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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 thiourea
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 fluorescein treatment.
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 but irritation 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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