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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
22 February - 18 April 1991
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study performed according to an international accepted method (NEN) and in compliance with generally accepted principles of GLP.
Qualifier:
equivalent or similar to
Guideline:
other: NEN 6515: Water-repetitive biodegradability test of organic compounds (1989)
Deviations:
yes
Remarks:
A two-phase closed bottle BOD method for oxygen uptake after repetitve aditionas. NEN 6515: Water repetitive biodegradability test of organic compounds of 1989 (ISO 10708).
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, adapted
Details on inoculum:
Activated sludge sampled at De Bilt (Netherlands) municipal sewage plant 21 February 1991.
Inoculum concentration 20 mg d.s./l
Duration of test (contact time):
49 d
Initial conc.:
26.6 mg/L
Based on:
test mat.
Initial conc.:
22.2 mg/L
Based on:
other: ThOC
Reference substance:
acetic acid, sodium salt
Remarks:
ThOD 0.471 mg/mg and ThOC 0.167 mg/mg
Parameter:
% degradation (O2 consumption)
Value:
21
Sampling time:
3 wk
Parameter:
% degradation (O2 consumption)
Value:
14
Sampling time:
7 wk
Remarks on result:
other: after multiple AHTN additions.
Details on results:
AHTN showed 21% oxidation after 3 weeks and after repetitive additions of AHTN a marginal 12% after 7 weeks.
Results with reference substance:
oxygen contents in reference-test bottles (sodium acetate): spreading in triplicate values: 0-0.8 mg/l (required <1 mg/l).
oxydation of sodium-acetate was 69% after 1 and 4 weeks.

Table 1 showed the measured oxygen concentration as function of time.

Time O2 con- ThOD Oxidation
weeks sumption /mg mg %
0 - - 0
7 0.58 15.1 4
14 2.02 15.1 13
21 3.17 15.1 21
28 4.32 30.2 14
35 4.61 45.3 10
42 4.61 45.3 10
49 5.47 45.3 12
Validity criteria fulfilled:
yes
Remarks:
The results are valid since they meet the requirements for validity stated in the protocol.
Interpretation of results:
other: Oxidation observed
Conclusions:
The maximum oxidation percentage determined is 21% of the theoretical oxygen demand. The mean percentage after adaptation is 14%. Biosolubilisation has not been observed.
Executive summary:

AHTN was incubated with activated sludge for up to 49 days with additional loads after 7, 14 and 21 days. Percent oxydation was measured. Toxicity check show the absence of any toxicity of AHTN to the inoculum at 22mg/l. A positive control of sodium acetate was included showing sufficient oxidation. The maximum oxydation percentage determined is 21% and the mean percentage after adaptation 14% of the theoretical oxygen demand.

Endpoint:
biodegradation in water: screening tests
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: According to normalisation (NEN/ISO "repetitve die away test", protocol revised in December 1983).
Qualifier:
according to
Guideline:
other: Int. Biodeterior. Bull. 15(2), 57-63
Principles of method if other than guideline:
Normalisation committee: Onderzoek van de afvalwater (Investigation discharge water);
Sub-committee: Biologische afbreekbaarheid van het Nederlands Normalisatie Instituut (Biodegradation of the Dutch Bureau of Standards)
GLP compliance:
not specified
Oxygen conditions:
not specified
Inoculum or test system:
not specified
Details on inoculum:
Activated sludge from STP De Bilt
27 mg ds/L
Duration of test (contact time):
42 d
Initial conc.:
ca. 33 mg/L
Based on:
other: ThOC
Initial conc.:
ca. 39 mg/L
Based on:
test mat.
Reference substance:
acetic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Remarks:
oxidation
Value:
< 10
Validity criteria fulfilled:
yes
Remarks:
although oxygen consumption due to slib is too high, this would have no influence on the result of the test.
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
In a repetitive die-away study, the BOD/ThOD ratio reached up to 25%, but after repetitive additions, this relatively high level was not maintained. Tonalid is not readily biodegradable.
Executive summary:

The biodegradability of Tonalid has been studied as part of the requirements for a discharge license. The test was performed according to a repetitive die away test as presecribed by the Dutch Bureau of Standards. The initial test concentration was 39 mg AHTn/l, the inoculum concentration was 27 mg/l of unadapted activated sludge.

The oxygen consumption was measured after during repetive additions of Tonalid in time. After 14 days incubation, BOD/ThOD ratio reached up to 25%, with an average degradability >15%, but during repetitive loadings at days 14, 28 and 35, the average ultimate degradability after 42 days was 9%. Tonalid was not readily biodegradable.

Description of key information

Although many screening tests were referenced in the EU Risk Assessment Report, the test according to the protocol of the Dutch Bureau of Standards has been selected. It is considered sufficient and more extensive than the conventional screening methods. This two-phase closed bottle test (oxygen uptake) displayed 21% oxidation after 3 weeks and after repetitive additions of AHTN, an oxygen consumption of 14% was found.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria
Type of water:
freshwater

Additional information

The EU risk assessment report reported absence of mineralisation under the conditions of the standard tests for ready biodegradation. Mineralisation of the test item remained low, even though bioavailability was enhanced by use of solvents, dispersants or emulsifiers. Despite all these measures, it is still possible that the test item does not show degradation in these screening tests due to its low water-solubility or that the inoculum was not fully adapted to the test item. In order to exclude the latter cause, a test dealing with continuous load of the test item was selected as the key study. The tests demonstrated that the test item is not toxic to the activated sludge up to a content of 22 mg ThOD/L (7.4 mg of the test item/L). The probability of adaptation was increased by exposure of the inoculum to repetitive additions of the test substance. Some biodegradation was observed, but it remained poor.

The EU Risk Assessment Report adopted the key value "inherent biodegradable, not fulfilling specific criteria", that was based on all the available information about the environmental degradation of of the test item.