Bioavailable soil Pb minimized by in situ transformation to plumbojarosite

Abstract

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.

Keywords: bioavailability; lead; plumbojarosite; remediation; speciation.

Fig. 1.

XAS data showing Pb speciation spectra for Soil 1 (Left) and Soil 2 (Right) at different reaction times of 1, 3, 5, and 8 h. The top spectrum in blue shows a pure PLJ reference compound.

Fig. 2.

Pb species in D and F of mice that consumed Ds amended with Soil 1 or Soil 2. Soils tested in U or T forms with data for both 8 and 67 h of treatment. Fraction of total Pb accounted for by each Pb species present shown. PLJ; PbSO₄; Ads; Humic, Pb bound to organic matter; PbO.

Fig. 3.

Pb species in D and F of mice that consumed Ds amended with Pb minerals. Minerals tested in U (Untrx) or T (Trx) forms. Fraction of total Pb accounted for by each Pb species present shown. PLJ; OH-Cer, PbO₃; PbSO₄; Pyr; Ads; Humic; PbO; PbPO₄; PbAc, Pb acetate.