Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
0.01 mg/L
Assessment factor:
10
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
0.038 mg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.001 mg/L
Assessment factor:
100
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
0.38 mg/L
Assessment factor:
1
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
0.072 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
0.007 mg/kg sediment dw
Extrapolation method:
equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
2.725 mg/kg soil dw
Assessment factor:
50
Extrapolation method:
assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

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.

Conclusion on classification

Thiourea does not hydrolyse and is not readily biodegradable. According to EC 1272/2008 (chapter 4.1.2.9) 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.

Based on the data presented above classification for environmental hazards in category aquatic chronic 2 (H411) is warranted.