1127

AbstractWater quality threats associated with using phosphate-based amendments to remediate Pb-contaminated soils are a concern, particularly in riparian areas. This study investigated the effects of P application rates to a Pb-contaminated alluvial soil on Pb and P loss via surface water runoff, Pb accumulation in tall fescue (Festuca arundinacea Schreb; Kentucky 31), and Pb speciation. An alluvial soil was treated with triple superphosphate at P to Pb molar ratios of 0:1 (control), 4:1, 8:1, and 16:1. After a 6-mo reaction period, rainfall simulation (RFS) studies were conducted, followed by tall fescue establishment and a second set of RFS studies (1 yr after treatment). Results from the first RFS study (unvegetated) demonstrated that the total Pb and P concentrations in the effluents of 8:1 and 16:1 (P:Pb molar ratio) treatment levels were significantly greater (p < 0.05) than the control. One year after P treatment and 6 mo after vegetation establishment, total P and Pb concentrations of the effluents from a second RFS decreased by one to three orders of magnitude. Total and dissolved P concentration in runoff from the 16:1 P:Pb treatment remained significantly greater than all other treatments. However, total Pb concentration in the runoff was comparable among the treatments. Phosphorus treatment also reduced Pb uptake into tall fescue by >55%. X-ray absorption near-edge structure spectroscopy data showed that pyromorphite [Pb5(PO4)3OH,Cl,F] abundance ranged from 0% (control) to 32% (16:1 P:Pb; 1 yr after treatment) of the total soil Pb. Although P treatment stimulated pyromorphite formation, pyromorphite abundance was comparable between the P-treated soils. These findings suggest that a 4:1 (P:Pb molar ratio) P treatment may be a sufficient means of reducing Pb bioavailability while minimizing concerns related to P loss in an alluvial setting.

Phosphate Treatment of Lead-Contaminated Soil: Effects on Water Quality, Plant Uptake, and Lead Speciation

John S. Weber,* Keith W. Goyne, Todd P. Luxton, and Allen L. Thompson

Southern Missouri contains several mining districts, including the Southeast Missouri Pb mining district, home to the world’s largest known deposit of galena (PbS)

(Seeger, 2008). As a consequence of the long-term exploita-tion of PbS deposits, contamination of soils and sediments in southeastern Missouri is widespread and may pose an ecologi-cal and human health risk to communities inhabiting the region (USEPA, 2007). Recent investigation into soil Pb concentrations has indicated that the vast majority of the alluvial soils along the Big River of St. Francois, Jefferson, and Washington Counties in Missouri are contaminated with Pb above thresholds of concern for human health and the environment (Pavlowsky, 2010).

Remediation of Pb-contaminated areas by traditional means of soil excavation, disposal, and replacement can be extremely expensive to complete on a large scale (USEPA, 1993). In situ remedial technologies were shown to be less invasive, reducing undesirable conditions such as fugitive dust emissions and heavy equipment exhausts as well as overall disruption of the landscape (Ma et al., 1993, 1995; Xu and Schwartz, 1994). Additionally, the volume and concentrations of Pb present in the alluvial soils of the Big River make excavation and disposal technically impractical (Pavlowsky, 2010).

A number of previous studies have successfully altered soil Pb chemistry through the addition of inorganic phosphate compounds that convert soil Pb species to less soluble pyromorphite minerals [Pb5(PO4)3(OH,Cl,F)]. Pyromorphites are the most thermodynamically stable and insoluble Pb minerals over a large pH range (Nriagu, 1974). The stability of pyromorphites under a wide variety of environmental conditions makes Pb immobilization by P amendments an effective technique because accidental pyromorphite ingestion will not yield bioavailable Pb (Zhang et al., 1998; Arnich et al., 2003). The creation of pyromorphites and commensurate reductions in bioavailability of Pb-contaminated soils has been well documented (Ma et al., 1993, 1995; Xu and Schwartz, 1994; Ruby et al., 1994; Laperche et al., 1996; Zhang et al., 1998).

Abbreviations: DIRO, deionized reverse osmosis; LCF, linear combination fitting; RFS, rainfall simulation; TSP, triple superphosphate; XANES, X-ray absorption near-edge spectroscopy.

J.S. Weber, U.S. Fish & Wildlife Service, Columbia, MO Field Office, 101 Park DeVille Dr., Suite A, Columbia, MO 65203; J.S. Weber and K.W. Goyne, Dep. of Soil, Environmental and Atmospheric Sciences, Univ. of Missouri, 302 ABNR Bldg., Columbia, MO 65211; T.P. Luxton, USEPA, Office of Research and Development, National Risk Management Research Lab., 26 W. Martin Luther King Dr., Cincinnati, OH 45268; A.L. Thompson, Dep. of Bioengineering, Univ. of Missouri, 251 Agricultural Engineering Bldg., Columbia, MO 65211. Assigned to Associate Editor Markus Grafe.

Copyright © 2015 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. J. Environ. Qual. 44:1127–1136 (2015) doi:10.2134/jeq2014.10.0447 Supplemental material is available online for this article. Received 28 Oct. 2014. Accepted 4 May 2015. *Corresponding author (John_S_Weber@fws.gov).

Journal of Environmental QualityHeAvy MetAls in tHe environMent

teCHniCAl rePorts

Published July 10, 2015

1128 Journal of Environmental Quality

However, adding large quantities of P to soils is an environmental concern because P loss to aquatic ecosystems is associated with eutrophication (Theis and McCabe, 1978; Sharpley and Halvorson, 1994; Sims, 1993; Dermatas et al., 2008). There is a paucity of research investigating the consequences of P treatment under conditions likely to occur in the environment (Scheckel et al., 2013; Dermatas et al., 2008). Yet, potential issues of P leaching from Pb-contaminated soils treated with P amendments have only been lightly discussed or mentioned by studies investigating the feasibility of P treatments (Basta and McGowen, 2004; Cao et al., 2002; Chen et al., 2006; Dermatas et al., 2008; Tang et al., 2009; Yang and Tang, 2007). Previous research has demonstrated that substantial leaching of P from P-treated soils occurs in acidic and alkaline soils under a variety of experimental conditions, demonstrating the potential importance of research focused on P loss from alluvial soils (Dermatas et al., 2008; Kilgour et al., 2008; Stanforth and Qiu, 2001).

In addition to considering P fate and transport after P treatment of Pb-contaminated soils, it is important to confirm pyromorphite formations as an indicator of reduced Pb bioavailability in the soil (Scheckel et al., 2003; Scheckel et al., 2013). Numerous techniques have been used to confirm pyromorphite formation, including selective sequential extraction procedures, in vitro physiologically based extraction tests, energy-dispersive X-ray spectroscopy, and scanning electron microscopy (Ryan et al., 2001; Cao et al., 2003; Scheckel et al., 2003, 2005; Davis et al., 1993; Yang et al., 2001). However, selective sequential extraction and the physiologically based extraction tests are known to artificially create pyromorphites during the digestion phase of the analyses (Scheckel et al., 2003, 2005), and visual confirmation of pyromorphites using scanning electron microscopy and energy dispersive X-ray spectroscopy has been shown to be of limited utility due to the similarity of hexagonal pyromorphite crystals to a variety of crystalline soil components (Scheckel and Ryan, 2003). Consequently, advanced synchrotron spectroscopic techniques are necessary to confirm pyromorphite formation in an exacting and nondestructive manner (Cotter-Howells et al., 1994; Ryan et al., 2001; Scheckel and Ryan, 2002; Scheckel and Ryan, 2003; Scheckel and Ryan, 2004). X-ray absorption spectroscopy (XAS), in combination with advanced statistical models, is frequently used to identify different metals species in soil environments, and XAS is particularly useful when studying Pb-contaminated soils amended with P (Manceau et al., 2002).

