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Biodegradation in soil

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Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
Aerobic batch laboratory microcosm experiments using different soils to determine the loss rate of o-cresol
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
no
Oxygen conditions:
aerobic
Soil classification:
other: natural soils
Soil no.:
#1
Soil type:
other: Typic Paleudults
% Clay:
8.6
% Silt:
23.4
% Sand:
68
% Org. C:
0.94
pH:
4.8
CEC:
6.4 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
Mollisol
% Clay:
7.4
% Silt:
31.1
% Sand:
61.5
% Org. C:
3.25
pH:
7.8
CEC:
10.8 meq/100 g soil d.w.
Details on soil characteristics:
Texture of soil no.1 is a sandy loam; Texture of soil no. 2 is a sandy silt loam
Soil No.:
#1
Duration:
64 d
Soil No.:
#2
Duration:
64 d
Soil No.:
#1
Initial conc.:
120 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
130 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Soil No.:
#1
Temp.:
20°C
Humidity:
80% of field capacity
Soil No.:
#2
Temp.:
20°C
Humidity:
80% of field capacity
Soil No.:
#1
DT50:
11.3 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r²=0.97
Soil No.:
#2
DT50:
0.6 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r²=0.87
Transformation products:
not measured

The recovery efficiencies for m-cresol of the soils were 81% and 88%. The chemical concentrations were corrected by the recovery efficiencies.

Executive summary:

The degradation behaviour of m-cresol was investigated by Loehr & Matthews (1992) in two different soils. The first soil (acidic) was a sandy loam with an organic carbon content of 0.94%. The second was a sandy silt loam with an organic carbon content of 3.25%. The loadings of the soils and the degradation were monitored by an HPLC method. Maintained in the dark at 20°C, m-cresol degraded with half-live times of 0.6 d for the sandy loam and 11.3 d for the sandy silt loam.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
Aerobic batch laboratory microcosm experiments using different soils to determine the loss rate of o-cresol
GLP compliance:
not specified
Test type:
laboratory
Oxygen conditions:
aerobic
Soil classification:
other: natural soils
Soil no.:
#1
Soil type:
other: Typic Paleudults
% Clay:
8.6
% Silt:
23.4
% Sand:
68
% Org. C:
0.94
pH:
4.8
CEC:
6.4 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
Mollisol
% Clay:
7.4
% Silt:
31.1
% Sand:
61.5
% Org. C:
3.25
pH:
7.8
CEC:
10.8 meq/100 g soil d.w.
Details on soil characteristics:
Texture of soil no.1 is a sandy loam; Texture of soil no. 2 is a sandy silt loam
Soil No.:
#1
Duration:
64 d
Soil No.:
#2
Duration:
64 d
Soil No.:
#1
Initial conc.:
500 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
250 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Soil No.:
#1
Temp.:
20°C
Humidity:
80% of field capacity
Soil No.:
#2
Temp.:
20°C
Humidity:
80% of field capacity
Soil No.:
#1
DT50:
5.1 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r²=0.88
Soil No.:
#2
DT50:
1.6 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r²=0.83
Transformation products:
not measured
Details on transformation products:
no transformation products detected

The recovery efficiencies for o-cresol of the soils were 57% and 63%. The chemical concentrations were corrected by the recovery efficiencies.

Executive summary:

The degradation behaviour of o-cresol was investigated by Loehr & Matthews (1992) in two different soils. The first soil (acidic) was a sandy loam with an organic carbon content of 0.94%. The second was a sandy silt loam with an organic carbon content of 3.25%. The loadings of the soils and the degradation were monitored by an HPLC method. Maintained in the dark at 20°C, o-cresol degraded with half-live times of 1.6 d for the sandy loam and 5.1 d for the sandy silt loam.

Description of key information

Based on all the available information (weight-of-evidence) and following an analogue read-across approach there is evidence that Tar acids, Xylenol fraction (CAS 84989-06-0) has a low potential for accumulation in soil.

Key value for chemical safety assessment

Additional information

For biodegradation in soil data on two constituents of Tar acids, Xylenol fraction (CAS 84989-06-0) are available. Batch laboratory microcosm experiments using two different soils were conducted by Loehr & Matthews (1992) to determine the loss rate of o-cresol and m-cresol under aerobic conditions. The first soil (acidic) was a sandy loam with an organic carbon content of 0.94%. The second was a sandy silt loam with an organic carbon content of 3.25%. The loadings of the soils and the degradation were monitored by an HPLC method. Maintained in the dark at 20 °C, o-cresol degraded with half-live times of 1.6 d for the sandy loam and 5.1 d for the sandy silt loam. m-cresol degraded with half-live times of 0.6 d for the sandy loam and 11.3 d for the sandy silt loam.

In summary screening data on several constituents demonstrated ready biodegradability, among them the cresol isomers, some xylenol isomers and mixed ethylphenols. Other xylenol isomers are inherently biodegradable. In a test with a similar UVCB substance, i.e. Tar acids, 3,5-xylenol fraction, 39% degradation were observed after 28 days. Data on biodegradation in water and sediment are available for o- and p-cresol. Nevertheless, results of these investigations provide evidence that these constituents will be ultimately degraded under aerobic conditions with half-lives between 9.4 and 43 h for p-cresol in water and between 5.9 and 11 h in water/sediment systems. In so-called eco-cores, p-cresol degraded with half-lives between 3.0 and 16 h. Although no significant mineralization was observed under anaerobic conditions, this is not considered to be of concern, since due to ready biodegradation it is unlikely that cresols released into waste / surface waters will reach anaerobic zones. O-cresol was completely biodegraded within at least 4 weeks in freshwater sediment and studies on the metabolic pathway showed significant degradation after 24 hours with subsequent significant diminishment of metabolites.

Based on all the available information (weight-of-evidence) and following an analogue read-across approach there is evidence that Tar acids, Xylenol fraction (CAS 84989-06-0) has a low potential for accumulation in soil.