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Environmental fate & pathways

Biodegradation in soil

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Reference
Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Principles of method if other than guideline:
The US EPA method 8330 was used to extract and determine TNT and associated nitroaromatics. See also other information on methods and materials.
GLP compliance:
not specified
Test type:
other: a laboratory spiking experiment and field sampling experiment
Radiolabelling:
no
Oxygen conditions:
aerobic
Soil classification:
not specified
Year:
1998
Soil no.:
#1
Soil type:
sandy loam
% Clay:
7
% Silt:
23
% Sand:
70
% Org. C:
11.2
pH:
6.9
Soil no.:
#2
Soil type:
silty clay loam
% Clay:
30
% Silt:
59
% Sand:
11
% Org. C:
3.5
pH:
6.5
Duration:
1 wk
Initial conc.:
0 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
25 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
50 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
100 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
200 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
400 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
800 mg/kg soil d.w.
Based on:
test mat.
Initial conc.:
1 000 mg/kg soil d.w.
Based on:
test mat.
Temp.:
25
% Degr.:
> 40
Parameter:
other: recovery is mostly below 60%
Sampling time:
1 wk
Transformation products:
yes
No.:
#1
No.:
#2
Details on results:
TNT was transformed to the amino-nitro intermediated: 2-ADNT and 4-ADNT. No other metabilites were detected. Both soil and TNT concentration showed significant influences on both TNT recovery and the concentration of TNT metabolites. The TNT (acetonitrile extractable) recovered after 1 week varied 4% (soil nr2) at 25 mg/kg to 82% (soil nr2) at 1000 mg/kg. If both TNT and its metabolites were summated, the total recovery was between 18% (soil nr1) and 86% (soil nr 2), but most recoveries were below 60%.

NFA (nitrogen-fixation activity) appeared to be more sensitive in the GS1 (soil nr1), whereas PNA (potential nitrification activity) was more sensitive in the GS3 (soil nr2). These can be attributed to the sensitivity of the different indigenous microbal groups or communities and the influence of soil characteristics. A recent study shows that both the level of the soil humic substances and the soil pH have significant effects on TNT binding to humic acid, which might cause bioavailability and thus toxicity of TNT to differ in the two garden soils.

The LOEC derived from the spiking experiment was 1 to 2 mg AE TNT/kg soil. The lowest NOEC and LOEC in the field soils were 0.4 and 1 mg AE TNT/kg soil. The estimated IC50 was in the range of 40 to 540 mg AE TNT/kg in the spiked soils and of 50 to 160 mg AE TNT/kg in the field soils. These results indicate that soil microorganisms are very sensitive to TNT toxicity and that laboratory and field studies are consistent and comparable. However, the toxicity exerted by TNT depended on measurement endpoints and many environmental factors, indicating a battery of toxicity tests should be used when assessing impact of toxicants on soil microbal community.

Description of key information

TNT was transformed to the amino-nitro intermediated: 2-ADNT and 4-ADNT. No other metabilites were detected. Both soil and TNT concentration showed significant influences on both TNT recovery and the concentration of TNT metabolites. The TNT (acetonitrile extractable) recovered after 1 week varied 4% (soil nr2) at 25 mg/kg to 82% (soil nr2) at 1000 mg/kg. If both TNT and its metabolites were summated, the total recovery was between 18% (soil nr1) and 86% (soil nr 2), but most recoveries were below 60%.

Key value for chemical safety assessment

Additional information