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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Stability

Both HEDTA and a structural analogue of the substance, EDTA, form complexes with ions. Therefore, both exist naturally as a mixture of chelate complexes (for justification of read-across, see Section 13). No emission into the atmosphere is expected based on the very low vapour pressure of the substance(s). Thus photodegradation in air will not play an important role in breakdown processes in the environment.

HEDTA and its surrogate EDTA are resistant to hydrolysis. Neither strong acids nor alkalis cause any degradation. However photodegradation of EDTA in natural water has been observed by Metsärine (2001) and some species of EDTA, especially the iron complexes, are potentially photolysable.

 

Biodegradation

Information on HEDTA itself is limited to a single, poorly documented, study of inherent biodegradation. A large number of degradation tests are available for the surrogate, EDTA. Results from OECD guideline tests indicate that EDTA is not readily biodegradable and tests on inherent biodegradability result in low biodegradation rates. It has however been shown that, under special conditions such as slightly alkaline pH or adaptation, biodegradability is considerably improved. EDTA was biodegradable in an enhanced test using pre-adapted activated sludge. Therefore, the substance may be regarded as ultimately biodegradable under such conditions. Complexes of HEDTA are similar to those of EDTA and thus the two chelates are expected to follow the same pathways of degradation, e.g. photodegradation and microbial degradation in wastewater, sediments and soils. Sykora et al. (2001) describes the biological degradation of ethylenediamine-based complexing agents decreasing in order of the following structural substitutions: -COOH3, -CH3, -C2H5, -CH2CH2OH and -CH2COOH. This suggests that HEDTA may be more susceptible to degradation than EDTA.

 

Bioacumulation

Given the chemical structure of HEDTA and its high water solubility (480 g/L), bioaccumulation is unlikely to occur. This is in line with a (Q)SAR model estimation which predicts a BCF of 3.162 for the substance in the aquatic environment. This estimation is supported by an experimentally derived BCF value of 1-2 for the structural analogue tetrasodium EDTA. No information is available regarding bioaccumulation in the terrestrial environment.

Transport and distribution

Due to the ionic structure under environmentally relevant pH conditions, no adsorption onto the organic fraction of soil or sediments of EDTA, a structural analogue of the substance, 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.

 

References

Sykora, V., P. Pitter, I. Bittnerova and T. Lederer. 2001. Biodegradability of ethylenediamine-based complexing agents. Wat. Res. 35:2010-2016.

European Union (EU) (2004). Risk Assessment Report, TETRASODIUM ETHYLENEDIAMINETETRAACETATE (Na4EDTA), CAS No: 64-02-8, EINECS No: 200-573-9, RISK ASSESSMENT. Final Report.