Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Introduction

In this section a summary is provided with regard to the chemical reactivity and fate in the environment of the substance “Reaction mass of calcium peroxide, calcium hydroxide and calcium carbonate”.

The main chemical in this reaction mass is calcium peroxide. The composition of the reaction mass can be characterized as follows:

·     ca. 75% calcium peroxide (CaO2)

·     ca. 15% calcium hydroxide (Ca(OH)2)

·     ca. 10% calcium carbonate (CaCO3)

Chemical reactivity of the reaction mass of calcium carbonate, calcium dihydroxide and calcium peroxide

In aqueous solution, the calcium peroxide in the reaction mass decomposes into hydrogen peroxide and calcium hydroxide. The hydrogen peroxide will subsequently further decompose into water and oxygen. Furthermore, the calcium hydroxide and calcium carbonate present in the reaction mass also dissociate when brought into aqueous medium. The different chemical reactions are:

CaO2 + 2 H2O -> Ca2 + + 2 (OH)- + H2O2

H2O2 + H2O -> 2 H2O + O2

Ca(OH)2 -> Ca2 + + 2 OH-

CaCO3 -> Ca2 + + CO32 -

Water solubility of the relevant molecular species

The water solubility of calcium dihydroxide was experimentally determined as 1.84 g/L at 20°C. On the other hand, the water solubility of calcium carbonate was found to be 16.6 mg/L at 20°C. The calcium carbonate thus is less soluble than calcium dihydroxyde by more than a factor 100.

Due to this low water solubility and due to the fact that calcium carbonate is not hazardous (no physicochemical, toxicological or ecotoxicological classification following the criteria of the CLP regulation), this substance has been omitted from the risk assessment.

Water solubility testing of the reaction mass of calcium carbonate, calcium dihydroxide and calcium peroxide

A water solubility study was performed that used the reaction mass as the test substance (2012, GLP, OECD 105). In this test, known amounts of the reaction mass (100, 1000 and 10000 mg/L) were stirred with double distilled water for 24, 48 or 96 hours. Subsequently the water phase was centrifuged to remove all undissolved test substance and the concentration of calcium and hydrogen peroxide in the supernatant was determined.

The results from the 100 mg/L test run show that the theoretical maximum concentration of calcium is obtained within 24 hours. This means that 100 mg of the test substance was dissolved. For the tests at higher nominal concentrations, the theoretical maximum Ca concentration was not reached. It can be concluded that the water solubility will be > 0.1 g/L but less than 1 g/L.

Hydrolysis of calcium peroxide and subsequent decomposition of hydrogen peroxide

The water solubility test on the reaction mass of calcium carbonate, calcium hydroxide and calcium peroxide also demonstrates the formation of hydrogen peroxide upon reaction of the reaction mass of calcium carbonate, calcium hydroxide and calcium peroxide with water, and the subsequent decomposition of the formed hydrogen peroxide.

 

Indeed, after 24h the measured hydrogen peroxide concentration is about 12% of the value that would theoretically be expected in the 100 mg/L experiment, whereas the concentration of dissolved calcium shows that the substance is fully dissolved. The remaining hydrogen peroxide further decomposes, and after 48 hours, no more hydrogen peroxide was detected in the test solution.

Presence of the hydroxyl anions

From the chemical reactions depicted in the figure above it is clear that hydroxyl anions will be formed upon addition of the reaction mass of calcium carbonate, calcium hydroxide and calcium peroxide to water. Those hydroxyl anions originate from the hydrolysis of the calcium peroxide, and from the calcium dihydroxide present in the reaction mass. This results in a solution with a high pH value, as can also be seen in the water solubility experiment described above.

 

From a toxicological point of view, the high pH value implies that the substance could show the typical local effects associated with basic solutions. The systemic effects of the hydroxyl anions are mitigated by the buffer capacity of the blood.

Likewise, the buffer capacity of the environment will also attenuate the ecotoxicological effects of the hydroxyl anions.

Biodegradation and bioaccumulation

As the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide is a multi-constituent substance containing only inorganic constituents, biodegradation is not a relevant parameter. The removal of the different constituents from the environment is driven by the abiotic processes described above.

 

Bioaccumulation of the species formed upon dissolution of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide in water can be excluded based on the following argumentation:

·     Hydrogen peroxide has not only a short half life and a low log Kow, it is also destroyed by the enzyme “catalase” which is ubiquitously present in biotic systems.

·     Both the pH effect cause by the presence of the hydroxyl anions and the intake of the essential element calcium are actively regulated in biotic systems.

Transport and distribution

As the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide rapidly hydrolyses and dissociates in aqueous environment, the potential of the thus formed chemical species to adsorp to soil and sediment is examined:

·     For hydrogen peroxide no remarkable adsorption to soil and sediment is expected based on its high polarity and water solubility. An estimated Koc value of 1.58 L/kg is available in the REACH registration dossier for hydrogen peroxide. Furthermore, Mackay Level 1 modelling indicates that the substance will partition into the aquatic compartment for > 99% at 20°C, and that negligible fractions will be found in the air, soil or sediment compartment.

·     For the hydroxyl anions a Koc or Kd value is not relevant as the behaviour of this anion depends on the buffer capacity of the receiving environment.

·     For the calcium cations measured Kd values ranging from 5.3 to 49.1 L/kg were determined according to the REACH registration dossier for calcium dihydroxide.

Conclusion

The reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide is an inorganic multi-constituent substance that will not persist in the environment nor bioaccumulate in living organisms. Abiotic processes such as hydrolysis and dissociation are responsible for the fate of this multi-constituent substance in the environment. The constituent calcium peroxide is hydrolyzed to calcium hydroxide and hydrogen peroxide. The alkaline constituents calcium hydroxide and calcium carbonate will be neutralized in the environment, while hydrogen peroxide will be degraded by abiotic and biotic processes to oxygen and water.