An article published recently in Toxicology Letters (Yang and Watts, 2005) received significant national and international media attention (UPI, 2005). This article was used in the media to claim that nanoparticles exert a negative impact on plants. This media coverage reflects the increasing public attention to biological effects of nanoscale particles, as well as the growing number of scientific publications reporting both positive (for example, nanoscale titanium oxide improved growth of spinach seeds, see Zheng et al., 2005) and negative (Holsapple et al., 2005) effects. However, effects due to the chemical nature, in contrast to unique features of nanoparticles such as quantum effects and ability to translocate, are not always distinguished despite the importance of these issues for understanding the mechanisms of biological activity/inactivity of nanoscale materials. Yang and Watts (2005) failed to make this distinction and, therefore, reached some unsupported conclusions. These limitations necessitate care in the interpretation of these research findings. The toxicology of nanoscale particles is a very broad area potentially encompassing an enormous variety of materials. There are still many unresolved issues and challenges concerning the biological effects of nanoscale particles (EPA, 2005; Holsapple et al., 2005). In order to conduct research activities most effectively, it is of paramount importance to quantify exposures and to conduct thorough physical and chemical characterization of test materials as recommended (Oberdörster et al., 2005). Attention to appropriate experimental design and interpretation will be needed to provide a defensible scientific understanding of the biological effects of nanoscale particles.
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