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EC number: 200-543-5
CAS number: 62-56-6
Five studies are available on skin irritation of thiourea. A study conducted by the CIVO Institute (1983), a study by Korte and Greim (1981) and a publication by Kosova (1970). In all studies thiourea did not induce skin irritation; results from a study on dermal absorption reports slight irritation at a dose of 2.000 mg/kg (TNO 1978).Three studies are available on eye irritation of thiourea. Korte and Greim (1981) reported thiourea to be slightly irritating but not subject to classification. In a study by TNO (1983) a 10 % thiourea solution was shown to be not irritating to the eye. The UBA-FB (1982) reports slight, reversible irritation.
Table 1: Individual and average skin irritation scores of undiluted
In a primary dermal irritation study 12
healthy, adult New Zealand White albino rabbits were dermally exposed to
0.5 g of undiluted thiourea on 1 inch² of the body surface area on the
back of the animals. Test sites were covered with an occlusive dressing
for 24 hours. Animals were then observed for 72 hours. Irritation was
scored by the method of Draize (1944) and the CIVO grading system. After
24 hours dermal effects were observed in seven out of twelve rabbits.
These effects consisted of very slight to well-defined erythema with or
without very slight or slight oedema. After 72 hours one rabbit treated
on the abraded skin showed slight scaliness. No other dermal effects
were observed. In this study, thiourea is very slightly to slightly
irritatin but not relevant for classification.
No effects were reported after examination of the eyes following the
In a primary eye irritation study similar to the OECD guideline 405, 100
mg Thiourea were instilled undiluted without any vehicle into the
conjunctival sac of the left eye of 6 male Himalayan rabbits. The eye
lids were kept close for 1 second and the application lasted during the
whole observation period for 72 hours as the eyes were not washed after
application. Animals were observed immediately after application, and 1,
24 and 72 hours after the treatment. Irritation was scored according to
Draize et al. (1944). Fluorescein was used to assess the score. The
right eye in which 0.1 ml isotonic NaCl were instilled served as control.
A deficiency of the study is that there is no detailled documentation of
individual animal data. Due to the fact that thiourea is not considered
to be irritating in this eye irritation test and the detailled
description of the procedure of the test this fact can be neglected.
The scores were reported as mean. Thiourea is reported to be not
irritating to the eye. Nevertheless a with respect to the conjunctiva an
irritation score of 1-2 has been reported for swelling and redness.
Thiourea was shown to be non-irritating to
the skin and the eyes according to the CLP. A study conducted by the
CIVO Institute (1983) showed that undiluted thiourea is a very slight to
slight primary skin irritant but scores were below the threshold for
classification. In a study by Korte and Greim (1981) no erythema and
oedema were observed. In a publication by Kosova (1970) thiourea did not
induce skin irritation.
Three studies are available on eye
irritation of thiourea. Korte and Greim (1981) reported thiourea to be
slighlty irritating to the eyes. In a study by TNO a 10 % thiourea
solution was shown to be not irritating to the eye. This study was rated
as reliable. Nevertheless it is not adequate as a 10 % solution of
Thiourea was tested.
Taken together the results of the studies
show that thiourea is slightly irritating to the skin and to the eyes
scores are below the threshold for classification.
Thiourea is only very slightly to slightly irritating to the skin with
scores below the threshold for classification. The same is true for
irritation to the eyes based on the results of appropriate studies.
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