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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil: simulation testing
Data waiving:
exposure considerations
Justification for data waiving:
the study does not need to be conducted because direct and indirect exposure of soil is unlikely
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: Studies reviewed in EU RAR
Principles of method if other than guideline:
Degredation in soil
GLP compliance:
not specified
Test type:
not specified
Radiolabelling:
yes
Oxygen conditions:
not specified
Soil classification:
not specified
Details on soil characteristics:
Donberg used a variety of surface soils, Wenzhong isolated bacteria from nitrile-polluted soils.
Details on experimental conditions:
See below
DT50:
6 d
Type:
other: Over 50% of radioactivity was recovered as CO2 after 6 days
Remarks on result:
other: Donberg et al (1991; 1992)
Transformation products:
not specified
Details on transformation products:
No information available
Details on results:
See below
Results with reference substance:
No applicable

Donberg et al. (1991; 1992) showed, in a study investigating the biodegradation of [14C]-acrylonitrile in a variety of surface soils, that concentrations of up to 100 ppm were degraded in under 2 days. Over 50% of radioactivity was recovered as CO2 after 6 days, with transient formation of acrylamide and acrylic acid. Higher concentrations (500 and 1,000 ppm) were degraded only slowly, and this correlates with experimental evidence that these levels inhibit respiration of soil microbes, with gradual acclimation.

Wenzhong et al. (1991) isolated 2 strains of bacterium, Corynebacterium hoffmanii and Arthrobacter flavescens, from nitrile-polluted soils. Aqueous cultures of these bacteria were able to degrade 5g/l acrylonitrile. There is also evidence (Giacin et al., 1973) that acrylonitrilebutadiene-methyl methacrylate polymers and acrylic fibres can be slowly broken down by soil fungi (Penicillium, Bacillus, Aspergillus, Cladosporium). Similar breakdown by microbial populations present in sediments is likely. Overall significant accumulation in the soil or sediment compartments is not anticipated.

Executive summary:

Donberg et al. (1991; 1992) showed, in a study investigating the biodegradation of [14C]-acrylonitrile in a variety of surface soils, that concentrations of up to 100 ppm were degraded in under 2 days. Over 50% of radioactivity was recovered as CO2 after 6 days, with transient formation of acrylamide and acrylic acid. Higher concentrations (500 and 1,000 ppm) were degraded only slowly, and this correlates with experimental evidence that these levels inhibit respiration of soil microbes, with gradual acclimation.

Wenzhong et al. (1991) isolated 2 strains of bacterium, Corynebacterium hoffmanii and Arthrobacter flavescens, from nitrile-polluted soils. Aqueous cultures of these bacteria were able to degrade 5g/l acrylonitrile. There is also evidence (Giacin et al., 1973) that acrylonitrilebutadiene-methyl methacrylate polymers and acrylic fibres can be slowly broken down by soil fungi (Penicillium, Bacillus, Aspergillus, Cladosporium). Similar breakdown by microbial populations present in sediments is likely. Overall significant accumulation in the soil or sediment compartments is not anticipated.

