Tris(2-ethylhexyl) phosphate

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Remarks:

NOTE: Data presented in this section has been transcribed from a draft report. This summary will be updated in due course upon finalization of the report by the conducting CRO.

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2020-2022

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Study was conducted in accordance with OECD 307 and the principles of GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

not specified

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

loamy sand

% Clay:

7

% Silt:

19.8

% Sand:

73.1

% Org. C:

0.96

pH:

5.7

CEC:

14

Soil no.:

#2

Soil type:

silt loam

% Clay:

16

% Silt:

78.2

% Sand:

5.7

% Org. C:

1.05

pH:

6.8

CEC:

115

Soil no.:

#3

Soil type:

loam

% Clay:

25.9

% Silt:

42

% Sand:

32

% Org. C:

1.95

pH:

7.4

CEC:

212

Soil no.:

#4

Soil type:

clay

% Clay:

41.2

% Silt:

35.5

% Sand:

23.3

% Org. C:

1.7

pH:

7.3

CEC:

232

Details on soil characteristics:

See above

Soil No.:

#1

Duration:

120 d

Soil No.:

#3

Duration:

120 d

Soil No.:

#4

Duration:

120 d

Soil No.:

#1

Initial conc.:

0.5 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

0.5 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

0.5 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#4

Initial conc.:

0.5 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

test mat. analysis

other: Organic Volatiles

Soil No.:

#1

Temp.:

12 Degrees Celsius

Humidity:

Water Saturated Air

Microbial biomass:

98.6 (non treated) and 97.6 (treated with solvent) Biomass (Cmic/kg dry mass) at day 119

Soil No.:

#2

Temp.:

12 Degrees Celsius

Humidity:

Water Saturated Air

Microbial biomass:

236.4 (non treated) and 224.9 (treated with solvent) Biomass (Cmic/kg dry mass) at day 119

Soil No.:

#3

Temp.:

12 Degrees Celsius

Humidity:

Water Saturated Air

Microbial biomass:

593.8 (non treated) and 598.9 (treated with solvent) Biomass (Cmic/kg dry mass) at day 119

Soil No.:

#4

Temp.:

12 Degrees Celsius

Humidity:

Water Saturated Air

Microbial biomass:

612.0 (non treated) and 568.0 (treated with solvent) Biomass (Cmic/kg dry mass) at day 119

Details on experimental conditions:

See above

Soil No.:

#1

Sampling day(s):

120 d

% Total extractable:

>= 87.2 - <= 97.5

% Non extractable:

>= 1.1 - <= 4.5

% CO2:

>= 1.8 - <= 7.1

% Recovery:

98.1

Remarks on result:

other: The following data is not available in the draft report; volatile traps, std deviation of recoveries. % recovery data is presented as a mean of all timepoints. Mean values calculated from the individual data points tabulated in the draft report.

Soil No.:

#2

Sampling day(s):

120 d

% Total extractable:

>= 82.2 - <= 95.6

% Non extractable:

>= 2.1 - <= 7.3

% CO2:

>= 2.2 - <= 11.6

% Recovery:

98.4

Remarks on result:

other: The following data is not available in the draft report; volatile traps, std deviation of recoveries. % recovery data is presented as a mean of all timepoints. Mean values calculated from individual data points tabulated in the draft report.

Soil No.:

#3

Sampling day(s):

120 d

% Total extractable:

>= 73.7 - <= 95.9

% Non extractable:

>= 2.8 - <= 10.3

% CO2:

>= 1.4 - <= 15.7

% Recovery:

98.3

Remarks on result:

other: The following data is not available in the draft report; volatile traps, std deviation of recoveries. % recovery data is presented as a mean of all timepoints. Mean values calculated from individual data points tabulated in the draft report.

Soil No.:

#4

Sampling day(s):

120 d

% Total extractable:

>= 69 - <= 96.4

% Non extractable:

>= 2.6 - <= 10.5

% CO2:

>= 1 - <= 17.5

% Recovery:

98

Remarks on result:

other: The following data is not available in the draft report; volatile traps, std deviation of recoveries. % recovery data is presented as a mean of all timepoints. Mean values calculated from individual data points tabulated in the draft report.

Parent/product:

parent

Key result

Soil No.:

#1

% Degr.:

82.8 - 91.6

Parameter:

radiochem. meas.

Remarks:

Soil Extracts quantified by LSC for % applied radioactivity then analysed for peak ratio by HPLC.

Remarks on result:

other: The data presented in % Degr is the range of % applied radioactivity (confirmed to be parent) determined during the study for this soil type.

Parent/product:

parent

Key result

Soil No.:

#2

% Degr.:

76.9 - 89.7

Parameter:

radiochem. meas.

