Comparison between toxicity effects of ZnO nanoparticles and their bulk on fenugreek (Trigonella foenum-graceum) growth under greenhouse environment

Backgrounds and Widespread use of nanoparticles increases their release to the environment. Soil may be a major sink for released nanoparticles to the environment. These nanoparticles interact with ecosystem component specially plants and their symbiosis. Therefore understanding nanoparticles behavior in the soil and plants is essential to restrict potentially toxic effects of nanoparticles. On the other hand, due to metal nanoparticle solubility, their toxicology studies are need to comparative evaluation of their toxicity with non-nanoparticles.
Material and Thus we designed an experiment to investigate effect of different zinc oxide nanoparticles concentration (125, 250, 375 and 500 mg/kg) on fenugreek as a nitrogen-fixing plants that form symbiotic relationship with Sinorhizobium melliloti. For comparison between nano and bulk, the same concentrations of zinc oxide and bulk nanoparticles were applied. Control treatment for both experiment had neither zinc oxide nanoparticles and their bulk. Both experiments were conducted based on completely randomized design. Contrasts were used for comparison between nano and bulk means.
Results showed that increase in zinc oxide nanoparticles and their bulk had negative effect in rhizobium nodule biomass (P˂ 0.05). Apparently, inhibition effect of zinc oxide nanoparticles on rhizobium nodule biomass was more than zinc oxide bulk (P˂ 0.05). Increase in zinc oxide particles and their bulk increased Zn concentration in the root and shoot and decreased P concentration in the root and shoot (P˂ 0.05). Nano group decreased P concentration in the root more than bulk group (P˂ 0.05). Level of 125 mg/kg zinc oxide nanoparticles increased shoot length, however level of 375 and 500 mg/kg zinc oxide nanoparticles decreased shoot length (P˂ 0.05). Shoot length decreased at all level of zinc oxide bulk compared to control. Root dry weight showed reduction at level 375 and 500 mg/kg zinc oxide nanoparticles and only at level 500 mg/kg zinc oxide bulk. Contrast between nano and bulk showed that there is no significant difference, though Zn concentration in the root was more than Zn concentration in the shoot. Shoot dry weight decreased at level up to 250 mg/kg zinc oxide nanoparticles and at all level of zinc oxide bulk. Shoot dry weight at nano group was more than that of bulk group, and Zn concentration of shoot at bulk group was more than that of nano group.
In summary, the phytotoxicity of zinc oxide particles was similar in the nano and bulk forms, but we find more toxicity of zinc oxide nano particles than their bulk for rhizobium nodules in the fenugreek plant and P concentration in the root, and this increase concerns about effects nanoparticles in agricultural ecosystems.