Lead (Pb) and arsenic (As) are common environmental contaminants resulting from industrial activity and agricultural products such as pesticides.  Discreet areas of highly Pb and/or As contaminated soil can be effectively remediated by soil removal.  However, widely disseminated, lower-level contamination in populated areas like inner cities is not as easily addressed.  Excavation is rarely a suitable solution in such situations.  Consequently, the remedial challenge for widespread soil contamination, especially in populated areas, requires alternative approaches.  Such strategies should endeavor to reduce Pb and As exposure in a cost effective, minimally disruptive manner.

Lead immobilization is a cost-effective remediation technology based on adding easily available amendments to polluted soils to reduce the solubility, mobility, and bioavailability of Pb in the soil without altering total concentration.  A number of research studies have highlighted the ability of phosphate amendments to reduce Pb extractability and bioavailability.  Adding phosphate amendments to Pb contaminated soils may decrease the bioavailability of Pb, thus limiting the negative health impacts to children eating soils.  However the use of phosphate as an amendment to Pb contaminated soil may have an impact on the mobility of other soil contaminants such as arsenic.

We established a pot study of five Pb and As co-contaminated soils with five phosphate amendments including phosphoric acid, diammonium phosphate, struvite (NH₄MgPO₄·6H₂O) derived from swine manure, and two commercially available remediation products (Apatite II and Lock Up Lead) at a 3% P₂O₅ application rate.  The amended soils were allowed to react for 3 months.  The amended and non-amended soils were characterized and examined for changes in Pb and As speciation via X-ray absorption spectroscopy.  The soils were subjected to a standard in-vitro bioaccessibility extraction test at pH 1.5 and 2.5.  Finally, selected soil treatments were examined by the mouse in-vivo bioassay to determine relative bioavailability.