Registration Dossier

Environmental fate & pathways

Biodegradation in soil

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
8 June 2018 to ****
Reliability:
1 (reliable without restriction)
Qualifier:
according to guideline
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Particle size, pH, organic carbon and cation exchange capacity (by NRM) and water content at pF2 (by CEMAS) were measured in separate non-GLP studies.
Test type:
laboratory
Specific details on test material used for the study:
Radiolabeled Test Item
Radiochemical purity: The radiochemical purity was measured to be 97.1% prior to application

Non-Radiolabeled Test Item
Purity: UVCB substance
Description: Light yellow to tan solid
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil no.:
#1
Soil type:
other: sand (Cuckney soil)
% Clay:
7
% Silt:
4
% Sand:
89
% Org. C:
1.3
pH:
7.2
CEC:
5.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.313
Soil no.:
#2
Soil type:
other: clay loam (Drayton soil)
% Clay:
33
% Silt:
23
% Sand:
44
% Org. C:
2
pH:
7.6
CEC:
26 meq/100 g soil d.w.
Bulk density (g/cm³):
1.227
Soil no.:
#3
Soil type:
other: sandy clay loam (Elmton soil)
% Clay:
25
% Silt:
24
% Sand:
51
% Org. C:
2.7
pH:
8
CEC:
20.5 meq/100 g soil d.w.
Bulk density (g/cm³):
1.169
Soil no.:
#4
Soil type:
other: sandy loam (Calke soil)
% Clay:
16
% Silt:
22
% Sand:
62
% Org. C:
2.8
pH:
6.1
CEC:
13.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.147
Details on soil characteristics:
The test soils were supplied by LandLook (Midlands), UK, and LRA Labsoil, UK. The soils were passed through a 2 mm sieve. Additional water was added to bring the water content of the soils to that equivalent to pF2. Microbial biomass measurements conducted at the start and end of the incubation period demonstrated that all soils were microbiologically viable throughout. Additional details on soil characteristics are provided in Table 1 (below).
Soil No.:
#1
Duration:
119 d
Soil No.:
#2
Duration:
119 d
Soil No.:
#3
Duration:
119 d
Soil No.:
#4
Duration:
119 d
Initial conc.:
1.02 mg/kg soil d.w.
Based on:
other:
Remarks:
Application rate calculated from radioactivity and volume applied, and specific activity of the test material. The radiochemical purity of [14C]-test item was confirmed by HPLC prior to application to be 96.8%.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Soil No.:
#1
Temp.:
12 +/- 2 deg C
Humidity:
pF2
Microbial biomass:
Non-treated: 664 mg C/kg soil (Day 0); 571 mg C/kg soil (Day 119); Solvent (THF) treated: 562 mg C/kg soil (Day 119)
Soil No.:
#2
Temp.:
12 +/- 2 deg C
Humidity:
pF2
Microbial biomass:
Non-treated: 411 mg C/kg soil (Day 0); 715 mg C/kg soil (Day 119); Solvent (THF) treated: 684 mg C/kg soil (Day 119)
Soil No.:
#3
Temp.:
12 +/- 2 deg C
Humidity:
pF2
Microbial biomass:
Non-treated: 1804 mg C/kg soil (Day 0); 1582 mg C/kg soil (Day 119); Solvent (THF) treated: 1587 mg C/kg soil (Day 119)
Soil No.:
#4
Temp.:
12 +/- 2 deg C
Humidity:
pF2
Microbial biomass:
Non-treated: 1504 mg C/kg soil (Day 0); 1110 mg C/kg soil (Day 119); Solvent (THF) treated: 1092 mg C/kg soil (Day 119)
Details on experimental conditions:
Individual soil samples (approximately 50 g soil on a dry weight basis) treated with radiolabeled (14C) test item were contained in glass dishes and housed in glass chambers. Aliquots of a stock solution of [14C]-test item, prepared in tetrahydrofuran (THF) at a nominal concentration of 500 µg/mL, were applied to the surface of each soil sample. The solvent was allowed to evaporate and the soil was mixed using a spatula. Each dish was weighed and distilled water added as necessary to maintain the moisture content at that equivalent to pF2.

Each chamber was incorporated into a separate gas flow-through system arranged in a series as follows: a humidifying vessel (with sintered stem for uniform gas dispersion) containing water to humidify the air-flow; a chamber containing the dishes of soil; a vessel containing ethyl digol(to trap organic volatile compounds; a vessel containing 1M aqueous potassium hydroxide solution with phenolphthalein indicator to trap 14CO2; and a non-return valve to prevent accidental backflow through the test apparatus. Each chamber only contained dishes of one soil type. During the acclimatization phase all traps except the humidifying water bottle were empty.

