Thymol

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Data is from peer reviewed journal and secondary source

Justification for type of information:

Data is from peer reviewed journal and secondary source

Qualifier:

according to guideline

Guideline:

other: as mentioned below

Principles of method if other than guideline:

Biodegradation study in soil was conducted for 30 days for determining the dissipation half-life (DT50) of the chemical 2-Isopropyl-5-methylphenol.

GLP compliance:

not specified

Test type:

laboratory

Specific details on test material used for the study:

- Name of test material (IUPAC Name): 2-Isopropyl-5-methylphenol- Common name: Thymol- Molecular formula: C10H14O- Molecular weight: 150.2196 g/mol- Smiles notation: c1(c(cc(C)cc1)O)C(C)C- InChI: 1S/C10H14O/c1-7(2)9-5-4-8(3)6-10(9)11/h4-7,11H,1-3H3- Substance type: Organic- Physical state: Solid- Locations of the label (if radiolabelling): Radiolabeling was done at the 3rd position of hydrogen i.e 3H-Thymol was synthesized. - Other: 3H-Thymol was synthesized by PerkinElmer Life Sciences and Analytical Sciences (Boston, MA). The specific activities of thymol was 27.7 mCi/mmol, respectively. Analytical standards of thymol was purchased from Lancaster Synthesis, Inc. (Pelham, NH)

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

sandy loam

% Clay:

18

% Silt:

22

% Sand:

60

% Org. C:

1.6

pH:

7

Details on soil characteristics:

SOIL COLLECTION AND STORAGE- Geographic location: Soil was collected at the Iowa State University Agronomy and Agricultural Engineering Research Farm near Ames, Iowa (field 55).PROPERTIES OF THE SOILS (in addition to defined fields)- Moisture at 1/3 atm (%): Soil moisture content was adjusted to 75% of −33 J/ kg moisture.

Soil No.:

#1

Duration:

30 d

Soil No.:

#1

Initial conc.:

10 other: mg/g

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

Soil No.:

#1

Temp.:

25± 2°C

Humidity:

No data available

Microbial biomass:

No data available

Details on experimental conditions:

EXPERIMENTAL DESIGN- Soil (g/replicate): 50 g/4 replicates for each group.- No. of replication treatments: 4 replicates - Test apparatus (Type/material/volume): French square bottles of 250 ml volume were used as a test vessel for the study.- Details of traps for CO2 and organic volatile, if any: Polyurethane foam was suspended above the treated soils inside each bottle to capture volatile compounds. Polyurethane foam was changed biweekly. Anhydrous calcium sulfate (Drierite; 1.5g) was used to trap 3H2O in the air in the container. Drierite was changed when it turned pink.SAMPLING DETAILS- Sampling intervals: Soil samples were taken at pretreatment and 1, 3, 7, 14 and 30 days post-treatment. > Sample storage before analysis: Soil samples were stored in the −20 ◦C freezer prior to analysis.

Soil No.:

#1

% Recovery:

90

Remarks on result:

other: %Recovery is >90%.

Key result

Soil No.:

#1

% Degr.:

50

Parameter:

test mat. analysis

Remarks:

(% degradation)

Sampling time:

5.35 d

Remarks on result:

other: Other details not known

Key result

Soil No.:

#1

DT50:

5.35 d

Temp.:

25 °C

Remarks on result:

other: Other details not known

Transformation products:

not specified

Evaporation of parent compound:

not specified

Volatile metabolites:

yes

Residues:

yes

Details on results:

Test chemical thymol was quantified by a HPLC method coupled with LSC. The retention times for thymol was 12.5 on the HPLC chromatogram. Recoveries of 3H-thymol was more than 90% from soil, as determined by spike-recovery experiments at the initial time point.In soil, the cumulative volatilization of test chemical in 1 month reached 26%. The lower volatilization from soil compared with that from water is probably due to adsorption to soil colloids. The evolved 3H2O remained consistently less than 1% throughout the study period, indicating that little mineralization occurred. The average radioactivity as bound residues remained below 3% in 1month.

Table: Dissipation half-lives(DT50)of thymol in water.

 

Incubation conditions	DT50 (days) (± S. D.)	R^2a	Replications (n)
Thymol in soil	5.35 (± 0.13)	0.79	4

 

a =R2 is the correlation coefficient for the first-order dissipation model.

 

In soil, the DT50 of thymol was 5 days.

Conclusions:

The percentage degradation of test chemical 2-Isopropyl-5-methylphenol in soil was determined to be 50% in 5.35 days (128.4 hrs).

