Registration Dossier

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
Data waiving:
other justification
Justification for data waiving:
other:
Endpoint:
biodegradation in soil
Type of information:
experimental study
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
Principles of method if other than guideline:
Soil treatment: The soils were passed through a 2 mm sieve and stored at 5 ºC prior to use. Each undried soil equivalent to 40 g on a dry weight basis was taken into a 100 mL beaker, moistened to 40% of maximum water-holding capacity and incubated for a week at 25 ºC in the dark. After preincubation, methanol solution of 14C-BHT (50 µL) was added to each soil and mixed thoroughly to give a concentration of 1 ppm. Each of these soil samples was placed in a 3-liter glass jar covered with aluminium foil and kept at 25 ± 2 ºC. Each jar was continuously purged with CO2-free air at 100 mL/h and the effluent air was passed serially through a polyurethane foam plug and gas-washing bottles containing 400 mL of 0.5N NaOH solution to trap volatile 14C including 14CO2. For sterilized condition, moist soil samples were autoclaved at 20 psi and 120 ºC and then treated with 1 ppm of 14C-BHT.

At specified intervals, each polyurethane plug was removed and eluted three times with 30 mL of methanol. Each of the soil samples was extracted with 180 mL of ethyl acetate-1N HCl (2/1). The soil residue separated by centrifugation at 3000 rpm for 10 minutes was further extracted with 200 mL of methanol-1N HCl (3/1) by refluxing for 1 hour. An aliquot of each combined extracts was radioassayed by LSC while the remaining portions were evaporated to ca. 2 mL at 30 ºC for TLC analysis.
GLP compliance:
no
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
not specified
Year:
1979
Soil no.:
#1
Soil type:
other: light clay
% Clay:
29
% Silt:
40
% Sand:
31
% Org. C:
15.3
pH:
5.5
CEC:
53.7 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy clay loam
% Clay:
17
% Silt:
18
% Sand:
65
% Org. C:
2.5
pH:
6.3
CEC:
13.5 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
sandy loam
% Clay:
2
% Silt:
3
% Sand:
95
% Org. C:
2.7
pH:
7
CEC:
9.6 meq/100 g soil d.w.
Soil No.:
#1
Duration:
24 d
Soil No.:
#2
Duration:
24 d
Soil No.:
#3
Duration:
24 d
Soil No.:
#1
Initial conc.:
1 ppm
Based on:
not specified
Soil No.:
#2
Initial conc.:
1 ppm
Based on:
not specified
Soil No.:
#3
Initial conc.:
1 ppm
Based on:
not specified
Parameter followed for biodegradation estimation:
CO2 evolution
Details on experimental conditions:
Soil treatment: The soils were passed through a 2 mm sieve and stored at 5 ºC prior to use. Each undried soil equivalent to 40 g on a dry weight basis was taken into a 100 ml beaker, moistened to 40% of maximum water-holding capacity and incubated for a week at 25 ºC in the dark. After preincubation, methanol solution of 14C-BHT (50 µl) was added to each soil and mixed thoroughly to give a concentration of 1 ppm. Each of these soil samples was placed in a 3-liter glass jar covered with aluminium foil and kept at 25 ± 2 ºC. Each jar was continuously purged with CO2-free air at 100 ml/h and the effluent air was passed serially through a polyurethane foam plug and gas-washing bottles containing 400 ml of 0.5N NaOH solution to trap volatile 14C including 14CO2. For sterilized condition, moist soil samples were autoclaved at 20 psi and 120 ºC and then treated with 1 ppm of 14C-BHT.

