1. Advancements in the field of nanotechnology have attracted global attention both in the industrial and scientific world. There has also been increasing efforts to investigate the release, toxicity and environmental fate of ENPs. The interaction of ENPs with plants is a subject of continued study and there is a growing body of research in this area. The present study investigated the phytotoxic effects of ZnO and CuO ENPs on carrot and parsnip and accumulation of metals in the edible portion of these plants. The results have potential implications for agriculture, remediation and human health.  ENP suspensions were prepared by mixing nanoparticles in deionized water and sonicating the solutions for one hour to suspend and distribute the ZnO or CuO.  The characteristics of the suspensions were determined using TEM and a Malvern Zetasizer ZS90. Particle size distribution and zeta potential measurements were taken for each treatment.  A dissolution experiment was done with each suspension to determine the ratio of ionic metal to intact NP at equilibrium to provide a more realistic view of the chemical forms plants would be exposed to.  Plants were initially grown in a mixture of vermiculite and perlite and later transferred to a hydroponic system containing one-fifth strength Johnson's solution and allowed to grow before the application of the treatments.  Plants were exposed to increasing concentration of the nanoparticle suspension (10, 100, 500, 1000 ppm), an ionic treatment, and a control with 6 replicates for each treatment. The plants were harvested after an exposure time of 10 days.  Visual examination was done for symptoms of toxicity. Relative chlorophyll, relative water content and transpiration rate measurements were taken for all the treatments.  All experiments were done separately for both ZnO and CuO ENPs with carrot and parsnip.  TEM images and particle size distribution data shows that both types of ENPs aggregated in their respective suspensions in concentration-dependent manner.  The zeta potential values had no clear trend and indicated that the suspensions were not stable.  The maximum dissolution on day 7 was less than 15 μg/L for CuO and 4 mg/L for ZnO indicating more dissolution for ZnO ENPs.  The relative chlorophyll measurements in parsnips showed no treatment effect for both the ENPs.  Both the peels and flesh show a concentration-dependent trend for the metal accumulation in both the ENPs. The metal content in peels were more than that of the flesh in the storage organ of both the species suggesting some adsorption on the surface. (Figure 3)  The shoots for CuO treatments showed a loss of turgor with higher concentrations. Relative water content values for the shoots show an inverse trend with concentration for both ENPs. (Figure 4)  There was a greater decrease in cumulative transpiration as the ENP treatment concentration increased. (Figure 5)  There is little variation in the root biomass for both the ENP treatments but there is no clear trend.  The data on particle characterization showed that the particle aggregate in their respective suspensions and tend to settle down over time. The zeta potential values indicate that the suspensions were not in stable range and there is no clear trend.  The loss of turgor in shoots, relative water content and cumulative transpiration measurements indicated that the nanoparticles might play a role in altering the plant water relations.  A significant increase in the metal content suggested that there is a high chance of ENPs accumulating in the storage organ of carrot and parsnip. The higher concentration in peels indicated that the outer surface retains the largest fraction of the accumulated metals possibly due to adsorption.  Short exposure time may not be sufficient enough to produce an appreciable change in the relative chlorophyll content and storage organ biomass.  The results show that there is a possibility of ENPs entering the plant systems and the human food supply. Efforts are going on to measure the effect of the ENPs to the nutritional quality of the edible portion of these plants. Figure 3 - Variation of metal concentration in edible peel and flesh of carrot roots. Figure 4 - Relative water content in leaves of carrot in response to ENP treatments Figure 5 - Cumulative transpiration measurements for different treatments in parsnips Figure 1 - Experimental setup for carrots Uptake and accumulation of ZnO and CuO engineered nanoparticles in carrot and parsnip Pawan Kumar 1 and Stephen Ebbs 1 Pawan Kumar 1 and Stephen Ebbs 1 1 Department of Plant Biology, Southern Illinois University, Carbondale, IL 1 Department of Plant Biology, Southern Illinois University, Carbondale, IL Introduction Thanks to Dr. Ebbs, Dr. Ma, Ebbs lab members for their support and USDA for funding. Acknowledgements Figure 2 - Examples of replicates for each treatment Methods Results Discussion 420 Life Science II, 1125 Lincoln Drive, Carbondale, IL 62901-6509; pawank@siu.edu, +1 618 303-1315 Contact information Increasing CuO Cu 2+