2.3.1. Total Metal Digestion

Air-dried and sieved soil aliquots of 0.5 g were digested in 2.5 mL of *aqua regia* (HNO3: HCl, 1:3) at 105 ◦C for 2 h, followed by the addition of 1 mL of H2O2 30% (*w*/*w*). Digested soil samples were cooled and final volumes were diluted to 50 mL using ultrapure water. Diluted acid digestate was then filtered using 0.45 μm nylon filter membranes. To determine the contamination, precision and bias of the analysis, reagent blanks which represented 10% of the total digested sample population and replicated certified reference materials (DO82-540, ERA) were incorporated into the analysis. The findings of the analytical results showed no signs of contamination, and the accuracy was found to be consistently within 10% of the certified values [20].
