Mittwoch, 24. Februar 2016

Biodegradation in soil

Biodegradation in soil


Administrative data

Purpose flag:
key study
Study result type:
experimental result
Reliability:
1 (reliable without restriction)

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2004

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Deviations:
no
GLP compliance:
yes
Test type:
laboratory

Test materials

Identity of test material same as for substance defined in section 1 (if not read-across):
no
Test material identity
Identifier:
CAS number
Identity:
7775-09-9
Details on test material:
Lot/ Batch Number: 1E0103QF

Purity: 99.66 %

Further relevant properties: Solid, soluble in water

Composition of product:
H2O = 0.062 %
NaCl = 0.022 %
Ca3(PO4)2 = 0.16 %
Fe2O3 = 0.09 %
Radiolabelling:
no

Study design

Oxygen conditions:
aerobic/anaerobic
Soil classification:
USDA (US Department of Agriculture)
Soil propertiesopen allclose all
Soil no.:
#1
Loamy sand
Org. C (%):
2.3
pH:
5.6
CEC:
11 other: mval/100g
Soil no.:
#2
Loam
Org. C (%):
2.6
pH:
7.1
CEC:
19 other: mval/100g
Soil no.:
#3
Sandy loam
Org. C (%):
1.6
pH:
7
CEC:
13 other: mval/100g
Soil no.:
#4
Clay
Org. C (%):
2
pH:
6.8
CEC:
18 other: mval/100g
Details on soil characteristics:
Loamy sand, loam, sandy loam and clay were purchased from the Landwirtshaftliche Untersuchungs – und S Forschungsanstalt Speyer, Obere Langgasse 40, 67346 Speyer, Germany. These soils were stored in the refrigerator in polyethylene bags, until use in the experiment. The soils were sieved through screens with openings of 2-5 mm diameter to improve the uniformity of the application. Next, the soils were preconditioned by incubating the soils for one week at 20 °C at 30% of their water holding capacity. A part of these soils was used for the determination of the biomass concentration. The remainder of the soils was used for the test. See Table A7_2_2_1-1 for soil characteristics. The soils were incubated at 20 ± 1 °C for several weeks.
Duration of test (contact time)
Duration:
120 d
Initial test substance concentration
Initial conc.:
0.25 other: mg/mL of soil
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
Test mat. analysis
Experimental conditionsopen allclose all
Soil No.:
#1
Microbial biomass:
0.32 mg/g of soil (t = 0 d), 0.22 mg/g soil (t = 120 d)
Soil No.:
#2
Microbial biomass:
0.36 mg/g of soil (t = 0 d), 0.33 mg/g soil (t = 120 d)
Soil No.:
#3
Microbial biomass:
0.23 mg/g of soil (t = 0 d), 0.15 mg/g soil (t = 120 d)
Soil No.:
#4
Microbial biomass:
0.28 mg/g of soil (t = 0 d), 0.18 mg/g soil (t = 120 d)
Details on experimental conditions:
The biodegradation of sodium chlorate was evaluated in four soils. For each soil there was one treatment, i.e. test substance mixed with soil. Each treatment had two replicates. The test was carried out in bottles closed with septa. Each Erlenmeyer flask had 200 grams dry weight of soil. In the bottles, aerobic conditions in the soils were maintained through diffusion, for 28 days. After this period, the loam was waterlogged (1-3 cm water layer). In addition the oxygen from the gas phase of the bottle was removed through flushing the gas phase with nitrogen gas. Anaerobic conditions were established in one soil (loam). 

The test samples were incubated at 20 ± 2 °C and the test was run for a period of 120 days.

Method of preparation of the test solution: The test substance was dissolved in appropriate amounts of deionised water, not exceeding that required for bringing the soils to 50% of the maximum moisture capacity. Sodium chlorite was added to he soils using solutions of 2.46 g/L (loamy sands), 2.56 g/L (loam), 2.80 g/L (sandy loam), and 2.67 g/L (clay). Addition of the stock solutions also resulted in water contents of 50% of their water holding capacity.

