Determination of selected heavy metals in leaves of the medicinal plants Calpurnia aurea and Zehneria scabra from East Gojjam, Ethiopia, and their health risk assessment

Abstract

This study investigates the levels of selected heavy metals (Zn, Pb, Cd, and Cr) in the leaves of C. aurea and Z. scabra. Flame atomic absorption spectrophotometry (FAAS) was used for the determination of these metals. Wet digestion of the C. aurea and Z. scabra required 4:1 HNO₃/HCl (v/v) for 1:45 h, with a temperature of 210 °C and 3:1 HNO₃/HCl (v/v) for 1:30 h, with a temperature of 240 °C, respectively, for complete digestion of 0.5 g of both medicinal plant leaves using the Kjeldahl apparatus. The experimental results revealed that the metals studied found in the plants were determined as follows, in mg/kg: Zn (0.5727, 0.4547); Pb (0.2394, 0.2334) and Cd (0.0365, 0.0468) in C. aurea and Z. scabra, respectively, while Cr was not detected in both plant samples. The recovery percentages for C. aurea and Z. scabra samples ranged from 88.2-95.8% and 90.0-98.9%, with LOD values of 0.0087-0.1476 and 0.0174-0.1176, respectively. The levels of these metals were found to be below the allowable limits of the World Health Organization. The plant C. aurea was found to contain higher concentrations of Zn and Pb compared to Z. scabra, which had a slightly higher Cd level. The hazard quotient and hazard index values of Zn, Pb, and Cd in both medicinal plants were lower than one, which may ensure that these plant spices do not pose substantial health risks to consumers.