In-Situ Soil Lead Remediation:
Investigating the Effectiveness of Soil Amendments in Reducing the Bioaccessibility of Lead, Pb, on Vacant Lots in South Providence

Rebekah L. Doyle

The contamination of soil with lead (Pb) presents a health hazard to living organisms and is a difficult problem to address due to the persistent and ubiquitous nature of lead in our environment. Providence has an especially high amount of land with elevated lead levels for both historical and geographical reasons. While there has been a widespread effort to educate and curb lead exposures in the city, there has been very little effort to reduce the lead content of soil, and an uncounted number of properties remain contaminated. Recently the field of remediation strategies has begun to expand and alternative techniques are being employed to reduce the health threat posed by soil lead on a property. Chemical interactions resulting from the addition of phosphates and organic amendments to soil could potentially reduce the bioavailability of lead. The aim of this research was to investigate the effectiveness of in-situ soil amendments at reducing soil lead bioavailability.

The experimental phase of this research began on vacant lots in the Elmwood section of Providence where plots were established and samples for testing collected. X-Ray fluorescence spectrometry provided the lead concentration for the 48 separate plots. After establishment of initial lead concentrations, black rock phosphate and compost were selectively added to different plots. The plots were then resampled to establish their lead concentrations after dilution by the amendments. The effectiveness of the amendments was assessed through laboratory procedures that simulated the absorption of lead in the human stomach and the amount of extractable lead was measured by atomic absorption. Extractions were performed on all of the pre-amended plot samples as well as all of the post-amended plot samples in order to gain a clearer sense of the differences in lead bioavailability under varying conditions. The soil amendment treatments did not yield significant and consistent reductions in lead extractability. While the results are tentative and tenuous as they represent localized situations, they do provide insights into implementing a viable remediation strategy. In some situations lead soluble concentrations would need to be reduced more substantially than they have been by the amendment treatments conducted here. The amendment "recipe" needs additional research and development to further identify the most effective amounts of amendments to apply and the most efficient and accurate means of doing so. There is great potential for a systematic approach to soil amendment application to assist those faced with the challenges of soil lead. These alternatives may be preferable to the expensive alternatives that cover over or transfer the lead, not chemically bind it.