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Adsorption / desorption

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Endpoint:
adsorption / desorption: screening
Remarks:
adsorption
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
The substance falls within the applicability domain of the selected (Q)SAR method.
Principles of method if other than guideline:
KOCWIN V2
Type of method:
other: modeled data
Media:
other: none specified from modeling program
Key result
Type:
Koc
Value:
ca. 0
Conclusions:
Koc estimate from Molecular Connectivity Index (MCI) (Na removed) 10 L/kg, Koc estimate from log Kow (Na retained) 2.138E-07 L/kg.
Endpoint:
adsorption / desorption: screening
Remarks:
adsorption
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Justification for type of information:
The study with the read across substance is considered sufficient to fulfil the information requirements.
Principles of method if other than guideline:
Experimental methods were similar to those described by Gardiner (1974). Gardiner J (1974). Water Res. 8: 157-164.
GLP compliance:
no
Media:
sediment
Radiolabelling:
yes
Details on test conditions:
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.
Key result
Type:
Koc
Remarks on result:
not measured/tested
Transformation products:
not measured

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.

Description of key information

Key value for chemical safety assessment

Koc at 20 °C:
0

Additional information

The adsorption/desorption coefficient for HEDTA or its structural analogue EDTA has not been determined in experimental studies. Due to the ionic structure under environmentally relevant pH conditions, no adsorption onto the organic fraction of soil or sediments is expected (EU Risk Assessment, 2004). HEDTA is expected to behave in a similar manner to EDTA given their similar ionisation and binding potentials. As such it is likely that HEDTA will remain in salt form in typical environmental conditions (e.g. neutral to mild acidic/alkaline conditions). Based on QSAR modelling (KOCWIN) the Koc is likely to be in the order of 2.138E-07 L/kg in salt form. In highly alkaline conditions the Koc is estimated to be in the order of 10 L/kg for the ionised compound. It should also be noted that, in accordance with REACH Regulation 1907/2006, Annex VIII, Column 2 an adsorption/desorption screen does not need to be conducted as HEDTA has a low potential for adsorption based on a log Pow of -11.36.