| dc.description.abstract | The unregulated use of elemental mercury (Hg) in artisanal and small-scale gold mining (ASGM) to extract gold from its ore results in metal pollution of various environmental systems. ASGM employs the mercury amalgamation method to obtain gold using locally-made technologies and tools such as hoes, pickaxes, and basins. The amalgamation method results into the emission of elemental mercury as vapor into the atmosphere and the discharge of wastewater as tailings, which drain along streams with a good percentage adsorbing onto the soils and sediments before final deposition in low altitude areas such as swamps, lakes, and rivers. Vaporized mercury is deposited on the vegetation and soil, which prompts vegetation absorption through the stomata during respiration. Direct uptake through the roots is the main absorption route of soil mercury to plants. Soils and plants are therefore of concern because man, who is at the top of the food chain, is exposed to elevated levels of mercury. This study aimed to assess mercury bioavailability in soils and its potential uptake by food crops grown around selected ASGM areas in Namayingo and Busia of Eastern Uganda. The acid digestion method was used for extraction and spectrometry used for analysis of mercury in soils and plants. All the soils from the three sites of Agata, Nakudi and Bukana were slightly acidic with mean pH values of 6.6, 6.9 and 6.5 and electric conductivity values were 176.3, 169.0 and 143.1 s/m, respectively. Agata site had least total organic matter content of 2.0%, Nakudi site with 2.1% whereas Bukana site had the highest total organic matter content of 3.5%. Total mercury concentrations of soils in the study sites was in the order; Agata > Nakudi > Bukana with mean values of 88.1, 51.2 and 44.0 mg/kg, respectively. It was observed that 2.3% of total mercury in soils was bioavailable for plant uptake, with 0.7% of total mercury in the methyl mercury form which is very mobile and toxic to plant and animal life. Hg was more bioavailable in the Agata ASGM site with a mean total mercury concentration in the mobile phase at 2.1 mg/kg followed by the Nakudi ASGM site with 1.1 mg/kg of total mercury whereas the Bukana site was observed with the least bioavailable mercury with a mean total mercury concentration in the mobile phase as 0.9 mg/kg. Total mercury concentrations in food crops were observed highest in leafy crops, moderate in tubers, and least in grains, with 87% of the studied food crops having total mercury concentrations above the acceptable maximum limit of 0.05mg/kg (FAO/WHO). Health risk assessment from consumption of studied crops using the Health Risk Index (HRI) was observed above the acceptable limit of 1 in 57% of the total food crops, which indicated high toxicity upon ingestion. | en_US |
