D-gluconic acid, compound with N,N''-bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecanediamidine (2:1)

Biodegradation in water: screening tests

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Type of water:

freshwater

Additional information

The biodegradability of Chlorhexidine digluconate was investigated in two standard tests on ready biodegradability according to the OECD Guidelines 301 A and D. Degradation after 28 days was found to be 71% in the DOC Die-Away-Test (OECD 301 A) fulfilling the 10-day window criterion (2001-0256-DGO). The applied test substance concentration (4.7 mg DOC/L = 10.3 mg TS/L) was below the EC₂₀ of 11 mg/l (EC₅₀ of 25 mg/L) determined in a sludge respiration inhibition test. Therefore, an influence of the antimicrobial activity on the result was not expected. This was confirmed by the toxicity control. No adsorption onto sludge was observed by DOC measurements after 3 hours of incubation. However, an adsorption is expected due to a Kp value of 26700 L/kg which was obtained by Freitag et al. (1982, 1985). This adsorption on sludge was also observed in the Zahn-Wellens-Test.

In the Closed-Bottle Test (Zoellner, 1995), the test substance was applied at a very low concentration (0.1 mg/l). 100% degradation was observed even after 5 days. Due to the low test substance concentration, the results scattered pronouncedly, as the analytical method is probably unsuitable to measure such low differences in oxygen consumption with sufficient precision. Therefore, the test is considered as reliability 4 (not assignable).

In a second Closed-Bottle Test (2010-0196-DGO) only 5% biodegraration (ThOD_NH4 decrease) were obtained in the course of 28 days. As the test substance concentration was probably in the toxic range, the test is considered as reliability 3 (unsuitable test system).

Additionally, in a Zahn-Wellens-Test on inherent biodegradability similar to OECD 302B, a DOC removal of about 90% after 28 days were observed at concentrations of 23.8 and 39.7 mg TOC/L (95-0113-FKO). However, in the toxicity control flask, complete damage of the inoculum was observed. Therefore, the test is considered as reliability 3 (not valid) regarding biodegradation. In addition, the DOC removal was approximately 42% immediately after start of the test for the test item solutions and 57.8% after 28 days in the abiotic control. Therefore, the decrease of DOC can probably be attributed to adsorption.

Further, the mineralization and primary degradation of 14C-labelled Chlorhexidine digluconate was investigated in a modified CO2 Evolution test at a concentration of 0.20 mg/L 14C-labelled Chlorhexidine digluconate. Only minor amounts of 2.3% were found mineralized in the adsorption solutions after 60 days of incubation. In the aqueous supernatant 12.9% of the applied radioactivity (AR) were found. Further 38.0% could be extracted from filtered particulate matter. Not-extractable residues were determined by combustion of the particulate matter after extraction to be 21.1% AR.