Alkanes, C16-47, branched and linear

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Soil No.:

#1

% Degr.:

ca. 85

Parameter:

test mat. analysis

Remarks:

Biotic

Sampling time:

120 d

Soil No.:

#1

% Degr.:

ca. 46

Parameter:

test mat. analysis

Remarks:

Sterile

Sampling time:

120 d

Soil No.:

#1

DT50:

ca. 35.6 d

Type:

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

Remarks on result:

other: Biotic

Soil No.:

#1

DT50:

ca. 101.9 d

Type:

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

Remarks on result:

other: Sterile

Transformation products:

not measured

Evaporation of parent compound:

not measured

Volatile metabolites:

not measured

Residues:

not measured

Details on results:

RESULTS
Rate of Test Item Disappearance
The results are summarised in Tables 2 and 3 in terms of percentage of fortification (see "Any other information on results incl. tables"). The rate of disappearance is shown graphically in Figure 1 and 2 (see "Attached background material").

The percentage fortification was established for each sampling interval. On the whole, duplicate samples gave similar results; therefore the results in the following sections are expressed as mean values, with the exception of sterile day 0.

The total mean recovery in terms of percentage fortification immediately after treatment (Day 0) and Day 120 is shown in the table below:

Recovery at Day 0 (% Fortification) Recovery at Day 120
(% Fortification)
Biotic Sterile Biotic Sterile
98 105 15 54

The measured amounts of the test item were subjected to first-order reaction kinetics. The following DT50, DT75 and DT90 values were calculated for the test item:

1000 mg/kg
Disappearance
Rate (days) Aerobic Sterile
DT50 35.6 101.9
DT75 72.1 217.4
DT90 120.3 > 1 Yr
r2 0.893 0.889

Microbial Biomass
The microbial biomass of the biotic soil was determined to be 8.12 mg C/ 100 g dry soil prior to the start of incubation. At the end of the incubation period, the microbial biomass of the biotic soil was determined to be 10.98 mg C/ 100 g dry soil (Table 1, see "Any other information on results incl. tables"). These results demonstrate that the aerobic soil remained viable during the study.

The results for the sterile soil at the beginning and end of the study showed no microbial activity.

Tables

Table1     Soil Characteristics

Parameters	Soil
Site location:	Ingleby (Site B2)
Batch:	EF76
Soil characteristics:
pH	5.21
*Cation exchange capacity (meq/100g)	8.5
*Organic carbon (% w/w)	1.1
Bulk Density (g/ml)	1.32
*Soil type (according to USDA)	Loamy Sand
[1]*Particle size analyses (% w/w)USDA[2]**:
2.00-0.050 mm (Sand)	82
0.050-0.002 mm (Silt)	9
< 0.002 (Clay)	10
*5MWHC[3](% w/w) at pF 2.0	15.7
Microbial Biomass (mg C/100 g):
Start of incubation	8.12*
End of incubation	10.98*

 

Table2     Pattern of Disappearance of the Test Item (Biotic)

1000 mg/kg Biotic	Replicate	Incubation Time (Days)
		0	7	14	27	59	90	120
Amount of Test Item                 (% Fortification)	A	104	79	79	64	44	9	17
	B	91	70	94	59	26	11	12
	Mean	98	75	87	62	35	10	15

 

Table3     Pattern of Disappearance of the Test Item (Sterile)

1000 mg/kg Sterile	Replicate	Incubation Time (Days)
		0	7	14	27	59	90	120
Amount of Test Item                 (% Fortification)	A	115[4]	90	92	82	78	47	48
	B	105	85	91	75	69	52	60
	Mean	105	88	92	79	74	50	54

 

^*      Parameters as determined by CEM Analytical Services, Glendale Park, Fernbank Road, North Ascot,  Berkshire, UK (Study Number: CEMS-5391)

^**[2]       According to USDA soil texture classification system

MWHC[3]= Moisture content at water holding capacity

[4]Result not included in mean calculation as considered to be anomalous

Conclusions:

The total mean recovery in terms of percentage fortification immediately after treatment (Day 0) and Day 120 is shown in the following table:

Recovery at Day 0 (% Fortification) Recovery at Day 120 (% Fortification)
Biotic Sterile Biotic Sterile
1000 mg/Kg 98 105 15 54

The measured amounts of the test item were subjected to first-order reaction kinetics. The following DT50, DT75, DT90 and r2 values were calculated for the test item:

1000 mg/kg
Disappearance
Rate (days) Aerobic Sterile
DT50 35.6 101.9
DT75 72.1 217.4
DT90 120.3 > 1 Yr
r2 0.893 0.889

The rate of disappearance of the test item in a single soil type incubated in the dark under aerobic conditions at 20 ± 2 °C was investigated.