Vessels (1000 mL) for microbiological activity measurement, each containing approximately 500 g soil on a dry weight basis, were connected in one or more series to separate gas flow systems. Vessels used for microbial activity measurements were not treated with the test item; however, two of the five vessels for each soil type were used as a solvent-control and were treated with an equivalent volume of organic solvent as used for test item application. Humidified air was passed through these vessels, but no traps were included.

The air flow was maintained at approximately 60 mL/minute. The test systems were incubated at 12 +/- 2 deg C in the dark in a temperature-controlled room. The temperature of the incubation room deviated from the specified range on four occasions due to a failure of the cooling unit for the room. As the temperature reached a maximum of 2.5°C above tolerance and a minimum of 0.9°C below tolerance, with exceedances during only 5% of the total incubation period (119 days), it is considered that these temperature deviations did not affect the integrity or the outcome of the study. This is supported by the TLC analyses, which indicate that no degradation of the test item occurred.

Duplicate dishes of each soil type were taken for analysis immediately after application and after 7, 14, 31, 60, 90 and 119 days of incubation. Trapping solutions were taken for analysis and replaced with fresh media as necessary at 7, 14, 31, 45, 60, 74, 90, 104 and 119 days after application. One untreated vessel of each soil type, established for the determination of microbial biomass, was taken for analysis on the day of application. One untreated and one solvent-treated vessel of each soil type were taken for analysis after 119 days of incubation.
Remarks on result:
not determinable
Transformation products:
not specified
Remarks:
; mostly unchanged test item was detected from the TLC analysis of all soil extracts, with only minor amounts of unassigned radioactivity (up to 6.4% applied radioactivity).
Details on transformation products:
There was very little evidence for degradation of test item in the soils. The mean proportions of test item relative to total radioactive components in the soils ranged from 93.4% to 101.7% applied radioactivity in Cuckney soil (#1), 84.6% to 96.2% applied radioactivity in Drayton soil (#2), 85.9% to 99.0% applied radioactivity in Elmton soil (#3), and 86.8% to 99.6% applied radioactivity in Calke soil (#4).

The retention factor of parent test item in the TLC analyses shifted throughout testing. To investigate any possible degradation, selected extract pool samples with apparently different retention factors were analyzed together on the same plate. Two Elmton soil samples from different sampling intervals and three samples from the remaining soil types, were applied so the application bands of each group partially overlapped. The TLC plate was developed and imaged, confirming that the main band in all soils and sampling intervals were attributed to parent test item.
Details on results:
Total recoveries of radioactivity (‘mass balances’, i.e. the sum of extractable and non extractable radioactivity in soil and volatile radioactivity) in the individual soil samples were in the range 92.6 to 107.8% of the amount of applied radioactivity (AR), except for Calke soil sample CA13 (Day 119, 112.9% AR). Mean distribution and recovery of radioactivity in the four soils are summarized in Table 2 (below).

Table 2:  Mean Distribution and Recovery of Radioactivityin Four Treated Soils

 

Cuckney Soil (#1)

Fraction

Sampling time (days)

0

7

14

31

60

90

119

Total extractable

104.9

97.7

98.1

99.4

97.0

95.8

97.8

Non-extractable

1.3

2.4

1.5

1.2

1.8

1.7

1.8

Total in soil

106.2

100.0

99.6

100.5

98.7

97.4

99.6

Volatiles:

 

 

 

 

 

 

 

Organics

na

nd

nd

nd

nd

nd

nd

CO2

na

0.1

0.1

0.2

0.2

0.3

0.3

Total volatiles

na

0.1

0.1

0.2

0.2

0.3

0.3

Total recovered

106.2

100.1

99.7

100.7

98.9

97.7

99.9

Results expressed as % applied radioactivity.                                                                

nd       Not detected

na        Not applicable

 

Drayton Soil (#2)

Fraction

Sampling time (days)

0

7

14

31

60

90

119

Total extractable

97.7

88.5

89.4

93.8

91.2

93.2

90.1

Non-extractable

5.8

5.3

4.8

2.3

3.0

2.3

6.8

Total in soil

103.4

93.8

94.2

96.1

94.1

95.5

96.9

Volatiles:

 

 

 

 

 

 

 

Organics

na

nd

nd

nd

nd

nd

nd

CO2

na

0.1

0.1

0.2

0.3

0.3

0.5

Total volatiles

na

0.1

0.1

0.2

0.3

0.3

0.5

Total recovered

103.4

93.9

94.3

96.3

94.4

95.8

97.4

Results expressed as % applied radioactivity.                                                                

nd       Not detected

na        Not applicable

 

Elmton Soil (#3)

Fraction

Sampling time (days)

