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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Most sensitive algae: Selenastrum capricornutum
72h-EC50 = 3.3 mg PBS/L; 1.1 mg H2O2/L; 0.36 mg B/L

Key value for chemical safety assessment

Additional information

Three studies on the effect of sodium perborate on cell multiplication of the green algae Selenastrum capricornutum and Scenedesmus quadricauda revealed similar results. The EC50 value of 3.3 mg PBS/L (1.1 mg H2O2/L; 0.36 mg B/L) from the test on Selenastrum capricornutum performed by Solvay Duphar (1993) was the lowest valid EC50 value reported for aquatic species. Only in this test the active oxygen content has been monitored during exposure. Thus, it is the only test among the algal test performed which can be considered valid. A rapid decrease of active oxygen, probably due to biotic elimination (cf. 5.2.1), was observed in this test: 35% after one day and nearly 90% after 2 days of incubation. As stated in OECD-guideline 201, however, disappearence of the test compound in the test solution does not necessarily invalidate the test. So, considering the removal of the test substance in the test medium, the results are taken into account for the evaluation of the aquatic toxicity of sodium perborate.

Furthermore, an inhibition of the biomass growth was observed in this study at the lowest nominal concentration tested (0.62 mg PBS/L), but not at the higher concentrations. This leads to an unclear monotonic dose response curve and consequently no NOEC could be derived (NOEC should be 2.5 mg PBS/L, but has to be confirmed by repeating the test).

No information on the effects of sodium perborate on marine plants could be identified.

Further information from tests with degradation products

The lowest LOEC/NOEC values from long-term tests on the effect of hydrogen peroxide on different algal species were in general ≤ 1 mg/L (EU Risk Assessment Report on Hydrogen Peroxide) and therefore comparable to the results observed in tests with sodium perborate.

The most sensitive effect value on the toxicity of boric acid on algae reviewed by ECB (2009, Assessment Report Boric acid. Product-type 8 (Wood preservative). 20 February 2009) was Selenastrum capricornutum with a 74.5h-NOEC of 17.5 mg B/L. This value is considerably higher that the LC50 value (in boron equivalents) determined for sodium perborate monohydrate on Selenastrum capricornutum (see above), demonstrating that the effects of sodium perborate are mainly caused by hydrogen peroxide.