Automatic Kinetic Bioaccessibility Assay of Lead in Soil Environments Using Flow-through Microdialysis as a Front End to Electrothermal Atomic Absorption Spectrometry

In-line microdialysis is in this work hyphenated to electrothermal atomic absorption spectrometry via a dedicated flow-based interface for monitoring the batchwise leaching test endorsed by the Standards, Measurements and Testing Program (SM&T) of the European Commission. The bioaccessible pool of lead in soils is measured using 0.43 mol/L AcOH as extractant. The proposed method allows to gain knowledge of leaching kinetics at real-time, simplify the overall procedure by accurate detection of steady-state conditions and overcome sample filtration or centrifugation. Soil leachates were automatically sampled at specified timeframes (e.g, every 20 or 80 mm), processed in an external container (where dilution can be applied at will) and further injected into the atomizer. The method was experimentally validated by comparison of in situ micro dialysis sampling results with in-line microfiltration in two soils of varying physicochemical properties. A mathematical framework was used for discrimination of different metal fractions (that is, readily mobilizable against slowly mobilizable lead) and also for estimating the total extractable lead under actual steady-state conditions. We have demonstrated that bioaccessibility tests lasting 16 h as endorsed by SM&T might not suffice for ascertainment of maximum (steady-state) bioaccessibility of lead in terrestrial environments as demanded in risk assessment programs.