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Immunotoxicity
Risk Assessment for Children with Joint Exposure to Sunlight and Permethrin
Longstreth, J.1,3,
Blaylock, B.2, Prater, M..3,
Gogal, R.3 and Holladay, S.3
The Institute for Global Risk Research1
University of Louisianna at Monroe2
VA-MD Regional College of Veterinary Medicine3
Abstract-
In the sustained absence of sun exposure, human skin contains virtually
only trans urocanic acid (t-UCA). With sun exposure, t-UCA converts
to cis-UCA up to a maximum cis:trans ratio of about 75:35. In type I-II
skin (i.e., very fair, susceptible to sunburn), one-quarter of the dose
that would produce erythema (i.e., 0.25 MED) is enough to convert 60%
of tUCA to cUCA.. For fair-skinned individuals, this would be equivalent
to a 5- to10-minute exposure on an average summer day. Within the human
population, there is a ten-fold variation in the basal amount of tUCA
found in the skin,i.e., between 400 to 4000 ng/cm2. Thus,
depending on the individual's phenotype, 5-10 minutes of exposure
to sun could produce between 240 and 2400 ng per cm2 of skin
exposed. In a 6-year old, assuming that only the upper and lower extremities
(4755 cm2) are exposed to sun, a 5-10 minute exposure would
produce a dose of between 1 and 11 mg. In a 20 kg child, this would
equate to a dose of between 57 and 570 ug/kg/day. In C57Bl/6 mice, five
daily dermal doses of about 200 ug/kg/day are enough to suppress the
CHS response by 50%. Assuming that a child is as susceptible as a C57Bl/6
mouse, this suggests that there is likely to be a population of children
who produce enough endogenous c-UCA that they have a compromised CHS
response at least some of the time; indeed, with regard to those children
at the high end of the t-UCA concentration, it seems likely that they
could have impaired CHS responses most of the time. Given this postulate,
what then would happen were they exposed dermally to another immunotoxic
agent?. We have explored this question, looking at the pesticide permethrin,
the active agent in widely used treatments for headlice and scabies.
Our presentation will present the data from these experiments and discuss
how the results need to be considered in assessing the risk to children
from joint exposure to these two compounds.
Keywords: cis
urocanic acid, child, immunotoxicity, permethrin
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