Environmental Engineering Reference
In-Depth Information
Exposure Through Vegetable Consumption
The exposure through vegetable consumption is an important pathway, especially
for mobile contaminants. Tsukahara et al. ( 2003 ), for example, demonstrated that
the consumption of rice was the major source for cadmium exposure in Japan, for
10 out of the 47 provinces (prefectures) where this was investigated. Tao et al. ( 2004 )
found PAHs in all eight investigated vegetables, in Tianjin, Northeast China.
Exposure through vegetable consumption is dependent on the representative con-
centration in vegetables, the total vegetable consumption rates and the fraction of
vegetables from the contaminated area to total vegetable consumption. Actually, the
relative oral bioavailability in the human body also plays a role for this pathway
(e.g., Intawongse and Dean ( 2006 ), who investigated the oral bioavailability of cad-
mium, copper, manganese and zinc through consumption of leaves of lettuce and
spinach and the radish and carrot roots), although this process is less important than
for exposure through soil ingestion.
It is important to focus on the most relevant concentration in vegetables, that is,
the amount of accumulated contaminants in the vegetable at the moment of harvest-
ing and after 'normal kitchen preparation'. Moreover, since the purpose of exposure
calculations is to assess the exposure from contaminated sites, only contaminants
that originate from soil are of importance. This means that contaminants that are
deposited on crops due to rain splash must be included in the exposure calcula-
tions, in so far as they are not washed from the vegetables during 'normal kitchen
preparation'. However, contaminants from outside the contaminated site that are
atmospherically deposited on crops must be excluded from the exposure calcula-
tion. This 'outside' atmospheric deposition, however, contributes to the background
exposure (see Section 5.5.4 ).
The accumulated concentration in vegetables is often described on the basis of
a BioConcentration Factor (BCF), that is, a linear relationship between the con-
centration in vegetables and in soil. In regard to more sophisticated models for the
relationship between contaminant concentrations in soil and in vegetables, it is nec-
essary to distinguish between metals and organic contaminants. The reason for this
is that the behaviour in soil and the uptake of these two types of contaminants is
fundamentally different. Therefore, different methodologies are used to calculate
the concentrations in vegetables for metals and organic contaminants. For metals,
more sophisticated models enable the calculation of their concentration in vegeta-
bles on the basis of total soil concentration and soil properties (e.g., Krauss et al.
2002 ). The concentration of organic contaminants is best based on crop type-specific
uptake models that follow the Trapp and Matthiess ( 1995 ) concept. An example of
this model is given in Kulhánek et al. ( 2005 ) who calculated the PAH concentrations
of leafy vegetables, fruits, root vegetables and potatoes.
Oral exposure through vegetable consumption, including parameter identifica-
tion, is described in detail in Elert et al. ( Chapter 11 of this topic). The calculation
of the metal and organic contaminant concentration in vegetables, including input
parameter identification, is described in detail in McLaughlin et al. ( Chapter 8 of
this topic) and Trapp and Legind ( Chapter 9 of this topic), respectively.
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