Accumulation and bioaccessibility of toxic metals in root tubers and soils from gold mining and farming communities in the Ashanti region of Ghana

The presence of metal contaminants in agricultural soils and subsequent uptake by food crops can pose serious human health risk. In this study, we assessed the levels of toxic metals - arsenic, chromium, copper, iron, manganese, nickel, and zinc - in soils and some edible root tuber crops from two gold mining and two non-mining communities in Ghana to evaluate the potential human health risks associated with exposure to these metals. Concentrations of the metals in 154 soil and edible root tuber samples were analyzed using field portable x-ray fluorescence spectrometer prior to confirmation by inductively coupled plasma mass spectrometry. Bioaccessibility of the metals was determined using an in vitro physiologically based extraction technique. Concentrations of the metals were generally higher in the gold mining communities than in the non-mining communities. The contamination indices indicated low to moderate contamination of the soil and food crops. Bioaccessibility for the metals varied from 1.7% (Fe) to 62.3 (Mn). Overall, the risks posed by the metals upon consumption of the tubers were low.

Human Health Risk and Bioaccessibility of Toxic Metals in Topsoils from Gbani Mining Community in Ghana

BACKGROUND

Anthropogenic activities such as artisanal mining pose a major environmental health concern due to the potential for discharge of toxic metals into the environment.

OBJECTIVES

To determine the distribution and pollution patterns of arsenic (As), iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), manganese (Mn), copper (Cu) and zinc (Zn) in the topsoil of a mining community in Ghana, along with potential human health risks and in vitro bioaccessibility.

METHODS

Concentrations of metals were determined using X-ray fluorescence techniques and validated using inductively coupled plasma-mass spectrometry.

RESULTS

Concentrations of the metals in topsoil were in the order of magnitude of Cu (31.38 mg/kg) < Ni (45.39 mg/kg) < As (59.66 mg/kg) < Cr (92.87 mg/kg) < Zn (106.98 mg/kg) < Mn (1195.49 mg/kg) < Fe (30061.02 mg/kg). Geo-statistical and multivariate analyses based on hazard indices including contamination, ecological risks, geo-accumulation, and pollution load suggest that the topsoils are contaminated in the study area. The potential ecological risk index (PERI) showed high ecological risk effects (PERI=269.09), whereas the hazard index (1×10-7) and carcinogenic risk index (1×10-5) indicated low human health risks. Elevated levels of As, Cr, Ni, and Zn were found to emanate from anthropogenic origins, whereas Fe, Mn, and Cu levels were attributed mainly to geological and atmospheric depositions. Physicochemical parameters (pH, electrical conductivity and total organic carbon) showed weak positive correlations to the metal concentrations. Elemental bioaccessibility was variable, decreasing in the order of Mn (35± 2.9%) > Cu (29± 2.6%) > Ni (22± 1.3%) > As (9± 0.5%) > Cr (4± 0.6%) > Fe (2± 0.4%).

CONCLUSIONS

Incorporation of in-vitro bioaccessibility into the risk characterization models resulted in a hazard index of less than 1, implying low human health risks. However, due to accumulation effects of the metals, regular monitoring is required.

COMPETING INTERESTS

The authors declare no competing financial interests.