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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil, other
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Reason / purpose for cross-reference:
reference to same study
Remarks:
WSSA 1983
Qualifier:
no guideline available
Principles of method if other than guideline:
See Any other information on materials and methods below.
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
no
Oxygen conditions:
not specified
Remarks:
Not relevant, the study addressed abiotic decompostion.
Soil classification:
not specified
Soil no.:
#1
pH:
ca. 7.6
Soil no.:
#2
pH:
ca. 7.5
Soil no.:
#3
pH:
ca. 7.4
Soil no.:
#4
pH:
ca. 7.2
Soil no.:
#5
pH:
ca. 6.6
Soil no.:
#6
pH:
ca. 6.4
Soil no.:
#7
pH:
ca. 6.2
Soil no.:
#8
pH:
ca. 5.8
Soil no.:
#9
pH:
ca. 5.7
Soil no.:
#10
pH:
ca. 5.5
Soil no.:
#11
pH:
ca. 5.4
Soil no.:
#12
pH:
ca. 5.2
Soil no.:
#13
pH:
ca. 5.1
Soil No.:
#1
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#2
Initial conc.:
ca. 31.3 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#3
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#4
Initial conc.:
ca. 27.8 other: No information of soil mass used.
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#5
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#6
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#7
Initial conc.:
ca. 31.3 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#8
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#9
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#10
Initial conc.:
ca. 30.6 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#11
Initial conc.:
ca. 27.8 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#12
Initial conc.:
ca. 27.3 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#13
Initial conc.:
ca. 27.3 other: mg
Based on:
test mat.
Remarks:
No information of soil mass used.
Soil No.:
#1
Sampling time:
4 d
Remarks on result:
not measured/tested
Remarks:
Nitrogen not determined; hydrazoic acid evolved: 0.7 mg from 27.8 mg NaN3 = 2.5 %.
Key result
Soil No.:
#2
% Degr.:
ca. 14.4
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 1.4 mg from 31.1 mg NaN3 = 4.5 %.
Sampling time:
4 d
Soil No.:
#3
Sampling time:
4 d
Remarks on result:
not measured/tested
Remarks:
Neither nitrogen nor hydrazoic acid determined.
Soil No.:
#4
Sampling time:
4 d
Remarks on result:
not measured/tested
Remarks:
Nitrogen not determined; hydrazoic acid evolved: 2.0 mg from 27.8 mg NaN3 = 7.2 %.
Key result
Soil No.:
#5
% Degr.:
ca. 9.8
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 2.9 mg from 27.8 mg NaN3 = 10.4 %.
Sampling time:
4 d
Key result
Soil No.:
#6
% Degr.:
ca. 21.2
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 9.9 mg from 27.8 mg NaN3 = 35.6 %.
Sampling time:
4 d
Key result
Soil No.:
#7
% Degr.:
ca. 46.6
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 7.7 mg from 31.3 mg NaN3 = 24.6 %.
Sampling time:
4 d
Key result
Soil No.:
#8
% Degr.:
ca. 57.4
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 4.8 mg from 27.8 mg NaN3 = 17.3 %.
Sampling time:
4 d
Key result
Soil No.:
#9
% Degr.:
ca. 68.3
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 5.4 mg from 27.8 mg NaN3 = 19.4 %.
Sampling time:
4 d
Key result
Soil No.:
#10
% Degr.:
ca. 69.6
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 9.1 mg from 30.6 mg NaN3 = 29.7 %.
Sampling time:
4 d
Key result
Soil No.:
#11
% Degr.:
ca. 67.1
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 3.6 mg from 27.8 mg NaN3 = 13.0 %.
Sampling time:
4 d
Key result
Soil No.:
#12
% Degr.:
ca. 94.1
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 1.6 mg from 27.3 mg NaN3 = 5.9 %.
Sampling time:
4 d
Key result
Soil No.:
#13
% Degr.:
ca. 88.7
Parameter:
other: Nitrogen formed (mass spectrometry)
Remarks:
Hydrazoic acid evolved: 1.7 mg from 27.3 mg NaN3 = 6.2 %.
Sampling time:
4 d
Transformation products:
yes
No.:
#1
No.:
#2
Details on transformation products:
- Formation and decline of each transformation product during test:
Both evolution of hydrazoic acid and subsequent formation of nitrogen are dependent on pH, as detailed under "% degradation" above. Lower pH seems to stimulate evolution of hydrazoic acid, and also formation of nitrogen is is clearly favoured with decreasing pH.
- Pathways for transformation: The mechanism of dissipation is not fully clear. However, it has been suggested that - apart from volatilisation as hydrazoic acid - azide is chemically transformed in the soil. Bradbury et al. suggest that organo-azide compounds may be formed in the soil, and that they may subsequently decompose via a Curtius rearrangement to nitrogen and the isocyanate (which finally undergoes hydrolysis to CO2).
RCON3 -> RNCO + N2
However, neither the nature of the target organo compounds nor the formation mechanisms are explicitly described.
Evaporation of parent compound:
no
Remarks:
Sodium azide is not volatile.
Volatile metabolites:
yes
Remarks:
Hydrazoic acid, nitrogen (N2)
Residues:
not specified
Conclusions:
Azide is decomposed in soil, ultimately resulting in formation of nitrogen. The first reaction step is evolution of hydrazoic acid (maximally 9.9 % at any pH), which is partly volatillised, and the larger fraction reacts further with soil organic acids to form acid azides which then decompose to nitrogen by the Curtius rearrangement.
Executive summary:

