Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
of venipuncture, finger sticks can be the collection method of choice.
The analytes of interest influence the sample collection regimen.
Concerns about external contamination, interaction between the analyte
and the sample collection vessel, and degradation, bacterial
contamination and time until processing should be considered when
designing the sampling protocol (Aitio & Järvisalo, 1984). Test tubes,
additive agents such as EDTA and sample stoppers all represent
potential contamination sources. Processing of serum samples should
occur in a timely fashion to prevent degradation of the analytes of
interest. For example, collection of serum samples for organochlorine
pesticide analysis requires that:
* all equipment be solvent-rinsed before collection and processing
* care be taken to avoid contact between the blood and the stopper of
the test tube
* the sample be centrifuged within 24 h of collection
* the serum be kept frozen prior to analysis.
Shipment of frozen samples requires special precautions to
prevent thawing during transport. For results to be valid, the
biological sample should be analysed within holding time, as required
by the specific medium and analyte.
10.6.2 Urine
Urine is another frequently collected biological medium. The
concentrations of compounds found in urine usually reflect
time-weighted averages in plasma during collection and storage in the
bladder (Que Hee, 1993). The presence of a contaminant or its
metabolite in urine generally represents recent exposure, though in
some cases it may represent release from storage within the body
(Lauwerys, 1983). Urine can be analysed for metabolites of organic
chemicals (e.g., benzene and styrene), metals (e.g., arsenic and
mercury) and pesticides as well as for mutagenic potential (Lauwerys,
1983; Baselt, 1988; Que Hee, 1993). Since collection of urine samples
is non-invasive, some investigators feel that, when validated, urine
may be a better sampling medium than blood for monitoring (Smith &
Suk, 1994).
Three types of urine samples are used for biological monitoring:
spot urine specimens, first morning voids and 24-h urine specimens
(Baselt, 1988).
* Spot urine samples are relatively easy to collect but there may
be significant variability with respect to exposure prediction as a
result of metabolism, liquid consumption and kidney function.
* First morning void samples have less variability since they are
more concentrated than spot samples, but require motivated subjects
to collect the samples.
* Twenty-four hour urine samples control much of the
intraindividual variability but require highly motivated subjects
in order to collect useful samples (Baselt, 1988).
http://www.inchem.org/documents/ehc/ehc/ehc214.htm
Page 181 of 284
6/1/2007