Foliar use of TiO2-nanoparticles for okra (Abelmoschus esculentus L. Moench) cultivation on sewage sludge-amended soils: biochemical response and heavy metal accumulation

Considering its richness in organic and inorganic mineral nutrients, the recycling of sewage sludge (SS) is highly considered as a soil supplement in agriculture. However, the fate of hazardous heavy metal accumulation in the crops cultivated in SS amended soils is always a source of concern. Since nanoparticles are widely recognized to reduce heavy metal uptake by crop plants; thus, the present experiment deals with okra (Abelmoschus esculentus L. Moench) cultivation under the combined application of SS and TiO2-nanoparticles (NPs). Triplicated pot experiments were conducted using different doses of SS and TiO2-NPs such as 0 g/kg SS (control), 50 g/kg SS, 50 g/kg SS + TiO2, 100 g/kg SS, and 100 g/kg SS + TiO2, respectively. The findings of this study indicated that among the doses of treatment combinations investigated, 100 g/kg SS + TiO2 showed a significant (p < 0.05) increase in the okra plant yield (287.87 +/- 4.06 g/plant) and other biochemical parameters such as fruit length (13.97 +/- 0.54 cm), plant height (75.05 +/- 3.18 cm), superoxide dismutase (SOD: 110.68 +/- 3.11 mu/mg), catalase (CAT: 81.32 +/- 3.52 mu/mg), and chlorophyll content (3.12 +/- 0.05 mg/g fwt.). Also, the maximum contents of six heavy metals in the soil and cultivated okra plant tissues (fruit, stem, and root regions) followed the order of Fe > Mn > Cu > Zn > Cr > Cd using the same treatment. Bioaccumulation and health risk assessment indicated that foliar application of TiO2-NPs significantly reduced the fate of heavy metal accumulation under higher doses of SS application. Therefore, the findings of this study suggested that the combined use of SS and TiO2-NPs may be useful in ameliorating the negative consequences of heavy metal accumulation in cultivated okra crops.