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EC number: 237-864-5
CAS number: 14025-15-1
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.
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
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.
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).
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.
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