The use of 204Pb stable isotope dilution to measure lead lability in soils

Isotopic dilution was used to quantify the mobility or ‘reactivity’ of lead in a range of contaminated soils. Lead is a common contaminant in soils and the mobility of lead is not easily measured, but is an important factor in the prediction of toxicity and risk assessment. The technique developed here uses 204Pb to spike soils and thereby alter the ratio of abundance in the reactive or ‘labile’ pool of soil Pb. The atom ratio 204Pb/208Pb in the solution phase of equilibrated soil suspensions is then measured by ICPMS to resolve the total amount of isotopically exchangeable (Labile) Pb present. The method development involved testing several pre- and post-spike equilibration times, and electrolyte concentrations to provide the most robust method. The final method was then tested on five soils with different contamination histories to demonstrate the range of application of this method. The soils tested had been historically contaminated from a range of sources, including petrogenic Pb, Pb/Zn minespoil, sewage sludge, C19th urban waste and artificial contamination as Pb(NO3)2 salt.