Human Health Risk Assessment - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 244

(Dybing et al. 1997 ), a Risk Characterisation based on children will result in a more
stringent Risk Assessment. In the Netherlands, lifetime average exposure is calcu-
lated, except for the assessment of lead exposure, where the child is also considered
to be part of a susceptible subpopulation. Grosse et al. ( 2002 ), for example, showed
that because of falling lead-blood levels, U.S. preschool-aged children in the late
1990 s had IQs that were, on average, 2.2-4.7 points higher than they would have
been if they had the blood lead distribution observed among U.S. preschool-aged
children in the late 1970s.
For commercial sites, the United Kingdom and Flanders (Belgium) limit expo-
sure duration and averaging time to a high-end estimate of the duration of a
professional career. With regard to non-threshold carcinogens, the general approach
is that a lifelong average exposure should be calculated, even if the toxicologically
relevant exposure duration is shorter than a lifetime.
5.5.4 Background Exposure
Humans are in constant contact with contaminants. They eat and drink contaminant-
holding foods. Contaminants can enter the food chain during primary production
(e.g., pesticide residues in vegetables from the super market) or are created during
the production of food (e.g., Polycyclic Aromatic Hydrocarbons from the grilling of
meat). Humans inhale contaminated air or volatile contaminants from glues, paint,
petrol, and printed works. They also put contaminant-holding materials on their skin
such as cosmetics and lotions.
From the perspective of exposure on contaminated sites, these exposures can be
considered as background exposure . Falcó et al. ( 2004 ), for example, showed a sig-
nificant contribution of hexachlorobenzene exposure through the consumption of
dairy products for the population of Catalonia, Spain. Cetin et al. ( 2003 ) demon-
strated elevated VOC-concentrations in ambient air, mainly of ethylene dichloride,
ethyl alcohol and acetone, from a petrochemical complex and oil refinery in Izmir,
Turkey.
It makes an important difference if background exposure is of a voluntary or
imposed nature. Voluntary exposure, such as exposure to cadmium through smok-
ing, or exposure to alcohol in drinks, can be controlled by humans. Exposures to
soil contaminants or to industrial emissions are typically imposed exposures.
Typically, the amount of background exposure is very contaminant-specific.
Moreover, background exposure differs among regions, depending on food pattern,
lifestyle, traffic density, and the presence of urban or industrialised areas. Therefore,
background exposure varies on a regional scale and is specific for different coun-
tries or regions. Several sources give estimates of background exposure for specific
regions.
From a medical viewpoint , total exposure (i.e., exposure from the contaminated
site, and voluntary and imposed background exposure combined) must be regarded
in cases of contaminants showing threshold effects. The reason for this is that
the human body does not distinguish between exposure from background sources