Heavy Metal Contamination in Nigerian Spices and Seasonings: Occurrence, Sources, and Health Risk Implications— A Narrative Review with Descriptive Quantitative Analysis

Abstract

Heavy metal contamination in spices and seasonings is an important food safety concern because of the potential health effects associated with repeated dietary exposure. This narrative review, supported by descriptive quantitative analysis, synthesised evidence from eleven Nigerian studies on the occurrence, sources, analytical methods, exceedance patterns, and health-risk implications of heavy metals in spices and seasonings. The reviewed studies reported lead (Pb), cadmium (Cd), chromium (Cr), nickel (Ni), arsenic (As), mercury (Hg), and other elements at varying concentrations across different spice types and locations. Exceedances of selected permissible limits were reported for cadmium, chromium, nickel, arsenic, and lead, although contamination patterns varied substantially among studies. Reported contamination sources included polluted soils, irrigation water, fertiliser use, atmospheric deposition, adulteration, drying practices, grinding and milling equipment, packaging materials, and storage conditions. Atomic Absorption Spectroscopy was the dominant analytical technique, while ICP-based methods were used less frequently. Most health-risk assessments reported estimated daily intake, target hazard quotient, and hazard index values within acceptable limits for individual spices or seasonings. However, some studies indicated potential concerns related to cumulative exposure, multi-metal intake, bioaccumulation, and long-term consumption. The review highlights the need for broader geographical surveillance, harmonised analytical reporting, routine monitoring of priority toxic metals, and stronger quality-control measures across the spice production and distribution chain in Nigeria.