Disodium [[N,N'-ethylenediylbis[N-(carboxylatomethyl)glycinato]](4-)-N,N',O,O',ON,ON']zincate(2-)

Adsorption / desorption

Description of key information

The estimated log Koc for EDTA-ZnNa2 is 1 (worst case, MCI method) (Zvinavashe)) based on QSAR calculations and confirmed by information from literature (weight of evidence). Due to the ionic structure no adsorption onto the organic fraction of soil or sediments is expected.

 

Key value for chemical safety assessment

Koc at 20 °C:

10

Additional information

Due to the ionic structure under environmental relevant pH conditions, no adsorption onto the organic fraction of soil or sediments is expected [EU Risk Assessment, 2004]. This is confirmed by experimental results where EDTA was almost entirely present in the form of negatively-charged complexes with alkaline earth and trace metals, and neither of these complexes nor the free or protonated ligand itself could have been significantly adsorbed on the surfaces of the solids [Gardiner, 1976; Cheng et al., 1972 and Hernandez-Apaolaza and Lucerna, 2011)]. Further on, it is confirmed due to the low log Pow of -3.86. in accordance with column 2 of REACH Annex VIII, a Adsorptions-/Desorption-Screening test (required in section 9.3.1) does not need to be conducted.   Gardiner J, 1976. Complexation of trace metals by ethylenediaminetetraacetic acid (EDTA) in natural waters. Water Res. 10:507-514.
EDTA (19 µg/L) labelled with C-14 was added to suspensions of representative solids and the proportion remaining in solution was determined at intervals. Particulate humic acid (300 mg/L), kaolin (650  mg/L) and silica (500 mg/L) suspended separately in hard ground water, river sediment (7.0 g/L) suspended in river water and a sample of effluent containing 40 mg solids/L from a percolating filter were used. Radioactivity was measured using KL 353 liquid scintillator and a Tracerlab Corumatic scintillation counter. The suspended humic acid, kaolin etc. concentrations were intentionally  chosen to be unrealistically high because it was suspected that the extent of adsorption would be small.
The extent of adsorption of EDTA on container walls and on humic acid, silica, kaolin, river sediment and humus solids (in effluent from a percolating filter treating domestic sewage) was measured and was found  to be negligible, even after contact periods of up to 48 h. The EDTA was almost entirely present in the form of negatively-charged complexes with alkaline earth and trace metals, and neither of these complexes nor the free or protonated ligand itself could have been significantly adsorbed on the surfaces of the solids.   Cheng S.M. et al., 1972. Reaction and movement of EDTA and ZnEDTA in Soils. Can. J. Soil Sci. 52: 337-341. Hernandez-Apaolaza L. and J.J. Lucerna 2011. Influence of the Soil/Solution ratio, Interaction Time and Extractant on the evaluation of Iron Chelate Sorption/Desorption by Soils. J. of Agri and Food Chem. 59, 2493-2500.