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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: Data is from peer reviewed journal
Justification for type of information:
Data is from peer reviewed journal
Qualifier:
according to
Guideline:
other: as mentioned below
Principles of method if other than guideline:
Biodegradation study in four different soils was conducted for evaluating the half-life value of test chemical.
GLP compliance:
not specified
Test type:
laboratory
Radiolabelling:
not specified
Oxygen conditions:
aerobic
Soil no.:
#1
Soil type:
sandy loam
% Clay:
12
% Silt:
24
% Sand:
64
% Org. C:
0.41
pH:
6.42
CEC:
9.6 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy loam
% Clay:
14
% Silt:
13
% Sand:
73
% Org. C:
0.5
pH:
7.67
CEC:
18.5 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
sandy clay loam
% Clay:
20
% Silt:
23
% Sand:
57
% Org. C:
1.25
pH:
7.39
CEC:
27 meq/100 g soil d.w.
Soil no.:
#4
Soil type:
sandy loam
% Clay:
14
% Silt:
15
% Sand:
71
% Org. C:
0.86
pH:
7.23
CEC:
18.2 meq/100 g soil d.w.
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: Soil samples of different textures (abbreviated herein as soil A, B, C, and D) were collected from the surface layer (0-10 cm) at two different locations. Soil A (sandy loam) was taken from the Experimental Station of University of California in Riverside, CA, while soils B, C, and D were taken from fields at the University of California Research and Education Center in Irvine, CA.
- Storage conditions: All soils were air dried and sieved using a 2-mm sieve before use.
Duration:
200 d
Initial conc.:
2 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Temp.:
25°C
Details on experimental conditions:
EXPERIMENTAL DESIGN
- Soil pre-incubation conditions (duration, temperature if applicable): 7 days pre-incubation period
- Soil (g/replicate): An aliquot of 200 g (dry weight) soil was placed in a 500-mL glass jar.
- No. of replication treatments: Triplicate
- Test apparatus (Type/material/volume): 500 ml glass jar was used as a test vessel for the study.

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: The soil moisture was adjusted to 30% of the soil water holding capacity using deionized water. After a 7-d pre-incubation, 200 mL of test chemical stock solution (2000 mg/L in methanol) was spiked to the soil to arrive at a nominal spiked concentration of 2 mg/kg. The soil moisture was maintained by adding deionized water every two days.
- Continuous darkness: Yes, the soil jars were loosely covered with aluminum foil and kept in the dark.

Other details, if any: After spiking, the jars were left open in a fume hood until the solvent was evaporated. Deionized water was then added to adjust the soil moisture to 60% of the water holding capacity. The soil samples were mixed thoroughly with a stainless steel spatula.

OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: To maintain the aerobic conditions during the incubation experiment, each jar was opened every other day for aeration.

SAMPLING DETAILS
At 0, 5,11, 29, and 46 d after treatment, aliquots of 10 g soil (in triplicate) were
removed from each jar and used for analyzing the test chemical concentration remaining in the soils.
Remarks on result:
other: Details not known
Remarks on result:
other: Details not known
Key result
Soil No.:
#1
DT50:
74 d
Type:
(pseudo-)first order (= half-life)
Temp.:
25 °C
Remarks on result:
other: Soil A, half-life = 74±34 days
Key result
Soil No.:
#2
DT50:
82 d
Type:
(pseudo-)first order (= half-life)
Temp.:
25 °C
Remarks on result:
other: Soil B, half-life = 82±20 days
Key result
Soil No.:
#3
DT50:
101 d
Type:
(pseudo-)first order (= half-life)
Temp.:
25 °C
Remarks on result:
other: Soil C, half-life = 101±30 days
Key result
Soil No.:
#4
DT50:
81 d
Type:
(pseudo-)first order (= half-life)
Temp.:
25 °C
Remarks on result:
other: Soil D, half-life = 81±5 days
Transformation products:
not specified
Evaporation of parent compound:
not specified
Volatile metabolites:
not specified
Residues:
not specified
Details on results:
The dissipation of chemicals over time was well described by the first-order decay model and good fit (r2 > 0.88) was consistently found for all treatments. In the four soils, t1/2 ranged for the test chemical ranges from 74 to 101 d. Thus, considering all available data, the mean t1/2 value of test chemical in soil was determined to be 84 days.

Table: T1/2 (d) of test chemical in different soils.

