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EC number: 200-543-5
CAS number: 62-56-6
In screening level tests (OECD test
guideline 301) thiourea could not be demonstrated to be readily
biodegradable. However, additional data from a three year project
investigating the biological degradation of various xenobiotics in
natural water and sediment samples are available. During this project
the microbial degradability of thiourea at low, environmentally relevant
concentrations (1 µg/L radiolabelled 14C-thiourea) in
samples taken from the Elbe estuary as well as from the North Sea and
the Baltic Sea was investigated (incubation at 10 °C and 20 °C,
respectively). Degradation was followed by measurement of CO2
formation. The river Elbe and its estuary served as example for a highly
contaminated habitat, whereas the western Baltic Sea can be regarded as
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
Degradation half-lives (DT50)
based on mineralization to CO2 were derived from the
degradation graphs reported in the study. The DT50 in marine
water and sediment samples taken in the North Sea ranged between 20-39
days and 17-28 days, respectively. These samples were incubated at 10 °C
and are therefore considered to be more representative for environmental
conditions than the results obtained with Baltic Sea samples, which were
incubated at 20 °C. The hazard assessment is based on the means of the DT50
values reported above (marine water: DT50 = 29.5 d; marine
sediment: DT50 = 22.5 d).
Results from freshwater and freshwater
sediment samples taken at Hamburg-Teufelsbrück and Cuxhaven did not
reach 50 % mineralization during the total incubation time of up to 85
days. However, the experiment demonstrates that thiourea serves as
nitrogen (N) source for degrading microorganisms. Thiourea is more
easily biodegraded in N-limited environments:
1) Elbe estuary
Thiourea biodegradation is more extensive
and faster in habitats with lower nitrogen (N) content. Therefore higher
thiourea biodegradation can be found in the saltwater samples (e.g.
annual average of the total N-content at the area “Großer
Vogelsand/Scharhörn: 1.6 mg/L, Elbe I and Helgoland: < 0.5 mg/L) from
the Elbe estuary compared to its highly eutrophic freshwater parts (e.g.
annual average of the total N-content at Hamburg-Teufelsbrück, 1988: 6.2
mg/L). Thiourea is used as N source. Its mineralization proceeds slowly
and continuously and takes place parallel to the degradation of other
carbon (C) sources.
The same relationship could be observed for
the sediment samples: Thiourea biodegradation increases with increasing
distance from the coast.
2) Baltic Sea
The biodegradation of thiourea strongly
differed between different sampling points: In the surface water samples
from the Trave estuary (A, 1m) thiourea was completely and rapidly
mineralised. Presumably the test substance was consumed by bacteria that
otherwise degrade urea. These bacteria exist predominantly in wastewater
and are regarded as tracers for water pollution, as urea is rated to be
an anthropogenic pollutant. Thiourea competitively inhibits the
absorption of urea, thus the same transport mechanism is used.
In the water samples that were taken close
to the sediment layer from the Trave estuary (A, sw) biodegradation of
thiourea was much slower compared to the water sample A, 1m. This may
either be attributed to a reduced number of degrading bacteria that
could immediately make use of thiourea (however, after 40 days thiourea
biodegradation increased), or to the higher amount of N-sources in the
water layer close to the sediment.
In the water sample from the Lübeck bay (B,
1m) thiourea was almost as rapidly used as in the underlying sediment
sample (B, sediment). However, the extent of mineralisation was much
higher in the water sample due to a lower N-content.
In the sediment sample B only 24 % of
thiourea were mineralised, but only 41 % of thiourea could be found in
the water phase above the sediment layer. This indicates high adsorption
of 35 % in the silty sediment.
In sediment sample C, 52 % of thiourea were
mineralised, with a maximum of 13 % adsorbed in the sediment, as 35 % of
the test substance could be found in the water phase.
At station D (Oderbank) which is influenced
by the river Oder 72 % mineralization of thiourea could be measured in
the respective sediment sample (D, sediment). Unfortunately, no water
sample could be analysed for thiourea biodegradation. Sediment sample D
showed almost exactly the same biodegradation behaviour as water sample
A, 1m. Analysis of the water layer above the Oderbank sediment revealed
high nutrient contents. However, in this case the high NH4-N content did
not inhibit thiourea mineralisation.
In a supporting study (Tomlinson et al.,
1966) also complete degradation (mineralisation) of thiourea by
activated sewage sludge could be demonstrated, as evidenced by formation
of nitrate and sulphate.
Thus it could be demonstrated that thiourea
can be degraded under appropriate environmental conditions and the
substance shall therefore not be considered persistent, as:
1. Biodegradation in marine environments is
usually slower compared to freshwater habitats, which is also the reason
for less strict P-criteria in marine water and sediment as compared to
2. REACH does not require registrants to
investigate biodegradation in simulation tests in all environemntal
compartments; this is normally restricted to the freshwater compartment
and soil. For thiourea a study is available that does even surpass the
requirements of REACH as investigations in seawater samples (water phase
and sediment) have been conducted. Within the PBT assessment of a
substance it has to be demonstrated whether a substance is generally
biodegradable in the environment or not. Thiourea biodegradation can be
clearly demonstrated by the results of the Rheinheimer study for the
marine compartment. In addition, rapid biodegradation of the substance
in soil with half-lives ranging between 12.8 days and 18.7 days could be
shown (Loehr & Matthews, 1992);
3. The structural analogue urea is readily
biodegradaed in the environment. The degrading microorganisms are
expected to be generally capable of degrading these chemical structures
even in the case that the oxygen atom (urea) is replaced by sulfur
In conclusion, thiourea cannot be considered
to be a P or vP substance.
Thiourea does not have a significant
potential for bioaccumulation as the measured log Kow of the substance
is -0.92. This is further supported by two studies:
- Geyer et al. (1985) exposed algae (Chlorella)
to 14C-labelled thiourea for at least 24 h at room
temperature (20-25 °C). The subsequently determined bioconcentration
factor for the alga Chlorella was determined to be 54.
- Freitag et al. (1985) experimentally
determined the bioconcentration factor of thiourea to be < 10 in the
fish Leuciscus idus melanotus after 3 days of exposure.
Thus it can be concluded that thiourea has
neither B nor vB properties.
Thiourea is legally classified as Carc. 2
and Repr. 2 according to EC No 1272/2008. Thus thiourea is considered to
fulfil the T criteria.
Thiourea is neither persistent nor bioaccumulating,
hence not a PBT or vPvB substance.
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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