Concentration Levels of Heavy Metals in Tailings, Water and Sweet Potatoes in Artisanal Gold Mining Areas of Kuria West Sub-county, Kenya

Abstract

Artisanal gold mining is an important economic activity in many regions of the world. However, mining activities can lead to the production of large quantities of heavy metal laden wastes which can result to widespread contamination of the environment. This study investigated the levels of heavy metals (Cr, Cu, Zn, As, Cd and Pb) in gold mine tailings, panning pond water, river water and sweet potatoes obtained from Kuria West Sub-County, Kenya and evaluated potential health risks among local residents. One-way analysis of variance (ANOVA) was used to test significant difference (p < 0.05) of heavy metal concentrations across the different sampling sites. The mean concentrations for heavy metals such as chromium, copper, arsenic, cadmium and lead differed significantly (p <0.05) among the study sites for tailings. With regard to river water all the heavy metals differed significantly among the study sites (p <0.05). For sweet potatoes, there was no significant difference recorded (p > 0.05) between the study sites. Results showed that tailings had the highest heavy metal mean concentrations (mg/kg) of As (946.45 – 2789.88), Pb (31.71 – 366.21), Zn (54.17 – 118.07), Cr (34.14 – 87.42), Cu (16.97 – 55.52) and Cd (0.32 – 1.85). Heavy metal concentrations in panning ponds water were comparatively lower (i.e., < 2mg/l) and were within the same range (0.0001 – 1.26mg/l). Heavy metal concentrations in river water (mg/l) recorded were Cr (0.031 – 0.184), Cu (0.063 -4.058), Zn (0.097 – 0.824), As (0.002 – 0.666), Cd (0.0001 – 0.0036) and Pb (0.008 – 0.009). The concentrations of heavy metals recorded at the downstream sampling site except Zn exceeded World Health Organization (WHO) set limit for drinking water. The average concentrations for heavy metals in sweet potatoes such as chromium (3.32mg/kg), zinc (12.02mg/kg), Pb (0.44mg/kg) and As (0.31mg/kg) exceeded WHO set limit while Cu (7.57mg/kg) and Cd (0.08mg/kg) were within the recommended levels. The presence of heavy metals (Cr, Zn, Pb, and As) in higher concentrations than WHO set limits for sweet potatoes poses a health risk to the residents of Kuria west. In conclusion, it is recommended that mining activities should be regulated and licensed by relevant government agencies. Tailings and waste waters emanating from mining activities should be kept safely before treatment and disposal. Continuous monitoring of heavy metals should be undertaken to determine heavy metal concentrations in areas close to gold mines and further tests should be undertaken to determine heavy metal concentrations in soil, other crops, air and ground water.