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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Alkyl-1,3-diaminopropanes are in general poorly soluble in water and at normal test concentrations toxic to the micro-organisms in the inoculum. Silica gel may be added to reduce the exposure concentration and to facilitate the slow release of the test substance. Under these conditions, the substances are observed to be readily biodegradable in closed bottle tests.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Diamines (alkyl-1,3-diaminopropanes) are well-known for their biocidal properties and are expected to inhibit growth in ready biodegradability tests carried out at “high” initial concentrations (van Ginkel, 1995). Concentrations of 2 mg/L of the test substance are prescribed in the closed bottle test, which is very low compared to the initial concentrations used in other ready biodegradability tests. The closed bottle test is therefore the superior ready biodegradability test for alkyl-1,3-diaminopropanes. The result of many ready biodegradability tests including the closed bottle test may not necessarily reflect the true biodegradation potential of alkyl-1,3 -diaminopropanes due to the toxicity. To minimize the biocidal effect, silica gel has been added to closed bottle tests (see table below). Before the start of the test, the test substance is sorbed onto silica. During the test period, the test substance will slowly release from the silica and will be degraded. The use of silica gel, allowed the demonstration of the ready biodegradability of oleyl-1,3-diaminopropane, coco-1,3 -diaminopropane and N-C16-18-alkyl-(evennumbered) C18 unsaturated-1,3-diaminopropane.

Most ready biodegradability test results with Diamines have been found through investigations with Closed Bottle tests, (OECD 301D). The 10-day time window has been ignored as a pass fail criterion as these substances are UVCB's. Poor water solubility of Diamines and/or adsorption of the substance onto solids do affect biodegradation kinetics because of low desorption and dissolution rates of the test substance. Dissolution and desorption rates in the tests do probably not reflect these processes in the environment because concentrations used in the tests are a few orders higher than the environmental concentrations. The biodegradation curves of substances with a poor water solubility and/or limited bioavailability due to adsorption usually show a linear curve instead of the anticipated S-shaped curve (logistic growth or growth with Monod).

Over the past decade, comprehensive knowledge has been gained on the biodegradation mechanism of many fatty amine derivatives. All research to date identifies a central cleavage of the fatty amine derivatives as initial biodegradation step giving alkanals as intermediates (van Ginkel, 1996; van Ginkel 2008). The central fission of the fatty amine derivatives also results in the formation of hydrophilic degradation products. Starting from an enrichment culture a bacterium capable of degrading diamines with alkyl chains ranging from C10 to C18 was isolated. Dodecylamine, dodecanoic acid, acetic acid and ß-alanine also served as carbon and energy sources for the isolate. This bacterium was not capable of utilizing 1,3-diaminopropane (Akzo Nobel unpublished results). These results strongly indicate that bacteria capable of degrading diamines catalyze a central fission resulting in the formation of alkylamines and 3 -aminopropionaldehyde. 3-Aminopropionaldehyde is further oxidized to ß-alanine. Alkylamines are converted into alkanals (Yoshimura et al, 1980; van Ginkel et al, 2008). One microorganism is therefore capable of degrading diamines with varying alkyl chain lengths.

Based on the broad substrate specificity of microorganisms degrading diamines and fatty amine derivatives in general with respect to the alkyl chain length it is unlikely that the biodegradability of diamines differs significantly with varying alkyl chain lengths. Indeed, the degradation observed in closed bottle tests with proper amounts of silica gel were comparable for the diamines tested. The adequate ready biodegradability test results in combination with scientific evidence that a single micro-organism degrades all diamines lead to the conclusion that all diamines are readily biodegradable. Typical members of the family are given in the table below.

 

Table Typical members of the family of alkyl-1,3-diaminopropanes.

Chemical name

CAS

EINECS

N-(C14-18and C16-18-unsaturated alkyl) propane-1,3 -diamine

68439-73-6

270-416-7

N-(hydrogenated N-C16-18-alkyl-(evennumbered) propane-1,3 -diamine

Old CAS no: 68603-64-5

New CAS no: 133779 -11-0

271-669-6

(Z)-N-9-octadecenylpropane-1,3-diamine

7173-62-8

230-528-9

N-C16/C22-propane-1,3-diamine

90640-45-2

292-564-1

N-Dodecylpropane-1,3-diamine

5538-95-4

226-902-6

N-C16-18-alkyl-(evennumbered) C18 unsaturatedpropane-1,3 -diamine

Old CAS no: 61791 -55 -7

New CAS no:1219010-04-4

263—189-0

N-C12-14–propane-1,3-diamine

 90640 -43 -0  292-562-0

N-C12-18 (coco)-propane-1,3-diamine

 Old Cas no: 61791 -63 -7New Cas no: 68155 -37 -3  268 -959 -9
     

Composition of N-C14 -18 and N-C16-18-alkyl-(evennumbered) C18 unsaturated-alkyl chains are specified by Karleskind (1996).