Point of zero charge: Role in pyromorphite formation and bioaccessibility of lead and arsenic in phosphate amended soils.

Ranju Karna,Todd Luxton,Matthew Noerpel,Kirk Scheckel

doi:10.3390/soilsystems2020022

Ranju Karna, Todd Luxton + Show 2 more

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https://doi.org/10.3390/soilsystems2020022

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Abstract

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite by adding sources of phosphorus (P), but uncertainties still remain in natural systems. Knowledge of PZC is important to predict the ionization of functional groups and their interaction with metal species in solution. This study utilized the Pb- and As-contaminated soils to determine the combined effect of pH with respect to PZC and different rates of P-application on pyromorphite formation, and Pb and arsenic (As) bioaccessibility as impacted by speciation changes. Solution chemistry analysis along with synchrotron-based Pb- and As-speciation, and bioaccessibility treatment effect ratios (TERs) were conducted. Results indicated no significant effect of PZC on pyromorphite formation in P-amended soils; however, the TERPb appeared significantly lower at pH>pHPZC and higher at pH<pHPZC (α = 0.05). In contrast, the TERAs was significantly higher at pH>pHPZC, compared to the other two treatments, for the tested soils. The lack of conversion of soil Pb to pyromorphite may be attributed to presence of stable minerals limiting soluble-Pb availability and high organic matter content of the tested soils.

Highlights

Lead is toxic to humans, especially to young children and animals [1]
When phosphoric acid (PA) was added to the soil suspensions, its influence on pH was variable depending on the buffering capacity of each individual soil
The highest buffering of pH was observed in BO due to the presence of high organic matter content

Summary

Introduction

Lead is toxic to humans, especially to young children and animals [1]. Lead contamination of soil is so pervasive that excavation and subsequent back-filling with clean soil is unsustainable, very costly, and requires an impractically large volume of clean soil. Alternative approaches are required to protect the human lives that are in regular contact with Pb-impacted soils. Alteration of Pb species can significantly benefit humans and environmental health by reducing its toxicity even if the total Pb concentration may remain the same [2,3]. Amending Pb-contaminated soils with phosphorus (P) as an in situ remediation option has been proposed as an alternative to soil removal [4]. For the cases of Pb-contaminated sites, evidence has shown that phosphorous (P) compounds have been used to form highly insoluble, highly stable Pb precipitates that are not biologically available [5,6,7,8,9,10,11,12]

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