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Environmental fate & pathways

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Distribution

The following processes are involved in the distribution of hypochlorite in the environment.

• Fraction of substance in air associated with aerosol

• Partitioning between air and water

• Partitioning between solids and water in soil, sediment and suspended matter

Adsorption to aerosol particles

The fraction of substance associated with aerosol particles can be estimated on the basis of the vapour pressure of the substance

Fassaer = CONjunge x SURFaer / VP + CONjunge x SURFaer

Fassaer = fraction of the substance associated with aerosol particles

CONjunge = constant of Junge equation [Pa x m]

SURFaer = surface area of aerosol particles [m2 x m3] According to TGD as a default the product of CONjunge x SURFaer is set to10-4 Pa.

VP = Vapour pressure of hypochlorous acid [Pa] = 2500

This results in Fassaer = 4.0 x 10-7.

Thus, most atmospheric hypochlorous acid is not associated with atmospheric aerosols.

Volatilisation from water

At environmental pH values (6.5-8.5) half of the hypochlorite is in the undissociated form of hypochlorous acid and half is dissociated to the hypochlorite anion. Only the hypochlorous acid fraction is volatile. The measured Henry’s Law constant for hypochlorous acid of 0.097 Pa m³ mol-1 indicates that volatilisation from surface water is not expected to be an important process.

Adsorption onto / desorption from soils

As hypochlorite is a very strong oxidising substance, an adsorption/desorption test is technically not feasible. Hypochlorite would react with organic substance present in the test system and degrades to chloride within minutes. The adsorption coefficient Koc can only be calculated applying QSAR:

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 to be mobile in soil and sediment.

Summary of environmental distribution

The adsorption of hypochlorous acid to aerosol particles, the volatilisation from water into air and the adsorption of hypochlorite onto soil are very low. Thus, hypochlorite remains in the aqueous phase where it degrades very rapidly to chloride.

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