Tar bases, coal, lutidine fraction

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:

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:

Surface and subsurface soils were collected from two locations. Soils at one site were already exposed to pyridine derivatives, whereas soils at the other site were not contaminated. The soils were incubated under aerobic or anaerobic conditions in sealed bottles. A mixture containing 10 mL of appropriate medium and 20 mg substrate per L was inoculated with 1 g (dry weight) soil and kept at 28 °C for 12 weeks. Periodically, 0.5 mL samples were removed and the amount of substrate remaining was determined by analysis with HPLC.

GLP compliance:

no

Test type:

laboratory

Radiolabelling:

no

Oxygen conditions:

aerobic/anaerobic

Details on soil characteristics:

Transformation of the pyridine derivatives was studied with four soil types, surface and subsurface soils with prior or no prior exposure to pyridine derivatives.
Soils with prior exposure to pyridine derivatives came from a chemical plant in Indianapolis. The already exposed surface soil consisted of a brown humus soil type. The subsurface soil was sampled from a depth of 10 m and consisted of granular black, sandy material.
All collected soil samples were stored in airtight containers which were flushed with nitrogen in order to preserve anaerobic microorganisms.
Non-exposed soils were received from the Savannah River plant in South Carolina. The unpolluted surface soil consisted of a fine brown, organic rich sandy material. The subsurface soil was obtained from a depth of 35 m and consisted of white, clay-rich medium to coarse sand.

Soil No.:

#1

Duration:

12 wk

Soil No.:

#2

Duration:

12 wk

Soil No.:

#3

Duration:

12 wk

Soil No.:

#4

Duration:

12 wk

Soil No.:

#1

Initial conc.:

20 other: mg/L

Based on:

test mat.

Soil No.:

#2

Initial conc.:

20 other: mg/L

Based on:

test mat.

Soil No.:

#3

Initial conc.:

20 other: mg/L

Based on:

test mat.

Soil No.:

#4

Initial conc.:

20 other: mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

Details on experimental conditions:

Different culture medium containing selected salts was used for the tests under aerobic or anaerobic conditions.
AEROBIC CONDITIONS: NH4Cl at 0.54 g/L, MgCl2.6H2O at 0.41 g/L, CaCl2.2H2O at 0.07 g/L, NaCl at 1.17 g/L and KCl at 0.18 g/L. The salt solution was acidified with 0.6 mL 2 M HCl/L and then autoclaved and cooled. The medium was then supplemented with sterile stock solutions per L of medium at: 20 mL 300 mM potassium phosphate (pH 7.0), 0.5 mL trace elements, 1 mL vitamins, 2.5 mL 100 mM sulfide and 30-50 mg pyridine derivatives.
ANAEROBIC CONDITIONS: A similar medium was used, but NaS04 at 2.84 g/L was added instead of NaCl. Following autoclaving, the medium was cooled down under an oxygen-free gas phase and then supplemented with sterile stock solutions per L of medium at: 20 mL 300 mM potassium phosphate (pH 7.0), 0.5 mL trace elements and 1 mL vitamins. Nitrogen was passed through the solutions to completely replace oxygen and the medium was amended with 2.5 mL 100 mM sulfide, 10 mg sodium dithionite and 30-50 mg pyridine derivatives.
GROWTH OF MICRO-ORGANISMS UNDER DENITRIFYING CONDITIONS: a salt medium containing 0.87 g/L K2HPO4, 0.54 g/L KH2PO4 and 0.3 g/L KNO3 was used. The medium was autoclaved and cooled down under an oxygen-free gas phase. Supplementation with sterile stock solutions per L medium was performed: 2 mL 400 mM MgSO4.7 H2O, 0.5 mL trace elements, 1 mL vitamins, 2.5 mL 100 mM sulfide, 10 mg sodium dithionite and 30-50 mg pyridine derivatives.

Transformation products:

not measured

Details on results:

AEROBIC, NON-ADOPTED SOILS: In the experiments with suspended surface soil, pyridine and 2-methylpyridine were completely degraded within 2 weeks; 4-methylpyridine and 2,6-dimethylpyridine were completely degraded within 1-3 months; 3-methylpyridine, 2,4- and 3,4-dimethylpyridine and 2,4,6-trimethylpyridine were only partially degraded during the 3-months exposure period.
In the experiments with suspended subsurface soil, pyridine showed no significant degradation; degradation of methylated pyridines was in the range from 20-40%.

