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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:
21 days
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: no positive controls and no negative controls included
Principles of method if other than guideline:
the disappearance of the test substance was determined analytically, the exposure period was only 21 days
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Settled sewage obtained from the Highland Park Municipal Treatment Plant.
Duration of test (contact time):
ca. 21 d
Initial conc.:
ca. 0.01 mg/L
Based on:
act. ingr.
Initial conc.:
ca. 1 mg/L
Based on:
act. ingr.
Initial conc.:
ca. 10 mg/L
Based on:
act. ingr.
Initial conc.:
ca. 100 mg/L
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
test mat. analysis
Remarks:
gas chromatography with electrone capture
Details on study design:
The cultures were inoculated with the test substance and maintained under aerobic conditions at room temperature for 21 days. Water samples were obtained at weekly intervals.
Test performance:
No biological degradation of Dechlorane Plus was observed. Viable bacteria were found in all samples obtained during the whole test duration.
Key result
Parameter:
% degradation (test mat. analysis)
Value:
0
Sampling time:
0 d
Remarks on result:
other: no degradation observed
Key result
Parameter:
% degradation (test mat. analysis)
Value:
0
Sampling time:
7 d
Remarks on result:
other: no degradation observed
Key result
Parameter:
% degradation (test mat. analysis)
Value:
0
Sampling time:
14 d
Remarks on result:
other: no degradation observed
Key result
Parameter:
% degradation (test mat. analysis)
Value:
0
Sampling time:
21 d
Remarks on result:
other: no degradation observed
Details on results:
The test substance precipitated in the stock solution, therefore only part of the nominal concentration could be detected analytically in the water samples. As the concentrations did not further decrease over the exposure time, this was not caused by biodegradation but by the inhomogenous distribution of the test substance in the stock solution.

nominal concentration              sampling time /analytical concentration

test day 0        test day 7       test day 14       test day 21

0.01 ppm                               0.008 ppm       0.007 ppm       0.006 ppm       0.006 ppm

1.0 ppm                                 0.46 ppm        0.50 ppm        0.43 ppm        0.42 ppm

10.0 ppm                               8.0 ppm            7.0 ppm        8.3 ppm           8.2 ppm

100.0 ppm                             82.0 ppm           80.0 ppm       79.0 ppm        82.0 ppm

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Dechlorane Plus was not biodegradable at room temperature under aerobic conditions.
Executive summary:

Dechlorane Plus was incubated with domestic sewage sludge under aerobic conditions at room temperature at concentrations of nominal 0.01, 1.0, 10.0, and 100.0 ppm corresponding to analytical concentrations of initial 0.008, 0.46, 8.0, and 82 ppm as determined by gas chromatography with electrone capture for 21 days. No biodegradation was observed as determined by test substance analysis.

Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2 or 6 weeks
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Different extraction methods were used without concurrent controls. Degradation was determined as loss of radioactivity from the cultures.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Radiolabeled Dechlorane Plus was incubated with either aerobe or anaerobe sewage sludge under aerobic or anaerobic conditions for 2 or 6 weeks at two nominal concentrations of 218 and 872 ng/ml. Parallel cultures were autoclaved to kill the sludge bacteria and served as negative controls. The water samples were extracted, and the radioactivity was determined by liquid scintillation.
GLP compliance:
no
Oxygen conditions:
aerobic/anaerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
The effluent containing aerobic organisms had a pH of 7.1 and a total suspended matter concentration of 185 mg/l. The effluent containing anaerobic organisms had a pH of 6.9 and a total suspended matter concentration of 3,910 mg/l. All effluents were from a sewage treatment plant in Menlo Park, California.
Duration of test (contact time):
2 - 6 wk
Initial conc.:
218 - 872 µg/L
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
radiochem. meas.
Remarks:
liquid scintillation
Details on study design:
Radiolabeled Dechlorane Plus was incubated with either aerobe or anaerobe sewage sludge under aerobic or anaerobic conditions for 2 or 6 weeks at two nominal concentrations of 218 and 872 ng/ml. Parallel cultures were autoclaved to kill the sludge bacteria and served as negative controls. The water samples were extracted, and the radioactivity was determined by liquid scintillation.
Key result
Parameter:
% degradation (radiochem. meas.)
Value:
0
Sampling time:
2 wk
Remarks on result:
other: 2 weeks aerobic incubation, 218 or 872 ng/ml
Key result
Parameter:
% degradation (radiochem. meas.)
Value:
0
Sampling time:
2 wk
Remarks on result:
other: 2 weeks anaerobic incubation 218 or 872 ng/ml
Key result
Parameter:
% degradation (radiochem. meas.)
Value:
ca. 99
Sampling time:
6 wk
Remarks on result:
other: 6 weeks aerobic incubation 872 ng/ml
Key result
Parameter:
% degradation (radiochem. meas.)
Value:
ca. 4
Sampling time:
6 wk
Remarks on result:
other: 6 weeks of anaerobic incubation 872 ng/ml
Details on results:
Degradation was determined as loss of radioactivity. No loss of radioactivity was seen after 2 weeks of incubation at aerobic and anaerobic conditions. After 6 weeks of incubation at aerobic conditions, almost all radioactivity had disappeared from the cultures, while after 6 weeks of incubation under anaerobic conditions only about 4% of the radioactivity had disappeared.

