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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Administrative data

Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline/GLP-compliant study performed by an experienced contract laboratory

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
other: OECD 314C
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
14C-ring labeled decabromodiphenyl ethane of 94.5% radiochemical purity and 32.4 mCi/mmol (33.3 uCi/mg)
Radiolabelling:
yes

Study design

Oxygen conditions:
anaerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Anaerobic digester sludge was collected from the Back River Wastewater Treatment Plant (Baltimore, Maryland) five days prior to start of the test, sieved through a 2 mm screen, purged with nitrogen, and held under anaerobic conditions at 35°C. The total sludge solids were determined by combustion after drying, and adjusted to 4.17% by discarding supernatant after centrifugation. The sludge inoculum was prepared by combining equal volumes of mineral salts solution and the adjusted anaerobic digester sludge. The pH (Orion pH/ISE Meter, model: 520A) and total solids concentration of the test inoculum were 7.6 and 20,820 mg/L, respectively. The test inoculum was held at 35°C under anaerobic conditions until used in the test.
Duration of test (contact time):
63 d
Initial test substance concentrationopen allclose all
Initial conc.:
0.1 mg/L
Based on:
test mat.
Initial conc.:
12 other: Ci/mL
Based on:
test mat.

Results and discussion

Test performance:
The test met the validity criteria specified in the guideline. 14C-volatiles evolved from [14C]d-Glucose positive control chambers (n=2/interval) were quantitated at weekly intervals. By the end of the study, evolved [14C]-volatiles from the [14C]d-Glucose chambers totaled 45.29% and 74.83% of the administered dose, indicating the inocula were viable. The majority of the remaining 14C-activity was detected in the solids (20.0 and 29.3%) with lesser amounts in the aqueous layer (7.8 and 8.7%).
Mean total recovery
Compartment:
other: water / sediment, material (mass) balance
Remarks on result:
other: see below
% Degradationopen allclose all
% Degr.:
0
Parameter:
CH4 evolution
Sampling time:
63 d
% Degr.:
0
Parameter:
CO2 evolution
Sampling time:
63 d
Transformation products:
no
Details on transformation products:
See below.
Evaporation of parent compound:
no
Volatile metabolites:
no

Any other information on results incl. tables

The entire contents, less three 1 mL aliquots each, of two biotic and two abiotic test chambers treated with [14C]DBDP-Ethane were analyzed on Day 0, 30 and 63 for14C-activity. Results from the biotic and abiotic chambers were similar when compared by day and fraction. On Day 0, the mean total14C-activity from the 4 test chambers (2 biotic, 2 abiotic) was 118.1 ± 15.02%. The mean totals on Days 30 and 63 were lower than on Day 0, but similar to one another, e.g. 78.63 ± 5.12% and 76.65 ± 1.14%, respectively. The majority of14C-activity on all days was associated with the sludge solids. 14C-volatiles and supplemental extraction of test chambers and solids contributed negligible amounts to the total14C-activity recovered on any day. Mineralization was not observed.

With respect to analysis for parent compound and metabolites, results from the biotic and abiotic chambers were again similar on all days. HPLC/β-RAM analysis of sludge extracts detected one peak containing the14C-radiolabel. The peak had a retention time identical to that of the parent compound. 

The mass balance in control and treatment chambers was determined using the triplicate 1 mL samples of Day 0, 30 and 63 sludge and cumulative evolved14C-volatiles. The sludge samples were centrifuged, the solids fraction combusted, and the14C-activity in the supernatant (aqueous) and combustion gases determined on Day 63. The mass balance for the[14C]d-Glucosechambers was similarly determined on Day 63, and was 73.1% and 112.8% of the Day 0 dose (Table 3). Mass balance in the treatment groups were more variable, ranging from 42.1 – 95.1% in the biotic chambers and 36.1 – 155.1% in the abiotic chambers. The greatest variability was observed in the solids fraction, with the lowest value in the biotic Day 63 samples. In contrast, Day 63 solids extraction results (Table 2) were similar in the biotic and abiotic groups and contained a higher percentage of the dose than that of the Day 63 solids measurement, e.g. approximately 76% compared to approximately 42%. The Day 63 solids mass balance in the abiotic chambers (132.8%, 76.0%) was similar to that of the Day 63 solids extraction results (approximately 76%). 

