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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Based on the justification of the three main components of the test substance:
Literary studies investigating the effects of aluminum in the aquatic environment have extensively used test solutions with aluminum concentrations above that of its solubility limit. Results of these studies therefore have limited value for the investigation of intrinsic toxicity. ECr10s and ECr50s ranged from 0.051 to 3.15 mg Al/L and 0.024 to 4.93 mg Al/L, respectively.
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:

The algae data for aluminium compounds from the 2009 and 2010 CIMM datasets demonstrate that elevated pH and elevated DOC are protective against aluminium toxicity, whereas hardness appeared to have a minimal effect. The evidence of both pH and DOC effects are consistent with the Al BLM. Multiple linear regression models (MLRM) based on nominal DOC, and pH were developed to predict nominal EC10 and EC50 values for the algae dataset. The EC50 and EC10 MLRMs performed reasonably well for the dataset. The EC50 MLRM produced an adjusted R2of 0.747, and the EC10 MLRM produce an adjusted R2of 0.987 (see attachment Figures 7.1.1.3-2, and 7.1.1.3-3, respectively).

Literature Review for aluminium compounds: Six chronic toxicity studies to a freshwater microalga (Pseudokirchneriella subcapitata) were identified in the literature as Klimisch 1 or 2 studies. Additional algal studies with Pseudokirchnerella subcapitata were performed at CIMM to evaluate acute and chronic toxicity to algae and for evaluation of water chemistry effects for modelling purposes. All endpoints from CIMM (2009; 2010a) were reported on the basis of nominal Al concentrations because total Al was not measured in these studies. However, CIMM (2010b) compared nominal to measured total Al concentrations in an identical set of algal test solutions prepared to match all water quality conditions and nominal Al exposure concentrations as used in the previous studies (2009; 2010a). In these new test solutions, average total Al concentrations were within 10% of nominal Al concentrations. A linear regression between total and nominal Al concentrations demonstrated a strong relationship with an r2value of 0.99 (Figure 7.1.1.3 -1, see attachment). Therefore, nominal Al concentrations can be considered a reliable estimator of total Al concentrations in these studies. ECr10s were calculated using raw data provided from each study using the statistical program Toxicity Relationship Analysis Program (TRAP) version 1.10 from the US EPA National Health an Environmental Effects Research Laboratory (NHEERL). All other endpoints were as reported in each study. ECr10s and ECr50s ranged from 0.051 to 3.15 mg Al/L and 0.024 to 4.93 mg Al/L, respectively. Water quality data for these studies suggest a direct relationship between toxicity and pH, hardness, and DOC. Studies that experimentally manipulated water quality were reported by CIMM 2009 and 2010a. 

 

Calcium-compounds:

One study for toxicity to freshwater algae is available for calcium dihydroxide. This study (Egeler et al., 2007) was conducted according to OECD 201 with Pseudokirchnerella subcapitata and resulted in EC50 (72h) of 184.57 mg/L (nominal) and NOEC (72h) of 48 mg/L (nominal) based on growth rate.

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.