Viable                            Sterile

Radioactivity nominal                                   1.97 dpm       7.88 dpm       197 dpm       7.88 dpm

Recovery after 2 weeks anaerobic                  89.4%           91.6%            84.9%        85.5%

Recovery after 6 weeks anaerobic                   87.5%        84.1%            -                   88.4%

Recovery after 2 weeks aerobic                      77.1%        85.6%            76.5%        85.5%

Recovery after 6 weeks aerobic                     42.9%            0.16%              -                  92.1%

      

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
Dechlorane Plus was almost completely degraded after 6 weeks of aerobic incubation with sewage sludge.
Executive summary:

Radiolabeled Dechlorane Plus was incubated with aerobic and anaerobic sewage sludge for 2 or 6 weeks under aerobic and anaerobic conditions at two concentrations, 218 and 872 ng/ml. After two weeks of incubation, no degradation was seen. After 6 weeks of incubation, the recovery of radioactivity at aerobic conditions was 42.9% at the low concentration and 0.16% at the high concentration when compared to 92.1% in the sterile negative control at the high concentration. After 6 weeks of incubation at anaerobic conditions, the recovery of radioactivity was 87.5% at the low concentration and 84.1% at the high concentration, when compared to 88.4% in the sterile negative control at the high concentration. At the high concentration, Dechlorane Plus was almost completely degraded after 6 weeks of aerobic incubation with sewage sludge.

Description of key information

The substance is considered non-biodegradable, although some elimination had been observed in a biodegradation study, but the study as such is of limited value. Considering the hydrophobic character of the substance, the chemical structure and the extremely low water solubility, biodegradation appears unlikely.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Dechlorane Plus was investigated for biodegradation in two non-standard tests. In a first study by Boudreau et al. (1973) the disappearance of the substance was measured analytically (GC-EC) over a 21d-period with a domestic activated sludge (non-adapted) being present. Initial nominal test substance concentrations of ca. 0.01 mg/l, ca. 1 mg/l, ca. 10 mg/l and ca. 100 mg/l (active ingredient) were used (stock solution prepared in acetone and precipitation was observed, resulting in measured concentrations of 0.008 mg/l, 0.46 mg/l, 8.0 mg/l and 82 mg/l). Water samples were obtained on days 0, 7, 14 and 21. Concentrations did not decrease over the exposure time, and thus no biodegradation was observed in the study. No positive controls and no negative controls were included in the study.

In a second experiment by Chou et al. (1979) radiolabelled Dechlorane Plus was investigated for biodegradation. The radiolabelled test item was incubated with sewage treatment plant sludge under aerobic or anaerobic conditions for 2 or 6 weeks at two nominal concentrations of 218 and 872 ng/ml. Parallel cultures, autoclaved to kill the sludge bacteria, served as negative controls. The water samples were extracted, and the radioactivity was determined by liquid scintillation. Degradation was determined as loss of radioactivity. No loss of radioactivity was seen after 2 weeks of incubation at aerobic and anaerobic conditions. After 6 weeks of incubation, the recovery of radioactivity at aerobic conditions was 42.9% at the low concentration and 0.16% at the high concentration when compared to 92.1% in the sterile negative control at the high concentration. After 6 weeks of incubation at anaerobic conditions, the recovery of radioactivity was 87.5% at the low concentration and 84.1% at the high concentration, when compared to 88.4% in the sterile negative control at the high concentration. Volatilisation of the test substance causing reduction of radiolabelled material is unlikely, given the physico-chemical properties of the substance (melting point >300 °C and vapour pressure considered negligible), but adsorption to sludge or bacteria cannot be excluded. Also the position of radiolabelling in the molecule is not described. Thus, the findings have to be seen with caution and cannot be considered as proof for biodegradation. Hence, the substance is considered non-biodegradable.