The inability to recover approximately 22% of the anaerobic dose, when using a14C-labelled test material by an experienced laboratory, illustrates the difficulties encountered in working with DBDP-Ethane.  DBDP-Ethane is highly insoluble in water and most organic solvents and has a pronounced tendency to adsorb to surfaces. These properties suggest adherence to glassware during the incubation and extraction steps contributed to lower than expected recovery. Supplemental extraction of the glassware was unable to recover significant amounts of14C-activity, and it was not possible to measure14C-activity on the glassware itself. The majority of the dose was detected in the solids as expected, which raises the possibility that the unaccounted for fraction of the dose was also in this matrix. Incomplete combustion of the sludge solids could have resulted in a lower recovery, however the solids combustion apparatus was routinely tested during the analytical phase and performed properly. Another possible explanation is loss as unrecovered14C-volatiles, however this is highly unlikely.  DBDP-Ethane is not volatile, and mineralization of a substantial fraction of the dose within the timeframe of the study would be exceptional. 

Distribution of14C-activity in anaerobic digester sludge treated with14C-Decabromodipehnyl Ethane.

               

Day

Chamber

14C-Activity (% of Day 0 Dose)

Sludge

Supplemental Extraction

Evolved14C-VOC

Σ

Extracted

Non-extracted+

Sludge

Test Chamber

0

3-Biotic

92.6

22.6

--*

--

--

115.1

4-Biotic

101.7

38.1

--

--

--

139.8

9-Abiotic

99.4

12.3

--

--

--

111.7

10-Abiotic

93.6

12.1

--

--

--

105.6

Mean ± SD

96.83 ± 4.42

21.3 ± 12.2

--

--

--

118.05 ± 15.02

30

5-Biotic

73.9

4.4

--

0.5

0.4

79.2

6-Biotic

69.8

3.5

--

0.5

0.4

74.1

11-Abiotic

77.8

6.7

--

0.8

0.4

85.6

12-Abiotic

71.9

2.5

--

0.8

0.3

75.6

Mean ± SD

73.35 ± 3.41

4.28 ± 1.79

--

0.65 ± 0.17

0.4 ± 0.1

78.63 ± 5.12

63

7-Biotic

73.5

0.9

0.2

0.0

0.8

75.4

8-Biotic

70.6

2.0

0.6

0.2

0.9

74.2

13-Abiotic

72.8

1.9

0.3

0.2

0.8

76.1

14-Abiotic

72.5

2.8

0.1

0.1

1.4

76.9

Mean ± SD

72.35 ± 1.24

1.9 ± 0.78

0.3 ± 0.22

0.13 ± 0.1

0.98 ± 0.29

75.65 ± 1.14

 +Determined by combustion of sludge after extraction.

*Not performed or not measured.

Mass balance expressed as percentage of14C-d-glucose (control) or14C-decabromodiphenyl ethane administered on Day 0. 

Test Day

Chamber

14C-Activity (% of Day 0 Dose)

Solids

Aqueous

Evolved Volatiles

                           

63

1- d-Glucose

20.0

7.8

45.3

73.1

           63

2- d-Glucose

29.3

8.7

74.9

112.8

0

3-Biotic

48.5

1.8

--

50.3

0

4-Biotic

93.5

1.6

--

95.1

30

5-Biotic

71.9

1.5

0.4

73.8

30

6-Biotic

72.5

1.8

0.4

74.7

63

7-Biotic

36.5

5.6

0.8

42.9

63

8-Biotic

37.0

4.2

0.8

42.1

0

9-Abiotic

35.6

0.5

--

36.1

0

10-Abiotic

153.6

1.5

--

155.1

30

11-Abiotic

75.1

6.0

0.4

81.5

30

12-Abiotic

72.7

5.3

0.4

78.4

63

13-Abiotic

126.0

6.0

0.8

132.8

63

14-Abiotic

73.3

1.3

1.4

76.0

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
Evidence for the biodegradation of DBDP-Ethane in anaerobic sewage sludge was not observed over a 63 day period.
Executive summary:

Evidence for the biodegradation of DBDP-Ethane by anaerobic digester sludge was not observed over a 63-d period. Results of the biotic and abiotic chambers were comparable.14C-DBDP-Ethane was used to definitively identify the parent molecule and any degradants.  Only one peak containing the14C-label and having a retention time of DBDP-Ethane was detected in any of the extracts.