Executive summary:

Biodegradation study in soil was conducted under aerobic conditions for 30 days for determining the dissipation half-life (DT50) of the chemical 2-Isopropyl-5-methylphenol (Thymol) (CAS no. 89-83-8).3H-Thymol was synthesized by PerkinElmer Life Sciences and Analytical Sciences (Boston, MA).The specific activities of thymol was 27.7 mCi/mmol,respectively.Analytical standards of thymol was purchased from Lancaster Synthesis, Inc. (Pelham, NH).Initial test substance conc. used in the study was 10 mg/g. Sandy loam soilcollected at the Iowa State University Agronomy and Agricultural Engineering Research Farm near Ames, Iowa (field 55) was used as a test inoculum for the study. The soil was classified as a sandy loam, a Nicollet–Webster complex with 1.6% organic matter, 60% sand, 22% silt and 18% clay, and pH 7.0.Soil (50 g) was kept in a 250mL French square bottle, and soil moisture content was adjusted to 75% of−33 J/ kg moisture. The temperature was maintained at 25±2◦C. Soil samples were treated with 3H-thymol in 300μL of acetone carrier at 10μg/g. Thymol had a total radioactivity of 1.8μCi applied in this study. There were four replications for each group. Bottles were sealed with perforated caps to maintain an aerobic condition.Polyurethane foam was suspended above the treated soils inside each bottle to capture volatile compounds.Polyurethane foam was changed biweekly. Anhydrous calcium sulfate (Drierite; 1.5g) was used to trap 3H2O in the air in the container. Drierite was changed when it turned pink.Soil sampleswere taken at pretreatment and 1, 3, 7, 14 and 30 days post-treatment. These soil sampleswere then stored in the−20◦C freezer prior to analysis. Quantitative analysis of thymol was performed using a Hewlett-Packard (Palo Alto, CA) series 1100 HPLC system with a quaternary pump, an autosampler, a thermostatted column compartment and a Spectroflow 757 absorbance detector (ABI Analytical, Kratos Division, Ramsey, NJ). Data were collected and analyzed using HP Chemstation system software (REV. A.04.01). An Alltech Adsorbosphere(Deerfield, IL) C18 column (4.6×250mm, 5μm particle size) was used. Detection was conducted at 270nm with a flowrate of 1.0mL min−1 at room temperature. The mobile phase was methanol+distilled water (70+30 by volume).Soil samples (50 g) were extracted with methanol + distilled water (95 + 5 by volume) 3 times, and the resulting extracts were pooled. Filtered samples were directly injected for HPLC analysis. HPLC fractions were collected for liquid scintillation counting (LSC). Drierite and polyurethane foam were extracted with methanol 4 times, and the resulting extracts were subjected to LSC to measure trapped radioactivity. Non-extractable radioactive residues in soil were measured by soil combustion using a Packard sample oxidizer.14 Briefly, a 0.5 g soil sample was incorporated into a cellulose pellet, and they were combusted for capture of 3H2O, and three replications were performed for each treatment.The dissipation half-lives(DT50)were calculated using a first-order dissipation model.A Student’st-test was used to compare dissipation rates of thymol in light and in dark from the water dissipation studies. The criterion for statistical significance was set at theP<0.05 level.Test chemical thymol was quantified by a HPLC method coupled with LSC. The retention times for thymol was 12.5 on the HPLC chromatogram. Recoveries of 3H-thymol was more than 90% from soil, as determined by spike-recovery experiments at the initial time point. In soil, the cumulative volatilization of test chemical in 1 month reached 26%. The lower volatilization from soil compared with that from water is probably due to adsorption to soil colloids. The evolved 3H2O remained consistently less than 1% throughout the study period, indicating that little mineralization occurred. The average radioactivity as bound residues remained below 3% in 1month.The percentage degradation of test chemical 2-Isopropyl-5-methylphenol in soil was determined to be 50% in 5.35 days (128.4 hrs). Thus, based on percentage degradation, it is concluded that the chemical 2-Isopropyl-5-methylphenol 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 soil was conducted under aerobic conditions for 30 days for determining the dissipation half-life (DT50) of the chemical 2-Isopropyl-5-methylphenol (Thymol) (CAS no. 89-83-8) (Dingfei Hu et. al.; 2008). 