Due to their superparamagnetic properties, iron oxide nanoparticles are mainly used as contrast agents in magnetic resonance tomography (MRT) . Several variants of dextran-coated SPION have been approved already.
Moreover, these special properties can offer the advantage of selective SPION distribution in the body. The SPION can be fixed in the desired target region (the tumor, for example) by means of an external magnetic field. Once fixed, the particles can release attached drugs or substances to the respective area, thus reducing the dose of active agents and minimizing the systemic effects (side effects in the remaining organism) ^[2,3,4,5,6]. Besides, SPION can be heated through oscillating magnetic fields. This method is used already in cancer therapy. Without damage to the surrounding tissues, tumor cells are killed selectively through local heat development of SPION placed in the tumor ^[1,7,8].

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6. Rudge, S  et al. (2001) J. Controlled Release 74, 335 - 340.
7. Jordan, A et al. (1997) in U. Häfeli, et al. (Eds.), Scientific and Clinical applications of Magnetic Carriers, Plenum Press, New York, 1997,p. 569-595.
8. Jordan, A et al. (1999), J. Magn. Magn. Mater, 201. 413 - 419.
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10. Hamm, B et al. (1994) J Magn Reson Imaging 4 659-668.
11. Reimer P et al. (2003) Eur Radiol 13, 1266-1276.

After treatment with iron oxide nanoparticles, the bacteria did not exhibit reduced growth as compared with untreated bacteria. There were no indications of an uptake of particles into the cells ^[2,3]. Only very high concentrations were found to impair growth ^[3,4]. Compared with iron oxides, iron nanoparticles, however, were observed to impede bacterial growth at lower concentrations ^[2,3].
Both in adult medaka and in embryos, high concentrations of iron nanoparticles cause oxidative stress occurring at the beginning of exposure and subsiding subsequently ^[5]. Moreover, modifications caused by contact of the particles with tissues were found in tissues of the gills and intestines of adult fishes.
The viability of isolated cells of gills of rainbow trout is not affected by the iron oxide particles ^[6]. Although gills of the common mussel take up iron oxide particles, the changes in their function after exposure proved to be minimal. Interestingly, the nanoparticles did not exhibit increased or different effects compared with soluble iron salt ^[7].
Pumpkin plants growing in water containing iron oxide particles were found to take up particles in leaves, roots, and sprouts. There was no uptake when the plants were grown in soils containing particles.

In spite of uptake, the plants were found to grow unchanged and appear normal compared with the untreated specimens.  Interestingly, another plant species, the lima bean, was not capable of taking up particles ^[8]. Moreover, another type of pumpkin and the rye grass, which both had been treated with comparable particle concentrations in hydroponic water, did not take up coated iron oxide particles ^[9].
With this in view, iron and iron oxide particles are not toxic to plants, bacteria, fishes, and cultivated cells. Effects were only observed when applying exceptionally high concentrations. Comparative studies showed that the iron particles had stronger effects than the iron oxides. Therefore, it is important to differentiate between effects of iron, effects of different types of iron oxides, and effects of applied coatings.

Literature

1. Scheffel A. et al. 2005, Nature, 440, 110-114.
2. Lee C. et al. 2008, Environ Sci Technol., 42, 4927-4933.
3. Auffan M. et al. 2008, Environ Sci Technol., 42, 6730-6735.
4. Tran N. et al. 2010, Int J Nanomedicine, 5, 277-283.
5. Li H. et al. 2009, Ecotoxicol. Environ. Saf., 72, 684-692.
   
6. Hildebrand H. et al., 2010, Environ Pollut., 158, 65-73.
   
7. Kadar E. et al. 2010, A nal Bioanal Chem, 396, 657-666.
8. Zhu H et al. 2008, J Environ Monit., 10, 713-717.
9. Wang H. et al. 2010, Nanotoxicology, 5, 30-42.