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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
EDTA degrading strain (DSM 9103) was isolated and incubated to EDTA and EDTA complexes with Mg, Ca, Mn, Zn, Co, Cu and Pb.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
not specified
Duration of test (contact time):
>= 24 - <= 48 h
Initial conc.:
1 mmol/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
The ability of strain DSM 9103 to degrade uncomplexed EDTA or EDTA complexes with Mg2+, Ca2+, Mn2+, Zn2+, Co2+, Pb2+, Cu2+, Cd2+, and Fe3+ was investigated by incubating resting cells with the appropriate EDTA species.
Key result
Parameter:
% degradation (test mat. analysis)
Value:
100
Sampling time:
10 h

Uncomplexed EDTA and its metal complexes with comparably low stability constants (below 10E16) were consumed at a constant rate down to very low concentrations. MgEDTA, CaEDTA, uncomplexed EDTA and MnEDTA was degraded to completion within less than 10 h.

Other EDTA (CuEDTA, CoEDTA, ZnEDTA, and PbEDTA) complexes were degraded only partly within 48 h (EDTA-Co complexes are more stable, stability constant K = 10E18.1).

In all cases a significant degradation of the chelating agent was observed only within the first 5-10 h, and then the rate of degradation slowed considerably or even ceased before the compound was exhausted. Within 48 h only 30% of the initially present CuEDTA had disappeared. In contrast, the extent of CoEDTA, ZnEDTA, and PbEDTA degradation was in the range of 55-85%.

Fe(III)EDTA and CdEDTA were not utilized by resting cells of strain DSM 9103 within 48 h of incubation, at least not at a detectable rate.

Interpretation of results:
inherently biodegradable
Conclusions:
EDTA-degrading bacterial strains degraded EDTA and EDTA complexes with Mg, Ca, Mn and Zn at a concentration of 1mM within 24 h. 1mM EDTA complexes of Cu, Zn, Co and Pb degraded in a range of 30 to 85 % within 48 h.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
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:
For the assessment of the toxicity and environmental toxicity of the EDTA-CoNa2 complex it is important to identify how stable the complex is and how good its components can be degraded. As the Na+ ions are known to be non-toxic only the EDTA-Co complex must be regarded.
This study shows that EDTA is inherently biodegradable and includes information about the degradation and stability of EDTA-Co complexes.
Reason / purpose:
read-across source
Principles of method if other than guideline:
EDTA degrading strain (DSM 9103) was isolated and incubated to EDTA and EDTA complexes with Mg, Ca, Mn, Zn, Co, Cu and Pb.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
not specified
Duration of test (contact time):
>= 24 - <= 48 h
Initial conc.:
1 mmol/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
The ability of strain DSM 9103 to degrade uncomplexed EDTA or EDTA complexes with Mg2+, Ca2+, Mn2+, Zn2+, Co2+, Pb2+, Cu2+, Cd2+, and Fe3+ was investigated by incubating resting cells with the appropriate EDTA species.
Key result
Parameter:
% degradation (test mat. analysis)
Value:
100
Sampling time:
10 h

Uncomplexed EDTA and its metal complexes with comparably low stability constants (below 10E16) were consumed at a constant rate down to very low concentrations. MgEDTA, CaEDTA, uncomplexed EDTA and MnEDTA was degraded to completion within less than 10 h.

Other EDTA (CuEDTA, CoEDTA, ZnEDTA, and PbEDTA) complexes were degraded only partly within 48h

(EDTA-Co complexes are more stable, stability constant K= 10E18.1).

In all cases a significant degradation of the chelating agent was observed only within the first 5-10 h, and then the rate of degradation slowed considerably or even ceased before the compound was exhausted. Within 48 h only 30% of the initially present CuEDTA had disappeared. In contrast, the extent of CoEDTA, ZnEDTA, and PbEDTA degradation was in the range of 55-85%.

Fe(III)EDTA and CdEDTA were not utilized by resting cells of strain DSM 9103 within 48 h of incubation, at least not at a detectable rate.

