Imongben et al. 2026 — Heavy metals and health risk in Kaduna market vegetables, Nigeria

Imongben and colleagues measured Cr, Mn, Fe, Co, Ni, Cu, Mo, and Zn in 12 commonly consumed vegetable types purchased from five markets in Kaduna Metropolis, Nigeria, using energy-dispersive X-ray fluorescence (ED-XRF) spectrometry. The authors computed Estimated Maximum Daily Intake (EMDI), Hazard Quotient (HQ), Hazard Index (HI), and Incremental Lifetime Cancer Risk (ILCR) for adults (60 kg body weight) and toddlers 1–2 y (10 kg body weight). HI exceeded 1 for every vegetable and both age groups; Cr, Cu, and Ni ILCR values were in the moderate-to-high risk range for most vegetables. The authors attribute the contamination to irrigation with River Kaduna water, which receives untreated effluent from the city’s refinery, textile, food and beverage, ceramics, fertilizer, and paper industries.

Key numbers

All vegetable concentrations are in mg/kg (basis not explicitly stated by the authors; ED-XRF was performed on oven-dried, pulverized vegetable powder pressed into pellets, so values are presumed dry-weight). EMDI values are in mg/kg body-weight/day. HQ, HI, and CR are unitless health-risk indices computed per the paper’s equations.

Table 1 — Heavy metal content of selected vegetables (mean ± SD, mg/kg):

The “Potato” row corresponds to the “sweet potatoes” entry in the methods enumeration of 12 vegetable types — see verification notes for the within-paper terminology discrepancy.

Reference limits cited by the authors (mg/kg):

• Cr: EU permissible limit 0.3 mg/kg (EU, 2006). All vegetables except carrot (LOD) exceeded this limit.
• Fe: FAO/WHO safe limit 425 mg/kg (FAO/WHO, 2011). Avocado, cabbage, celery, lettuce, spinach, and potato exceeded this limit.
• Ni: FAO/WHO permitted level 67.9 mg/kg (FAO/WHO, 2011). All vegetables were below this limit.
• Cu: FAO/WHO acceptable limit 2.0 mg/kg. All vegetables substantially exceeded this limit; lowest measured Cu was 46.1 mg/kg (broccoli) and highest 479 mg/kg (beans).
• Zn: WHO permissible limit 60 mg/kg (WHO, 2007). All vegetables except broccoli (33.7) and cauliflower (52.2) exceeded this limit.

Table 2 — EMDI (mg/kg body-weight/day), adults (60 kg) / toddlers (10 kg):

EMDI ranges as authors summarise (mg/kg body-weight/day, adult / children): Cr 0–0.16 / 0–0.97; Mn 0.12–0.56 / 0.32–3.36; Fe 0.34–4.09 / 2.02–24.51; Ni 0–0.01 / 0–0.41 (authors’ text); Zn 0.14–0.92 / 0.86–5.53; Co 0–0.12 / 0–0.72; Cu 0.2–1.32 / 0.76–7.91 (authors’ text — Table 2 Cu_Ad column min is 0.13 for broccoli; see verification notes); Mo 0–0.26 / 0.02–1.56.

Table 3 — Hazard quotients (HQ) and Hazard Index (HI), adult/children:

(Table 3 lists vegetables in the source order: Cauliflower, Carrot, Avocado, Cabbage, Celery, Potato, Pea, Lettuce, Spinach, Beans, Broccoli, Eggplant.)

HQ > 1 (non-carcinogenic concern) for most metal-vegetable combinations in both age groups. The highest single HQ recorded was Fe in avocado (adults 583; children 3502), driven by the very high Fe concentration in avocado combined with the low EPA RfD of 0.007 mg/kg/day used by the authors. HI ranged from 140 (broccoli, adults) to 828 (potato, adults) for adults and from 843 (broccoli) to 4966 (potato) for children; HI > 1 for every vegetable and both age groups.

Table 4 — Incremental Lifetime Cancer Risk (CR) for Cr, Cu, and Ni, adult/children:

Authors classify CR using the NYSDOH scheme: ≤10⁻⁶ low, 10⁻⁵–10⁻³ moderate, 10⁻³–10⁻¹ high. The authors note in text that CR ranges (adult / children) are: Cr 0.00–0.08 / 0.00–0.1 (text); Cu 0.22–2.20 / 0.69–7.19 (text); Ni 0.00–0.06 / 0.00–0.69 (text). Table 4 values are reproduced verbatim above; see verification notes for the within-paper text-vs-table rounding discrepancy.

