Environmental Engineering Reference
In-Depth Information
appraisal of the status of the contaminated site in terms of risks for one of the pro-
tection targets (human health, the ecosystem, groundwater or Food Safety). Let's
consider, as an example, the appraisal of a PCB soil concentration of 1 mg/kg dw
soil. Without Risk Assessment, it is extremely difficult to give an objective and use-
ful opinion about this measured concentration. To some, it might be a non-problem,
since 1 mg/kg dw soil implies one in a million, and that seems very low when com-
pared with some (undefined) standard of high and low. But another person might
approach the case differently, that is, by noting that 1 mg PCBs equals about 1.8.
10 18 molecules. 1 Such a high amount of a contaminant that is able to impact the
immune, hormone, nervous, and enzyme systems is associated with serious health
problems, again by comparing it with some (undefined) standard of high and low.
But obviously both positions are not very useful, since the numbers do not tell any-
thing about the magnitude of the problem. And it is exactly that, an estimate of the
magnitude of the problem, which is the purpose of Risk Assessment.
1.5.2 The Concept of Risk
Risk is a concept that denotes a potential negative impact to an asset . There must
be a source for this potential negative impact, and this is generally called a hazard.
With regard to contaminated sites, the hazards are the adverse effects on human
health from contaminants in the soil or groundwater.
Many authors describe the magnitude of a risk in terms of probability (or change,
or frequency) and effect (harm). Since a doubling of the probability of a negative
impact on an asset often is judged similar to the doubling of the effect, risk is
often described as the multiplication of probability and effect. The determination
and often the evaluation of risks are called Risk Assessment and helps in making
transparent, rational, and defendable decisions.
With regard to the seriousness of an effect, it is very important if, and if so, to
what extent, one can influence the probability of a negative impact on an asset. In
this respect, it is useful to distinguish between a risk that humans deliberately take,
for example, the risk of getting lung cancer from smoking (a voluntary risk ), and
a risk that is beyond human control, for example, the risk of a natural catastrophe
(an imposed risk ). Humans can control voluntary risks, for example, by reducing the
number of cigarettes they smoke. Imposed risks, on the contrary, are not or are diffi-
cult to manage. At best, if one is prepared to take extreme measures that often impact
one's personal circumstances, some risks can be reduced, for example, by moving
to a place on the globe where the chance of natural catastrophes is relatively low.
Risk, both voluntary and imposed risks, relates to a concept we deal with on
a daily basis. Some examples of familiar voluntary risks, with human health as
the asset that can be negatively impacted, relate to the consumption of alcohol-
containing drinks, going out in traffic, and engaging in sport activities where injuries
1 Assuming an average average molecular weight for PCBs of 327 g/mol.
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