The aim of the present work was to investigate the toxic effects of zinc oxide nanoparticles (ZnO NPs, particle size < 50 nm) on the physiological and anatomical indices of spring barley (Hordeum sativum L.). The results show that ZnO NPs inhibited H. sativum growth by affecting the chlorophyll fluorescence emissions and causing deformations of the stomatal and trichome morphology, alterations to the cellular organizations, including irregularities of the chloroplasts, and disruptions to the grana and thylakoid organizations. There was a lower number of chloroplasts per cell observed in the H. sativum leaf cells treated with ZnO NPs as compared to the non-treated plants. Cytomorphometric quantification revealed that ZnO NPs decreased the size of the chloroplast by 1.5 and 4 times in 300 and 2000 mg/L ZnO NP-treated plants, respectively. The elemental analysis showed higher Zn accumulation in the treated leaf tissues (3.8 and 10.18-fold with 300 and 2000 mg/L ZnO NPs, respectively) than the untreated. High contents of Zn were observed in several spots in ZnO NP-treated leaf tissues using X-ray fluorescence. Deviations in the anatomical indices were significantly correlated with physiological observations. The accumulation of Zn content in plant tissues that originated from ZnO NPs was shown to cause damage to the structural organization of the photosynthetic apparatus and reduced the photosynthetic activities.

The presence of heavy metals in the soil could impose serious problems on soil-plant systems due to the accumulation of heavy metals in plants. Even vital elements such as Cu and Zn have a toxic effect in the case of excessive intake by living organisms. The present work aimed to investigate the content of loosely bound (exchangeable, complexed, and specifically sorbed) compounds of Cu and Zn and their availability to spring barley (Hordeum sativum distichum) in contaminated Haplic Chernozem soil under the conditions of a model experiment (five approximate permissible concentrations (APC) and 10 APC of metal). Changes in the bioavailability of the metals upon application of carbon sorbents were observed. An increase in loosely bound metal compounds has been shown under conditions of soil contamination with metals (up to 57% of the total content). The increase in the availability of Cu in the soil was mainly due to the formation of complexed metal forms with organic matter (up to 17%). The availability of Zn was found to be associated with an increase in exchangeable (up to 21%) and specifically sorbed compounds (up to 27%). Granular activated carbon (GAC) and biochar have high sorption properties. A decrease in the content of loosely bound compounds of metals was established, especially in the most mobile forms such as exchangeable and complexed forms. The introduction of sorbents into the soil opened up a new venue for binding heavy metals in situ, eventually leading to a decrease in their bioavailability. The inactivation of Cu and Zn in the soil upon the application of sorbents led to a decrease in metal absorption by spring barley. The highest efficiency of biochar application was established at a dose of 2.5% and 5% in soil contaminations of 5 APC and 10 APC of Cu or Zn. The efficiency of the use of sorbents was more influenced by the dose of application than by the type of sorbent. There was no significant difference between biochar and GAC. Stabilization and inactivation of metals may improve soil fertility and plant growth.

Heavy metals such as cadmium (Cd) and zinc (Zn) could be dangerous and pollute the environment due to their high migration ability, robust bioavailability, and acute toxicity to soil biota and plants. Considering the above characteristics of these elements, the study’s aim was to explore the individual and combined impact of Cd and Zn contamination of Haplic Chernozem on growing two-row spring barley (Hordeum vulgare L.). The accumulation and distribution of Cd and Zn in various parts of H. vulgare have also been studied, which showed that Cd accumulation by H. vulgare occurred more intensely than that by Zn up to eight times. Cadmium and Zn suppress plant growth up to two times, more effect was noted by the combined impact of Cd and Zn. The study of plant morphological characteristics revealed that growth suppression and structural changes in the root and leaf tissues increased in proportion to Cd and Zn concentrations. Detailed analysis of the localizations of Zn and Cd in various organelles of H. vulgare cells was performed. Heavy metals change the ultrastructure of prominent energy-producing organelles in leaf cells, especially chloroplasts and mitochondria. Overall, the current findings offer insights into phytotoxicity induced by Cd and Zn individual application as well as in combination with the H. vulgare plant. Zinc showed protective effects against high doses of Cd under the combined application. These antagonistic interactions reduce their accessibility to H. vulgare. The present work can be useful in restricting the entry of these elements into the food chain and preventing creating a threat to human health.