Toxic-element summary (authors’ framing):

The authors describe Fe, Mn, Cu, and Zn as essential metals that nonetheless exceed dietary recommendations in many vegetables, and Cr, Ni, and Co as the analytes carrying carcinogenic concern. Cu is described as “the most dominant carcinogen” among the three CR-evaluated metals (Cr, Ni, Cu) under their CSF values (Cr 0.5, Ni 0.91, Cu 1.7 mg/kg/day, citing Gebeyehu & Bayissa 2020). Authors attribute observed contamination to Kaduna River irrigation and discharge from the city’s refinery, textile, food and beverage, ceramic, fertilizer, and paper industries, drawing on Mahre et al. (2007), Yusuf et al. (2008), Abui et al. (2017), Butu et al. (2019), and Isah et al. (2025).

Methods (brief)

Twelve vegetable types (carrots, sweet potatoes, celery, lettuce, spinach, cabbage, broccoli, cauliflower, eggplant, avocado, peas, beans) were purchased from five Kaduna Metropolis markets (Sabo, Central, Tudun Wada, Kawo, Mando) by random systematic sampling: 5 samples of each vegetable type per market (different vendors). Samples were tagged, wrapped in nylon bags, transported to the lab, and authenticated by the Botanical Unit of the Department of Biological Science, Nigeria Defence Academy (with voucher numbers).

Sample preparation: vegetables were destalked where required, washed with tap water then rinsed with distilled water, chopped with a stainless steel knife, oven-dried at 105 °C until crisp, pulverised with an agate mortar and pestle, and sieved through a British Standard (BS 125mm) mesh. Powdered, sieved samples from the same market were combined using the coning and quartering method (Noli & Tsamos 2016) to form one composite per vegetable type per market. Composites were stored in airtight containers.

ED-XRF analysis: 0.5 g of powder was mixed with three drops of organic liquid binder and pressed at 10 tons hydraulic pressure into 19 mm pellets. A 25 mCi 109Cd annular excitation source emitting Ag-K X-rays (22.1 keV) was used at 9 W maximum power. Detection used a Si(Li) detector with thin beryllium (Be) window at 170 eV resolution for the 5.90 keV line, coupled to a computer-controlled ADC card. 1000-second spectra were acquired per sample. Quantification used the Emission-Transmission (E-T) method; spectra were processed with Bruker remote control software and quantified with Bruker instrument tool software (citing Dehayem-Kamadjeu & Okonda 2019).

Risk indices: EMDI = (Cm × Cr) / BW where Cm = metal concentration (mg/kg), Cr = consumption rate of vegetables in Nigeria per FAO 2021 (authors report 2.3 mg/day; this is taken at face value despite the apparent unit anomaly — see verification notes), BW = body weight (adult 60 kg; toddler 1–2 y 10 kg). HQ = EDI / RfD using US EPA (2020) RfD values: Cr 0.005, Mn 0.007, Fe 0.0003, Co 0.005, Ni 0.002, Cu 0.04, Mo 0.005, Zn 0.3 mg/kg/day (authors’ citation). HI = ΣHQ. CR = EDI × CSF using oral slope factors Cr 0.5, Ni 0.91, Cu 1.7 mg/kg/day (citing Gebeyehu & Bayissa 2020).

Method limitations: ED-XRF measures total elemental composition without speciation, so Cr is total chromium (Cr-VI not separated), no Pb/Cd/As/Hg are reported (these analytes were not included in the analytical scheme described). No certified reference material recovery is reported; no internal LOD/LOQ values are tabulated. The five-vegetables-per-market-then-composited design yields one value per (vegetable × market) cell, with mean ± SD reported across the five markets (n = 5 per vegetable). Adults’ assumed body weight is 60 kg; the vegetable consumption rate cited as “2.3 mg/day” is inconsistent with FAO vegetable-intake norms (which are typically in g/day or kg/day) and propagates into all EMDI calculations.

Implications

• Certification (HMTc): Of the eight metals reported, only Ni is on the HMTc 10-analyte certification list. The paper does not measure Pb, Cd, tAs/iAs, MeHg/tHg, Al, Cr-VI, or Sn, so it contributes no occurrence rows to the HMTc-relevant analytes other than Ni. Even the Ni data should be used cautiously because the EMDI calculations rest on an unusual vegetable-consumption-rate assumption (see Methods).
• Courses: Useful case study for the contaminated-irrigation-water exposure pathway in low-income urban settings, where domestic and industrial effluent reaches the irrigation water supply. The differential between adult and toddler HI values (1–2 y toddlers carry 6× the per-kg dose at the same consumption rate) is a useful instructional anchor for the vulnerable-population module.
• App: Not suitable as a direct contamination-profile contributor for North American or European supply chains; the matrix (oven-dried, ED-XRF analysed Kaduna market vegetables irrigated with contaminated river water) is not representative. Contextual use only — the paper documents what poor irrigation-water quality can do to vegetable metal content, not what well-regulated supply chains produce.

