Cadmium toxicity in cowpea plant: Effect of foliar intervention of nano-TiO₂ on tissue Cd bioaccumulation, stress enzymes and potential dietary health risk

The study was conducted to investigate the effects of foliar-intervention of nano-TiO₂ on Cd toxicity in cowpea plants. Cowpea plants were exposed to Cd toxicity at 10 mg/kg soil for 21 days and afterwards, subjected to six episodes of foliar application of nano-TiO₂ intervention. Results showed that foliar-applied nano-TiO₂ significantly promoted chlorophyll b and total chlorophyll contents after Cd stress as compared to Cd-stressed plants without the intervention. Interestingly, Cd contents of roots, shoots and grains were significantly reduced (p < 0.05) after nano-TiO₂ sprays compared to Cd-stressed plants. However, the Cd contents in edible tissues (leaves and seeds) after interventions remained above recommended threshold. Furthermore, nano-TiO₂ interventions promoted stress enzymes activity in both roots and leaves as well as increased Zn, Mn and Co levels in seeds compared to Cd-stressed plants without intervention. Estimated daily intake of Cd in leaves and seeds for adult subpopulation exceeded the WHO recommended daily intake by some folds in Cd-stressed and nano-TiO₂-treated plants. The health risk quotient (HQ) for adult subpopulation exceeded unitary in seeds from nano-TiO₂ treatments (HQ = 1.75 and 1.96, respectively) while no potential risk was obtained for leaves. Overall, foliar application of nano-TiO₂ portends significant ameliorative potential for Cd toxicity in cowpea plants.