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Adsorption / desorption

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Description of key information

In accordance with column 2 of REACH Annex VIII, a adsportion/desorption screening (required in section 9.3.1) does not need to be conducted as sodium hypochlorite can be expected to have a low potential for adsorption (calculated log Koc  =  -2.97 to 1.12).
Hypochlorite as an inorganic substance with an infinite water solubility and very low partitioning coefficients should be considered as mobile in soil and sediment. Yet, it has to be underlined that hypochlorite is evanescent in these matrices as it reacts instantly with organic matter by oxido-reduction.

Key value for chemical safety assessment

Koc at 20 °C:
0.001

Additional information

Adsorption/desorption studies are performed for generating information on the mobility of substances and their distribution in the three compartments: soil, water and air.

Due to its oxidising properties, hypochlorite reacts with organic matter in soil and degrades very rapidly. The kinetic model of Vandepitte and Schowanek (No. 989-003) indicates that hypochlorite is eliminated within the first minutes of the test. Thus, it is not possible to determine the concentration in the aqueous phase and in the soil. Therefore an adsorption/desorption test is technically not feasible. It is also not possible to use the HPLC screening method (OECD 121). In this method a cyanopropyl HPLC phase should be used and this phase will be also oxidised by hypochlorite.

An hypothetical Koc can be calculated from Kow through different linear regression equations reported un Guidance (R.7.1.15.3). It can also be calculated by KOCWIN that delivers 2 figures

- using Molecular Connectivity Indices: log Koc = 1.12 (Koc = 13.22 L/kg)

- using regression equation: logKoc = 0.8679 logKow - 0.0004 = -2.9686 (Koc = 0.001075 L/kg).

Hypochlorite as an inorganic substance with an infinite water solubility and very low partitioning coefficients should be considered as mobile in soil and sediment (if it were not fleeting).

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