Human Health Risk and Bioaccessibility of Toxic Metals in Topsoils from Gbani Mining Community in Ghana (original) (raw)

Journal of Health and Pollution

Metals found in the environment generally originate from natural processes such as weathering of rocks, atmospheric deposition, or from anthropogenic sources, but their distributions are influenced by the properties of the metals and physicochemical factors of soil such as organic matter content and pH. The widespread distribution of metals in the environment is explained by the stability of the forms in which they occur. Whereas low concentrations of essential metals such as copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) are beneficial for the growth and maintenance of the human body, toxic metals (cadmium (Cd), mercury (Hg) and lead (Pb)) can have harmful effects on animal and plant life, as well as the environment. 1-3 Some toxic metals such as Cd, Pb, and Hg are widely used in the manufacturing, mining, agricultural and medical fields and are eventually discharged into the environment. 4-6 Accumulation of excess amounts of metal contaminants in the environment threatens the health of plants and animals because these metals exert biological effects on all life forms. 7,8 Metal pollution in soils is of concern to researchers and regulatory agencies because most metals have adverse health effects. 9 Long term exposure to metals can result in reduced intelligence in humans, DNA damage, and memory impairment. 10,11 The toxic effects of metals are normally defined by their nature. For example, mercury and lead affect almost every human organ, arsenic is known to be a human 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.