Potassium superoxide

Endpoint summary

Description of key information

KO2 reacts rapidly with water to produce potassium hydroxyde (KOH), oxygen (O2) and potassium hydrogen peroxide (KHO2), which further slowly decomposes to KOH, H2O2, and O2: 2 KO2 + 2 H2O ---> 2 KOH + H2O2 + O2 (De Kumar, 2007).

Additional information

Based on the chemistry and the inorganic nature of the substance, testing to meet requirements on the fate of KO2 in the environment is scientifically not necessary. KO2 degradation products can be assessed separately.

KOH:

KOH is a strong alkaline substance that dissociates completely in water to K+ and free hydroxydes: OH-

- OH- ions.

The formation of hydroxyl radicals is known to induce changes in pH. The OH- ions can then react with free H+ or any acidic species that may be present, forming water.

- K+ ions.

The release of potassium from KOH is negligible comparison of the global anthropogenic potassium (Ullmann, 1998).

The solubility of hydroxides is affected by pH, temperature and the presence of other species in solution: 

- increased pH causes decreased solubility because a higher OH- concentration reduces the amount of solid hydroxide that can dissociate into free metal ions and OH- ions.

- with increased temperature, the alkali metal hydroxide becomes more soluble.

H2O2 (H2O2 - EU RAR, 2003; JACC no.22 - Hydrogen Peroxide, 1993):

H2O2 is a reactive and short-lived polar substance that presents a high solubility.

- Degradation:

Hydrogen peroxide is a quite reactive substance in the presence of other substances, elements, radiation, materials or cells. Both biotic (aerobic bacteria-mediated process. Barenschee, 1990; Spain, 1989; Zepp, 1987; Cooper, 1990) and abiotic (Degussa, 1977a; Goor, 1989; Schumb, 1955; Olszyna, 1988; Sakugawa, 1990; Kleinman, 1986) degradation processes are important routes in the removal of hydrogen peroxide in the environment. Biological degradation of hydrogen peroxide is an enzyme-mediated process whereas abiotic degradation of H2O2 is due to reaction with itself (disproportionation), reaction with transition metals, organic compounds capable to react with H2O2, reaction with free radicals, heat or light. Hydrogen peroxide is normally a short-lived substance in the environment. Rapid degradation will occur due to many alternative and competitive degradation pathways. However, like most substances, in special circumstances when degradation processes are inactive, hydrogen peroxide can be an extremely persistent substance in the environment.

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”.

- Bio-accumulation:

H2O2 decomposes rapidly into water and oxygen in water or when organic material is present (Degussa, 1977a). There are actually no experimental results on bioaccumulation available. As hydrogen peroxide is reactive and a short-lived polar substance, no bioaccumulation is expected. Also the estimated log Kow of about -1.5 indicates negligible potential of bioconcentration in aquatic organisms (Degussa, 1998). BCFs calculated according to the TGD for fish and earthworm are low, 1.4 and 3.3, respectively.

- Absorption:

No experimental results were found concerning adsorption and desorption behaviour of H2O2. Being highly soluble in water (in all proportions) and highly polar substance, no remarkable adsorption to soil and sediment is expected and the mobility in soil is expected to be high.