Phenyl isocyanate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

activated sludge nitrification inhibition testing

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

Duration:

2 h

Dose descriptor:

EC50

Effect conc.:

7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

2 h

Dose descriptor:

NOEC

Effect conc.:

2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

test concentration   nitrate and nitrite   inhibition
                     produced (mg/L)       (%)
blank                3.05                  
ref. inhib.          < 1.0                 100
aniline (mg/L):
 0.5                 3.05                    0
 1.0                 3.15                    0
 2.0                 3.05                    0
 4.0                 2.65                   16
 8.0                 1.75                   52
16.0                 < 1.0                 100
32.0                 < 1.0                 100

quantification limit of nitrate-N and nitrite-N: 1 mg/L
half of the quantification limit was used for calculation of
% inhibition.

Conclusions:

The toxicity of aniline to microorganisms was tested according to ISO DIS 9509 (Method for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms by Chemicals and Waste Waters). After 2 hours an EC50 of 7mg/L and a NOEC of 2 mg/L were calculated.

Executive summary:

The toxicity of aniline to microorganisms was tested according to ISO DIS 9509 (Method for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms by Chemicals and Waste Waters). After 2 hours an EC50 of 7mg/L and a NOEC of 2 mg/L were calculated.

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:

activated sludge nitrification inhibition testing

Type of information:

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

Adequacy of study:

key study

Study period:

2000

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

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

Qualifier:

according to guideline

Guideline:

ISO 9509 (Toxicity test for assessing the inhibition of nitrification of activated sludge microorganisms)

Deviations:

yes

Remarks:

activated sludge of wwtp treating industrial sewage, inoculum with lower nitrification rate (0.5 mg/g/h) and incubation time: 2 h

GLP compliance:

not specified

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge, industrial

Details on inoculum:

- Type: mixed population of aquatic microorganisms
- Origin: aeration tank of sewage treatment plant Uerdingen of the Bayer AG
- Pretreatment: sludge was washed one time

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

2 h

Test temperature:

22+/-1 °C

Nominal and measured concentrations:

0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0 and 32.0 mg/L

Details on test conditions:

- test concentration of activated sludge: 3 g/L ss
- specific nitrification rate: 0.5 mg/g/h (inoculum with lower nitrification rate than specified in guideline; nevertheless the inhibition of nitrification could be determined.)
- incubation time: 2 h (deviation from guideline)

Reference substance (positive control):

yes

Remarks:

allylthiourea (11.6 g/L)

Duration:

2 h

Dose descriptor:

EC50

Effect conc.:

7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

2 h

Dose descriptor:

NOEC

Effect conc.:

2 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

test concentration   nitrate and nitrite   inhibition
                     produced (mg/L)       (%)
blank                3.05                  
ref. inhib.          < 1.0                 100
aniline (mg/L):
 0.5                 3.05                    0
 1.0                 3.15                    0
 2.0                 3.05                    0
 4.0                 2.65                   16
 8.0                 1.75                   52
16.0                 < 1.0                 100
32.0                 < 1.0                 100

quantification limit of nitrate-N and nitrite-N: 1 mg/L
half of the quantification limit was used for calculation of
% inhibition.

Validity criteria fulfilled:

not specified

Conclusions:

The toxicity of aniline to microorganisms was tested according to ISO DIS 9509 (Method for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms by Chemicals and Waste Waters). After 2 hours an EC50 of 7 mg/L and a NOEC of 2 mg/L were calculated.

Executive summary:

The toxicity of aniline to microorganisms was tested according to ISO DIS 9509 (Method for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms by Chemicals and Waste Waters). After 2 hours an EC50 of 7 mg/L and a NOEC of 2 mg/L were calculated.

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 phenyl isocyanate, results from the hydrolysis product aniline are also taken into account for assessment.
In order to protect the efficiency of domestic and industrial waste water treatment plants, inhibition of nitrification by the hydrolysis product aniline is identified to be the most sensitive test system. Nitrification inhibition was measured on activated sludge determined according to ISO DIS 9509 (Method for Assessing the Inhibition of Nitrification of Activated Sludge Microorganisms by Chemicals and Waste Waters). An EC50 of 7 mg/l and and a NOEC of 2 mg/L was determined after 2 hours incubation.

Key value for chemical safety assessment

EC50 for microorganisms:

7 mg/L

EC10 or NOEC for microorganisms:

2 mg/L

Additional information

The toxicity to microorganisms of phenyl isocyanate was tested according to OECD Guideline 209 "Activated Sludge, Respiration Inhibition Test". During 3 hours an EC10 of 309 mg/L and an EC50 of 702 mg/L was measured. Due to the rapid hydrolysis of phenyl isocyanate, results from the hydrolysis product aniline are also taken into account for assessment, based on the justification for read-across:

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.