Mobility of Potentially Toxic Elements in Urban Soils of Zagreb: A Single-Step Extraction Approach for Evaluating the Efficiency of Three Extraction Agents

This study extends previous investigations of soils in Zagreb, the capital of Croatia, by focusing on 25 urban samples selected on the basis of their magnetic susceptibility values. A single-step extraction was performed using 1 M HCl, 2 M HNO3, and 1 M CH3COONH4 as extraction reagents. The contents of As, Ba, Cd, Co, Cr, Cu, Fe, K, Mn, Ni, Pb, Sb, and Zn in the extracts were determined using inductively coupled plasma–optical emission spectrometry (ICP-OES). Extraction efficiency was evaluated by comparing element contents obtained with each reagent and their ratios to the corresponding total element contents. Efficiency varied significantly; 1 M HCl showed the highest average efficiency for most elements (range 0.64–59.9%), while 2 M HNO3 achieved the highest maximum efficiency values (0.31–75.6%). The 1 M CH3COONH4 was more efficient for K and Ba than for other elements (0.010- 57.7%). The extraction efficiency of the two acids followed a clear pattern—similar recoveries for some samples, HCl-favoured for others, and HNO3-favoured for the rest. The elemental contents were found to reflect contributions from Mount Medvednica, the Sava River floodplain, and anthropogenic sources. These results indicate that single-step extraction is a valuable method for estimating element mobility.