Estimating Pb Bioavailability in Contaminated Soils to Humans and Effect of Remediation Techniques Using In Vitro and Cell Culture Assays

Soils in urban/industrial areas are often contaminated by Pb, and quantification of potential bioavailability to humans is necessary for accurate assessment of health risks. We examined control and remediated contaminated soils and households dusts collected in the vicinity of a large Pb/Zn smelter and estimated potential bioavailability to humans using an in vitro two phase digestion method (PBET) in conjunction with a human cell bioassay (Caco-2 cell model). Of the total Pb in household dust (5515 mg/kg), less than 30% was found to be bioaccessible using the PBET assay, and only 25% of this bioaccessible Pb was found to be bioavailable using the Caco-2 assay. Of total Pb in road dust (2675 mg/kg) 45% was found to be bioaccessible, and 19% of the bioaccessible Pb was found to be bioavailable. Treatment of household dust with pyrophosphate and Calgon® solutions (simulating steam cleaning with these reagents) significantly reduced total dust Pb concentrations by ~50%. However while treatment with Calgon® increased residual Pb bioaccessibility for household and road dust (depending on solution concentration used), bioavailability as assessed using the Caco-2 cell model was extremely low (9.6% and 10.5% of dose, respectively). This study demonstrates that the remediation of in situ urban/industrial dust materials with polyphosphates can not only remove dust Pb, but also reduce bioavailability of residual Pb in the dust, therefore potentially reducing risk to human health from dust-Pb exposure.