Registration Dossier

Diss Factsheets

Environmental fate & pathways

Biodegradation in soil

Currently viewing:

Administrative data

Link to relevant study record(s)

Referenceopen allclose all

Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Principles of method if other than guideline:
Static soil microcosm incubation test according to the general principles of OECD guideline 307: based on measurement of residual unaltered compounds, no mineralisation test.
GLP compliance:
no
Test type:
laboratory
Specific details on test material used for the study:
14 PAH were tested in this study ranging from naphthalene to indeno[1,2,3-cd]pyrene (two- to six-ring PAH). Four compounds among them are relevant as constituents of anthacene oil (AOL). These are covered in this study record.

The following polycyclic aromatic compounds are relevant constituent of anthracene oil. They were purchased from Aldrich Chemical Co. Inc., Milwaukee, WI, USA.

Initial soil concentrations [mg/kg]
Kidman loam McLaurin soil
(No. #1) (No. #2)
==============================================
Phenanthrene 902 893
Anthracene 210 199
Fluoranthene 883 913
Pyrene 686 697
==============================================

(Note: Other 2- to 6-ring PAHs were also examined, but are not shown here, as they are not relevant for anthracene oil. These substances are naphthalene, 1-methylnaphthalene, chrysene, benz[a]anthracene, 7,12-dimethylbenzanthracene, benzo[b]fluoranthene, benzo[a]pyrene, dibenz[a,h]anthracene, indeno[1,2,3-cd]pyrene, and dibenzo[a,i]pyrene.)
Radiolabelling:
no
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
sandy loam
% Org. C:
0.5
pH:
7.9
CEC:
10.1 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy loam
% Org. C:
1.1
pH:
4.8
CEC:
4.4 meq/100 g soil d.w.
Details on soil characteristics:
SOIL SAMPLES:
Two types of non-acclimated soil were used:
No. #1: Kidman sandy loam (Calciaquoll/Utah) and
No. #2: McLaurin sandy loam (Paleudult/Mississippi)
Soil of the top 15-cm zone was used.

SOIL PROPERTIES of top 15-cm zone:
- #1: Kidman sandy loam (Calciaquoll/Utah)
Microbial colonisation: 6.7 x 10E6 bacterial CF/g soil; 1.9 x 10E4 fungal CF/g soil (CF = colony forming units)
Electrical conductivity (EC): 0.2 dS/m
Moisture: 16.3 %
- #2: McLaurin sandy loam (Paleudult/Mississippi)
Microbial colonisation: 1.1 x 10E5 bacterial CF/g soil; 5.3 x 10E4 fungal CF/g soil (CF = colony forming units)
Electrical conductivity (EC): 0.09 dS/m
Moisture: 12.4 %
- Pesticide use history at the collection sites: no data
- Collection procedures: no data
- Sampling depth (cm): Soil of the top 15-cm zone was used.
- Storage conditions: no data
- Storage length: no data
- Soil preparation: Air dried, 2 mm sieved

(CF = colony forming units)
Soil No.:
#1
Duration:
196 d
Soil No.:
#2
Duration:
105 d
Soil No.:
#1
Initial conc.:
902 mg/kg soil d.w.
Based on:
test mat.
Remarks:
phenanthrene
Soil No.:
#1
Initial conc.:
210 mg/kg soil d.w.
Based on:
test mat.
Remarks:
anthracene
Soil No.:
#1
Initial conc.:
883 mg/kg soil d.w.
Based on:
test mat.
Remarks:
fluoranthene
Soil No.:
#1
Initial conc.:
686 mg/kg soil d.w.
Based on:
test mat.
Remarks:
pyrene
Soil No.:
#2
Initial conc.:
893 mg/kg soil d.w.
Based on:
test mat.
Remarks:
phenanthrene
Soil No.:
#2
Initial conc.:
199 mg/kg soil d.w.
Based on:
test mat.
Remarks:
anthracene
Soil No.:
#2
Initial conc.:
913 mg/kg soil d.w.
Based on:
test mat.
Remarks:
fluoranthene
Soil No.:
#2
Initial conc.:
697 mg/kg soil d.w.
Based on:
test mat.
Remarks:
pyrene
Parameter followed for biodegradation estimation:
test mat. analysis
Soil No.:
#1
Temp.:
20 °C
Humidity:
>= 60 % of water holding capacity
Soil No.:
#2
Temp.:
20 °C
Humidity:
>= 60 % of water holding capacity
Details on experimental conditions:
STATIC SOIL INCUBATION TEST

EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): one week, temperature not specified
- Soil condition: dry, non-acclimated
- Soil (g/replicate): 40
- No. of replication controls: 1 (abiotic controls - reactors treated with 2% solution of mercuric chloride)
- No. of replication treatments: 3
- Test apparatus (Type/material/volume): 500 mL glass beakers
- If no traps were used, is the system closed/open: beakers were covered with polyethylene film

Test material application
- Application method (e.g. applied on surface, homogeneous mixing etc.): test materials dissolved in dichloromethane were mixed with the soil
- Is the co-solvent evaporated: yes, for 24 h
- Soil conditions: after evaporation of the solvent, water was added to adjust soil moisture to -33 J/kg matric potential (>= 60 % water holding capacity)

Experimental conditions
- Incubation temperature: 20 °C
- Moisture maintenance method: periodic addition of water
- Continuous darkness: Yes

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Method used to create the aerobic conditions: the polyethylene film covers of the test vessels (beakers) are permeable to oxygen

4. SAMPLING DETAILS
- Sampling scedule: soil # 1: 0, 42, 84, 140, and 196 d
soil # 2: 0, 25, 70, and 105 d
both soils: 0, 14, 28, and 56 d (phenanthrene and 7,12-dimethylbenzanthracene)
- Sampling method for soil samples: complete test vessels were used for analysis
- Method of collection of CO2 and volatile organic compounds: not measured (release of volatiles was determined in a pretest over 48 h)
Key result
Soil No.:
#1
DT50:
16 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance phenanthrene; 95% CI: 13-18 d
Key result
Soil No.:
#1
DT50:
134 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance anthracene; 95% CI: 106-182 d
Key result
Soil No.:
#1
DT50:
377 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance fluoranthene; 95% CI: 277-578 d
Key result
Soil No.:
#1
DT50:
260 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance pyrene; 95% CI: 193-408 d
Key result
Soil No.:
#2
DT50:
35 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance phenanthrene; 95% CI: 27-53 d
Key result
Soil No.:
#2
DT50:
50 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance anthracene; 95% CI: 42-61 d
Key result
Soil No.:
#2
DT50:
268 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance fluoranthene; 95% CI: 173-630 d
Key result
Soil No.:
#2
DT50:
199 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance pyrene; 95% CI: 131-408 d
Transformation products:
not measured
Details on transformation products:
no data
Evaporation of parent compound:
no
Volatile metabolites:
not measured
Residues:
yes
Remarks:
residual test substance

Abiotic removal [%]

    

Kilman sandy loam

(No. #1)

McLaurin sandy loam

(No. #2)

Anthracene

8.7

7.9

Phenanthrene

17.4

14.2

Fluoranthene

0

3.1

Pyrene

4.4

3.2

Statistical analysis indicated that abiotic degradation was significant for 3-ring compounds as well as for 2-ring compounds (data not shown except for anthracene and phenanthrene).

The losses were statistically insignificant for those PAH that contained more than 3 rings.

Half-lives of biodegradation [days] in brackets: 95-% Confidence Intervals

    

Kilman sandy loam

McLaurin sandy loam

Anthracene

134 [106-182]

50 [42-61]

Phenanthrene

16 [13-18]

35 [27-53]

Fluoranthene

377 [277-578]

268 [173-630]

Pyrene

260 [193-408]

199 [131-408]

The estimated amount biologically degraded was

= mass added – (volatilised mass + abiotic loss of mass + mass of soil residue).

The measured biological degradation rates of PAHs were not statistically different between the two soils studied. The kinetic calculations for the four compounds under consideration resulting in first order rate constants and half-lives gave r² values ranging from 0.71 to 0.95 and 0.58 to 0.93 for the Kidman and McLaurin soils, respectively.

