Phenyl isocyanate

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption: screening

Remarks:

adsorption

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.
* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.
Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

Reason / purpose for cross-reference:

read-across: supporting information

Principles of method if other than guideline:

Adsorption equilibrium study and Adsorption isotherm study

GLP compliance:

not specified

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

22°C

Analytical monitoring:

yes

Details on sampling:

at 11 equilibrium periods of 1-120h

Details on matrix:

Details on soil:
COLLECTION AND STORAGE
- Geographic location:Hagerstown (from Maryland, in Northeastern USA) and Palouse (Washington, in Northwestern USA)
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): both soils were sieved at 2mm and stored moist (Hagerstown at 22% as received; Palouse, moistened from air-dry to 11%) at 4°C.
- Soil sterilization was by autoclaving at 121°C and 100 kPa for 1 h on each of two consecutive days

PROPERTIES: Soil 1
- Soil type: Hagerstown clay loam
-Subgroup classification: typic hapludalfs
- % organic matter: 2.5
- % silt: 42
- % clay:34
- pH:6.6
- CEC (meq/100 g): 10
- Special chemical/mineralogical features: vermiculite, kaolinite
- Moisture at 1/3 atm (%):31.3
- surface area (m2/g): 25

PROPERTIES: Soil 2
- Soil type: Palouse silt loam
-Subgroup classification: pachic ultic Hepaloxerolls
- % organic matter: 3.4
- % silt: 58
- % clay:25
- pH:5.1
- CEC (meq/100 g): 22
- Special chemical/mineralogical features: montmorillonite
- Moisture at 1/3 atm (%):32.0
- surface area (m2/g): 90

Details on test conditions:

Adsorption equilibrium study:
The oven-dry equivalent of 1.6 g soil was added to 13 x 100 mm glass culture tubes, with Teflon-lined screw caps. Half of the samples were autoclaved; the moisture loss during this step was measured. Adsorption was conducted with essentially no headspace, so these volumes of 10 ppm [14C]aniline (6840 dpm/ml) were used: 7.8, 8.0, 8.1, and 8.2 ml for nonsterile and sterile Hagerstown, and nonsterile and sterile Palouse, respectively.
This represents a 1:5 soil:solution ratio. The tubes were vigorously shaken for 30 sec, then shaken more gently at 22°C for II equilibration periods of 1-120 h.
Asorption isotherm study:
Adsorption of [14C]aniline was measured at six concentrations (0.0317-10 ppm), with two soils, two sterility levels (nonsterile and autoclaved),
and three replications. Other conditions were as in the preceding kinetics experiment. Here, the nonradioactive aniline had not been redistilled.
The batch adsorption was repeated again, using only three concentrations (0.1, 1, 10 ppm) and only autoclaved soils. A 1 ppm "no shaking" treatment was also included. After removing 1 ml for counting, the soil and remaining decantate were each extracted 3x with 15 ml CHCl3; each combined extract was concentrated under N2 to 0.5 ml. Subsamples of each soil extract were counted before combining them. The concentrated soil and decantate CHCI3 extracts were analyzed for potential transformation products by thin-layer chromatography (TLC), using silica gel 60 F254 plates developed in darkness with CHCI3:HOAc (90:10, v/v) in a N2 atmosphere.
Visualization was by autoradiography, and spots were later removed and counted.

Type:

Koc

Value:

130

Temp.:

20 °C

% Org. carbon:

2.5

Remarks on result:

other: Hagerstown sterile soil

Type:

Koc

Value:

310

Temp.:

20 °C

% Org. carbon:

2.5

Remarks on result:

other: Hagerstown nonsterile soil

Type:

Koc

Value:

410

Temp.:

20 °C

% Org. carbon:

3.4

Remarks on result:

other: Palouse sterile soil

Type:

Koc

Value:

910

Temp.:

20 °C

% Org. carbon:

3.4

Remarks on result:

other: Palouse nonsterile soil

Adsorption and desorption constants:

Freundlich K values:
Hagerstown soil:
nonsterile: 4.45
sterile: 1.85
Palouse soil:
nonsterile: 17.8
sterile: 7.97

