Assessment of toxic trace metal contamination in food spices sold in Nigerian markets

Overview

This study measured total arsenic (As), cadmium (Cd), and lead (Pb) in seven spice/herb samples: six coded commercial spice samples A–F purchased from New Heaven market in Enugu, Nigeria, plus one scent leaf sample collected from a nearby garden at Ugwuaji. The most alarming finding is cadmium: all seven samples exceeded the FAO/WHO permissible limit of 0.02 µg/g by a substantial margin, with values ranging from 2.58 to 6.45 µg/g — between 129 and 322 times the limit. Arsenic exceeded the upper end of the source’s 0.1–0.5 µg/g permissible range in two samples (C: 1.68, E: 1.26 µg/g); Sample D (0.315 µg/g) exceeded the lower end but not the 0.5 µg/g upper threshold. Lead exceeded the 2.0 µg/g threshold in two samples (A: 2.16, B: 2.19 µg/g). The authors discuss possible contamination pathways including improper drying practices, polluted irrigation sources, atmospheric deposition, and poor post-harvest handling.

Key numbers

Concentrations in µg/g (= mg/kg), n = 7 total samples:

All Cd values exceed the permissible limit by 129–322x. Samples C and E exceed the upper end of the source’s As permissible range; Sample D is above the lower bound but below 0.5 µg/g. Samples A and B exceed the Pb threshold. Method: Agilent FS240AA AAS, APHA 1998, aqua regia acid digestion. No LOD/LOQ values explicitly reported for the samples; no speciation of As (total As reported, not iAs/organic split).

Methods (brief)

Samples were labelled A–F (product identities not disclosed) plus one scent leaf grown locally and washed. Digestion used aqua regia (HNO3 + HClO4 + H2SO4 mixture) heated at 60°C to clear digest. Analysis by AAS with calibration curves from single-element stock solutions. Study limitations: very small n (7), single market, no certified reference material reported, no LOD/LOQ stated, specific spice identity not disclosed for A–F, and As is reported as total As without iAs/organic speciation.

Implications

Certification: The cadmium results in this study are extraordinary — 129–322x over FAO/WHO limits — and should be treated as evidence of a severely contaminated informal-market supply chain rather than a representative distribution for certified supply chains. The study contributes occurrence context for spice Cd, Pb, and total-As screening, but these values should not anchor threshold math.

Courses: Excellent case study for contamination-pathway modules: improper or roadside drying as a possible pathway, atmospheric deposition, and informal market monitoring failure. Pair with better-controlled A-tier spice studies for a balanced picture.

App: Contributes a high-contamination informal-market scenario for spices as a Cd- and total-As-relevant ingredient category. The extremely high values here are likely outliers from local market conditions rather than typical commercial-grade supply.

Wiki pages updated on ingest

• Spices
• Spices
• Condiments (hot sauce, soy sauce, mustard, ketchup, mayonnaise, salsa)

Verification notes

• 2026-05-18 Codex merge-enhance against the source PDF in condiment_papers: corrected the truncated raw_path, broadened product routing to include [[products/condiments-general]], and generalized “brands” wording to coded samples because the source does not disclose product identities.
• Numerical fidelity correction: the prior page repeated the source abstract/discussion phrasing that three samples exceeded a 0.5 µg/g As limit, but Table 1 shows only Sample C (1.68 µg/g) and Sample E (1.26 µg/g) exceed 0.5 µg/g; Sample D is 0.315 µg/g and only exceeds the lower end of the source’s 0.1–0.5 µg/g permissible range. Lead exceedances remain Samples A and B; Cd exceedance remains all seven samples.
• Part 2 firewall: softened the HMT&C monitoring/testing sentence to source-level occurrence context and explicitly kept the values out of threshold math.
• Cross-vendor audit (Codex, 2026-05-18) corrected the sample-population description: the six coded spice samples were purchased from New Heaven market, while the scent leaf was collected from a nearby garden at Ugwuaji. Pathway language is treated as author-discussed possibilities, not confirmed source attribution for each sample.

Update history

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