate,
behavior and the effect of chemicals approach reality at different scales and yield dif-
ferent uncertainty levels of the risk value. Even on-site environmental assessment may
carry high uncertainty due to partial characterization and poor representativeness.
Quantitative RA can rely on short- or long-term data and information. Natural
attenuation may decrease the risk (biodegradation of a contaminant) but may also
decrease by dispersion or transport of contaminants to more sensitive areas. Short- and
long-term risk values may differ significantly. It is the responsibility of the risk manager
to identify the relevant spatial and time-based scale to be taken into consideration.
Some typical trends are shown in Figure 9.6.

- Single stroke with rapidly increasing and rapidly decreasing risk is typical of acci-

dental emissions, tank leaking, dam breach, etc. The cyanide spill in River Tisza,
Hungary, in 2000, for example, not only caused extremely high acute risk and
damage but also a relatively rapid decay and good opportunity for regeneration.
A one-off or regular release of biodegradable pollutants, e.g., petroleum hydro-
carbons can spontaneously disappear from the environment, mainly if the affected
ecosystem has adapted to the pollutant.

- Rapid or moderate increase with moderate or slow decrease of risk can be observed

when emission and natural attenuation occur simultaneously. Depending on the
nature of the contaminants, the RR capacity and adaptability of the recipient