As the microbial activity measurements confirmed that sterility was maintained, the losses from the sterile system were due to abiotic factors. These were considered to be mainly via binding to the soil since, due to the physical chemical nature of the test item, these losses were unlikely to be via volatilization. The results indicate that microbial degradation plays a significant role in removing the test item in the biotic soil.

The test item has a DT50 disappearance rate, at 1000 mg/kg, of 35.6 days in aerobic soil, incubated in the dark at 20 ± 2 °C. In sterilized soil the test item has a disappearance rate, at 1000 mg/kg, of 101.9 days, incubated in the dark at 20 ± 2 °C.

Executive summary:

Introduction

The purpose of the study was to determine the rate of degradation of the read across substance GTL Base Oil Distillates in one soil incubated in the dark under aerobic conditions at 20 ± 2°C. The test item was treated to a single soil and the rate of degradation monitored. Sterile soil was also treated with test item to assess any loss due to volatilization and/or bound residues. The information will be used to predict the likelihood of the substance persisting in the environment.

 

The OECD 307 test was designed to assess the degradation rate of single chemicals in soil. However, for complex substances the test will in effect measure the rate of disappearance of the test item. This is because some components may be lost by abiotic factors and not biodegradation per se.

 

Methods

The following soil was used for the study: Site B2 Ingleby, Derbyshire; Loamy Sand.

 

The freshly collected soil was supplied sieved to <2 mm. The test item was then applied to soil samples (100 g dry weight) at a concentration of approximately 1000 mg/kg. The soil moisture content, of aerobic samples, was adjusted with purified water. Sterile samples were prepared by the addition of an aqueous solution of cycloheximide and sodium azide to assess any loss due to volatilization and/or bound residues. The treated soil samples were incubated at 20 ± 2 ºC in the dark. Prior to treatment and at the end of the incubation period, the microbial biomass was determined. The results show that the aerobic soil remained viable during the study and that the sterile sample remained sterile over the duration of the study.

 

Samples were taken from each soil immediately after treatment with test item (Day 0) and after 7, 14, 27, 59, 90 and 120 days. Each sample was extracted by solvent extraction using acetone and hexane. The extracts were then subjected to chromatographic analysis.

 

 

Results

The total mean recovery in terms of percentage fortification immediately after treatment (Day 0) and Day 120 is shown in the following table:

 

	Recovery at Day 0 (% Fortification)		Recovery at Day 120 (% Fortification)
	Biotic	Sterile	Biotic	Sterile
1000 mg/Kg	98	105	15	54

 

The measured amounts of the test item were subjected to first-order reaction kinetics. The followingDT₅₀, DT₇₅, DT₉₀and r²values were calculated for the test item:

 

	1000 mg/kg
Disappearance Rate (days)	Aerobic	Sterile
DT50	35.6	101.9
DT75	72.1	217.4
DT90	120.3	> 1 Yr
r^2^[1]	0.893	0.889

 

The rate of disappearance of the test item in a single soil type incubated in the dark under aerobic conditions at 20 ± 2 °C was investigated.

 

As the microbial activity measurements confirmed that sterility was maintained, the losses from the sterile system were due to abiotic factors. These were considered to be mainly via binding to the soil since, due to the physical chemical nature of the test item, these losses were unlikely to be via volatilization. The results indicate that microbial degradation plays a significant role in removing the test item in the biotic soil.

 

The test item has a DT₅₀disappearancerate, at 1000 mg/kg, of 35.6 days in aerobic soil, incubated in the dark at 20 ± 2 °C. In sterilized soil the test item has adisappearancerate, at 1000 mg/kg, of 101.9 days, incubated in the dark at 20 ± 2 °C.