Remarks:

Soil Extracts quantified by LSC for % applied radioactivity then analysed for peak ratio by HPLC.

Remarks on result:

other: The data presented in % Degr is the range of % applied radioactivity (confirmed to be parent) determined during the study for this soil type.

Parent/product:

parent

Key result

Soil No.:

#3

% Degr.:

69.6 - 89.2

Parameter:

radiochem. meas.

Remarks:

Soil Extracts quantified by LSC for % applied radioactivity then analysed for peak ratio by HPLC.

Remarks on result:

other: The data presented in % Degr is the range of % applied radioactivity (confirmed to be parent) determined during the study for this soil type.

Parent/product:

parent

Key result

Soil No.:

#4

% Degr.:

67.7 - 90.5

Parameter:

radiochem. meas.

Remarks:

Soil Extracts quantified by LSC for % applied radioactivity then analysed for peak ratio by HPLC.

Remarks on result:

other: The data presented in % Degr is the range of % applied radioactivity (confirmed to be parent) determined during the study for this soil type.

Key result

Soil No.:

#1

DT50:

1 620 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Chi2 = 2.14 and r2 = 0.2697

Key result

Soil No.:

#2

DT50:

1 010 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Chi2 = 2.46 and r2 = 0.4206

Key result

Soil No.:

#3

DT50:

491 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Chi2 = 1.96 and r2 = 0.8043

Key result

Soil No.:

#4

DT50:

436 d

Type:

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

Temp.:

12 °C

Remarks on result:

other: Chi2 = 2.07 and r2 = 0.8336

Transformation products:

no

Remarks:

Three unknowns (1-3)accounting for a total approx. 5% of applied radioactivity were observed in the soil extracts. All three unknowns were impurities present in the Day 0 dosing solution and not degradation products formed during the incubation process.

Details on transformation products:

Unknowns were titled Unknown 1, 2 and 3.

Evaporation of parent compound:

not measured

Conclusions:

In the present study the transformation of 14C-Tris(2-ethylhexyl) phosphate (TEHP) under aerobic conditions was investigated according to the OECD-Guideline 307 "Aerobic and anaerobic Transformation in Soil” [4] in four biologically active soils. The incubation was performed using 14C-labelled test item at an application rate of 0.5 mg/kg soil dry weight.

Soil samples were prepared by placing 50 g of appropriate soil (dry weight basis) into glass vessels and were incubated in a flow-through system at 12 ± 2 °C in the dark for up to 120 days. Sterile samples were prepared in order to distinguish between biotic and abiotic degradation of the test item and were incubated gas tight.
Microbiological activity of the test soils was monitored at the beginning of incubation, during the incubation and at the end of the incubation. Biomass determination was performed by means of the substrate induced respiration method. Possible effects of the organic solvent used for application on the microbial activity were monitored by separate control samples. The results of microbial biomass show the existence of an active microbial population throughout the incubation period. No significant effect on microorganism activity by application of the organic solvent was observed.
Prior to application, a purity check of the treatment solution was performed by radio-HPLC. For each soil type replicate soil samples were taken for analyses at 0, 7, 14, 28, 42, 80 and 120 days after treatment. Sterilised soils were sampled after 60 and 120 days of incubation. Soil samples were extracted and the extracts were analysed for the test substance and possible degradation products by radio-HPLC.
A total radioactivity balance and the distribution of radioactivity in every subsample were established at each sampling day. The total mass balance for each sample was calculated by the sum of the applied radioactivity (AR) detected in combined organic soil extracts, non-extractable residue (NER) and volatile mineralisation products (non-sterile samples only). The total recoveries ranged between 90 and 110% of applied radioactivity.