Recovery of test material:

Losses of 14C associated with concentrating a CHCI3 extract of [14C]aniline under a N2 Stream, or with leaching and recovery after TLC, were 11% and 4%, respectively.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on results (Batch equilibrium method):

Autoclaving has reduced the capacity of the soil to adsorb aniline. The authors staded that autoclaving did reduce the specific surface of Hagerstown and Pal ouse soils by ca. 10%, and organic carbon content by ca. 5%, but did not significantly change pH or other properties likely to affect aniline adsorption per se. Autoclaving is known to inactivate soil peroxidase, an enzyme potentially contributing to formation of strongly adsorbed aniline products. It appears most plausible that the lower aniline K values in autoclaved soils are chiefly due to inhibition of biotic transformation and only secondarily due to diminished soil surface area and slower abiotic transformation.

RS-Freetext:
soil               Koc (l/kg)       log Koc
clayey loam
  - sterile        310              2.49
  - non-sterile    130              2.11

silty loam
  - sterile        410              2.61
  - non-sterile    910              2.96

- adsorption behaviour superimposed by simultaneous biodegradation

- equilibrium was reached within 60 h in nonsterile soil

Validity criteria fulfilled:

not specified

Conclusions:

The adsorption of aniline was measured at clayey loam: sterile at 310 L/kg and non-sterile at 130 L/kg, silty loam: sterile at 410 L/kg and non-sterile at 910 L/kg.

Executive summary:

In a distribution experiment with radiolabelled aniline (6 concentrations, 0.0317-10 ppm), the radioactivity was measured in the supernatant water phase and the Freundlich adsorption

constants were determined. Equilibrium was reached in nonsterile soils within 60 h, but was not attained in sterile soils by 120 h. With 2 nonsterile soils Koc values of 310 resp. 910 L/kg were calculated, while the values decreased to 130 resp. 410 L/kg when the same soils were autoclaved before the experiment. Aniline is degraded partially before adsorption, and the distribution constants for the degradation products (azobenzene, azoxybenzene, phenazine) are much higher;therefore the constants determined in nonsterile soils seem to be overestimated. A minor effect is that the surface is slightly reduced leading to few lower constants.

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.

* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.

Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

Reference 2

Endpoint:

adsorption / desorption: screening

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.
* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.
Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

Reason / purpose for cross-reference:

read-across source

Type:

Koc

Value:

130 L/kg

Temp.:

20 °C

% Org. carbon:

2.5

Remarks on result:

other: Hagerstown sterile soil

Type:

Koc

Value:

310 L/kg

Temp.:

20 °C

% Org. carbon:

2.5

Remarks on result:

other: Hagerstown nonsterile soil

Type:

Koc

Value:

410 L/kg

Temp.:

20 °C

% Org. carbon:

3.4

Remarks on result:

other: Palouse sterile soil

Type:

Koc

Value:

910 L/kg

Temp.:

20 °C

% Org. carbon:

3.4

Remarks on result:

other: Palouse nonsterile soil

Adsorption and desorption constants:

Freundlich K values:
Hagerstown soil:
nonsterile: 4.45
sterile: 1.85
Palouse soil:
nonsterile: 17.8
sterile: 7.97

Recovery of test material:

Losses of 14C associated with concentrating a CHCI3 extract of [14C]aniline under a N2 Stream, or with leaching and recovery after TLC, were 11% and 4%, respectively.

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on results (Batch equilibrium method):

Autoclaving has reduced the capacity of the soil to adsorb aniline. The authors staded that autoclaving did reduce the specific surface of Hagerstown and Pal ouse soils by ca. 10%, and organic carbon content by ca. 5%, but did not significantly change pH or other properties likely to affect aniline adsorption per se. Autoclaving is known to inactivate soil peroxidase, an enzyme potentially contributing to formation of strongly adsorbed aniline products. It appears most plausible that the lower aniline K values in autoclaved soils are chiefly due to inhibition of biotic transformation and only secondarily due to diminished soil surface area and slower abiotic transformation.