Samples of aerobic soil were withdrawn for analyses for chlorate (four soils), chlorite (loam) and chloride (loam) at day 0, 7, 14, 21, 28, 42, 56, 84 and 120. 
The chlorate reduction in the presence of an electron donor sodium acetate was measured at day 134 and 148. 
The following time intervals were adopted for the anaerobic bottles starting after introducing the anaerobic conditions – day 0, 4, 7, 10, 14, 21, 28, 35, 42, 56, 84 and 120.

Results and discussion

Half-life / dissipation time of parent compoundopen allclose all
Soil No.:
#1
Half-life:
52 d
Type:
(pseudo-)first order (= DT50)
Soil No.:
#2
Half-life:
39 d
Type:
(pseudo-)first order (= DT50)
Soil No.:
#3
Half-life:
58 d
Type:
(pseudo-)first order (= DT50)
Soil No.:
#4
Half-life:
47 d
Type:
(pseudo-)first order (= DT50)
Transformation products:
yes
Identity of transformation productsopen allclose all
No.:
#1
Identifier:
common name
Identity:
Chlorite
No.:
#2
Identifier:
common name
Identity:
Chloride
Details on transformation products:
Chlorite is the intermediate formed during the ultimate degradation of chlorate to chloride. The study shows that chloride is stoichiometrically released from chlorate which confirms that chlorate is entirely reduced without the accumulation of chlorite. Chlorite was not detected in any of the samples at any of the sampling time periods. This indicates that although chlorite was formed, it is rapidly degraded in the soil to chloride.
Details on results:
Degradation rate:
The rate of degradation was determined in four soils. The results of the degradation are given in Table A7_2_2_1-2 (also see graph in 4.1.3). The chlorate concentration in the soils decreased for approximately 4 weeks. After this period, no degradation was observed. Absence of chlorate degradation may be attributed to deficiency of reducing compounds. However, deficiency of reducing power is not the cause of negligible chlorate reduction after 4 weeks, because addition sodium acetate after 120 days did not result in chlorate reduction. Under anaerobic conditions, chlorate reduction resumed without the addition of sodium acetate (see below). This result also demonstrates that shortage of reducing power did not occur. The ion chromatogram showed the appearance of the new peak. This coincided with nitrate. Compared to chlorate, micro-organisms prefer nitrate as electron acceptor. The absence of chlorate reduction after four weeks can therefore best be explained by the presence of chlorate reduction after four weeks can therefore be explained by the presence of nitrate. Chlorate does not appear to be toxic to microbes, because the oxidation of nitrogen by the micro-organisms present in the soils was observed. Nitrifying bacteria capable of oxidising ammonium are known to be very sensitive. No lag periods were observed for chlorate degradation in soils. Absence of a lag period of chlorate reduction is in agreement with the ubiquitous presence of (per)chlorate reducing micro-organisms in soils. The times required for 50, 75 and 90% degradation of chlorate (DT50, DT75 and DT90) in loamy sand, loam, sandy loam and clay can not be estimated because after approximately four weeks, the reduction of chlorate in all soils was negligible. However, half-lives (only valid in “environmentally realistic” nitrate concentrations) of chlorate in soils may be determined using data of the first weeks of the test period. The first order degradation rates and initial concentrations of chlorate in the soils were calculated with data obtained during the test period from day 0 to 28. In aerobic soils, chlorate degradation probably follows the first order reaction kinetics during the first weeks. The half-lives calculated are given in Table A7_2_2_1-3. The results indicate that the lowest chlorate reduction occurs in soils with the lowest initial biomass, and the lowest organic matter.

Degradation route:
The route of degradation was assessed in loam. Chlorite was not detected in the soil samples during the test period. The degradation of chlorate and release of chloride are shown in Table A7_2_2_1-4. Chlorate was stoichiometrically converted to chloride. The stoichiometric release of chloride from chlorate confirms chlorate is entirely reduced without accumulation of other chlorine containing compounds.

