Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Available literature on phototransformation of thiourea in air reports that the substance is degraded by 0.23 to 4.7 % under the conditions of the GSF test and when irradiated at a wavelength of 290 nm (Freitag et al., 1985), respectively. In addition, an atmospheric half-life (t1/2) of about 3 hours at an atmospheric concentration of 5 × 105 hydroxyl radicals per cm³ was determined.

Regarding the phototransformation of thiourea in water, the calculated half-life of thiourea in sunlit natural water at a hydroxyl radical concentrations of 1 × 10-17 M is 171 days.

Measurable degradation of thiourea in sterilized soils could be observed, although the mechanism for the degradation was not studied. The extent of degradation is also not reported.

Thiourea is stable to hydrolysis at pH 4, 7, and 9.

Thiourea is not readily biodegradable in a OECD 301 screening level test but inherently biodedegradable (not fulfilling specific criteria) under the conditions of the SCAS Test. Significant mineralisation of thiourea at environmentally relevant concentrations (1 µg/L) could be demonstrated by Rheinheimer et al. (1990) in marine and brackish water and sediment samples. The river Elbe and its estuary served as an example for a highly contaminated habitat, whereas the western Baltic Sea can be regarded as less polluted.

The biodegradability of thiourea differed strongly between habitats. Overall, the biodegradation of thiourea ranged between 28 % (after 70 d of incubation) and 87.3 % (after 14 days of incubation). The experiment demonstrates that thiourea serves as nitrogen (N) source for degrading microorganisms. Thiourea is more easily biodegraded in N-limited environments.

Mineralisation half-lives (measured by CO2 formation) in marine water and sediment samples taken in the North Sea ranged between 20 and 39 days for water, and 17-28 days for sediment, respectively. Water and sediment samples from the North Sea were incubated at 10 °C. Therefore, these experiments are considered to more appropriately represent realistic environmental conditions than the results obtained with Baltic Sea samples, which were incubated at 20 °C. The hazard assessment is based on the mean value of the mineralisation half-lives reported above (marine water t1/2 = 29.5 d, marine sediment t1/2 = 22.5 d).

Also microorganisms in activated sewage sludge are able to completely biodegrade thiourea after adaption to the substance. Degradation products are nitrate and sulphate, indicating complete mineralisation.

Thiourea has a low potential for bioaccumulation as the substance has a measured log octanol-water partition coefficient of -0.92. This finding is supported by literature data for algae (Chlorella, BCF = 54) and fish (Leuciscus idus melanotus, BCF < 10).

According to the experimental Koc value of 36.49 for adsorption to soil thiourea is expected to be mobile in soil. The available Kd value characterizing adsorption of thiourea to sewage sludge was determined to be 90. Therefore, adsorption to sludge is considered to be of minor importance in the environmental fate assessment of thiourea.

The estimated Henry constant of thiourea is H = 5.58 × 10-9 Pa m³/mol. Therefore, thiourea is considered to be non-volatile from water surfaces. Furthermore, thiourea is not expected to volatilise from soil based on its vapour pressure.