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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Qualifier:
according to guideline
Guideline:
other: U.S. Environmental Protection Agency method 8330A for analysis of explosives
Deviations:
yes
Remarks:
Because of the design of the experiment (multiple aging periods and three TNT treatment levels), the experiments were conducted with fewer replicates and toxicant treatment levels than suggested by standard protocol.
GLP compliance:
not specified
Radiolabelling:
no
Inoculum or test system:
natural sediment
Duration of test (contact time):
ca. 57 d
Compartment:
sediment
DT50:
ca. 6 d
Temp.:
23 °C
Remarks on result:
other: TNT concentration: 1.409 nmol/g dry weight
Compartment:
sediment
DT50:
ca. 11 d
Temp.:
23 °C
Remarks on result:
other: TNT concentration: 4,403 nmol/g dry weight
Key result
Compartment:
sediment
DT50:
ca. 24 d
Temp.:
23 °C
Remarks on result:
other: TNT concentration: 440 nmol/g dry weight
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3

The primary degradation products were 2 -amino-4,6 -dinitrotoluene, 4 -ADNT, and 2,4 -DANT, accounting for most (>90%) of the sediment mass balance of NA compounds in the lower TNT spiking levels.

Degradation rates of NA compounds, expressed as half-lives, were 6, 11, and 24 d for the low, middle, and high TNT spiking levels, respectively.

Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Principles of method if other than guideline:
All photocatalytic degradation experiments were performed in a batch, recirculating annular ring photoreactor (Blake et al., 1995).
GLP compliance:
not specified
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
other: Phanerochaete chrysosporium (ATCC 1767)
Initial conc.:
0.44 other: mM
Based on:
test mat.
Remarks on result:
not measured/tested
Remarks on result:
not measured/tested
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
No.:
#5

Byproducts from the photocatalytic reduction of TNT (at pH 3.1 to 6.6 under a nitrogen atmosphere) were observed: 4 -amino-2,6 -dinitrotoluene, 2,4 -diamino-6 -nitrotoluene, 4 -hydroxylamino-2,6 -dinitrotoluene, 2,4 -dihydroxylamino-6-nitrotoluene, and 2 -hydroxylamino-4 -amino-6 -nitrotoluene. The extent of TNT mineralization was approximately 14% by biological transformation alone and improved to approximately 32% using the combined photocatalytic and fungal treatment.

When the initial pH was lowered to 3.1 using a combination of acid-form EDTA and disodium EDTA the final pH was 6.6 and no azoxynitrotoluenes were detected.

Significant mineralization was seen in all flasks inoculated with P. chrysosporium. The experiment with no added nitrogen gave the greatest amount of mineralization, approximately 20%, with lesser extents of mineralization in the presence of added nitrogen. No significant mineralization was observed in the uninoculated control.

Mineralization without photocatalytic pretreatment was 13.7 +/- 1.5% (initial TNT concentration 19.6 +/- 3.5%).

Biological mineralization with photocatalytic pretreatment was 31.8 +/- 0.5% (at similar concentrations).

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Principles of method if other than guideline:
Disposable solid-phase microextraction fibers(SPMEs) were used to measere the availability of 2,4,6-trinitrotoluene (TNT) and its two primary transformation products (2ADTN, 4ADTN).
GLP compliance:
not specified
Inoculum or test system:
natural sediment
Duration of test (contact time):
ca. 96 h
Remarks on result:
not measured/tested
Transformation products:
not specified

Linear regression was used to evaluate relationships between bioavailability (Tubifex NA concentrations) and chemical measures of availability (sediment concentrations and SPME concentrations). The SAS/LABt (Ver 8.02; SAS Institute, Cary, NC, USA) was used to test parametric assumptions and to identify outliers.Student’s t tests, Transformation enabled the use of parametric regression to develop models with which to examine the ability of SPMEs to predict bioavailability; however, the need for transformation may suggest that the relationship in the untransformed data may not be linear.

Because both metabolism and bioavailability determine the concentrations of the three main NAs measured in the animals, the relationships between bioavailability and SPME concentrations reported here are purely empirical and may be specific to this organism. The relationship between SPME and Tubifex TNT concentrations was relatively constant among TNT-spiked sediment, TNT-spiked carbon-amended sediment, and TNT-spiked water, suggesting that SPMEs may be able to provide matrix-independent measures of TNT availability.

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2005
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Qualifier:
according to guideline
Guideline:
other: Toxicity experiments were conducted following U.S. Environmental Protection Agency guidance 1994. Methods for measuring the toxicity of sediment-associated contaminants with estuarine and marine amphipods. EPA 600/R-94/025. Narragansett, RI
GLP compliance:
not specified
Radiolabelling:
yes
Inoculum or test system:
natural sediment
Remarks on result:
not measured/tested
Transformation products:
yes
No.:
#1
No.:
#2

The TNT spiked into sediment degraded to aminated transformation products during mixing and also during the sediment exposure. Different patterns of TNT degradation were observed for the two sediments. Although TNT comprised the largest fraction of HPLC-identified compounds during the experimentin YB sediment, aminated transformation products were the dominating compounds in extracts collected for most treatments of the SDB sediment. The extent of TNT degradation decreased with increasing spiking concentration at all sampling times for SDB sediments, and a similar trend clearly was observed for the day 10 samples from YB sediments.

TNT was not observed in any of the tissue extract. The compounds 2 -ADNT and 4 -ADNT were the only degradation products quantified in tissue extracts, with 4 -ADNT representing 83 and 72% of the total for YB and SDB sediment-exposed amphipods an avarage, respectively.This is consistent withthe increased presence of 4 -ADNT abserved in the sediments.

Description of key information

Sediment: degradation rates of nitro aromatic compounds, expressed as half-lives, were 6, 11, and 24 d for the low, middle, and high TNT spiking levels, respectively. For the chemical safety assassment the highest value was taken into account.

Key value for chemical safety assessment

Half-life in freshwater sediment:
24 d
at the temperature of:
23 °C

Additional information