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Biodegradation in water: screening tests

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Description of key information

Amines C36-alkylenedi-  did not degrade in a ready biodegradability test. The test substance was toxic to the microorganisms present in the test (AkzoNobel 2011). Due to the relatively high initial test concentration in standard ready tests needed to monitor the degradability, no reproducible result could be obtained in a ready test. In two tests where the toxicity was sufficiently mitigated, >60% degradation was observed. Based on the biodegradability data it can be concluded that the substance is either sorbed or degraded.This is a strong indication that the substance is readily biodegradable at low concentrations. Considering the high observed Kd for soil of 43664 L/kg only low concentrations will be present in the aqueous compartment and pore water and rapid biodegradation of the bioavailable fraction is therefore anticipated. For risk assessment purposes the substance is more conservatively considered to be inherently biodegradable until readily biodegradability at low concentrations has been demonstrated.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Amines C36-alkylenedi- did not degrade in a ready biodegradability test. The test substance was toxic to the microorganisms present in the test (AkzoNobel 2011). Toxicity of test substances in ready biodegradability tests is best detected prior to the onset of the biodegradation of the test substance through suppression of the endogenous respiration (lower oxygen consumption in the presence of a test substance as compared to the control). In the standard Closed Bottle test, inhibition by amines C36-alkylenedi- was still noted after 56 days (AkzoNobel, 2011). For very toxic substances, the specified high test substance concentrations are controversial because organic substances are present in the environment in the sub μg/Lrange. Biocidal effects of amines C36-alkylenedi- hydrogenated, may therefore be responsible for false negative results obtained in the ready biodegradability tests.

Reduction of the toxicity of fatty amine derivatives in ready biodegradability tests has been achieved through the addition humic acid and silica gel (van Ginkel et al, 2008). The true biodegradability of amines C36-alkylenedi- hydrogenated can therefore probably only be assessed in ready biodegradability tests with the help of either silica gel or humic acid.

Closed Bottle tests inoculated with acclimated sludge carried out with silica gel and a test substance concentration of only 1.0 mg/L did give biodegradation results showing complete degradation of amines C36-alkylenedi-. Biodegradation in excess of 60% was found twice with acclimatized activated sludge (AkzoNobel, 2012). Reduction of the toxicity by humic acid was less compared to silica gel. These results show that biodegradation of amines, C36- alkylenedi- cannot be attained consistently in ready (enhanced) biodegradability tests probably due to toxicity.

Acclimatization was achieved in Semi-Continuously-fed Activated Sludge (SCAS) units. Amines, C36- alkylenedi- was administered at a concentration of 5.0 mg/L. The SCAS test unit was operated for more 12 months. The operation of the SCAS units was checked by measuring the NPOC content in the control and test unit. The NPOC values in both units were always <15 mg/L and comparable (data not shown). These results demonstrate that amines, C36- alkylenedi- did not affect the biodegradation of organic substances present in the domestic wastewater. The NPOC concentrations were not used to assess the biodegradability of amines, C36- alkylenedi- because possible adsorption makes a proper interpretation impossible. Sludge from the SCAS test unit was ONLY used to inoculate Closed Bottle tests. The biodegradation found with acclimatized activated sludge does demonstrate that amines C36-alkylenedi- hydrogenated, is biodegradable.

Inhibition of the endogenous respiration of the acclimated micro-organisms by the test substance was found all Closed Bottle tests even in the presence of silica gel and humic acid. As a consequence, inhibition of the biodegradation by acclimated activated sludge due to the "high" initial concentration of the test substance cannot be excluded in all Closed Bottle test using low biomass concentrations. Microorganisms at low concentrations as prescribed in the ready biodegradability tests are more susceptible to toxic substances compared to microorganisms present in tests (ecosystems) with high biomass concentrations.

In conclusion, the positive results with acclimated sludge demonstrate that amines, C36- alkylenedi- is biodegradable. The biodegradation percentages in excess of 60 do also demonstrate complete degradation of amines, C36- alkylenedi- . Non persistency of amines, C36- alkylenedi- can probably be demonstrated in a simulation test as for instance the CAS test (OECD TG 303). Use of high concentrations of activated sludge will reduce the influence of toxic effects on the biodegradation of Amines, C36- alkylenedi-. 

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