In Situ Remediation of Metal-Contaminated Sites and Soils Using Phosphorus: The Ryan Effect.

Phosphorus amendment has been used extensively for in situ remediation of lead-contaminated soils as a risk-based approach and as an alternative to soil excavation.  A variety of studies have been conducted to elucidate the soil chemical and mineralogical changes induced by P amendment as they influence the bioavailability of Pb.  Soil fractionation schemes indicate a shift in Pb toward residual (less bioavailable) fractions upon addition of P. Similar results are found with TCLP-extractable Pb.  Plant uptake of Pb is also reduced although the impact on co-contaminant metals is variable.  Rat feeding studies indicate reductions in Pb bioavailability for P amended soils compared to treatments without P additions.  These changes are correlated with changes in soil Pb as assessed with a physiologically based extraction test.  Mineralogical changes induced by P amendment include the conversion of soil Pb to a variety of insoluble Pb phosphate minerals including pyromorphites and plumbogummite.  The Ryan Effect describes the influence of the work of James Ryan at the intersection of academic research, practicing professionals, policy, and intellectual property rights as these pertain to the use of P to remediate metal-contaminated sites and soils.