Effects of four different amendments on bioavailable lead in contaminated soils: coupling sequential extraction with in vivo and in vitro assays

Applying amendments to contaminated soil has been considered a successful strategy to control lead (Pb) pollution. In this study, four different types of amendment (calcium hydrogen phosphate, CHP; hydroxyapatite, HA; ordinary Portland cement, OPC; lime, LI) at two treatment levels were used to immobilize Pb in three contaminated soils. The effectiveness of Pb immobilization was assessed by coupling a sequential extraction procedure (fraction) with in vivo mouse model (Pb relative bioavailability, Pb RBA) and in vitro gastrointestinal assays (bioaccessibility). For all four amendments, Pb RBA generally decreased in YNGJ and HNZZ, with a stronger effect at a high treatment level, but less effective in HNJY. In contrast, when in vitro gastrointestinal simulation tests were used, Pb bioaccessibility determined by SBRC and PBET was generally reduced in most cases, especially in soils treated with phosphate amendments. Sequential extraction procedure demonstrated that the addition of 4 amendments generally decreased the proportion of E1 + C2 compared to untreated soils, while increasing R5, O4, or F3. The relationship between Pb fractions and RBA/bioaccessibility indicated that the bioavailable Pb is primarily from the sum of E1 and C2. The finding of this study highlighted reducing E1 + C2 was a primary strategy to further decrease bioavailable Pb in amended soils, and monitoring Pb fractions may provide a concise and alternative method for comprehending the oral bioavailability of Pb to humans.