Registration Dossier

Environmental fate & pathways

Biodegradation in soil

Currently viewing:

Administrative data

Endpoint:
biodegradation in soil: simulation testing
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study

Data source

Reference
Reference Type:
publication
Title:
Fate of PAH compounds in two soil types: influence of volatilization, abiotic loss and biological activity.
Author:
Park KS, Sims RC, Dupont RR, Doucette WJ, Matthews JE
Year:
1990
Bibliographic source:
Environ. Toxicol. Chem., 9, 187-195

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
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 material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
aromatic compounds:
(Commercial sources of single substances: Aldrich , Foxboro, and Sigma)

Initial soil concentrations [mg/kg]
Kidman loam McLaurin soil
(No. #1) (No. #2)
===================================
Naphthalene 101 101
1-Methylnaph. 102 106
Phenanthrene 902 893
Anthracene 210 199
Fluoranthene 883 913
Pyrene 686 697
===================================

(Note: Other 4- and 5-ring PAHs were also examined, but are not shown here, as they are not relevant for Anthracene oil <50 ppm BaP:)
Radiolabelling:
no

Study design

Oxygen conditions:
aerobic
Soil classification:
not specified
Soil propertiesopen allclose all
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 x10^6 bacterial CF/g soil; 1.9 x10^4 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 x10^5 bacterial CF/g soil; 5.3 x10^4 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)
Duration of test (contact time)open allclose all
Soil No.:
#1
Duration:
196 d
Soil No.:
#2
Duration:
105 d
Parameter followed for biodegradation estimation:
test mat. analysis
Experimental conditionsopen allclose all
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:
40 g of non-acclimated soil (dry weight), two types, and for 14 compounds were each placed in 500-ml glass beakers
capped with PE-film to limit water loss.
Following one week of incubation, PAHs were added individually in dichloromethane solution.
After evaporation of the solvent (24 h), water moisture was adjusted, and incubation started.

MOISTURE:
>=60 % of water holding capacityEach incubation was carried out in triplicate.
All flasks were kept in the dark to prevent photodegradation.
INCUBATION TEMPERATURE: 20 °C.

SAMPLING SCHEDULE:
0, 42, 84, 140, and 196 d (Kidman soil)
0, 35, 70, and 105 d (McLaurin soil)
0, 14, 28, and 56 d (phenanthrene and 7,12-dimethylbenzanthracene)
Number of replicates: Triplicate for each soil type and PAH

Results and discussion

Half-life / dissipation time of parent compoundopen allclose all
Soil No.:
#1
DT50:
134 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance anthracene; 95% CI: 106-182 d
Soil No.:
#1
DT50:
16 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance phenanthrene; 95% CI: 13-18 d
Soil No.:
#1
DT50:
377 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance fluoranthene; 95% CI: 277-578d
Soil No.:
#1
DT50:
260 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance pyrene; 95% CI: 193-408 d
Soil No.:
#2
DT50:
50 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance anthracene; 95% CI: 42-61 d
Soil No.:
#2
DT50:
35 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance phenanthrene; 95% CI: 27-53 d
Soil No.:
#2
DT50:
268 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: substance fluoranthene; 95% CI: 173-630d
Soil No.:
#2
DT50:
199 d
Type:
(pseudo-)first order (= half-life)
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:
yes
Volatile metabolites:
not measured
Residues:
not measured

Any other information on results incl. tables

Abiotic removal [%]

    

Kilman sandy loam

(No. #1)

McLaurin sandy loam

(No. #2)

Naphthalene

12.0

14.1

1-Methylnaphthalene

12.3

1.8

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 2- and 3-ring compounds.

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

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

    

Kilman sandy loam

McLaurin sandy loam

Naphthalene

2.1 [1.7-2.7]

2.2 [1.7-3.4]

1-Methylnaphthalene

1.7 [1.4-2.1]

2.2 [1.6-3.2]

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 resulting in first order rate constants and half-lives gave r2 values ranging from 0.71-0.95 and 0.57-0.93 for the Kidman and McLaurin soils, respectively.

Applicant's summary and conclusion

Conclusions:
The soil half-lives and the corresponding degradation rate constants 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 very 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.