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Advisory Committee on Health Effects of Endocrine Disruptors
The Supplement II to the Intermediary Report
1.4.1.4 |
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4 Approach to exposure in living organisms
The exposure in living organisms is a very important factor of
health risk of chemical substances. The observed concentrations
of substances in biological samples should be carefully
interpreted in this context, taking the following into account.
The half-life of the chemical agent in the living body
(particularly in blood) must be taken into account in evaluating
the observed values. For example, a BPA level measured does not
necessarily reflect the maximum exposure, since it is rapidly
eliminated from the body.
Metabolism is also to be considered. Since, for example,
phthalates are rapidly metabolized to mono- and diethyl
derivatives, the level of major metabolites often reflect the
exposure more exactly than phthalic acid level in the blood
Estimation of exposure from metabolites in the urine as a marker
may deserve studying in future.
A second factor to be considered is contamination on sampling.
This is essential since estimation of exposure in the living
body requires detection of very low concentration of substances
in the sample. Apart from the selection of sampling devices, air
pollution in the sampling and laboratory environment is easily
overlooked. Blank analysis resulting from one and the same
measuring system (background) is a useful means to deal with
these problems.
Precision control is indispensable in chemical analysis, even if
the procedure follows strictly the guideline. Double check using
the same sample must regularly be performed for this purpose in
addition to the measurement of background and precautions about
sampling mentioned above.
It should also be noted that the values observed are not always
equal to the true concentration of the substance in question in
the organism. For example, the ELISA or RIA technique, which is
based on the reaction of the antibody that has an epitope
corresponding to the analye, may give values higher than the
actual concentration of the analyte.
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