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Environmental fate & pathways

Biodegradation in soil

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Administrative data

Endpoint:
biodegradation in soil
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: well-documented publication, which meets basic scientific principles

Data source

Reference
Reference Type:
publication
Title:
Microbial Degradation Of Polyurethane Foams And Isocyanate Based Polyureas In Different Media
Author:
Martens, T. and Domsch, K.H.
Year:
1981
Bibliographic source:
Water, Air, and Soil Pollution 15 (1981) 503-509.

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
To assess the possibility of liberation of toxic aromatic amines under different conditions of disposal, the degradation of different 14C-labelled polyurethane foams was investigated in the leachate of a refuse tip, in composted municipal waste and in an agricultural soil.
Unlabelled foam cubes experiments were run under the environmental conditions of a refuse tip. The degradation of 14C-labelled polyureas was studied in different agricultural soils. In the laboratory tests the criteria of degradation were the liberation of aromatic amines and the production of 14CO2. The degradation in the refuse tip was estimated on the basis of weight loss.
GLP compliance:
not specified
Test type:
other: field trials and laboratory experiments

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Test material form:
liquid
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
No test surrogate or analogue material used.
Radiolabelling:
yes

Study design

Oxygen conditions:
aerobic
Soil classification:
not specified
Soil propertiesopen allclose all
Soil no.:
#1
Soil type:
other: Leachate from a refuse tip near Braunschweig
pH:
7.5
Soil no.:
#2
Soil type:
other: composted municipal waste from the city of Duisburg (water content 49 %)
pH:
7.2
Soil no.:
#3
Soil type:
other: soil (Para brown earth, water content 18 %)
% Org. C:
1.3
pH:
6.9
Soil no.:
#4
Soil type:
other: municipal refuse, sewage sludge and caustic lime (weight proportions 25 : 10 : 1) from an experimental refuse tip of the University of Braunschweig.
Soil no.:
#5
Soil type:
loamy sand
% Clay:
8.5
% Silt:
12.1
% Sand:
79.4
% Org. C:
3.2
pH:
6.6
Soil no.:
#6
Soil type:
sandy loam
% Clay:
5
% Silt:
32.6
% Sand:
62.4
% Org. C:
0.95
pH:
5.2
Soil no.:
#7
Soil type:
Chernozem
% Clay:
20.1
% Silt:
27.7
% Sand:
52.2
% Org. C:
2.58
pH:
6.9
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location:
Soil1#: Leachate from a refuse tip near Braunschweig (pH 7.5);
Soil2#: composted municipal waste from the city of Duisburg (water content 49 % pH 7.2);
Soil3#: soil (Para brown earth, water content 18 %, pH 6.9, organic C 1.3 %).

