Trichloroethylene

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published in peer reviewed literature, notable limitations in design and/or reporting, but adequate for assessment

Principles of method if other than guideline:

Degradation of trichloroetylene was tested in contaminated and uncontaminated soil materials under aerobic conditions in soil in which toluene was added as a co-substrate

GLP compliance:

not specified

Test type:

not specified

Oxygen conditions:

aerobic

Soil classification:

other: contaminated and uncontaminated soil materials

Duration:

220 h

Initial conc.:

1 other: microgram/ml

Based on:

test mat.

Remarks on result:

not measured/tested

Transformation products:

not measured

Details on results:

Substantial trichloroethylene degradation only occurred in the uncontaminated sample after 220 hours and trichloroethylene did not degrade at all in the absence of toluene. The results indicated that mineral nutrients limited the rate of trichloroethylene and toluene degradation by indigenous populations.

The potential for microbial communities in contaminated and uncontaminated soil materials to aerobically degrade trichloroethylene and toluene was measured. The biodegradation of trichloroethylene (1mg/l) and toluene (20mg/l) was measured in samples of material from contaminated and uncontaminated sites. Substantial trichloroethylene degradation only occurred in the uncontaminated sample after 220 hours and trichloroethylene did not degrade at all in the absence of toluene. The results indicated that mineral nutrients limited the rate of trichloroethylene and toluene degradation by indigenous populations.

Reference 2

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published in peer reviewed literature, notable limitations in design and/or reporting, but adequate for assessment

Principles of method if other than guideline:

Static microcosms were constructed with a low carbon content, field-contaminated soil containing 18.1 µmol/kg ww trichloroethylene. Incubation at 20 C resulted in reductive dechlorination under sulfate-reducing conditions.

GLP compliance:

not specified

Test type:

laboratory

Radiolabelling:

no

Oxygen conditions:

anaerobic

Soil classification:

other: natural soil

Soil no.:

#1

% Clay:

25

% Silt:

70

% Sand:

5

% Org. C:

0.17

pH:

8.1

Details on soil characteristics:

A contaminated soil sample was obtained from a photocopier refurbishing facility in New York State (USA). The soil samples were collected from a depth of 0.6-1.8 m in mid 1990 and stored in sealed, amber glass jars with minimum headspace at 4 C in the dark

Soil No.:

#1

Duration:

332 d

Soil No.:

#1

Initial conc.:

18.1 other: µmol/kg ww

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

Soil No.:

#1

Temp.:

20 oC

Key result

DT50:

61.3 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Transformation products:

yes

No.:

#1

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

no

Incubation of trichloroethylene with a contaminated soil was carried out at 20 °C. Reductive dechlorination of trichloroethylene was observed under both sulphate-reducing and methanogenic conditions. Low levels of vinyl chloride were produced.

Reference 3

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published in peer reviewed literature, notable limitations in design and/or reporting, but adequate for assessment

Principles of method if other than guideline:

Trichloroethylene (200-300 microgram/l) was incubated in the presence of methane with a mixed soil culture.

GLP compliance:

not specified

Test type:

not specified

Soil classification:

other: mixed soil culture

Duration:

30 d

Initial conc.:

ca. 250 other: microgram/l

Based on:

test mat.

Key result

% Degr.:

90

Parameter:

not specified

Sampling time:

8 d

Key result

% Degr.:

100

Parameter:

not specified

Sampling time:

30 d

Transformation products:

not measured

Trichloroethylene (200-300 microgram/l) was incubated in the presence of methane with a mixed soil culture. After 8 days, 10% of trichloroethylene remained; after 30 days, 100% of the trichloroethylene was degraded.

Description of key information

Within a weight of evidence approach it was concluded that as well in soil, biotransformation seems to occur more readily under anaerobic conditions under specific conditions like co-substrates.

Additional information

Various information is available for TCE investigating the biodegradation in soil under certain conditions. It can be deduced from available data that degradation is more pronounced under anaerobic conditions and in the presence of co-substates.

However, trichloroethylene can also be degraded also under aerobic conditions by a process of co-oxidation when other suitable co-substrates (e.g. methane or toluene) are also present to support growth of the microorganisms and induce the formation of enzymes which due to their broad substrate specificity, can also degrade trichloroethylene.

There is extensive work which shows that under anaerobic conditions, trichloroethylene degrades by a process of reductive dehalogenation, resulting in the formation of lower chlorinated homologues as reaction products. Although metabolites are known to occur, the terminal product of reductive dehalogenation is ethylene.