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Environmental fate & pathways

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Hydrogen peroxide is ubiquitous in air and all types of natural waters. Highest concentrations are typically found in water of clouds or in raindrops.

Air: A complex equilibrium exists in air among molecular oxygen, hydroxyl radicals, nitrogen oxides and other photooxidants. This equilibrium system is influenced by solar radiation and natural as well as anthropogenic emissions. Hydrogen peroxide is part of this equilibrium system, being formed from hydrogen superoxide (HO2) radicals (e.g. Sakugawa et al. 1990). The formation of hydrogen peroxide is favoured by factors leading to high radical concentrations (e.g., solar radiation or emissions of volatile organic carbon (VOC) or carbon monoxide), while the presence of radical scavengers such as NOx counteracts the formation of hydrogen peroxide. Major sinks for atmospheric hydrogen peroxide are the oxidation of sulphur dioxide, reaction with hydroxyl radicals as well as wet deposition (see table on high concentrations found in rain water). The photochemical dissociation of hydrogen peroxide is considered to be a minor sink (Sakugawa et al. 1990).

Surface water: Formation of hydrogen peroxide in surface waters was found to be due to UV radiation in the presence of DOC and oxygen (Sturzenegger 1998, Scully et al. 1996). Other processes are deemed not to contribute significantly to the overall formation rate (Herrmann and Herrmann 1994). Hydrogen peroxide is decomposed in water to form water and oxygen, both compounds of no concern: H2O2 --> H2O + 0.5 O2 This reaction has been investigated and discussed by many authors (e.g. Degussa AG 1997, Goor et al. 1989, Schumb et al. 1955). The main conclusions are that a catalyst is needed for the decomposition reaction to proceed at a significant rate under environmental conditions. Suitable catalysts are ions of transition metals such as iron, manganese or copper, as well as the enzyme catalase (e.g. Spain et al. 1989). Biotic and abiotic catalysis of the decomposition reaction proceeds in parallel under environmental conditions, and are in equilibrium with formation reactions.

Soil: Hydrogen peroxide is present in the soil water, due to its high polarity and full miscibility with water. Therefore, the same decomposition mechanisms apply for soil as discussed for surface water (Aggarwal et al. 1991, Spain et al. 1989, Pardieck et al. 1992).

In summary, hydrogen peroxide concentrations in environmental media depend on the equilibrium of formation and decomposition reactions. Environmental media are therefore expected to possess substantial capacities to buffer anthropogenic emissions of hydrogen peroxide. Furthermore, the decomposition of hydrogen peroxide in air, water or soil generally cannot be investigated by standard guideline tests designed for biotic or abiotic degradation of organic compounds.