Risk management of chemicals and contaminated land – from planning to verification - Environmental Deterioration and Contamination: Problems and their Management - page 248

Verification of environmental technologies can be a generic performance assess-
ment based on the summary of the published references and evaluated applications,
concluding by issuing a statement on the acceptability and applicability, in some
countries with a license of a certain type of technology, e.g. thermal desorption for
contaminated soil treatment under defined conditions (volatility of the contaminants,
temperature and other technological parameters of the desorber). In the case of inno-
vative technologies the retrospective evaluation is based on technology demonstration
which is usually the first and the only problem- or site-specific application.
Environmental efficiency has further components on both sides of the balance such
as environmental costs or benefits. The main goal of the environmental technology is
RR of contaminated air, water, soil or waste at a certain location. The benefits of RR
for the treated air, water and soil and for their human and ecological users can be
expressed as the difference between the initial and final risks.
Assessing risk in a broader sense than the application's location, the risk-benefit
balance of technologies may differ to a large extent due to the environmental risks
and costs. Excavation, transportation and disposal of contaminated soil—depending
on the type of contaminants as well as the sensitivity of the transport route and the
disposal site—may pose higher risk to other environmental media and locations than
to the initial site.
The excavation of soil with high volatile chlorinated contaminant content probably
involves too high a “cost'' in terms of pollution to the atmosphere. It may be higher
than the cost of an in situ remediation, but the two costs are hardly comparable due
to different units of measurement (the value of clean air, the cost of ozone depletion,
the expenditures of a technology application and the value of a marketable ground
should have been aggregated in this case). Different spatial scopes also cause difficulties
in the comparative evaluation of, for example, decontamination of a local soil and
groundwater compared with global atmospheric deterioration.
The example of toxic metal-contaminated bed sediments in surface waters or the
soil of wetlands also provide a good example for demonstrating the sensitive balancing
of environmental risks when making a decision. Lead, mercury, zinc and cadmium may
contaminate bed sediments in high concentration due to historical industrial pollution.
Under anoxic or fully anaerobic conditions, the toxic metals are present in completely
insoluble form as sulfidic precipitates (MeS). When the redox potential increases, MeS
molecules are oxidized to MeSO 4 , which at an acidic pH will be dissociated and mobi-
lized as a water-soluble and bioavailable toxic Me + ion. Dredging the contaminated
sediment and suspending it in water or disposing of it under atmospheric conditions
is a rather risky undertaking compared to the previous stable, physically, chemically
and biologically inaccessible state. Water contamination by sediment dredging should
always be thoroughly considered and supported by risk calculations. The expenditures
of dredging, sediment transportation and disposal are further economic disadvantages,
in addition to the increased environmental risk.
Environmental technologies accompanied by high energy and material consump-
tion are generally disadvantageous from both economic and environmental points of
view. This is why a progress in the application of natural and ecological technologies
would be logical. Unfortunately the spread of these green technologies is very slow.
Widespread use of the results of the retrospective evaluation of RR mea-
sures requires a uniform evaluation and characterization methodology, access to