Conclusions:
The soil half-lives and the corresponding degradation rate constants, determined in two different soils, can be considered to be acceptable estimates for two- to three ringed PAHs. For the four- and five ringed PAHs, the half-lives estimated were longer than the study duration, which indicates that these values are quite uncertain (confirmed by large confidence intervals for many of these PAHs). Due to the nature of these recalcitrant PAHs the values presented must be considered to be best available estimates. Half-lives of relevant PAH constituents of anthracene oil (AOL), (phenanthrene, anthracene, fluoranthene, pyrene) range from 16 and 35 days for phenanthrene to 377 and 268 days for fluoranthene (soil #1 and soil #2, respectively).
Endpoint:
biodegradation in soil: simulation testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Justification for type of information:
REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
The source test materials are individual polycyclic aromatic hydrocarbons ranging from two- to six-ring PAH. Depending on size/molecular weight and state of condensation, physico-chemical and environmental properties can be different. The target substance anthracene oil (benzo[a]pyrene < 50 ppm, AOL) is as well composed of a broad range of PAH consisting of two to four aromatic rings.
The potential for biodegradation of anthracene oil in soil will be characterised by the range of PAH that constitute its composition. Some of the source substances are major constituents of anthracene oil. Therefore, results obtained from biodegradation studies in soil with these compounds can be used in order to characterise the soil biodegradation potential of anthracene oil.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source chemicals are individual PAH. These include major constituents of anthracene oil. The specific analytical purity of individual chemicals is not reported in the publication. But they are obtained from commercial sources (Aldrich Chemical Co. Inc.), and they are considered to be of adequate purity for the purpose of the study. Tests have been performed with individual PAH and the test results reported relate to the individual test substances.
The target material anthracene oil (AOL) is a UVCB substance produced by the distillation of coal tars extracting the approximate distillation range from ca. 300 °C to 400 °C. This distillation range excludes mostly low molecular aromatic hydrocarbons (especially one-ring and to a lower extent two-ring aromatics) as well as polycyclic aromatic hydrocarbons composed of more than four to five rings depending on the respective boiling points of the individual aromatic substances. Major constituents are three- and four-ring aromatics from acenaphthene to pyrene.

3. ANALOGUE APPROACH JUSTIFICATION
Properties of the target substance anthracene oil regarding behaviour and fate in the environment will be determined by the properties of the PAH that are constituents of anthracene oil. Under environmental conditions or during processing of the target substance, environmentally available or volatile/water soluble components of anthracene oil can be released. These will be three- and four-ring PAH (see above). They will be distributed in the environment and may also undergo biodegradation in soil.
Four of these PAH (two three-ring and two four-ring PAH) are included within the set of source substances. Biodegradation properties of these PAH in soil considered together will be specific for the environmental behaviour of anthracene oil. Therefore, it is justified to use date determined for individual PAH that are constituents of anthracene oil to characterise the environmental behaviour (biodegradation in soil) of anthracene oil itself.
Reason / purpose for cross-reference:
read-across source
Principles of method if other than guideline:
Read-across to preceding entry:
Source test material: polycyclic aromatic hydrocarbons (PAH), generic mixture;
Reference: Park et al. 1990
Key result
Soil No.:
#1
DT50:
16 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance phenanthrene; 95% CI: 13-18 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#1
DT50:
134 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance anthracene; 95% CI: 106-182 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#1
DT50:
377 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance fluoranthene; 95% CI: 277-578 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#1
DT50:
260 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance pyrene; 95% CI: 193-408 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#2
DT50:
35 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance phenanthrene; 95% CI: 27-53 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#2
DT50:
50 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance anthracene; 95% CI: 42-61 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#2
DT50:
268 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance fluoranthene; 95% CI: 173-630 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Key result
Soil No.:
#2
DT50:
199 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: substance pyrene; 95% CI: 131-408 d
Remarks:
the test result of the source substance is adopted as weight of evidence for the target substance anthracene oil
Transformation products:
not measured

The soil half-lives determined in this study and the corresponding degradation rate constants can be considered to be acceptable estimates for two- to three-ring PAHs. For the four- and five-ring PAHs, the half-lives estimated were longer than the study duration, which indicates that these values are very uncertain. This can also be seen in that the confidence intervals for many of these PAHs are very large. But due to the nature of these recalcitrant PAHs the values presented must be considered to be best available estimates.

 

(Note: The results do not represent ultimate degradation and mineralisation. But they indicate that PAH in soil undergo primary ring oxidation, the most important reaction which is considered the rate-limiting step.

