Efficiency of liming in controlling the mobility of lead in shooting range soils as assessed by different experimental approaches

Shooting range soils contaminated by lead (Pb) are a great environmental risk. Reducing mobility and leaching of Pb by liming, for example, has produced contradictory results. This laboratory study compares the efficiency of two liming agents differing in their reactivity, CaCO3 and blast furnace slag (BFS), in diminishing the mobility of Pb. In a batch test, contaminated humic soil samples were incubated in closed vessels without and with liming materials added in quantities to correspond additions of 5 t ha− 1. Water soluble Pb (Pbw), dissolved organic carbon (DOC), pH and substrate induced respiration (SIR) in soils were monitored for 21 days. In the experiment carried out with freely drained vessels, contaminated humic soil treated without and with liming agents was leached five times during the experimental period of 141 days. Leachates were analyzed for pH, DOC and Pb. At the end of the experiment, soil samples were analyzed for pH, DOC, Pbw, and SIR. In both systems, CaCO3 raised pH and DOC more than BFS. The liming agents did not significantly differ in their effect on Pb chemistry. Neither had any effect on SIR: however, liming agents markedly reduced the leaching of Pb in the open system, while in the closed system they increased rather than reduced the extractability of Pb. Incubation in a closed vessel proved not to be a suitable experimental system for Pb mobility estimation, since the ionic strength may be raised to abnormal levels, resulting from accumulated reaction products of liming agents.