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EC number: 247-148-4
CAS number: 25637-99-4
Table 5. Distribution of Radioactivity (% Applied Dose) at 24-h
Post Dose Following Topical Application of HBCD to Human Split-Thickness
Table 6. Cumulative absorption (% Applied Dose) of [14C]-HBCD
into Receptor Fluid Dollowing Topical Application of HBCD to Human
Table 7. Distribution of [14C]-HBCD (µg equiv./cm2)
at 24-h Post Dose Following Topical Application of HBCD to Human
Table 8. Cumulative Absorption (ng equiv./cm2) of[14C]-HBCD
into Receptor Fluid Following Topical Application of HBCD to Human
*Results calculated from
data less than 30 d.p.m. above background
includes results calculated from data less than 30 d.p.m. above
Cell 2 was rejected from
Mean and SD due to mass balance being less than 90%
Cell 9 was rejected as it
had high tritiated water barrier integrity value and a high exposed skin
Hexabromocyclododecane (CAS No. 25637‑99‑4), also known as HBCD, is a
brominated flame retardant that is managed under the American Chemistry
Council – Brominated Flame Retardant Industry Panel (ACC‑BFRIP)
HBCD is a homogeneous mixture of three diastereomers (alpha, beta and
gamma). The gamma is present at the highest percentage
level of the three when manufactured. HBCD has very
low solubility in most common solvents.
As part of the safety evaluation of HBCD, a study was conducted to
assess the rate and extent of absorption of HBCD following topical
application of HBCD to human skin.
The split-thickness skin membranes were mounted into flow-through
diffusion cells. Receptor fluid (tissue culture medium
containing bovine serum albumin, glucose, streptomycin and penicillin G)
was pumped underneath the skin at a flow rate ofca 1.5 mL/h and a
tritiated water barrier integrity test performed. The
skin surface temperature was maintained at ca 32°C
throughout. All skin samples with a tritiated water
permeability coefficient (kp) less than 2.5 x 10-3 cm/h
were accepted for use.
[14C]‑HBCD was applied in an acetone vehicle at ca 47 µL/cm2in
5 applications of 6.0 µL over a ca 15 min period to
human split‑thickness skin membranes mounted in flow‑through diffusion
cells in vitro. The [14C]‑HBCD could
not be applied as the powder as the mass to be applied (ca 640 µg,
1 mg/cm2) could not be accurately dispensed. Therefore,
[14C]-HBCD was applied as a solution using acetone as the
vehicle. The test preparation ([14C]-HBCD
in acetone) could not be applied in a single volume application because
the solubility of HBCD in acetone was too low. The
acetone evaporated rapidly from the skin surface leaving behind the [14C]‑HBCD.
Absorption was assessed by collecting receptor fluid in hourly fractions
from 0 to 8-h post dose and then in 2‑hourly fractions from 8 to 24-h
post dose. At 24-h post dose, the exposure was
terminated by washing and drying the skin. The stratum
corneum was then removed by successive tape stripping. All
samples were analysed by liquid scintillation counting.
A summary of the results is provided in the table below:
In conclusion, following topical application of [14C]-HBCD to
human split‑thickness skin in vitro, the absorbed dose and
dermal delivery were 0.01% (0.06 µg.equiv./cm2) and
1.35% (12.82 µg.equiv./cm2) of the applied dose,
respectively. At 8-h post dose, 34.62% of the applied
dose was removed from the skin by washing and drying. At
24-h a further 28.76% was recovered in the 24-h skin drying and cell
wash. Therefore, the dislodgeable dose was 63.37% of
the applied dose. The stratum corneum contained a
further 31.49% of the applied dose. The bulk of this
(25.70%) was recovered in the first 5 tape strips. Since
the bulk of the stratum corneum associated material was found in the
first 5 tapes strips, this indicated that the [14C]‑HBCD was
on the surface of the skin and that the stratum corneum was an efficient
barrier to [14C]-HBCD penetration.
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