Exogenous application of nanohydroxyapatite and its derivatives in mitigating arsenic toxicity in rice grown in arsenic-contaminated soil and hydroponic conditions.

Arsenic (As) contamination in rice is a global health concern. This study evaluates the effectiveness of nanohydroxyapatite (nHAP) and its derivatives nano-wool-hydroxyapatite (nWHAP) and nano-rice husk-hydroxyapatite (nCHAP) in mitigating As toxicity in rice plants grown in soil and hydroponic conditions. Functional and structural properties of nHAP, nWHAP, and nCHAP was determined by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) before plant experiments. The treatments were (1) control, (2) As, (3) As + nHAP, (4) As + nWHAP, and (5) As + nCHAP. This study analyzes nHAP, nWHAP, and nCHAP in terms of morphology, crystallinity, and functional groups. SEM confirmed their spherical shape with particle sizes of 47.19-71.76 nm. XRD identified distinct diffraction peaks, confirming crystallinity, while FTIR detected characteristic vibrations at 1022-1029 cm⁻¹ with weak peaks at 870 and 1400 cm⁻¹. These findings highlight their potential for As remediation and plant nutrient management. In soil conditions, As toxicity reduced plant dry weight from 39.2 g to 7.92 g, whereas nWHAP and nCHAP increased the dry weight to over 15 g. Under hydroponic conditions, As reduced shoot weight from 2.87 to 0.54 g, while nWHAP and nCHAP increased it to 3.81 g and 2.39 g, respectively. Nanohydroxyapatite, nWHAP, and nCHAP effectively lowered As levels, with nCHAP reducing concentrations in shoots from 20.7 to 8.03 mg kg^-1 and in roots from 752 to 262 mg kg^-1. Applying nHAP as a phosphorus (P) source achieved the highest plant P levels, and nCHAP yielded the highest P concentration under hydroponic conditions. This research demonstrates the effectiveness of nHAP and its derivatives, nWHAP and nCHAP as new materials, in mitigating As toxicity in rice, laying the groundwork for future studies on practical and sustainable solutions to reduce As levels in rice.