Environmental Engineering Reference
In-Depth Information
Ideal Case
Quantity of
contaminant
in target
organ
Metal absorbed from
reference matrix
Metal absorbed
from soil
Ingested dose
Relative Bioavailability = Ratio of Slopes (soil/reference matri
x)
Fig. 7.6
Relative bioavailability value (RBV) assessment using dose response slopes
the complex animal manipulations required to obtain the plasmatic kinetics within
juvenile swines, concentrations in alternative targets can be chosen. For lead, liver,
kidney or bone concentrations at the end of the exposure period are considered to
be proportional to the bioavailable fraction (Jondreville and Revy
2003
). Unlike the
area under the plasma lead concentration-time curve, these concentrations in target
organs cannot be used to assess the actual amount which has been absorbed and
has reached the systemic circulation. However, these concentrations do allow for a
comparison to be made with the effects of the soil matrix on the bioavailability. In
this case, the relative bioavailability can be expressed according to Eq. (
7.4
) and
Fig.
7.6
:
RBA
=
Ratio of slopes (test matrix/reference matrix)
(7.4)
Specific conditions are necessary to validate this calculation (Littell et al.
1997
):
•
there should be a linearity of response of both the reference and the test matrix
over the dose range under investigation;
•
the two lines should have a common intercept;
•
the common intercept should be equal to the mean of the reference blank.
Depending on the contaminants of interest, specific target organs are relevant.
The liver, kidney, bones and also urine give satisfactory responses for cations (lead,
cadmium), urine and liver for anions (arsenic, antimony). In addition to using the
AUC to study the oral bioavailability of contaminants, three additional primary
methods are routinely employed (Kelley et al.
2002
). Where the contaminant of
interest is rapidly excreted, urine is a common end-point used in bioavailability
Search WWH ::
Custom Search