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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The substance is not readily biodegradable according to OECD criteria but may be regarded as inherently biodegradable. The substance is expected to exhibit ultimate biodegradation.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

Information on the substance itself is limited to a single, poorly documented study of inherent biodegradation. A large number of degradation tests are available for EDTA and its salts, a structural analogue of the substance (for justification on read-across see Section 13). Results from OECD guideline tests indicate that EDTA is not readily biodegradable and tests on inherent biodegradability result in low biodegradation rates.

 

Influence of pH

It could be shown that a change of the pH-value have a great impact on the biodegradability of EDTA. Results obtained in a DOC removal test according to the principles of the OECD guideline 301 using natural surface water from the river Rhine as inoculum showed up to 100 % EDTA was degraded after 60 days at pH 8.5 but less than 10 % at pH 6.5. Such slightly alkaline conditions are realistic in environmental surface water compartments.

  

Degradation pathway

The degradation pathway of EDTA has been summarised in the EU Risk Assessment (2004). The first degradation product described is ethylenediaminetriacetate (ED3A) which can react spontaneously to ketopiperazinediacetate (KPDA) by intramolecular cyclisation. KPDA itself is biodegradable.

 

Conclusion

EDTA, and by analogy HEDTA, is not readily biodegradable according to OECD criteria. It has been shown that under special conditions like slightly alkaline pH or adaptation the biodegradability of EDTA is considerably improved. EDTA was biodegradable in an enhanced test using pre-adapted activated sludge. Therefore it can be concluded that the substance may be regarded as ultimately biodegradable under such conditions.