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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:
11 Sep - 9 Oct 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP - Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
other: SEPA, Guidelines for the Testing of Chemicals. 301 F Ready Biodegradability: Manometric Respirometry Test (2004)
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: aeration tank of the Long Hua Wastewater Treatment Plant in Shanghai which treats predominantly domestic sewage. Collected on 2013.09.11.
- Storage conditions: kept aerobic until use
- Preparation of inoculum for exposure: the sludge was washed with mineral medium. After centrifugation, the supernatant was decanted. This procedure was repeated three times (4000 rpm, 4 °C, centrifuge 20 minutes). A small amount (0.1 - 0.5 g) of the washed sludge was weighed and then dried by moisture meter at 105 °C for 1 h to calculate the dry weight. The dry weight of sludge was 6.64%.
- Concentration of sludge: suspended solids 3g/L
- Initial cell/biomass concentration: suspended solids 30 mg/L
- Water filtered: no
Duration of test (contact time):
28 d
Initial conc.:
ca. 55.5 mg/L
Based on:
test mat.
Initial conc.:
ca. 50 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Basal Salts Medium (BSM)
- Test temperature: 21 .7- 22.4 °C
- pH: 6.202 - 6.398
- pH adjusted: no
- Aeration of dilution water: no
- Suspended solids concentration: 30 mg/L
- Continuous darkness: no

TEST SYSTEM
- Culturing apparatus: brown bottles, volume of 500 mL
- Number of culture flasks/concentration: 2
- Measuring equipment: BOD respirometer (WTW, OxiTop 110C, Weilheim, Germany)

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (2 replicates)
- Abiotic sterile control: yes (1 replicate)
- Toxicity control: yes (2 replicates)
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
During the 28-day test period, the biochemical oxygen demand (BOD) of test substance didn't increase from test start until test termination after 28d. Therefore, the test substance cannot be considered to be readily biodegradable under the experimental conditions according to this test method.
Results with reference substance:
Pass level of the ready biodegradation test (>60% within 14 days) was reached. Biodegradation was 85.66% at Day 14.

Table 1: Biodegradability in %.

Day Test substance Reference Substance Toxicity
Control
1 0.5 17.85 9.17
7 -6.46 81.77 61.39
14 -6.86 85.66 63.92
28 -1.59 96.98 79.73
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16 Aug - 19 Dec 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP-Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 302 C (Inherent Biodegradability: Modified MITI Test (II))
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
mixture of sewage, soil and natural water
Details on inoculum:
SOURCE OF INOCULUM
Sludge, water and soil was sampled from 10 sites on May 24th, 2013
1. Sludge: city sewage plant (JiangQiao Wastewater Treatment Plant, JinShan Wastewater Marine Disposal Treatment Plant, LangXia Wastewater Treatment Plant), Industry sewage plant (Sino French water)
2. Water: river (Suzhou River, Chuanyang River, Huangpu River), Lake (Oianshan Lake), estuary (Changjiang estuary)
3. Sea: Jinshan

PRETREATMENT / STORAGE CONDITIONS
All 10 samples were mixed by stirring in a single container, and the mixture is transferred into a culture tank after removing the floating particles and debris. The culturing is aerated and carried out at 25±2°C and adjusted to pH 7.0±1 .0.

PREPARATION OF INOCULUM FOR EXPOSURE
A fresh sample of activated sludge was collected from the culture tank cleaned and washed three times with mineral medium.
The sludge was separated by centrifuging for 20 minutes at about 4000rpm.
Wet sludge was suspended in the mineral culture medium to obtain a concentration of 2g dry matter/L.
The sludge suspension was used as the inoculum after 30min stirring at 500rpm.
The concentration of the sludge in the final test solution was 100 mg dry matter/L.
Duration of test (contact time):
28 d
Initial conc.:
ca. 30 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
TEST CONDITIONS
- Test medium: artificial mineral medium
- Solubilising agent (type and concentration if used): none
- Test temperature: 24.5-24.9°C
- pH: 6.5-7.9

TEST SYSTEM
- Culturing apparatus: BOD-meter (WTW Oxitop 110 C)
- Number of culture flasks/concentration: 3 replicates
- Sampling frequency: Continuously measurement of the oxygen consumption

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes (2 replicates)
- Abiotic sterile control: Yes
- Toxicity control: Yes
- Reference (procedure control): Yes (2 replicates)
Reference substance:
other: sodium benzoate
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Parameter:
% degradation (test mat. analysis)
Value:
0
Sampling time:
28 d
Details on results:
The degradation percentage of toxicity control on day 14 was 60.76%, which was higher than the toxicity inhibition level (>25%). Hence, it can be concluded that the test substance has no inhibitory effects on inoculum at the concentration of 30mg/L
Results with reference substance:
According to the cumulative oxygen consumption, the mean degradation percentage of the reference substance were 63.95% and 71.74% after 7 and 14 days, respectively.

Table1: Biodegradation based on biochemical oxygen consumption [%]:

Day

Test substance

(mean of three replicates)

Reference Substance

(mean of two replicates)

Toxicity Control

1

5.89

29.88

18.44

7

10.12

63.95

49.97

14

10.24

71.74

60.76

28

-1.22

93.71

80.63

Table 2: Biodegradation based on test substance analysis:

Day

Test substance concentration [mg/L]

Residual rate of test substance [%]

Biodegradation rate [%]

0

29.0

 

 

28

29.4

101.4

-0.687

Interpretation of results:
under test conditions no biodegradation observed

Description of key information

The substance Reaction mass of 1,1'-(isopropylidene)bis[3,5-dibromo-4-(2,3-dibromo-2-methylpropoxy)benzene] and 1,3-dibromo-2-(2,3-dibromo-2-methylpropoxy)-5-{2-[3,5-dibromo-4-(2,3,3-tribromo-2-methylpropoxy)phenyl]propan-2-yl}benzene is not readily and not inherent biodegradable according to OECD criteria.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Two key studies are available on the biodegradability potential of Reaction mass of 1,1'-(isopropylidene)bis[3,5-dibromo-4-(2,3-dibromo-2-methylpropoxy)benzene] and 1,3-dibromo-2-(2,3-dibromo-2-methylpropoxy)-5-{2-[3,5-dibromo-4-(2,3,3-tribromo-2-methylpropoxy)phenyl]propan-2-yl}benzene. The first study focuses on the ready biodegradability of the test substance while further study evaluates its inherent biodegradation.

 

In the study by Jing (2014) the ready biodegradability of the test substance was investigated according to the OECD guideline 301 F and GLP. A non-adapted, activated sludge from a domestic sewage treatment plant was used as inoculum and was exposed to an initial nominal test substance concentration of 55.5 mg/L (50.0 mg ThOD/L). After 28 d test duration, 0% degradation of the test substance (based on O2 consumption) was observed. A toxicity control containing both, reference substance (sodium benzoate) and test substance did not indicate inhibitory effects to the inoculum, as 63.92% biodegradation, of the reference item took place within 14 d.

 

In a further study of Jing (2014) the inherent biodegradation of the substance was tested according to OECD 302 C and GLP. A mixture of sewage soil and natural water was exposed to 30 mg/L test material for 28 d. Sodium benzoate was used as the reference substance. The test substance was analyzed by UPLC. No degradation was recorded after 28 d (0%) based on O2 consumption and on test substance analysis. The degradation percentage in the toxicity control on day 14 was 60.76 %, which shows that the test substance has no inhibitory effects on the inoculum at the given concentration.

 

Based on the above described results it is assumed that the substance is persistent in the environment.