Diguanidinium carbonate

Biodegradation in water: screening tests

Description of key information

Standard testing protocols may be unsuitable as natural degradation driven by use as nitrogen rather than carbon/energy source, not toxic to aquatic sewage microorganisms in a concentration of 150.4 mg/L

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

The relevant part of the submission item Guanidine carbonate is the Guanidine (CAS 113-00-8) as discussed in the section on Environmental fate and pathways above. It is present as the Guanidinium kation (see section Dissociation constant). The carbonate, which is fully mineralized, is negligible for the environmental assessment and disregarded in the following discussion.

Applicability of the standard screening test approach

The screening test protocols (OECD TG 301) are generally considered representative for ready biodegradation in the environment. The fact that sewage water treatment plant (SWTP) microorganism activated sludge is used as inoculum is due to its good availability and its rather standardised organism composition. The actual retention time of sewage water in SWTPs is intentionally not comparable to the incubation period of 28 days in the screening tests. To give evidence that a test item is likely to be biodegraded in the environment it is mandatory to add it as the sole source of carbon in the test vessels. The pass level criteria demand that 28 days suffice for complete mineralization where a 10 days window must not be exceeded after the allowed adaptation is reached, which is considered after 10 % of a test item is mineralized. In consequence only test items suitable as such carbon source are in the scope of the test principle and e.g. inorganic compounds cannot give any useful response. Therefore alternative assessment approaches have been evaluated for the most environmentally critical group of inorganic compounds, the metals (ECHA 2011, p 475). Nonetheless it seems justifiable to assess as well on non-metal compounds in a similar approach. Guanidine, present as the Guanidinium kation (see section Dissociation constant) is formally considered an organic chemical, but more for historical reasons. In fact Guanidine has similarities to inorganic substances. With a nitrogen to carbon ratio of 3 it seems to be a nitrogen rather than a usable carbon source. Nonetheless it ranges much lower in preference as the more easily accessible inorganic nitrogen sources. Thus it should be tested in screening assays in analogy to common organic chemicals as a sole source of nitrogen, which is at variance to the OECD TG 301 protocols, which foresees the provision of the activated sludge organisms with sufficient Ammonium chloride (CAS 12125-02-9) for the whole incubation period. Experimental data show that guanidine degradation is quite significantly accelerated in natural surface waters in presence of a readily accessible carbon source such as glucose or arginine (Mitchell 1987 Chemosphere and Bull Environ contam Toxicol).

In consequence the OECD TG 301 protocols are considered unsuitable for the biodegradation assessment of Guanidines as their adequacy is in doubt when a negative response is observed. Data from water/sediments or soil studies can be used to assess on rapid biodegradability using the criteria as outlined in ECHA (2012, Annex II.4 Decision scheme, p 502).

Experimental data

The submission item showed no biodegradation in a modified OECD screening test according to the OECD TG 301 E protocol (Kocsis 1998). Guanidine alone (at 100 mg/L achieved 0 % of its theoretical BOD over a 2 week incubation period using an activated sludge inoculum at 30 mg/L in the Japanese MITI test, NITE 1997, reported in the HSDB 2008 record) and other guanidine salts with inorganic anions (nitrate, cyanide) gave comparable results (ECHA webpage http://www.echa.europa.eu/web/guest/information-on-chemicals EC 208-060-1 and 207-312-8).

• ECHA European Chemicals Agency (2011). Guidance on the Application of the CLP Criteria Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures. Self-published April 2011 ECHA Reference: ECHA-11-G-06-EN. 490 p
• ECHA European Chemicals Agency (2012). Guidance on the Application of the CLP Criteria. Version 3.0, November 2012. Self-published by ECHA. Reference: ECHA-12-G-14-EN, Date: 11/2012. 573 p.
• HSDB Hazardous Substances Databank (2008). GUANIDINE, CASRN: 113-00-8, Number: 7603. Last Revision Date: 2008-08 -26, Last Review Date: Reviewed by SRP 5/8/2008, Update History: Complete Update on 2008 -08-26, 38 fields added/edited/deleted, Created 2007-12-13
• Mitchell WR (1987). Microbial Degradation of Guanidinium Ion. Chemosphere 16(5):1071-86
• NITE National Institute of Technology and Evaluation (1997). Biodegradation and Bioconcentration of Existing Chemical Substances under the Chemical Substances Control Law. Information on the chemical published in the Official Bulletin of Economy, Trade and Industry. Published Date: 1997/12/26. Published Chemical Name: Guanidine [Class-Reference No. : 2-1773]. Chemicals Inspection and Testing Institute. Japan Chemical Industry Ecology - Toxicology and Information Center. Available at: http://www.safe.nite.go.jp/english/kizon/KIZON_start_hazkizon.html as of November 11, 2011.