There are numerous Cr(III)-contaminated sites on Department of Defense (DoD) and Department of Energy (DOE) lands that are awaiting possible clean up and closure. Ingestion of contaminated soil by children is the risk driver that generally motivates the likelihood of site remediation. The purpose of this study was to develop a simple statistical model based on common soil properties to estimate the hioaccessibility of Cr(III)-contaminated soil upon ingestion. Thirty-five uncontaminated soils from seven major soil orders, whose properties were similar to numerous U.S. DoD contaminated sites, were treated with Cr(III) and aged. Statistical analysis revealed that Cr(III) sorption (e.g., adsorption and surface precipitation) by the soils was strongly correlated with the clay content, total inorganic C, pH, and the cation exchange capacity of the soils. Soils with higher quantities of clay, inorganic C (i.e., carbonates), higher pH, and higher cation exchange capacity generally sequestered more Cr(III). The amount of Cr(III) bioaccessible from the treated soils was determined with a physiologically based extraction test (PBET) that was designed to simulate the digestive process of the stomach. The bioaccessibility of Cr(III) varied widely as a function of soil type with most soils limiting bioaccessibility to <45 and <30% after I and 100 d soil-Cr aging, respectively. Statistical analysis showed the bioaccessibility of Cr(III) on soil was again related to the clay and total inorganic carbon (TIC) content of the soil. Bioaccessibility decreased as the soil TIC content increased and as the clay content decreased. The model yielded an equation based on common soil properties that could be used to predict the Cr(III) bioaccessibility in soils with a reasonable level of confidence.

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Laser‐induced breakdown spectroscopy (LIBS) is an elemental analysis technique that is based on the measurement of atomic emissions generated on a sample surface by a laser‐induced microplasma. Although often recognized in the literature as a well‐established analytical technique, LIBS remains untested relative to the quantitative analysis of elements in chemically complex matrices, such as soils. The objective of this study was to evaluate the capabilities of LIBS relative to the elemental characterization of surface soils. Approximately 65 surface soil samples from the Pond Creek watershed in east Tennessee were collected and subjected to total dissolution and elemental analysis by inductively coupled argon plasma‐optical emission spectroscopy (ICP–OES). The samples were analyzed by LIBS using a Nd:YAG laser at 532 nm, with a beam energy of 25 mJ per pulse, a pulse width of 5 ns, and a repetition rate of 10 Hz. The wavelength range for the LIBS spectra collection was 200 to 600 nm, with a resolution of 0.03 nm. Elemental spectral lines were identified through the analysis of analytical reagent‐grade chemicals and the NIST and Kurucz spectral databases. The elements that dominated the LIBS spectra were Al, Ca, Fe, and Mg. In addition, emission lines for Ti, Ba, Na, Cu, and Mn were isolated. The emission lines of Cr, Ni, and Zn, which were >100 mg kg−1 in numerous soil samples, were not detected. Further, spectral emission lines for P and K are >600 nm, eliminating them from LIBS analysis. The integrated peak areas of interference‐free elemental emission lines were determined, then normalized to the area of the 288.16 nm Si(I) emission (internal standard) to reduce the variability between replicate analyses. The normalized spectral areas, coupled with linear regression (standard curves for single wavelength response) and multivariate techniques (chemometrics and multiple wavelengths), were used to predict ICP–OES elemental data. In general, the quantitative capabilities of LIBS proved disappointing. Detection and quantitation were generally restricted to those elements with concentrations > 0.5 g kg−1 The correlation between LIBS response and elemental content was poor (r < 0.98). Further, the relative errors of prediction for the LIBS‐detected elements were less than acceptable for an analytical technique (<20%), ranging from ∼20 to ∼40% using linear regression analysis, and from 18 to 48% using partial least squares analysis. Based on these findings, the analytical capability of the LIBS method for soil metals analysis should be considered questionable.

In-situ stabilization using phosphate (P) amendments, such as P-based fertilizers and rock, are a potentially cost-effective and minimally disruptive alternative for stabilizing Pb in soils. We examined the effect of time (0-365 d), in vitro extraction pH (1.5 vs. 2.3), and dosage of three P-based amendments on the bioaccessibility (as a surrogate for oral bioavailability) of Pb in 10 soils from U.S. Department of Defense facilities. Initial untreated soil bioaccessibility consistently exceeded the U.S. Environmental Protection Agency default value of 60% relative bioavailability, with higher bioaccessibility consistently observed at an in vitro extraction pH of 1.5 vs. 2.3. Although P-based amendments statistically (P < 0.05) reduced bioaccessibility in many instances, with reductions dependent on the amendment and dosage, large amendment dosages (approximately 20-25% by mass to yield 5% P by mass) were required to reduce average bioaccessibility by approximately 25%. For most amendment combinations, reductions continued to occur for periods up to 1 yr, indicating that the observed reductions were not merely experimental artifacts of the in vitro extraction procedure. Although our results indicated that reductions in Pb bioaccessibility with P amendments are technically feasible, relatively large amendment masses were required to achieve relatively modest reductions in bioaccessibility. The cost and potential environmental implications of adding such large amounts of P may limit the practicality of in situ immobilization for some Pb-contaminated soils, industrial and firing range soils in particular.