Pk. Scott et Dm. Proctor, EVALUATION OF 10-PERCENT MINIMUM ELICITATION THRESHOLD FOR CR(VI)-INDUCED ALLERGIC CONTACT-DERMATITIS USING BENCHMARK DOSE METHODS, Journal of soil contamination, 6(6), 1997, pp. 707-731
Historical patch test data have been used to propose health-based soil
cleanup levels for Cr(VI) that are protective of eliciting allergic c
ontact dermatitis (ACD) among previously sensitized individuals. Short
comings regarding the use of these historical studies in the risk asse
ssment of Cr(VI) have been identified and include the use of concentra
tion as the dosimetric for ACD elicitation rather than the mass per su
rface area. Information on the surface areas of the patches used by th
e authors of three of the historical studies have been made available
recently, and their dose levels have been converted from units of conc
entration to mass per surface area. For this study, benchmark dose met
hods were used to estimate the 10% minimum elicitation threshold (MET)
based on the converted patch test data from these historical studies
and from the data presented in a more recent patch test study by Nethe
rcott et al. (1994). A truncated lognormal model was fitted to the his
torical data from each individual historical patch test study, and to
the data from the Nethercott et al. (1994) study using maximum likelih
ood methods. The 10% MET from the Nethercott et al. (1994) study is se
ven times lower than those from the historical studies. There are two
primary reasons for this result First, Nethercott et al. used a 0.25%
potassium dichromate patch to screen study participants, whereas the h
istorical studies used patches with up to 0.5%. Hence, individuals who
were less senstive and those who had irritant, rather than allergic r
eactions at the high doses, were excluded. Second, Nethercott et al. u
sed a TRUE-Test patch that is a more efficient and reliable allergen d
elivery device than those used in the historical studies. Assuming 100
% bioavailability, the 10% MET from Nethercott et al. (1994) produces
an ACD-based soil standard of 445 mg/kg compared with the ACD-based so
il standards of 2,750 to 62,500 mg/kg calculated using the historical
studies. The most recent patch study of Nethercott et al. (1994), whic
h is based on modern patch testing methods and standardized diagnostic
criteria, is the most scientifically appropriate for use in the risk
assessment of Cr(VI) and produces the most conservative estimate of th
e 10% MET.