College of Natural and Computational Sciences
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Item Comparative Evaluation of Digestion Methods for Heavy Metal Analysis in Soil, Water, and Plants from Tigray, Ethiopia(Mekelle University, 2025-08-25) Robel Dawit AregayHeavy metal contamination is a growing concern in Tigray, Ethiopia, due to mining activities, agricultural inputs, and potential risks to public health, yet no standardized local protocol exists for reliable, cost-effective, and accurate digestion methods essential for environmental monitoring. This study compared four wet digestion methods—Method A (HCl–HNO₃, 3:1), Method B (HCl–HNO₃–H₂SO₄), Method C (HCl–HNO₃–HClO₄), and Method D (HCl–HNO₃– HClO₄–HF)—for determining total concentrations of Cu, Zn, Pb, Co, Cr, Cd, Mn, Fe, and Ni in soil, plant, and water samples from Ezana Mining Development PLC, Mekelle, Ethiopia, using Flame Atomic Absorption Spectrophotometry (FAAS). Performance evaluation based on accuracy (Z-scores and spiking recovery), precision (relative standard deviation), and costeffectiveness, supported by one-way ANOVA (p < 0.05), revealed significant differences among methods, with overall recoveries ranging from 88% to 102% across matrices. Methods A and D showed superior accuracy and precision compared to Methods B and C, with Method A offering comparable performance to Method D while being simpler, safer, and more economical, making it suitable for routine monitoring. Although Method D achieved slightly higher extraction efficiencies for refractory metals, it demands specialized infrastructure, HFhandling safety, and advanced technical expertise. The findings suggest Method A is best suited for general environmental assessments in resource-limited laboratories, while Method D is recommended for targeted analyses requiring maximum recovery, thereby enhancing environmental data quality, strengthening heavy metal monitoring programs, and supporting evidence-based policy decisions in Tigray.Item Assessment of Heavy Metal Levels in Soil, Vegetables and Wastewater used for Irrigation in Wukro, Tigray, Ethiopia(Mekelle University, 2025-09-25) Nigisti GirumFresh vegetables and fruits are the most common foods of human diet all around humankind often used for balanced diet, prevention and treatment of various diseases. However, if these vegetables and fruits grow in a polluted environment they can be a major public concern due to their toxic property which leads to acute and chronic health effects. The aim of this study was to determine the level of manganese, chromium, copper, zinc and lead and to estimate their health risks associated with their daily intake in vegetables grown in Wukro town, Tigray. FAAS was used to determine concentrations of those heavy metals in selected vegetables (cabbage, onion, spinach, lettuce and tomato). 1 gm of each sample was digested by wet digestion method using a mixture of HNO3 (69%), HClO4 (70%) and H2O2 (30%) until a clear solution was prepared. After proper dilutions, the solutions were aspirated into the FAAS. The absorbance value of heavy metals was converted in to concentration using linear calibration curve equation. Finally, the concentration of each metal was expressed in mg/Kg of dry weight of each sample and health risk was estimated by using estimated daily intake (EDI), target hazard quotient (THQ), and hazard index (HI) for selected heavy metals. The validity of the method was checked by the analysis of spiked samples whose recovery was found in the range of 90.8-107.0% and %RSD value in the range of 0.03-7.7%. The average concentrations of Cr and Cu in all of the selected vegetables were lower than the maximum limit of normal values. However, concentrations (mg/kg) of Pb in cabbage (2.05), spinach (2.47), and lettuce (1.56) had exceeded the safe limit, 0.3 mg/Kg set by FAO/WHO. Hence, consuming plant products grown from contaminated water sources such as municipal wastes, industrial effluents, engine fuels, garages disposals, constructions and car washes are potentially toxic to plants, animals and humans. Therefore, people and concerned bodies should take care of the sources of water for irrigation