Analysis of Nigella sativa L. (Black Cumin) seeds for levels of heavy metals using FAAS: geospatial profiling and regional safety implications

This study quantifies the concentrations of heavy metals, iron (Fe), copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd), in Nigella sativa L. (black cumin) seeds, a widely consumed ethnobotanical agent in Ethiopia for culinary and therapeutic purposes. Seed samples were collected from three districts in East Gojjam, Ethiopia, subjected to microwave-assisted acid digestion, and analyzed via flame atomic absorption spectrometry (FAAS). Spike experiments and percentage recovery results indicated that the accuracy of the method for determination of Fe, Cu, Zn, Pb and Cd in the analyzed samples ranged from 94.8 to 108%, underscoring the methods robustness and reliability for quantifying heavy metals in medicinal plants. Mean metal concentrations (mg/kg, dry weight) across districts ranged as follows: Fe (71.38 ± 1.34 to 82.90 ± 0.75), Cu (9.18 ± 0.22 to 22.24 ± 2.03), Zn (55.27 ± 0.33 to 71.25 ± 2.79), Pb (0.11 ± 0.005 to 0.21 ± 0.01), and Cd (0.09 ± 0.01 to 0.14 ± 0.007). One-way ANOVA revealed statistically significant regional variations (p < 0.05) in Fe, Cu, Zn, and Cd levels, whereas Pb concentrations remained consistent across sampling sites. All measured values complied with world health organization (WHO) permissible limits for medicinal plants, indicating that Nigella sativa seeds from these regions pose no appreciable health risks for human consumption. These findings underscore the importance of geospatial monitoring in ethnopharmacological safety assessments and affirm the suitability of N. sativa as a safe dietary adjunct within the studied localities.