Phenyl isocyanate

Endpoint summary

Description of key information

Fish

The acute toxicity to fish was measured of the hydrolysis product anilin in a flow-through study yielding a LC50 of 10.6 mg/L.

The long-term toxicity to fish (pimephales promelas) of the hydrolysis product aniline was measured during 32 days and a NOEC of 0.39 mg/L was obtained.

Daphnia

Short-term toxicity to aquatic invertebrates (Daphnia magna) of the hydrolysis product aniline was measured during 48 hours and showed an EC50 of 0.16 mg/L.

Due to the rapid hydrolysis of the substance, long-term toxicity results for aquatic invertebrates of the hydrolysis product aniline is taken into account for assessment. Three results are available:
Daphnia magna: NOEC (21d) = 0.016 mg/L
Daphnia magna: NOEC (21d) = 0.004 mg/L
Daphnia magna: NOEC (21d) = 0.024 mg/L .
Three Daphnia long-term tests are available that are regarded of equal value. The lowest of the three NOECs results in a value of 4 μg/L.

Algae:

The toxicity to aquatic algae (chlorella pyrenoidosa) of the hydrolysis product aniline was tested according to OECD guideline 201 "Alga, Growth Inhibition Test, 1984". During 72 hours an EC50 of 175 mg/L and a NOEC of 90 mg/L was shown.

Microorganisms

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.

Additional information

As phenyl isocyanate hydrolysis rapidly the results of the hydrolysis compound aniline are taken into account 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.