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Adsorption / desorption

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Description of key information

Adsorption to the solid soil phase is not expected.

Key value for chemical safety assessment

Additional information

Experimental data are only available for one of the major components of the reaction mass of 2 -piperazin-1 -ylethanol, piperazine-1,4 -diethanol and piperazine (50, 25 and 25%).

The log Koc was experimentally determined for piperazine (CAS 110 -85 -0) according to OECD 106. Three soils were tested, sandy loam, loam and sand. Kd values between 7.9 and 20.1 L/kg were measured, giving Koc values between 507 and 2233 (log Koc: 2.7 to 3.3). The Koc was not correlated to the organic carbon content of the soils.

In absence of experimental data for the other major components, the adsorption potential was estimated for all three major components using the MCI and the Kow methods of the PCKOCWIN v2.00 module from SRC EPI Suite v4.11. These estimates are representative for uncharged molecules. All three substances ionise in aqueous solutions, therefore the adsorption coefficients were calculated according to Franco & Trapp (2008, 2009, 2010) to correct for the charged molecules at pH 5, 7 and 8. This pH range represents 98% of the European soils. The value at pH 7 will be used as key value, i.e. for PEC and PNEC calculations.

The Koc values are listed below:

2 -Piperazin-1-ylethanol (CAS 103-76-4):

Uncharged molecule:

- MCI method: Koc = 3.38; log Koc = 0.53

- Kow method: Koc = 0.39; log Koc = -0.41

Charged molecule:

- Franco & Trapp, 2008, 2009, 2010:

pH 5 to 8: Koc = 16; log Koc = 1.2

Piperazine-1,4-diethanol (CAS 122-96-3):

Uncharged molecule:

- MCI method and Kow method: the substance was not within the applicability domain of the estimation model.

Charged molecule:

- Franco & Trapp, 2008, 2009, 2010:

pH 5: Koc = 29; log Koc = 1.47

pH 7: Koc = 29; log Koc = 1.46

pH 8: Koc = 25; log Koc = 1.40

Piperazine (CAS 110 -85 -0):

Measured Koc (AkzoNobel, 2003):

loam: 507 (log Koc = 2.7)

sandy loam: 2233 (log Koc = 3.3)

sand: 637 (log Koc = 2.8)

Uncharged molecule:

- MCI method: Koc = 21; log Koc = 1.31

- Kow method: Koc = 1.5; log Koc = 0.15

Charged molecule:

- Franco & Trapp, 2008, 2009, 2010:

pH 5 to 8: Koc = 18; log Koc = 1.25

Regarding the experimental result for piperazine, adsorption to the solid soil phase is expected in sandy loam (log Koc > 3), but not in loam and sand (log Koc < 3). Since piperazine is readily biodegradable, the potential for adsorption in sandy loam can be neglected.

In a weight of evidence approach for the reaction mass, adsorption to the solid soil phase is not expected.

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