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm (%): soil 2#: 49 %, soil 3#: 18 %
Duration of test (contact time)open allclose all
Soil No.:
#1
Duration:
3 mo
Soil No.:
#2
Duration:
3 mo
Soil No.:
#3
Duration:
3 mo
Soil No.:
#4
Duration:
13 mo
Soil No.:
#5
Duration:
4 mo
Soil No.:
#6
Duration:
4 mo
Soil No.:
#7
Duration:
4 mo
Parameter followed for biodegradation estimation:
CO2 evolution
Experimental conditionsopen allclose all
Soil No.:
#1
Temp.:
22 +/- 1°C
Humidity:
100 mL of the leachte were mixed each with 1.0 g of one of the freely chopped foams (particle size 1-5mm) in 300 mL Erlenmeyer flasks. For absorption of evolved 14CO2, a glass tube was fitted to flask and filled with 10-18 g soda-lime (2-5 mm grain size).
Soil No.:
#2
Temp.:
22 +/- 1°C
Humidity:
50 g (dry weight basis) of composted waste were mixed each with 1.0 g of one of the freely chopped foams (particle size 1-5 mm) in 300 mL Erlenmeyer flasks.For absorption of evolved 14CO2, a glass tube was fitted to flask and filled with 10-18 g soda-lime
Soil No.:
#3
Temp.:
22 +/- 1°C
Humidity:
100 g (dry weight basis) of the soil were mixed each with 1.0 g of one of the freely chopped foams (particle size 1-5 mm) in 300 mL Erlenmeyer flasks. For absorption of evolved 14CO2, a glass tube was fitted to flask and filled with 10-18 g soda-lime.
Soil No.:
#5
Temp.:
22 +/- 1°C
Humidity:
After wetting the mixture (containg pulverized 14C-labelled polyurea) to a water content corresponding to 90 % of the water holding capacity of the soil, the flasks were sealed with the 14CO2 adsorption traps.
Soil No.:
#6
Temp.:
22 +/- 1°C
Humidity:
After wetting the mixture (containg pulverized 14C-labelled polyurea) to a water content corresponding to 90 % of the water holding capacity of the soil, the flasks were sealed with the 14CO2 adsorption traps.
Soil No.:
#7
Temp.:
22 +/- 1°C
Humidity:
After wetting the mixture (containg pulverized 14C-labelled polyurea) to a water content corresponding to 90 % of the water holding capacity of the soil, the flasks were sealed with the 14CO2 adsorption traps.
Details on experimental conditions:
STUDIES ON PUR-FOAMS UNDER LABORATORY CONDITIONS
Leachate from a refuse tip near Braunsehweig (pH 7.5); composted municipal waste from the city of Duisburg (water content 49 % pH 7.2); and soil (Para brown earth, water content 18 %, pH 6.9, organic C 1.3 %). 100 mL of the leachte, 50 g (dry weight basis) of the composted waste and 100 g (dry weight basis) of the soil were mixed each with 1.0 g of one of the freely chopped foams (particle size 1 to 5 mm) in 300 mL Erlenmeyer flasks.
For absorption of evolved 14CO2, a glass tube was fitted to each flask and filled with 10 to 18 g soda-lime (2 to 5 mm grain size). In order to prevent any volatile 14C-metabolites except 14CO2 from being trapped in the soda-lime, a glass-wool plug impregnated with paraffin oil was inserted between the latter and the contents of the flask. By this arrangement complete adsorption of the 14CO2 and also adequate aeration of the flask contents were achieved. The PER-foams were incubated for 3 month at 22 +/- 1 °C. Because of the possible occurrence of high temperature in sanitary fills, additional experiments were run at 50 °C for the media leachate and refuse compost. Each experiment was duplicated.

STUDIES ON PER-FOAMS UNDER ENVIRONMENTAL CONDITIONS
The degradation of TDI-based PER-foams (polyester and polyether type) under environmental conditions was investigated in an experimental refuse tip of the University of Brannschweig. The components, municipal refuse, sewage sludge and caustic lime (weight proportions 25:10:1) were deposited either in layers or after premixing. In both versions, three plastic gauze bags each containing four cubes of PER-foams (5 em square) were deposited at a depth of 50 to 60 cm. In the stratified filling, the plastic material was placed in the refuse layer. After 13 months, the tips were opened and the cubes of PER-foams were checked for weight loss after having been freed of foreign material.

STUDIES ON POLYUREAS UNDER LABORATORY CONDITIONS
To investigate the fate of polyurea compounds contaminating a soil after spillage of highly reactive isocyanates, three different air dried soils (see Table I) were mixed in 200 mL Erlenmeyer flasks with the pulverized 14C-labelled polyurea in a volume ratio 50:50 mL. The volume of 50 mL soil corresponded to 56.0 g of soil S, 51.0 g of soil SL and 59.8 g of Soil Ch. The volume of 50 mL polyurea was equivalent to 32.4 g of TDI-polyurea and 28.5 g of the MDI-polyurea. After wetting the mixture to a water content corresponding to 90 % of the water holding capacity of the soil, the flasks were sealed with the 14CO2 adsorption traps mentioned above and incubated for 4months at 22 +/- 1°C. Each experiment was duplicated.

