Copper Oxide Nanoparticle Effects on Crop Growth and Root Hydraulic Conductivity.

The uptake of engineered nanoparticles has potential to threaten the growth and safety of harvested food crops. The short-term response of root physiology and function to copper oxide (CuO) nanoparticles (NP) with reference to a Cu²⁺ control (CuCl₂) on two food crop species of contrasting root architecture was investigated. In addition to determining effects on germination and root physiology, acute exposure root hydraulic conductivity was examined. CuO NP (16 nm diameter; 1, 10, 100, 500, 1000 mg L^-1) had no significant effect on lettuce and carrot germination, but CuCl2 (0.1, 1, 5, 10, 100 mg L^-1) decreased germination at concentrations ≥ 10 mg Cu L^-1 by up to 86% for carrot and 50% for lettuce. Seedling root length decreased with concentration of CuO NP and CuCl₂ in a similar manner for both species; greater inhibition occurred for CuCl₂ than for CuO NP. Root thickening induced by CuO NP was greater for lettuce (+52% diameter) than carrot (+26%) at 1000 mg L^-1 CuO NP. Hydraulic conductivity was reduced in acute exposure to CuO NP (1000 mg L^-1) for lettuce (-46%) but not carrot (Fig. 1). These results indicate the CuO NPs exert acute effects on root physiology and function that are distinct from Cu²⁺, and can be crop-specific.