Calcium hydride

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

other: ead-across based on hydrolysis product (Ca(OH)2)

Adequacy of study:

supporting study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Metal hydrides react quickly with water, forming metal hydroxide and hydrogen gas. Calcium hydride has been shown to be hydrolytically unstable at various temperature and pH conditions (see section 5.1.2 Hydrolysis for further details) . The hydrolysis study has been shown that the reaction speed was less than 1 seconde at all conditions. Therefore, calcium hydride cannot be found as such in the environment. However, instead of calcium hydride, the hydrolysis product "calcium dihydroxide" (Ca(OH)2) is the form which will be available in the environment. The water solubility of Ca(OH)2 is about 1.7 g/L*.
Due the particular environmental fate of calcium hydride, a read-across with the toxicity of calcium hydroxide has been made to better assess the risk when the environment is facing to a calcium hydride release.

* GESTIS database on hazardous substances, www.dguv.de/ifa/gestis/index-2.jsp

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Hydrolysis product of calcium hydride in water following normal environmental conditions. The hydrolysis product present in water would be the "calcium dihydroxide" (Ca(OH)2).

3. ANALOGUE APPROACH JUSTIFICATION
--> See point 1. "HYPOTHESIS FOR THE ANALOGUE APPROACH"

4. DATA MATRIX
Not applicable

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2007

Report date:

2007

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Test material

Test material information

Constituent 1

Reference substance name:

Calcium dihydroxide

EC Number:

215-137-3

EC Name:

Calcium dihydroxide

Cas Number:

1305-62-0

Molecular formula:

CaH2O2

IUPAC Name:

calcium dihydroxide

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The toxicity of algae (Pseudokirchneriella subcapitata) following a growth inhibition test (OECD guideline N°201) has been conducted with calcium dihydroxide (Egeler et al., 2007).
A clear concentration-response relationship was observed. The pH of the medium at concentrations resulting in a considerable growth inhibition, was below 8 and the biological findings are therefore not attributed to the initial pH of the test solutions. It was observed that, however, that with increasing test item concentrations precipitates were formed over time to which algae adhered, leading to their flocculation. The flocculation of algae is thus considered to be the predominant biologically relevant effect in this system test.
The recovery of the test item at the end of the test was below 80% of the nominal concentration. This can be explained since the test item is known to react with CO2 to calcium carbonate, which is poorly soluble in water leading to the formation of precipitates. However, after acidification, the test item recovery was 97,7% of the nominal concentration, which conforms the establishment of the target concentration.
* Growth rate of Pseudokirchneriella subcapitata:
- nominal EC50(72h) = 184.57 mgCa(OH)2/L ,
- nominal NOEC(72h) = 48 mg Ca(OH)2/L.