The objectives of this study were (i) to determine the relationship between concentrations of P and metals eluviated from three treatment classes of P-treated, Pb-contaminated soils during simulated rainfall events conducted using unvegetated soils at 6 mo after treatment and vegetated soils at 12 mo after treatment; (ii) to confirm potential reductions in Pb phytoavailability within the P-treated soils by measuring the metal content of tissues from vegetation grown on the treatment units; and (iii) to investigate pyromorphite formation as a function of P application. We hypothesize that (i) soils with greater levels of applied P will release commensurately greater levels of P to surface water, overall Pb release will be unaffected by treatment, and vegetation establishment and time elapsed will significantly reduce both metals and P transport from the soils; (ii) Pb phytoavailability in soil will decrease with increasing P

fertilizer application; and (iii) pyromorphite formation will be enhanced as P fertilizer application is increased.

Materials and MethodsSoil Collection

Kaintuck fine sandy loam soil (coarse-loamy, siliceous, superactive, nonacid mesic Typic Udifluvents) was collected from the Big River floodplain near DeSoto, MO (38°5¢13¢¢ N, 90°40¢28¢¢ W). Vegetative cover at the site was predominantly tall fescue (Festuca arundinacea Schreb; Kentucky 31). A hand-held X-ray fluorescence spectrometer (Thermo Fisher) was used to target surface soil concentrations of >1500 mg kg-1 Pb (Table 1). Samples were collected at a depth of 0 to 15 cm from several locations within a 100-m2 area. Soils were bulked and mechanically mixed to create a single stockpile of soil. Undisturbed core samples (7.5 cm by 7.5 cm, diameter by height) used to quantify soil bulk density were collected within the sample area using an Uhland core sampler.

Initial Soil Sample CharacterizationAfter air drying and hand mixing, the bulk soil stockpile was

sieved to <2 mm for use in all experimental trials. Ten composite

table 1. selected properties of untreated bulk stockpile, data represent the arithmetic mean of 10 samples.

soil property† resultUSDA classification Typic UdifluventTextural class Silt loamBulk density, g cm-3 1.2 ± 0.0‡

CEC NH4OAc, cmol kg-1 22.5 ± 0.2

CEC NH4Cl, cmol kg-1 16.0 ± 0.1Percent base saturation 92.4 ± 0.5pH water 7.8 ± 0.0pH salt (0.01 mol L-1 CaCl2) 7.6 ± 0.0

BaCl2–extractable acidity, cmol kg-1 1.7 ± 0.1

TOC, g kg-1 21.0 ± 0.0

TN, g kg-1 2.0 ± 0.1

Mehlich 3–extractable elements, mg kg-1

Al 528 ± 4 Ca 2572 ± 11 Cu 25.2 ± 0.1 Fe 263 ± 1 K 53.4 ± 0.1 Mg 611 ± 2 Mn 100 ± 1 Na 60 ± 2 P 32 ± 1 Zn 226 ± 1

Total elemental concentration, mg kg-1

As 7.3 ± 0.1 Ba 940 ± 11 Cd 10.6 ± 0.4 Cu 72.4 ± 0.3 Pb 2190 ± 13 Mn 1980 ± 15 Zn 634 ± 4

† CEC, cation exchange capacity; TN, total N; TOC, total organic C.

‡ Values are mean ± SE.

Journal of Environmental Quality 1129

samples were collected from the bulk stockpile for determination of general soil properties before P treatment. Analyses were performed, including pHwater, pHsalt (0.01 mol L-1 CaCl2), particle size distribution, extractable Al, titratable acidity, pH 7 buffered and unbuffered cation exchange capacity, organic C, Mehlich 3 P, and total N content, following procedures recommended by the USDA–NRCS (Soil Survey Staff, 2009). Total elemental analysis of the soils (As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) was determined using the HNO3 digestion procedure (USEPA Method 3050B; USEPA, 1996) and inductively coupled plasma–mass spectrometry (Table 1).

Phosphate Treatment of SoilsBased on previous research (Ma et al., 1993, 1995; Xu and

Schwartz, 1994; Ruby et al., 1994; Zhang et al., 1998), soil was amended with triple superphosphate (TSP) [Ca(H2PO4)2] at four molar ratios of P to Pb (P:Pb): 0:1 (control), 4:1, 8:1, and 16:1. Four replicates of each treatment level were created by placing 108 kg of air-dried soil (1.5% moisture by mass) from the bulk stockpile into 70-gallon polyethylene tanks. The soils were then treated with granulated TSP (Bonide Products, Inc.) as an equivalently split application on two separate dates. The initial application was used to induce acidification. The second application, 40 d later, was performed to achieve the desired P:Pb molar ratios for each treatment (Melamed et al., 2002). On each application date, one quarter of the total TSP mass required to achieve the desired molar ratio was added to the soil and thoroughly mixed into the soils with a power auger, and then the process was repeated (Yang et al., 2001). Treated soils were moistened with deionized water to field capacity and allowed to react for 60 d (deionized water was added to maintain field capacity throughout the reaction period). After the reaction period, soils were amended with hydrated lime [Ca(OH)2] to achieve a soil pH of 6.5 to 7.5, thereby simulating normal agronomic conditions and enhancing pyromorphite formation (Chappell and Scheckel, 2007). The control treatment was not limed because native pHwater was approximately pH 7.8 (Table 1). After liming, all treatment soils were kept moist for 90 d in a greenhouse at approximately 25°C.

Rainfall Simulations and Vegetation EstablishmentRainfall simulation (RFS) test beds (50 cm × 30 cm × 25 cm,

length × width × depth) were fabricated using 16-gauge sheet steel (Supplemental Fig. S1). An adjustable V-notch was attached to the front of the RFS test beds to channel surface runoff to a collection point. Perforated, 1.27-cm schedule 40 PVC pipe was used to construct a subsurface drainage collection point with two ports located on the exterior of the drainage box below the V-notch. All surfaces of the test beds were painted using Pb-free latex paint, and all test beds were cleaned with a dilute HNO3 (1% by volume) and rinsed in triplicate with deionized water.

The RFS beds were filled with screened and washed medium-grade (0.08–0.3 mm) sand (Quikrete) to a depth of 10 cm, completely covering the PVC drainage tubing. The sand was covered with landscape fabric to prevent intrusion of the treatment soil into the sand. Soil from the four P:Pb treatment levels was placed into individual test beds to a depth of approximately 10 cm in two separate 5-cm lifts and compacted to a field bulk density of 1.2 g cm-3 (Table 1) at each lift. Soils were moistened to facilitate uniform and homogeneous packing.

A total of 16 test beds were prepared, and each treatment level was replicated in quadruplicate.

Rainfall simulation studies were completed using the rainfall simulation tower at the University of Missouri using deionized, reverse osmosis (DIRO) water (Regmi and Thompson, 2000). Briefly, the 1-m × 1-m laboratory-scale simulator operates under a positive displacement principle to provide a mean droplet diameter of 2.6 mm. Adjustable stands used to hold the RFS test beds were set to 2% slope for all experiments. Soils were exposed to simulated rainfall for 1.5 h at an average rate of 5 cm h-1. A storm of this intensity is predicted to occur at approximately 15-yr intervals in DeSoto, MO (Huff and Angel, 1992). All effluents from the V trough of the test beds were collected in preweighed, 3.8-L, high-density polyethylene buckets; a shield was used to prevent simulated rainfall from directly entering the sampling containers. Sediments deposited in the trough were collected for analysis. Leachate did not emanate from drainage tubes located within the sand substrate, thus eliminating the need to collect subsurface drainage waters.

After the first RFS, the test beds were planted with F. arundinacea to simulate pastures observed in the Big River floodplain. The tall fescue was watered once a week with a volume of DIRO equal to one half of the soil volume in the test beds (i.e., 8 L per test bed per week). Air temperature was kept constant at 25°C. At 30 d after the first RFS, all vegetation above the top lip of the test beds was removed for metals analysis. Tissue samples were also collected 180 d after the first RFS and analyzed.

