IOP PUBLISHING NANOTECHNOLOGY Nanotechnology 20 (2009) 195103 (9pp) doi:10.1088/0957-4484/20/19/195103 The impact of ZnO nanoparticle aggregates on the embryonic development of zebrafish (Danio rerio) Xiaoshan Zhu 1 , Jiangxin Wang 2 , Xuezhi Zhang 1 , Yung Chang 2,3 and Yongsheng Chen 1,3 1 Department of Civil and Environmental Engineering, Arizona State University, Tempe, AZ 85287, USA 2 School of Life Sciences, Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA E-mail: yung.chang@asu.edu and yschen@asu.edu Received 17 December 2008, in final form 21 March 2009 Published 20 April 2009 Online at stacks.iop.org/Nano/20/195103 Abstract With extensive use of metal oxide nanoparticles (NPs) in a variety of applications comes a higher potential of release into aquatic environments. NPs tend to form much larger aggregates in water, which are expected to settle down to the bottom of the water column and possibly get mixed with the sediments. However, little is known about the environmental impacts and biological effects of these aggregated NPs in the sediment column. In this study, we examined the sedimentation of nanoscale ZnO particles (nZnO) in zebrafish culture medium, and assessed the toxicity of settled nZnO aggregates on developing zebrafish embryos and larvae. Given the known dissolution of nZnO particles to release Zn 2+ , we also assessed the toxic effect of soluble Zn 2+ in this organism. We demonstrated that within 48 h, micron-sized nZnO aggregates were formed and settled out of the culture medium. These aggregates were found to exert dose-dependent toxicity to zebrafish embryos and larvae, reducing the hatching rate and causing pericardial edema. The observed toxicity of the nZnO aggregates was not likely a result solely of particle dissolution, as soluble Zn 2+ alone caused much less toxicity to zebrafish embryos than nZnO. Instead, the combination of both nZnO and Zn 2+ may contribute to the embryonic toxicity, possibly by increasing reactive oxidative species (ROS) and/or compromising the cellular oxidative stress response. Interestingly, we demonstrated that one type of formulated sediments could mitigate the toxicity of nZnO aggregates, highlighting a possible countermeasure to reduce the adverse impact of nZnO aggregates on the environment. (Some figures in this article are in colour only in the electronic version) 1. Introduction Commercial manufacture of nanoparticles (NPs) is already underway; the market for nanotechnology has been projected to reach $100 billion by 2025 [1]. This rapid development means that humans and the environment will be exposed to more and more nanotechnology-based products. People have begun to raise concerns about the health risks and environmental impacts of NPs, which may outweigh their benefits [2]. 3 Authors to whom any correspondence should be addressed. Several studies have focused on the cytotoxicity and respiratory toxicity of various types of NPs. However, much less is known about the environmental fate of NPs and their potential toxicity to aquatic biota. It is conceivable that aquatic environments may be polluted with NPs resulting from consumer products as well as from accidental releases during NPs production, transportation, and disposal operations. Thus, these NPs pose risks of causing damage to aquatic organisms, and eventually becoming a new class of hazardous material to humans through food webs. Some of these concerns were confirmed by recent studies, in which aqueous suspensions of 0957-4484/09/195103+09$30.00 © 2009 IOP Publishing Ltd Printed in the UK 1