Abstract:
Metalloids and heavy metals are considered major contributors to environmental pollution. Mining activities cause metal pollution and soil degradation, impacting nearby organisms through heavy metal absorption by plants. These metals increase disease risk and can be ingested by aquatic life for further spreading contamination. The research aimed to evaluate the uptake and accumulation of metalloids and heavy metals in soil, wastewater, and different plant species in a mining-affected region of Rwinkwavu, Kayonza district, Rwanda. Samples were collected from various locations, including soils, tailings, and wastewater from a nearby river, a processing plant, and a farmer's storage field. Cassava and sweet potato plants, along with their roots, stems, and leaves, were included. Papaya peels were collected for their potential to remove metalloids from the wastewater. Samples were analyzed using standardized laboratory methods, including Flame Atomic Absorption for heavy metals and the Hydride method for metalloids. Bioconcentration and removal efficiency were calculated, and Rstudio software was used for multivariate analysis to identify correlations among heavy metals and metalloids such as arsenic (As), lead (Pb), chromium (Cr), cadmium (Cd), nickel (Ni), copper (Cu), manganese (Mn), and zinc (Zn) across various environmental matrices. Robust ANOVA with post-hoc tests compared contaminant levels across sampling sites, while correlation analysis explored relationships between different heavy metal concentrations. Soil pH at the mining site ranges from moderately acidic (4.47) to neutral (7.09), with tailings showing low cation exchange capacity (CEC1.3-3.3 cmol(+)/kg). Arsenic contamination is notably high, with concentrations from 5.64 mg/kg to 546 mg/kg, and significant positive correlations between Cu, Pb, and As are expected, especially at tailing sites. In wastewater, arsenic levels peak at 1.675 mg/L in the farmer's storage field. Sweet potatoes exhibit high chromium accumulation in tubers (318.4 mg/kg), while cassava shows moderate levels in roots (45.56 mg/kg) and substantial arsenic contamination (80.98 mg/kg). Arsenic in sweet potatoes is mainly found in stems and leaves, and both crops preferentially accumulate manganese in leaves, with cassava having higher concentrations (318.4 mg/kg) than sweet potatoes (223.4 mg/kg). Papaya peel ash demonstrates an arsenic removal efficiency of 80.08%.The study found strong arsenic pollution in the soil and wastewater at the Rwinkwavu mining site, with chromium identified as a hyperaccumulator in farmer's fields. It recommends using papaya peels for metalloid removal and emphasizes on the importance of sustainable environmental management and strategies for managing contamination in the Rwinkwavu mining area.