To gauge the impact of time and vegetative cover on the erosion of soil and the loss of associated contaminants from the test beds, a second RFS test was conducted 180 d after the first simulation. At the conclusion of the second RFS, composite soil samples were collected and analyzed for available P using Mehlich 3 analyses.

Effluent Water Sample ProcessingEffluents collected during a given RFS test period were

weighed to determine the combined total mass of the water, eroded sediment, and bucket. Samples were then thoroughly mixed for 5 min at 1000 rpm using a stir plate and stir bar. Aliquots of solution and suspended sediments for total metals and total P analyses were collected using a Geotech GeoPump peristaltic pump and Masterflex Platinum Silicone L/S 15 tubing by submerging the tubing into a continuously stirred sample. Samples for dissolved metals and dissolved orthophosphate analysis were collected by attaching a Geotech Dispos-a-filter (a 0.45-µm, high-capacity, in-line filter) to the peristaltic pump and tubing. Samples for total and dissolved metals were immediately preserved using a 10% (v/v) HNO3 solution (Ricca Chemical Co.). Samples for total P were preserved using 1:1 H2SO4 sample preservation ampules (EaglePicher Scientific). All water samples were stored in 250-mL, high-density polyethylene containers, certified I-CHEM clean (Nalgene Corp.), at 4°C.

The remaining bulk effluent samples and sediments removed from the trough were filtered through preweighed Fisher Scientific Q2 Fine Porosity Filter Paper (particle retention, 1–5 µm). Soil plus filter papers were dried at 70°C for 48 h, and the mass of filter paper plus soil was measured. The mass of total P and total metals lost per unit area to erosive flows was calculated (Table 2) by multiplying the concentration of a contaminant by

1130 Journal of Environmental Quality

the volume of runoff collected and dividing by the surface area of the RFS test bed.

Sediment, Water, and Plant Tissues AnalysesUnfiltered water samples collected for total and dissolved

metals were digested by placing 5 mL of sample and 1 mL of HNO3 into a 50-mL quartz reaction vessel and heating the sealed high-pressure vessel assembly in a PerkinElmer Multiwave Digestion System. After cooling, digested samples were transferred to a storage container and diluted to a final volume of 50 mL (2% HNO3 matrix). Total P and dissolved ortho-P samples were processed using the procedures described in USEPA Method 365.1 (USEPA, 2007b).

Total and dissolved metals contents of digested water samples were quantified with a PerkinElmer Sciex Elan DRCe inductively coupled plasma–mass spectrometer using the quantitative analysis mode. Multipoint standard curves were developed for analytes of interest, and rhodium (0.01 mg L-1) and bismuth (0.01 mg L-1) were used as internal standards. Where multiple masses were monitored, masses were selected for reporting based on least interference. Lead was reported as the sum of three masses (206Pb + 207Pb + 208Pb). Digested water samples for total P and dissolved orthophosphate were analyzed colorimetrically using a Lachat QuikChem 8500 Series 2 FIA System following USEPA Method 365.1 (USEPA, 2007b).

Harvested grass tissue samples were rinsed with DIRO for 1 min to remove soil particles, and tissue samples were oven-dried at 70°C for 48 h before digestion by USEPA Method 3052 (with HNO3 and HF) (USEPA, 2012) and total metals analysis by inductively coupled plasma–mass spectroscopy.

Statistical Analyses for Rainfall Simulation and Metals Content of Grass Tissue

A one-way ANOVA was used to analyze the RFS data using the statistical analysis software SAS 9.3 (SAS Institute, 2013).

Fisher’s LSD method was used to evaluate differences between the means (SAS Institute, 2013). Treatments included phosphate application rate (0:1, 4:1, 8:1, and 16:1 P:Pb) and vegetative cover with grass (grass cover and no grass cover). Statistical differences were tested at a = 0.05.

X-ray Absorption Near-Edge Structure SpectroscopyLead LIII-edge (13, 035 eV) X-ray absorption spectra (XAS)

were collected at the Materials Research Collaborative Access Team’s beamline 10-ID, Sector 10 at the Advanced Photon Source at the Argonne National Laboratory, Argonne, IL. The electron storage ring was operated in top-up mode at 7 GeV. Spectra were collected in fluorescence mode with either a Lytle or a solid-state silicon drift detector at room temperature. The samples were prepared as thin pellets using an IR pellet press, and samples were secured to sample holders using Kapton tape. For each sample, 15 to 17 scans were collected using the Lytle detector or four to five scans using the solid-state detector and averaged. Before averaging the data, the spectra were inspected to ensure that beam-induced damaged had not occurred during analysis. Data were analyzed using the Athena software program (Ravel and Newville, 2005). Sample spectra were compared with synthesized minerals and mineral specimens acquired from the Smithsonian National Museum of Natural History. All minerals were verified with X-ray diffraction before use as reference materials.

Soil Pb speciation was determined by comparison of Pb standards to the field samples via linear combination fitting (LCF). Linear combination fitting refers to the process of selecting a multiple component fitting function with a least-squares algorithm that minimizes the sum of the squares of residuals. A fit range of -20 to 50 eV was used for the X-ray absorption near-edge structure (XANES) portion of the XAS spectra and up to four variables. The best fitting scenarios are determined by the smallest residual error (c2) and the sum of all component fractions being close to 1. The first derivative of the XANES spectra was used in the LCF analysis. This was done to exploit the subtle changes that exist in the Pb-L3 line shape. Fitting the additional peaks and shoulder features in the first derivative spectra provides for a more robust fit of the data and greater confidence in the LCF results. Detailed descriptions of the fitting procedure are described elsewhere (Manceau et al., 2002). The reference samples used in the LCF model were plumboferrite (PbFe4O7), plumbonacrite [Pb5O(OH)2(CO3)3], chloropyromorphite [Pb5(PO4)3Cl], Pb sorbed to hydroxyapatite complex (Ca5Pb5(PO4)6(OH)2], PbS, hydrocerussite [Pb3(CO3)2(OH)2], anglesite (PbSO4), plumbomagnetite (PbFe2O4), litharge (PbO), Pb hydroxide [Pb(OH)2], Pb sorbed to humic acid, goethite, and kaolinite.

Results and DiscussionEffluent Water Chemistry from Unvegetated and Vegetated Soils

Unvegetated control and P-treated soils were exposed to RFS after P application and a 6-mo reaction period to capture water quality and soils data that could approximate field conditions for a P-treated, Pb-contaminated soil. Total and dissolved P concentrations in effluent from the 16:1 P:Pb phosphorus

table 2. Mass of P and Pb lost during the first and second rainfall simulation experiments.

rainfall simulation and treatment class† P loss‡§ Pb loss

—————— kg ha-1 ——————RFS1-UAC 0.18a,A 1.54a,ARFS1–4:1 0.76ab,ABC 1.81ab,ABRFS1–8:1 1.75b,C 2.76ab,CRFS1–16:1 6.01c,D 2.45b,BCRFS2-UAC 0.09a,AB 0.004a,DRFS2–4:1 0.17b,AB 0.004a,DRFS2–8:1 0.25c,AB 0.007a,DRFS2:16:1 0.38d,AB 0.005a,D

† RFS, rainfall simulation; UAC, unamended control; 4:1, 4:1 P:Pb molar ratio treatment; 8:1, 8:1 P:Pb molar ratio treatment; 16:1, 16:1 P:Pb molar ratio treatment.

‡ Values represent the arithmetic mean of four replicates per treatment level. Within a column, mean values followed by different lowercase letters are significantly different within a given rainfall simulation experiment (1 or 2) as determined using a one-way ANOVA and Fisher’s LSD means separation test (a= 0.05).

§ Within a column, mean values followed by different uppercase letters are significantly different between the rainfall simulation experiments as determined using a one-way ANOVA and the Fisher’s LSD means separation test (a= 0.05).