Soil

Test chemical

T1/2 (d)

A

B

C

D

74±34

82±20

101±30

81±5

Conclusions:
The half-life value of test chemical in four different soils, i.e, soil A, B, C and D was determined to be 74±34, 82±20, 101±30 and 81±5 days, respectively.
Executive summary:

Biodegradation study in four different soils was conducted for evaluating the half-life value of test chemical. The study was performed under aerobic conditions at a temperature of 25°C.Soil samples of different textures (abbreviated herein as soil A, B, C, and D) were collected from the surface layer (0-10 cm) at two different locations. Soil A (sandy loam) was taken from the Experimental Station of University of California in Riverside, CA, while soils B, C, and D were taken fromfields at the University of California Research and Education Center in Irvine, CA. All soils were air dried and sieved using a 2-mm sieve before use.500 ml glass jar was used as a test vessel for the study. Initial test chemical conc. used for the study was 2 mg/kg.The stock solutions of these compounds were prepared in methanol and the working solution was prepared by diluting the stock solution with methanol. All stock and working solutions were stored in amber glass vials at-20°C. An aliquot of 200 g (dry weight) soil was placed in a 500-mL glass jar. The soil moisture was adjusted to 30% of the soil water holding capacity using deionized water. After a 7-d pre-incubation, 200mL of test chemical stock solution (2000 mg/l in methanol) was spiked to the soil to arrive at a nominal spiked concentration of 2 mg/kg. After spiking, the jars were left open in a fume hood until the solvent was evaporated. Deionized water was then added to adjust the soil moisture to 60% of the water holding capacity. The soil samples were mixed thoroughly with a stainless steel spatula. The soil jars were loosely covered with aluminum foil and kept in the dark.To maintain the aerobic conditions during the incubation experiment, each jar was opened every other day for aeration.The soil moisture was maintained by adding deionized water every two days. At 0, 5,11, 29, and 46 d after treatment, aliquots of 10 g soil (in triplicate) were removed from each jar and used for analyzing the test chemical concentration remaining in the soils.Soil samples collected at different time intervals were freeze dried, and 1.0 g soil subsamples (dry weight) were extracted three times. The extracts were condensed to near dryness under a gentle nitrogen stream, re-dissolved in 1.0mL methanol and thenfiltered into 2-mL amber glass vials through a 0.22-mmPTFEfilter membrane. Allfinal samples were stored at-20°C prior to instrumental analysis. Instrumental analysis was performed on a Waters ACQUITY ultra-performance liquid chromatography (UPLC) combined with a Waters Micromass electrospray ionization tandem mass spectrometer (ESI-MS/MS) (Waters, Milford, MA). Separation was achieved with an ACQUITY UPLC BEH C18 column (2.1 mmX100 mm, 1.7mm particle size, Waters). Pure methanol and 5% methanol in water (containing 0.001% formic acid) were used as the mobile phases B and A, respectively, which was programmed (with respect to mobile phase A) as below: 0-5 min, 90%-0%; 5-6 min, 0-90%; and 6-8min, 90-10%, at aflow rate of 0.2 mL/min. The injection volume was 5mL and the column temperature was 40°C. The mass data was acquired under the multiple reactions monitoring (MRM) in the negative ESI mode. All data were expressed as the mean and standard deviation of triplicates. One-way ANOVA test was performed ata¼0.05 to evaluate the significance of difference between treatments. Statistical analyses were completed using the SPSS 19.0 software (IBM SPSS Statistics, Armonk, NY).The half-life value of test chemical in four different soils, i.e, soil A, B, C and D was determined to be 74±34, 82±20, 101±30 and 81±5 days, respectively, i.e, in the four soils,t1/2 ranged for the test chemical ranges from 74 to 101 d, respectively. Thus, considering all available data, the mean t1/2 value of test chemical in soil was determined to be 84 days.Based on this half-life value of test chemical, it is concluded that the test chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Description of key information

