Investigating the phytoavailability of metals in roots of Croton macrostachyus and Phytolacca dodecandra: induced rhizosphere processes

Medicinal plants are key component of complementary and alternative medicine, and constitute the first therapeutic strategy for majority of the global population, particularly in developing nations. Croton macrostachyus and Phytolacca dodecandra are among such plants, widely used to treat various diseases. The present study aimed at investigating the elemental composition of both plant root samples collected from four districts in the Central Gondar Zone, Northwest Ethiopia. An optimized wet-digestion procedure was applied with 0.5 g of root sample using HNO₃: HCl: H₂O₂ (v/v) in the ratio of 8:2:1 at 240 °C for 3:00 h (for P. dodecandra), and 5:2:2 at 300 °C for 3:00 h (for C. macrostachyus). Then, concentrations of metals in the digested samples were determined using a flame atomic absorption spectrophotometer; and the validity of the optimized procedure was evaluated by spiking experiments. Results showed good accuracy and repeatability of the methods with percent of recoveries ranging from 85 to 103%. The mean concentrations of metals in C. macrostachyus root samples were higher than their P. dodecandra counterparts, and the distribution of metals showed the following decreasing order: Mg > Ca ≈ Fe > Mn > Zn > Cu > Cr. One-way ANOVA revealed no significant differences (p > 0.05) between the mean concentrations of the same metals in both plant root samples, except for Mg and Cr. Correlation matrix, principal component and cluster analyses suggested that accumulation of metals in the root samples originated from both natural and anthropogenic sources. In conclusion, the roots of both medicinal plants contained substantial amounts of metals, thereby serving as valuable sources of essential elements.