Phosphoric acid, mono- and di-C16-18-alkyl esters

Biodegradation in soil

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:

June 2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

This experimental study is a preliminary test performed to establish the feasibility of the full and definitive test according the TG OECD 307.

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

April 2002

Deviations:

yes

Remarks:

This study was designed to provide information on the feasibility of conducting a transformation study in natural soil (OECD Guideline 307).

GLP compliance:

no

Remarks:

This experimental study is a preliminary test performed to establish the feasibility of the full and definitive test according the TG OECD 308.

Test type:

laboratory

Radiolabelling:

yes

Remarks:

Phosphoric acid octadecyl ester, [14C], dose solution, 90.2%

Oxygen conditions:

aerobic

Soil classification:

not specified

Remarks:

Texture class : sandy clay loam soil (for more details on the tested soil, please refer to the attached background document)

Year:

2017

Soil no.:

#1

Soil type:

sandy clay loam

% Org. C:

3.8

pH:

7.7

CEC:

23.9 meq/100 g soil d.w.

Bulk density (g/cm³):

1.078

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Name : Elmton; Origin : SP 10320 33205 Gloucestershire; Batch number : H151117A
- Pesticide use history at the collection site: None for 5 years.
- Collection procedures: The Elmton soil (Batch H151117A) was collected from Gloucestershire, UK on 06 November 2017, and supplied by LandLook (Midlands), UK. Characterization of the soil was carried out (not as part of this study) by NRM Ltd, Bracknell, UK.
- Sampling depth (cm): 5 – 15 cm
- Storage conditions: All test systems were maintained in darkness at 12 degree (°C). Air was drawn through each system at a flow rate of approximately 60 mL/minute.
- Storage length: The soil was acclimatised under aerobic study conditions for approximately two weeks prior to dose application.
- Soil preparation (e.g., 2 mm sieved; air dried etc.): none.

PROPERTIES OF THE SOILS
- Moisture at 1/3 atm (%): Water content at pF2 (% dry weight) = 31,5 %. Portions of Elmton soil (50 g, dry weight equivalent) were added to glass vessels and water added to adjust the moisture content to that at pF 2. Measurement of the soil water content at pF2 was performed (not as part of this study) by Envigo CRS Ltd, UK.
- Bulk density (g/cm3): 1,078 g/cm3

Soil No.:

#1

Duration:

14 d

Soil No.:

#1

Initial conc.:

0.94 other: mg/kg

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

not reported

Humidity:

31,5%

Microbial biomass:

not reported

Details on experimental conditions:

1. PRELIMINARY EXPERIMENTS: yes

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): The soil was acclimatised under aerobic study conditions for approximately two weeks prior to dose application. All test systems were maintained in darkness at 12 degree (°C). Air was drawn through each system at a flow rate of approximately 60 mL/minute.
- Soil condition: fresh air
- Soil (g/replicate): Portions of Elmton soil (50 g, dry weight equivalent) were added to glass vessels and water added to adjust the moisture content to that at pF 2.
- Control conditions, if used (present differences from other treatments, i.e., sterile/non-sterile, experimental conditions): no controls were performed.
- No. of replication controls, if used: none
- No. of replication treatments: 3 replicates / treatment
- Test apparatus (Type/material/volume): flow-through systems
Three vessels established for treatment with radiolabelled phosphoric acid octadecyl ester were incorporated into individual flow-through systems each arranged in series as follows:
(i) Humidifying vessel (with sintered stem for uniform gas dispersion) containing water to humidify the air-flow;
(ii) Test vessel containing the soil;
(iii) Vessel containing ethyl digol to trap volatile organic compounds (Trap 1);
(iv) Vessel containing 1 M aqueous potassium hydroxide solution with phenolphthalein indicator to trap 14CO2 (Trap 2);
(v) Vessel containing 1 M aqueous potassium hydroxide solution with phenolphthalein indicator as a backup 14CO2 trap (Trap 3); and
(vi) A non-return valve to prevent accidental backflow through the test apparatus.
- Details of traps for CO2 and organic volatile, if any: yes. Please find the description of the vessels above.
- If no traps were used, is the system closed/open: not applicable.
- Identity and concentration of co-solvent: acetonitrile to dissolve the test item (at concentration of 199 µg/mL).

Test material application
- Volume of test solution used/treatment: A treatment solution of phosphoric acid octadecyl ester, [14C] was prepared in acetonitrile : water (1 : 1, v/v) at concentration of 199 µg/mL. An aliquot (0.25 mL) of the application solution was applied to each soil sample and the treated soils were gently shaken. This achieved application rate of 0.94 mg/kg
- Application method (e.g. applied on surface, homogeneous mixing etc.): mixing.
- Is the co-solvent evaporated: not reported.