0

7

14

31

60

90

119

Total extractable

105.3

88.6

100.4

101.2

97.2

97.9

98.1

Non-extractable

1.9

9.0

2.6

1.7

2.2

2.1

2.9

Total in soil

107.2

97.5

103.0

102.8

99.3

100.0

101.0

Volatiles:

 

 

 

 

 

 

 

Organics

na

nd

nd

nd

nd

nd

nd

CO2

na

0.1

0.1

0.2

0.3

0.4

0.6

Total volatiles

na

0.1

0.1

0.2

0.3

0.4

0.6

Total recovered

107.2

97.6

103.1

103.0

99.6

100.4

101.6

Results expressed as % applied radioactivity.                                                                

nd       Not detected

na        Not applicable

 

Calke Soil (#4)

Fraction

Sampling time (days)

0

7

14

31

60

90

119

Total extractable

103.1

88.8

90.0

97.2

93.0

93.6

100.7

Non-extractable

3.1

10.6 ^a

5.1

1.9

2.6

2.6

3.6

Total in soil

106.2

99.3

95.1

99.0

95.6

96.2

104.3

Volatiles:

 

 

 

 

 

 

 

Organics

na

nd

nd

nd

nd

nd

nd

CO2

na

0.1

0.1

0.3

0.4

0.7

0.9

Total volatiles

na

0.1

0.1

0.3

0.4

0.7

0.9

Total recovered

106.2

99.4

95.2

99.3

96.0

96.9

105.2

Results expressed as % applied radioactivity.                                                                

nd       Not detected

na        Not applicable

^a  The mean recovery for Day 7 post-extraction soil debris was just over 10% applied radioactivity; however, no overall trend was observed for the non-extractable radioactivity and therefore the characterization by fractionation of this soil debris was not performed.

Conclusions:
Mean distribution and recovery of radioactivity ranged from 99.7 to 106.2% AR in Cuckney soil, 93.9 to 103.4% AR in Drayton soil, 97.6 to 107.2% AR in Elmton soil, and 95.2 to 106.2% AR in Calke soil. Low levels of radioactivity were detected in the bound residues (mean values ≤10.6% applied radioactivity) and mean mineralization of the test item to CO2 was less than or equal to 0.9% applied radioactivity. There was little or no evidence for degradation of test material in soil at 12 +/- 2 deg C and pF2, under aerobic conditions, and kinetic analysis of the data was therefore considered inappropriate.
Executive summary:

The fate of test material was studied in four soils types under laboratory conditions based on the aerobic test design in OECD Guideline for the Testing of Chemicals No. 307 (April 2002). Samples of each soil type were allowed to acclimatize before being treated with [14C]-test item at a rate of 1.02 mg/kg. The samples were incubated at approximately 12 deg C, in the dark and at a moisture content equivalent to pF2, for periods of up to 119 days after application.

The overall recoveries of radioactivity from the individual soil samples were in the range 92.6 to 107.8% applied radioactivity (AR), except for one Calke sample (Day 119, 112.9% AR). Extractable radioactivity showed a small decline over the incubation period in the four soils treated. Immediately after application of [14C]-test item, 97.7 to 105.3% applied radioactivity was extracted from the soils, declining to 90.1-100.7% applied radioactivity after 119 days. Non-extractable radioactivity remained approximately constant over the study, with mean values of 1.3 to 5.8% applied radioactivity at time zero and 1.8-6.8% after 119 days. Very little volatile radioactivity was recovered in the trapping solutions (≤0.9% applied radioactivity after 119 days), all presumed to be associated with 14-CO2.

Mass balance (i.e. the sum of extractable and non-extractable radioactivity in soil and volatile radioactivity) ranged from 99.7 to 106.2% AR in Cuckney soil, 93.9 to 103.4% AR in Drayton soil, 97.6 to 107.2% AR in Elmton soil, and 95.2 to 106.2% AR in Calke soil.

Mostly test material was detected in the extracts of all four soils. There was little or no evidence for degradation of test item and kinetic analysis of the data was therefore considered inappropriate.

Description of key information

In an OECD 307 study, conducted according to GLP, the mean distribution and recovery of radioactivity ranged from 99.7 to 106.2% AR in Cuckney soil, 93.9 to 103.4% AR in Drayton soil, 97.6 to 107.2% AR in Elmton soil, and 95.2 to 106.2% AR in Calke soil.  Low levels of radioactivity were detected in the bound residues (mean values ≤10.6% applied radioactivity) and mean mineralization of the test item to CO2 was less than or equal to 0.9% applied radioactivity.  There was little or no evidence for degradation of test material in soil at 12 +/- 2 deg C and pF2, under aerobic conditions, and kinetic analysis of the data was therefore considered inappropriate.

Key value for chemical safety assessment

Additional information