Selenious acid

Ecotoxicological Summary

Conclusion on classification

Acute and chronic reference values for environmental classification are based on standard test as laid down in Council Regulation (EC) No 440/2008 on “test methods pursuant to Regulation (EC) No 1907/2006 of the European Parliament and of the Council on the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)”

For seleniuous acid, reliable acute toxicity data are only available for aquatic invertebrates, resulting in a 48-h EC50 of 1.22 mg Se/L for immobilisation of Daphnia magna (Kimball, 1978). Reliable chronic toxicity data for are available for both fish (28-d NOEC of 0.083 mg Se/L for post-hatch mortality of Promephales promelas, Kimball, 1978) and invertebrates (28-d NOEC of 0.07 mg Se/L for reproduction of Daphnia magna, Kimball, 1978).

Acute and chronic toxicity data to fish, invertebrates and algae are also available for other inorganic selenium compounds. The lowest L(E)C50 for fish, crustacean or algae growth rate are 2.06, 0.55 and 44.24 mg Se/L, respectively. The 48-h LC50 of 0.55 mg Se/L (based on dissolved Se concentration) was observed for the effect of Na₂SeO₃ on Daphnia magna (Maier et al., 1993). This value is selected as the acute reference value for classification of inorganic selenium compounds.

The lowest chronic NOEC or EC10 for the toxicity of Se to freshwater fish, invertebrates or algae are 0.01, 0.07 and 4.57 mg Se/L, respectively. The lowest value of 0.010 mg Se/L was oserved in a 258-d study on the effect of Na₂SeO₃ on pre-spawning mortality of Lepomis macrochirus (Hermanutz et al., 1992). This is however neither a standard fish species, nor a standard test and therefore not selected for classification. The lowest standard test resulted in a 90-d NOEC of 0.021 mg Se/L for the effect of Na₂SeO₃ on mortality of Oncorhynchus mykiss (Hunn et al., 1992) and this value was selected as chronic reference value for classification of selenium.

All results are based on dissolved elemental Se concentrations. Because selenium is an inorganic element, there is no potential for degradation.

For the classification of selenious acid, the acute and chronic reference values based on mg Se/L must be corrected for the molecular weight of selenious acid (128.98 g/mol, 61% Se), resulting in 0.90 and 0.034 mg H₂SeO₃/L, respectively. Both values are below the solubility limit of selenious acid. Based on these reference values, the classification for selenious acid is “Aquatic Chronic Category 1” (acute reference value ≤1 mg/L and chronic reference value ≤1 mg/L).