Any indication of the test material adsorbing to the walls of the test apparatus: none

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: After application water was added to the soil as necessary to maintain the moisture content at the pF2 level. Water content at pF2 (% dry weight) = 31,5%
- Continuous darkness: Yes. All test systems were maintained in darkness at 12°C.

Other details, if any: /

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: flow-through systems
- Evidence that an/aerobic conditions were maintained during the experiment (e.g. redox potential): not reported

4. SUPPLEMENTARY EXPERIMENTS: none

5. SAMPLING DETAILS
- Sampling intervals: A single sample of soil was taken for analysis immediately after application, and after 7 and 14 days of incubation.
- Sampling method for soil samples: not reported.
- Method of collection of CO2 and volatile organic compounds: not fully detailed. Trapping media were taken for analysis with the associated samples at sampling.
- Sampling intervals/times for: see the sentence above.
> Sterility check, if sterile controls are used : no sterile control was tested.
> Moisture content: After application water was added to the soil as necessary to maintain the moisture content at the pF2 level.
> Redox potential/other: not reported.
> Sample storage before analysis: not reported.
- Other observations, if any: none

Soil No.:

#1

% Recovery:

86.6

Remarks on result:

other: Total recovery

Remarks:

Day 14

Soil No.:

#1

% Recovery:

2.4

Remarks on result:

other: % of applied radioactivity

Remarks:

Total extracted

Soil No.:

#1

% Recovery:

75.5

Remarks on result:

other: % of applied radioactivity

Remarks:

Non extracted solid

Soil No.:

#1

% Recovery:

8.7

Remarks on result:

other: % of applied radioactivity

Remarks:

Traps (KOH)

Key result

Soil No.:

#1

Parameter:

radiochem. meas.

Sampling time:

14 d

Remarks on result:

not determinable because of methodological limitations

Remarks:

Some phosphoric acid octadecyl ester and its degradates were rapidly degraded on soil to unidentified products or were mineralised to carbon dioxide, but the majority of the applied radioactivity was incorporated as bound residues in the soil. It is unlikely that the degradates could be identified due to their chemical nature and/or non-extractability.

Key result

Soil No.:

#1

Type:

not specified

Temp.:

12 °C

Remarks on result:

not determinable because of methodological limitations

Remarks:

Some phosphoric acid octadecyl ester and its degradates were rapidly degraded on soil to unidentified products or were mineralised to carbon dioxide, but the majority of the applied radioactivity was incorporated as bound residues in the soil. It is unlikely that the degradates could be identified due to their chemical nature and/or non-extractability.

Transformation products:

not specified

Remarks:

It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

Details on transformation products:

- Formation and decline of each transformation product during test: not reported
- Pathways for transformation: none
- Other: It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

Evaporation of parent compound:

not specified

Volatile metabolites:

not measured

Remarks:

Not detected (for more details, please see the ethyl dygol trap results in the attached background document)

Residues:

yes

Remarks:

Non-extractable radioactivity in the soil (bound residues) accounted for 72.4 – 85.5% applied radioactivity.

Details on results:

TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: not reported
- Anomalies or problems encountered (if yes): not reported

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: none
- Range of maximum concentrations in % of the applied amount at end of study period: none
Rapid degradation of phosphoric acid octadecyl ester proceeded via binding of residues to the soil and mineralisation to CO2, but the majority of the applied radioactivity remained as bound residues in the soil. It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: none
- Range of maximum concentrations in % of the applied amount at end of study period: none
Rapid degradation of phosphoric acid octadecyl ester proceeded via binding of residues to the soil and mineralisation to CO2, but the majority of the applied radioactivity remained as bound residues in the soil. It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT: The mean total recoveries of radioactivity (‘mass balances’, i.e. the sum of radioactivity in the extractable and non-extractable soil and volatile radioactivity) were in the range 86.6 to 93.4% applied radioactivity. Therefore, the total range of unindentified radioactivity is 6,6% - 13,4% of applied radioactivity.

EXTRACTABLE RESIDUES
- % of applied amount at day 0: The extractable radioactivity accounted for 17.9% applied radioactivity at the start of the test.
- % of applied amount at end of study period: The extractable radioactivity was measured at 2.4% applied radioactivity after 14 days.
The extractable radioactivity accounted for 17.9% applied radioactivity at zero-time and this declined to 2.4% applied radioactivity after 14 days.

