Chlorine

CAS RN: 7782-50-5

Environmental Fate

TERRESTRIAL FATE: If liquid chlorine is spilled onto soil, it will react with both organic and inorganic mater in the soil; however, much of the chlorine is expected to volatilize immediately(1). Chlorine is expected to dissolve and disproportionate in the water of moist soils to form chloride and hypochlorite(1). Chlorine in a gas cloud is expected to react with soil surfaces that it comes into contact with(1). Chlorine is toxic to microbial communities; therefore, biodegradation is not considered to be a relevant fate process(1).
AQUATIC FATE: Chlorine gas released into water first dissolves and then undergoes a disproportionation within seconds at environmental pH to form hydrochloric and hypochlorous acid(1,2). Under acidic conditions (pH <4.5), the formation of molecular chlorine is possible(2). Volatilization of molecular chlorine from water surfaces is expected to occur rapidly(2,3) based upon a Henry's Law constant of 0.0104 atm-cu m/mole at 25 deg C(4). Chlorine is toxic to microbial communities; therefore, biodegradation is not considered to be a relevant fate process(2). The hypochlorous acid formed during the disproportionation of chlorine in natural waters reacts with organic and inorganic materials, ultimately forming chloride, oxidized inorganics, chloramines, trihalomethanes, oxygen, and nitrogen(2). Chlorine is not expected to bioaccumulate or bioconcentrate in plants or animals since it reacts with the moist tissues of living systems(1,5). In water chlorine/hypochlorite undergoes direct photolysis with an estimated half-life of 1-4 hours, depending on the time of the day(5).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), chlorine, which has a vapor pressure of 5850 mm Hg at 25 deg C(2), is expected to exist solely as a gas in the ambient atmosphere. Gas-phase chlorine is removed from air primarily by direct photolysis(3-5). At tropospheric wavelengths the gas-phase chlorine molecule (Cl-Cl) undergoes photodissociation, forming two chlorine radicals, which abstract a hydrogen atom from any available organic molecule to form hydrochloric acid(4). A lifetime of 7.3 hours was reported for the photolysis of chlorine, based on a measured rate constant of 2.3X10-3/second(4). In the atmosphere chlorine/hypochlorite undergoes photolysis with an estimated half-life of 1-4 hours, depending on the time of the day(6). Chlorine is also expected to react with cloud particulates and rain drops that it comes into contact with in the atmosphere, forming hydrochloric and hypochlorous acids(3). These acids can then be washed out of the atmosphere by precipitation(3).
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