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Environmental fate & pathways

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Description of key information

The fate of diammonium hydrogen citrate in the environment is most accurately evaluated by separately assessing the fate of its moieties ammonium and citrate. In the assessment of environmental fate and behaviour of diammonium hydrogen citrate, available data indicate that ammonium and citrate are readily biodegradable. Hence, diammonium hydrogen citrate is also expected to be readily biodegradable.

Ammonium is not persistent in water. Available evidence points to a ready biodegradability of ammonium under aerobic conditions.

 

Citrate in the form of citric acid is ready biodegradable according to studies of biodegradation in water and sewage sludge and QSAR-based estimates.

Additional information

The fate and toxicity of diammonium hydrogen citrate in the environment is most accurately evaluated by separately assessing the fate of its moieties “ammonium (NH3, NH4+)” and “citrate”.

 

Read-across approach

Diammonium hydrogen citrate consists of two ammonium [NH4]+ ions and one hydrogen citrate ion [C6H6O7]2-. Based on the solubility of diammonium hydrogen citrate in water (1,000 g/L at 20°C), a complete dissociation of diammonium hydrogen citrate, resulting in ammonium (NH4+) and (hydrogen)citrate, may be assumed.

In aquatic and terrestrial environments, ionic ammonium (NH4+) is in equilibrium with ammonia (NH3), and the respective speciation is influenced by various parameters, including temperature, pH, salinity and ionic strength. The main factors, however, that influence the equilibrium between un-ionized and ionized ammonia are pH and temperature (Environment Canada 2010 and references therein). Raising pH by one unit can cause the un-ionized ammonia concentration to increase nearly tenfold, while a 5 °C temperature increase can cause an increase of 40-50% (Environment Canada 2010 and references therein). The ionic strength of the water is also an important influence on the un-ionized ammonia concentration. As the ionic strength increases in hard or marine waters, there is a decrease in the un-ionized NH3 concentration (Environment Canada 2010 and references therein). Ammonia (NH3) and ionic ammonium (NH4+) are referred to as total ammonia nitrogen (TAN).

With pKa values of 3.13, 4.76, and 6.4, citric acid is expected to be present as citrate ion [C6H5O7]3- or hydrogen citrate ion [C6H6O7]2- under environmentally relevant conditions.

Thus, under environmentally relevant conditions, ammonium (NH4+) and (hydrogen)citrate are expected to be present in ionic form and rather mobile.

Reference:

Environment Canada (2010). Canadian Council of Ministers of the Environment. Canadian water quality guidelines for the protection of aquatic life: Ammonia. In: Canadian environmental quality guidelines, 1999, Canadian Council of Ministers of the Environment, Winnipeg.