Registration Dossier

Administrative data

Endpoint:
mode of degradation in actual use
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Biogeochemistry of Chelating Agents. In Biogeochemistry of Chelating Agents
Author:
Ginkel van CG, Geerts R, Nguyen PD
Year:
2005
Bibliographic source:
ACS Symposium Series 909, 183-194
Reference Type:
publication
Title:
Biodegradation of L-glutamatediacetate by Rhizobium radiobacter strain BG-1
Author:
Ginkel van CG, Geerts R, Nguyen PD
Year:
2008
Bibliographic source:
Int Biodeg Biodeter 62, 31-37
Reference Type:
publication
Title:
A mathematical model of biodegradability screening tests as an aid to interpretation of observed results
Author:
Painter HA, King EF
Year:
1983
Bibliographic source:
Reg Toxicol Pharmacol 3, 144-151

Materials and methods

Test guideline
Qualifier:
no guideline required
Principles of method if other than guideline:
Not relevant
Type of study / information:
Explanation on the biodegradation pathways for the test substance as well as on the rate of biodegradation and the occurrence of competent micro-organisms

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
No additional information

Results and discussion

Any other information on results incl. tables

Ready biodegradability test results are available for L-glutamatediacetate (L-GLDA) (Garttener and van Ginkel, 2002; van Ginkel et al, 2005). Ready biodegradability test results inform about the following aspects of biodegradation; a) ultimate (complete) biodegradation, b) rate of biodegradation and c) number and occurrence of competent micro-organisms present in “unacclimated” ecosystems and biological treatment plants. Below all three aspects are dealt with to refine the ready biodegradability classification of L-GLDA using evidence obtained through environmental microbiology studies.

 

Ultimate biodegradation (biodegradation pathways):The first step in the degradation pathway of L-GLDA is the cleavage of a C-N bond liberating glyoxylate. Formation of glyoxylate from L-GLDA is catalysed by a monooxygenase. As the next step in L-GLDA degradation, a second C-N bond cleavage is anticipated. This C-N bond cleavage results in the formation of a second glyoxylate and L-glutamate. The feasibility of a biodegradation route yielding L-glutamate was further substantiated by measuring L-glutamate dehydrogenase activity in extracts from cells grown on L-GLDA. L-GLDA-degrading microorganisms therefore require only two enzyme reactions to produce two intermediates, i.e. glyoxylate and L-glutamate that can enter pre-existing pathways. The glyoxylate formed is processed via the glyoxylate shunt of the tri-carboxylic acid (TCA) cycle and L-glutamate is converted into oxoglutarate, an intermediate of the TCA cycle (van Ginkel et al, 2008). This biodegradation pathway demonstrates that L-GLDA is completely (ultimately) degraded by micro-organisms.

Biodegradation rates; The maximum growth rate of Rhizobium radiobacterstrain BG-1 on L-GLDA is ~0.1 h-1(van Ginkel et al 2005). Painter and King (1983) used a model based on the Monod equation to interpret the biodegradation curves in ready biodegradability tests. According to this model growth rates of competent micro-organisms of 0.01 h-1or higher do result in a ready biodegradation of the test substance. The isolate capable of growing on L-GLDA easily fulfils this prerequisite.

Number of competent micro-organisms (ubiquitousness);Biodegradation of L-GLDA has been detected in terrestrial ecosystems, fresh water i.e. riverand beck, and unacclimated activated sludge (van Ginkel et al 2005; Akzo Nobel unpublished work). These findings demonstrate the ubiquitousness of L-GLDA degrading micro-organisms in the environment. The type strainsAminobacter aminovoransDSMZ 6449 andChelatococcusasaccharovoransDSMZ 6461 isolated onNTA were also capable of growing on L-GLDA.The capability of these micro-organisms to utilize both L-GLDA and NTA (ready biodegradability of NTA shows that NTA degrading micro-organisms are widely distributed) as sole carbon and energy source also indicates that L-GLDA degrading micro-organisms occur widely in the environment (van Ginkel et al, 2005).

The wide distribution of L-GLDA degrading micro-organisms, the very high growth rate of the Rhizobium, and the evidence of ultimate degradation of L-GLDA further underpinthe ready classification of L-GLDA.

 

References

 

CG van Ginkel, R Geerts, and PD Nguyen (2005) Biodegradation of L-glutamatediacetate by mixed cultures and an isolate. In Biogeochemistry of Chelating Agents. In Biogeochemistry of Chelating Agents.ACS Symposium Series Volume 909 pp 183-194

CG van Ginkel, R Geerts PD Nguyen and CM Plugge (2008) Biodegradation of L-glutamatediacetate byRhizobium radiobacterstrain BG-1. International Biodegradation & Biodeterioration 62 31-37

HA Painter and EF King (1983) A mathematical model of biodegradability screening tests as an aid to interpretation of observed results. Reg Toxicol Pharmacol 3 144-151

Applicant's summary and conclusion

Conclusions:
The wide distribution of GLDA degrading micro-organisms, the very high growth rate of an isolate growing on GLDA, and the evidence of ultimate degradation of GLDA further underpin the classification of GLDA as readily biodegradable.
Executive summary:

Ultimate biodegradation: The biodegradation pathways are described showing that L-GLDA gedrading micro-organisms require only two enzyme reactions to produce two intermediates that can enter pre-existing pathways. This pathway demonstrates that GLDA is completely degraded by micor-organisms.

Biodegradation rates: The maximum growth rate of an isolate growing on GLDA was above the prerequisite for a ready biodegradation by an order of magnitude.

Number of competent micro-organisms: The capacity to biodegrade GLDA was detected in inocula from a range of environmental compartments, showing the ubiquitousness of GLDA degrading micro-organisms.

The wide distribution of GLDA degrading micro-organisms, the very high growth rate of an isolate growing on GLDA, and the evidence of ultimate degradation of GLDA further underpin the classification of GLDA as readily biodegradable.