2. EXPERIMENTAL DESIGN
- Soil condition: air dried
- Soil (g/replicate): 100 mL of the leachte, 50 g (dry weight basis) of the composted waste and 100 g (dry weight basis) of the soil or: the volume of 50 mL soil corresponded to 56.0 g of soil S (soil5#), 51.0 g of soil SL (soil 6#) and 59.8 g of Soil Ch (soil 7#)
- No. of replication treatments: 2
- Test apparatus (Type/material/volume): 300 mL Erlenmeyer flasks or 200 ml Erlenmeyer flasks
- Details of traps for CO2 and organic volatile, if any: For absorption of evolved 14CO2, a glass tube was fitted to each flask and filled with 10 to 18 g soda-lime (2 to 5 mm grain size). In order to prevent any volatile 14C-metabolites except 14CO2 from being trapped in the soda-lime, a glass-wool plug impregnated with paraffin oil was inserted between the latter and the contents of the flask. By this arrangement complete adsorption of the 14CO2 and also adequate aeration of the flask contents were achieved.

Test material application
- Volume of test solution used/treatment: 1.0 g of one of the freely chopped foams (particle size 1 to 5 mm) or pulverized 14C-labelled polyurea in a volume ratio 50:50 mL
- Application method (e.g. applied on surface, homogeneous mixing etc.): mixed

3. OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: In order to prevent any volatile 14C-metabolites except 14CO2 from being trapped in the soda-lime, a glass-wool plug impregnated with paraffin oil was inserted between the latter and the contents of the flask. By this arrangement complete adsorption of the 14CO2 and also adequate aeration of the flask contents were achieved.

5. SAMPLING DETAILS
- Method of collection of CO2 and volatile organic compounds: For absorption of evolved 14CO2, a glass tube was fitted to each flask and filled with 10 to 18 g soda-lime (2 to 5 mm grain size). In order to prevent any volatile 14C-metabolites except 14CO2 from being trapped in the soda-lime, a glass-wool plug impregnated with paraffin oil was inserted between the latter and the contents of the flask. By this arrangement complete adsorption of the 14CO2 and also adequate aeration of the flask contents were achieved.

Results and discussion

% Degradationopen allclose all
Soil No.:
#1
% Degr.:
0
Parameter:
CO2 evolution
Remarks:
The weekly monitoring of 14CO2 indicated that in the case of all leachate experiments, no liberation of 14C-labelled CO2 could be detected.
Soil No.:
#5
% Degr.:
0
Parameter:
CO2 evolution
Remarks:
No indication of any degradation of the isocyanate based polyureas was found.
Soil No.:
#6
% Degr.:
0
Parameter:
CO2 evolution
Remarks:
No indication of any degradation of the isocyanate based polyureas was found.
Soil No.:
#7
% Degr.:
0
Parameter:
CO2 evolution
Remarks:
No indication of any degradation of the isocyanate based polyureas was found.
Soil No.:
#2
% Degr.:
0.015
Parameter:
CO2 evolution
Remarks:
Radioactivity was found only as a very small percentage of the originally applied activity. At the incubation temperature of 22 °C, 0.015 % was released as 14CO2
Soil No.:
#2
% Degr.:
0.15
Parameter:
CO2 evolution
Remarks:
Radioactivity was found only as a very small percentage of the originally applied activity. At the incubation temperature of 50 °C, the values from all types of foams involved, 0.15 % was released as 14CO2
Transformation products:
yes
Identity of transformation productsopen allclose all
No.:
#1
Reference
Reference substance name:
Unnamed
IUPAC name:
2,4 Toluene diamine
No.:
#2
Reference
Reference substance name:
Unnamed
IUPAC name:
2,6 Toluene diamine
Details on transformation products:
As a result of the low amounts of radioactivity found in the chloroform extracts, TLC analysis could only be made with the extracts of the leachate experiments carried out at 50 °C. These analyses showed that in the case of PUR-polyester foam, an average of 0.25 % (values from duplicate experiments) of the original activity was identical to the Rfvalue of 2,4-TDA and 0.38 % with that of 2,6-TDA. A further 0.26 % appeared as unknown degradation products. Of the initial activity of the PUR-polyether foam (TDI-based), 0.015 % could be associated with 2,4-TDA and 0.025 % with 2,6-TDA.
Evaporation of parent compound:
not specified
Volatile metabolites:
not specified
Residues:
not specified
Details on results:
TEST CONDITIONS
- Aerobicity, temperature maintained throughout the study: Yes

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT: 0.26 % appeared as unknown degradation products.