Journal of Environmental Quality 1131

treatment class were substantially elevated; total P concentration in effluent from the 16:1 P:Pb treatment was 36 times greater than the control soil (0:1 P:Pb) and nine times greater than the 4:1 P:Pb treatment class (Fig. 1a). Due to the novelty of this work, direct comparisons of P concentrations to previous studies are not readily facilitated by the existing literature. However, concentrations of P released into solution during this study are similar to those observed for column leaching and batch reaction experiments conducted by Dermatas et al. (2008) (1–40 mg L-1 P) and Kilgour et al. (2008) (up to 23 mg L-1 P), although they are substantially less than P concentrations within column leachates reported by Yang et al. (2002) (>300 mg L-1). In general, it is reported that 10 to 20% of total P added may be leached vertically through the heavy metals–contaminated soils treated with P (Cao et al., 2002; Basta and McGowen, 2004).

Significantly greater concentrations of total Pb were observed in runoff effluents as a function of P treatment (Fig. 1b), particularly from the two elevated treatment levels (8:1 and 16:1 P:Pb). Total Pb concentration in the effluents from the 8:1 and 16:1 P:Pb treatments exceeded 14.5 mg L-1, and total Pb concentrations in effluents from these treatments were significantly greater (p < 0.05) than the control soil (<8.7 mg L-1). However, P treatment did not significantly affect dissolved Pb concentrations (Fig. 1b). We postulate that elevated concentrations of total Pb in the runoff waters are due to increased colloidal transport commensurate with disturbance introduced during the P treatment regimen described above.

The total volume of runoff effluents and the mass of eroded sediments were not significantly different among the treatments (Supplemental Table S1). However, the overall mass of P and total Pb lost via runoff increased significantly for the two highest treatment classes (8:1 and 16:1 P:Pb ratios) (Table 2). Total P loss at the 16:1 P:Pb ratio treatment (6.01 kg ha-1) was 33 times greater than P loss from unamended soils, which parallels trends reported for effluent P concentrations. These results are up to two orders of magnitude greater than results reported from other P transport studies using RFS (Blanco-Canqui et al., 2004; Sharpley and Kleinman, 2003; Schroeder et al., 2004). However, the final Mehlich 3–extractable P concentrations of the P-treated soils from the current study (4:1 P:Pb, 481 mg kg-1; 8:1 P:Pb, 947 mg kg-1; and 16:1 P:Pb, 2074 mg kg-1) are an order of magnitude greater than the above-mentioned agronomic studies. Differences in P loss among these studies and the current study are likely attributable to methods used for the RFS, including air drying, sieving, and thorough mechanical mixing of soils, as well as greater quantities of P applied and the use of DIRO water rather than natural rainfall.

A second RFS experiment was conducted 1 yr after P application and the establishment of tall fescue. Concentrations of total and dissolved P and Pb dramatically decreased during the second RFS study (Fig. 2). Total Pb concentrations in runoff effluents were reduced by up to three orders of magnitude, and total P concentration was reduced by one order of magnitude, when compared with results from the first RFS. Total P concentrations in runoff effluents were significantly different between the treatments, with the greatest concentration corresponding to the 16:1 P:Pb treatment. Dissolved Pb and P concentrations were reduced by nearly one half relative to the first RFS experiment. Although no significant differences in

dissolved Pb were observed between the vegetated treatments, dissolved P concentration remained significantly greater for the 16:1 P:Pb treatment. Interestingly, no significant difference in dissolved P concentration was observed between the control and the 4:1 P:Pb treatment, and total P concentrations of effluents from these treatments are within the range observed for agricultural watersheds of Missouri (Udawatta et al., 2004).

Overall, the total mass of soil (Supplemental Table S1) and elements (Table 2) transported during the second RFS were significantly less than those lost during the first RFS (Table 2). The reduction in mass lost is especially pronounced for Pb at the 8:1 P:Pb treatment (RFS1 = 2.76 kg ha-1; RFS2 = 0.007 kg ha-1) and for P at the 16:1 P:Pb treatment (RFS1 = 6.01 kg ha-1; RFS2 = 0.38 kg ha-1). Although the establishment of vegetation and the increased reaction time reduced total P and Pb loss in the second RFS, P loss continued to positively correlate with P application. For example, P losses from the 16:1 P:Pb treatment were 4.2- and 2.2-fold greater than the control and 4:1 P:Pb treatments, respectively.

The effluent water chemistry results from the first and second RFS illustrate the benefits of establishing vegetation on P-treated, heavy metals–contaminated soils as a means to reduce total Pb and P transport to surface water resources. Implementation of specific best management practices (e.g., the installation of vegetative buffer strips, riparian offsets, and exclusions on the use

Fig. 1. effluent chemistry data from the first rainfall simulation including (a) total P and dissolved orthophosphate and (b) total and dissolved Pb. values followed by different lowercase letters are significantly different between treatment classes for dissolved orthophosphate (a) and dissolved Pb (b) determined using a one-way AnovA and Fisher’s lsD means separation test (a = 0.05). values followed by different uppercase letters are significantly different between treatment classes for total P (a) and total Pb (b) determined using a one-way AnovA and Fisher’s lsD means separation test (a = 0.05). error bars represent se.

1132 Journal of Environmental Quality

of the P-based technology near sensitive aquatic areas) should be considered before application. Furthermore, the data strongly support the need for optimized P applications that minimally alter surface runoff chemistry and reduce Pb phytoavailability. The 4:1 P:Pb molar ratio treatment resulted in the least P loss among soils receiving P application, and Pb transport from the 4:1 P:Pb treatment was not significantly greater than from unamended soils. However, the RFS studies did not provide a measure of Pb phytoavailability reduction, which necessitated investigations of Pb uptake by plants and pyromorphite formation that are described in subsequent sections.

Influence of P Treatment on Pb Uptake by Tall FescueTall fescue established on the different P treatments and

control soil was harvested and analyzed for Pb content at 30 and 180 d after establishment. Overall, the results indicate a significant reduction of plant bioavailable Pb in contaminated soils treated with TSP (Fig. 3). Importantly, the use of the 4:1 P:Pb molar ratio treatment resulted in a >50% reduction in plant bioavailable Pb, which was significantly (a = 0.05) less than Pb content of plant tissues collected from unamended (i.e., control) soils. No significant differences in Pb content were observed in tissues harvested from the 4:1 and 8:1 P:Pb treatments. However, plant tissues harvested from the 16:1 P:Pb treatment contained significantly less Pb relative to all other

treatments. Similar results were observed for the total Pb content in plant tissues harvested 30 d after establishment (Supplemental Fig. S2). These findings are in agreement with previous studies illustrating reductions in bioavailable Pb in plants and animals associated with the formation of pyromorphite minerals in soil after P treatment of Pb-contaminated soils (Brown et al., 2004; Hettiarachchi et al., 2001; Cao et al., 2002).

X-ray Absorption Near-Edge Spectra and Linear Combination Fitting AnalysisBackground Pb Mineralogy

Results from the XANES analysis and linear combination fitting of standards to fit the XANES spectra are shown in Fig. 4 for the unamended soil and selected P-treated soils collected from RFS test beds after the second runoff experiment. The LCF fits were developed using reference spectra (Supplemental Fig. S3) and eliminating insignificant component reference spectra until the best statistical fit was acquired. In general, LCF results are accurate to ±5%; thus, results with <10% weight contribution should be interpreted with caution even though these components improve the overall error within the fitting process (Scheinost et al., 2002).

