Reaction mass of calcium dihydroxide and calcium peroxide

Endpoint summary

Additional information

The acute aquatic toxicity of “reaction mass of calcium dihydroxide and calcium peroxide” has been investigated in a few valid assays. The experimental concentrations in those studies were based on the initial loading rates to which the test organisms were exposed. Studies on fish Cyprinus carpio using the reaction mass showed no toxicity at 100 mg/L (i.e. 96h-LL50 > 100 mg/L). The48h-EL50 forDaphnia magnaexposed to the reaction mass was 8.7 mg/L. For algae, the 72h-ErL50 and NOELr for growth rate inhibition (72h-ErL50) was determined to be 36 mg/L and 1 mg/L, respectively. The results showed that fish is less sensitive to the reaction mass than Daphnia and algae. No experimental study on the chronic toxicity of the reaction mass to Daphnia is available. However, the information can be derived from test data available for the primary hydrolysis product of the reaction mass “hydrogen peroxide”.  As evidenced in a water solubility study, the reaction mass goes into the chemical reactions below in water rapidly (i.e. wihing 24 hours) and hydrogen peroxide subsequently occurred. 

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

- H2O2 + H2O -> 2 H2O + O2

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

Thus, the aquatic toxicity observed for the reaction mass can be attributed to the adverse effects exerted by the hydrogen peroxide formed upon hydrolysis of calcium peroxide. Indeed, the 48h-LC50 value for daphnia calculated from test data available for hydrogen peroxide based on the chemical reactions above was comparable with the value experimentally determined in the study conducted on the reaction mass. Accordingly, the 21d- NOEC value for Daphnia was derived from test data available for hydrogen peroxide and it was determined to be 1.67 mg/L. Therefore, the lowest chronic toxicity value of 1 mg/L determined for algae was used to calculate PNECs for the aquatic environments.