Heavy metal contamination and health risk of soils and vegetables grown near a gold mine area: a case study of Barberton, South Africa.

Abstract

Pollution from mining operations has a direct impact on agricultural production and can lead to potential health risks because of the accumulation of heavy metals in vegetables. Vegetables and soil samples collected from Thaba Nchu farm located near a gold mining site were analysed to determine the concentration of heavy metals. Soil and vegetable samples were digested using the wet method and heavy metals were analysed using the inductively coupled plasma-mass spectrometry technique. The soil-to-plant Transfer Factors (TF) and Health Risk Index (HRI) were calculated. The highest mean levels of Fe, Mn, Ni, Pb, and Cu were detected in spinach while the highest mean level of Zn was found in onion. Iron levels in lettuce, spinach, beetroot, onion, and carrot ranged from 2203 to 3404 mg/kg which was above the permissible limits (450 mg/kg) recommended by the Food and Agriculture Organization–World Health Organization (FAO/WHO). The concentration of Pb (0.4 mg/kg) and Cr (13.8 mg/kg) in spinach exceeded the permissible level recommended by FAO/WHO of 0.3 mg/kg and 1.3 mg/kg, respectively. The metal transfer factors in vegetables were in the order: Cd>Pb>Cu>Fe>Ni>Co>Zn>Cr>Mn. The daily intake and HRI of Mn and Fe in vegetables were above safe levels. There was no obvious heavy metal contamination in the soil and irrigation water. These results suggest that the consumption of vegetables grown on the study site could pose danger to human health. High heavy metal content in crops was attributed to the accumulation of Fe and Mn, which are the major ores extracted from the mining activities in the study area. Given the potential health risks, regular monitoring of heavy metal contamination in the soils and crops is recommended.