The predominant Pb species present in unamended soils samples collected from the field were plumbonacrite (38%) and plumboferrite (62%), both of which are more soluble than pyromorphite (Krivovichev and Burns, 2000; Ostergren et al., 1999). These findings are reasonable because the source of Pb contamination to the floodplain of the Big River is attributed to crushed PbS ores known to weather to Pb carbonate compounds such as plumbonacrite (Moles et al., 2004; Hillier et al., 2001; Cotter-Howells et al., 1994), a poorly crystalline precursor to hydrocerussite [Pb3(CO3)2(OH)2] and cerussite (PbCO3) (Krivovichev and Burns, 2000). The presence of plumboferrite in the control sample data is consistent with soil Pb mineral assemblages near Leadville, CO, where Pb associated with Fe oxides constitutes >50% by mass of Pb species present (Ostergren et al., 1999; Davis et al., 1993). Manganese and Fe-Pb oxides at the Leadville, CO site occur as discrete grains, coatings on

Fig. 2. effluent chemistry data from the second rainfall simulation, including (a) total P and dissolved orthophosphate and (b) total and dissolved Pb. values followed by different lowercase letters are significantly different between treatment classes for dissolved orthophosphate (a) and dissolved Pb (b) determined using a one-way AnovA and Fisher’s lsD means separation test (a = 0.05). values followed by different uppercase letters are significantly different between treatment classes for total P (a) and total Pb (b) determined using a one-way AnovA and Fisher’s lsD means separation test (a = 0.05). error bars represent se.

Fig. 3. Arithmetic mean of total Pb concentration in aboveground tissue of tall fescue (Festuca arundinacea schreb; Kentucky 31) 6 mo after planting. values followed by different lowercase letters are significantly different between treatment classes determined using one-way AnovA and Fisher’s lsD means separation test (a = 0.05). error bars represent se.

Journal of Environmental Quality 1133

non-Pb minerals, and alteration rinds on Fe oxide particles (Davis et al., 1993). Model system investigations suggest that Pb associated with Fe oxides may also be bound as adsorption complexes (Ford et al., 1997). However, including spectra of Pb sorbed to a suite of minerals (e.g., goethite) did not improve LCF models developed for the unamended soil studied here.

Noteworthy are the substantial differences in Pb species found in the alluvial, heavy metals–contaminated soil we studied and residential soil from southwestern Missouri that was contaminated by a Pb smelter (Scheckel and Ryan, 2004; Scheckel et al., 2005). The Pb species in the alluvial soil were predominantly plumbonacrite and plumboferrite, whereas the residential soil contained mostly PbS, anglesite, and Pb sorbed to organic matter (21, 32, and 37%, respectively). The lack of PbS and the enhanced association of Pb with Fe oxides in the alluvial soil studied is consistent with previous studies of Big River sediments showing little presence of PbS 20 nautical km downstream from the Desloge Tailings Pile in Desloge, MO and an increased presence of Pb in Fe-rich particles (Wronkiewicz et al., 2006); for reference, the Desloge Tailings Pile is approximately 50 nautical km upstream from our sampling location. Although the nature of the association between Pb- and Fe-rich materials has not been characterized in previous studies in southeastern Missouri, the soils most likely contain Pb as plumboferrite precipitates and, to a lesser extent, Pb adsorption complexes.

Pb Species Transformations after Phosphate TreatmentAfter the first RFS experiment (i.e., a 6-mo reaction period),

control and P-treated soils were analyzed using XANES to quantify Pb species present in our experimental soils. The

addition of TSP resulted in the transformation of up to 35% soil Pb to chloropyromorphite, concurrent with a 20% decrease of plumbonacrite (Fig. 5a). The proportion of chloropyromorphite formed was nominally different among the P-treated soils (29%, 4:1 and 16:1 P:Pb molar ratio treatments; 35%, 8:1 P:Pb molar ratio treatment) and comparable to previous studies using nondestructive synchrotron spectroscopic techniques to quantify pyromorphite formation (Scheckel and Ryan, 2004; Scheckel et al., 2005).

The addition of TSP also stimulated formation of a Pb sorbed to hydroxyapatite complex that was absent in the control samples and more prevalent with increased P addition. Although plumbonacrite appears to undergo complete transformation to other Pb species (i.e., chloropyromorphite and Pb-hydroxyapatite complex) in samples from the 16:1 P:Pb molar ratio treatment, the relatively more insoluble plumboferrite continues to represent the major Pb species present in all P-treated soils after the first RFS event (Fig. 5a). Chloropyromorphite is the least soluble Pb species observed in this experiment, followed by plumboferrite and finally the Pb-hydroxyapatite complex (Nriagu, 1973; Ostergren et al., 1999).

Soil collected from test beds after the second RFS event (i.e., 1 yr reaction period after P application) were also analyzed using XANES and modeled using LCF, and a similar distribution of Pb species abundance was observed (Fig. 5b). The LCF model indicated that soluble plumbonacrite was absent within soils treated with the 16:1 P:Pb molar ratio, and plumboferrite remained the predominant (>40%) Pb species in all treatments. Chloropyromorphite formation increased from 29 to 32% of the Pb species present at the 4:1 P:Pb treatment level, which is identical to the amount of chloropyromorphite formed in samples receiving greater P application (8:1 and 16:1 P:Pb molar ratios). Similar to LCF results of XANES from samples collected after the first RFS, the amount of the Pb sorbed to hydroxyapatite species (29%) was greatest in 16:1 P:Pb treatment soil. Interestingly, the proportions of the Pb-hydroxyapatite within soils collected after the second RFS study are consistently less than within samples collected after the first RFS study, and the species is completely absent from the 4:1 P:Pb molar ratio treated soil. The reduction in the proportion of Pb-hydroxyapatite corresponds with increased proportions of chloropyromorphite and plumboferrite within the P-treated soils, suggesting that the Pb sorbed to hydroxyapatite may be transforming to thermodynamically stable Pb minerals over time

Although P treatment of the Pb-contaminated soils resulted in comparable proportions of pyromorphite formation in our work and that of Scheckel and Ryan (2004), differences in the initial Pb species present within the alluvial soil and smelter-contaminated soil result in some dissimilar mineral transformations after P application. Where XANES analyses of the P-treated alluvial soil demonstrated greater to complete dissolution of plumbonacrite, partial dissolution of plumboferrite, and enhanced formation of Pb sorbed to hydroxyapatite with increased P application, Scheckel and Ryan (2004) report the complete transformation of PbS and partial transformation of anglesite (PbSO4) with marked increases in the relative abundance of cerussite and inner-sphere complexes in soils treated with TSP compared with unamended control samples.

Fig. 4. First derivative of normalized X-ray absorption near-edge spectroscopy spectra of untreated soils and select treated soils. the solid curve represents the raw sample data, and the dotted curve represents fit results from a linear combination of the reference spectra. labels represent the rainfall simulation and the treatment class (1–4, rainfall simulation 1, 4:1 P:Pb treatment class; rFs2–4, rainfall simulation 2, 4:1 P:Pb treatment class, etc.).

1134 Journal of Environmental Quality

Factors Potentially Limiting Pyromorphite FormationThe kinetics of Pb species transformation to pyromorphite is

dependent on soil pH, and the transformation is favored under acidic to weak acidic conditions (Xu and Schwartz, 1994; Zhang and Ryan, 1999). Other studies have not reported data for soil pH alteration on the addition of acidic P amendments (e.g., H3PO4 and TSP), but the very high stoichiometric ratios of P:Pb used by Scheckel and Ryan (2004) suggest that soil acidification and favorable kinetic conditions for the formation of pyromorphites must have been present in the system. However, even under the most favorable stoichiometric and kinetic conditions created by Scheckel and Ryan (2004), the maximum level of pyromorphite formation achieved peaked at 45% when using a 1% H3PO4 treatment. After treatment with TSP, the lowest values for pHwater of the 4:1, 8:1, and 16:1 P:Pb molar ratio treatment classes studied here were pH 6.90, 6.08, and 5.43, respectively, compared with a control pH of 7.8 (Table 1). These acidic and weakly acidic pH values place them within the range where transformation to pyromorphite is kinetically favorable (Xu and Schwartz, 1994; Zhang and Ryan, 1999; Scheckel et al., 2003). Accordingly, there must be other factors limiting the formation of pyromorphite in soils.

