The toxicity and uptake of bulk and nano-sized ZnO particles in wheat (Triticum aestivum) seedlings

The effect of synthesized nano-sized ZnO particles (ZnO NPs) on wheat germination and growth parameters (Triticum aestivum L.) was studied compared to bulk Zn. Results showed that adding bulk Zn resulted in no significant differences in germination parameters compared to the control samples. On the other hand, the addition of ZnO NPs showed significant differences (p < 0.05) in all germination parameters in comparison to the blank (control) samples. Moreover, the general average Zn concentrations in the plant were 141 and 253 mg kg(-1) (dry weight) for bulk Zn and ZnO NPs treated plants, respectively, indicating preferential uptake of ZnO NPs. The addition of c. 10 mg L-1 of ZnO NPs to the wheat shoot system promoted chlorophyll formation equal to 100 mg L-1 addition of bulk Zn. Adding bulk Zn and ZnO NPs reduced root growth substantially compared to the control samples. The effective toxic dose (so-called EC50) for ZnO NPs and bulk Zn was 20.7 and 522 mg Zn L-1, respectively, indicating much higher toxicity of ZnO NPs and highlighting the nano-specific toxicity of nano-sized Zn. The wheat uptake of ZnO NPs was well fitted to a nonlinear Freundlich-like expression, suggesting that our model could effectively predict mass production fertilization procedures. The present study may thus help to increase Zn biofortification in cereals by using ZnO NPs, which may in turn be very helpful for populations suffer from Zn malnutrition.