Plumbojarosite Remediation of Soil Affects Lead Speciation and Elemental Interactions in Soil and in Mice Tissues

Abstract

Lead (Pb) contamination of soils is of global concern due to the devastating impacts of Pb exposure in children. Because early-life exposure to Pb has long-lasting health effects, reducing exposure in children is a critical public health goal that has intensified research on the conversion of soil Pb to low bioavailability phases. Recently, plumbojarosite (PLJ) conversion of highly available soil Pb was found to decrease Pb relative bioavailability (RBA <10%). However, there is sparse information concerning interactions between Pb and other elements when contaminated soil, pre- and post-remediation, is ingested and moves through the gastrointestinal tract (GIT). Addressing this may inform drivers of effective chemical remediation strategies. Here, we utilize bulk and micro-focused Pb X-ray absorption spectroscopy to probe elemental interactions and Pb speciation in mouse diet, cecum, and feces samples following ingestion of contaminated soils pre- and post-PLJ treatment. RBA of treated soils was less than 1% with PLJ phases transiting the GIT with little absorption. In contrast, Pb associated with organics was predominantly found in the cecum. These results are consistent with transit of insoluble PLJ to feces following ingestion. The expanded understanding of Pb interactions during GIT transit complements our knowledge of elemental interactions with Pb that occur at higher levels of biological organization.

Successful Conversion of Pb-Contaminated Soils to Low-Bioaccessibility Plumbojarosite Using Potassium-Jarosite at Ambient Temperature

“…Spatially resolved elemental correlation plots reveal strong association of Pb and Fe for KJ-treated samples ( r 2 = 0.50) (Supporting Information Figure S4B), whereas Pb and Fe were found to have a weaker association for the untreated BO soil ( r 2 = 0.14) (Supporting Information Figure S4A). Recently published μ-XRF maps of PLJ-converted soil were found to possess similarly strong Pb and Fe spatial correlation . The same BO soil treated using the heated PLJ precipitation technique resulted in some similarities in Pb co-associations, but unique elemental interactions were observed overall.…”

“…Recently published μ-XRF maps of PLJ-converted soil were found to possess similarly strong Pb and Fe spatial correlation. 12 The same BO soil treated using the heated PLJ precipitation technique resulted in some similarities in Pb co-associations, but unique elemental interactions were observed overall. Similar to the KJ treatment, areas of Pb−Fe interactions were observed; however, S and Pb−S signatures were of apparent increased presence in the heated PLJ precipitation-treated samples.…”

“…Similar to the KJ treatment, areas of Pb–Fe interactions were observed; however, S and Pb–S signatures were of apparent increased presence in the heated PLJ precipitation-treated samples. This is sensible as the heated PLJ precipitation-treated soil was exposed to aqueous sulfate, , likely increasing S interactions for all soil mineral present. Additionally, direct Pb–S interactions may be indicative of anglesite formation, but this was not detectable in the bulk XANES analysis.…”

“…Chemical remediation technologies that promote in situ immobilization of Pb phases are particularly favorable as these methods are cost-effective and promote formation to less bioaccessible forms. ,, Bioaccessibility is defined as the proportion of a contaminant that is solubilized in chemical conditions simulating the gastric environment (pH ∼ 1.5–2.5) of the gastrointestinal tract (GIT) under fasting conditions. , To simulate these conditions, in vitro bioaccessibility (IVBA) assays are utilized and allow for the assessment of the bioaccessible fraction of a contaminant initially present in soil to provide insight into the efficacy of a remediation treatment. IVBA may be used to predict relative bioavailability (RBA), representing the ratio of Pb retained by an in vivo animal model upon ingestion of contaminated soils compared to ingestion of a Pb acetate standard assumed to be 100% bioavailable. ,,− …”

“…Chemical remediation techniques have, until recently, focused on the application of phosphate-based treatments (e.g., conversion to pyromorphite following triple super phosphate application). ,, While phosphate treatment can promote soil Pb bioaccessibility decrease, success is variable and can promote increased arsenic (As) bioaccessibility due to competitive sorption interactions between phosphate and arsenate. , Due to a need for additional treatment options, recent interest has been shown in methods for converting soil into plumbojarosite (PLJ), a highly insoluble, Pb-containing hydroxysulfate (Pb 0.5 2+ Fe 3 3+ (OH) 6 (SO 4 ) 2 ) mineral. , This PLJ synthesis methodology is adapted from Dutrizac et al using a reverse methodological approach where a ferric sulfate-H 2 SO 4 solution is applied to a heated soil (95–100°) suspended in deionized (DI) water, facilitating conversion of soil Pb to PLJ phases. , Due to the insolubility and high stability of PLJ under acidic conditions (pH < 4), PLJ phases are exceedingly unavailable when exposed to gastric condition following ingestion. ,,, Therefore, converted PLJ phases using this technique have been found to have exceptionally low in vitro bioaccessibility and in vivo mouse model bioavailability (<1% IVBA and <10% RBA) . Using this work, two additional research efforts have found congruent results supporting the utilization of PLJ as a Pb remediation technology, , but increased investigation is needed to facilitate continued development of this potential soil Pb remediation technology.…”