Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

PHOTOTRANSFORMATION IN AIR, SOIL AND WATER

According to REACH Regulation (EC) 1907/2006 this information is not mandatory for a registration of a chemical at a tonnage band of 100 - 1000 tons/year. However, regarding phototransformation in air a QSAR prediction was performed for bis(2,6 -diisopropylphenyl)carbodiimide by the computer program AOPWIN v1.92 (Chemservice S.A., 2011). An atmospheric half-life of 0.322 days (3.87 hours) was calculated. Neither an ozone reaction nor any nitrate radical reaction is important for the substance.

HYDROLYSIS

The tests were performed based on OECD Guidelines for Testing of Chemicals, Section 1 – Physical-Chemical Properties, OECD 111, Council Regulation (EC) No 440/2008, Guideline Part C – Methods for the Determination of Ecotoxicity, C.7. “Abiotic Degradation: Hydrolysis as a Function of pH” in a GLP-study.

As the test item was expected to hydrolysis in aqueous media the hydrolysis behavior was investigated at different temperatures and pH values in demineralized water up to a degradation of > 90 %. The stability was monitored by HPLC analysis with MS/MS-detection.

The concentration of the test item in the hydrolysis test solutions was determined by HPLC-MS/MS at defined time intervals. In addition, the development of the proposed degradation product was screened in all test solutions (counts).

According to OECD 111 Guideline a sterility test was conducted at the end of the hydrolysis tests. No microbes (colonies) were found in all test solutions. Therefore, biotic degradation can be excluded for all tested solutions.

Due to the poor water solubility of the test item, a test concentration of approx. 20 μg/L (including 1 % acetone as organic solvent additive) had to be applied for adequate dissolution. In addition to the test item itself the mass trace of the proposed degradation product 2,6-Diisopropylaniline was screened. The counts were recorded without external calibration.

Preliminary tests

Test concentration

Because the test item is not soluble in water in sufficient quantities (water solubility < 0.53 μg/L, an organic solvent has to be used to obtain an adequate dissolution in the different buffer solutions. According to the guideline the organic solvent does not exceed 1 % (v/v).

Before the hydrolysis study itself was initiated, solubility pre-tests of the test item were performed at three different concentration levels in buffer solutions. One individual sample was prepared for each concentration (10, 20 and 40 μg/L) and the concentration of the test item in the test solutions was determined by HPLC-MS/MS.

The test item was found to be soluble in demineralized water including 1 % acetone as organic solvent additive with a solubility of at least 40 μg/L.

According to OECD Guideline 111 the concentration of the test item should not exceed 0.01 mol/L or half of the saturation concentration. Consequently, the test item was applied in buffer solutions (including 1 % acetone) with a concentration of 20 μg/L. Clear solutions were obtained which fulfills the requirements of OECD 111 allowing the use of low amounts of water miscible solvents (max. 1 % v/v) for adequate dissolution of the test item.

Freezing of test samples

To have the opportunity to measure the test samples preferably together, freezing of the test samples was tested.

It has to be ruled out that the test item precipitates due to the freezing which would lead to wrong concentrations.

The test solutions from the solubility test of the concentrations of 10 and 20 μg/L each were a) frozen directly, b) diluted 1:1 with acetone and c) diluted 1:1 with acetonitrile and afterwards frozen in with liquid nitrogen.

The frozen samples were kept frozen until the next day and then defrosted right before measurement. The recoveries after measurement were acceptable. Because the LOQ raises by dilution and a new source of error by dilution occurs, the freezing of the undiluted sample solution was chosen for the main test.

Analytical result

For the test item abiotic degradation > 90 % was observed for all measured test solutions.

The tests were performed in buffer solutions at pH values of 4, 7 and 9 at different temperatures.

For pH 4 the temperatures of 10, 20 and 50 °C were investigated. For pH 7 and pH 9 it was 20, 30 and 50 °C.

Calculated hydrolysis rate at 25 °C

Based on the measurements at different temperatures the correlating hydrolysis rate and the Half-Life time at 25 °C was calculated according to the Arrhenius equation:

 Calculated hydrolysis of the test item at 25 °C

 pH 4

 pH 7

 pH 9

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Test item

 28.36

 6.79 • 10-8

 153.62

 1.25 • 10-6

 186.31

 1.03 • 10-6

 Correlation coefficient

 0.99121

 0.99757

 0.99785

pH 4

The test item is shown to be hydrolytically unstable at 10, 20 and 50 °C for pH value 4. The concentration of the test item after the last measurements was < 10% of the initial value. Therefore the test item is considered to be hydrolytically unstable within the tested parameters.

The degradation of the test item can be described by first order kinetics. Half-life times and hydrolysis rates were calculated:

 Calculated hydrolysis of the test item at 25 °C

10 °C

20 °C

 50 °C

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Test item

 102.35

 1.88 • 10-6

 32.93

 5.85 • 10-6

 5.79

 3.33 • 10-5

pH 7

The test item is shown to be hydrolytically unstable at 20, 30 and 50 °C for pH value 7. The concentration of the test item after the last measurement was < 10% of the initial value. Therefore the test item is considered to be hydrolytically unstable within the tested parameters.

The degradation of the test item can be described by first order kinetics.

Half-life times and hydrolysis rates were calculated:

 Calculated hydrolysis of the test item at 25 °C

20 °C

30 °C

 50 °C

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Test item

 222.46

 8.66 • 10-7

 104.50

 1.84 • 10-6

 36.309

 5.30 • 10-6

pH 9

The test item is shown to be hydrolytically unstable at 20, 30 and 50 °C for pH value 9. The concentration of the test item after the last measurement was < 10% of the initial value. Therefore the test item is considered to be hydrolytically unstable within the tested parameters.

The degradation of the test item can be described by first order kinetics. Half-life times and hydrolysis rates were calculated:

 Calculated hydrolysis of the test item at 25 °C

20 °C

30 °C

 50 °C

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Half-life-time [h]

 Hydrolysis rate constant k [1/s]

 Test item

 227.56

 8.46 • 10-7

 156.38

 1.23 • 10-6

 64.13

 3.00 • 10-6

As degradation product 2,6-Diisopropylaniline was detected and its qualitative increase monitored over the time.

The above mentioned hydrolysis study was performed after the final decision of ECHA on a compliance check, which was issued 01 August 2017. The study is in line with the provided supporting information (Cizek, 2012 and EFSA 2010) regardind hydrolysis.The rate of hydrolysis increases with decreasing pH and temperature. 2,6 -Diiospropyleaniline is the hydrolyisis product. Only the determined half-lives are lower in the new key study than in the supporting study (Cicek, 2012). This can be explained by the improved analytical method and the enhanced test-design, which becomes necessary because of the very low water solubility (< 0.53 µg/L - Holzaht-Grimme, 2019). To achieve a stable and measureable concentration for hydrolysis-testing in water it was necessary to work with an organic solvent additive. This is described in the preliminary work on the developement of a suiteable analytical method for the determination of the hydrolysis properties, where amongst others some solvents were tested for their applicability, because it was observed that the sample builds adducts with some solvents like for example methanol (Ranz, 2020).