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EC number: 233-162-8
CAS number: 10049-04-4
Bubnis (2009) reported the loss of chlorine
dioxide in ballast water. This experiment clearly demonstrated that any
chlorine dioxide residuals that might be present following the treatment
of ballast water will quickly be consumed by dilution and demand.
Chlorine dioxide and its transformation products (chlorite and chlorate)
showed similar demand features when tested in diverse waters. The author
observed an initial fast demand for chlorine dioxide along with a slower
continuing loss of chlorite and chlorate ions.
Hydrolysis is a reaction in which a water
molecule or hydroxide ion substitutes for another atom or group of atoms
present in a chemical resulting in a structural change of that chemical.
Potentially hydrolysable groups include alkyl halides, amides,
carbamates, carboxylic acid esters and lactones, epoxides, phosphate
esters, and sulfonic acid esters. The lack of a suitable leaving group
renders compounds resistant to hydrolysis.
Results from Medir and Giralt (1982) demonstrated that aqueous
solutions of chlorine dioxide are fairly stable at 25°C and pH 9 for an
initial period of time before a fast decomposition takes place. The
length of the initial stable period decreases with increasing chlorine
dioxide concentration and in the presence of inert electrolytes. The
reaction products are chlorate, chlorite, chloride and oxygen. Addition
of sodium chloride reduces significantly the induction time, but slows
down the second reaction and changes the product distribution to equal
amounts of chlorite and chlorate.Therefore,
this degradative process will contribute to their removal from the
Two laboratory based experiments were carried out, one on abiotic
chlorite degradation in 3 Swedish river waters with medium to low TOC
values, and one using seawater. In the case of river water, a series of
concentrations was prepared directly in river water with known total
Organic Carbon values and degradation was measured over time. A strong
correlation was found between TOC and half-life. At TOCs found in medium
to low TOC, rivers' half-life was determined as minutes to hours but
degradation rate depended upon chlorite concentration. Above 0.075 mg/L
chlorite was more stable in river water. In the river water with the
lowest TOC (8 mg/L), a half-life could only be calculated at the lowest
concentration of 0.025 mg/L as at higher chlorite concentrations,
insufficient oxidisable material was present for complete degradation to
Bubnis (2009) for chlorite, demonstrated that dilution
of the treated water with the source water showed demand for chlorine
dioxide, chlorite and much slower loss of chlorate beyond what can be
accounted for by dilution.
Other forms of abiotic transformations:
Phototransformation in air:
Standard tests for atmospheric oxidation
half-lives are intended for single substances. Study from Cosson and
Ernst (1994) showed that concentration of substance: 0.020 - 0.024 mol/L
Products: Chlorine dioxide residual concentration vs. time. Quantum
Yield (number of chlorine dioxide molecules divided by the number of
photons adsorbed by the solution): 1.4 at 300 nm and 0.44 at 253.7 nm,
both at 25°C.
Phototransformation in water and soil:
The direct photolysis of an organic molecule
occurs when it absorbs sufficient light energy to result in a structural
transformation. The absorption of light in the ultra violet (UV)
-visible range, 110-750 nm, can result in the electronic excitation of
an organic molecule. The stratospheric ozone layer prevents UV light of
less than 290 nm from reaching the earth's surface. Therefore, only
light at wavelengths between 290 and 750 nm can result in photochemical
transformations in the environment.
Zika et al. (1984) demonstrated that ClO2 is
readily decomposed by sunlight and fluorescent lights. This can lead to
significant losses during water treatment. The characteristics of the
water play an important role in the nature of products resulting from
light-initiated reactions. The bromide ion was found to play a
particularly important role in THM formation and in initiating light
reactions that accelerated the decomposition of ClO2 in the
Photodecomposition of chlorite in aqueous solution is rapid with a
half-life of about 10 minutes depending on concentration. Oxygen,
chloride and chlorate are produced as stable end-products with the
formation of chlorine and chlorine dioxide as intermediates. pH (5<pH<9)
had no effect on the productions of chlorine and chlorine dioxide or of
chlorate and chloride.
As demonstrated by different studies in this
section, chlorine dioxide reacts with a number of inorganic and organic
substances like iron, sulphuric compounds (organic as well as
inorganic), phenolic compounds and humus acids. Surface waters, ground
water, waste water etc. are unique in terms of their composition and
therefore the combination of substances that can react with and degrade
chlorine dioxide. The laboratory study has consequently to be seen as an
example of how chlorine dioxide may decay in the aqueous environment.
Studies from Ottaviani et al. (2002)
and Belluati (2007) demonstrated that Chlorine dioxide is completely
degraded within 37 and 18 min respectively.
No decay of ClO2 could be detected
using tap water during the evaluated time frame. The reason for the slow
decay in tap water is the low amount of substances that can be oxidized.
Still a low amount of ClO2 in the water leaving the water
treatment plant is desired in order to prevent recontamination of the
water and to avoid bio-fouling of the water pipes. The study from Van
der Togt and van Ginkel (2005), on chlorate degradation, concluded that
while chlorate is degraded to chloride, no chlorite is observed. Thus,
chlorite is completely degraded within few minutes.
Chlorine dioxide is completely degraded within seconds to minutes
under the conditions of use. It is considered that no chlorine dioxide
reaches the environment. Chlorine dioxide is entirely degraded to
chloride and chlorate ions, via the transient intermediate of
chlorite which has a really short half-life (few seconds).
Based on the criteria for bioaccumulation stipulated in REACH
Annex IX (9.3.2), low Log Kow and high water solubility and the expected
rapid metabolism of chlorine dioxide and chlorite, it is considered that
the potential for bioaccumulation is low. Therefore, the substance is
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