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Environmental fate & pathways

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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 degradated 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 degradated to chloride, no chlorite is observed. Thus, chlorite is completely degradated within few minutes.

Degradation rates

Chlorine dioxide is completely degradated 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).

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