Interpretation of results:
inherently biodegradable
Conclusions:
EDTA-degrading bacterial strains degraded EDTA and EDTA complexes with Mg, Ca, Mn and Zn at a concentration of 1mM within 24 h. 1mM EDTA complexes of Cu, Zn, Co and Pb degraded in a range of 30 to 85 % within 48 h.
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
EDTA degrading cultures were incubated in a trickle-bed reactor and turnover of EDTA was measured.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
other: nutrient media contained 2.0 mmol/L MgSO4*7H2O, 0.85 mmol/L CaCl2, 0.02 mmol/L FeCl3*6H2O, 1.0 mL/L trace element solution, 10 mL/L vitamin solution and 25.0 mmol/L phosphate buffer.
Details on results:
The growth rate (µmax) of the bacterial mixed culture with EDTA was 0.03 - 0.07/h. The Ks-value of the mixed culture with 8 µmol/L EDTA is advantageous for a wastewater treatment because it affords low residual EDTA-concentrations in the effluent.
Interpretation of results:
readily biodegradable
Conclusions:
EDTA is efficiently degraded by cells of a specially enriched and adapted bacterial mixed culture in which the primary utilizer was strain BNC1, and by cells of the strain DSM 9103.
Metal-EDTA chelates with stability constants below K = 10E12 were degraded by the strain of BNC1. Metal-EDTA chelates with stability constants above this value were not metabolized (CoEDTA, K = 10E13.9). However, these strong chelates did not inhibit the oxidation of uncomplexed EDTA or degradable metal-EDTA complexes. In the presence of Fe-, Co-, Cd-, Pb-, Ni- or CuEDTA, a given surplus of uncomplexed EDTA was always consumed at the same rate as observed in the absence of the added complex. Comparable results were also obtained by the strain DSM 9103.
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
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:
For the assessment of the toxicity and environmental toxicity of the EDTA-CoNa2 complex it is important to identify how stable the complex is and how good its components can be degraded. As the Na+ ions are known to be non-toxic only the EDTA-Co complex must be regarded.
This study shows that EDTA is inherently biodegradable and includes information about the degradation and stability of EDTA-Co complexes.
Reason / purpose:
read-across source
Principles of method if other than guideline:
EDTA degrading cultures were incubated in a trickle-bed reactor and turnover of EDTA was measured.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
other: nutrient media contained 2.0 mmol/L MgSO4*7H2O, 0.85 mmol/L CaCl2, 0.02 mmol/L FeCl3*6H2O, 1.0 mL/L trace element solution, 10 mL/L vitamin solution and 25.0 mmol/L phosphate buffer.
Details on results:
The growth rate (µmax) of the bacterial mixed culture with EDTA was 0.03 - 0.07/h. The Ks-value of the mixed culture with 8 µmol/L EDTA is advantageous for a wastewater treatment because it affords low residual EDTA-concentrations in the effluent.
Interpretation of results:
readily biodegradable
Conclusions:
EDTA is efficiently degraded by cells of a specially enriched and adapted bacterial mixed culture in which the primary utilizer was strain BNC1, and by cells of the strain DSM 9103.
Metal-EDTA chelates with stability constants below K = 10E12 were degraded by the strain of BNC1. Metal-EDTA chelates with stability constants above this value were not metabolized (CoEDTA, K = 10E13.9). However, these strong chelates did not inhibit the oxidation of uncomplexed EDTA or degradable metal-EDTA complexes. In the presence of Fe-, Co-, Cd-, Pb-, Ni- or CuEDTA, a given surplus of uncomplexed EDTA was always consumed at the same rate as observed in the absence of the added complex. Comparable results were also obtained by the strain DSM 9103.

Description of key information

For the assessment of the toxicity and environmental toxicity of the EDTA-CoNa2 complex it is important to identify how stable the complex is and how good its components can be degraded. As the Na+ ions are known to be non-toxic only the EDTA-Co complex must be regarded.

It could be shown that EDTA is inherently biodegradable but relatively high stability constants for EDTA-Co complexes were published (K = 10E13.9 and 10E18.1). Therefore, the substance EDTA-CoNa2 will be considered as not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information


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