At specified intervals, each polyurethane plug was removed and eluted three times with 30 ml of methanol. Each of the soil samples was extracted with 180 ml of ethyl acetate-1N HCl (2/1). The soil residue separated by centrifugation at 3000 rpm for 10 minutes was further extracted with 200 ml of methanol-1N HCl (3/1) by refluxing for 1 hour. An aliquot of each combined extracts was radioassayed by LSC while the remaining portions were evaporated to ca. 2 ml at 30 ºC for TLC analysis.
Key result
% Degr.:
63 - 82
Parameter:
radiochem. meas.
Sampling time:
1 d
Key result
% Degr.:
> 77 - 92
Parameter:
radiochem. meas.
Sampling time:
24 d
Transformation products:
yes
No.:
#1
No.:
#2
Details on transformation products:
The findings suggest that BHT was altered to non-volatile products mainly by biological factors in nonsterilised soils soon after treatment and further degraded to 14CO2 via several intermediates. In soils, more than 10 degradation products were present, among which, five products were identified. Of these products, BHT-OOH and BHT-OH were major components under nonsterilised condition and other products oxidised at 4-methyl group such as BHT-CH2OH, BHT-CHO and BHT-COOH were found in minor amounts. These products were also detected in sterilised condition.

- Description of biotransformation pathway: Fig II - Attached document

Evaporation of parent compound:
yes
Volatile metabolites:
yes
Residues:
yes

BHT was quite unstable in soils and approximately 20% of the applied BHT was degraded immediately after treatment while recovery of 14C ranged from 90 to 100%.

In non-sterilized condition, BHT was degraded promptly to leave only 11 to 16% one day after treatment. After 24 days, BHT decreased to 5% or less. No significant difference was observed between the soils tested. Accompanied with the decrease of 14C in soils, the amounts of 14C in polyurethane plugs and alkaline solutions gradually increased and reached to 5-14 and 21-29% in 24 days, respectively.

Even under sterilised condition, degradation of BHT proceeded, although much more slowly. One day after treatment, about half of the applied BHT remained in soil and gradually degraded afterwards; the 14C trapped in polyurethane plugs rapidly increased with time and accounted for 40 to 50% of the applied in 24 days, whereas 14C in alkaline solutions was less than 2% during the same period. A large portion of 14C in polyurethane traps proved to be intact BHT and the 14C in alkaline solutions was considered to be 14CO2 since more than 95% of the radioactivity was precipitated as Ba14CO3.

Conclusions:
BHT, as well as its degradation products, is quite biodegradable and hardly persists in the soil environment.
Executive summary:

According to the results obtained, BHT is relatively unstable in the three soils tested: With non sterilized soils about 63-82 % of BHT were decomposed after one day (about 1-2 % mineralized to CO2) and 77-92 % (21-29 % mineralized) after 24 days of incubation. Under sterilized conditions 25-35 % BHT were decomposed after one day and 27-41 % after 24 days, mineralization was negligible ( 2 %). After one day 57-68 % of BHT and after 24 days 50-61 % remained unchanged. Under non-sterilized conditions the amount of total volatile 14C was 26 to 42 % (21 to 29 % 14CO2).Under sterilized conditions the amount of volatile 14C was 43 to 56 % after 24 days ( 2 % 14CO2). From these results it can be concluded that BHT is altered to nonvolatile products mainly by biological processes. In soil more than 10 degradation products were found. As major decomposition products BHT-OOH and BHT-OH were identified

Description of key information

A soil simulation test (OECD 307) is currently on-going and will be submitted later based on ECHA decision number CCH-D-2114346399-37-01/F

Key value for chemical safety assessment

Additional information

According to the results obtained, BHT is relatively unstable in the three soils tested: With non sterilized soils about 63-82 % of BHT were decomposed after one day (about 1-2 % mineralized to CO2) and 77-92 % (21-29 % mineralized) after 24 days of incubation. Under sterilized conditions 25-35 % BHT were decomposed after one day and 27-41 % after 24 days, mineralization was negligible ( 2 %). After one day 57-68 % of BHT and after 24 days 50-61 % remained unchanged. Under non-sterilized conditions the amount of total volatile14Cwas 26 to 42 % (21 to 29 %14CO2).Under sterilized conditions the amount of volatile14Cwas 43 to 56 % after 24 days ( 2 %14CO2). From these results it can be concluded that BHT is altered to nonvolatile products mainly by biological processes. In soil more than 10 degradation products were found. As major decomposition products BHT-OOH and BHT-OH were identified