Cyclohexanone, 4-methoxy-

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

Study period:

2006-02-28 to 2006-08-03

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

2002

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Remarks:

C14 Labelling in Synthesis.

Oxygen conditions:

aerobic/anaerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

2006

Soil no.:

#1

Soil type:

silt loam

% Clay:

19

% Silt:

52

% Sand:

29

% Org. C:

2.4

pH:

>= 6.5 - <= 6.9

CEC:

12.8 meq/100 g soil d.w.

Bulk density (g/cm³):

0.89

% Moisture content:

>= 20.6 - <= 65

Soil no.:

#2

Soil type:

loam

% Clay:

23

% Silt:

34

% Sand:

43

% Org. C:

1

pH:

>= 6.6 - <= 7

CEC:

9.3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.07

% Moisture content:

>= 13 - <= 45.1

Soil no.:

#3

Soil type:

loamy sand

% Clay:

7.1

% Silt:

14.5

% Sand:

78.4

% Org. C:

0.7

pH:

>= 5.9 - <= 6.7

CEC:

5 meq/100 g soil d.w.

Bulk density (g/cm³):

1.35

% Moisture content:

>= 8.8 - <= 34.6

Details on soil characteristics:

The test soils were used in fresh condition, collected from the A horizons (approximately 0-20 cm depth) of the respective sampling areas. Soil collection and handling prior to the experimental work were in accordance to ISO 10381-6:1993(E)[3].

Stones and plant material were removed. Soil moisture was partially reduced by soil spreading at ambient temperature, to allow for sieving to a particle size < 2 mm. Finally, the soil batches were each mixed thoroughly for optimal batch homogeneity.

Soil No.:

#1

Duration:

14 d

Soil No.:

#2

Duration:

14 d

Soil No.:

#3

Duration:

14 d

Soil No.:

#1

Initial conc.:

0.05 kg/ha d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

0.05 kg/ha d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

0.05 kg/ha d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

20 +/- 1°C

Humidity:

55%

Soil No.:

#2

Temp.:

20 +/- 1°C

Humidity:

55%

Soil No.:

#3

Temp.:

20 +/- 1°C

Humidity:

55%

Details on experimental conditions:

The biotransformation of radiolabeled test item was studied in two European soils (Laacher Hof: loam, pH 7.0, org. C 1.0% / Hoefchen: silt loam, pH 6.8, org. C 2.4%) and in one US soil (Molino: loamy sand, pH 6.7, org. C 0.7%), under aerobic laboratory conditions for 14 days (Laacher Hof, Hoefchen) and 3 days (Molino) at 20 ± 1 °C in the dark. Soil moisture was maintained constant throughout the test, targeting 55% of maximum water holding capacity. The test item is a soil photolysis transformation product of the active substance [trade name]. It was applied at the nominal rate of 0.133 mg/kg soil, equivalent to a virtual field rate of 0.050 kg/ha (conversion based on homogenous distribution within 2.5 cm top soil layer, bulk density 1.5 g/cm3). The study was performed according to the OECD Test Guideline No. 307, Aerobic and Anaerobic Transformation in Soil and in compliance with OECD-GLP standards.

Parent/product:

parent

Key result

Soil No.:

#1

Sampling date:

2006

% Degr.:

74.1

Parameter:

CO2 evolution

Sampling time:

3 d

Parent/product:

parent

Key result

Soil No.:

#2

Sampling date:

2006

% Degr.:

75.8

Parameter:

CO2 evolution

Sampling time:

3 d

Parent/product:

parent

Key result

Soil No.:

#3

Sampling date:

2006

% Degr.:

66.3

Parameter:

CO2 evolution

Sampling time:

3 d

Key result

Soil No.:

#1

DT50:

< 1 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Key result

Soil No.:

#2

DT50:

< 1 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Key result

Soil No.:

#3

DT50:

0.6 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Transformation products:

not specified

Remarks:

The test item was degraded in the tested soil systems to the main transformation product 14C02. The formation of several minor degradates was observed and non-extractable soil residues were found as terminal products.

Evaporation of parent compound:

not specified

Volatile metabolites:

yes

Residues:

not specified

Details on results:

The laboratory half-life of 4-methoxycyclohexanone in aerobic soil is < 1 day under the conditions of the test. No major degradates (> 5 % of the AR) were observed. The predominant degradate was 14C02, formed at a maximum rate of 66.3 % to 75.8 % of the AR until study termination. Further degradates were observed in trace amounts only, accounting for < 5 % of the AR. Non-extractable soil residues were observed with a maximum rate of about 25 % of the AR in the soils Hoefchen and Laacher Hof and 23 % of the AR in the soil Molino, respectively. At the end of the study the NER declined to < 20 % of the AR for all tested soils. No volatile organic compounds were formed at any time of the tests.