ANAEROBIC, NON-ADAPTED SOILS:
Under denitrifying conditions, the surface soil degraded ca. 50% of the added 3- and 4-methylpyridine. Removal of the other methylated pyridines was in the range from 10-30%. Under sulfate-reducing conditions, 3,4-lutidine was removed by 35%, whereas removal of the other methylated pyridines ranged from 10-20%.
Degradation by the subsurface soil was further reduced under anaerobic conditions. Only 4-methylpyridine was notably degraded bby ca 35% when nitrate served as an electron acceptor. Under sulfate-reducing conditions, a few methylated pyridines were partially degraded by the subsurface soil.

AEROBIC, POLLUTED SOILS:
Under aerobic conditions, all tested pyridine derivatives were degraded after 2 weeks by the contaminated surface and subsurface soils.

ANAEROBIC, POLLUTED SOILS:
Pyridine was completely removed within a month when incubated with either soil under denitrifying conditions and under sulfate-reducing conditions with surface soild, and within 3 months under sulfate-reducing conditions with subsurface soil. The lutidines were removed between 20-70% under sulfate-reducing and denitrifying conditions with both types of soil. Significant difference occurred in the removal of the different methylpyridines: under sulfate-reducing conditions, the subsurface soil degraded 3- and 4-methylpyridine completely and 2-methylpyridine by 30%. The surface soil degraded 4-methylpyridine by 90% and 2- and 3-methylpyridine by 20-30%. Under denitrifying conditions, subsurface soil removed 60-65% of 3- and 4-methylpyridine, whereas surface soil degraded only 2- and 4-picoline by about 20-30% and did not degrade 3-picoline.

Conclusions:

In a well-documented study conducted to acceptable scientific standards, it was demonstrated that pyridine and various methylated pyridine derivatives were degraded to various degrees by soil micro-organisms. Biodegradation of the tested compounds was generally faster and more efficient under aerobic conditions, and soils that had already been exposed to pyridine derivatives achieved higher degradation rates compared to uncontaminated soils.

Executive summary:

The potential of four different soils to degrade a range of pyridine derivatives under aerobic and anaerobic conditions was investigated. Surface and subsurface samples of two soils were taken at two different locations. While one location had been exposed to pyridine derivatives over several decades, the other location had not been exposed to these substances. The different test substances were incubated over a period of three months at a temperature of 28 °C. All tests were performed in sealed bottles (13 mL volume) at an initial concentration of 20 mg/L with 1 g soil (dry weight) per litre in nutrient medium under aerobic or anaerobic (both sulfate-reducing and denitrifying) conditions.

Under aerobic conditions, there was little difference in the observed metabolic potential of the uncontaminated surface or subsurface soils. Pyridine was more rapidly removed than the methylated pyridine derivatives. Under anaerobic conditions, none of the methylated peridine derivatives was completely removed during the 3 months of incubation. All pyridine derivatives were completely degraded within 2 weeks by the contaminated soils under aerobic conditions. Under anaerobic conditions, longer exposure durations were required to remove the test substances. In the presence of sulfate, 3- and 4 -methylpyridine were degraded completely within three months. On the other hand, the dimethyl- and trimethylpyridines were only partially removed during the incubation of 3 months.

Overall, the study demonstrated that methylated pyridine derivatives are biodegraded to various degrees by soil micro-organisms, depending on the environmental conditions, with highest degradation rates occurring under aerobic conditions.

Reference 2

Endpoint:

biodegradation in soil, other

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:

The approach involved the incubation of soil with a pyridine derivative (2 mmol/kg) in 100-mL glass vials at 25 °C for 0 to 64 days. Replicate experimental systems were prepared by adding 1.1 mL water and 0.1 mL of a pyridine derivative solution to an incubation vessel and then adding 10 g of soil (Fincastle silt loam (Aeric Ochraqualfs)) carefully to maintain the soil structure (final soil moisture was -0.03 MPa).
Each test solution contained 200 mmol/kg of a pyridine derivative dissolved in water and ethanol (2:1, v/v). The test vessels were plugged with polyurethane stoppers. At regular intervals, water was added to adjust for loss of 0.3 to 0.4 g of water. After 0, 1, 2, 4, 8, 16, 32 and 64 days, the foam stopper and soil from replicate containers were extracted separately and analysed. If required, samples were stored at -20 °C for a few days prior to extraction. To assess the effect of storage on the nitrogen content and recovery of pyridine derivatives, a second set of replicate samples was taken at 0 days of incubation and stored at -20 °C for the duration of the experiment before analysis.

