3,3'-dimethylbiphenyl-4,4'-diyl diisocyanate

Endpoint summary

Description of key information

Abiotic degradation / hydrolysis

TODI was assessed in an abiotic degradation study, according to EU-method C.7 and OECD guideline no. 111.The hydrolysis of TODI was found to be very fast, therefore no further testing was necessary. At pH 4 and 9 decomposition product had reached a plateau at the earliest measurement time, the half-life was less than the minimum time taken to make the initial sample analysis (the t1/2 at pH 4 and 9, at 25 and 50 °C was lower than or equal as 2 minutes). At pH 7 only, the hydrolysis reaction could be followed and a half-life calculated. The calculated half-life was 1.2 hours at 50°C at pH 7 for TODI (analysed by the degradation product).

Biotic degradation

Biodegradation in water: screening test

Based on the results obtained in a biodegradation study according to EU-method C.4–E and OECD guideline 301 D, TODI was considered to be not readily biodegradable.The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure control.

Under the test conditions the percentage biodegradation of TODI reached a mean of -4.8 % after 28 days based on ThODNO3.

This result is supported by a study performed with 4,4'-MDI according to OECD Guideline 302 C (Inherent Biodegradability). Here, the average percent biodegradability of MDI and resulting compounds in water were 0% and 6.4%, respectively.

Furthermore, the ready biodegradability of TODI's hydrolysis product (TODA) was investigated over a period of 28 days. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item aniline was tested simultaneously under the same conditions as the test item. Under the test conditions the percentage biodegradation of TODA reached 3% based on TOD and reached 6% by HPLC after 28 days. Therefore the test item can be considered to be not ready biodegradable.

Biodegradation in water and sediment: simulation tests

In accordance with column 2 of REACH Regulation 1907/2006/EC Annex IX section 9.2.1.2, the study “Biodegradation in water: simulation test” does not need to be conducted as the test substance is highly insoluble in water. During experimental tests organic solution was required to allow good mixing of test item with water. Also, hydrolysis of TODI was found to be very fast.

Biodegradation in soil

Due to the fast reaction with moisture, MDI (methylenediphenyl diisocyanate; CAS no. 26447-40-5, EC no. 247-714-0, structural similar to TODI) isomers and polymers are assumed to form inert, insoluble solid polyureas in soil. As MDI is structural similar to TODI, this can also be assumed for TODI.

Bioaccumulation in aquatic species

In accordance with column 2 of REACH 1907/2006/EC Annex IX, section 9.3.2, a bioaccumulation test in aquatic species does not need to be conducted as

- TODI was found insoluble in water (thus uptake into biological cells is very unlikely)

- TODI did not reveal aquatic toxicity at concentrations below water solubility

- TODI’s hydrolysis was found to be very fast

- TODI’s degradation product was found to be insoluble in organic and aqueous solvents (See IUCLID sections 6.1.1, short-term toxicity to fish and 6.1.3, short-term toxicity to aquatic invertebrate)

- For TODI’s degradation product TODA the measured BCF was below 100 (0.2 mg/L: 4.8 - 34; 0.02 mg/L: 10-83) and the estimated BCF was 16.25 L/kg wet-wt.

Thus, based on the fast hydrolysis of TODI (The t1/2 at pH 4 and 9, at 25 and 50 °C was lower than or equal as 2 minutes; at pH7 the t1/2 was 16 hours and 1.2 hours at 25 and 50 °C respectively.) and the low BCF value of the degradation product TODA, bioaccumulation of the environmentally relevant degradation product TODA is considered negligible and no further information concerning bioconcentration or bioaccumulation for TODI is required.

Adsorption/ desorption

In accordance with column 2 of REACH Annex VIII, the test on adsorption/desorption (required in REACH Regulation, ANNEX VIII, Section 9.3.1) does not need to be conducted if the substance and its degradation products decompose rapidly. According to the study on determination of the hydrolysis of TODI as a function of pH (see IUCLID section 5.1.2), the half-life of TODI was determined to be far below 12 hours (max.: 1.2 h at pH 7) and therefore was found to be hydrolytically unstable.

Further, due to the very low water solubility a test is technical not feasible.

Nevertheless, to address this endpoint, estimations using KOCWIN of EPI Suite compilation were performed for TODI and TODA (the product of hydrolysis of TODI), resulting in Koc values of or 1.8exp5 L/kg (Kow method) or 4.2exp5 L/kg (MCI method) for TODI, and 3190 L/kg (MCI method) or 150 L/kg (Kow method) for TODA at 25°C. Based on hydrolysis data of TODI and the calculated adsorption (to sediment and to soil) data of TODA, adsorption can be assumed to be very low or negligible.

Furthermore, the Koc values of TODI's hydrolysis degradation product TODA ([1,1'-Biphenyl]-4,4'-diamine, 3,3'-dimethyl-) were estimated by calculation to be 1, 1, 3.03, 61.9, 258, 347, 359, 361, 361 and 361 at pH 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, respectively (all values at 25 °C).