Toxicity of dimercaptosuccinate-coated and un-functionalized magnetic iron oxide nanoparticles towards aquatic organisms

Magnetic iron oxide nanoparticles (IONP) have gained growing attention in recent years for their promising applications in medical treatment and environmental remediation. Among the IONP, dimercaptosuccinic acid coated-IONP (DMSA-IONP) have great potential because of their rapid uptake into cells and their potential to effectively adsorb heavy metals. The widespread use and potential release of IONP into the environment raises concern about their environmental impact. To date, little is known about the consequences of the exposure of aquatic organisms to such particles. In this context we investigated the colloidal stability of DMSA-IONP in different test media as well as their effects on green algae (Raphidocelis subcapitata), duckweed (Lemna minor) and water fleas (Daphnia magna). Moreover, a comparative analysis of stability and ecotoxicity data of DMSA-IONP with freshly prepared and aged uncoated IONP dispersions was performed, considering the importance of stability of particles in determining their toxicity. The green algae were the most sensitive organism with EC50 values (72 h) ranging between 0.86-2.27 mu M Fe (i.e. 0.05 to 0.13 mg Fe L-1) for the three types of IONP. The observed flocculation and (co-) sedimentation of algae with IONP are assumed to reduce the access of cells to nutrients and light. Lemna was not affected by any of the IONP due to the low availability of IONP induced by fast aggregation of IONP in the medium. Minor toxic effects on Daphnia were found for uncoated IONP (EC50 between 374-1181 mu M Fe, i.e. 21-66 mg Fe L-1) after 72 h. However, the ingestion and accumulation of coated and uncoated IONP in the gastrointestinal tract of daphnids was observed. Our evaluation of IONP has revealed a certain hazard potential to aquatic organisms. In this light it appears important to prevent the release of large amounts of IONP into the environment, which might limit their applicability.