- In comparison to air sampling and even biological monitoring, dermal
dosimetry is not a simple or routine procedure. Thus far, its use is limited
to research and to specially designed studies. An individual applying dermal
dosimeters should be thoroughly trained regarding the placement and
retrieval of the dosimeters and recording of observations and other
information about the activity. In addition to objective parameters,
observed work practices can also have statistically significant important
influences on dermal exposure, as observed by Popendorf.(8)
- Each patch dosimeter is a sandwich holding a passive matrix (like a cotton
gauze sponge) flat and to protect it from skin perspiration. Either one or
two sets of patch dermal dosimeters can be used. The most important is the
set placed against the skin under the clothing, typically at the locations
noted in Table
2. It is believed that errors will result from using patch dosimeters
attached to the inside of clothing that is free to move relative to the
skin; such dosimeters will neither collect contaminants reaching the skin
via penetration through openings (such as the neck, sleeves, or cuffs) nor
be affected by the air motion carrying contaminant through the weave of the
fabric. A second set of dosimeters may be placed outside of any clothing; it
is also important that no inner dosimeter is placed beneath an outer
dosimeter. A more detailed description of
placement
and handling of dermal dosimeters is available.
- After dosimeters have been in place throughout an activity involving
exposure, they are carefully removed, prepared for extraction (the
quantitative removal of the chemical from the collection matrix), and the
extract is analyzed for the mass of chemical. Various
calculations
can be made to determine the deposited dose (typically mg) and perhaps the
dose density (µg/cm²), the dose rate (mg/hr), or/and equivalent dose (mg
of total product such as a solution or powder in which the toxic chemical
has been diluted). Thus, in addition to quantifying the magnitude of the
dose, dermal monitoring can also describe the deposition density and pattern
of that exposure, which can easily vary one-hundred fold among individual
body locations.(8)
While most dermal dosimetry has used the patch technique,(2-16)
whole body dosimeters have also been used.(2,11)
Whole body dosimeters are typically a set of long cotton underwear (a
one-piece set is sometimes called a union suit) that minimizes the effect of
non-uniform depositions within a body part, but suffers from the lack of a
barrier between the skin and dosimeter and may add heat stress to the
wearer. After use, the whole body dosimeter may still be dissected into
portions covering individual body parts.(2)
- Equivalent dose is just one means that has been used to reduce the
variability of reported dose rates among studies by adjusting for the
chemical concentration (% by volume, lb/gal or g/L). Formulated products
vary widely, perhaps from near 100% to fractions of percent toxic ingredient(15-16);
pesticide tank mixes may range over a factor of 5 (concentrations from as
low as .04% to .2%). Other adjustments have included use rate (lb/hr, L/hr,
or kg/hr) and the activity (pouring, pumping, wiping; mixing-loading or
applying pesticides, or conducting some other task in a contaminated
workplace like re-entry for harvest).
- As with all other approaches to assessing dermal exposures, there are
limitations to the use of dermal dosimeters. Among the most important of
these limitations (not restricted to dermal dosimeters) is the difficulty in
accurately collecting depositions of volatile chemicals.(2,5,28)
An alternative type of pad was designed to retain a high fraction of
volatile chemicals, either agricultural or industrial; but adjusting dermal
measurements for ambient vapors complicates its use.(28)
In order for a pesticide to be efficacious for a long time, volatile
pesticides are rare.
|
Back to Top
