Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Stability

The phototransformation in air of 2,4,6-triisopropyl-m-phenylene diisocyanate was predicted with the help of the computer program AOPWIN v1.92 (EPIWIN software) by US-EPA , resulting in an atmospheric half-life of 0.280 days (around 3.40 hours) (Chemservice S.A., 2011).

Regarding hydrolysis, one experimental result as well as one QSAR prediction is available for the test substance. Based on the results of the experimental study, the test substance is hydrolytically unstable and undergoes rapid hydrolysis. Abiotic degradation > 90% was observed within 3 min at 20 °C in demineralized water with a half life time of about 37 seconds (Neuland, 2020). This result is supported by the prediction of HYDROWIN v2.00 (EPIWIN software) by US-EPA, which detected ISOCYANATES as hydrolysable substance class (Chemservice S.A., 2012). Accordingly, the hydrolysis half-life will be less than 10 minutes at 25 °C and even at low pHs.

Biodegradation

Regarding biodegradation in water, one experimental result as well as one QSAR prediction is available for the test substance. Based on the results of the experimental study, no degradation had been occurred after 28 days of test duration and the substance was not found to be bacteriotoxic (Müller, 1997). This result is supported by the prediction of BIOWIN v4.10 (EPIWIN software), which concludes that the substance is not readily biodegradable (Chemservice S.A., 2011). TheSTART plug-in in Toxtree (v.2.1.0) assigns the chemical as "class III - unknown" (Chemservice S.A., 2011).

Regarding biodegradation in soil, sediment and surface water no information is provided, since direct as well as indirect exposure to the environment is unlikely, which is proven by the conducted exposure assessment. For further information please refer to Section 9 and 10 of the CSR. Hence, these endpoints are waived based on exposure considerations.

Bioaccumulation

Due to the very fast hydrolysis (DT50 = 37s) and the resulting instability of the test substance, it was considered most meaningful to cover the information on the bioaccumulative potential by the consideration of the degradation products. Based on the results of the hydrolysis study conducted at CURRENTA GmbH according to OECD 111, 2,4,6-triisopropyl-m-phenylene diamine (TRIDA, CAS 6318-09-08) was expected as major hydrolysis product and polymeric ureas as potential minor hydrolysis products (Neuland, 2020).

A study with 2,4,6-triisopropyl-m-phenylene diamine (TRIDA) according to OECD TG 305-I (Aqueous Exposure) is currently running at ibacon GmbH, which is presented as key study. Therefore, no final results on the bioaccumulative potential of TRIDA as major hydrolysis product can be presented so far but will be added as soon as the final report is available.

Polymeric ureas are considered as polymers under REACH. Therefore they do not have to be registered and evaluated according to Chapter 1; Article 2, Paragraph 9 Regulation No. 1907/2006. Regardless of the evaluation of available data, the determination of the bioaccumulative potential of the polymeric ureas as minor hydrolysis product is waived accordingly.

As supporting information a WoE approach using QSAR prediction (BCFBAF v3.01) is presented for the test substance itself, indicating a low potential for bioaccumulation in fish. For the lower trophic level a BCF of 232.2 L/kg wet-wt is calculated, whereas for the mid trophic level the BCF will result in 210.5 L/kg wet-wt and the higher trophic level gives a value of 152.8 L/kg wet-wt.

A terrestrial bioaccumulation study is not triggered for a registration of a tonnage band of 100 - 1000 tons/year according to REACH Regulation (EC) 1907/2006.

Transport and distribution

Regarding the soil adsorption potential for 2,4,6-triisopropyl-m-phenylene diisocyanate only a QSAR prediction is reported which was performed by the computer program KOCWIN v2.00 (Chemservice S.A., 2011). A Koc value of 539300 L/kg (5.393 E+005 L/kg) was estimated by the Salbjic molecular connectivity (MCI) method, which is taken more seriously into account, due to the fact that it includes improved correction factors. The traditional method gives a value of 3639000 L/kg (3.639 E+006 L/kg).

Henry´s law states that the solubility of a gas in a liquid solution at a constant temperature will be proportional to the partial pressure of the gas which is above the solution (Henry, 1803). This information is not mandatory for a registration under REACH Regulation (EC) 1907/2006 in a tonnage band of 100 - 1000 tons/year. However, the Henry´s Law Constant can be predicted with the help of HENRYWIN v3.20 (Chemservice S.A., 2011). A constant of 7.49 Pa*m³/mol was predicted at 25 °C for the substance 2,4,6-triisopropyl-m-phenylene diisocyanate.

Monitoring data

Monitoring data are only available for the read across substance toluene diisocyanate. Atmospheric emissions are low, typical emission losses for TDI are 25 g/t (Tury, 2004). Laboratory studies show that the substance does not react with water in the gas phase at a significant rate. The primary degradation reaction of these aromatic diisocyanates in the atmosphere is expected to be oxidized by OH radicals with an estimated half-life of one day. Laboratory studies also show that this reaction is not expected to result in increased ground-level ozone accumulation. It is indicated that degradation by photolytically generated radicals, rather than by direct photolysis will occur. In a vapour phase no hydrolysis was detected. The reaction rate of TDI with OH radicals, measured relative to that of toluene, was estimated as >= 7.4 x 10E12 cm³/molecule/ sec. Both isomers of TDI were found to inhibit ozone formation and radical levels in all experiments. This atmospheric degradation of TDI by OH radicals raises concerns that the process might lead to ozone or smog formation. Smog chamber studies have shown that this is not the case. Furthermore, TDI should not be considered an ozone precursor. Overall, it can be concluded that no significant long-term or wide-ranging environmental effects would be expected from current emissions of TDI to air.