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Zirconium, acetate lactate oxo ammonium complexes consists of ammonium [NH4]+ and zirconium [Zr]4+ cations and acetate [CH3COO]2- and lactate [CH3CH(OH)COO]2- anions. A complete dissociation of zirconium, acetate lactate oxo ammonium complexes resulting in ammonium, zirconium, acetate and lactate ions may be assumed under environmental conditions. Since acetate, ammonium, lactate and zirconium ions upon release behave differently in the environment, the fate of acetate, ammonium, lactate and zirconium ions in the environment is most accurately assessed separately.

 

In the assessment of environmental fate and behaviour of zirconium, acetate lactate oxo ammonium complexes, data available for zirconium and ammonium cations and acetate and lactate anions indicate that abiotic degradation is not a relevant pathway. Biotic degradation is expected for acetate, ammonium and lactate ionswithout any transformation products of environmental concern.Zirconium is an inorganic element and thus biodegradation is not relevant.

 

Acetate:

Abiotic degradation is not relevant for acetate as it does not contain any hydrolysable structures.Acetate is ready biodegradable. Under aerobic conditions, acetate rapidly degrades to carbon dioxide and water in sediment, soil and water. As most important fermentation product, acetate is naturally produced during anaerobic decomposition of organic matter (e.g. acidogenic bacteria), during anaerobic waste water treatment and during photosynthesis. Even after a long anaerobic incubation, acetate is rapidly degraded in soil upon oxygen availability indicating an acetate tolerance of natural microbial communities.Acetate is present in equilibrium between the water column and sediments.The log Kow of acetate is with -0.17 (Hansch et al. 1995) low.Due to its low Log Kow and being ready biodegradabale, adsorption / desorption and bioaccumulation do not significantly affect the fate of acetate in the environment.

 

Ammonium:

Abiotic degradation is not relevant for ammonium as it does not contain any hydrolysable structures.Ammonia is a natural component of the environment and living organisms. It is considered to be readily biodegradable under aerobic conditions and thus, considered not to be persistent in water or soil.In soil, ammonium is rapidly degraded. Moreover, it does not permanently adsorb to soil, but rather variably binds to soil organic matter via ion exchange. Hence, the cation exchange capacity (CEC) of the respective soil determines the fate of ammonium. In aquatic and terrestrial environments, ammonium exists in two forms, the un-ionized, free ammonia (NH3) and the ionic ammonium (NH4+), which together are often referred to as total ammonia nitrogen (TAN). NH3 and NH4 both exist in an equilibrium, which depends on temperature, pH, salinity and ionic strength of the respective environment. With a pKa of 9.26, ammonium at relevant environmental pH conditions exists predominantly as NH4+ ions.

Lactate:

Abiotic degradation is not relevant for lactate as it does not contain any hydrolysable structures and thus is stable to hydrolysis.Lactate is ready biodegradable and transformation products of environmental concern are also not expected. Available data and QSAR estimates suggest a high mobility of lactic acid in soil. According the Level III fugacity model (U.S. EpiSuite v4.11), lactate partitions to soil (~ 62%) where it is rapidly degraded by soil microorganisms. In aquatic systems, lactate is present in equilibrium between the water column and sediments. At common pH conditions of most natural surface waters, lactate is expected to dissociate to the ionised form and therefore to remain largely in water.

