Dermal Dosimetry

  • 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.