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EC number: 203-016-8
CAS number: 102-24-9
TMBX is hydrolytically unstable and breaks down to form methanol and
boric acid in the presence of water. Skin absorption can be predicted
for TMBX based on molecular weight and chemical structure. Subsequent
hydrolysis to borate and methanol can be expected in epidermal tissues.
Therefore, an assessment of skin sensitisation potential was conducted
taking account of the hydrolysis breakdown products of TMBX.
Both Boric acid (m.w. 61 g/mol) and methanol (m.w. 32 g/mol) can be
expected to readily penetrate the stratum corneum based on their
physical properties (see IUCLID Section 4.7 Partition Coefficient and
IUCLID Section 4.8 Water Solubility) and be available as potential
haptens for skin sensitisation induction.
A study in Guinea pigs was conducted according to OECD Guide-line 406
(Buehler test) using 95 % w/w boric acid moistened with distilled water
to enhance skin contact. Very faint erythema was observed in one animal
at induction stage and 2 animals at challenge stage and also in one
naïve control. No other adverse effects were
observed therefore the test substance was considered a non-sensitiser.
The sensitising potential of Methanol was examined using a modified
Magnusson-Kligman assay in Guinea Pigs (OECD 406). In the first run,
3/10 females exhibited a slight skin response (erythema score 1) 24 h
after challenge with 50% methanol, which can be interpreted as weak
sensitizing potential. In a second run using 12 female animals at a
concentration of 50 % methanol, 1/12 exhibited a slight skin response
(erythema score 1), 24 and 48 h after challenge which can be interpreted
as a weak sensitising potential. Neither studies contained enough
animals to have sufficient statistical power to discount a false
positive result, therefore the results of the studies were combined to
ensure a large enough experimental population. 4/22 animals were noted
with slight erythema (score 1), this does not meet the criteria for a
positive sensitisation reaction (>=30% of animals tested) Therefore
there is no significant evidence for the sensitisation potential of
In the first study, 3/10 females exhibited a slight skin response
(erythema score 1) 24 h after challenge, in the parallel test with
formaldehyde 1/10 females exhibited a slight skin response (erythema
score 1) 24 h after challenge, which can be interpreted as weak
In the second study using 12 female animals at a concentration of 50 %
methanol, 1/12 exhibited a slight skin response (erythema score 1) 24
and 48 h after challenge which can be interpreted as a weak sensitising
The intracutane inductions produced necroses and some open ulcerations
in both studies.
In summary, the low number of 4/22 animals with slight erythema (score
1) gives no evidence of a notable sensitisation potential of methanol.
Day of treatment
Very faint erythema (0.5) observed at one test site at 24 hours after first induction dose. No other irritation observed
No irritation observed
Very faint erythema (0.5) observed at two test sites at 24 hours after challenge dose. Irritation persisted at one site for 48 hours. Very faint erythema (0.5) observed at one test site at 24 hours in one naive control.
Results of skin sensitisation test:
Number of animals with signs of allergic reactions /number of animals in group
scored after 24h
0 / 10
0 / 20
scored after 48h
Based upon the lack of skin sensitisation potential for the hydrolysis
products of TMBX, which would be available as potential haptens for skin
sensitisation induction, the criteria set out in 1272/2008/EC for
classification of TMBX as a skin sensitiser are not met.
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