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The EU risk assessment report for hydrogen peroxide (European Commission 2003) comes to the following conclusion with regard to biodegradation of the substance (pp. 33/34): “On the basis of the available biodegradation tests it is possible to conclude that the substance is biodegraded under environmental conditions. The observed biodegradation rates of hydrogen peroxide are high and half-lives are short enough to fulfil the criterion “readily biodegradable” (10-day window criterion fulfilled) concerning the degradation rate. Hydrogen peroxide can therefore be considered as readily biodegradable in the aquatic compartment including sewage treatment plant. The simulation test results show that in most cases biodegradation seems to be the dominant and rate determining degradation pathway of hydrogen peroxide in the aquatic environment. The rate of biodegradation is proportional to the microbial population density and the concentration of hydrogen peroxide. Typical natural concentrations of hydrogen peroxide in freshwater and sea are from a few micrograms to some tens of micrograms per litre. Degradation half-lives observed are typically of the order of some hours. The microorganism/hydrogen peroxide ratio is high and degradation is favoured because there is a substantially large amount of catalase active microbes present compared to the concentration of hydrogen peroxide. If the concentration of hydrogen peroxide is remarkably higher than natural concentrations, other factors remaining constant, the inhibitive effect of hydrogen peroxide on naturally occurring microbes is beginning to have more influence thus giving longer half-lives. In extreme cases the toxicity of hydrogen peroxide will slower the degradation process remarkably (test by L'Air Liquide 1991).

Shortest half-lives <<1d can be found in surface waters of eutrophic lakes. These tests are carried out in summer time in warm surface waters and do not represent very well average degradation rates in natural waters of more unfavourable conditions and seasons. Half-lives of 1-3 days may represent quite well annual average degradation rate in mesotrophic/oligotrophic surface waters with low microbial density. Longest half-lives can be found in oligotrophic cold waters with low microbial density and low transition metal concentrations (Fe/Mn). A half-life of 5 days in surface water has been estimated to represent realistic (worst case) half-life in surface water.

As a conclusion half-lives of 2 minutes and 5 days in STP and in surface water, respectively, will be used in the risk assessment.”

The biodegradation of the substance in sediment is of no relevance as hydrogen peroxide will not partition into sediments. The degradation of hydrogen peroxide in soil is expected to be fast in the presence of organic material with half-lives of a few minutes. However, degradation may be slower in soils with low bioactivity and a half-life of 12 hours for biodegradation in soil is considered as a reasonable worst case in the present assessment.