Comparative Evaluation of Digestion Methods for Heavy Metal Analysis in Soil, Water, and Plants from Tigray, Ethiopia

Abstract

Heavy 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.