The dissipation of azides in soil is not by microbial action but is strictly a chemical process accelerated by increasing acidity and elevated temperatures. As in plants, azide dissipates quite rapidly in soils by oxidation or by reaction of hydrazoic acid with soil organic acids to form azides of these acids which then decompose by the Curtius rearrangement:

RCON3 --> RNCO + N2

followed by the reaction with water of the isocyanate produced:

2 RNCO + H2O --> RNHCONHR + CO2

This mechanism would give gaseous reaction products containing two parts of nitrogen to one part of carbon dioxide.

Higher temperatures and lower pH levels accelerate dissipation.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
The effect of soil pH, moisture, relative humidity, and incorporation on the dissipation of sodium azide from the soil was studied. Sodium azide concentration in soil was assessed using a colometric assay.
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
no
Oxygen conditions:
aerobic
Soil classification:
not specified
Year:
1976
Soil no.:
#1
Soil type:
sandy loam
% Clay:
14
% Silt:
31
% Sand:
55
% Org. C:
0.76
pH:
5.5
CEC:
>= 5 - <= 10 meq/100 g soil d.w.
Details on soil characteristics:
Lufkin fine sandy loam soil having 55, 31, and 14 % of sand, silt, and clay respectively was used in all experiments. The soil had a pH of 5.5, an organic matter content of 0.76 %, and a 25 % moisture content at field capacity.
Soil No.:
#1
Duration:
>= 0 - <= 15 d
Parameter followed for biodegradation estimation:
test mat. analysis
Soil No.:
#1
Temp.:
24-33 °C
Humidity:
0-100 %
Microbial biomass:
no data
Details on experimental conditions:
The effect of pH, soil moisture, and placement in the dissipation of sodium azide from a 1.5-cm layer of soil contained in 10-cm diameter glass petri dishes was studied. Sodium azide at 112 kg/ha was either incorporated or applied to the surface of soil with pH of 4.0, 5.7, or 8.0. Soil moisture was maintained at 100 % field capacity or air dry at 24 °C. Samples were analyzed for azide at 0, 1, 3, 6, and 10 days after treatment. Treatments were replicated four times and the experiment performed twice.
The effect of relative humidity was determined by applying sodium azide at a rate of 112 kg/ha to the surface of air dry soil with pH values of 5.5 or 8.0. The samples were incubated at 24 °C in air tight chambers with containers of either water or anhydrous CaSO4 to provide relative humidity of either 100 or 0 %. Four samples of treated soil at each pH were taken from each of the two environments at 0, 1/6, 1, 3, 6, 10, and 15 days after treatment for chemical analysis.
The effect of soil moisture on dissipation of Sodium azide incorporated at a rate of 100 ppm into Lufkin fine sandy loam soil having pH values of 5.5 or 8.0 was studied by incubating 500-g soil samples contained in plastic pots 8 cm tall and 11 cm in diameter at 33 °C. Soil moisture was maintained at 0, 20, 40, 60, 80, 100 and 120 % of field capacity by adding distilled water every 8 hr. The relative humidity in the chamber was maintained at 90 %. Additional dry soil samples were incubated in a 0 % relative humidity environment. Treatments were replicated 4 times and samples were taken after 1 week for chemical analysis.
The interaction of pH and soil moisture on the persistence of Sodium azide in Lufkin fine sandy loam with pH values of 5.5 or 8.0 was determined using 500 g soil samples treated at 40 or 100 ppmw. Samples were maintained at 40 and 80 % of field capacity. Four samples were taken each week for chemical analysis. Radish (Raphanus sativus L.) seed were used as bioassays to confirm the chemical analysis.
Remarks on result:
other: See Executive summary
Remarks:
All azide had dissipated from acid soil treated at either 40 or 100 ppm and from alkaline soil treated with 40 ppm within 4 weeks after treatment.
Remarks on result:
other: See executive summary
Remarks:
All azide had dissipated from acid soil treated at either 40 or 100 ppm and from alkaline soil treated with 40 ppm within 4 weeks after treatment.
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Details on results:
Dissipation studies in the laboratory indicated that most rapid loss of Sodium azide occurred in wet, acid soil (Table 2). Losses were more rapid when granules were placed on the surface of dry soil than when incorporated. Dissipation was least in a dry, incorporated, alkaline system.