EXTRACTABLE RESIDUES
- After the extraction of composted refuse with acidified water, the radioactivities found in all extracts (see Table II) indicated a degradation only to a very small extent.
-The highest values (max. 0.3 % of the original activity) were found in the case of the rigid polyether foam (MDI-based).
- The radioactivities found in the extracts of the soil gave values within the range of normal background activity so that further experimentation was pointless.
- The extraction of the pure PUR-foams with acidified water (pH 1) gave no indication that radioactivity was liberated by this procedure.
Results with reference substance:
Not applicable.

Any other information on results incl. tables

PUR-FOAMS

In the tests with leachate from a refuse tip, the macroscopic observation of the foams at the end of the incubation time showed a partial breakdown of the structure depending on the temperature and the PUR-foam involved. This degradation could best be seen in the case of PUR-polyester foam incubated at 50 °C where a considerable amount of the foam had been transformed into a pulverised condition with a deep brown coloration; a much smaller change was observed at 22 °C. Structural breakdown of the PUR-polyether foams (TDI- and MDI-based) at 50 °C occurred only to a very small extent. At 22 °C no change could be detected in these foams. These visual assessments of the relative degrees of degradation were confirmed by the amounts of activity found in the filtrates.

After the extraction of composted refuse with acidified water, the radioactivities found in all extracts indicated a degradation only to a very small extent. The highest values (max. 0.3 % of the original activity) were found in the case of the rigid polyether foam (MDI-based). The radioactivities found in the extracts of the soil gave values within the range of normal background activity so that further experimentation was pointless. The extraction of the pure PUR-foams with acidified water (pH 1) gave no indication that radioactivity was liberated by this procedure.

As a result of the low amounts of radioactivity found in the chloroform extracts (see Table II), TLC analysis could only be made with the extracts of the leachate experiments carried out at 50 °C. These analyses showed that in the case of PUR-polyester foam, an average of 0.25~o (values from duplicate experiments) of the original activity was identifical to the Rfvalue of 2,4-TDA and 0.38 %with that of 2,6-TDA. A further 0.26 % appeared as unknown degradation products. Of the initial activity of the PUR-polyether foam (T-DI-based), 0.015 %could be associated with 2,4-TDA and 0.025 % with 2,6-TDA.

The weekly monitoring of 14CO2 indicated that in the case of all leachate experiments, no liberation of 14C-labelled CO2 could be detected. In the test with composted refuse, radioactivity could be found in the 14CO2 absorption systems but only as a very small percentage of the originally applied activity. At the incubation temperature of 22 °C, 0.015 % was released as 14CO2, at 50 °C, the values from all types of foams involved increased by a factor of ten to 0.15 % In the experiment with the soil (22 °C), a release of 0.01 % (TDI- and MDI-based PUR-polyether foam) or 0.06 % (TDI-based PUR-ester foam) was detected.

The experiments with TDI-based PUR-foams (polyester and polyether types) incubated under environmental condition in a refuse tip confirmed the results found in the laboratory test, i.e., that the PUR-ether foams highly resist degradation and that the PUR-ester-foams are quite susceptible (see Table III).

POLYUREAS

The test carried out to simulate a high content of TDA- and MDA-polyureas after a spillage of the monomeric isocyanates gave no indication of a degradation of these polymeric products. Radioactivity was found neither in the extracts nor in the COE absorption systems of all three soils under investigation.

In the experiments carried out in the laboratory, two criteria of degradation were selected: (a) the appearance of the aromatic amines in the extracts, and (b) the liberation of 14CO2. The results obtained from the tests with PUR-foams show that these two criteria did not correspond with one another. In the case of all three PUR-foams in the leachate at 50°C, the presence of TDAs and MDA was definitely detected, but no 14CO2. In the test with soil and compost, the conversion of small amounts of the 14C-labelled foams to 14CO2 was established, but no aromatic amines could be detected.