3H-Thymol was synthesized by PerkinElmer Life Sciences and Analytical Sciences (Boston, MA).The specific activities of thymol was 27.7 mCi/mmol,respectively.Analytical standards of thymol was purchased from Lancaster Synthesis, Inc. (Pelham, NH).Initial test substance conc. used in the study was 10 mg/g. Sandy loam soilcollected at the Iowa State University Agronomy and Agricultural Engineering Research Farm near Ames, Iowa (field 55) was used as a test inoculum for the study. The soil was classified as a sandy loam, a Nicollet–Webster complex with 1.6% organic matter, 60% sand, 22% silt and 18% clay, and pH 7.0.Soil (50 g) was kept in a 250mL French square bottle, and soil moisture content was adjusted to 75% of−33 J/ kg moisture. The temperature was maintained at 25±2◦C. Soil samples were treated with 3H-thymol in 300μL of acetone carrier at 10μg/g. Thymol had a total radioactivity of 1.8μCi applied in this study. There were four replications for each group. Bottles were sealed with perforated caps to maintain an aerobic condition.Polyurethane foam was suspended above the treated soils inside each bottle to capture volatile compounds.Polyurethane foam was changed biweekly. Anhydrous calcium sulfate (Drierite; 1.5g) was used to trap 3H2O in the air in the container. Drierite was changed when it turned pink.Soil sampleswere taken at pretreatment and 1, 3, 7, 14 and 30 days post-treatment. These soil sampleswere then stored in the−20◦C freezer prior to analysis. Quantitative analysis of thymol was performed using a Hewlett-Packard (Palo Alto, CA) series 1100 HPLC system with a quaternary pump, an autosampler, a thermostatted column compartment and a Spectroflow 757 absorbance detector (ABI Analytical, Kratos Division, Ramsey, NJ). Data were collected and analyzed using HP Chemstation system software (REV. A.04.01). An Alltech Adsorbosphere(Deerfield, IL) C18 column (4.6×250mm, 5μm particle size) was used. Detection was conducted at 270nm with a flowrate of 1.0mL min−1 at room temperature. The mobile phase was methanol+distilled water (70+30 by volume).Soil samples (50 g) were extracted with methanol + distilled water (95 + 5 by volume) 3 times, and the resulting extracts were pooled. Filtered samples were directly injected for HPLC analysis. HPLC fractions were collected for liquid scintillation counting (LSC). Drierite and polyurethane foam were extracted with methanol 4 times, and the resulting extracts were subjected to LSC to measure trapped radioactivity. Non-extractable radioactive residues in soil were measured by soil combustion using a Packard sample oxidizer.14 Briefly, a 0.5 g soil sample was incorporated into a cellulose pellet, and they were combusted for capture of 3H2O, and three replications were performed for each treatment.The dissipation half-lives(DT50)were calculated using a first-order dissipation model.A Student’st-test was used to compare dissipation rates of thymol in light and in dark from the water dissipation studies. The criterion for statistical significance was set at theP<0.05 level.Test chemical thymol was quantified by a HPLC method coupled with LSC. The retention times for thymol was 12.5 on the HPLC chromatogram. Recoveries of 3H-thymol was more than 90% from soil, as determined by spike-recovery experiments at the initial time point. In soil, the cumulative volatilization of test chemical in 1 month reached 26%. The lower volatilization from soil compared with that from water is probably due to adsorption to soil colloids. The evolved 3H2O remained consistently less than 1% throughout the study period, indicating that little mineralization occurred. The average radioactivity as bound residues remained below 3% in 1month.The percentage degradation of test chemical 2-Isopropyl-5-methylphenol in soil was determined to be 50% in 5.35 days (128.4 hrs). Thus, based on percentage degradation, it is concluded that the chemical 2-Isopropyl-5-methylphenol 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:

