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EC number: 200-543-5
CAS number: 62-56-6
As a result of the hazard assessment it can
be concluded that thiourea meets the criteria for clasification as
dangerous to the environment (Aquatic Chronic 2, H411), but is not
considered as PBT/vPvB.
Thiourea does not hydrolyse and is not readily biodegradable. According to EC 1272/2008 (chapter 188.8.131.52) the criteria for rapid degradation are defined as follows:
- ready biodegradability
- BOD (5 days) / COD ≥ 0.5
- Actual degradation (biotic or abiotic) in the aquatic environment by > 70 % within 28 days
- Degradation half-lives with proof of ultimate degradation (full mineralization).
The study conducted by Rheinheimer et al. (1990) could demonstrate that thiourea is actually biodegraded in the aquatic environment, but biodegradation is dependent on the habitat. Overall, biodegradation of thiourea ranged between 28 % (after 70 d of incubation) and 87.3 % (after 14 days of incubation). These figures are not related to primary degradation but reflect mineralisation of thiourea to CO2. As the actual (ultimate!) degradation of thiourea in the aquatic environment can reach or even exceed 70% within 28 days the substance is considered to be rapidly degradable.
Thiourea has no potential for bioaccumulation as the measured log Kow is significantly lower than 3 (measured value: - 0.92).
Acute toxicity values are available for all three trophic levels. The lowest aquatic acute toxicity value is an EC50 (96 h) of 3.8 mg/L (Friesel et al., 1984) as reported for Scenedesmus subspicatus.
Chronic toxicity data are available for algae and daphnia. Daphnia were more sensitive than algae. The 21-day NOEC for reproduction was determined to be 0.1 mg/L.
As chronic toxicity values are available for only two trophic levels, the substance is assessed based on both acute and chronic toxicity data and classified according to the most stringent outcome.
A comparison of the lowest acute toxicity value (EC50, 96 h = 3.8 mg/L) with the environmental classification criteria shows that the substance does not qualify for the classification categories for acute (short-term) aquatic hazards: As the EC50 is not ≤ 1 mg/L classification as category acute 1 is not warranted. In addition, the EC50 is in the range of > 1 to ≤ 10 mg/L. However, since thiourea is rapidly degradable as demonstrated by marine water-sediment simulation studies (Rheinheimer et al., 1990), and has no potential for bioaccumulation, classification as category chronic 2 is not warranted based on data for acute toxicity.
A comparison of the most sensitive chronic toxicity value with the classification categories for rapidly degradable substances, however, results in classification of the substance because the 21-day NOEC for reproduction of Daphnia magna fulfils the classification criterion for category chronic 2 of > 0.01 to ≤ 0.1 mg/L.
The available experimental test data are reliable and suitable for classification purposes under Regulation (EC) No 1272/2008. Based on available data, the test item is not classified and labelled as aquatic short-term (acute) toxicity, but as aquatic ling-term (chronic) toxicity category 2 (H411:"Toxic to aquatic life with long lasting effects") according to Regulation (EC) No 1272/2008 (CLP), as amended for the seventeenth time in Regulation (EU) 2021/849.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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