Effects of different treatments on the bioavailability of lead (Pb) in soil from a smelter emission contaminated site in Joplin, Missouri, were evaluated in a mouse model. Similar estimates of relative bioavailability for Pb in untreated or treated soil were obtained in mice and in the well-established juvenile swine model. In the mouse model, treatments that used phosphate (phosphoric acid or triple superphosphate) combined with iron oxide or biosolids compost significantly reduced soil Pb bioavailability. Notably, effects of these remediation procedures were persistent, given that up to 16 years had elapsed between soil treatment and sample collection. Remediation of soils was associated with changes in Pb species present in soil. Differences in Pb species in ingested soil and in feces from treated mice indicated that changes in Pb speciation occurred during transit through the gastrointestinal tract. Use of the mouse model facilitates evaluation of remediation procedures and allows monitoring of the performance of procedures under laboratory and field conditions.

House dust and soils can be major sources of lead (Pb) exposure for children. The American Healthy Homes Survey (AHHS) was developed to estimate Pb exposure from house dust and soil, in addition to other potential household contaminants and allergens. We have combined Xray absorption spectroscopic (XAS) fingerprinting and in vivo mouse relative bioavailability (RBA) measurements for a subset of house dust and residential soils collected in the AHHS, with the primary objective of gaining a better understanding of determinants of house dust Pb bioavailability. Lead speciation was well related to variations in RBA results and revealed that highly bioavailable Pb (hydroxy)carbonate (indicative of Pb-based paint) was the major Pb species present in house dusts. Measured Pb RBA was up to 100% and is likely driven by paint Pb. To our knowledge, this is the first report of in vivo Pb RBA for U.S. house dust contaminated in situ with paint Pb and corroborates results from a previous study that demonstrated high RBA of paint Pb added to soil. We also report a relatively low RBA (23%) in a residential soil where the major Pb species was found to be plumbojarosite, consistent with a previous report that plumbojarosite lowers Pb RBA in soils.

Exposure to lead (Pb) during early life has persistent adverse health effects. During childhood, ingestion of bioavailable Pb in contaminated soils can be a major route of Pb absorption. Remediation to alter physiochemical properties of soil-borne Pb can reduce Pb bioavailability. Our laboratory-based approach for soil Pb remediation uses addition of iron (Fe) sulfate and application of heat to promote formation of plumbojarosite (PLJ), a sparingly soluble Pb-Fe hydroxysulfate mineral. We treated two soils with anthropogenic Pb contamination and samples of clean topsoil spiked with various Pb compounds (i.e., carbonate, chloride, phosphate [P], or sulfate) to convert native Pb species to PLJ and used a mouse assay to assess relative bioavailability (RBA) of Pb in untreated (U) and remediated soils. Bone and blood Pb levels were significantly lower (P < 0.001, Student's t test) in mice that consumed diets amended with remediated soils than with U soils. Estimated RBA for Pb in both remediated natural soils and Pb-mineral spiked soils were reduced by >90% relative to Pb RBA for U soils, which is substantially more effective than other soil amendments, including P. X-ray absorption spectroscopy showed that >90% of all Pb species in remediated soils were converted to PLJ, and ingested PLJ was not chemically transformed during gastrointestinal tract transit. Post treatment neutralization of soil pH did not affect PLJ stability, indicating the feasibility in field conditions. These results suggest that formation of PLJ in contaminated soils can reduce the RBA of Pb and minimize this medium’s role as a source of Pb exposure for young children.

Predicting the environmental fate of lead relies on a detailed understanding of its coordination to mineral surfaces, which in turn reflects the innate reactivity of the mineral surface. In this research, we investigated fundamental dependencies in lead adsorption to hematite by coupling extended X-ray absorption fine structure (EXAFS) spectroscopy on hematite particles (10 and 50 nm) with resonant anomalous X-ray reflectivity (RAXR) to single crystals expressing the (001), (012), or (110) crystallographic face. The EXAFS showed that lead adsorbed in a bidentate inner-sphere manner in both edge and corner sharing arrangements on the FeO octahedra for both particle sizes. The RAXR measurements confirmed these inner-sphere adsorption modes for all three hematite surfaces and additionally revealed outer-sphere adsorption modes not seen in the EXAFS. Lead uptake was larger and pH dependence was greater for the (012) and (110) surfaces, than the (001) surface, due to their expressing singly- and triply coordinated oxygen atoms the (001) surface lacks. In coupling these two techniques we provide a more detailed and nuanced picture of the coordination of lead to hematite while also providing fundamental insight into the reactivity of hematite.

Ibuprofen, a frequently detected pharmaceutical in natural and engineered waters, was studied in both neutral and anionic forms using density functional theory at the B3LYP/6-31111G**//B3LYP/6-31G* level of theory in its reaction with hydroxyl radical ( • OH). The reaction pathways included • OH addition to aromatic ring, abstraction of a H-atom, and nucleophilic attack on the carbonyl group. The results showed that H-atom abstraction pathways are the most favorable. The free energy change for H-atom abstraction reaction ranges from 237.8 to 215.9 kcal/mol; for • OH addition ranges from 23.85 to 21.23 kcal/mol; and for nucleophilic attack on the carbonyl group is 13.9 kcal/mol. The calculated rate constant between neutral ibuprofen and • OH, 6.72 3 10 9 M 21 s 21 , is consistent with the experimental value, 6.5 6 0.2 3 10 9 M 21 s 21 . Our results provide direct evidence for byproduct formation and identification on the molecular level.