 

Zirconium:

Abiotic degradation (hydrolysis) is not relevant for inorganic substances including zirconium. In general, (abiotic) degradation is irrelevant for inorganic substances that are assessed on an elemental basis. Biotic degradation is not relevant for inorganic metals and metal compounds. Zirconium as an element is not considered to be (bio)degradable. Zirconium has a very low mobility under most environmental conditions, mainly due to the stability of the mineral zircon (Zr(SiO4)) and the low solubility of the hydroxide Zr(OH)4. This limits the concentration of Zr in most natural water to <0.05 μg/L even in saltwater. Depending on the solution pH, Zr4+ and different zirconium hydroxides (i.e. Zr(OH)(3+), Zr(OH)2(2+), Zr(OH)3(+), Zr(OH)4) exist in solution. At pH 7, a Zr(OH)2(CO3)2(2-) complex can form, but this is unstable and decomposes with decreasing pH to form Zr(OH)4. The hydro-bicarbonate (Zr(OH)4-HCO3-H2O) complex may be the most significant Zr complex in natural water. Colloidal zirconium is also readily adsorbed by organic matter, macroplankton and siliceous material. Zirconium is considered to be only slightly mobile in soil with organic acids the main transporting agents for its transport and distribution (Salminen et al. 2005 and references therein).

Batch equilibrium experiments with solutions of soluble ZrOCl2 seem to indicate a very fast adsorption of zirconium to soil (1/k = ~ 3 min) and resulted in Kd values of 6,000 and 30,000 L/kg (dw) for an acidic and calcareous soil, respectively. The most important process appears to be adsorption to ferric oxides. However, very low soil/solution ratios favoring an adsorption were applied and resulting Kd values may be overestimated. Desorption experiments indicated very limited desorption, suggesting that non-reversible adsorption processes such as innersphere complexation or surface precipitation are involved. Considering the low solubility of zirconium in environmental solutions, a precipitation of zirconium hydroxides may also (at least in parts) explain the derived Kd values. Thus, zirconium is expected to be rather immobile in soils.

Additional information

Read-across approach

Zirconium, acetate lactate oxo ammonium complexes consists of a ammonium [NH4]+ and a zirconium [Zr]4+ ion as well as an acetic acid [CH3COO]2- and a lactic acid [CH3CH(OH)COO]2- anion. A complete dissociation of zirconium, acetate lactate oxo ammonium complexes resulting in ammonium, zirconium, acetate and lactate ions may be assumed under environmental conditions.

Acetate and lactate under predominating environmental pH conditions will be present in the ionic forms CH3COO- and CH3CH(OH)COO- and biodegrade rapidly.

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 unionized and ionized ammonia are pH and temperature (Environment Canada 2010 and references therein). Raising pH by one unit can cause the unionized ammonia concentration to increase nearly tenfold whereas 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 unionized ammonia concentration. As the ionic strength increases in hard or marine waters, there is a decrease in the unionized NH3 concentration (Environment Canada 2010 and references therein). Ammonia (NH3) and ionic ammonium (NH4+) are referred to as total ammonia nitrogen (TAN).

Based on analysis of thermodynamic stability of aqueous zirconium species, the concentration of free Zr4+ ions under environmental conditions is barely detectable. Ionic zirconium (Zr4+) at relevant pH conditions (pH 7 - 8) of aquatic and terrestrial environments will rapidly transform to zirconium-oxide and -hydroxide complexes, precipitate and not be bioavailable to aquatic organisms. Therefore, zirconium has a very low mobility and bioavailability under most environmental conditions. 

Thus, under environmentally relevant conditions, acetate, ammonium and lactate are expected to be present in ionic form and rather mobile whereas zirconium is rather immobile and complexed as zirconium (hydr)oxides. However, ammonium, acetate and lactate are expected to be rapidly biodegraded.

Thus, in the assessment of environmental toxicity and fate of zirconium, acetate lactate oxo ammonium complexes, read-across to zirconium and ammonium substances as well as acetic and lactic acid is applied since the individual ions of zirconium, acetate lactate oxo ammonium complexes determine its environmental fate. Since the dissociation products behave differently in the environment, regarding their fate and toxicity, a separate assessment of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

In order to evaluate the environmental fate of zirconium, acetate lactate oxo ammonium complexes, information on the assessment entities zirconium and ammonium substances as well as acetic and lactic acid were considered. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for zirconium, acetate lactate oxo ammonium complexes.

 

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.

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