Disodium [[N,N'-ethylenebis[N-(carboxymethyl)glycinato]](4-)-N,N',O,O',ON,ON']cuprate(2-)

Endpoint summary

Description of key information

EDTA-metal complexes with a stability constant >= 10E14 like EDTA-CuX complexes (where X stands for K2, Na2 or (NH4)2) should be considered "Completely and inherently biodegradable". The dissociation rates are however considered too low to allow classification as not persistent.

Additional information

EDTA is not found to be readily biodegradable according to OECD criteria. In standard OECD 301D ready biodegradability tests with natural river water as inoculum it was shown that EDTA complexes with a stability constant lower than 10E14 like EDTA-Na4, EDTA-CaNa2, EDTA-MgNa2 etc. less than 60% biodegradation was observed after 28 days indicating that these substances should indeed not be classified as readily biodegradable. In these same tests however > 60% biodegradation was observed when these tests are prolonged to day 60 (Ginkel, 2018) indicating that these compexes, having stability constants < 10E14, are ultimately biodegradable and should be classified as "not persistent".

EDTA-CaNa2 has a stability constant < 10E14 and is therefore under the conditions applied considered to be inherently biodegrable fulfilling specific criteria.

Complexes with a stability constant >= 10E14 like EDTA-CuX complexes (where X stands for K2, Na2 or (NH4)2) should be considered "Completely and inherently biodegradable". The dissociation rates are however considered too low to allow classification as not persistent.

 

Influences of the stability constant

As a chelating agent, EDTA forms complexes with cationic ions. Fundamental EDTA exists naturally as a mixture of chelate complexes. The biodegradability differs between the acid resp. their salts and on the other side the metal complexes. Investigations show, that EDTA complexes with a thermodynamic stability constant below 10E14, like Ca, Mg and Mn, were degraded. On contrast heavy metal EDTA complexes with stability constants above 10E14, such as Cu and Fe, were not significantly degraded [Klüner & al. 1998, Van Ginkel, 1999 and Nörtemann, 2003]. In addition a degradation of Zn-EDTA was observed by Satroutdinov, 2003.

 

Degradation pathway

Several investigations revealed that it is possible to enrich cultures of EDTA-utilizing microorganisms. Different bacteria strains were isolated which can mineralised EDTA completely [Nörtemann, 1992 and Van Ginkel, 1999]. The degradation pathway of EDTA was described from Klüner & al. (1998) and summarised in the EU Risk Assessment (2004). The first intermediate described is ethylenediaminetriacetate (ED3A). ED3A can react spontaneously to ketopiperazinediacetate (KPDA) by intramolecular cyclisation [Ternes et al., 1996]. KPDA itself is biodegradable which could be shown by Van Ginkel & Stroo (1999).

 

Conclusion

EDTA is not readily biodegradable according to OECD criteria. It was shown that with natural river water as inoculum, in standard OECD 301D tests, EDTA complexes with a stability constant lower than 10E14 like EDTA-Na4, EDTA-CaNa2, EDTA-MgNa2 etc. less than 60% biodegradation was observed after 28 days indicating that these substances should be not classified as readily biodegradable but in these tests > 60% biodegradation was observed after 60 days in the prolonged (enhanced) tests indicating that these complexes, having stability constants < 10E14, are not persistent. This stability constant threshold of 10E14 will be dependent on the concentration balance between the starting complex and free metal ions (alkali and alkaline earth metals). The lower the starting concentration of the EDTA-metal complex the higher this stability constant threshold for biodegradation.