Morpholine, 4-C12-14-alkyl derivs.

Toxicity to microorganisms

Description of key information

In the absence of a standard microbial inhibition test, the ready biodegradation test (Closed Bottle test) was used to assess the toxicity of the substance to microorganisms.  

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

2 mg/L

Additional information

The ready biodegradability of C12-14 alkylmorpholine was determined in the closed bottle test performed according to the OECD Guideline 301D, EU method C.4 and ISO 10707 (1994) in compliance with GLP with few minor deviation. The test was prolonged because the pass level was not reached at Day 28. The test substance was exposed to the inoculum, consisting of relatively low numbers of microorganisms from an activated sludge plant, under aerobic conditions for a period of at least 28 d. The concentrations of the test substance and the reference substance, sodium acetate in the BOD (biological oxygen demand) bottles were 2.0 and 6.7 mg/L, respectively.  The test substance did not cause a degradation of sodium acetate as well as reduction in the endogenous respiration, nor inhibited the microorganisms degrading acetate. Therefore, no inhibition of the biodegradation due to the high initial concentration of the test substance is expected. The validity of the test is demonstrated by an endogenous respiration of 0.9 mg/L at Day 28. Furthermore, the differences of the replicate values at Day 28 were less than 20%. The biodegradation percentage of the reference substance, sodium acetate, at Day 14 was 80. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period. The test substance is biodegraded by 64% at day 28 in the test. The pass level of 60% was not reached within 14 d upon achieving 10% biodegradation. The reason for failing the 14-day window is the chemical structure, a surfactant consisting of a hydrophilic group linked to a hydrophobic moiety. Biodegradation of both moieties of surfactants requires the concerted action of at least two microorganisms as a single organism usually lacks the full complement of enzymatic capabilities. In ready biodegradability tests, the two moieties of this fatty amine derivative are therefore degraded sequentially. The time window criterion was developed on the assumption that a substance is degraded by one microorganism according to the “standard” growth curve. The degradation curve of the test substance is the sum of growth curves of the two moieties of the test substance i.e. morpholine and the alkyl chain. The biodegradability of the two moieties in the closed bottle test may be fully in line with the time window criterion when judged as separate substances. The time window should therefore be ignored as a pass fail criterion for the test substance.

Under the study conditions, the test substance is classified as readily biodegradable only based on the biodegradation percentage of 64% at Day 28.

The test substance was exposed to the inoculum, consisting of relatively low numbers of microorganisms from an activated sludge plant, under aerobic conditions for a period of at least 28 d. The concentrations of the test substance and the reference substance, sodium acetate in the BOD (biological oxygen demand) bottles were 2.0 and 6.7 mg/L, respectively.