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Stability


Hydrolysis


The substance has not been tested as a study is scientifically not justified. According to REACh regulation EG Nr. 1907/2006 Annex VIII Column 2, 9.2.2.1 the study does not to be conducted if the substance is highly insoluble in water.


The substance is a high molecular weight complex, self-assembled via organized network of hydrogen bonds and aromatic ring stacking. The molecules of melamine and cyanuric acid are strongly bound in the crystal lattice and require considerable energy to remove them. The absence of a melting point, the high decomposition temperature and the poor solubility in any solvent is a consequence of this complexation behaviour. The substance is only defined through the solid state. In such a case, water solubility is the composition of the aqueous solution formed at equilibrium under a defined set of conditions. Due to the measurement of solubility, the composition consists of dissolved melamine and dissolved cyanuric acid.  Therefore read-across  is justified from the supporting substances melamine (CAS 108-78-1) and cyanuric acid (CAS 108-80-5) .


 


Melamine is hydrolyzed only by mineral acid or inorganic alkali. Hydrolysis proceeds stepwise, with loss of one, two, or all three amino groups, i.e. producing ammeline, ammelide and cyanuric acid. The product spectrum varies with temperature, pH, and concentration; the final product is cyanuric acid. However, there is no indication that the substance hydrolyses under conditions defined by testing guidelines (Gmelin 1971 and Ullmann 2006). Regarding cyanuric acid, no hydrolysis occurred at any of the 3 pHs tested (Hu HC 1981).


 


Therefore and according to structural properties and a low water solubility (see chapter 4.8), hydrolysis is not expected/probable. Nevertheless, if it gets dissolved the decomposition products melamine and cyanuric acid are hydrolytically stable in the aqueous environment.


 


Biodegradation


Biodegradation in water: screening test


The substance has been tested according to OECD 301B with a concentration exceeding the solubility limit by the factor 16. Practically no indication of biodegradation was observed, thus, the substance is not readily biodegradable. Read-across studies with the components melamine and cyanuric acid themselves are available, which also show that they are not readily biodegradable nor inherently biodegradable (Nite 2010, Fimberger 1997, MITI/UNEP publication 1999).


 


Biodegradation in water and sediment: simulation test


Simulation tests are normally applied to chemicals which have failed a screening test for ready biodegradability, but have passed a test for inherent biodegradability. The substance is therefore not a candidate for a simulation test, as it did not pass the tests for inherent biodegradability. Additionally, a low log Kow of -2.28 and an expected log Koc in the range of 1 indicate low potential for adsorption to solid soil/sediment. No further scientific knowledge is expected. The compound is regarded as persistent.


 


Biodegradation in soil


A log kow of -2.28 (at 25 °C) and an expected log Koc in the range of 1 indicate low potential for adsorption to solid soil. Additionally, there is no direct or indirect exposure to soil for this test substance. Thus, a simulation test on biodegradation in soil does not need to be conducted. No further scientific knowledge is expected.


 


Bioaccumulation


Bioaccumulation: aquatic / sediment


The calculated log Kow of -2.28 at 25 °C (see section 4.7) of the test substance is below the threshold value of 4 (according to GHS criteria) and thus, accumulation in organisms of the test substance is not expected. The same holds true for the components melamine (log Kow = -1.22) and cyanuric acid (log Kow = 0.61).


A read-across from the source substance melamine is justified. Three experimental determinations of the bioconcentration factor BCF in 3 species of fish were reported confirming very low bioaccumulation potential (BCF < 3.8) (Lech 1984, Nite 2010).


 


Transport and distribution


Adsorption/desorption


The substance has not been tested as a study is scientifically not justified. Adsorption to solid soil phase is not expected because the substance has a low octanol water partition coefficient (log Kow of -2.28 at 25 °C) and the adsorption potential of this substance is related to this parameter.


The substance is a high molecular weight complex, self-assembled via organized network of hydrogen bonds and aromatic ring stacking. The molecules of melamine and cyanuric acid are strongly bound in the crystal lattice and require considerable energy to remove them. The absence of a melting point, the high decomposition temperature and the poor solubility in any solvent is a consequence of this complexation behaviour. The substance is only defined through the solid state. In such a case, water solubility is the composition of the aqueous solution formed at equilibrium under a defined set of conditions. Due to the measurement of solubility, the composition consists of dissolved melamine and dissolved cyanuric acid. Therefore read-across it is justified from the supporting substance melamine.


 


For the component 108 -78 -1(melamine):


The QSAR-estimated logKoc is low, i.e. in the range of 1.1 to 1.5, depending on the 2 methods used. A relevant adsorption of melamine to soil is therefore not expected.