Xylene

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, near guideline study, published in peer reviewed literature, acceptable with restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 304 A (Inherent Biodegradability in Soil)

Deviations:

yes

Remarks:

only one soil type tested, higher test substance concentration than recommended, variation in apparatus, different type of control

GLP compliance:

no

Test type:

laboratory

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
Data not reported

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

other: sandy loam

Details on soil characteristics:

Freshly collected from a lawn area of the New Jersey Agricultural Experiment Station, New Brunswick. The soil had no history of hydrocarbon exposure. Natural pH of 5.5-6 was raised to pH 7 by addition of CaCO3 at least five days prior to testing. Soil sieved to 2 mm size before use.

Soil No.:

#1

Duration:

28 d

Soil No.:

#1

Initial conc.:

3 other: µL/g soil

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on experimental conditions:

Sealed aerobic system at 28°C. Three replicates per test concentration. 50 g (dry weight) soil samples were incubated in 1 litre flasks closed with teflon lined screw caps. Two syringe needles were inserted through cap. The long needle was closed with a stopper and attached to its lower end was a glass vial containing 10 mL of 0.5 N KOH. This KOH was periodically withdrawn by syringe and replaced. The withdrawn KOH was used for counting trapped 14C02. The short syringe needle was connected by a three way valve to an oxygen reservoir and a port used to sample the flask headspace for solvent vapours. 150 µL test substance added to semi dry soil and then water added to bring soil to 60% holding capacity. Abiotic soil (autoclaved) was included as a control.

Soil No.:

#1

% Recovery:

94

Soil No.:

#1

% Degr.:

50

Parameter:

CO2 evolution

Sampling time:

23 d

Soil No.:

#1

DT50:

4 d

Type:

not specified

Remarks on result:

other: loss of test substance from soil based on analysis of flask headspace vapours (read from graph)

Transformation products:

not measured

Details on transformation products:

Not discussed, but authors note lag between 50% loss of substance from soil and 50% 14CO2 evolution.

Evaporation of parent compound:

yes

Volatile metabolites:

no

Residues:

yes

Details on results:

After 4 weeks incorpation into biomass was ~3% and incorporation into soil humus ~30% (read from graph). In abiotic controls only a negligible amounts of test substance were lost to sampling process and no measurable 14CO2 was evolved. Cumulatively over the course of the experiment 2-3% of the radiolabelled test substance dissolved in the KOH trap without prior conversion to 14CO2. Corrections were not made for this.

Results with reference substance:

Not applicable

N/A

Conclusions:

50% of applied radiolabelled o-xylene was mineralised in 23 days.

Executive summary:

This study was selected as the key study as it approximates OECD 304A. There are several differences between the protocol followed and the standard guidelines. Only one soil type is tested and the concentration of test substance is higher than recommended (150 µL/50g soil compared to 100 µL/50g soil). The control test used autoclaved soil, rather than no soil. Despite these differences the study is well described and the mass balance of applied test substance is 94%. This study demonstrates that o-xylene is degraded in soil.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1998

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, near guideline study, published in peer reviewed literature, acceptable with restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 304 A (Inherent Biodegradability in Soil)

Deviations:

yes

Remarks:

only one soil type tested, higher test substance concentration than recommended, variation in apparatus, different type of control

GLP compliance:

no

Test type:

laboratory

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material:
Not applicable

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

other: sandy loam

Details on soil characteristics:

Freshly collected from a lawn area of the New Jersey Agricultural Experiment Station, New Brunswick. The soil had no history of hydrocarbon exposure. Natural pH of 5.5-6 was raised to pH 7 by addition of CaCO3 at least five days prior to testing. Soil sieved to 2 mm size before use

Soil No.:

#1

Duration:

28 d

Soil No.:

#1

Initial conc.:

3 other: µL/g soil

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on experimental conditions:

Sealed aerobic system at 28°C. Three replicates per test concentration. 50 g (dry weight) soil samples were incubated in 1 litre flasks closed with teflon lined screw caps. Two syringe needles were inserted through cap. The long needle was closed with a stopper and attached to its lower end was a glass vial containing 10 mL of 0.5N KOH. This KOH was periodically withdrawn by syringe and replaced. The withdrawn KOH was used for counting trapped 14C02. The short syringe needle was connected by a three way valve to an oxygen reservoir and a port used to sample the flask headspace for solvent vapours. 150 µL test substance added to semi dry soil and then water added to bring soil to 60% holding capacity. Abiotic soil (autoclaved) was included as a control.

Soil No.:

#1

% Recovery:

90

Soil No.:

#1

% Degr.:

50

Parameter:

CO2 evolution

Sampling time:

13 d

Soil No.:

#1

DT50:

7 d

Type:

not specified

Remarks on result:

other: loss of test substance from soil based on analysis of flask headspace vapours approx 7 days (read from graph)

Transformation products:

not specified

Details on transformation products:

Not discussed, but authors note lag between 50% loss of substance from soil and 50% 14CO2 evolution.

Evaporation of parent compound:

yes

Volatile metabolites:

no

Residues:

yes

Details on results:

After 4 weeks incorpation into biomass was ~3% and incorporation into soil humus ~12% (read from graph). In abiotic controls only a negligible amounts of test substance were lost to sampling process and no measurable 14CO2 was evolved. Cumulatively over the course of the experiment 2-3% of the radiolabelled test substance dissolved in the KOH trap without prior conversion to 14CO2. Corrections were not made for this.

Results with reference substance:

Not applicable

N/A

Conclusions:

50% of applied radiolabelled p-xylene was mineralised in 13 days.

Executive summary:

This study was selected as the key study as it approximates OECD 304A. There are several differences between the protocol followed and the standard guidelines. Only one soil type is tested and the concentration of test substance is higher than recommended (150 µL/50 g soil compared to 100 µL/50 g soil) although the amount of radioactivity applied is within the recommendation levels. The control test used autoclaved soil, rather than no soil. Despite these differences the study is well described and the mass balance of applied test substance is ~90%. This study demonstrates that p-xylene is degraded in soil.

Description of key information

50% of applied radiolabelled o-xylene was mineralised in 23 days and 50% p-xylene was mineralised in 13 days.

Key value for chemical safety assessment

Half-life in soil:

23 d

Additional information

A study that approximates OECD 304A was identified for o-xylene and p-xylene (Tsao et al. 1998). There are several differences between the protocol followed and the standard guidelines. Only one soil type is tested and the concentration of test substance is higher than recommended (150 µL/50 g soil compared to 100 µL/50 g soil). The control test used autoclaved soil, rather than no soil. Despite these differences the study is well described and the mass balance of applied test substance is ~90 to 94%. This study demonstrated that 50% of the o-xylene and p-xylene applied to soil was mineralised to carbon dioxide in 23 and 13 days, respectively.