Influence of Nutrient Supplement in the Single Heavy Metal (Pb2+, Cd2+, Cr3+) Uptake and Mineral Nutrients Absorption by Water Kangkong (Ipomoea aquatica forsk)

Abstract

The heavy metal contamination in the food crop has posed global concern due to its harmful effects on both humans and animals. Hence, its uptake and bioaccumulation study are in utmost importance. The present study investigated the effects of Cd2+, Pb²⁺, and Cr³⁺ stress on mineral contents (K⁺, Na⁺, Ca²⁺, P, Mg²⁺, Fe²⁺, Cu²⁺, Zn²⁺, and Mn²⁺) in the different parts of water kangkong (Ipomoea aquatica forsk) by point analysis method. Water kangkong cuttings were grown in tap water supplemented with a very small amount of NPK fertilizer and treated with Pb (NO₃)₂, Cd (NO₃)₂∙4H₂O, and K₂Cr₂O₇ under two soaking solutions – hydroponics solution and tap water solution. Results revealed that Pb²⁺, Cd²⁺, and Cr³⁺ alter the mineral nutrient absorption of kangkong. Particularly, the approximate concentrations of most mineral ions (K⁺, Ca⁺, Fe²⁺, Zn²⁺, Cu²⁺, and Mn²⁺) in the leaves and stems were reduced by Pb²⁺, Cd²⁺, and Cr³⁺ exposure, thus making kangkong deficient in nutrients when consumed as food. It was also observed that these heavy metals caused a disturbance in K/Ca and K/Na ratios, which could greatly impact water balance. Data also suggest that nutrient optimization may help kangkong to develop tolerance to Cd²⁺, Pb²⁺, and Cr³⁺ and can be a good strategy to alleviate the accumulation of heavy metals by kangkong. The results also indicate that the translocation of ions of Pb, Cd, and Cr from roots to shoots behave differently in the presence of nutrients.