Dermal exposure can be estimated by direct
methods, such as skin surrogate techniques, removal
techniques and tracer techniques. It can
also be determined indirectly with surface sampling
techniques, and as a summation with all
other routes of exposure by biological monitoring.
These methods are not validated in the sense that
the numbers that are obtained have an absolute
meaning but, as estimates of potential or actual
dermal exposure to (parts) of the body their value
is not to be under-estimated. In sampling the techniques can sometimes be used in
conjunction to each other. The most sophisticated
technique is described in detail by Chester [27].
He proposes to use the normal worker clothing as
a means for obtaining the potential dermal exposure,
special underclothing as a measure of obtaining
the actual dermal exposure, together with
the normal hygienic procedure of hand washing,
and finally biological monitoring as a measure of
internal dose along all routes of entry. This
method is of course very time- and money-consuming
and is not easily applicable for large
populations. The other techniques mentioned
have their respective advantages and disadvantages
as described.
For many situations, a more indirect method of
estimating exposure may be by using generic values
for specific activities, such as pesticide application,
gardening (soil contact) and swimming,
bathing and showering (contact with water).
Together with estimates of the time periods and
body part surfaces involved, this may lead to
appropriate estimates of exposure.
In some instances the use of surface sampling
may give adequate indications for the amount of
transfer to the body during contact. In any case it
is clear that the direct methods, although suitable
and sound for good estimates, fail without the
availability of data on skin absorption when
knowledge on the uptake through the skin is the
goal for the estimate.
The generalizability of the estimates of external
exposure (with regard to extrapolation between
chemicals) is in many cases quite large as has
been shown from the work on dermal exposure to
pesticides. This is not the case for biological monitoring,
which is a compound-specific method. Biological
monitoring is also not suitable for estimating
a relation with local health effects, in
contrast with systemic health effects.