PRINCIPLES OF TOXICOLOGY

542 CONTROLLING OCCUPATIONAL AND ENVIRONMENTAL HEALTH HAZARDS
exposures occur from both inhalation and dermal routes, and that industrial hygiene is a valuable tool
in the risk assessment process.
Herbicides are routinely applied by foresters as a management practice to maximize yields of crop
species. Weed species that compete against the crop species for nutrients and space within the
developing forest are eliminated by the application of herbicides.
Toxicology studies in the laboratory were performed to describe the oral and dermal pharmacokinetics
of the herbicide as well as to determine a skin absorption factor for the herbicide. Volunteers
ingested known amounts of the herbicide in juice, and the portion of the total dose that was excreted
in the urine was determined. The time it took to excrete the material was also noted, and half-lives
were calculated. A correction factor to account for the uncollected herbicide was also calculated.
Known quantities were applied to the skin of volunteers for 8 h, and then washed off. Their urine was
collected for 3 days after exposure and analyzed to determine the total amount that was excreted in the
urine. The correction factor was applied to the amounts found in the urine to determine the total amount
absorbed.
A variety of toxicological studies looking at various organs and biochemical pathways were also
completed, and the most sensitive effect was competition with an organic acid excretion pathway. The
no-observed-effect level (NOEL) was determined as 2.5 mg/kg per day.
To assess the occupational risks associated with use of the herbicide, a field study was initiated to
determine exposure and dose to the herbicide. The study was conducted at four different sites, and five
or six workers were monitored for both inhalation and dermal exposure at each site. The workers also
collected their urine for 5 days: the day before the survey, the day of the survey, and 3 days after the
survey. The collected urine was analyzed for the herbicide, and the total dose was estimated.
For application, workers mix the herbicide into backpacks which can be slightly pressurized by a
hand pump. The herbicide mix is sprayed onto vegetation through a wand several feet long, or through
a gunjet which looks like a small gun, releasing herbicide under pressure by squeezing the trigger. The
spray pattern and size of the droplets is controlled by the tip inserted into the opening at the end of the
applicator. When the herbicide is released, some of it remains airborne, causing some exposure by
inhalation and deposition onto clothing and skin surfaces.
While applying the herbicide, applicators must walk near and sometimes brush against the
vegetation that has already been sprayed, exposing the skin. Since many of the herbicides are
formulated to penetrate through the waxy surface of the leaves, they are lipid-soluble, and, therefore,
can more easily penetrate the skin.
Evaluation of the potential inhalation exposure was fairly routine for the herbicides. An air-sampling
pump was worn by each worker for the duration of the mixing and application period, and the pump
pulled ambient air from the worker’s breathing zone through two filters in series: a mechanical filter
to collect the mist and a solid sorbent to collect vapors.
Dermal exposure evaluation was not as straightforward, however. The workers wore patches on
their clothing that were intended to absorb the herbicide they contacted. The patches were placed to
represent various portions of the body. Some additional patches were worn under the clothing to
determine the penetration through the clothing. In addition to the patches, hands were washed in a soap
solution and rinsed with water. The soapy wash water was collected to determine dermal exposure to
the hands.
The amount of herbicide that actually penetrated the skin (the dermal dose) was estimated by
• Adding the surface deposition on exposed body areas (DE), such as the face, hands, and
neck, to the product of the deposition on clothed body surfaces (DC), such as the chest, arms,
and legs, and the average clothing penetration (CP)
• Multiplying this sum by the skin absorption factor (SAF), the fraction of material that
impinged on the skin that was expected to penetrate the skin.
Estimated dermal dose = [DE + (DC × CP)] × SAF