RS-Freetext:
soil               Koc (l/kg)       log Koc
clayey loam
  - sterile        310              2.49
  - non-sterile    130              2.11

silty loam
  - sterile        410              2.61
  - non-sterile    910              2.96

- adsorption behaviour superimposed by simultaneous biodegradation

- equilibrium was reached within 60 h in nonsterile soil

Conclusions:

The adsorption of aniline was measured at clayey loam: sterile at 310 L/kg and non-sterile at 130 L/kg, silty loam: sterile at 410 L/kg and non-sterile at 910 L/kg.

Executive summary:

In a distribution experiment with radiolabelled aniline (6 concentrations, 0.0317-10 ppm), the radioactivity was measured in the supernatant water phase and the Freundlich adsorption constants were determined. Equilibrium was reached in nonsterile soils within 60 h, but was not attained in sterile soils by 120 h. With 2 nonsterile soils Koc values of 310 resp. 910 L/kg were calculated, while the values decreased to 130 resp. 410 L/kg when the same soils were autoclaved before the experiment. Aniline is degraded partially before adsorption, and the distribution constants for the degradation products (azobenzene, azoxybenzene, phenazine) are much higher; therefore the constants determined in nonsterile soils seem to be overestimated. A minor effect is that the surface is slightly reduced leading to few lower constants.

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.

* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.

Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

Description of key information

Due to the rapid hydrolysis of phenylisocyanate, results of the hydrolysis product aniline are taken into account for assessment.
Adsorption of aniline to solid soil phase is possible. The empirically determined Koc-value of 410 l/kg (log Koc of 2.6) is used, describing the adsorption potential of aniline.

Key value for chemical safety assessment

Koc at 20 °C:

410

Additional information

Due to the rapid hydrolysis of phenyl isocyanate, adsorption behaviour of its hydrolysis product aniline is assessed, based on the following assumption:

According to handbook data, isocyanates react rapidly with water forming aminic structures as well as carbamic acids, which are mostly unstable, and ureas under release of carbon dioxide. Monitoring the amine formation in hydrolysis studies gives a picture of the degradation of the isocyanate. This behaviour of isocyanates has been used in studies to determine the rate of degradation*. In Guidance on IR & CSA Chapter R.6 it is mentioned that degradation products instead of parent substance can be investigated for ecotoxicological effects if the hydrolysis is very rapidly (t1/2 <1 h), OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (2000) and Guidance on IR & CSA Chapter R.7b state the same. As phenyl isocyanate hydrolyses to aniline this is the ecotoxicological relevant species. Concluding, tests performed using the corresponding amine can equally be used to assess the ecotoxicological hazards of phenyl isocyanate. An underestimation of environmental hazards is thus avoided supporting a conservative and thus protective hazard assessment.

* Bayer Industry Services (2004), 4-chlorophenyl-isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300181. Leverkusen, Germany.

Bayer Industry Services (2003), Isopropyl isocyanate: Investigation on Stability in Aqueous Test Solutions. Project No: 200300095. Leverkusen, Germany.

First, it should be considered, that in soil, two competitive reactions occur: biodegradation and formation of covalent bounds onto the organic matter. The latter pathway leads to aniline-humic acid adducts which are immobile and only slowly degraded. Thus accumulation of the reaction product with humic substances occurs. The fate in sediments is considered to be similar than in soils. The formation of covalent bonds with humic matter is a general property of aniline and its derivatives. Adsorption measurements on soil and sewage sludge revealed moderate adsorption properties of aniline. In a distribution experiment with radiolabelled aniline (6 concentrations, 0.0317-10 ppm), the radioactivity was measured in the supernatant water phase and the Freundlich adsorption constants were determined. Equilibrium was reached in nonsterile soils within 60 h, but was not attained in sterile soils by 120 h. With 2 nonsterile soils Koc values of 310 resp. 910 l/kg were calculated, while the values decreased to 130 resp.410 l/kg when the same soils were autoclaved before the experiment. Aniline is degraded partially before adsorption, and the distribution constants for the degradation products (azobenzene, azoxybenzene, phenazine) are much higher;therefore the constants determined in nonsterile soils seem to be overestimated. A minor effect is that the surface is slightly reduced leading to few lower constants.