Studies (Hashimoto et al., 2009; Scheckel and Ryan, 2004) have suggested that greater organic matter levels in treated soils

may control the activity of free Pb2+ species via formation of Pb-dissolved organic C complexes in solution and organic coatings on chloropyromorphite crystals, which inhibit further transformation of Pb. Chappell and Scheckel (2007) also suggest a role for humic substances in the disproportionate transformation of the carbonate species to pyromorphite but do not discuss a full mechanism for this transformation. Although we cannot completely rule out the role of Pb complexation by organic matter as a limitation to further pyromorphite formation in the soils studied (organic C = 21 g kg-1), the inclusion of a Pb–humic acid species did not improve the LCF model used to describe the XANES spectra.

A lack of available P and soluble Pb in the soil solution is known to halt the formation of pyromorphite (Cao et al., 2003; Li et al., 2014). Recently, Li et al. (2014) used additions of Ca (200 and 400 mg kg-1 Ca) to enhance soluble Pb concentrations via ion exchange reactions. In our study, the soil contained >2500 mg kg-1 Mehlich-extractable Ca (Table 1) before the addition of Ca(OH)2 to increase soil pH after P amendments. The liming process resulted in the addition of approximately 300 and 800 mg kg-1 Ca to soils associated with the 8:1 and 16:1 P:Pb molar ratio treatments. However, the addition of Ca at rates comparable to double those used by Li et al. (2014) did not increase dissolved Pb within effluents derived from P-treated soils relative to the control (Fig. 1 and 2). The apparent ineffectiveness of the Ca addition can be attributed to differences in Pb forms within the two studies. Li et al. (2014) spiked an uncontaminated soil with Pb dissolved in solution, which likely adsorbed to cation exchange sites, whereas the soils we studied contained Pb primarily within the minerals plumbonacrite and plumboferrite.

Thus, it is plausible that the dissolution of plumbonacrite and plumboferrite or the transformation of metastable Pb phosphate minerals (Baker et al., 2014) are rate-limiting steps controlling pyromorphite formation.

Alternatively, the plateau in chloropyromorphite formation observed in our data and other studies may be attributable to reductions in P available for reaction. Dissolved P concentration was noted to decrease between RFS studies 1 and 2, which is likely due to the complexation of P with Al, Ca, Fe, and Mn in soil solution; P sorption to metal oxides and hydroxyapatite; and plant uptake. Aluminum and Fe oxides are known to have a great affinity for P, and the metal oxides may be sorbing P on release into soil solution (Cao et al., 2002). Additionally, Hashimoto et al. (2007) reports that soils with abundant Al and Fe hydroxides tend to increase their ability to sorb anions at acidic pH conditions where mineral surface functional groups are positively charged. Consequently, the creation of acidic pH soil conditions that kinetically favor the formation of pyromorphite may also induce the sorption of P to protonated Al and Fe hydroxides surfaces, as described by Hashimoto et al. (2009). The most acidic pH measured in this study was in soil from the 16:1 P:Pb treatment at 60 d after treatment (pHwater = 5.43), which is within a range favorable for pyromorphite formation as well as Al and Fe oxide

Fig. 5. relative abundance of Pb species determined by an linear combination fitting model fitted to the X-ray absorption near-edge spectroscopy spectra at (a) first rainfall simulation and (b) second rainfall simulation. rFs1–4, rainfall simulation 1, 4:1 P:Pb treatment class; rFs2–4, rainfall simulation 2, 4:1 P:Pb treatment class, etc. UAC, unamended control. error bars represent se.

Journal of Environmental Quality 1135

protonation (Xu and Schwartz, 1994; Zhang and Ryan, 1999; Hashimoto et al., 2009).

The marked increase in Pb sorbed to hydroxyapatite species formation in conjunction with the observed plateau of chloropyromorphite formation (Fig. 5) has been observed previously (Ma et al., 1993; Ma et al., 1994; Ma et al., 1995). Hydroxyapatite is known to selectively remove Pb from solution in the presence of aqueous metallic cations such as Al, Cd, Cu, Fe, Ni, or Zn (Ma et al., 1994; Xu and Schwartz, 1994; Laperche et al., 1996). Thus, an abundance of dissolved metallic cations in conjunction with the presence of hydroxyapatite may also explain the limitations on chloropyromorphite formation in this study. However, the plateau in pyromorphite formation observed in Fig. 5b combined with the formation and subsequent reduction of the Pb–hydroxyapatite complex over time, as well as the continued dissolution of the plumbonacrite, suggests that Pb–hydroxyapatite formation did not completely inhibit chloropyromorphite development. In fact, the data suggest that Pb desorbed from the hydroxyapatite surface with time (35% in RFS1 to 29% RFS2 at 16:1 P:Pb) resulted in the formation of small quantities of additional chloropyromorphite.

We speculate that slow dissolution of Pb minerals initially present in the contaminated soil, P sorption and the formation of aqueous metallic P complexes, and Pb sorption to hydroxyapatite may be limiting pyromorphite formation in the alluvial soils studied. However, we cannot rule out the formation and influence of other phosphate minerals and ideal solutions as inconsequential contributors to the limited amount of pyromorphite formed across all treatment classes in this study (Ma et al., 1994; Eighmy et al., 1997; Crannell et al., 2000; Baker et al., 2014).

ConclusionsThe overarching goal of this work was to evaluate potential

water quality challenges and benefits associated with the application of P to Pb-contaminated soils with the hopes of identifying a reasonable remediation scenario for alluvial soils. To the best of our knowledge, this is the first reported experiment to use RFS to evaluate P and metals loss from heavy metal–contaminated soils remediated via P application. As a consequence of the multiple lines of evidence generated by this experiment, including effluent and soil chemistry from the rainfall simulation studies, direct measurement of Pb uptake in plants, and speciation via XANES, we conclude that applying TSP to the alluvial soil at a rate necessary to achieve a 4:1 P:Pb molar ratio would be a viable remediation strategy. Out of range of the full range of P treatments considered, the 4:1 P:Pb molar ratio treatment offers a great likelihood of success for reducing soil Pb bioavailability and the lowest likelihood of potentially adverse environmental consequences.

AcknowledgmentsThe authors thank Dr. Kirk Scheckel of the USEPA and the employees of Advanced Photon Source at the Argonne National Laboratory for their assistance. This work was partially funded by the Missouri Trustee Council for Natural Resource Damage Assessment and Restoration, the Byron Barnes Endowment to the University of Missouri’s Department of Soil, Environmental and Atmospheric Sciences, and USDA NIFA Hatch Formula Funding provided to the University of Missouri. The findings and conclusions in this article are those of the authors and do

not necessarily represent the views of the US Fish and Wildlife Service, the State of Missouri, the USEPA, or the funding agencies/sources.

ReferencesArnich, N., M.C. Lanhers, F. Laurensot, R. Podor, A. Montiel, and D.

Burnel. 2003. In vitro and in vivo studies of lead immobilization by synthetic hydroxyapatite. Environ. Pollut. 124:139–149. doi:10.1016/S0269-7491(02)00416-5

Baker, L.R., G.M. Pierzynski, G.M. Hettiarachchi, K.G. Scheckel, and M. Newville. 2014. Micro-X-ray fluorescence, micro-X-ray absorption spectroscopy, and micro-X-ray diffraction investigation of lead speciation after the addition of different phosphorus amendments to a smelter-contaminated soil. J. Environ. Qual. 43:488–497. doi:10.2134/jeq2013.07.0281

Basta, N.T., and S.L. McGowen. 2004. Evaluation of chemical immobilization treatments for reducing heavy metal transport in a smelter-contaminated soil. Environ. Pollut. 127:73–82. doi:10.1016/S0269-7491(03)00250-1

Blanco-Canqui, H., C.J. Gantzer, S.H. Anderson, E.E. Alberts, and A.L. Thompson. 2004. Grass barrier and vegetative filter strip effectiveness in reducing runoff, sediment, nitrogen, and phosphorus loss. Soil Sci. Soc. Am. J. 68:1670–1678. doi:10.2136/sssaj2004.1670