 

Key components of anthracene oil examined in this study are anthracene, phenanthrene (tree-ring PAH), fluoranthene and pyrene (four-ring PAH). The primary biodegradation rates of these compounds in non-acclimated soil are listed in the following table. Values are extracted from Tables 5 and 6 of the publication cited under Reference:

 

 

Rate constant (-k)
[1/day]

95% C.I. (lower / upper limit)
[1/day]

 

Soil #1

Soil #2

Soil #1

Soil #2

Anthracene

0.0052

0.0138

0.0065 / 0.0038

0.0164 / 0.0113

Phenanthrene

0.0447

0.0196

0.0514 / 0.0380

0.0259 / 0.0132

Fluoranthene

0.0018

0.0026

0.0025 / 0.0012

0.0040 / 0.0011

Pyrene

0.0027

0.0025

0.0036 / 0.0017

0.0053 / 0.0017

 

The most resistant PAHs of the spectrum shown above, fluoranthene and pyrene, are supposed to be eliminated from soil at a rate of approx. 0.2 %/day, while anthracene and phenanthrene may disappear at a somewhat higher rate (ca. 0.5 to 1.3 and 2.0 to 4.4 %/day, respectively).

 

Conclusions:
In a study similar to OECD TG 307 (Aerobic and Anaerobic Transformation in Soil), the aerobic degradation rates and resulting half-lives of 14 PAH were investigated in two different soils. Four of these PAH (phenanthrene, anthracene, fluoranthene, and pyrene) are major constituents of anthracene oil. Half-lives were determined to be 16 and 35 days (phenanthrene), 134 and 50 days (anthracene), 377 and 268 days (fluoranthene), and 260 and 199 days (pyrene).
The test results of the source substances (range of half-lives from 16 (phenanthrene) to 377 (fluoranthene) days) are adopted as weight of evidence for the target substance anthracenen oil.

Description of key information

Biodegradation half-lives of PAH in soil have been investigated in a study similar to OECD TG 309. Half-lives increased with increasing size of PAH. Four of the substances examined are constituents of anthracene oil. Half-lives determined in two different soils ranged from 16 days to 377 days. The 90th percentile value is selected as key value for the chemical safety assessment.

Key value for chemical safety assessment

Half-life in soil:
300 d
at the temperature of:
20 °C

Additional information

Anthracene oil is a liquid to pasty UVCB substance mainly consisting of three- and four-ring polycyclic aromatic compounds. Major constituents are fluorene, phenanthrene, anthracene, and fluoranthene with typical concentrations between about 7 and 28 %. Acenaphthene and pyrene are minor constituents contributing ca. 3 and 4 %. Biodegradation studies in soil (simulation tests) for anthracene oil itself are not available.

Due to the complex composition of anthracene oil, a distinct half-life in soil for the substance as a whole cannot be experimentally determined. Main components (all PAH) will have their individual half-lives and in combination can be used to specify a soil biodegradation half-life of anthracene oil.

Experimental results for individual PAH (Park et al. 1990) show that soil biodegradation half-lives of PAH increase with growing molecular size and ring-number. Four PAH that are constituents of anthracene oil were used in this study, two PAH with three fused aromatic rings (phenanthrene and anthracene) and two PAH comprising four-ring aromatic systems (fluoranthene and pyrene). Biodegradation of test materials was investigated in two different soils.

For components of anthracene oil, half-lives between 16 and 377 days were determined. Phenanthrene was best biodegraded in the two different soils with half-lives of 16 and 35 days. Anthracene was more persistent with half-lives of 134 and 50 days. For the two four-ring PAH, half-lives were found to range from 199 to 377 days (pyrene: 260 and 199 days; fluoranthene: 377 and 268 days). The values for the four-ring PAH bear some uncertainties, as the duration of the tests was shorter than the half-lives determined. But presently, they are best available half-life estimates of these substances and will be used in the assessment of anthracene oil.

The study results clearly indicate that soil biodegradation half-lives of substantial components of anthracene oil have values above 120 and 180 days, respectively (persistent/very persistent criteria of REACH regulation). In order to specify a value for the total of anthracene oil used as key value in the chemical safety assessment, the 90th percentile of the eight half-lives determined for the individual components of AOL is used (half-life 300 days, calculated using the QUANTIL.INKL function in MS Excel 2013). This approach takes into account that anthracene oil is composed of a large number of different individual compounds and that the fraction of four-ring PAH is only approx. 10 %.