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Adsorption / desorption

KOCWIN model of Estimation Programs Interface was used to predict the soil adsorption coefficient i.e Koc value of test chemical. The soil adsorption coefficient i.e Koc value of test chemical was estimated to be 13670 L/kg (log Koc=4.1359) by means of MCI method (at 25°C). This Koc value indicates that the test chemical has a strong sorption to soil and sediment and therefore have negligible to slow migration potential to ground water.

Additional information

Adsorption / desorption

Various predicted data for the target chemical andsupporting weight of evidence studies of its read across chemicalswere reviewed for the adsorption end point which are summarized as below:

In a prediction done using KOCWIN Program of Estimation Programs Interface, the soil adsorption coefficient i.e Koc value of test chemical was predicted. The soil adsorption coefficient i.e Koc value of test chemical was estimated to be 13670 L/kg (log Koc=4.1359) by means of MCI method (at 25°C). This Koc value indicates that the test chemical has a strong sorption to soil and sediment and therefore have negligible to slow migration potential to ground water.

 

Another predicted data was estimated using Chemspider database (2020) for predicting the adsorption coefficient (Koc) of test chemical. The adsorption coefficient (Koc) of test chemical was estimated to be 767.50 (logKoc = 2.885) at pH 5.5 and 4239.84 (logKoc = 3.627) at pH 7.4, respectively. This Koc value indicates that the test chemical has a moderate to strong sorption to soil and sediment and therefore have negligible to slow migration potential to ground water.

 

The adsorption coefficient (Koc) for test chemical was predicted by Scifinder database at pH 1-10 and temperature 25 °C. The adsorption coefficient (Koc) of test chemical was estimated to be 1, 2.85, 138, 1430, 2910, 3220, 3250 and 3260 (at 25°C) (logKoc value ranges from 0 to 3.513) at pH 1-3, 4, 5, 6, 7, 8, 9 and 10, respectively.  The Koc value (i.e., logKoc = 3.46 at pH 7.0) indicates that the test chemical has a strong sorption to soil and sediment and therefore have negligible to slow migration potential to ground water.

 

In a supporting weight of evidence study from study report (2019),the adsorption coefficient Koc in soil and in sewage sludge of test chemical was determined by the Reverse Phase High Performance Liquid Chromatographic method according to OECD Guideline No. 121 for testing of Chemicals. The solutions of the test substance and reference substances were prepared in appropriate solvents. The sample of test chemical was prepared by adding 10 mg in acetonitrile to prepare 1000 mg/L test solution, sonicated for 1 mins and filtered through 0.22 μm nylon syringe filter. pH of the resulting solution was 7.4. The analysis was performed at constant recommended conditions such as temperature 25°C (solvent: water) ratio 55:45 at the flow rate of 1 mL/min at 210 nm. The reference substances were chosen according to estimated Koc range of the test substance and generalize calibration graph was prepared. Selected reference substances and test chemical were prepared in acetonitrile with concentration of 400 mg/L. Both were analyzed on HPLC considering the similar conditions. After analyzing on above conditions calibration curve of selected reference substances was prepared to obtain log Koc value. The reference substances were p-Toluamide, Aniline, N-methylaniline, 4-Chloroaniline, phenanthrene, Naphthalene, DDT, having Koc value ranging from 1.8 to 2.9. The Log Koc value of test chemical was determined to be 2.787±0.001 dimensionless at 25°C.This log Koc value indicates that the substance has a moderate sorption to soil and sediment and therefore have slow migration potential to ground water.

 

For the test chemical, the adsorption coefficient Koc in soil and in sewage sludge of test chemical was determined by the Reverse Phase High Performance Liquid Chromatographic method according to OECD Guideline No. 121 for testing of Chemicals (Experimental study report, 2018). The solutions of the test substance and reference substances were prepared in appropriate solvents. A test chemical solution was prepared by accurately weighing 4 mg of test item and diluted with Methanol up to 10 ml. Thus, the test solution concentration was 400 mg/l. The pH of test substance was 8.3. Each of the reference substance and test substance were analysed by HPLC at 210 nm. After equilibration of the HPLC system, Urea was injected first, the reference substances were injected in duplicate, followed by the test chemical solution in duplicate. Reference substances were injected again after test sample, no change in retention time of reference substances was observed. Retention time tR were measured, averaged and the decimal logarithms of the capacity factors k were calculated. The graph was plotted between log Koc versus log k. The linear regression parameter of the relationship log Koc vs log k were also calculated from the data obtained with calibration samples and therewith, log Koc of the test substance was determined from its measured capacity factor. The reference substances were chosen according to estimated Koc range of the test substance and generalized calibration graph was prepared. The reference substances were Benzamide, 4 -methylaniline(p-Tolouidine), N-methylaniline, Nitrobenzene, 4-Nitrobenzamide, N,Ndimethylbenzamide, N-methylbenzamide, 2 - nitrophenol having Koc value ranging from 1.239 to 2.47. The Log Koc value of test chemical was determined to be 3.055± 0.005 dimensionless at 25°C.This log Koc value indicates that the substance has a moderate sorption to soil and sediment and therefore have slow migration potential to ground water.

 

On the basis of above results, it can be concluded that the logKoc value of test chemical was evaluated to be ranges from 2.787 to 4.13, respectively, indicating that the test chemical has as a moderate to strong sorption to soil and sediment and therefore have negligible to slow migration potential to ground water.