The effect of CuO nanoparticles on gene expression patterns in Daphnia magna

There is still a lot of contradiction on whether metal ions are solely responsible for the observed the toxicity of ZnO and CuO nanoparticles to aquatic species. While most tests have studied nanoparticle effects at organismal levels (e.g. mortality, reproduction), effects at suborganismal levels may clarify the role of metal ions, nanoparticles and nanoparticle aggregates. In this study, the effect of ZnO, CuO nanoparticles and zinc, copper salts was tested on the gene expression levels in Daphnia magna. D. magna was exposed during 96 hours to 10% immobilization concentrations of all chemicals, after which daphnids were sampled for a differential gene expression analysis using microarray. When comparing the nanoparticle exposed daphnids (ZnO or CuO) to the metal salt exposed daphnids (zinc or copper salt), the microarray results showed no significantly differentially expressed genes. These results indicate that the toxicity of the tested ZnO and CuO nanoparticles to D. magna caused is solely caused by toxic metal ions. 4 replicate exposures of ZnO nanoparticles, ZnCl2, Blank (for Zn); 4 replicate exposures of CuO nanoparticles, CuCl2.2H2O, Blank (for Cu); Individual reference design with swapped dyes for zinc (e.g. ZnO-REFZn; REFZn-bl) and copper exposure (e.g. CuO-REFCu; REFCu-bl); Zinc reference sample is a mixture of equal aliquots of ZnO nanoparticle, ZnCl2 and blank; Copper reference sample is a mixture of equal aliquots of CuO nanoparticle, CuCl2.2H2O and blank