Relative humidity influenced loss of Sodium azide from a dry soil surface more than pH (Table 3). However, relative humidity did not affect dissipation of Sodium azide from moist soil (data not shown).

Analysis of soil samples treated with 100 ppm of Sodium azide, incorporated, and incubated at 33 °C at various soil moisture levels showed that 20 – 60 % field capacity was optimum for azide loss (Table 4). Soil moisture of 80 % field capacity (fc) or higher slowed the rate of dissipation of azide. The effects of soil moisture and humidity were much less pronounced on alkaline soil than on acid soils but fit the same pattern.

Dissipation studies conducted on soil treated at rates of 40 and 100 ppmw with Sodium azide, incorporated, and incubated at 24 °C with moisture levels of 35 or 80 % field capacity confirmed that dissipation from alkaline soil was much slower than from acid soil and that dissipation was reduced by higher moisture conditions (Table 5). All azide had dissipated from acid soil treated at either 40 or 100 ppm and from alkaline soil treated with 40 ppm within 4 weeks after treatment. However, detectable quantities of azide remained in alkaline soil treated at 100 ppm through the tenth week.

Table 1: Effects of placement, pH, and soil moisture on the percentages of sodium azide, remaining in a Lufkinfine sandy loam soil treated at 100 kg/ha and incubated at 24 °C and 80 % rel. humidity in petri dishes.

Placement

Soil moisture [%]

pH

Days after treatment

1

3

4

10

Surface

100

4.0

6.5 e

0.2 g

0.1 e

0.3 e

 

 

5.7

55.0 c

19.0 f

1.2 e

0.2 e

 

 

8.0

92.0 a

91.0 a

18.5 cd

14.8 c

 

0

4.0

78.0 b

35.0 d

16.5 d

5.8 d

 

 

5.7

58.0 c

38.0 d

17.3 cd

5.5 d

 

 

8.0

90.0 a

56.8 c

29.5 b

8.7 d

Incorporated

100

4.0

5.8 e

0.3 g

0.1 e

0.3 e

 

 

5.7

29.0 d

16.0 f

1.7 e

0.1 e

 

 

8.0

100.0 a

92.0 a

20.0 c

21.0 b

 

0

4.0

79.0 b

27.0 e

28.3 b

20.8 b

 

 

5.7

97.0 a

87.0 a

34.3 a

17.5 bc

 

 

8.0

96.0 a

68.5 b

29.3 b

32.0 a

Values in columns followed by the same letter do not differ at the 1 % significance level as determined by Duncan’s multiple range test.

 

Table 2: Effects of relative humidity and soil pH on the percentages of granular sodium azide remaining when applied at 112 kg/ha to the surface of dryLufkinfine sandy loam soil and incubated at 24 °C.

Rel. humidity [%]

Soil pH

Days after treatment

0

1/6

1

3

6

10

15

100

8.0

100 a

73.2 c

60.5 d

35.1 f

17.4 g

8.1 ghi

1.9 hi

 

4.0

100 a

62.5 d

46.1 e

12.1 gh

5.6 hi

3.6 hi

1.5 i

0

8.0

100 a

98.5 a

93.1 ab

85.3 b

87.8 b

95.0 ab

98.0 a

 

4.0

100 a

102.0 a

102.0 a

93.5 ab

86.1 b

98.0a

101.0a

Values followed by the same letter do not differ at the 1% significance level as determined by Duncan's multiple range test.

 

Table 3: Effect of soil moisture and pH on the percentages of Sodium azide remaining after 1 week when incorporated at 100 ppm into Lufkinfine sandy loam soil and incubated at 33 °C.

 

Rel. humidity [%]

Soil moisture [%]

Soil pH

5.5

8.0

0

0

71.5 a

100.0 a

90

0

32.0 c

74.0 cd

90

20

1.9 e

60.4 d

90

40

2.3 e

72.1 cd

90

60

7.4 de

71.1 cd

90

80

17.5 cd

79.4 bc

90

100

50.3 b

93.1 ab

90

120

55.2 b

96.1 a

Values followed by the same letter do not differ at the 1% significance level as determined by Duncan's multiple range test.

