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EC number: 216-653-1
CAS number: 1634-04-4
permeability coefficient of MTBE of 0.028
cm/hour at a skin temperature of 38.5 °C was
temperature chosen in the experiment was not realistic for the actual
situation since the skin of hands is about 25.4
°C and of the lower arms about 30.3 °C (at an ambient temperature of 25
°C) (Cross et al. 2008). As
such, skin permeation coefficients measuredin vitroare determined
at 32 °C (OECD TG 428 “skin Absorption: in vitro method”).
coefficients are strongly temperature dependent (Gordon et al. 1998), a
correction for temperature is needed to extrapolate the coefficient
measured by Prah et al. to an actual situation. In a study of Gordon et
al. (1998), the effect of water temperature on skin penetration of
chloroform was studied. The difference between the permeation
coefficient at 38 °C and 32 °C was estimated to be about an order of
magnitude of 8 (Gordon et al. 1998).
the skin permeation coefficient of MTBE (measured at 38.5
temperature according to the results found in the study of Gordon,
results in a corrected permeation coefficient of 0.028/8 = 0.0035
cm/hour (at a realistic temperature of 32 °C).
the calculation of the percentage dermal absorption, an aqueous Kp of
0.004 cm/hour was used (which is more worse-case)
of initial absorption
deduced in EHC 235 (2006), the following equation is true:
Kmx D/h 
is the permeability coefficient; Km is the
pseudo-homogeneous partition, or distribution coefficient between the
stratum corneum and the vehicle; D is the effective diffusion
coefficient; h is the membrane thickness)
derive the Kp for the neat substance, the aqueous Kp has
to be divided by the stratum corneum/water partition coefficient (Km).
The Km (stratum corneum/water) for MTBE was calculated to be
2.06 by using the QSAR described by Ten Berge (2009).
the aqueous Kp was 0.004 cm/hour, the Kp for neat
liquid is: 0.004 / 2.06 = 0.00194 cm/hour.
derive the initial absorption of neat MTBE, the Kp for neat
liquid has to be multiplied by the density. The density of MTBE is 741
the initial absorption of neat MTBE is 0.00194 cm/hour x 741 mg/cm3=
above mentioned explanation can alternatively be expressed as follows:
absorption (mg/cm2/hr) = rholiquid* (D/h) 
is the density of the liquid (mg/m3); D is the diffusion
coefficient of the liquid in the stratum corneum (cm2/hr); h is the
tickness of the stratum corneum)
is the permeability coefficient; Km is the stratum
corneum/water partition coefficient)
of equation 3 in 2 gives:
absorption (mg/cm2/hr) = rholiquid* Kp/Km 
density of MTBE is741
the Kpand Kmwere determined to be 0.004 cm/hour
and 2.06, respectively.
such, the initial absorption (mg/cm2/hr) = 741 * 0.004/2.06 =
conclusion, the initial absorption of neat MTBE is 1.44 mg/cm2/hour.
MTBE is very volatile, a strong competition between evaporation and skin
absorption will occur in case the skin is exposed to neat MTBE.
on the REACH Guidance appendix R14.1, it was calculated that the
evaporation rate of MTBE is 1008 mg/cm2/hour.
of each dose of MTBE exposed to the skin 0.143% (1.44/1008) is available
for skin absorption because of the majority of the MTBE evaporates
before absorption can occur.
such, the percentage of dermal absorption of MTBE is assumed considered
to be 0.143%. For the calculation of the dermal DNEL, a percentage of
dermal absorption of 0.2% is used (to be at the safe site).
conclusion, the percentage of dermal absorption of MTBE is 0.2%. This
value is used for the calculation of the DNEL for dermal exposure.
A, Collard M, Nelson A, 2008. Body Segment Differences in Surface Area,
Skin Temperature and 3D Displacement and the Estimation of Heat Balance
during Locomotion in Hominins. PLosONE 3(6),1-9 [e:2464].
235 Environmental Health Criteria 235: Dermal Absorption, World Health
SM, Wallace LA, Callahan PJ, Kenny DV, Brinkman MC, 1998. Effect of
Water Temperature on Dermal Exposure to Chloroform Environ Health
Perspect 106, 337-345.
J, Ashley D, Blount B, Case M, Leavens T, Pleil J, Cardinali F, 2004.
Dermal, Oral, and Inhalation Pharmacokinetics of Methyl Tertiary Butyl
Ether (MTBE) in Human Volunteers. Toxicological Sciences 77, 195–205.
TG 428 “skin Absorption: in vitro method”
Berge W, 2009. A simple dermal absorption model: derivation and
application. Chemosphere 75(11), 1440-5.
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