Alleviation of tannery wastewater toxicity in Spinacia oleracea through application of metal oxide nanoparticles.

Hexavalent chromium [Cr(VI)] rich tannery wastewater has negative impacts on physiological functions and growth of plants. We examined the effectiveness of foliar application of metal oxide nanoparticles including magnesium oxide, zinc oxide and iron oxide in mitigating chromium induced toxicity in Spinacia oleracea under 0%, 50%, and 100% tannery wastewater irrigation levels. The results reveal that chromium stress notably reduced plant growth, chlorophyll content, increased oxidative stress (H2O2 and MDA), electrolyte leakage and build up of Cr both in roots and shoots of plants. The stress also reduced mineral nutrient acquisition including Mg, Fe and Zn. However, foliar application of MgO, FeO and ZnO nanoparticles strengthened the activities of antioxidant enzymes (SOD, POD and CAT) thus resulting in lowered oxidative stress and concentration of Cr within plant body. Application of nanoparticles helped the plants to absorb more mineral nutrients (Mg, Fe and Zn) as well. ZnO nanoparticles proved to be the most effective in mitigating Cr stress in Spinacia oleracia followed by MgO and FeO. This study demonstrates the effectiveness of ZnO NPs along with MgO and FeO in preventing Cr-actuated pressure in degraded conditions.