Phenyl isocyanate

Endpoint summary

Description of key information

Hydrolysis:

The stability of an other isocyanate, isopropyl isocyanate, was tested in an aqueous test solution showing a rapid degradation (half live less than 1 hour). Further the stability of 1-chloro-4-isocyanatobenzene in a second test yielded a half-life of 7.3 h. The only hydrolysis products of both isocyanates were found to be the corresponding amines. These results can be taken as read-across for the isocyanate examined here, a rapid hydrolysis in water with the corresponding amine as degradation product.

A study was conducted with phenyl isocyanate which examined just the first stage of the hydrolysis to carbamic acids. The half-life of this reaction was reported as 20 s.

Biodegradation

The biodegradation of the hydrolysis product aniline was tested according to OECD Guideline 301 D showing that approx. 70% degradated after 15 days. Aniline is therefore classified as readily biodegradable. Due to the rapid hydrolysis of phenyl isocyanate to aniline, it is assumed that the substance is also readily biodegradable.

Bioaccumulation

The aquatic bioaccumulation of the hydrolysis product aniline was measured, yielding a BCF of 2.6 L/kg wwt.

Adsorption

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.

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.