Phosphate Amendments in Co-Contaminated Soils: Speciation, Bioaccessibility, and Bioavailability.

A number of urban soils are affected by lead (Pb) contamination through a variety of anthropogenic inputs; likewise, these soils can contain other contaminants of concern such as arsenic (As).  This is also a concern for expanding suburban environments where new homes are built on soils previously utilized for agriculture and industry.  In this work, we examined five soils with dual Pb and As contamination amended with a variety of phosphate sources to examine alterations in Pb and As speciation and the potential risks of Pb and As through bioaccessibility assays and in-vivo animal feeding studies.  Synchrotron speciation demonstrates that Pb forms changed as a result of phosphate amendments to varying degrees, while As speciation remaining relatively unchanged.  In-vitro bioaccessibility results showed significant reductions of Pb release and significant increases in As release.  In-vivo animal relative bioavailability studies are on-going to determine the influence of phosphate amendments of Pb and As bioavailability.  Marginally contaminated urban soils may benefit from phosphate as well as other soil amendments to sequester soil contaminants in place as long as it can be demonstrated to reduce risks and shown to have long-term stabilty.  It is, therefore, imperative to utilize validated methods when evaluating in-situ amendments in urban soils.