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Key value for chemical safety assessment

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No studies on toxicokinetics are available. However, toxicokinetic information can be derived from the physicochemical properties and the chemical reactivity of the constituents of the reaction mass of calcium carbonate, calcium dihydroxide and calcium peroxide.

 

The reactions that take place when the different components of the reaction mass of calcium carbonate, calcium hydroxide and calcium peroxide are dissolved in water are equally applicable when the systemic availability of the reaction mass of calcium carbonate, calcium hydroxide and calcium peroxide is assessed. Indeed, the chemicals can only be systemically available to the organs when they can be transported to different parts of the body, which requires dissolution of the chemicals in the blood.

 

As a consequence, the chemical reactions driving the environmental fate and the environmental toxicity of the reaction mass of calcium carbonate and calcium dihydroxide and calcium peroxide are also relevant for the assessment of the toxicokinetics of this multi-constituent substance.

 

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

H2O2 + H2O               -->       2 H2O + O2

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

CaCO3                      -->       Ca2++ CO32 -

 

Therefore, the read-across from test results available for hydrogen peroxide and calcium dihydroxide is considered justified not only for ecotoxicological but also for toxicological endpoints. According to the applicable chemical reaction (see above), the amount of hydrogen peroxide formed is equimolar to the amount of calcium peroxide present in the reaction mass. As the concentration of calcium peroxide in the reaction mass is ca. 75%, 100 mg of the reaction mass contains 75 mg of calcium peroxide, which corresponds to 1,04 mmol of calcium peroxide. Therefore, 1.04 mmol (= 35,36 mg) of hydrogen peroxide is formed upon dissolution of 100 mg of the reaction mass.

 

 

It is to be noted that hydrogen peroxide itself rapidly degrades both in tissues of first contact and blood due to the presence of catalase in these environments. Catalase is an iron-containing enzyme present in blood and many tissues. Its biological role is to scavenge the hydrogen peroxide that is formed as a byproduct in many normal metabolic processes.

 

The calcium dihydroxide that is both present in the reaction mass and formed upon hydrolysis of the calcium peroxide will mainly cause effects related to the pH change. This elevated pH value implies that the substance will show the typical local effects associated with basic solutions. The systemic effects of the hydroxyl anion are mitigated by the buffer capacity of the blood.

Because hydrogen peroxide is rapidly degraded in the blood, while calcium hydroxide is neutralized due to the buffer capacity, the reaction mass is not expected to be systemically available.