[1]r²=Coefficient of determination

Description of key information

Soil degradation (OECD 307): Half-life 35.6 days in one soil type only

Additional information

The results of experimental studies on biodegradation in soil of the read across substance GTL Base Oil Distillate are summarised in the following table.

Table Overview of tests for biodegradation in soil

Method	Results	Remarks	Reference
Test type: soil degradation   OECD Guideline 307	Half-life 35.6 days in one soil type only.	2 (reliable with restrictions) key study experimental study Test material: Distillates (Fischer-Tropsch), Heavy, C18-50 – branched, cyclic and linear	Bayliss, 2012a
Test type: soil degradation   OECD Guideline 307	Half-life 35.8 days in one soil type only.	2 (reliable with restrictions) supporting study experimental study Test material: GTL Base Oil 3	Bayliss, 2012b
Test type: soil degradation   OECD Guideline 307	-	3 (invalid) disregarded study experimental study Test material: Distillates (Fischer-Tropsch), Heavy, C18-50 – branched, cyclic and linear	Wadsley, 2011

 

A screening study of rate of degradation in one soil of the read across substance GTL Base Oil Distillates has been conducted (Bayliss, 2012a). In this study the test substance was applied in hexane to one soil (type: loamy sand) at a loading rate of 1000 mg/kg dry soil (a hexane control was included in the study). A sterile control was included to evaluate losses association with abiotic processes (volatilisation or adsorption). The soil sample was taken from a pasture-land location shortly before the study, sieved to 2 mm, and stored with watering as necessary. The microbial biomass of the biotic soil samples was determined to be 8.12 mg C/100 g dry soil at the start of the study and 10.98 mg C/100g dry soil at the end of the 120 day incubation period. The organic carbon content of the soil was 1.1%, thus meeting the recommendation of the test guideline by the end of the study, although the microbial biomass was slightly lower than recommended on Day 0 (0.5 – 2.5% OC; microbial biomass at least 1% of the total OC).

The study duration was 120 days and samples were incubated in the dark under aerobic conditions at 20 ± 2 °C. Degradation levels were determined on the basis of infra-red spectroscopy analysis of test substance extracted from the soil samples. The limits of detection and quantification for the analytical method were 5.53 and 11.05 mg/l, respectively.

For the biotic samples, recovery of test substance on Day 120 was 15% whereas for abiotic samples the recovery was 54%. The corresponding half-lives for ‘disappearance’ of the test material were reported as 35.6 and 101.9 days, respectively. For the sterile control, test substance disappearance is attributable to abiotic processes, most likely due to adsorption, given the low volatility of the constistuents present in the material. A significant degree of test substance disappearance in the biotic samples can be attributed to biodegradation.

The study is broadly of high quality but it should be noted that there are some important variations compared to the quoted OECD 307 guideline which affect the interpretation of the study results. In particular, OECD 307 is clear that if the objective of the test is to draw conclusions on rate, then a minimum of four varied soil types must be tested. Here only one soil has been tested.

A second study is available (Bayliss, 2012b), following a similar protocol to that described above but where the lowest viscosity grade product (GTL Base Oil 3) was tested and the contact time was 56 days. In this study, the microbial biomass of the biotic soil samples was determined to be 14.8 mg C/100 g dry soil at the start of the study and 17.8 mg C/100g dry soil at the end of the 56 day incubation period. The organic carbon content of the soil was 1.6%, thus meeting the recommendation of the test guideline by the end of the study, although again the microbial biomass was slightly lower than recommended on Day 0.

The limits of detection and quantification for the analytical method were 4.60 and 23 mg/l, respectively.

For the biotic samples, recovery of test substance on Day 56 was 33% whereas for abiotic samples the recovery was 99%. The corresponding half-lives for ‘disappearance’ of the test material were reported as 35.8 days and >1 year, respectively. The results indicate that for the low viscosity product, removal is mainly due to degradation rather than abiotic processes.

A third study (Wadsley, 2011) was disregarded as sterility of the abiotic controls was not maintained during the test.