The mean mass balances ranged from 94.9 to 100.3 % AR, with an overall mean of 98.1 % AR and from 95.4 to 101.5 % AR, with an overall mean of 98.4 % AR for soil IME 01-A and IME 02-A, respectively. For LUFA 2.4 and LUFA 6S soils, the mean mass balances ranged from 92.0 to 103.3 % AR, with an overall mean of 98.2 % AR and from 95.3 to 100.2 % AR, with an overall mean of 98.0 % AR, respectively.
The amount of radioactivity extracted from soil decreased in all soils from 94.6 % – 97.1 % AR at the beginning of incubation (0 days) to 72.0 % – 87.4 % AR after 120 days of incubation.
The amount of parent compound in the soil extracts decreased from maximum levels of 91.6 % (IME 01-A), 89.7 % (IME 02-A), 89.2 % (LUFA 2.4) and 90.5 % (LUFA 6S) at the day of treatment to amounts of 82.9 % and 76.9 % AR for IME 01-A and IME 02-A soil and amount of 70.0 % and 67.8 % AR for LUFA 2.4 and LUFA 6S soils after 120 days of incubation.
Almost the entire amount of volatile radioactivity was trapped in the alkaline sodium hydroxide traps and was assumed to be 14CO2 resulting from the mineralisation of 14C-Tris(2-ethylhexyl) phosphate. For each sample, detected radioactivity in different traps was summed to one total value of volatiles. None or only traces (< 0.1 % AR) of continuously collected radioactivity were trapped in ethylene glycol and sulphuric acid absorption solutions for all non-sterile samples over duration of the study. The total mean amount of trapped radioactivity increased to maximum level of 6.9 % AR (IME 01-A) at 80 day and 10.8 % AR (IME 02-A), 13.5 % AR (LUFA 2.4) and 15.5 % AR (LUFA 6S) at 120 day after treatment (DAT), respectively.
The amount of non-extractable residue (NER) in the non-sterile samples ranged from 1.2 % to 3.4 % AR at 0 day after treatment and increased to maximum mean amounts of 4.1 % and 6.9 % AR for IME 01-A and IME 02-A soils at 120 day after treatment, respectively. For LUFA 2.4 and LUFA 6S soils, maximum mean amounts of NER were observed at 10.2 % and 9.9 % AR, respectively.
Degradation of 14C-Tris(2-ethylhexyl) phosphate in all four soils was observed by mineralisation only. No metabolites were detected by radio-HPLC in the soil extracts. Minor unknown signals in the radio-HPLC analyses accounting for approx. 5% of applied radioactivity were constantly present in all soil extracts and also observed in the application solution. They were assumed to be impurities of the test item and not products of an anaerobic transformation in soil.
In the sterile samples item 14C-Tris(2-ethylhexyl) phosphate was found to be stable with 91.0 % AR (IME 01-A), 92.0 % AR (IME 02-A), 88.8 % AR (LUFA 2.4) and 88.9 % AR (LUFA 6S) remaining as the parent compound at the end of incubation period.
The degradation rates (DegT50) of 14C-Tris(2-ethylhexyl) phosphate were estimated using the program CAKE version 3.3. As the non-extractable residue (NER) was not further analysed for the kinetic calculation the amount of radioactivity detected as NER was accounted as parent test item. The kinetic models considered for the analysis of parent item were SFO (Single First Order), DFOP (Double First Order in Parallel), HS (Hockey Stick), and FOMC (First Order Multi Compartment).
According to the results, the best fitting were obtained when considering SFO kinetics and are summarised below:

Calculated DT50 and DT90 for the parent compound based on SFO kinetics.
SFO
Soil chi2 r2 Prob. > t DT50 DT90
(%) (days) (days)
Refesol 01-A 2.14 0.2697 0.02851 1620 5380
Refesol 02-A 2.46 0.4206 0.006192 1010 3350
LUFA 2.4 1.96 0.8043 8.29E-006 491 1630
LUFA 6S 2.07 0.8336 3.22E-006 436 1450
Geometric mean 769

The DT50 values of 14C-Tris(2-ethylhexyl) phosphate based on SFO kinetics (best fit) are in the range of 436 – 1620 days. The geometric mean DT50 of the recommended optimisation is 769 days for the parent compound.

Executive summary:

The Aerobic Transformation of ¹⁴C-Tris(2-ethylhexyl) phosphate in four soils was performed in accordance with the OECD Guideline for Testing of Chemical No. 307 "Aerobic and Anaerobic Transformation in Soil” (2002) with no study plan or GLP deviations.

The study was conducted under aerobic condition at 12ºC for 120 days. Mass balance for all samples was between 90-110 %. The amount of parent in soils extracts was recorded at each time point by HPLC. No major metabolites were observed during the test.

DT50 and DT90 kinetics were determined for the parent compound with SFO deemed the best fit for all soil types. The DT50 geometric mean was 769 days.

Description of key information

DT50 (geometric mean) = 769 days; OECD 307; M. Hüben (2022)

Key value for chemical safety assessment

Half-life in soil:

769 d

at the temperature of:

12 °C

Additional information

The Aerobic Transformation of ¹⁴C-Tris(2-ethylhexyl) phosphate in four soils was performed in accordance with the OECD Guideline for Testing of Chemical No. 307 "Aerobic and Anaerobic Transformation in Soil” (2002) with no study plan or GLP deviations.

The study was conducted under aerobic condition at 12ºC for 120 days. Mass balance for all samples was between 90-110 %. The amount of parent in soils extracts was recorded at each time point by HPLC. No major metabolites were observed during the test.

DT50 and DT90 kinetics were determined for the parent compound with SFO deemed the best fit for all soil types. The DT50 geometric mean was 769 days.