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Environmental fate & pathways

Biodegradation in soil

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Administrative data

Endpoint:
biodegradation in soil: simulation testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Although data provided have a report year after 2008, the data was obtained from a journal article which does not provide GLP information.
Cross-reference
Reason / purpose:
reference to same study

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2010

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Deviations:
yes
Remarks:
(study run for 180 days)
GLP compliance:
not specified
Test type:
other: laboratory (closed bottle)

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Purity: 99%
Radiolabelling:
no

Study design

Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil properties
Soil type:
sandy loam
% Clay:
14
% Silt:
34
% Sand:
52
% Org. C:
3.8
pH:
5.8
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Collection details: Sassafras soil (Ultisol) was used. It was collected from a forested area undisturbed for at least 40 years in Newark, Delaware and sieved via a 2-mm sieve immediately upon collection and stored at 4 °C and used within 3 months.

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture: The degradation study was conducted for 180 days at 40% of the field moisture capacity, corresponding to a gravimetric moisture content of 28%.
Duration of test (contact time)
Duration:
180 d
Initial test substance concentration
Initial conc.:
2.9 other: µg/g
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Details on experimental conditions:

EXPERIMENTAL DESIGN
- Test apparatus: The test substance was initially dosed at 2.9 µg/g soil. Parent and metabolites were measured in three compartments: volatile analytes in the headspace, volatile analytes absorbed onto the rubber septa, and study analytes in soil by exhaustive solvent extraction of the entire test vessel. 120-mL glass serum bottles were incubated statically in dark at 20 – 25 °C for 180 days. Approximately 10 g dry weight equivalent of sieved Sassafras soil was added to each vessel, and dosed with 10 µL of test substance stock solution prepared in ethanol. Sterile treatments were prepared by gamma irradiation (60Co) and additionally dosed with the triple antibiotics at respective 100 mg/kg final concentration. For each sampling time point, four treatments of triplicate vessels were prepared: (1) untreated (matrix) live soil with 10 µL ethanol; (2) test substance treated live soil; (3) test substance treated sterile soil; and (4) sterile soil treated with selected metabolites. In treatment group 4, the sterile soil was fortified with PFBA (0.13 nmol/g soil), PFPeA (0.10 nmol/g), and PFHxA (0.74 nmol/g) to evaluate the potential effects of abiotic processes on recovery of these three PFCAs over 120 days.

- Any indication of the test material adsorbing to the walls of the test apparatus: yes, septum and glass tube extracted

SAMPLING DETAILS
- Sampling intervals: 0, 2, 7, 14, 28 60, 90, 120, and 180 days
- Sampling method for soil samples: The O2 content was measured at each time point in untreated live soil to approximate O2 content in treated live sample bottles. Prior to opening the soil test vessels, the headspace gas of a sample bottle was pumped out through two needles inserted through the septum using an air pump at a rate of 1.5 L/min for 1 min. The outlet air went through two C18 cartridges in series to capture volatile fluorinated compound(s). Each cartridge was eluted with 5 mL acetonitrile and subject to chemical analysis. The rubber septum was then removed and extracted in 5 mL acetonitrile at 50 °C for 2 – 7 d. The soil was subjected to two sequential extractions in the test vessel sealed with a new rubber septum to enhance recovery.


Results and discussion

% Degradation
% Degr.:
>= 93.8 - <= 96.5
Parameter:
test mat. analysis
Remarks:
(Primary biodegradation)
Sampling time:
28 d
Half-life / dissipation time of parent compound
DT50:
1.6 d
Type:
(pseudo-)first order (= half-life)
Transformation products:
yes
Identity of transformation productsopen allclose all
Evaporation of parent compound:
yes
Volatile metabolites:
yes
Residues:
yes
Details on results:
TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: Yes

Any other information on results incl. tables

In soil, the treated sterile control samples showed satisfactory ≈87 – 113% test substance mass balance over 180 days. At the end of the study, ≈52% of the test substance was recovered from the rubber septa, ≈29% recovered from soil plus inner glass walls, and the remaining ≈3.5% was recovered from the headspace in sterile controls. The gradual decrease of the test substance in soil and increase in the rubber septum of the sterile control indicated that the septum was a preferred phase for partitioning when there was no microbial activity. The treated live soil samples had a mass balance of ≈67 – 88% from day 1 to 180, showing a slow decline of recovery over time. The declining overall mass balance in live soil is indicative of some metabolites irreversibly bound to soil and non-extractable with organic solvent plus alkaline treatment that may not be available for further biodegradation.

At day 180, the major terminal metabolites were PFPeA, [F(CF2)4COOH, 30%], PFHxA (8%), PFBA [F(CF2)3COOH, 2%], and 5-3 acid (15%). A new metabolite 4-3 acid [F(CF2)4CH2CH2COOH] accounted for 1%, the test substance for 3%, and 5-2 sFTOH for 7%.

Test substance biodegradation in the aerobic soil was rapid with an estimated half-life of 1.6 days assuming first-order kinetics. After an initial sharp decline, the test substance concentration gradually levelled off after 28 days at ≈3.5 – 6.2% of the total mass applied at day 0. This would be equal to 93.8- 96.5% primary degradation by day 28. Metabolite levels reached steady-state at 120 days.

Applicant's summary and conclusion

Conclusions:
93.8- 96.5% primary degradation by day 28
Executive summary:

Test substance biodegradation was evaluated at 2.9 µg/mL for 180 days in aerobic soil . Test vessels were 120-mL glass serum bottles sealed with natural rubber septa and the vessels were incubated statically in dark at 20 – 25 °C. The replicate test and control vessels were extracted and analysed at 0, 2, 7, 14, 28, 60, 90, 120 and 180 days for the test substance and metabolites.  

Biodegradation in the aerobic soil was rapid with an estimated half-life of 1.6 days assuming first-order kinetics. After an initial sharp decline, the test substance concentration gradually levelled off after 28 days at ≈3.5 – 6.2% of the total mass applied at day 0. This would be equal to 93.8- 96.5% primary degradation by day 28. Metabolite levels reached steady-state at 120 days.