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Environmental fate & pathways

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For the inorganic substance KHSO5 biodegradation tests are not relevant and not required. The abiotic decomposition in water is fast ultimately forming KHSO4 and H2O2, with the latter being “ready biodegradable”. None of these decomposition products are considered critical with regard to persistence or toxicity. H2O2 degraded to H2O + O2; KHSO4 is further degraded to form HSO4-/SO42-, ubiquitously presented in surface waters and sediments. As H2O2 is not absorpt to sediment and KHSO4 is no risk to the sediment, sediment nor surface water are considered at risk. Furthermore, the available information was considered sufficient to allow a scientific valid evaluation with regard to biodegradation and fate of KMPS in water in sediment systems. Further testing is therefore neither required nor scientifically meaningful.

Degradation in water

The rate of environmental surface water degradation may be conservatively estimated based on the hydrolysis rate at pH 7 and 12 °C (0.061)(DT50 = 11.4 d). In a study on the “Depletion of Potassium Monopersulfate in Synthetic Pool Water”, it was shown that the decomposition of KMPS triple salt in water is very dependent on the presence of oxidisable contaminants. The addition of a ‘body fluid analog’ to the synthetic pool water used in this laboratory test reduced the half-life for decomposition of KHSO5 from ca. 120 hours (synthetic pool water without ‘body fluid analog’) to ca. 3 hours. This is explained by the consumption of KHSO5 in many different oxidation reactions with reduced amine substrate components of the added ‘body fluid analog’, according to the general reaction:

KHSO5 + X -> KHSO4 + X=O.

It can be assumed that KHSO5 is degraded at similar rates in natural waters, such as pond and river water. The higher the concentration of oxidisable organic substrate is in the water, the faster KHSO5 will be degraded.

Degradation in soil

The soil degradation study with KMPS (triple salt) showed, that KHSO5 decomposes rapidly upon contact with soils. The DT50 value of KHSO5 in soils was conservatively calculated at < 11 minutes. After a one hour exposure no measurable KHSO5 was present in soil samples.

The decomposition of the inorganic compound KHSO5 in soil is due to the known abiotic processes also noted in aqueous systems.

1) the reaction of the monoperoxohydrogensulfate ion with H2O present in the soil solution (hydrolysis) in which monoperoxohydrogensulfate is reduced to hydrogensulfate and water is oxidised to hydrogen peroxide, and

2) the disproportionation of monoperoxohydrogensulfate to hydrogensulfate and oxygen.

The decomposition products hydrogensulfate and oxygen are ubiquitously present in the environment and therefore of no concern. On the basis of the available biodegradation tests for hydrogen peroxide, it can be concluded that H2O2 is “readily biodegradable” with the 10-day window criterion being fulfilled (EU RAR Hydrogen Peroxide, 2003).

The existing soil degradation study provides sufficient information on the degradation of KMPS (triple salt) in soil. Due to the very fast decomposition of KHSO5 in soil and the fact that the only decomposition products are potassium, hydrogensulfate, hydrogen peroxide and oxygen, no further studies on degradation in soil were made.