Wiki pages this source may touch

• vegetables
• leafy-vegetables
• root-vegetables
• avocado
• beans
• broccoli
• cabbage
• carrot
• cauliflower
• celery
• lettuce
• spinach
• sweet-potato
• chromium
• manganese
• iron
• cobalt
• nickel
• copper
• molybdenum
• zinc

Verification notes

• 2026-05-20 — Merge-enhance pass against the source PDF (raw/Manual Fetch Kimi /02_Vegetables_and_Vegetable_Products/02_Vegetables_and_Vegetable_Products/Determination of Some Heavy Metals and Their Potential Risk in Selected Vegetables on Sale within Kaduna Metropolis.pdf). Prior page version (updated 2026-05-13) had several defects that have been corrected here:
  • metals: previously listed only [Cr, Ni]; the paper reports eight metals (Cr, Mn, Fe, Co, Ni, Cu, Mo, Zn). Updated.
  • Prior Key numbers section reported “Spinach: 2.8 ± 0.26” for Cr, which was a transposition with Lettuce. Table 1 of the source shows Spinach Cr = 28.8 ± 0.26 and Lettuce Cr = 2.8 ± 0.26. Corrected.
  • raw_handle: was generic manual-fetch-kimi; updated to the specific MFK_ form per current convention.
  • Replaced legacy ## Wiki pages updated on ingest heading with ## Wiki pages this source may touch per current schema.
  • Added complete Table 1, Table 2, Table 3, and Table 4 transcriptions (all 12 vegetables × all 8 metals) so downstream synthesis can read every value rather than the handful previously surfaced.
  • Removed editorial commentary that had crept into the prior page (statements like “may reflect… and the biological significance is uncertain”, “warrants independent verification” for Cu values, “study notes possible measurement or unit interpretation issues”). The source page reports what the authors found; uncertainty about Fe HQ magnitudes or Cu concentration plausibility is for downstream synthesis to flag, not for the source page to editorialise.
• Sweet-potato vs Potato terminology: the Methods section explicitly lists “sweet potatoes” as one of the 12 vegetable types, but Table 1, Table 2, Table 3, Table 4, and the discussion (e.g., “upper limit of 59.1 mg/kg Cr concentration in potatoes”) all use the header/term “Potato”. The compositional values are reproduced under the source’s Potato label; the sweet-potato wikilink follows the Methods declaration. The ambiguity is the source’s, not the wiki’s. Eggplant and peas are also among the 12 declared vegetable types but do not currently have dedicated wiki ingredient pages; they are deferred to the auto-stub pass (freq-1 ingredient scaffolding is system work, not source-page-author work).
• Vegetable consumption rate: the authors state “consumption rate (Cr) of vegetables in Nigeria, according to FAO (2021), is 2.3 mg/day”. The unit “mg/day” is anomalous — FAO vegetable-intake statistics are typically expressed in g/day or kg/day, and a 2.3 mg/day consumption rate implies vanishingly small intake that is inconsistent with the EMDI magnitudes the authors report. The authors’ EMDI numbers are reproduced as-is and are internally self-consistent with their stated equation; the unit anomaly is the source’s, not the wiki’s.
• Text-vs-table discrepancies within the source: (a) Cu EMDI range in adults — text says 0.2–1.32 mg/kg BW/day, Table 2 column min is 0.13 (broccoli adult); (b) Cr CR range in children — text says 0.00–0.1, Table 4 column max is 0.49 (potato child); (c) Cu CR range in adults — text says 0.22–2.20, Table 4 column max is 2.24 (beans and potato adult). Table values are reported verbatim above; the table-vs-text text discrepancies are noted but treated as paper-internal rounding/typo rather than a data-integrity stop condition.
• Speciation discipline: Cr is reported as total chromium (paper used ED-XRF, no Cr-VI speciation); metals: [Cr ...] is correct (not Cr-VI). No As/Hg/Pb/Cd analyses are reported by this paper, so no speciation flags apply.
• Brand firewall: no brand names appear in the source page; no aggregation of brand-level data was required because the source does not report brand-level data — only market-aggregated composites from five general markets.
• Routing: products: [] is intentional (paper measures raw fresh produce; no packaged-product slug applies). matrices: includes leafy-vegetable, root-vegetable, fruit-vegetable, and the generic fresh-vegetable to cover the 12 vegetable types that span those plant-part classes.
• 2026-05-20 — Fresh-context audit subagent (verdict REVISE) flagged the Eggplant HQ_Co cell in Table 3 as 366 / nan when PDF Table 3 reads 61.0 / 366 (Eggplant column, HQCo row Ad = 61.0, Ch = 366). Re-verified against the PDF Table 3 image; correction applied (adult HQ_Co now 61.0, children 366). Single-cell transcription defect in the merge-enhance pass, not a row-wide shift. No other audit findings required action: Check 1 was otherwise clean across 17 spot-checks; Checks 2–5 were ✅. The auditor’s ⚠️ note about Broccoli HI adult (table 141 vs narrative 140) is preserved as a source-internal contradiction, not a wiki defect.

Page history

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