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of topical parathion ( Qiao and Riviere, 1995 ). Occlusion enhanced the cutaneous
metabolism of parathion to paraoxon and to p -nitrophenol as well as the percutane-
ous absorption and penetration of both parathion and p -nitrophenol. Occlusion also
reduced parathion and p -nitrophenol levels in the skin, but increased p -nitrophenol
and p -nitrophenol glucuronide in the blood.
Other in vivo studies ( Qiao et al., 1993 ) showed that dermal occlusion significantly
enhanced the rate and extent of parathion absorption in pigs in the abdomen (43.94
vs 7.47%), buttocks (48.47 vs 15.60%), back (48.82 vs 25.00%), and shoulder (29.28 vs
17.41%). Although significant anatomical site differences were observed with nonoc-
cluded skin, these site differences were concealed with occluded skin. In vitro studies
with parathion also demonstrated that occlusion increased absorption from 0.46-7.69
to 1.04-17.46% at doses ranging from 4 to 400 g/cm 2 ( Chang and Riviere, 1993 ).
Pesticides can be transferred from cotton fabric onto and through human skin as
demonstrated in several studies ( Snodgrass, 1992; Wester et al., 1996b ), but it should
be recognized that these studies were under occlusive conditions. Dermal absorp-
tion of malathion was 3.92% with ethanol-wet fabric and 0.6% with 2-day-treated
cotton sheets ( Wester et al., 1996b ). However, malathion absorption was increased to
7.34% when the 2-day-treated/dried cotton fabric was wetted with aqueous ethanol.
In the same study, absorption of glyphosate was 1.42% in water solution, 0.74% when
applied as wet cotton sheets, and 0.08% when applied as 2-day-treated/dried cotton
sheets. Absorption increased to 0.36% when the 2-day-treated/dried cotton sheets
were wetted with water to simulate sweating and wet conditions. Military uniforms are
impregnated with permethrin as a defense against nuisance and disease-bearing insects.
Application of fabric impregnated with permethrin to the backs of rabbits resulted in
a 3.2% migration to the skin surface with 2% of the impregnant being absorbed and
1.2% remaining on the skin surface after 7 days of continuous skin contact ( Snodgrass,
1992 ). The implications of these interactions, especially for agricultural workers during
pesticide application in humid climates or for military personnel under combat condi-
tions in the desert, should not be underestimated.
(c) Soil
Pesticide adsorption to soil can alter the amount of pesticide available for dermal
absorption. It should also be recognized that exposure conditions such as exposure
time, pesticide concentration, soil load, and soil characteristics are important variables
that can theoretically influence absorption ( Bunge and Parks, 1997 ). Soil adherence
to skin, for instance, can vary from 10 -3 to 10 2 mg/cm 2 and has been shown to be
activity-dependent ( Kissel et al., 1996 ). Predicting dermal absorption of pesticides
from contaminated soils is, therefore, not a simple process and becomes problematic
because there are very few studies that have addressed many of these issues. For sev-
eral pesticides (e.g., PCP, 2,4-D, chlordane), percutaneous absorption in an acetone
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