Results with reference substance:

none reported

4-Methoxycyclohexanone was shown to be subject to aerobic soil biodegradation.Degradation occurred at a very fast rate under the conditions of this laboratory experiment. This also was supported by the very high 14C02 formation rates. There is no potential for accumulation of 4-methoxycyclohexanone residues in viable soils.

 

Validity criteria for the measurement of the biodegradation in soil:

Target condition according to guideline:	Actual condition according to the study:	Validity criteria met:
Extraction and analysis of, at least, duplicate soil samples immediately after the addition of the test substance gives a first indication of the repeatability of the analytical method and of the uniformity of the application procedure for the test substance. Recoveries for later stages of the experiments are given by the respective mass balances. Recoveries should range from 90% to 110% for labelled chemicals and from 70% to 110% for non-labelled chemicals.	The extraction efficiency using six cycles of ambient temperature solvent extraction, ranged from 97.1 % to 99.5 % of the AR for the day 0 samples (approximately 1 h post-application), leaving only 0.2 % to 0.7 % of the AR nonextracted. These results indicated that the extraction method was well suited to extract the applied [14C] 4-methoxycyclohexanone from the test soil matrix. No systematic radioactive losses of significance occurred upon further sample processing prior to chromatography analysis of aliquots, the mean recovery upon concentration being 101.2 % of the AR. Radioactive recovery upon chromatography was 108.3 % of the AR in concentrated soil extract matrix, indicating absence of significant losses in the chromatography system.	Yes
The limit of detection (LOD) of the analytical method for the test substance and for the transformation products should be at least 0.01 mg⋅kg-1 soil (as test substance) or 1% of applied dose whichever is lower. The limit of quantification (LOQ) should also be specified.	The limit of detection (LOD) for HPLC was determined empirically by a series of injections of increasing radioactivity, respectively. The HPLC LOD projected for the entire test system is at least 576 Bq absolute for the soil extract, corresponding to 0.9 % of the applied radioactivity. The LOQ for the HPLC method was set to three times the LOD, which is 2.7 % of the AR.	Yes
To determine the transformation pathway, a representative soil can be used; a sandy loam or silty loam or loam or loamy sand [according to FAO and USDA classification] with a pH of 5.5-8.0, an organic carbon content of 0.5 - 2.5% and a microbial biomass of at least 1% of total organic carbon is recommended	The biotransformation was studied in two European soils (Laacher Hof: loam, pH 7.0, org. C 1.0% / Hoefchen: silt loam, pH 6.8, org. C 2.4%) and in one US soil (Molino: loamy sand, pH 6.7, org. C 0.7%). Soil biomass measurements (SIR method) returned initial microbial biomass carbon contents of 32, 260 and 756 mg Cbiom/kg (mean values) for soils Molino, Laacher Hof and Hoefchen, respectively, corresponding to 0.5 %, 2.6 % and 3.2 % relative to the soil total organic carbon contents.
All soils should be characterised, at least, for texture (% sand, % silt, % clay) [according to FAO and USDA classification], pH, cation exchange capacity, organic carbon, bulk density, water retention characteristic and microbial biomass (for aerobic studies only).	% of sand, slit and clay as well as pH, organic carbon, CEC, bulk density, water holding capacity and microbial biomass were analysed for each test soil.	Yes

 

Conclusions:

The substance was shown to be subject to aerobic soil biodegradation. Degradation occurred at a very fast rate under the conditions of this laboratory experiment. This also was supported by the very high 14C02 formation rates. There is no potential for accumulation of 4-methoxycyclohexanone residues in viable soils. The half-life of the substance was shown to be between 0.6 to 1 day in soil.

Executive summary:

The substance was shown to be subject to aerobic soil biodegradation. Degradation occurred at a very fast rate under the conditions of this laboratory experiment. This also was supported by the very high 14C02 formation rates. There is no potential for accumulation of 4-methoxycyclohexanone residues in viable soils. The half-life of the substance was shown to be between 0.6 to 1 day in soil.

Description of key information

The substance was shown to be subject to aerobic soil biodegradation. Degradation occurred at a very fast rate under the conditions of this laboratory experiment. This also was supported by the very high 14C02 formation rates. There is no potential for accumulation of 4-methoxycyclohexanone residues in viable soils. The half-life of the substance was shown to be between 0.6 to 1 day in soil.

Key value for chemical safety assessment

Half-life in soil:

1 d

at the temperature of:

20 °C