Multimodal Action and Selective Toxicity of Zerovalent Iron Nanoparticles against Cyanobacteria Blahoslav Marsalek, † Daniel Jancula, † Eliska Marsalkova, † Miroslav Mashlan, ‡ Klara Safarova, ‡,§ Jiri Tucek, ‡,§ and Radek Zboril* ,‡,§ † Institute of Botany, Academy of Sciences of the Czech Republic, Lidicka ́ 25/27, 657 20 Brno, Czech Republic ‡ Centre for Nanomaterial Research, Faculty of Science, and § Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University, Slechtitelu 11, 783 71 Olomouc, Czech Republic * S Supporting Information ABSTRACT: Cyanobacteria pose a serious threat to water resources around the world. This is compounded by the fact that they are extremely resilient, having evolved numerous protective mechanisms to ensure their dominant position in their ecosystem. We show that treatment with nanoparticles of zerovalent iron (nZVI) is an effective and environmentally benign method for destroying and preventing the formation of cyanobacterial water blooms. The nanoparticles have multiple modes of action, including the removal of bioavailable phosphorus, the destruction of cyanobacterial cells, and the immobilization of microcystins, preventing their release into the water column. Ecotoxicological experiments showed that nZVI is a highly selective agent, having an EC 50 of 50 mg/L against cyanobacteria; this is 20-100 times lower than its EC 50 for algae, daphnids, water plants, and fishes. The primary product of nZVI treatment is nontoxic and highly aggregated Fe(OH) 3 , which promotes flocculation and gradual settling of the decomposed cyanobacterial biomass. ■ INTRODUCTION The evolution of oxygen-producing cyanobacteria approxi- mately 2.5 billion years ago had a profound impact on the Earth’s atmosphere, changing its early reducing composition to its current oxygen-rich one. 1 As primary producers of organic compounds, cyanobacteria play crucial roles in aquatic and terrestrial ecosystems. They fulfill a number of key functions, including CO 2 and N 2 fixation, oxygen evolution, biomass production, and active colonization of substrates during primary and secondary succession in both terrestrial and aquatic ecosystems. 1-7 Despite their importance in the maintenance and evolution of ecosystems, cyanobacteria can also pose many serious environmental and health risks, depending on their abundance, which has been observed to be increasing in various waters around the world. Several hypotheses have been put forward to explain this increased abundance; it is generally accepted that the two most important factors in the increased formation of large cyanobacterial blooms are global climate change 8 and dramatic increases in the quantities of bioavailable nutrients in surface waters. 9-11 Cyanobacteria produce structurally diverse toxins (microcystins, nodularins, saxitoxins, anatoxins, cylin- drospermopsin), which can pose a significant health hazard in drinking water; among their potentially fatal effects are liver damage (including liver cancer), imunotoxicity, embryotoxicity, cytotoxicity, and neurotoxicity. 12-18 In recent years, various technologies for the elimination and removal of cyanobacterial water blooms have been developed. These methods differ in terms of their mechanism and selectivity of action, efficiency, large-scale applicability, environ- mental acceptability, financial cost, and technological sophisti- cation. The most widely used methods are designed to reduce phosphorus loads in catchment and sediments. 10,19 Because of their adverse ecological impacts and relatively brief duration of action, direct chemical methods based on the use of algaecides are not considered to be useful in advanced restoration projects. 20 Other approaches that have been considered involve the use of flocculants or coagulants, 21,22 oxidative techniques (e.g., ozonation, hydrogen peroxide application, chlorina- tion), 23-25 and physical methods such as ultrasound technologies. 26 The most modern methods are based on various ecotechniques such as lake destratification, food-web manipulation, 27 or biotic interactions such as those between cyanobacteria (and their toxins) and bacteria or macrophytes. 28 However, all of these technologies have several general disadvantages, including low selectivity and adverse environ- mental impact. Moreover, oxidative and ultrasonic methods do not destroy or inactivate already-released toxins. The effects of algaecides and flocculants are temporary; treatment with these agents does not preclude the future occurrence of cyanobacte- rial blooms. And while ecotechniques and methods based on Received: September 9, 2011 Revised: January 9, 2012 Accepted: January 11, 2012 Published: January 11, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 2316 dx.doi.org/10.1021/es2031483 | Environ. Sci. Technol. 2012, 46, 2316-2323