Overview
Usman and colleagues measured mercury, lead, cadmium and chromium by atomic absorption spectroscopy in one composite sample of rice and one of beans from farm harvests in each of the three senatorial zones of Yobe State. Mercury was high in Zone C rice and beans and in Zone B beans, and the authors’ health risk index for mercury exceeded 1 in every zone. Arsenic was not measured.
Key numbers
- Beans, Zone C composite: mercury 3.73 ± 0.15 mg/kg, lead 0.33 ± 0.06 mg/kg, cadmium 0.07 ± 0.01 mg/kg, chromium 0.14 ± 0.00 mg/kg (Table 1, ZCB).
- Beans, Zone A composite: mercury 0.14 ± 0.20 mg/kg, lead 0.05 ± 0.10 mg/kg, cadmium and chromium printed as 0.00 (Table 1, ZAB).
- Rice, Zone C composite: mercury 4.04 ± 0.17 mg/kg, lead 0.91 ± 0.02 mg/kg (Table 1, ZCR).
- Health risk index for mercury: 7.3 for rice and beans in Zone C (Table 3).
Methods (brief)
Samples were washed, oven-dried at 65 °C and ground, then dry-ashed at 450 °C and digested in nitric and hydrochloric acids before AAS reading against external calibration. Results are on a dry-weight basis by inference from the preparation. No detection limits, recoveries, blanks or reference materials are reported, and the mercury technique is not described.
Evidence Fitness
Six composite samples, one per crop and zone, with no stated replicate count. The abstract ranges do not match Table 1 (for example bean cadmium 0.05-0.07 mg/kg in the abstract against 0.00-0.07 in the table); table values are used as printed and flagged. The mercury levels are unusually high for grains and legumes and the method gives no basis for checking them. Samples are farm harvests, not market or canned products. The bean species and variety are not stated, so this is a proxy for pinto-beans, not direct evidence for that page.