Heavy metal contamination of selected spices obtained from Nigeria

Abstract

In this study, the levels of trace metals (Cd, Cr, Cu, Co, Fe, Mn, Ni, Mo, Pb, Zn) in twenty two spices representing four spice groups (seeds, bulbs, leaves, fruit pods and rhizome) from a major market in Northern Nigeria were determined using atomic absorption spectroscopy, and assessed based on regulatory standards. Garlic exhibited the highest zinc concentration (21.733 ±0.044 mg/kg), which falls lower than the upper toxic level for most plants. Lead concentrations peaked in African nutmeg (4.717 ± 0.017 mg/kg) but are lower than the normative for the final dosage form of medicinal plants. The daily intake-based hazard of the spices was assessed using the minimum risk levels set by WHO, and the FAO/WHO maximum tolerable intake limits. All the spices contain excessive cobalt and copper with maximum levels (mg/kg) in ginger cobalt (11.117±0.069) and African nutmeg (15.300 ± 0.041), respectively. The estimated daily intake values (μg/kg day) of onion (1.10), ginger (12.00), utazi (1.30), alligator paper (1.20), garlic (0.89), Ashanti leaves (0.88), castor seeds (1.20), and shallot (0.86)were higher than the provisional maximum tolerable intake set by FAO/WHO, constituting a potential risk to human health. These results show that spices can accumulate exceeding levels of toxic metals whose potential risk to human health should be given priority.

Keywords: heavy metal; contamination; Nigeria; spices; health; daily intake