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:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Published study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Biodegredation of acrylonitrile in 3 different types of soil
GLP compliance:
no
Remarks:
published study
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
sand
% Clay:
4
% Silt:
10
% Sand:
86
% Org. C:
0.53
pH:
5.4
CEC:
1.4 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy loam
% Clay:
14
% Silt:
20
% Sand:
66
% Org. C:
2.6
pH:
7.2
CEC:
9.2 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
other: Loamy clay
% Clay:
30
% Silt:
20
% Sand:
50
% Org. C:
4
pH:
7.3
CEC:
16.4 meq/100 g soil d.w.
Details on soil characteristics:
Three different soil types were collected representing sand (soil 1), sandy loam (soil 2) and loamy clay (soil 3). Sandy soil and loamy clay (classified in the Tappan series) were collected in Bay County Michigan. A second loam (classified in the Londo series) was collected from a noncultivated agricultural site at the DowElanco Agricultural Farm in Midland, Michigan. Surface soil samples were collected by first clearing the upper 2-5 cm of leaf debris and vegetation and then sampling the next 30 cm of the soil horizon with a clean shovel. The soil was sieved (2 mm) and stored in sealed polyethylene-lined cardboard containers at 4°C until used (soils were not stored not longer than 1 year).
Duration:
21 d
Initial conc.:
10 - 1 000 ppm
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on experimental conditions:
Aerobic biodegradation of acrylonitrile was examined in batch soil microcosms. Reaction mixtures containing 30 g (dry weight) of soil and 30 ml deionised water in sterile 160 ml glass serum bottles. In selected experiments deionised water was replaced with 26.5 ml of mineral salts base media. Bottles were purged with oxygen gas for 10 minutes before the addition of the test chemical to ensure maintenance of aerobic conditions throughout the incubation period. Preliminary calculations indicated that the amount of oxygen present in the microcosms was in excess of the oxygen demand over the tested range of acrylonitrile concentrations. The headspace of soil microcosms was periodically checked for the presence of oxygen by injecting samples of the gas phase into prereduced anaerobic media containing resazurin as the indicator. The reaction mixtures were amended with [14C]acrylonitrile at concentrations ranging from 10 to 1000 ppm (w/w) by the addition of 20 to 200 µl of an aqueous stock solution. The specific activity of the substrate in the stock solution was adjusted for each experiment by diluting the labelled material with unlabelled acrylonitrile. Approximately 1x10exp6 to 1x10exp7 dpm was added to each microcosm. For comparison, separate reaction mixtures were amended with 50 µl of [14C]glucose aqueous stock solution for a final concentration of 2.5 ppm. Following the addition of the substrate, the serum bottles were immediately sealed with Teflon faced silicon rubber septa and aluminium crimp seals. All bottles were incubated in the dark at 25°C with continuous mixing at 1 rpm on a tissue culture rotator. Biologically inhibited or killed controls were included to monitor for non-biological loss of the the test chemical. Control microcosms were prepared as above, except that the soil was autoclaveed and the samples were adjusted to contain 2000 ppm mercuric chloride.
DT50:
6 d
Type:
other: Over 50% of the radioactivity was recovered as [14C]CO2 after 6 d of incubation
Temp.:
25 °C
Transformation products:
yes
Details on transformation products:
The unknown products resulting from the biodegredation of acrylonitrile were tentatively identified as acrylamide and acrylic acid, based on comparison of the HPLC retention times with known standards.
Details on results:
Acrylonitrile was readily degraded in microcosms prepared with soil 2 (sandy loam), complete degradation of acrylonitrile (50 ppm) as noted after 2 d and resulted in the transient formation of two unknown intermediates. Following 6 d, approximately 60% of the original radioactivity was recovered as 14CO2. Acrylonitrile was biologically mediated, as >80% of the parent compound was recovered from control microcosms after 7 d of incubation.
The biodegradation of acrylonitrile at 50 ppm varied among the three soil types. The compound was completely degraded in soil 2 (sandy loam), and soil 3 (loamy clay) in < 2 d. In contrast, a 14-d lag phase was noted before acrylonitrile degredation in soil 1 (sand). Although rates were slower, over 87% of the parent compound was degraded in the saned after 22 d incubation. Negligible loss of acrylonitrile was noted in controls over the same period. Acyrylonitrile was rapidly converted to 14CO2 in soils 2 and 3. Greater than 50% of the parent compound was recovered as 14CO2 after 6 d. Mineralisation in sand was slower, as 19 d was required for 50% mineralisation of the parent compound.
Acrylonitrile concentrations ranging from 10 to 100 ppm were rapidly degraded in < 2 d in both soils 2 and 3.

Organic carbon content of the soils ranged from 0.53 to 4.0%.

Conclusions:
Acrylonitrile was rapidly degraded in sandy loam and loamy clay soil.
Executive summary:

The aerobic biodegradation of [14C]acrylonitrile at concentrations ranging from 10 to 1000 ppm was examined in three types of surface soil. At concentrations up to 100 ppm, complete degradation of the compound occurred in < 2 d in sandy loam soil. Greater than 50% of the radioactivity was recovered as [14C]carbon dioxide following 6 d of incubation. Because the soil had no known previous exposure to acrylonitrile, dissimilation did not appear to require acclimation of the microorganisms. Transient formation of acrylamide and acrylic acid as intermediates of degradation was also observed. Similar results were obtained in studies conducted with loamy clay (10, 50, 100 ppm) and sand (10 and 50 ppm). Acclimation of the microorganisms was required before degradation of 100 ppm acrylonitrile in sand. Degradation of higher concentrations (500 and 1000 ppm in sandy loam) was relatively slow and was thought to be due to inhibitory effects of the parent compound.

Description of key information

Overall significant accumulation in the soil or sediment compartments is not anticipated due to the rapid biodegradation of low levels of acrylonitrile by bacterial strains including Corynebacterium hoffmanii and Arthrobacter flavescens.

Key value for chemical safety assessment

Half-life in soil:
6 d

Additional information

The EU RAR reports a study investigating the biodegradation of [14C]- acrylonitrile in a variety of surface soils, in which concentrations of up to 100 ppm were degraded in under 2 days. Over 50% of radioactivity was recovered as CO2 after 6 days, with the transient formation of acrylamide and acrylic acid. Higher concentrations (500 and 1000 ppm) were degraded only slowly, and this correlates with experimental evidence that these levels inhibit respiration of soil microbes, with gradual acclimation. Wenzhong et al (1991) isolated 2 strains of bacterium, Corynebacterium hoffmanii and Arthrobacter flavescens, from nitrile-polluted soils. Aqueous cultures of these bacteria were able to degrade 5g/l acrylonitrile. Similar breakdown by microbial populations present in sediments is likely. Overall significant accumulation in the soil or sediment compartments is not anticipated.