5.35 d

at the temperature of:

25 °C

Additional information

Various experimental studies and predicted data for the target chemical 2-Isopropyl-5-methylphenol (CAS No. 89-83-8) were reviewed for the biodegradation in soil end point which are summarized as below:

 

In an experimental key study from peer reviewed journal (Dingfei Hu et. al.; 2008),biodegradation study in soil was conducted under aerobic conditions for 30 days for determining the dissipation half-life (DT50) of the chemical 2-Isopropyl-5-methylphenol (Thymol) (CAS no. 89-83-8).3H-Thymol was synthesized by PerkinElmer Life Sciences and Analytical Sciences (Boston, MA).The specific activities of thymol was 27.7 mCi/mmol,respectively. Analytical standards of thymol was purchased from Lancaster Synthesis, Inc. (Pelham, NH).Initial test substance conc. used in the study was 10 mg/g. Sandy loam soil collected at the Iowa State University Agronomy and Agricultural Engineering Research Farm near Ames, Iowa (field 55) was used as a test inoculum for the study. The soil was classified as a sandy loam, a Nicollet–Webster complex with 1.6% organic matter, 60% sand, 22% silt and 18% clay, and pH 7.0.Soil (50 g) was kept in a 250mL French square bottle, and soil moisture content was adjusted to 75% of−33 J/ kg moisture. The temperature was maintained at 25±2◦C. Soil samples were treated with 3H-thymol in 300μL of acetone carrier at 10μg/g. Thymol had a total radioactivity of 1.8μCi applied in this study. There were four replications for each group. Bottles were sealed with perforated caps to maintain an aerobic condition. Polyurethane foam was suspended above the treated soils inside each bottle to capture volatile compounds. Polyurethane foam was changed biweekly. Anhydrous calcium sulfate (Drierite; 1.5g) was used to trap 3H2O in the air in the container. Drierite was changed when it turned pink. Soil sampleswere taken at pretreatment and 1, 3, 7, 14 and 30 days post-treatment. These soil sampleswere then stored in the−20◦C freezer prior to analysis. Quantitative analysis of thymol was performed using a Hewlett-Packard (Palo Alto, CA) series 1100 HPLC system with a quaternary pump, an autosampler, a thermostatted column compartment and a Spectroflow 757 absorbance detector (ABI Analytical, Kratos Division, Ramsey, NJ). Data were collected and analyzed using HP Chemstation system software (REV. A.04.01). An Alltech Adsorbosphere(Deerfield, IL) C18 column (4.6×250mm, 5μm particle size) was used. Detection was conducted at 270nm with a flowrate of 1.0mL min−1 at room temperature. The mobile phase was methanol+distilled water (70+30 by volume).Soil samples (50 g) were extracted with methanol + distilled water (95 + 5 by volume) 3 times, and the resulting extracts were pooled. Filtered samples were directly injected for HPLC analysis. HPLC fractions were collected for liquid scintillation counting (LSC). Drierite and polyurethane foam were extracted with methanol 4 times, and the resulting extracts were subjected to LSC to measure trapped radioactivity. Non-extractable radioactive residues in soil were measured by soil combustion using a Packard sample oxidizer.14 Briefly, a 0.5 g soil sample was incorporated into a cellulose pellet, and they were combusted for capture of 3H2O, and three replications were performed for each treatment. The dissipation half-lives(DT50)were calculated using a first-order dissipation model. A Student’s t-test was used to compare dissipation rates of thymol in light and in dark from the water dissipation studies. The criterion for statistical significance was set at the P<0.05 level. Test chemical thymol was quantified by a HPLC method coupled with LSC. The retention times for thymol was 12.5 on the HPLC chromatogram. Recoveries of 3H-thymol was more than 90% from soil, as determined by spike-recovery experiments at the initial time point. In soil, the cumulative volatilization of test chemical in 1 month reached 26%. The lower volatilization from soil compared with that from water is probably due to adsorption to soil colloids. The evolved 3H2O remained consistently less than 1% throughout the study period, indicating that little mineralization occurred. The average radioactivity as bound residues remained below 3% in 1month.The percentage degradation of test chemical 2-Isopropyl-5-methylphenol in soil was determined to be 50% in 5.35 days (128.4 hrs).

 

Another biodegradation study in soil was carried out for determining the half-life of the test chemical 2-Isopropyl-5-methylphenol (CAS no. 89-83-8) (European Food Safety Authority, 2012).The half-life period of 2 -Isopropyl-5 -methylphenol in soil was determined to be 30 days.

 

In a supporting study from authoritative database (2017), biodegradation study in soil was carried out for determining the half-life of the test chemical 2-Isopropyl-5-methylphenol (CAS no. 89-83-8).The half-life period of 2 -Isopropyl-5 -methylphenol in soil was determined to be 5 days at 20°C.

 

For the target chemical2-Isopropyl-5-methylphenol(CAS no. 89-83-8) from modelling database (2018), the half-life period of 2-Isopropyl-5-methylphenol in soil was estimated using Level III Fugacity Model. If released into the environment, 74.2% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of 2-Isopropyl-5-methylphenol in soil is estimated to be 30 days (720 hrs).

 

On the basis of above results for target chemical 2-Isopropyl-5-methylphenol (from peer reviewed journal, authoritative and modelling databases), it can be concluded that the test substance 2-Isopropyl-5-methylphenol is not persistent in the soil environment and therefore the exposure risk to soil dwelling animals is moderate to low.