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Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The following processes are involved in the distribution of chlorine 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 SURFae / 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 to 10-4 Pa.

VP = Vapour pressure of chlorine gas [Pa] = 678000

This results in Fassaer = 1.47 x 10-10.

Thus, most atmospheric chlorine gas is not associated with atmospheric aerosols.

Volatilisation from water

Chlorine forms hypochlorous acid and hypochlorite anion in water at environmental pH values. At the conditions T = 20° C, P = 760 mm Hg, and pH = 6.5 - 8.5, after addition of 1.4 mg/l of chlorine gas to water (assuming no other chemicals are present) the following reactions occur:

Cl2 + H2O => H+ + Cl- + HClO, K1 = 10-3.3

HClO => H+ + ClO-, K2 = 10-7.3

The calculated chlorine gas concentration is between 3.0 x 10-13 and 4.0 x 10-14 mg/L and the calculated concentration of hypochlorous acid is between 2.0 x 10-5 and 1.8 10-5 mg/L. As the concentration of chlorine gas in water is low at environmentally relevant pH, the amount of chlorine that could volatilise from water into air is expected to be very low.

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 (kinetic model) The adsorption coefficient (log Koc) can only be calculated applying QSAR (page 26, chapter 4, part III of the TGD) for soil and sediment to be log Koc = 0.57. Hypochlorite as an inorganic substance with an infinite water solubility and very low partitioning coefficients (calculated log Kow = - 0.87 and log Koc = - 0.57) should be considered to be mobile in soil and sediment.

Summary of environmental distribution

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