Ethylenediaminetetraacetonitrile

Endpoint summary

Additional information

The inherent biodegradability of EDTN was determined by the Modified MITI Test (II) according to the OECD Guidelines for Testing of Chemicals, Method No. 302 C. Based on the result of the residue analysis, the biodegradation appeard to be 62.9%. The BOD results showed that biodegradation of EDTN was 32.6% after 14 days, 63.5% after 28 days.

Hydrolysis of ethylenediaminetetraacetonitrile(EDTN) results in the formation of ethylenediaminetetraacetate (EDTA) and ammonium. In nature hydrolysis of nitriles is catalyzed by enzymes denoted as nitrilases. Biodegradable nitriles are metabolized by microorganisms through an initial hydrolysis with nitrilases. The carboxylic acids formed by this initial reaction are utilized as carbon and energy source (Kobayashi and Shimizu, 2000; Wackett and Hershberger, 2001). Provided that EDTN is biodegradable, metabolism has to be initiated by hydrolysis. Key to justification of read-across of hydrolysis of nitriles is the unity of biochemistry first described by Kluyver and Donker (1926). The EDTA formed upon hydrolysis is not utilised by microorganisms as carbon and energy source under the conditions prescribed in the OECD 301, 302 and 303 tests (Witschel and Egli, 2001; van Ginkel et al, 1997). EDTN is therefore expected NOT to be biodegradable in OECD tests. Fortuitous biological removal of a few ammonium ions might be possible.The biodegradation found in the modified MITI (II) test (see robust summary) is, therefore, considered highly unlikely. The 64% biodegradation was calculated using an endogenous oxygen consumption of 86 mg/L and a mean oxygen consumption in the presence of the test substance of only 110 mg/L. The slight increase in oxygen consumption does not allow an accurate assessment of the biodegradability with the BOD. The nitrification potential in the MITI (II) test due to the biomass concentration used is high. Moreover, it is also expected that biodegradation starts by liberating ammonium which immediately results nitrification. Use of theThOD_NO3instead of ThOD_NH3to calculate the biodegradation is therefore more appropriate. With the ThOD_NO3the biodegradation percentage at day 28 is only 27. An almost complete recovery of EDTN is achieved using extraction with acetonitrile in the abiotic control. In the test, however, high concentrations of activated sludge are present. The 63% degradation found with the residue analysis is therefore most likely the result of extraction problems. In conclusion classification of EDTN as inherent biodegradable with the results obtained in the MITI (II) test is very doubtful.

The lack of EDTN biodegradation in OECD tests does not mean that this substance is recalcitrant in nature because the stringency of the test procedures could account for the recalcitrance. The OECD tests do only detect growth-linked biodegradation. Degradation of EDTN (removal of ammonium through hydrolysis by a co-metabolic (fortuitous) process) is envisaged.

The analogue substance PDTN was also not readily biodegradable (see also at section 13). However, both PDTN and EDTN are used as intermediates with no release to the environment.

References

Ginkel C.G van, K.L. VandenBroucke and C.A. Stroo (1997) Bioresour. Technol. 59: 151 -155

Key Lab of pesticide Environmental Assessment and Pollution Control MEP (2009) Report for inherent biodegradation Modified MITI (II) test EDTN Report no R2009NC007-02(see robust summary)

Kluyver A.J. and H.J.L. Donker (1926) Chemie der Zelle und Gewebe, 13: 134‑190

Kobayashi M. and S. Shimizu (2000) Nitrile hydrolases. Current Opinion in Chemical Biology 4: 95 -102

Wackett P. and C.D. Hershberger (2001) Biocatalysis and Biodegradation Microbial transformation of organic compounds. ASM Press, Washington DC 20036 -2904

Witschel M. and T. Egli (2001) FEMS Microbiol. Rev. 25: 69-106