 

Table 4. Sodium azide remaining after being incorporated into soil with varying pH and moisture values and incubated at 24 °C.

NaN3 applied [ppmw]

Soil pH

Soil moisture [% fc]

Weeks after treatment

1

2

4

6

10

40

8.0

80

32 e

12 h

0 i

0 i

0 i

40

8.0

35

26 ef

6 hi

0 i

0 i

0 i

40

5.5

80

5i

2i

0 i

0 i

0 i

40

5.5

35

2i

1 i

0 i

0 i

0 i

100

8.0

80

82 a

60 b

34 e

18 g

4 i

100

8.0

35

61 b

29 e

17 g

6 hi

0 i

100

5.5

80

21 fg

7 hi

0 i

0 i

0 i

100

5.5

35

3 i

1 i

0 i

0 i

0 i

Values followed by the same letter do not differ at the 1 % significance level as determined by Duncan's multiple range test.

 

Executive summary:

The dissipation of Sodium azide from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acid than from alkaline soils. Moist soil (20 to 60 % field capacity) or air dry soil in a moist environment (100 % RH) lost sodium azide more rapidly than air dry soil in a dry (0 % RH) environment. However, dissipation was decreased when soil moisture exceeded 60 % field capacity. All azide had dissipated from acid soil treated at either 40 or 100 ppm and from alkaline soil treated with 40 ppm within 4 weeks after treatment. However, detectable quantities of azide remained in alkaline soil treated at 100 ppm through the tenth week.

Endpoint:
biodegradation in soil
Type of information:
other: handbook data
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
secondary literature
Qualifier:
no guideline followed
Version / remarks:
Handbook data about the degradation mechanism in soil.
Principles of method if other than guideline:
Handbook data. Method is not described.
Remarks on result:
other: See Executive Summary
Remarks:
In acid soils, sodium azide is readily converted to hydrazoic acid, which is highly volatile, moves readily through the soil, and can account for a major part of azide dissipation unless some type of vapor seal is employed.
Remarks on result:
other: See Executive summary
Remarks:
In acid soils, sodium azide is readily converted to hydrazoic acid, which is highly volatile, moves readily through the soil, and can account for a major part of azide dissipation unless some type of vapor seal is employed
Transformation products:
not specified
Executive summary:

The dissipation of azides in soil is not by microbial action but is strictly a chemical process accelerated by increasing acidity and elevated temperatures. As in plants, azide dissipates quite rapidly in soils by oxidation or by reaction of hydrazoic acid with soil organic acids to form azides of these acids which then decompose by the Curtius rearrangement

RCON3 --> RNCO + N2

followed by the reaction with water of the isocyanate produced:

2 RNCO + H2O --> RNHCONHR + CO2

This mechanism would give gaseous reaction products containing two parts of nitrogen to one part of carbon dioxide.

Since surface applied sodium azide is readily leached into soil, photodecomposition is not an important means of dissipation. In acid soils, sodium azide is readily converted to hydrazoic acid, which is highly volatile, moves readily through the soil, and can account for a major part of azide dissipation unless some type of vapor seal is employed.

Description of key information

Ketchersid and Merkle (1976) showed that dissipation of sodium azide from soil was significantly affected by pH, soil moisture, and relative humidity (RH). Loss was more rapid from acidic than from alkaline soils. Moist soil (20 to 60 % field capacity) or air dry soil in a moist environment (100 % RH) lost Sodium azide more rapidly than air dry soil in a dry (0 % RH) environment. However, dissipation was decreased when soil moisture exceeded 60 % field capacity. All azide had dissipated from acid soil treated at either 40 or 100 ppm and from alkaline soil treated with 40 ppm within 4 weeks after treatment. However, detectable quantities of azide remained in alkaline soil treated at 100 ppm through the tenth week.

Beste (1983) and Bradburry et al. 1957 state that the dissipation of azides in soil is not by microbial action but is strictly a chemical process accelerated by increasing acidity and elevated temperatures. Upon contact with soil azide is degraded by the Curtius rearrangement, ultimately forming elemental nitrogen. Since surface applied Sodium azide is readily leached into soil, photodecomposition is not an important means of dissipation. In acid soils, sodium azide is readily converted to hydrazoic acid, which is highly volatile, moves readily through the soil, and can account for a major part of azide dissipation unless some type of vapor seal is employed.

In conclusion, the fate of sodium azide in soil does not give rise to any concern regarding environmental hazards.

Key value for chemical safety assessment

Additional information