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EC number: 237-864-5
CAS number: 14025-15-1
EDTA is resistant to hydrolysis.
Photolytic degradation is practically only
relevant for the Fe(III)EDTA complex and has been shown in surface
waters. It is depending on pH and irradiation; in summer
photodegradation rates will be higher and mainly when pH is <= 7.
Further abiotic degradation processes as
reaction with OH-radicals or single oxygen have (compared to the direct
photolysis) very low reaction constants and are of no environmental
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 complexes, 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
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
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.
Based on the estimated log Kow (<3) and
available BCF study in fish with radiolabelled EDTA (BCF range 1.1-1.8)
it can be concluded there is low potential for bioaccumulation for
The estimated log Koc value for EDTA-CuNa2
is 1.7 (worst case). This is less than the threshold value of 3
indicating no adsorbing potential for this compound.
Due to high water solubility and low
adsorption, EDTA will eventually leach to ground- and surface waters and
not accumulate in soil. Due to pH fluctuations in surface water,
moderate substitution rates and the combined photodegradation and
biodegradation, all EDTA salts will eventually disappear from surface
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