N,N'-diphenylguanidine monohydrochloride

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

The test item (target substances, CAS 24245-27-0) is the salt of 1,3-diphenylguanidine and mono-hydrochloride. As read-across source substance the uncharged free base of 1,3-diphenylguanidine (CAS 102-06-7) is applied. This is considered appropriate since the target substance is expected to readily dissociate in contact with water such as surface water in the environment or the intestinal fluids or mucosal membranes of an organism. 1,3-diphenylguanidine is considered a weak base. Therefore, it is expected to be present as uncharged molecule at neutral and high pH solutions. However, acidic conditions will lead to protonation of the molecule and the charged ion is expected to be the main present form. Since transformation of the target to the source substance and vice versa is anticipated, kinetics and toxicological behaviour are well transferable from the source to the target substance. This applies for human health endpoints as well as for the aquatic environment.
Moreover, chloride ions are ubiquitously present in every-day nutrition and are part of numerous physiological processes. Therefore, this constituent does not require further assessment in regards to its toxicological behaviour. It is expected to be well regulated by endogenous physiological mechanisms of the organism.
Based on the considerations above, a read-across is considered appropriate and further tests, especially vertebrate studies, are not needed to adequately address this endpoint. Information Requirements are fulfilled according to REACH Annex XI Section 1.5.

Reason / purpose for cross-reference:

read-across source

Key result

Parameter:

% degradation (O2 consumption)

Value:

86

Sampling time:

14 d

Remarks on result:

other: based on ThOD-NH3

Key result

Parameter:

% degradation (O2 consumption)

Value:

85

Sampling time:

28 d

Remarks on result:

other: based on ThOD-NO3

Description of key information

Based on results with the read-across substance the chemical structure of the test item is considered to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

Read-Across approach

There are no experimental data available regarding biodegradability of the test item. However, data are available with an structural analogue substance which are suitable and adequate to fulfill this endpoint. For Read-across justification please refer to the respective IUCLID Section.

Ready biodegradation (CAS 102 -06 -7)

In order to assess the biotic degradation of the read-across substance (1,3 -diphenylguanidine), a ready biodegradability test was performed in an aerobic aqueous medium. The ready biodegradability was determined in the Closed Bottle test performed according to slightly modified OECD, EU and ISO Test Guidelines, and in compliance with the OECD principles of Good Laboratory Practice. 1,3-Diphenylguanidine calculated with ThOD-NH3 was biodegraded 85% at day 28 in the Closed Bottle test. Over 60% biodegradation was achieved in a period of 8 days immediately following the attainment of 10% biodegradation. Hence, this substance should be classified as readily biodegradable. Complete recovery of 1,3-diphenylguanidine-nitrogen as nitrate nitrogen demonstrates ultimate biodegradation. The test is valid as shown by an endogenous respiration of 0.9 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 89% of its theoretical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations >0.5 mg/L in all bottles during the test period.