Biodegradation study in four different soils was conducted for evaluating the half-life value of test chemical (Qiuguo Fu et. al.; 2016). The study was performed under aerobic conditions at a temperature of 25°C.Soil samples of different textures (abbreviated herein as soil A, B, C, and D) were collected from the surface layer (0-10 cm) at two different locations. Soil A (sandy loam) was taken from the Experimental Station of University of California in Riverside, CA, while soils B, C, and D were taken fromfields at the University of California Research and Education Center in Irvine, CA. All soils were air dried and sieved using a 2-mm sieve before use.500 ml glass jar was used as a test vessel for the study. Initial test chemical conc. used for the study was 2 mg/kg.The stock solutions of these compounds were prepared in methanol and the working solution was prepared by diluting the stock solution with methanol. All stock and working solutions were stored in amber glass vials at-20°C. An aliquot of 200 g (dry weight) soil was placed in a 500-mL glass jar. The soil moisture was adjusted to 30% of the soil water holding capacity using deionized water. After a 7-d pre-incubation, 200mL of test chemical stock solution (2000 mg/l in methanol) was spiked to the soil to arrive at a nominal spiked concentration of 2 mg/kg. After spiking, the jars were left open in a fume hood until the solvent was evaporated. Deionized water was then added to adjust the soil moisture to 60% of the water holding capacity. The soil samples were mixed thoroughly with a stainless steel spatula. The soil jars were loosely covered with aluminum foil and kept in the dark.To maintain the aerobic conditions during the incubation experiment, each jar was opened every other day for aeration.The soil moisture was maintained by adding deionized water every two days. At 0, 5,11, 29, and 46 d after treatment, aliquots of 10 g soil (in triplicate) were removed from each jar and used for analyzing the test chemical concentration remaining in the soils.Soil samples collected at different time intervals were freeze dried, and 1.0 g soil subsamples (dry weight) were extracted three times. The extracts were condensed to near dryness under a gentle nitrogen stream, re-dissolved in 1.0mL methanol and thenfiltered into 2-mL amber glass vials through a 0.22-mmPTFEfilter membrane. Allfinal samples were stored at-20°C prior to instrumental analysis. Instrumental analysis was performed on a Waters ACQUITY ultra-performance liquid chromatography (UPLC) combined with a Waters Micromass electrospray ionization tandem mass spectrometer (ESI-MS/MS) (Waters, Milford, MA). Separation was achieved with an ACQUITY UPLC BEH C18 column (2.1 mmX100 mm, 1.7mm particle size, Waters). Pure methanol and 5% methanol in water (containing 0.001% formic acid) were used as the mobile phases B and A, respectively, which was programmed (with respect to mobile phase A) as below: 0-5 min, 90%-0%; 5-6 min, 0-90%; and 6-8min, 90-10%, at aflow rate of 0.2 mL/min. The injection volume was 5mL and the column temperature was 40°C. The mass data was acquired under the multiple reactions monitoring (MRM) in the negative ESI mode. All data were expressed as the mean and standard deviation of triplicates. One-way ANOVA test was performed ata¼0.05 to evaluate the significance of difference between treatments. Statistical analyses were completed using the SPSS 19.0 software (IBM SPSS Statistics, Armonk, NY).The half-life value of test chemical in four different soils, i.e, soil A, B, C and D was determined to be 74±34, 82±20, 101±30 and 81±5 days, respectively, i.e, in the four soils,t1/2 ranged for the test chemical ranges from 74 to 101 d, respectively. Thus, considering all available data, the mean t1/2 value of test chemical in soil was determined to be 84 days.Based on this half-life value of test chemical, it is concluded that the test chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Key value for chemical safety assessment

Half-life in soil:
74 d
at the temperature of:
25 °C

Additional information

Various experimental key and supporting studies of the test chemical were reviewed for the biodegradation in soil end point which are summarized as below:

 

In an experimental key study from peer reviewed journal (Qiuguo Fu et. al.; 2016),biodegradation experiment in four different soils was conducted for evaluating the half-life value of test chemical. The study was performed under aerobic conditions at a temperature of 25°C.Soil samples of different textures (abbreviated herein as soil A, B, C, and D) were collected from the surface layer (0-10 cm) at two different locations. Soil A (sandy loam) was taken from the Experimental Station of University of California in Riverside, CA, while soils B, C, and D were taken from fields at the University of California Research and Education Center in Irvine, CA. All soils were air dried and sieved using a 2-mm sieve before use.500 ml glass jar was used as a test vessel for the study. Initial test chemical conc. used for the study was 2 mg/kg. The stock solutions of these compounds were prepared in methanol and the working solution was prepared by diluting the stock solution with methanol. All stock and working solutions were stored in amber glass vials at-20°C. An aliquot of 200 g (dry weight) soil was placed in a 500-mL glass jar. The soil moisture was adjusted to 30% of the soil water holding capacity using deionized water. After a 7-d pre-incubation, 200mL of test chemical stock solution (2000 mg/l in methanol) was spiked to the soil to arrive at a nominal spiked concentration of 2 mg/kg. After spiking, the jars were left open in a fume hood until the solvent was evaporated. Deionized water was then added to adjust the soil moisture to 60% of the water holding capacity. The soil samples were mixed thoroughly with a stainless steel spatula. The soil jars were loosely covered with aluminum foil and kept in the dark. To maintain the aerobic conditions during the incubation experiment, each jar was opened every other day for aeration. The soil moisture was maintained by adding deionized water every two days. At 0, 5,11, 29, and 46 d after treatment, aliquots of 10 g soil (in triplicate) were removed from each jar and used for analyzing the test chemical concentration remaining in the soils. Soil samples collected at different time intervals were freeze dried, and 1.0 g soil subsamples (dry weight) were extracted three times. The extracts were condensed to near dryness under a gentle nitrogen stream, re-dissolved in 1.0mL methanol and then filtered into 2-mL amber glass vials through a 0.22-mmPTFEfilter membrane. All final samples were stored at-20°C prior to instrumental analysis. Instrumental analysis was performed on a Waters ACQUITY ultra-performance liquid chromatography (UPLC) combined with a Waters Micromass electrospray ionization tandem mass spectrometer (ESI-MS/MS) (Waters, Milford, MA). Separation was achieved with an ACQUITY UPLC BEH C18 column (2.1 mmX100 mm, 1.7mm particle size, Waters). Pure methanol and 5% methanol in water (containing 0.001% formic acid) were used as the mobile phases B and A, respectively, which was programmed (with respect to mobile phase A) as below: 0-5 min, 90%-0%; 5-6 min, 0-90%; and 6-8min, 90-10%, at a flow rate of 0.2 mL/min. The injection volume was 5mL and the column temperature was 40°C. The mass data was acquired under the multiple reactions monitoring (MRM) in the negative ESI mode. All data were expressed as the mean and standard deviation of triplicates. One-way ANOVA test was performed ata¼0.05 to evaluate the significance of difference between treatments. Statistical analyses were completed using the SPSS 19.0 software (IBM SPSS Statistics, Armonk, NY).The half-life value of test chemical in four different soils, i.e, soil A, B, C and D was determined to be 74±34, 82±20, 101±30 and 81±5 days, respectively, i.e, in the four soils,t1/2 ranged for the test chemical ranges from 74 to 101 d, respectively. Thus, considering all available data, the mean t1/2 value of test chemical in soil was determined to be 84 days. Based on this half-life value of test chemical, it is concluded that the test chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