In interpreting these results, the properties of the media, of the foam and of the aromatic amines must be considered. It is well known that a combination of moisture and heat favors the chemical hydrolysis, especially those of the polyester-based PURfoams. It is reasonable to suppose that this mechanisms was responsible for the formation of TDAs and MDA in the leachate experiments carried out at 50 °C. In accordance with present knowledge of the breakdown of aromatic compounds by microorganisms, the possibility of microbial degradation of TDAs and MDA liberated can be postulated. Therefore, it must be presumed that the microbial activity in the leachate was so minimal that an accumulation of the aromatic amines liberated by hydrolysis occurred.

In the tests with soil and refuse compost, the foams were subjected to both chemical hydrolysis and microbial attack. From the low amounts of radioactivity found in the extracts or as 14CO2 it can be concluded that chemical as well as microbial degradation was unimportant and negligible. The low amounts of aromatic amines liberated in these media were obviously easily degraded to CO2. The remarkable difference in degradation between the polyester-based foam and the polyether-based foams as found in the leachate experiments at 50 °C could not be confirmed in the tests with soil and compost.

Another factor influencing the appearance of aromatic amines under all experimental conditions tested is the known autoxidation of these compounds in the presence of water and air (Beilstein, XIII, Nr. 1740-1871). This chemical reaction is characterised by the formation of dark brown derivatives which are obviously responsible for the staining of the partially degraded PUR-foams, especially the PUR-ester foams.

The extent of such oxidation is a matter for conjecture and the compounds thus produced could represent the major part of the activity in the aqueous phase which could not be extracted by chloroform.

The results of the experiments carried out in the refuse tip confirmed the high stability of polyether-type foam in contrast to the susceptibility of the polyester-type foam. From the fact that degradation of this foam was less in the stratified fill, where the cubes had no direct contact with the strong basic caustic lime, it is supposed that chemical breakdown was a main factor for the degradation of the polyester-type foam.

TABLE II
Percent of the applied radioactivity extractable from14C-labelIed PUR-foams incubated in different media for three months
Media Incubation temperature Found in the water extracts (pH 1) Transferred from the water extracts into chloroform
PUR-ester TDI- based PUR-ether TDI- based PUR-ether MDI- based PUR-ester TDI- based PUR-ether TDI- based PUR-ether MDI- based
Leachate 50 °C 4.56a/5.00a 0.34/0.34 0.32/0.35 0.7/1.0 0.07/0.07 0.17/0.21
22 °C 0.33/0.33 0.10/0.09 0.06/0.06 0.03/0.02 0.02/0.02 0.02/0.01
Composted 50 °C 0.07/0.06 0.03/0.04 0.21/0.27 n.d. n.d. n.d.
refuse 22 °C 0.04/003 0.02/0.02 0.30/0.24 n.d. n.d. n.d.
Soil 22 °C n.d. n.d. n.d. n.e. n.e. n.e.
aThe two figures give the results of duplicate experiments:
n.d.: not detectable,
n.e.: no extraction of the water extracts with chloroform carried out.

TABLE III
Degradation of TDI-based PUR-foams in a refuse tip during a 13 month incubation period
  Weight loss in % of the initial
  stratified filling mixed filling
PUR-ether foam 0 0
0 0
0 0
PUR-ester foam 17 35
20 42
31 86

Applicant's summary and conclusion

Conclusions:
No indication of any degradation of the isocyanate based polyureas was found.
Executive summary:

To assess the possibilities of the liberation of toxic aromatic amines under different conditions of disposal, the degradation of different 14C-labelled polyurethane foams was investigated in the leachate of a refuse tip, in composted municipal waste and in an agricultural soil. With unlabelled foam cubes experiments were run under the environmental conditions of a refuse tip. In addition, the degradation of 14C-labelled polyureas was studied in different agricultural soils. In the laboratory tests the criteria of degradation were the liberation of aromatic amines and the production of 14CO2. The degradation in the refuse tip was estimated on the basis of weight loss.

From the results it can be assumed that the polyether based polyurethane foams are largely resistant to microbial as well as chemical attack under all practical conditions of disposal. Polyester based polyurethane foams are susceptible to chemical hydrolysis favored by extreme environmental conditions such as high temperature and/or low or high pH values. Under these circumstances an accumulation of aromatic amines can occur if their further microbial degradation is impeded by the lack of suitable conditions for the growth of microorganisms. No indication of any degradation of the isocyanate based polyureas was found.