Bioaccumulation of heavy metals in soil and selected food crops cultivated in Kogi State, north central Nigeria

Abstract

Abstract Background Heavy metal contamination in Nigeria soils is well documented. However, there is dearth of information on the intake of toxic heavy metals by some food crops cultivated in Nigeria soil. Accumulation of toxic heavy metals in edible food crops is a potential threat to human and animal health. Hence, a study on soil to food crop relation in terms of heavy metals accumulation is expedient. In this study, the levels of Cd, Co, Cu, Ni, Pb and Zn in soils and food crop samples from nine major commercial and individual farms were investigated for their contamination in soil and accumulation in food crops. Methods Soil samples were collected from thirty-two farmlands at two depths of 0–15 and 15–30 cm in each farm and control site, to make 320 composite samples. A total of 640 edible food crop samples (pumpkin 64, passion fruit 96, maize grain 96, sugar cane stem 64 and tubers of cassava 320) were collected. Results The results revealed that the levels of Cd ranged from 0.07 to 9.80 mg/kg, Co 0.05–38.1 mg/kg, Cu 0.33–16.9 mg/kg, Ni 3.81–93.1 mg/kg, Pb 4.45–47.7 mg/kg and Zn 5.02–81.4 mg/kg in topsoils. There was no significant difference (P > 0.05) in the levels of these heavy metals in subsoils and among farms. Except in pumpkin, nickel concentration in all the investigated food crops exceeded regulatory limits set by the World Health Organization and the Food and Agriculture Organization. Similarly, the concentration of Cd and Co in pumpkin exceeded regulatory limits. Soil–plant transfer factors indicated low accumulation into crops except Co in maize and Ni in cassava. Conclusion Therefore, soil may require mild remediation action to minimize possible sources of Co and Ni contamination such as irrigation and fertilizer application practices. The concentration of Cd in food crops could be of health concern if such crops are ingested.

Keywords

• Heavy metals
• Soil contamination
• Farmlands
• Food crops
• Metal uptake