Risk management of chemicals and contaminated land – from planning to verification - Environmental Deterioration and Contamination: Problems and their Management - page 273

soil or sediment can confirm the efficiency of the technology applied for the clean-
up (reducing the risk). In addition, ERA can detect the risky changes in contaminant
characteristics, fate and effect properties such as mobilization, production of toxic
metabolites, or their conversion into more toxic chemical forms. The risk scale of a
remediation technology can support, for example, the decision on the removal of
contaminated soil/sediment, in situ treatment or “leaving it as it is'' options. The risk of
physical destruction of the habitat caused by RR may be higher than the chemical risk.
Some RR measures completely destroy or remove habitats: for example, dig and dump,
soil removal, sediment dredging, or other extensive actions abolish soil, sediment and
wetland habitats. Decision makers have to evaluate and weigh environmental risks
and benefits, and the chance for recovery after clean-up.
Assessment before, during and after remediation of the risk posed by the con-
taminant is the main tool for the evaluation of the performance of alternative RR
measures. ERA based on monitoring data yields a risk-time curve and it can charac-
terize the environmental efficiency of an ERR measure. The spatial scale of the impact
of the remediation may be local, watershed-scale or even global (ban on locally emitted
chlorinated volatiles). Environmental monitoring and ERA of remedial technologies
are extremely important because every documented case contributes to our knowledge
and helps decision making in the selection of the management option.
The measurement end points of site assessment and remedial technology monitor-
ing should be selected based on the conceptual risk model of the site and the contextual
social and economic evaluation criteria. In this sense the selected assessment end points
should be susceptible and sensitive to the technological parameters, the contaminant
and environmental characteristics to satisfy biological, ecological, societal and eco-
nomic relevance. For example, a soil remediation based on bioventilation is best to
on-line monitor by measuring oxygen consumption and/or CO 2 production in soil
air. Detoxification of the contaminated water is worth monitoring by aquatic test
organisms, that of the contaminated soil by soil-living organism such as soil-dwelling
microorganisms, insects, soil-dwelling worms, collembolans, mollusks, mammalian
and avian species.

4.6 Uncertainties in environmental risk assessment
Uncertainties have already been dealt with in Chapter 8, therefore only some RA
relevant factors are listed here which greatly influence the result and its validity.

- Input data of ERA from archives, old documents, other databases may bear serious

errors; data quality requires a thorough examination;

- Input variables due to the heterogeneity of the environment may misguide the ERA

procedure;

- Identification of the chemicals is a great problem, not only on abandoned contam-

inated sites (where this problem is typical), but also in the case of newly produced
chemicals. The reason is that the by-products of chemical syntheses are present
in the products. If the by-product is 100-times more hazardous than the main
product, 2% by-product in the main product will triplicate the risk;

- The presence of mixtures and the interactions between contaminants may result

in significant differences in the risk value;