Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 248

occurs over a short term, a slight exceedance of a Toxicological Reference Value
is not expected to result in a substantial human health risk. This is different for an
exceedance of a Toxicological Reference Value over longer time periods, as over-
all safety is reduced and sensitive population subgroups become less well-protected
(ILSI 1999 ). The dose-effect relationship for threshold contaminants mostly follows
an S-shaped curve (Fig. 5.4 ). Thus, the consequence of exceeding the threshold
value will depend on the steepness of the slope of the curve and where on the
curve any particular exposure falls. An assessment of the increased risk for long-
term exceeding of a long-term Critical Exposure value can be made by comparing
NOAEL and LOAEL values or more explicit use of the dose-response curve.
If short-term exceeding of the Critical Exposure values occurs, as can be the
case in intermittent exposure scenarios, the Critical Exposure value for long-term
exposure can generally not be used to assess human health risks. In cases where
a contaminant with high accumulation potential in the human body is concerned
(e.g., cadmium or dioxins), and there is a large margin between the chronic NOAEL
and the acute toxic dose, the impact of the cumulative dose can be easily cal-
culated and an unacceptable human health risk is not expected as long as the
critical cumulative dose is not exceeded. If the half-life of a contaminant is short,
however, the risk results from chronic stress and the risk from short-term peak expo-
sures should be assessed using the evaluation of short-term toxicity studies (Walker
1999 ).
International bodies have published Critical Exposure values for threshold effects
for short-term exposure values such as the MRLs (Maximal Risk Levels) from
ATSDR (which also published longer term MRLs).

5.6.2 Odour Nuisance and Taste Problems

Contaminants in soil or groundwater may cause odour nuisance or taste problems ,
in addition to toxic effects. There is no significant association between odour per-
ceptibility and the potential of the contaminants present to induce health effects
(Rosenkranz and Cunninghal 2003 ). Non-odorous contaminants, however, are more
likely to cause adverse human health effects. Therefore, the authors concluded that
odour cannot be used as a sentinel for health hazards. Nevertheless, odour and taste
problems might be aesthetically unpleasant and annoying. It is a policy decision if
odour nuisance and/or taste problems should be used as criteria for contaminated
site appraisal or as a criterion in the design of Remediation objectives.
Although human perception strongly differs among individual humans, odour
and taste limit values for several contaminants do exist. The corresponding soil or
groundwater concentration, however, is for some contaminants very stringent as
compared to human health or ecologically based risk limits. Swartjes et al. ( 2004 ),
for example, derived odour and taste limit values for MTBE in groundwater of 15
and 40 g/l, respectively, while they derived a toxicologically based limit value in

groundwater of 9420

μ

μ g/l.