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Determination of traces of molybdenum and lead in foods by x-ray fluorescence spectrometry

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The authors developed an energy-dispersive x-ray fluorescence method in which food is dried, carbonized at low temperature and pressed into pellets, and then applied it to cereals, pulses, vegetables, meat, fish, milk products, eggs, fruit and tea bought in Bangladeshi markets. Pulses and cereals carried the most molybdenum. The paper also multiplies these concentrations by food-group consumption to estimate daily molybdenum intake for six population groups.

Key numbers

All food values are mg/kg fresh weight, mean ± counting uncertainty (Table 3, p. 6; Table 4, p. 6).

  • Pulses, group mean: 2.51 ± 0.09 mg/kg (range 0.77 to 3.18). Green gram 3.18 ± 0.07 (n = 3); lathyrus pea 2.93 ± 0.12 (n = 3); black gram 2.85 ± 0.07 (n = 3); lentils 2.83 ± 0.10 (n = 3); Bengal gram 0.77 ± 0.08 (n = 3).
  • Cereals, group mean: 1.50 ± 0.06 mg/kg (range 0.31 to 4.44). IRRI rice 4.44 ± 0.11 (n = 15); local rice 0.75 ± 0.01 (n = 12); sunned milled rice 0.49 ± 0.08 (n = 10); coarse wheat flour 0.31 ± 0.05 (n = 5).
  • Milk and milk products, group mean 0.26 ± 0.06 mg/kg; eggs 0.18 ± 0.03; fruits 0.13 ± 0.01; fishes 0.12 ± 0.03; vegetables 0.08 ± 0.03; meats 0.07 ± 0.01 mg/kg.
  • Tea: 0.34 ± 0.09 mg/kg (n = 3).
  • Food-group ranking reported for molybdenum: pulses > cereals > milk and milk products > eggs > fruits > fishes > vegetables > meats (pp. 5 to 6).
  • Detection limit stated in the abstract: 0.08 mg/kg; the text gives matrix-dependent minimum detection limits of 0.02 (molybdenum) and 0.08 (lead) for a dry pine-needle matrix, unit not restated (p. 7; abstract, p. 1).
  • Reference-material check after carbonization: rice flour measured 1.50 ± 0.15 vs certified 1.46 ± 0.10 mg/kg; bovine liver 3.30 ± 0.41 vs 3.5 ± 0.30 mg/kg (Table 1, p. 5).
  • Calculated total daily molybdenum intake: 0.45 mg (children), 0.86 mg (adolescents), 1.16 mg (adult men), 0.83 mg (adult women), 0.82 mg (pregnant women), 0.92 mg (lactating women) (p. 7).
  • The authors compare these intakes with older United States Food and Nutrition Board “safe” levels of 0.30 mg for children and 0.50 mg for other groups and describe Bangladeshi intakes as higher (p. 7; secondary reference values).

Methods (brief)

Edible portions (100 g) were washed, oven-dried at 85 °C, carbonized at 150 to 400 °C, powdered and pressed into 100 mg pellets. Pellets were excited with a cadmium-109 isotope source and read with a Si(Li) detector; spectra were fitted with the AXIL software. Calibration used NIST bovine liver and orchard leaves standards. Selected foods were cross-checked by PIXE.

Evidence fitness

Direct market-food occurrence data for Bangladesh, giving a clear ranking of food groups. Sample numbers per item are small (often 3) and sampling dates and sites are not stated, so values are not a representative national survey. Uncertainties are counting statistics, not between-sample variation. The intake estimates rest on a separate consumption source and are author-derived.

Limitations

Group means and ranges in Table 4 do not always match the item values in Table 3 (for example, the cereal mean of 1.50 mg/kg sits beside an IRRI rice value of 4.44 mg/kg). The text compares intakes with decades-old reference values. No speciation was done.

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