Brown, S.L., W. Berti, R.L. Chaney, J. Halfrisch, and J. Ryan. 2004. In situ use of soil amendments to reduce the bioaccessibility and phytoavailability of soil lead. J. Environ. Qual. 33:522–531. doi:10.2134/jeq2004.5220

Cao, X., L.Q. Ma, M. Chen, S.P. Singh, and W.G. Harris. 2002. Impacts of phosphate amendments on lead biogeochemistry at a contaminated site. Environ. Sci. Technol. 36:5296–5304. doi:10.1021/es020697j

Cao, R.X., L.Q. Ma, M. Chen, S.P. Singh, and W.G. Harris. 2003. Phosphate-induced metal immobilization in a contaminated site. Environ. Pollut. 122:19–28. doi:10.1016/S0269-7491(02)00283-X

Chappell, M.A., and K.G. Scheckel. 2007. Pyromorphite formation and stability after quick lime neutralization in the presence of soil and clay sorbents. Environ. Chem. 4:109–113. doi:10.1071/EN06081

Chen, S.B., Y.G. Zhu, and Y.B. Ma. 2006. The effect of grain size of rock phosphate amendment on metal immobilization in contaminated soils. J. Hazard. Mater. 134:74–79. doi:10.1016/j.jhazmat.2005.10.027

Cotter-Howells, J.D., P.E. Champness, J.M. Chamock, and R.P. Pattrick. 1994. Identification of pyromorphite in mine-waste contaminated soils by ATEM and EXAFS. Eur. J. Soil Sci. 45:393–402. doi:10.1111/j.1365-2389.1994.tb00524.x

Crannell, B.S., T.T. Eighmy, J.E. Krzanowski, J.D. Eusden, Jr., E.L. Shaw, and C.A. Francis. 2000. Heavy metal stabilization in municipal solid waste combustion bottom ash using soluble phosphate. Waste Manage. 20:135–148. doi:10.1016/S0956-053X(99)00312-8

Davis, A., J.W. Drexler, M.V. Ruby, and A. Nicholson. 1993. Micromineralogy of mine wastes in relation to lead bioavailability, Butte, Montana. Environ. Sci. Technol. 27:1415–1425. doi:10.1021/es00044a018

Dermatas, D., M. Chrysochoou, D.G. Grubb, and X. Xu. 2008. Phosphate treatment of firing range soils: Lead fixation or phosphorus release. J. Environ. Qual. 37:47–56. doi:10.2134/jeq2007.0151

Eighmy, T.T., B.S. Crannell, L. Butler, F.K. Cartledge, E.F. Emery, D. Oblas, J.E. Krzanowski, J.D. Eusden, Jr., E.L. Shaw, and C.A. Francis. 1997. Heavy metal stabilization in municipal solid waste combustion dry scrubber residue using soluble phosphate. Environ. Sci. Technol. 31:3330–3338. doi:10.1021/es970407c

Ford, R.G., P.M. Bertsch, and K.J. Farley. 1997. Changes in transition and heavy metal partitioning during hydrous iron oxide aging. Environ. Sci. Technol. 31:2028–2033. doi:10.1021/es960824+

Hashimoto, Y., T.J. Smyth, D. Hesterberg, and D.W. Israel. 2007. Soybean root growth in relation to ionic composition in magnesium-amended acid subsoils: Implications on root citrate ameliorating aluminum constraints. Soil Sci. Plant Nutr. 53:753–763. doi:10.1111/j.1747-0765.2007.00191.x

Hashimoto, Y., M. Takaoka, K. Oshita, and H. Tanida. 2009. Incomplete transformations of Pb to pyromorphite by phosphate induced immobilization investigated by X-ray absorption fine structure (XAFS) spectroscopy. Chemosphere 76:616–622. doi:10.1016/j.chemosphere.2009.04.049

Hettiarachchi, G.M., G.M. Pierzynski, and M.D. Ransom. 2001. In situ stabilization of soil lead using phosphorus. J. Environ. Qual. 30:1214–1221. doi:10.2134/jeq2001.3041214x

Hillier, S., K. Suzuki, and J. Cotter-Howells. 2001. Quantitative determination of cerussite by X-ray powder diffraction and inferences for lead speciation and transport in stream sediments from a former lead mining area in Scotland. Appl. Geochem. 16:597–608. doi:10.1016/S0883-2927(00)00059-7

Huff, F.A., and J.R. Angel. 1992. Rainfall frequency atlas of the midwest. Bulletin 71. Illinois State Water Survey, Champaign, IL.

Kilgour, D.W., R.B. Moseley, M.O. Barnett, K.S. Savage, and P.M. Jardine. 2008. Potential negative consequences of adding phosphorus-based fertilizers to immobilize lead in soil. J. Environ. Qual. 37:1733–1740. doi:10.2134/jeq2007.0409

1136 Journal of Environmental Quality

Krivovichev, S.V., and P.C. Burns. 2000. Crystal chemistry of basic lead carbonates: II. Crystal structure of synthetic plumbonacrite. Mineral. Mag. 64:1069–1075. doi:10.1180/002646100549887

Laperche, V., S.J. Traina, P. Gaddam, and T.J. Logan. 1996. In situ immobilization of lead in contaminated soils by synthetic hydroxyapatite: Chemical and mineralogical characterizations. Environ. Sci. Technol. 30:3321–3326. doi:10.1021/es960141u

Li, L., K.G. Scheckel, L. Zheng, G. Liu, W. Xing, and G. Xiang. 2014. Immobilization of lead in soil influenced by soluble phosphate and calcium: Lead speciation evidence. J. Environ. Qual. 43:468–474.

Ma, Q.Y., S.J. Traina, and T.J. Logan. 1993. In situ lead immobilization by apatite. Environ. Sci. Technol. 27:1803–1810. doi:10.1021/es00046a007

Ma, Q.Y., S.J. Traina, T.J. Logan, and J.A. Ryan. 1994. Effects of aqueous Al, Cd, Cu, Fe(II), Ni, and Zn on Pb immobilization by hydroxyapatite. Environ. Sci. Technol. 28:1219–1228. doi:10.1021/es00056a007

Ma, Q.Y., T.J. Logan, and S.J. Traina. 1995. Lead immobilization from aqueous solutions and contaminated soils using phosphate rocks. Environ. Sci. Technol. 29:1118–1126. doi:10.1021/es00004a034

Manceau, A., M.A. Marcus, and N. Tamura. 2002. Quantitative speciation of heavy metals in soils and sediments by synchrotron x-ray techniques. In: P. Fenter and N.C. Sturchio, editors, Applications of synchrotron radiation in low-temperature geochemistry and environmental science. Mineralogical Society of America, Washington, DC. p. 341–428.

Melamed, R., X. Cao, M. Chen, and L. Ma. 2002. Field assessment of lead immobilization in a contaminated soil after phosphate application. Sci. Total Environ. 305:117–127.

Moles, N.R., D. Smyth, C.E. Maher, E.H. Beattie, and M. Kelly. 2004. Dispersion of cerussite-rich tailings and plant uptake of heavy metals at historical lead mines near Newtownards, Northern Ireland. Applied Earth Sci. 113:21–30. doi:10.1179/037174504225004439

Nriagu, J.O. 1973. Lead orthophosphates: II. Stability of chloropyromorphite at 25°C. Geochim. Cosmochim. Acta 37:367–377. doi:10.1016/0016-7037(73)90206-8

Nriagu, J.O. 1974. Lead orthophosphates: IV. Formation and stability in the environment. Geochim. Cosmochim. Acta 38:887–898. doi:10.1016/0016-7037(74)90062-3

Ostergren, J.D., G.E. Brown, G.A. Parks, and T.N. Tingle. 1999. Quantitative speciation of lead in selected mine tailings from Leadville, CO. Environ. Sci. Technol. 33:1627–1636. doi:10.1021/es980660s

Pavlowsky, R. 2010. Distribution, geochemistry, and storage of mining sediment in channel and floodplain deposits of the Big River system in St. Francois, Washington, and Jefferson Counties, Missouri. The Ozarks Environmental and Water Resources Institute, Missouri State University, Springfield, MO.