Another biodegradation study in loam soil was conducted for evaluating the half-life value of test chemical (Guang-Guo Ying et. al., 2007). The study was performed under both aerobic and anaerobic conditions at a temperature of 22°C.A loam soil with pH value of 7.4 was collected from an agricultural land without sludge amendments and used in the laboratory biodegradation study. The soil contains52.1% of sand, 11.6% of silt, 34.7% of clay and 1.3% of organic carbon, respectively. For aerobic experiments, 5 g of soil was weighed into each scintillation vial (20 mL). The moisture level in each vial was adjusted using sterile water to 50% MWHC (maximum water holding capacity). Test chemical at a concentration of 1 mg/L in acetone was added into each vial to make 1 mg/kg in the soil. Lids were left open for 1 h to allow acetone to evaporate. Each vial was mixed well and incubated under darkness at 22°C in a constant temperature room. Half of the vials were sterilised by autoclaving at 120°C under 300 kPa chamber pressure for 30 min for three times within 3 days before adding the test chemical, and used as sterile controls. Each vial was opened weekly to let the air in to maintain its aerobic conditions during the incubation and for anaerobic experiments, preparation was carried in an anaerobic incubation chamber filled with nitrogen gas. Five grams of soil and 1 mL of sterile water was weighed into each Hungate anaerobic culture tube. Half of the tubes were taken out for autoclaving, and after sterilisation these tubes were placed back into the anaerobic chamber. Test chemical at a concentration of 1 mg/L in acetone was spiked into each tube to make 1 mg/kg in the soil. Lids were opened for some time to allow acetone to evaporate. Resazurin was added at a concentration of 0.0002% into two tubes as a redox indictor. Reducing conditions within the tubes were indicated by the disappearance of the red resazurin color. All Hungate tubes were incubated under darkness at 22°C.Concentrations of each compound in the samples were monitored at certain intervals (0, 1, 7, and weekly to 70 days) by utilising three samples from each treatment. Triplicate sterile controls were also monitored at the same time. For analytical analysis, test chemical in the soil samples was extracted twice using 20 mL of acetone. The extracts were blown to dryness by a gentle stream of nitrogen and re-dissolved in 0.5 mL of methanol. Test chemical was analysed on an Agilent 1100 series high performance liquid chromatograph (HPLC) fitted with a diode array detector and a SGE C18 RS column (100X4.6 mm, 5µm). Acetonitrile (ACN) and water were used as the mobile phase, which was programmed from 40% ACN at 0 min to 80% ACN at 10 min, 90% ACN at 12 min, 90% ACN at 20 min and back to 40% CAN at 25 min at a flow rate of 1 mL/min. The UV wavelength for detection was 265 nm. The retention time was 8.3 min. No changes in concentrations of test chemical were observed in the sterile soil within 70 days. This suggests that no degradation of test chemical by chemical processes occurred in the sterile soil. The half-life value of test chemical in loam soil was determined to be 108 days using a first order constant under both aerobic and anaerobic conditions. Based on this half-life value of test chemical, it is concluded that the test chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

On the basis of above results of the test chemical(from peer reviewed journals), it can be concluded that the half-life value of test chemical was determined to be ranges from 74 to 108 days, indicating that the test chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Biodegradation in soil endpoint can also be considered for waiver as per in accordance with column 2 of Annex IX of the REACH regulation, testing for this end point is scientifically not necessary and does not need to be conducted since the test chemical is readily biodegradable in water.