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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The partitioning of 1-methyl piperazine to soil is read-across from a sorption/desorption test result of piperazine. This read-across is considered to be justified for this endpoint since the only difference in structure is one methyl group.

For piperazine a mean Kd of 14.4 L/kg was calculated. There is no correlation between the organic carbon content of the soils used and the sorption observed. Sorption is higher than expected based on the measured log Kow. It is therefore expected that ionic interaction occurs between the negatively charged soil surface and positively charged nitrogens of piperazine. This fate will be identical for 1-methyl piperazine.

The mean Kd of 14.4 L/kg is used to predict the partitioning to soil, sediment and suspended sediment for risk assessment purposes.

For sorption to sludge however a Koc of 721.67 L/kg may be used

Key value for chemical safety assessment

Koc at 20 °C:
721.6

Additional information

The partitioning of 1-methyl piperazine to soil is read-across from a sorption/desorption test result of piperazine. This read-across is considered to be justified for this endpoint since the only difference in structure is one methyl group. For piperazine there is no correlation between the organic carbon content of the soils used and the sorption observed. Sorption is higher than expected based on the measured log Kow. For piperazine a mean Kd of 14.4 L/kg was calculated.

It is therefore expected that ionic interaction is the main driver in the sorption of piperazine.

Under environmental conditions both piperazine and 1 -methylpiperazine will have a single nitrogen protonated because piperazine has two pKa values one at ±9.7 and one at ±5.2. For 1-methyl piperazine one pKa was measured of ±9.4. This single protonated nitrogen accounts for the main fraction of sorption for both substances. This also means that sorption should not be normalized to the organic matter content in soil but instead it is better to use the average Kd value and use this value as the solids water partition coefficient in soil. When sorption is not correlated to the organic carbon content in soil and is actually not determining the distribution in soil, sediment and suspended sediment there is in principle no difference in adsorption to these three compartments (based on dry weight) as the organic matter content is for hydrophobic inter action considered to be the only sorption determining variable. This means that also the solids-water partition coefficient in sediment and suspended sediment can be considered equal to 14.4 L/kg.

As indicated sorption will be identical for 1-methyl piperazine. The mean Kd of 14.4 L/kg is used to predict the partitioning to soil, sediment and suspended sediment for risk assessment purposes. For the partitioning to sludge which mainly consists of organic matter a Koc of 721.67 L/kg may be used.

Other adsorption coefficient indicated as dimensionless:

- log Kp (solids-water in suspended matter) ,1.158 at the temperature 20.0°C

- log Kp (solids-water in sediment) ,1.158 at the temperature 20.0°C

- log Kp (solids-water in soil) ,1.158 at the temperature 20.0°C