Ravel, B., and M. Newville. 2005. Athena, Artemis, Hephaestus: Data analysis for X-ray absorption using IFEFFIT. J. Synchrotron Radiat. 12:537–541. doi:10.1107/S0909049505012719

Regmi, T.P., and A.L. Thompson. 2000. Rainfall simulator design for laboratory studies. Appl. Eng. Agric. J. 16(6):641–647.

Ruby, M.V., A. Davis, and A. Nicholson. 1994. In situ formation of lead phosphates in soils as a method to immobilize lead. Environ. Sci. Technol. 28:646–654. doi:10.1021/es00053a018

Ryan, J.A., P.C. Zhang, D. Hesterberg, J. Chou, and D.E. Sayers. 2001. Formation of chloropyromorphite in a lead-contaminated soil amended with hydroxyapatite. Environ. Sci. Technol. 35:3798–3803. doi:10.1021/es010634l

SAS Institute. 2013. SAS 9.3. SAS Institute, Cary, NC.Scheckel, K.G., C.A. Impellitteri, J.A. Ryan, and T. McEvoy. 2003. Assessment of a

sequential extraction procedure for perturbed lead-contaminated samples with and without phosphorus amendments. Environ. Sci. Technol. 37:1892–1898. doi:10.1021/es026160n

Scheckel, K.G., J.A. Ryan, D. Allen, and N.V. Lescano. 2005. Determining speciation of Pb in phosphate-amended soils: Method limitations. Sci. Total Environ. 350:261–272. doi:10.1016/j.scitotenv.2005.01.020

Scheckel, K.G., and J.A. Ryan. 2002. Effects of aging and pH on dissolution kinetics and stability of chloropyromorphite. Environ. Sci. Technol. 36:2198–2204. doi:10.1021/es015803g

Scheckel, K.G., and J.A. Ryan. 2003. In vitro formation of pyromorphite via reaction of Pb sources with soft-drink phosphoric acid. Sci. Total Environ. 302:253–265. doi:10.1016/S0048-9697(02)00350-9

Scheckel, K.G., and J.A. Ryan. 2004. Spectroscopic speciation and quantification of lead in phosphate-amended soils. J. Environ. Qual. 33:1288–1295. doi:10.2134/jeq2004.1288

Scheckel, K.G., G.L. Diamond, M.F. Burgess, J.M. Klotzbach, M. Maddaloni, B.W. Miller, C.R. Partridge, and S.M. Serda. 2013. Amending soils with phosphate as means to mitigate soil lead hazard: A critical review of the state of the science. J. Toxicol. Environ. Health Part B 16:337–380. doi:10.1080/10937404.2013.825216

Scheinost, A.C., R. Kretzschmar, and S. Pfister. 2002. Combining selective sequential extractions, X-ray absorption spectroscopy, and principal component analysis for quantitative zinc speciation in soil. Environ. Sci. Technol. 36:5021–5028. doi:10.1021/es025669f

Schroeder, P.D., D.E. Radcliffe, and M.L. Cabrera. 2004. Rainfall timing and poultry litter application rate effects on phosphorus loss in surface runoff. J. Environ. Qual. 33:2201–2209. doi:10.2134/jeq2004.2201

Seeger, C.M. 2008. History of mining in the southeast Missouri lead district and description of mine processes, regulatory controls, environmental effects, and mine facilities in the Viburnum trend subdistrict. In: M.J. Kleeschulte, editor, Hydrologic investigations concerning lead mining issues in southeastern Missouri. USGS Scientific Investigations Report 2008-5140. USGS, Reston, VA. p. 5–33.

Sharpley, A.N., and A.D. Halvorson. 1994. The management of soil phosphorus availability and its impact on surface water quality. In: R. Lal and B.A. Stewart, editors, Soil processes and water quality. Lewis Publ., Boca Raton, FL. p. 7–90.

Sharpley, A.N., and P. Kleinman. 2003. Effect of rainfall simulator and plot scale on overland flow and phosphorus transport. J. Environ. Qual. 32:2172–2179. doi:10.2134/jeq2003.2172

Sims, J.T. 1993. Environmental soil testing for phosphorus. J. Prod. Agric. 6:501–507. doi:10.2134/jpa1993.0501

Soil Survey Staff. 2009. Soil survey field and laboratory methods manual. Soil Survey Investigations Report No. 51, Version 1.0. USDA–NRCS, Washington, DC.

Stanforth, R., and J. Qiu. 2001. Effect of phosphate treatment on the solubility of lead in contaminated soil. Environ. Geol. 41:1–10. doi:10.1007/s002540100262

Tang, X., J. Yang, K.W. Goyne, and B. Deng. 2009. Long-term risk reduction of lead-contaminated urban soil by phosphate treatment. Environ. Eng. Sci. 26:1747–1754. doi:10.1089/ees.2009.0192

Theis, T.L., and P.J. McCabe. 1978. Phosphorus dynamics in hypereutrophic lake sediments. Water Res. 12:677–685. doi:10.1016/0043-1354(78)90178-1

Udawatta, R.P., P.M. Motavalli, and H.E. Garrett. 2004. Phosphorus loss and runoff characteristics in three adjacent agricultural watersheds with claypan soils. J. Environ. Qual. 33:1709–1719. doi:10.2134/jeq2004.1709

USEPA. 1993. Engineering evaluation/cost analysis for the Big River Mine Tailings Site, Desloge, Missouri. USEPA, Region 7, Kansas City, KS.

USEPA. 1996. Method 3050B. Acid digestion of sediments, sludges, and soils. http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3050b.pdf (accessed 15 Jan. 2015).

USEPA. 2007. The use of soil amendments for remediation, revitalization and reuse. EPA 542-R-07-013. USEPA, Office of Solid Waste and Emergency Response, Washington, DC.

USEPA. 2007b. Method 365.1: Phosphorus, all forms (colorimetric, ascorbic acid, two reagent). http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2007_07_10_methods_method_365_3.pdf (accessed 10 Oct. 2012).

USEPA. 2012. Method 3052: Microwave assisted acid digestion of siliceous and organically based matrices. http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3052.pdf (accessed 15 Jan. 2013).

Wronkiewicz, D.J., C.D. Adams, and C. Mendoza. 2006. Transport processes of mining related metals in the Black River of Missouri’s new lead belt. Center for the Study of Metals in the Environment, Newark, DE.

Xu, Y., and F.W. Schwartz. 1994. Lead immobilization by hydroxyapatite in aqueous solutions. J. Contam. Hydrol. 15:187–206. doi:10.1016/0169-7722(94)90024-8

Yang, J., D. Mosby, S.W. Casteel, and R.W. Blanchar. 2001. Lead immobilization using phosphoric acid in a smelter-contaminated soil. Environ. Sci. Technol. 35:3553–3559. doi:10.1021/es001770d

Yang, J., D. Mosby, S.W. Casteel, and R.W. Blanchar. 2002. In vitro lead bioaccessibility and phosphate leaching as affected by surface application of phosphoric acid in lead-contaminated soil. Environ. Contam. Toxicol. 43:399–405.

Yang, J., and X. Tang. 2007. Water quality and ecotoxicity as influenced by phosphate treatments in metal-contaminated soil and mining wastes. Environ. Monitor. Restor. 3:21–33.

Zhang, P.C., J.A. Ryan, and J. Yang. 1998. In vitro soil solubility in the presence of hydroxyapatite. Environ. Sci. Technol. 32:2763–2768. doi:10.1021/es971065d

Zhang, P., and J.A. Ryan. 1999. Transformation of Pb(II) from cerussite to chloropyromorphite in the presence of hydroxyapatite under varying conditions of pH. Environ. Sci. Technol. 33:625–630. doi:10.1021/es980268e