Tripotassium hydrogen ethylenediaminetetraacetate

Biodegradation in water: screening tests

Description of key information

The biodegradability of K3HEDTA is driven by the EDTA component of the substance.  Several tests on EDTA have been conducted and varying rates of biodegradation were observed.  Ultimately, EDTA is biodegradable by adapted organisms and or a change in pH.
It could be shown in three different experiments that a change of the  pH-value can result in a biodegradation of EDTA.    In a SCAS facility which had been inoculated with activated sludge from a  municipal wastewater treatment plant, a removal by biodegradation of EDTA  (65 mg/L) added to domestic wastewater could be observed at pH of 8.0 to  9.0. With a pH of 6.5 no biodegradation could be obtained. The removal at  pH 8.5 started 3 weeks after inoculation with a result up to 100 %  degradation after 28 days. The SCAS unit ran with sludge retention times  > 12 days. A maximum EDTA removal rate of 0.2 kg/m3/day was achieved.  In order to confirm the biodegradation of EDTA, closed bottle tests were  carried out with sludge originating from the SCAS unit. The tests were  conducted at a pH range from 8.0 to 8.5. The lag period was only few  days. The time to reach a BOD/ThOD ratio of 0.6 was 3 weeks after  initiation of detectable biodegradation. EDTA was not biodegraded at pH  7.0.  The removal of EDTA was investigated in a full-scale activated sludge  plant operated at pH values between 7.5 and 8.5 with dairy wastewater  containing ca. 30 mg/l EDTA. The dairy wastewater was treated at a  hydraulic residence time of one day and a sludge retention time of 20  days. The analysis of influent, effluent and sludge concentration resulted in  approximately 90 % removal. At a pH of 6.7 no biodegradation took place.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable

Additional information

Based on read-across from the disodium salt of EDTA, K3HEDTA is consdisered to be inherently biodegeradable. Sodium and potassium are both members of the 1a group of metals in the periodic table. Due to their low electronegativity they form ionic bonds and highly water soluble salts with inorganic and organic acids. The solution of these salts is therefore dominated by the property of the acid anion. This justifies reading across biodegradation from the sodium to the potassium salt and additional justification for basing the expected degradation on the EDTA anion.