GLP compliance:

no

Test type:

laboratory

Radiolabelling:

no

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

other: Aeric Ochraqualfs (Fincastle silt loam)

% Org. C:

1.2

pH:

6.7

CEC:

0.15 other: mol (+)/kg

Details on soil characteristics:

The soil was a Fincastle silt loam (Aeric Ochraqualfs) with a water pH of 6.7 (1:2 soil-water ratio), organic carbon content of 1.2%, total nitrogen content of 1300 mg/kg, CEC of 0.15 mol (+)/kg. The soil contained 0.25 kg water per kg soil (dry weight) at -0.03 MPa.

Soil No.:

#1

Duration:

64 d

Soil No.:

#1

Initial conc.:

2 other: mmol/kg

Based on:

test mat.

Parameter followed for biodegradation estimation:

test mat. analysis

other: inorganic nitrogen analysis

Details on experimental conditions:

Preliminary tests were conducted to evaluate the extraction efficiency with 2 M KCl, 0.01 M HCl, and 2 M KCl + 0.01 M HCl. The extractant 2 M KCl + 0.01 M HCl was selected because it extracted most of each of the tested pyridine derivatives.
At 32 and 64 days of incubation, foam plugs from tests containing volatile pyridines were extracted 3 times with 30 mL of 2 M KCl + 0.01 M HCl. These extracts were diluted to 100 mL with KCl + HCl, and the pyridine derivatives were determined spectrophotometrically. Preliminary experiments showed that the foam stoppers retained between 89 and 100% of the substances volatilised from solutions.
The KCl + HCl soil extract (20 mL) was adjusted to pH 7 with 2 M NaOH and steam distilled to recover NH4+; NO2-, and NO-. Nitrogen was measured by Nesslerisation rather than titrimetry as the volatile pyridine derivatives interferred with the latter procedure. An extract-soil ratio of 4:1 (w/v) was used to get optimal recovery and detection of test substances, which were expected to be degraded to low concentrations. This low ratio resulted in incomplete recovery of NH4+ from soil samples. The recovery of NH4+ was determined by amending soil samples with 0 to 42 mg NH4+-N/kg followed by KCl + HCl extraction. These data were then used to calculate a recovery used for correction of NH4+ concentrations. Inorganic nitrogen was measured on days 0, 16, 32 and 64.

Transformation products:

not specified

Evaporation of parent compound:

yes

Residues:

no

Details on results:

All the tested methylpyridines were degraded rapidly in soil under the conditions of the experiment. In the tested soil, all methylpyridines, including 2-, 3- and 4-methylpyridine and 2,4- and 2,6-dimethylpyridine, were degraded in 32 days. Volatilisation loss of all pyridine derivatives from soil was small over a period of 64 days, amounting to only 5% or less of the added amounts.

Conclusions:

In a well-documented study conducted to acceptable scientific standards, it was demonstrated that a number of methyl- and dimethylpyridines degraded within 32 days in a non-adapted soil under aerobic conditions.

Executive summary:

The fate of a range of methly- and dimethylpyridines in soil (Aeric Ochraqualfs) was studied by measuring the quantity of test substance remaining and the inorganic nitrogen released as a result of degradation for a period of 64 days. Each substance was added to soil at a concentration of 2 mmol/kg and incubated at 25 °C. Compounds studied included 2-, 3- and 4-methylpyridine and 2,4- and 2,6-dimethylpyridine. During the 64 days of incubation, extractability of the pyridine derivatives with 2 M KCl + 0.01 M HCl decreased from on average 88 ± 8.8% to essentially zero for all test substances. All methyl- and dimethylpyridines degraded completely in 8 to 32 days. Volatilisation loss from soil was small, amounting to only 5% or less of the amount added to the test vessels.

Description of key information

The biodegradation of methylated pyridine derivatives in soil was examined in a number of studies, including different types of non-adopted and adopted soils. Degradation experiments were conducted under aerobic and anaerobic conditions in the laboratory. Methyl- and dimethylpyridines generally were degraded within 32 days of incubation under aerobic conditions, whereas slower and in some cases only partial degradation of these substances was observed under anaerobic conditions. Based on a weight-of-evidence, the substance can be considered as degradable in soil under relevant environmental conditions, and it is expected to be non-persistent in soil.

However, the quality of the available public data is insufficient to derive reliable half-lives in soil that could be used for the assessment of the environmental persistence.