Anaerobic biodegradation:
The loam soil was first incubated in the presence of oxygen. Significant degradation of chlorate was noted during the first weeks. However, formation of nitrate was probably responsible for the levelling of the chlorate degradation. After one month, the soil was waterlogged. Under these conditions, chlorate reduction did not resume immediately. Only after the disappearance of nitrate chlorate reduction was noted. In water-logged loam in the absence of nitrate, remainder of the chlorate was reduced within approximately 6 weeks. Rapid reduction of chlorate under anaerobic conditions amounting to 100% degradation rate of chlorate in loam under anaerobic conditions was calculated with chlorate concentrations measured at day 56, 63, 70, 84 and 112. The half-life of chlorate in loam under anaerobic conditions was 7.5 days. Rates of degradation in aerobic soils are approximately 5 to 8 times lower than that found in flooded soil (presumed anaerobic).
Any other information on results incl. tables:
Table A7_2_2_1-2:             Chlorate concentration in various soils incubated with 0.25 mg of sodium chlorate per mL of soil (average of duplicates).
Time (days)
Loamy sand
Loam
Sandy loam
Clay
[ClO3-] (mg/g)
0
0.194
0.190
0.173
0.177
7
0.157
0.171
0.168
0.157
14
0.140
0.148
0.153
0.125
21
0.142
0.142
0.139
0.133
28
0.128
0.111
0.126
0.115
42
0.133
0.094
0.125
0.112
56
0.125
0.079
0.125
0.104
84
0.114
0.077
0.115
0.096
120
0.120
0.069
0.112
0.091
134
0.125
0.076
0.122
0.104
148
0.131
0.080
0.127
0.107
Table A7_2_2_1-3:             First order rate constants, and half-lives of chlorate in various soils maintained at 50% of the water holding capacity and in water logged loam containing no or very low concentrations of nitrate
Soil
First order rate constants
(days-1)
Half-life
(days)
Loamy sand
0.0133
52
Loam
0.0180
39
Sandy loam
0.0118
58
Clay
0.0147
47
Loam
0.0930
7.5
Table A7_2_2_1-4:             Formation of chloride from chlorate in loam incubated with 0.25 mg of sodium chlorate per mL of loam
Time (days)
[ClO3-]
[Cl-]
(mg/g)
(µmoll/g)
(mg/g)
(µmol/g)
0
0.190
2.274
0.007
0.187
7
0.171
2.054
0.011
0.314
14
0.148
1.776
0.017
0.472
21
0.142
1.700
0.042
1.179
28
0.111
1.331
0.031
0.866
42
0.094
1.132
0.035
0.991
56
0.079
0.943
0.037
1.048
84
0.077
0.918
0.046
1.306
120
0.069
0.833
0.054
1.530
134
0.076
0.906
0.053
1.500
148
0.080
0.953
0.057
1.599

Table A7_2_2_1-5:             Chlorate and chloride concentrations in loam incubated with 0.25 mg of sodium chlorate per mL of loam.
Time (days)
[ClO3-]
[Cl-]
(mg/g)
(µmoll/g)
(mg/g)
(µmol/g)
0
0.198
2.37
0.006
0.16
7
0.159
1.91
0.017
0.47
14
0.119
1.43
0.037
1.03
21
0.119
1.42
0.031
0.87
28
0.108
1.29
0.031
0.89
32
0.111
1.33
0.035
0.99
35
0.113
1.35
0.036
1.01
39
0.116
1.39
0.035
0.98
42
0.116
1.39
0.043
1.20
49
0.119
1.43
0.043
1.22
56
0.095
1.14
0.056
1.58
63
0.065
0.78
0.073
2.05
70
0.032
0.38
0.091
2.56
84
0.008
0.09
0.115
3.24
112
0.000
0.00
0.100
2.82

Applicant's summary and conclusion

Conclusions:
Chlorite, as the intermediate in the degradation of chlorate, undergoes rapid degradation in soil.
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