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Environmental fate & pathways

Biodegradation in soil

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Reference
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
20 November to 7 December 1995
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EPA OTS 796.3400 (Soil Biodegradation)
Deviations:
yes
Remarks:
Classifications of soils in the study is not fully consistent with the soil descriptions in the EPA Guideline.
GLP compliance:
yes
Test type:
laboratory
Specific details on test material used for the study:
The test material was 96% pure and had a specific activity of 335,510 dpm/μg.
Radiolabelling:
yes
Remarks:
[14C]NBPT, butyl-1-14C labeled, was studied utilizing radiochemically pure test substance.
Oxygen conditions:
aerobic
Soil classification:
not specified
Year:
1995
Soil no.:
#1
Soil type:
loam
% Clay:
24
% Silt:
31
% Sand:
45
% Org. C:
1.3
pH:
6.5
CEC:
10 meq/100 g soil d.w.
Bulk density (g/cm³):
1.26
Soil no.:
#2
Soil type:
loamy sand
% Clay:
4.8
% Silt:
12
% Sand:
83.2
% Org. C:
0.9
pH:
4.9
CEC:
3 meq/100 g soil d.w.
Bulk density (g/cm³):
1.42
Soil no.:
#3
Soil type:
sandy loam
% Clay:
12
% Silt:
22
% Sand:
66
% Org. C:
1.2
pH:
8
CEC:
11 meq/100 g soil d.w.
Bulk density (g/cm³):
1.31
Details on soil characteristics:
Soil source:
Soil 1 - Tulare County, California (USA)
Soil 2 - Antrim County, Michigan (USA)
Soil 3 - Frederick County, Maryland (USA)
Soil No.:
#1
Duration:
8 d
Soil No.:
#2
Duration:
8 d
Soil No.:
#3
Duration:
16 d
Soil No.:
#1
Initial conc.:
9.5 ppm
Based on:
test mat.
Soil No.:
#2
Initial conc.:
9.5 ppm
Based on:
test mat.
Soil No.:
#3
Initial conc.:
9.5 ppm
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
22.2 deg. C
Humidity:
27.2% (40% of the field moisture capacity at 1/3 bar)
Microbial biomass:
Day 0 total aerobic bacteria 3.8E06 (untreated) and 6.3E06 (14C treated); total actinomycetes 2.6E06 (untreated) and 2.2E06 (14C treated); total fungi 3.5E03 (untreated) and 2.6E04 (14C treated). results are total colony forming units per gram of soil.
Soil No.:
#2
Temp.:
22.2 deg. C
Humidity:
7.56% (40% of the field moisture capacity at 1/3 bar)
Microbial biomass:
Day 0 total aerobic bacteria 1.6E05 (untreated) and 9.5E04 (14C treated); total actinomycetes 5.5E04 (untreated) and 3.0E04 (14C treated); total fungi 1.0E04 (untreated) and 2.1E04 (14C treated). Results are total colony forming units per gram of soil.
Soil No.:
#3
Temp.:
22.2 deg. C
Humidity:
15.7% (40% of the field moisture capacity at 1/3 bar)
Microbial biomass:
Day 0 total aerobic bacteria 2.9E06 (untreated) and 1.3E06 (14C treated); total actinomycetes 2.6E06 (untreated) and 4.1E05 (14C treated); total fungi 5.6E03 (untreated) and 150 (14C treated). Results are total colony forming units per gram of soil.
Details on experimental conditions:
Microbial biomass:

Day 16 total aerobic bacteria 5.7E05 (14C treated); total actinomycetes 3.8E06 (14C treated); total fungi 4.3E03 (14C treated). Results are total colony forming units per gram of soil.
Soil No.:
#1
% Recovery:
91.6
Soil No.:
#2
% Recovery:
89.9
Soil No.:
#3
% Recovery:
93.9
Key result
Soil No.:
#1
% Degr.:
54.6
Parameter:
radiochem. meas.
Sampling time:
8 d
Key result
Soil No.:
#2
% Degr.:
53
Parameter:
radiochem. meas.
Sampling time:
8 d
Key result
Soil No.:
#3
% Degr.:
52.1
Parameter:
radiochem. meas.
Sampling time:
16 d
Transformation products:
not specified
Evaporation of parent compound:
not specified
Volatile metabolites:
not specified
Residues:
not specified
Details on results:
The overall recovery of radiocarbon was determined for the samples used in the extractability substudy. The overall average recovery was 91.8% of the applied dose.
Conclusions:
The viability of NBPT treated and non-treated soils was verified. No significant difference in the number of aerobic bacteria, actinomycetes or fungi was observed after treatment with NBPT.
Executive summary:

Three soils of diverse origins and characteristics were treated with [14C]NBPT at a nominal applied concentration of 9.5 ppm on dry weight basis (1,509,000 DPM of 14C-NBPT). The treated soils were maintained in biometer flasks at about 22 °C in darkness. The degree of NBPT mineralization, determined as 14CO2, was monitored periodically. The study was terminated after 50% of the applied NBPT was mineralized.

Mineralization of NBPT to CO2 was rapid in all three soils. In Soils 1 and 2, 53 to 55% of the applied dose was converted to 14C02 after 8 days of incubation. In Soil 3, 52% of the applied dose was mineralized after 16 days. Mineralization of NBPT is, therefore, considered a significant route of dissipation in soils.

Between 5.5 and 23.5% of the radiocarbon remaining on soils 1, 2 and 3 was extractable at the point of 50% mineralization. For all three soils, the bound soil 14C-residues accounted for 40% of the applied dose. NBPT readily forms bound residues in soil.

Recovery of applied radiocarbon averaged 91.8 ± 1.9% of the applied dose. No significant losses of radioactivity occurred during the study.

No loss of microbial viability occurred after application of NBPT.

Description of key information

Three soils of diverse origins and characteristics were treated with [14C]NBPT at a nominal applied concentration of 9.5 ppm on dry weight basis (1,509,000 DPM of 14C-NBPT). The treated soils were maintained in biometer flasks at about 22 °C in darkness. The degree of NBPT mineralization, determined as 14CO2, was monitored periodically. The study was terminated after 50% of the applied NBPT was mineralized.

Mineralization of NBPT to CO2 was rapid in all three soils. In Soils 1 and 2, 53 to 55% of the applied dose was converted to 14C02 after 8 days of incubation. In Soil 3, 52% of the applied dose was mineralized after 16 days. Mineralization of NBPT is, therefore, considered a significant route of dissipation in soils.

Between 5.5 and 23.5% of the radiocarbon remaining on soils 1, 2 and 3 was extractable at the point of 50% mineralization. For all three soils, the bound soil 14C-residues accounted for 40% of the applied dose. NBPT readily forms bound residues in soil.

Recovery of applied radiocarbon averaged 91.8 ± 1.9% of the applied dose. No significant losses of radioactivity occurred during the study.

No loss of microbial viability occurred after application of NBPT.

Key value for chemical safety assessment

Additional information

No loss of microbial viability occurred after application of NBPT.