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Assessing Public Health Risks from Trace Element Contamination in Common Leafy Vegetables from Ondo, Nigeria, Using PIXE and Multivariate Statistics

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Overview

This study measured trace elements in commonly consumed leafy vegetables from Ondo Metropolis using PIXE and evaluated non-carcinogenic health-risk indices for nickel and cobalt.

Key numbers

Source units are mg/kg dry weight.

  • Sample frame: ten composite samples collected September 2018 (late wet season) from six vegetables: Bitter Leaf (Vernonia amygdalina), Waterleaf (Talinum triangulare), Garden Egg Leaf (Solanum macrocarpon), African Spinach (Amaranthus hybridus), Fluted Pumpkin Leaf (Telfairia occidentalis), and Worowo (Solanecio biafrae).
  • Ni detected in 60% of samples; range 0.4-6.4; mean 2.3 +/- 2.1; median 1.6. Per the Table 2 footnote, the Ni mean and statistics are calculated only over the detected subset (n=6), not over the full ten-sample frame.
  • Co was present in all samples; range 0.8-6.1; mean 3.0 +/- 1.8; median 3.2.
  • Cd range 0.029-0.049; mean 0.038 +/- 0.007; median 0.036.
  • Pb was below LOD in the summarized table.
  • Bitter leaf and garden egg leaf were identified as higher accumulators for Co and Ni; the paper reports that median Ni in Bitter Leaf was approximately five times that in African Spinach.
  • Health-risk assessment using the highest mean concentration in Vernonia amygdalina as the worst-case (FIR 150 g/day, BW 70 kg, RfD Ni 0.02 mg/kg/day, RfD Co 0.0003 mg/kg/day) gave THQ 1.17 for Ni and 0.04 for Co, with Hazard Index 1.21.

Methods

Samples were oven-dried at 60 C, pulverized with an agate mortar, sieved through a 2 mm stainless steel sieve, and pressed into 13 mm pellets without binders. PIXE was performed at the Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, using a 2.5 MeV proton beam and a Si(Li) detector. Quality control used NIST SRM 1573a (Tomato Leaves) and IAEA V-10 (Hay Powder), with reported recoveries of 85-110% and RSD below 10%. Reported LODs included Co 0.2 mg/kg, Ni 0.3 mg/kg, Cd 0.02 mg/kg, and Pb 0.1 mg/kg. Below-LOD values were imputed as LOD/sqrt(2) for statistical work.

Implications

The source supports leafy-vegetable nickel/cobalt context for Ondo, Nigeria. Dry-weight basis must be preserved unless a moisture conversion is explicitly introduced.

Update history

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