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When ammonium carbamate is dissolved in water a rather complex overall equilibrium among the carbonate, bicarbonate, carbamate, ammonium and ammonia is initially established:

H2NCOO-(aq) + H2O(l) ↔ CO32-(aq) + NH4+(aq) ↔ HCO3-(aq) + NH3(aq)

The carbamate ion H2NCOO- is unstable in acidic medium. Even at weak acidic condition (acetic acid/acetate) a complete decomposition (into ammonia and carbon dioxide) occurs in less than a second.

Although the carbamate ion is reported to be more stable in basic and neutral solutions, a study on the stability of ammonium carbamate conducted by means of 13C-NMR spectoscopy has demonstrated that, at concentrations and pH-values normally expected in the environment, it will rapidly hydrolyzed to bicarbonate and carbonate.

Short-term toxicity

Acute toxicity of ammonium carbamate towards aquatic organisms has been determined for fish, daphnia and green algae resulting in the following effect concentrations:

  • Pimephales promelas LC50(96h) = 37 mg/L (Curtis and Ward 1981)
  • Daphnia magna EC50(48h) = 63.7 mg/L (BASF AG, 1989, 1/90/1649/50/1)
  • Scenedesmus subspicatus EgC50(72h) = 129.1 mg/L (Ökolimna 1991, BASF-Study no. 01/90/1649)
  • Scenedesmus subspicatus EbC50(72h) = 75.9 mg/L (Ökolimna 1991, BASF-Study no. 01/90/1649)

Toxicity towards bacteria was determined in a short term respiration test, revealing an EC20 of 1000 mg/l for acitvated, domestic sludge (BASF AG 1990, 1901649). This is supported by a single species test, performed according to a German guideline (DIN 38412, part 8) using Pseudomonas putida as test bacterium. This test resulted in an EC10(16h) of 830 mg/l. Therefore, the inhibition of degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.

Long-term toxicity

No chronic toxicity tests are available. However due to the low hazard potential of ammonium carbamate shown in acute studies and its instability in the aquatic compartment at environmental conditions , chronic studies are not needed.

In fact the chronic toxicity of ammonium carbamate can be assessed in a read-acroos approach using the data on chronic toxicity available for the ions ammonium (NH4 +), bicarbonate (HCO3 -) and carbonate (CO3 --),. These species are present in equilibrium when ammonium carbamate is dissolved in water and are also the products of decomposition of the carbamate ion.

Rationale for read-across

When ammonium carbonate, ammonium bicarbonate, ammonium carbamate, or ammonium chloride with sodium carbonate dissolves in water several equilibrium reactions establish:

NH4+(aq) + H2O(l)↔NH3(aq) + H3O+(aq)

CO32-(aq) + H2O(aq) ↔ HCO3-(aq) + OH-(aq)

CO32-(aq) + NH4+(aq) ↔ HCO3-(aq) + NH3(aq)

HCO3-(aq) + NH3(aq) ↔ H2NCOO-(aq) + H2O(l)

H2NCOO-(aq) + H2O(l) ↔ CO32-(aq) + NH4+(aq)

It was shown that aqueous solutions of ammonium carbonate, ammonium bicarbonate and ammonium carbamate give very similar Raman spectra. It was confirmed that the solutions contain common species such as CO32-(aq), HCO3-(aq), H2NCOO-(aq), NH4+(aq) and solvent H2O(l) (Reference: Nanping Wen and Murray H. Brooker; Ammonium carbonate, ammonium bicarbonate, and ammonium carbamate equilibria: A raman study,J. Phys. Chem.1995, 99,359-368).

The overall equilibrium among the carbonate, bicarbonate, carbamate, ammonium and free ammonia can be expressed as:

H2NCOO-(aq) + H2O(l) ↔ CO32-(aq) + NH4+(aq) ↔ HCO3-(aq) + NH3(aq)

This equilibrium is confirmed by the analysis of 13C{1H}-NMR spectra obtained dissolving ammonium carbonate in D2O, in which signals referred to the ions carbamate and bicarbonate/carbonate have been observed (BASF, 2014)

 

Taking into account that the species indicated in the overall equilibrium indicated above are formed regardless of which salt is dissolved in water (ammonium carbonate or ammonium bicarbonate or ammonium carbamate), data on acute and chronic toxicity of ammonium carbonate, ammonium bicarbonate and ammonium chloride can be used to evaluate the aquatic toxicity of ammonium carbamate.

  • Ammonium chloride:(CAS No. 12125 -02 -9)

Pimephales promelas EC10(28 d)) = 4.18 mg/L (Mayes, 1986)

Daphnia magna EC10(21d) = 4.81 mg/L (Gersich, 1986)

  • Bicarbonate ion:

Pimephales promelas IC20(37 d)) = 368 mg/L (Farag, 2014)

Ceriodaphnia dubia IC20(7d) = 274 mg/L (Farag, 2014)

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