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Environmental fate & pathways

Biodegradation in soil

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Reference
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:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
according to guideline
Guideline:
other: See Principles of method
Principles of method if other than guideline:
14C labelled TEL was used so that conversion from nonionic to ionic forms could easily be determined and evolution of CO2 from the mineralisation of TEL could be measured.

14C TEL and analytical grade TEL samples dissolved in n-hexane were added to fine sand/soil samples then wrapped in aluminium foil to reduce photodecomposition. Solvent extraction of the soil samples was undertaken, at periodic intervals and the remaining TEL / 14C TEL quantified by liquid scintillation counting of CO2 evolution from carbon 14 TEL treated soil over a total period of 28 days
GLP compliance:
not specified
Test type:
laboratory
Radiolabelling:
yes
Soil classification:
other: Arrendondo fine sand (loamy, siliceous, hyperthermic grossarenic paleudult
Year:
1994
Soil no.:
#1
Soil type:
sand
% Clay:
1
% Silt:
7
% Sand:
92
% Org. C:
11.8
pH:
5.5
Soil no.:
#2
Soil type:
sand
% Clay:
2
% Silt:
5
% Sand:
93
% Org. C:
4.7
pH:
4.6
Soil no.:
#3
Soil type:
sand
% Clay:
3
% Silt:
4
% Sand:
93
% Org. C:
3.9
pH:
5.6
Details on soil characteristics:
Arredondo fine sand (grossarenic paleudult)
Soil No.:
#1
Duration:
28 d
Soil No.:
#2
Duration:
28 d
Soil No.:
#3
Duration:
28 d
Soil No.:
#1
Initial conc.:
1 000 ppm
Based on:
test mat.
Soil No.:
#2
Initial conc.:
1 000 ppm
Based on:
test mat.
Soil No.:
#3
Initial conc.:
1 000 ppm
Based on:
test mat.
Soil No.:
#1
Temp.:
25°C
Soil No.:
#2
Temp.:
25°C
Soil No.:
#3
Temp.:
25°C
Soil No.:
#1
% Degr.:
50
Parameter:
radiochem. meas.
Sampling time:
2 h
Soil No.:
#2
% Degr.:
50
Parameter:
radiochem. meas.
Sampling time:
1.5 h
Soil No.:
#3
% Degr.:
50
Parameter:
radiochem. meas.
Sampling time:
2 h
Soil No.:
#1
DT50:
2 h
Temp.:
25 °C
Soil No.:
#2
DT50:
1.5 h
Temp.:
25 °C
Soil No.:
#3
DT50:
2 h
Temp.:
25 °C
Transformation products:
not measured

These studies report that the time required for 50% disappearance of14C-TEL in three layers of nonsterile soil samples was 2, 1.5 and 2 hr, respectively. The time required for 50% disappearance of14C-TEL in corresponding sterile samples was 14, 7 and 8 hr, respectively.

Furthermore the time required for 50% disappearance of nonionic14C plus ionic14C degradation products in the three layers of nonsterile samples was 14, 7 and 8 hr, respectively compared to 17, 12 and 12 hr for corresponding layers of sterile samples.

After 28 days TEL was completely degraded to ionic forms and unidentified volatile products.

Further analysis of14C levels in the sterile and non sterile soil samples suggests that, in addition to chemical degradation, biological degradation also plays a role in the transformation of TEL to ionic TREL and DEL.

Conclusions:
A 50% reduction in 14C TEL concentration occurred within 2 hours in non-sterile soils and within 14 hours in sterile soils.  After 28 days incubation no 14C TEL could be detected in the soil.    
Executive summary:

An investigation into the biological and chemical transformation rate of TEL in surface and sub-surface soils has been carried out by Ou and co-workers( L-T Ou, J.E. Thomas and W. Jing.: Biological and Chemical Degradation of Tetraethyl Lead in Soil, Bull. Environ. Contam. Toxicol.52, (1994), 238 - 245. ) using14C labelled TEL. 

These studies report that the time required for 50% disappearance of14C-TEL in three layers of nonsterile soil samples was 2, 1.5 and 2 hr, respectively. The time required for 50% disappearance of14C-TEL in corresponding sterile samples was 14, 7 and 8 hr, respectively.

Furthermore the time required for 50% disappearance of nonionic14C plus ionic14C degradation products in the three layers of nonsterile samples was 14, 7 and 8 hr, respectively compared to 17, 12 and 12 hr for corresponding layers of sterile samples.

After 28 days TEL was completely degraded to ionic forms and unidentified volatile products.

Further analysis of14C levels in the sterile and non sterile soil samples suggests that, in addition to chemical degradation, biological degradation also plays a role in the transformation of TEL to ionic TREL and DEL. The use of autoclaving for soil sterilization alters soil physical and chemical characteristics. Therefore, chemical degradation rates of TEL in nonsterile and autoclaved soils may not be the same. However, biological degradation certainly contributed to the disappearance of TEL in soil in these tests. Mineralization of TEL did occur in nonsterile soil.

The fact that, after 28 d of incubation, no TEL could be detected in the soil and considerable amounts of ionic ethyllead species were present suggests that TEL is less persistent in soil than its degradation products, ionic ethyllead species. This finding is in agreement with the fate of tetraalkyllead compounds and ionic alkyllead species in water, where ionic lead species are considerably more stable than tetraalkyllead compounds (Radojevic and Harrison, 1987b)

Description of key information

A 50% reduction in 14C TEL concentration occurred within 2 hours in non-sterile soils and within 14 hours in sterile soils.  After 28 days incubation no 14C TEL could be detected in the soil.    

Key value for chemical safety assessment

Half-life in soil:
2 h
at the temperature of:
25 °C

Additional information

An investigation into the biological and chemical transformation rate of TEL in surface and sub-surface soils has been carried out by Ou and co-workers using14C labelled TEL.(Ou et al 1994)

These studies report that the time required for 50% disappearance of14C-TEL in three layers of nonsterile soil samples was 2, 1.5 and 2 hr, respectively. The time required for 50% disappearance of14C-TEL in corresponding sterile samples was 14, 7 and 8 hr, respectively.

Furthermore the time required for 50% disappearance of nonionic14C plus ionic14C degradation products in the three layers of nonsterile samples was 14, 7 and 8 hr, respectively compared to 17, 12 and 12 hr for corresponding layers of sterile samples.

After 28 days TEL was completely degraded to ionic forms and unidentified volatile products.

Further analysis of14C levels in the sterile and non sterile soil samples suggests that, in addition to chemical degradation, biological degradation also plays a role in the transformation of TEL to ionic TREL and DEL.The use of autoclaving for soil sterilization alters soil physical and chemical characteristics. Therefore, chemical degradation rates of TEL in nonsterile and autoclaved soils may not be the same. However, biological degradation certainly contributed to the disappearance of TEL in soil in these tests. Mineralization of TEL did occur in nonsterile soil.

The fact that, after 28 d of incubation, no TEL could be detected in the soil and considerable amounts of ionic ethyllead species were present suggests that TEL is less persistent in soil than its degradation products, ionic ethyllead species. This finding is in agreement with the fate of tetraalkyllead compounds and ionic alkyllead species in water, where ionic lead species are considerably more stable than tetraalkyllead compounds (Radojevic and Harrison, 1987b)