Acute and chronic effects of magnetic microparticles used in lake restoration on Daphnia magna and Chironomus sp.

Abstract

Magnetic microparticles (MPs) have been recently proposed as a new and promising tool for restoring eutrophicated inland waters. In this study, we analyzed the acute and chronic effects of iron (Fe) MPs on Daphnia magna and on the benthic macroinvertebrate Chironomus sp. The endpoint in the acute toxicity tests was immobilization. In the chronic toxicity tests the offspring production (male and female) in D. magna and the mortality of larvae and pupae, and adult emergence in Chironomus sp. experiments were used as the endpoints. The concentration of MPs that caused 50% of immobilized individuals (EC50) in the acute toxicity test was much higher in D. magna (0.913 g Fe l-1) than in Chironomus sp. (0.445 g Fe l-1), which is likely to be the result of differences in the lifestyle of these organisms, planktonic and benthic respectively. Considering the regular dose of MPs that could be used in a restoration plan, slight effects on organism immobilization are expected. The results of chronic toxicity tests in D. magna showed that in presence of dissolved Fe (dFe), parthenogenetic reproduction was significantly affected, while no significant effect on mortality of larvae and pupae and on adult emergence was detected in Chironomus sp. test. Taking into account that long-term exposure is not likely to occur under the regular procedure of MPs, we conclude that MPs is a riskless (no toxic effect on planktonic and benthic organisms) and efficient (high P adsorption capacity) tool for lake restoration.