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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: See remarks
Remarks:
Paper presents a detailed description of method and of results. Results are consistent. A blank and an abiotic control were included but results were not reported separately.
Principles of method if other than guideline:
Methodological study with lab tests and field verification
Study on extent of biodegradation in soil solution by three biometer methods: soil flask biometer, in-situ field biometer and soil column biometer. Four soil horizons were used for each method. Radiolabeled test substance and analysis of evolved 14CO2.

GLP compliance:
not specified
Specific details on test material used for the study:
Unlabeled stock solution 10^-3 mol/L, pH adjusted to 4.5.
Specific activity of 3.7 x 10^4 Bq/ml.
Solution prepared containing 2 ml of 1x10^-3 mol/L non-labeled and 1 ml labeled acid.
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil no.:
#1
Soil type:
loamy sand
% Clay:
ca. 9.4
% Silt:
ca. 12.8
% Sand:
ca. 77.8
% Org. C:
ca. 3.3
pH:
ca. 4.9
Soil no.:
#2
Soil type:
sandy loam
% Clay:
ca. 12.1
% Silt:
ca. 13.9
% Sand:
ca. 74
% Org. C:
ca. 1.7
pH:
ca. 4.8
Soil no.:
#3
Soil type:
sandy loam
% Clay:
ca. 16.6
% Silt:
ca. 14.8
% Sand:
ca. 68.6
% Org. C:
ca. 1.4
pH:
ca. 5
Soil no.:
#4
Soil type:
sandy clay
% Clay:
ca. 39.3
% Silt:
ca. 13.4
% Sand:
47.3
% Org. C:
ca. 0.9
pH:
ca. 4.8
Details on soil characteristics:
Described as Cecil soil (Typic Kanhapludult), collected from 15-yr stand of loblolly pine at the Clemson Experimental Forest, Pickens.SC, USA.
# 1- # 4 above describes the four different horizonts Ap1 (0-4 cm), Ap2 (4-11 cm), BA (11-17 cm) and Bt1 (17 - 58 cm).
Org. C is given in % OM.
Soil No.:
#1
Duration:
ca. 30 d
Soil No.:
#2
Duration:
ca. 30 d
Soil No.:
#3
Duration:
ca. 30 d
Soil No.:
#4
Duration:
ca. 30 d
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Details on experimental conditions:
1. Soil biometer flask study: 50 g of sieved soil of each horizon in a biometer flask. Control with water only and abiotic control (NaN3) were included. 10kPa moisture capacity. Flasks were stoppered. Side arms of flasks contained CO2-trap. Initial concentration 5 mg/kg soil. Total addition of radio label was 3.7 x 10^4 Bq. 20+/- 1 degree C, 30 days incubation.
2. Soil column biometer study: Column with 7.5 cm internal diameter, 15 cm length. Soil material from Ap1 and Ap2 horizons were placed in column section to a depth of 4 and 7 cm, resp. Each column was packed with 250 g soil. Side arms of flasks contained CO2-trap. Initial conc. 1 mg/kg soil. Total addition of radio label was 3.7 x 10^4 Bq. 20+/- 1 degree C, 30 days incubation.
3. Field studies on the four horizons: Surface debris and ovelying horizons were removed to expose fresh soil surfaces at the top of the respective horizons. Field biometer frame suited to collect evolved CO2 and leachate. diameter 15.24 cm, depth 10.16 cm = 1.85 dm^3. Consultant estimation of soil density 1.7 kg/dm^3 --> 3 kg soil. Then initial soil concentration is 0.08 mg/kg. (And unknown but maybe not negligible contribution of radiolabeld test substance). Total addition of radio label was 3.7 x 10^4 Bq. 21.1- 23.4 degree C, 30 days incubation.
Key result
Soil No.:
#1
% Degr.:
ca. 70
Parameter:
CO2 evolution
Sampling time:
4 d
Transformation products:
yes
No.:
#1

Below the degradation expressed as % degradation (14C-label) per soil horizon and method is given. In all cases after a steep increase of evolved CO2, a plateau level was reached already after 5 to 20 days.

 Soil horizon  Soil biometer flask  Field biometer Soil column biometer       
 AP1  72.6 15.2  12       
 AP2  68.8  13.1  10.6      
 BA  51.1  10.2  8.0      
 Bt1  51.3  6.4  1.6      
   mean 61%          
Conclusions:
Oxalic acid is easily biodegradable in soil, but conditions determine the actual rate of degradation.
Executive summary:

The degradation of oxalic acid in soil was studied in different horizons and with different methods: soil biometer flasks, soil column biometer and in situ- field biometer. In almost all cases the degradation started immediately without a lag period. The degradation in the lowest Btq horizon was slower. Transport through the medium seems to be rate-limiting. Degradation after 30 days at circa 20 degree C was up to 73% (based on CO2 evolution). It is concluded that oxalic acid is easily biodegradable in soil, but conditions determine the actual rate of degradation.

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