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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1992.06.24 - 1992.11.18
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The test was prolonged because the pass level was not reached at day 28.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Principles of method if other than guideline:
The ready biodegradability was determined in the closed bottle test performed according to slightly modified OECD, EEC and ISO Test Guidelines. The test was prolonged because the pass level was not reached at day 28.
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
Secondary activated sludge was obtained from a plant treating predominately domestic wastewater. The sludge was pre-conditioned to reduce the endogenous respiration rates. To precondition, the sludge (200 mg Dry Weight (DW)/litre) was aerated for a period of one week. The sludge was diluted to a concentration in the BOD bottles of 2 mg DW/litre. Ammonium chloride was omitted from the medium to prevent nitrification. Due to omission the pH of the medium decreased slightly.
- Preparation of inoculum for exposure: The activated sludge was preconditioned to reduce the endogenous respiration rates.
- Pretreatment: The sludge was preconditioned to reduce the endogenous respiration rates, the sludge was diluted to a concentration of 2 mg DW/I i nthe BOD bottles.
- Concentration of sludge: 2 mg DW/litre
- Initial cell/biomass concentration:
- Water filtered: Deionized
Duration of test (contact time):
> 0 - <= 140 d
Initial conc.:
2.6 mg/L
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
ThoD ratio
Details on study design:
TEST SYSTEM
- Culturing apparatus: The test was performed in 250-300 ml BOD (Biological Oxygen Demand) bottles.

STATISTICAL METHODS:
The biodegradation was calculated as the ratio of the biochemical oxygen demand (BOD) to the theoretical oxygen demand (ThOD). The ThOD of the test compound is 2.6 g O2/g test substance. The BOD of the test substance and sodium acetate were calculated from the oxygen concentrations in the bottles without and with test substance (B, C) and the bottles without and with sodium acetate (B, D).
Reference substance:
acetic acid, sodium salt
Remarks:
Lot No. B 02099
Preliminary study:
No data supplied.
Test performance:
No data supplied.
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
33
Sampling time:
140 d
Details on results:
Ditallowdimethylammonium chloride is not biodegraded in the closed bottle test (28 days) and this even after 140 days
Results with reference substance:
Inhibition of the degradation of a well-degradable compound, eg sodium acetate by the test compound in the closed bottle test was not determined because possible toxicity of the test substance to micro-organisms degrading acetate is not relevant; Inhibition of hte endogenous respiration of the inoculum by the test substance was not detected. Therefore, no inhibition of the biodegradation due to "high" initial concentration of the test compound is expected.
Validity criteria fulfilled:
yes
Remarks:
The validity of hte test is demonstrated by an endogenous respiration of 0.9 mg/L at day 28. Furthermore, the differences of the replicate values of the control at day 28 were less than 20%. The biodegradation percentage of the reference substance, sodium
Interpretation of results:
other: During 28d biodegradation of DTDMAC was < 20% and therefore the test substance was not readily biodegradable under the test conditions chosen and described before. Over a prolonged exposure period of 140d up to 33% biodegradation is observed under the t
Conclusions:
Under the test conditions described before Ditallowdimethylammonium chloride is not readily biodegradable (biodegradation < 20% after 28d). Nevertheless DTDAMC is biodegradable.
Executive summary:

When assessing the biodegradation behaviour of cationic surfactants like DTDMAC / DHTDMAC it is important to consider the following facts:

1. Due to the low water solubility (CMC) bioavailability of the test substance is reduced. Therefore for cationic surfactant instead of an S shape biodegradation curve a more or less straight line may be observed which can be interpreted such that biodegradation is rate limited by the dissolution of the test item.

2. Cationic surfactants may show toxicity to microorganisms at concentration levels normally used for Biodegradation screening tests e.g. the EC50 for nitrifying bacteria is 2.1 mg/L for DHTDMAC. The EC50 is lower than the test concentration in this test which is 2.6 mg/L.

Based on these fact biodegradation of cationic surfactants is often higher at lower test item concentrations which is also more environmentally relevant. Also the conditions in surface water / sediment may enhance biodegradation additionally. Adaptation of the microorganisms is another important parameter for biodegradation.

The fact that the test item DTDMAC is not readily biodegradable under the conditions of this test after 28d does not allow the conclusion that DTDMAC is recalcitrant or persistent in theSewage treatment plant (STP) or the freshwater compartment. More adequate studies like e.g. OECD 303 A (STP Simulation Test) or e.g a River die away Test have to be used in order to derive adequate biodegradation kinetics (see IUCLID Chapter 5.2.2).

Description of key information

33% biodegradation (OECD 301D; BOD; 140 d) in the prolonged closed bottle test

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

Biodegradation Screening tests


In the ECETOC Technical Report No. 53 'DHTDMAC - Aquatic and Terrestrial Hazard Assessment, CAS No. 61789 -80 -8' (ECETOC, 1993) as well as in the EU Risk Assessment 'DODMAC/DTHDMAC' (EU, 2002) the available Biodegradation Screening test results are given.


Read across from a structurally similar Quat (DHTDMAC, CAS No. 61789-80-8 ) can be applied.


When assessing the biodegradation behaviour of cationic surfactants like DTDMAC / DHTDMAC it is important to consider the following facts:


1. Bioavailability of the test substance may be reduced due to the formation of liquid crystals and vesicals. Therefore for cationic surfactant instead of an S shape biodegradation curve a more or less straight line may be observed which can be interpreted such that biodegradation is rate limited by the dissolution of the test item.


2. Cationic surfactants may show toxicity to microorganisms at concentration levels normally used for Biodegradation screening tests e.g. the EC50 for nitrifying bacteria is 2.1 mg/L for DHTDMAC. Usual test item concentrations are between 5 and 20 mg/L. Based on these facts biodegradation of cationic surfactants is often higher at lower test item concentrations which is also more environmentally relevant. Also the conditions in surface water / sediment may enhance biodegradation additionally. Adaptation of the microorganisms is another important parameter for biodegradation.


The fact that the test item DTDMAC is not readily biodegradable under the conditions of the tests listed below after 28d does not allow the conclusion that DHTDMAC/DTDMAC is recalcitrant or persistent in the Sewage treatment plant (STP) or the freshwater compartment. More adequate studies like e.g. OECD 303 A (STP Simulation Test) or e.g a River die away Test have to be used in order to derive adequate biodegradation kinetics (see IUCLID Chapter 5.2.2). Table 4.xx list the most important tests with the test setting and results.


 


Table 4.xx Biodegradation Screening tests of DHTMAC/DTDMAC


 




























































































































































Test classTest typeGuide-lineEndpointExposure (d)Test conc. (mg/L)AdaptationElimination (%)Biodegradation (%)YearRemark
Screening tests          
 Ready301 BCO2
evolution
28not givennon.a.not observed1988Schöberl et al, 1988
 Ready301DBOD18010non.a.< 201991van Ginkel & Kolvenbach, 1991
 Ready301DBOD201yesn.a.191991Clancy & Tanner, 1991
    201yesn.a.81991
    200.8yesn.a.121991
    200.5yesn.a.171991
    200.4yesn.a.351991
 Ready301DBOD282.6non.a.<201993van Ginkel, 1993
   BOD1402.6non.a.331993
 Inherent302BDOC15not givenno92n.a.1989Hoechst, 1989d