Overview
Tura et al. analyzed proximate composition, phytochemicals, and heavy metal content in Nigella sativa seeds (called “black cumin”) and fenugreek (Trigonella foenum-graecum) collected from farmers in the Gamo Zone of Ethiopia. Nine heavy metals were analyzed by FAAS. For Nigella sativa, the essential metals Fe, Zn, Cu, Mn, and Co were detected; chromium (Cr), nickel (Ni), lead (Pb), and cadmium (Cd) were all not detected (ND). For fenugreek, Fe, Zn, Cu, Mn, Co, and Ni were detected; Cr, Pb, and Cd were not detected. The authors conclude that both crops were free from heavy metal toxicity.
Species disambiguation: “Black cumin” throughout this paper is Nigella sativa L. (family Ranunculaceae), botanically identified by the authors in Table 1 as Ranunculaceae. This is distinct from Cuminum cyminum L. (family Apiaceae, true cumin). The two plants share a common name in some regions but are unrelated species.
Key numbers
Nigella sativa (black cumin) heavy metal concentrations (mean +/- SD, mg/kg dry weight, FAAS):
Samples were drawn from three districts (Kamba, Daramalo, Dita); values represent means across the three collection sites.
Methods (brief)
Sampling: 500 g samples per species donated by farmers in three Gamo Zone districts; transported to Arba Minch University Department of Chemistry. Sample preparation: cleaned with tap water followed by deionized water, sun-dried 2 days, ground to fine powder with mortar and pestle, stored in polyethylene bags. Wet digestion: HNO3/HClO4 (species-specific ratios and times; black cumin: 5 mL HNO3 and 5 mL HClO4 at 240 degrees C for 2h 10min). Analysis: FAAS. Metal concentrations reported as mg/kg dry weight. ANOVA used for statistical comparison across sites.
Implications
Certification: Non-detection of Pb, Cd, Cr, and Ni in Nigella sativa from Ethiopia is consistent with the Imperl et al. 2023 result for Nigella sativa from Morocco. This consistent pattern across two independent studies and two geographic sources supports a preliminary conclusion that Nigella sativa seeds cultivated under traditional conditions carry negligible toxic-metal load. These results do not transfer to Cuminum cyminum (true cumin).
Species note: This source should not be cited as cumin heavy-metal evidence. It is Nigella sativa evidence only.
Related evidence
Update history
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