Overview
Zubairu Yusha’u and colleagues measured arsenic, lead, cadmium, copper and zinc by atomic absorption spectrophotometry in five improved crop varieties (millet, maize, rice, beans and sorghum) harvested by smallholder farmers in the Challawa industrial area of Kano State. Table 1 gives one mean value per crop. The authors report hazard indices below 1 for all crops. Mercury was not measured.
Key numbers
- Beans: arsenic 0.005 mg/kg, lead 0.015 mg/kg, cadmium 0.002 mg/kg, copper 7.0 mg/kg, zinc 22.0 mg/kg (Table 1).
- Rice: arsenic 0.020 mg/kg, lead 0.040 mg/kg, cadmium 0.050 mg/kg (Table 1).
- Maize: arsenic 0.010 mg/kg, lead 0.030 mg/kg, cadmium 0.030 mg/kg (Table 1).
- Hazard index via ingestion ranged from 1.1 x 10-2 (beans) to 2.8 x 10-2 (sorghum) (Table 3).
Methods (brief)
Crops were oven-dried at 50 °C, ground and sieved, then digested under reflux with concentrated nitric acid and read on a Shimadzu AA 6300 spectrophotometer. Results are on a dry-weight basis by inference from the preparation; the table does not label the basis. Triplicate readings with blanks; recoveries of 92-100% are stated. No certified reference material and no detection limits are reported.
Evidence Fitness
One value per crop with no sample count, dispersion, detection limit or collection date. The atomization mode is not stated, and quantifying arsenic and cadmium at a few micrograms per kilogram by conventional AAS is doubtful. The text cites the wrong table number for concentrations, and the daily intake table is partly garbled. The crops were grown near an industrial area, so they are not representative of ordinary market supply. The bean species and variety are not stated, so this is a proxy for pinto-beans, not direct evidence for that page.