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Toxicity to soil microorganisms

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Description of key information

Based on the justification of the three main components, it can be concluded:
Aluminium, aluminium powders and aluminium oxide are non hazardous (not classified for the environment). Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974) and is therefore found in great abundance in both the terrestrial and sediment environments.
In the environment, lime substances rapidly dissociate or react with water. From these reactions it is clear that the effect of calcium oxide will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions.
Magnesium oxide (MgO) is exempted from registration according to EC 1907/2006 Annex V Section 10.

Key value for chemical safety assessment

Additional information

There are no studies available for “Reaction product of thermal process between 1000°C and 2000°C of mainly aluminium oxide and calcium oxide based raw materials with at least CaO+Al2O3+MgO >80% , in which aluminium oxide, magnesium oxide and calcium oxide in varying amounts are combined in various proportions into a multiphase crystalline matrix”. As this substance is an UVCB substance with aluminium oxide (AL2O3), calcium oxide (CaO) and magnesium oxide (MgO) as main constituents, data and justification based on these main components were taken into account by read across following a structural analogue approach.

 

Aluminium-compounds:

Aluminium, aluminium powders and aluminium oxide are non hazardous (not classified for the environment). Aluminum (Al) is the most commonly occurring metallic element, comprising eight percent of the earth's crust (Press and Siever, 1974) and is therefore found in great abundance in both the terrestrial and sediment environments. Concentrations of 3-8% (30,000-80,000 ppm) are not uncommon. The relative contributions of anthropogenic aluminium to the existing natural pools of aluminium in soils and sediments is very small and therefore not relevant either in terms of added amounts or in terms of toxicity. Based on these exposure considerations additional sediment and/or soil testing is not warranted. More information about exposure based waiving for aluminium in soil and sediments can be found in attached document (White paper on exposure based waiving for Fe and Al in soils and sediments final 15-03-2010. pdf, see attachment).

Calcium-compounds:

The chronic study on the effect of calcium dihydroxide on the nitrogen transformation in an agricultural loamy sand soil (Schulz, 2007a) was carried out according to OECD 216. The study is well documented, all validity criteria are fulfilled. As such a Klimisch 1 score was assigned to the study. Reported 96d-EC50 and 96d-NOEC values for nitrogen transformation equalled >12 g Ca(OH)2 /kg soil dw and ≥12 g Ca(OH)2 /kg soil dw, respectively.

The chronic study on the effect of calcium dihydroxide on the dehydrogenase activity in an agricultural loamy sand soil (Schulz, 2007b) was conducted according to German guidelines for testing of plant protection products (BBA VI, 1-1, 1990). The methods and results are well documented. As such a Klimisch 1 score was assigned to the study. Reported 96d-EC50 and 96d-NOEC values for dehydrogenase activity equalled 8.7 g Ca(OH)2 /kg soil dw and 4 g Ca(OH)2 /kg soil dw, respectively.

In the environment, lime substances rapidly dissociate or react with water. These reactions, together with the equivalent amount of hydroxyl ions set free when considering 100mg of the lime compound (hypothetic example), are illustrated below:

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

100 mg Ca(OH)2 or 1.35 mmol sets free 2.70 mmol

CaO + H2O <-> Ca2+ + 2OH-

100 mg CaO or 1.78 mmol sets free 3.56 mmol

From these reactions it is clear that the effect of calcium oxide will be caused either by calcium or hydroxyl ions. Since calcium is abundantly present in the environment and since the effect concentrations are within the same order of magnitude of its natural concentration, it can be assumed that the adverse effects are mainly caused by the pH increase caused by the hydroxyl ions. Furthermore, the above mentioned calculations show that the base equivalents are within a factor 2 for calcium oxide and calcium hydroxide. As such, it can be reasonably expected that the effect on pH of calcium oxide is comparable to calcium hydroxide for a same application on a weight basis. Consequently, read-across from calcium hydroxide to calcium oxide is justified.

Magnesium oxide:

Magnesium oxide (MgO) is exempted from registration according to EC 1907/2006 Annex V Section 10.

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