Imongben et al. 2026 — Heavy metals and health risk in Kaduna market vegetables, Nigeria
This study measured Cr, Mn, Fe, Co, Ni, Cu, Mo, and Zn in 12 vegetable types from five markets in Kaduna Metropolis, Nigeria using energy-dispersive X-ray fluorescence (ED-XRF) spectrometry, and assessed non-carcinogenic (HQ, HI) and carcinogenic (CR) health risks for adults and children. Contaminated Kaduna River irrigation water is identified as the primary pollution pathway; the city’s major industries (refinery, textiles, food and beverage, ceramics, fertilizer, paper) continuously discharge untreated wastewater into the river. Heavy metal concentrations were generally high, with Cr, Cu, and Ni posing moderate-to-high carcinogenic risks and the HI exceeding 1 for all vegetables and both age groups, indicating cumulative non-carcinogenic risk. Fe in avocado and Cu in beans showed the highest individual HQ values.
Key numbers
All concentrations in mg/kg (assumed dry weight for ED-XRF pellet analysis). n = 5 composites per vegetable per market; total reported as 12 vegetable types × 5 markets.
Heavy metal concentrations (mg/kg), selected values from Table 1:
Chromium (Cr):
- Range: 0.00 (carrot, below LOD) to 59.1 (potato)
- Avocado: 28.2 ± 2.64; Beans: 58.8 ± 4.94; Cabbage: 19.3 ± 1.7; Pea: 28.8 ± 2.73; Spinach: 2.8 ± 0.26; Lettuce: 2.8 ± 0.26; Broccoli: 6.3 ± 0.4
- EU permissible limit for Cr: 0.3 mg/kg (EU, 2006); all vegetables except carrot exceeded this limit
Nickel (Ni):
- Range: 0.00 (beans, cauliflower, pea, below LOD) to 24.7 (potato)
- Avocado: 17.3 ± 1.73; Cabbage: 12.6 ± 1.32; Lettuce: 17.6 ± 2.18; Eggplant: 6.31 ± 0.66; Carrot: 2.36 ± 0.24; Broccoli: 2.33 ± 0.20
- FAO/WHO permitted level for Ni: 67.9 mg/kg; all vegetables below this limit
Copper (Cu):
- Range: 46.1 (broccoli) to 479 (beans)
- Beans: 479 ± 79.2; Cabbage: 424 ± 77.04; Potato: 470 ± 65.2; Avocado: 283 ± 48.4
- FAO/WHO limit for Cu: 2.0 mg/kg; all vegetables except broccoli and cauliflower substantially exceeded this limit (study notes possible measurement or unit interpretation issues given the extreme exceedances)
Iron (Fe):
- Range: 122 (broccoli) to 1485 (avocado)
- All reported in mg/kg; avocado (1485 ± 148) and cabbage (870.8 ± 87.08) highest
- FAO/WHO safe limit: 425 mg/kg; avocado, celery, cabbage, lettuce, spinach, and potato exceeded this
Manganese (Mn):
- Range: 19.5 (broccoli) to 203 (avocado)
- Comparable to or above published literature values; EMDI for children (3.36 mg/day for avocado) exceeds daily intake recommendations for children (0.3–1.0 mg for infants; 1.5 mg for children)
Zinc (Zn):
- Range: 33.7 (broccoli) to 335 (cabbage)
- WHO permissible limit: 60 mg/kg; exceeded by all vegetables except broccoli and cauliflower
Estimated Maximum Daily Intake (EMDI) ranges (mg/kg BW/day), adults/children:
- Cr: 0–0.16 adults; 0–0.97 children
- Ni: 0–0.07 adults; 0–0.41 children
- Cu: 0.13–1.32 adults; 0.76–7.91 children
Non-carcinogenic risk:
- HQ > 1 for most metals in most vegetables for both adults and children
- Fe HQ in avocado: adults = 583; children = 3502 (extreme value driven by very high Fe concentration and Fe RfD of 0.007 mg/kg/day used)
- HI range: 140–828 mg/kg (adults); 843–4966 mg/kg (children); all >1 for all vegetables
- Highest HI: potato (adults 828; children 4966)
Carcinogenic risk (CR) for Cr, Cu, Ni (adults/children):
- CR for Cu: 0.22–2.24 (adults); 0.69–7.19 (children) — moderate to high risk (10−3 to 10−1 range)
- CR for Cr: 0.00–0.08 (adults); 0.00–0.49 (children) — low to moderate risk
- CR for Ni: 0.00–0.06 (adults); 0.00–0.69 (children) — low to moderate risk
- Cu is identified as the dominant carcinogen among the three metals studied
Methods (brief)
Vegetable samples (12 types) purchased from 5 markets in Kaduna Metropolis; 5 samples per type per market composited using coning and quartering; destalked where required, washed with tap water then rinsed with distilled water, chopped with stainless knife, oven-dried at 105°C until crisp, pulverized with agate mortar and pestle, sieved through BS 125mm mesh. Pellets (19 mm diameter) pressed from 0.5 g powder + organic liquid binder at 10 tons hydraulic pressure. ED-XRF analysis: annular 25 mCi 109Cd excitation source emitting Ag-K X-rays (22.1 keV), Si-(Li) detector (170 eV resolution at 5.90 keV), 1000 s acquisition; Bruker remote control and instrument tool software; Emission-Transmission (E-T) method for quantification. Vegetable samples authenticated by NDA Biological Science Botanical unit with voucher numbers.
Method limitations: ED-XRF measures total elemental composition without speciation; Cr values represent total Cr (not Cr-VI); no inorganic arsenic speciation; no Pb, Cd, As, or Hg reported (these analytes not included in the ED-XRF analytical scheme described). The Fe HQ values (ranging to 583 for adults) appear exceptionally high and may reflect the very low EPA RfD for Fe (0.007 mg/kg/day from USEPA RfD table used in this paper) combined with genuinely elevated Fe levels; the biological significance of HQ values this far above 1 for Fe is uncertain and should be interpreted cautiously. Cu concentrations in beans (479 mg/kg) are approximately 240-fold above FAO/WHO limits and warrant independent verification. Paper was received October 2025 and published March 2026; this is classified B-tier given it is a regional survey using ED-XRF (less sensitive and specific than ICP-MS) with no reported certified reference material validation.
Implications
Certification: This study does not report Pb, Cd, As, or Hg, which are the primary HMTc analytes. Its contribution to the wiki is the documentation of elevated Cr, Ni, and Cu in Kaduna market vegetables attributed to contaminated River Kaduna irrigation, not to establish HMTc-relevant concentration baselines.
Courses: Useful case study for the contaminated-irrigation-water pathway to vegetable heavy metal accumulation in low-income urban settings; River Kaduna receives continuous industrial discharge from refinery, textile, ceramics, and fertilizer plants. Children’s health risks (HQ, HI, CR) substantially exceed adult values for all metals at the same consumption rates, illustrating vulnerability differential.
App: Not directly applicable for ingredient contamination profile values; ED-XRF method and Nigerian market survey context are not representative of North American or European supply chains. Contextual use only.