Assessment of toxic effects of magnetic particles used for lake restoration on Chlorella sp. and on Brachionus calyciflorus

- EC50 (algal growth) for Chlorella sp. was 0.15 g MPs l−1.
- High turbidity and Tot-Fedis cause negative effects on algal growth.
- For B. calyciflorus, LC50 was 1.63 g MPs l−1 (corresponding to 30.7 mg P l−1).
- Hatching rate of B. calyciflorus cysts was 100% for all treatments (Tot-Fedis).
- MPs in a real whole-lake application may cause minor lethal and sublethal effects.

Laboratory tests, by following standardized Organization for Economic Co-operation and Development (OECD) protocols, were run for evaluating the acute effects of iron magnetic microparticles (MPs), recently proposed for lake restoration, on Chlorella sp. (algal growth) and on the rotifer B. calyciflorus (mortality). In addition, the MPs potential indirect effects on rotifer egg bank were assessed by performing hatching rate test with B. calyciflorus cysts in contact with dissolved iron (Tot-Fedis). In the algal growth test, no inhibition occurred at the two lowest MPs concentrations (0.01 and 0.05 g l−1) which would correspond, considering the adsorption efficiency ratio (Phosphorus: MPs), to P concentrations lower than 0.94 mg P l−1, much higher than typical concentrations found in natural waters. For higher MPs dose (EC50 for Chlorella sp. was 0.15 g l−1), no nutrient limitations but high turbidity and Tot-Fedis values cause negative effects on algal growth. For the case of B. calyciflorus, LC50 was 1.63 g MPs l−1 (corresponding to 30.7 mg P l−1). When analyzing Tot-Fedis effect, the hatching rate of B. calyciflorus cysts was 100% for all treatments. To sum up our results for B. calyciflorus acute and chronic toxicity tests, it is extremely unlikely the mortality of adult organisms in contact with MPs as well as an affectation of the rotifer egg bank. In conclusion, it is expected that MPs addition in a real whole-lake application cause minor lethal and sublethal effects on both Chlorella sp. and B. calyciflorus.

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