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: The non-extractable radioactivity accounted for 72,4% applied radioactivity at the start of the test.
- % of applied amount at end of study period: The non-extractable radioactivity accounted for 75,5% applied radioactivity at the end of the test.
Non-extractable radioactivity in the soil (bound residues) accounted for 72.4 – 85.5% applied radioactivity.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: Volatile radioactivity, assumed to be associated with 14CO2, accounted for 8.7% applied radioactivity (AR) after 14 days. At day 7, it was measured 4,9% AR.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Not detected.

STERILE TREATMENTS (if used) : not used
- Transformation of the parent compound: not applicable
- Formation of transformation products: not applicable
- Formation of extractable and non-extractable residues: not applicable
- Volatilization: not applicable

RESULTS OF SUPPLEMENTARY EXPERIMENT (if any): none

Results with reference substance:

No reference substance was tested. There were no references available to aid identification or establish co-chromatographic correspondence with the authentic non-radiolabelled phosphoric acid octadecyl ester, which is a UVCB substance.

Although the purity was <95% this was considered sufficient to obtain the objectives of this feasibility study. As very little radioactivity was extracted from the soil the relatively low radiochemical purity did not impact the outcome of the study.

The mean total recoveries of radioactivity (‘mass balances’, i.e. the sum of radioactivity in the extractable and non-extractable soil and volatile radioactivity) were in the range 86.6 to 93.4% applied radioactivity (Table 2).

The extractable radioactivity accounted for 17.9% applied radioactivity at zero-time and this declined to 2.4% applied radioactivity after 14 days. Non-extractable radioactivity in the soil (bound residues) accounted for 72.4 – 85.5% applied radioactivity. Volatile radioactivity, assumed to be associated with 14CO2, accounted for 8.7% applied radioactivity after 14 days.

Phosphoric acid octadecyl ester was not detected in soil extracts at zero-time.

The decline of radiolabelled test item (DT50) in the aerobic soil system could not be described because the residues could not be extracted from the soil.

Conclusions:

The extractability of radioactivity from the soil was low. The applied parent substance, phosphoric acid octadecyl ester, was not detected in zero-time soil extracts. Rapid degradation of phosphoric acid octadecyl ester proceeded via binding of residues to the soil and mineralisation to CO2, but the majority of the applied radioactivity remained as bound residues in the soil. It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

This trial demonstrates that a full study conducted according to OECD Guideline 307, “Aerobic and Anaerobic Transformation in Soil”, would not be feasible.

Executive summary:

This non GLP study was designed to provide information on the feasibility of conducting a transformation study in natural soil (OECD Guideline 307). Soil collected from Gloucestershire, UK and described as a neutral sandy clay loam with high organic carbon content, was treated with phosphoric acid octadecyl ester, [14C] at a nominal concentration of 1 mg/kg and incubated at 12ºC in the dark. Water was added to bring the water content of the soils to that equivalent to pF2. Individual samples of treated soil were taken for analysis at zero-time and after 7 and 14 days.

Total recovery of radioactivity was in a range of 86.6 – 93.4% applied radioactivity (AR). The extracted radioactivity accounted for 2.4 – 17.9% AR. The non-extractable radioactivity accounted for 72.4 – 85.5% applied radioactivity. Volatile radioactivity accounted for 8.7% applied radioactivity after 14 days.

The parent substance, phosphoric acid octadecyl ester, was not detected in soil extracts at zero-time. Some phosphoric acid octadecyl ester and its degradates were rapidly degraded on soil to unidentified products or were mineralised to carbon dioxide, but the majority of the applied radioactivity was incorporated as bound residues in the soil. It is unlikely that the degradates could be identified due to their chemical nature and/or non-extractability.

The results of this feasibility trial demonstrate that conducting a full study according to OECD Guideline 307, “Aerobic and Anaerobic Transformation in Soil”, would not provide any further useful information. It is unlikely that a full study would meet the objectives of the OECD Guideline 307.

Description of key information

The applied parent substance, phosphoric acid octadecyl ester, was not detected in zero-time soil extracts. Rapid degradation of phosphoric acid octadecyl ester proceeded via binding of residues to the soil and mineralisation to CO2, but the majority of the applied radioactivity remained as bound residues in the soil. It is unlikely that degradation products could be identified due to their chemical nature and/or non-extractability.

Additional information

According the Decision TPE-D-2114349030-64-01/F on Phosphoric acid, octadecyl ester and physico-chemical properties, it is considered relevant to investigate the aerobic and anaerobic potential of transformation in the soil of the registered substance at 12°C and its degradation products.

This non GLP study was designed to provide information on the feasibility of conducting a transformation study in natural soil (according TG OECD Guideline 307). Soil collected from Gloucestershire, UK and described as a neutral sandy clay loam with high organic carbon content, was treated with phosphoric acid octadecyl ester, [14C] at a nominal concentration of 1 mg/kg and incubated at 12ºC in the dark.