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

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

Published July 10, 2015

Journal of Environmental Quality TECHNICAL REPORTS Heavy in the Environment

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

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

outhern Missouri contains several districts, Abstract including the Southeast Missouri Pb mining district, Water quality threats associated with using -based home to the world’s largest known deposit of galena (PbS) amendments to remediate Pb-contaminated are a concern, (Seeger,S 2008). As a consequence of the long-term exploita- particularly in riparian areas. This study investigated the effects tion of PbS deposits, contamination of soils and sediments in of P application rates to a Pb-contaminated alluvial soil on Pb and P loss via surface water runoff, Pb accumulation in tall fescue southeastern Missouri is widespread and may pose an ecologi- (Festuca arundinacea Schreb; Kentucky 31), and Pb speciation. cal and human health risk to communities inhabiting the region An alluvial soil was treated with triple superphosphate at P to Pb (USEPA, 2007). Recent investigation into soil Pb concentrations molar ratios of 0:1 (control), 4:1, 8:1, and 16:1. After a 6-mo reaction has indicated that the vast majority of the alluvial soils along the , rainfall simulation (RFS) studies were conducted, followed Big River of St. Francois, Jefferson, and Counties in by tall fescue establishment and a second set of RFS studies (1 yr after treatment). Results from the first RFS study (unvegetated) Missouri are contaminated with Pb above thresholds of concern demonstrated that the total Pb and P concentrations in the for human health and the environment (Pavlowsky, 2010). effluents of 8:1 and 16:1 (P:Pb molar ratio) treatment levels were Remediation of Pb-contaminated areas by traditional means significantly greater (p < 0.05) than the control. One year after P of soil excavation, disposal, and replacement can be extremely treatment and 6 mo after vegetation establishment, total P and expensive to complete on a large scale (USEPA, 1993). In situ Pb concentrations of the effluents from a second RFS decreased by one to three orders of magnitude. Total and dissolved P remedial technologies were shown to be less invasive, reducing concentration in runoff from the 16:1 P:Pb treatment remained undesirable conditions such as fugitive dust emissions and heavy significantly greater than all other treatments. However, total equipment exhausts as well as overall disruption of the landscape Pb concentration in the runoff was comparable among the (Ma et al., 1993, 1995; Xu and Schwartz, 1994). Additionally, treatments. Phosphorus treatment also reduced Pb uptake the volume and concentrations of Pb present in the alluvial into tall fescue by >55%. X-ray absorption near-edge structure soils of the Big River make excavation and disposal technically spectroscopy data showed that [Pb5(PO4)3OH,Cl,F] abundance ranged from 0% (control) to 32% (16:1 P:Pb; 1 yr after impractical (Pavlowsky, 2010). treatment) of the total soil Pb. Although P treatment stimulated A number of previous studies have successfully altered soil pyromorphite formation, pyromorphite abundance was Pb chemistry through the addition of inorganic phosphate comparable between the P-treated soils. These findings suggest compounds that convert soil Pb species to less soluble that a 4:1 (P:Pb molar ratio) P treatment may be a sufficient means of reducing Pb bioavailability while minimizing concerns related pyromorphite [Pb5(PO4)3(OH,Cl,F)]. Pyromorphites to P loss in an alluvial setting. 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).

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, Copyright © 2015 American Society of , Crop Science Society of America, Environmental and Atmospheric Sciences, Univ. of Missouri, 302 ABNR Bldg., and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. Columbia, MO 65211; T.P. Luxton, USEPA, Office of Research and Development, All rights reserved. National Risk Management Research Lab., 26 W. Martin Luther King Dr., Cincinnati, OH 45268; A.L. Thompson, Dep. of Bioengineering, Univ. of Missouri, 251 J. Environ. Qual. 44:1127–1136 (2015) Agricultural Bldg., Columbia, MO 65211. Assigned to Associate Editor doi:10.2134/jeq2014.10.0447 Markus Grafe. Supplemental material is available online for this article. Received 28 Oct. 2014. Abbreviations: DIRO, deionized reverse osmosis; LCF, linear combination fitting; Accepted 4 May 2015. RFS, rainfall simulation; TSP, triple superphosphate; XANES, X-ray absorption near- *Corresponding author ([email protected]). edge spectroscopy.

1127 However, adding large quantities of P to soils is an application; and (iii) pyromorphite formation will be environmental concern because P loss to aquatic enhanced as P fertilizer application is increased. is associated with (Theis and McCabe, 1978; Sharpley and Halvorson, 1994; Sims, 1993; Dermatas et Materials and Methods al., 2008). There is a paucity of research investigating the Soil Collection consequences of P treatment under conditions likely to occur in Kaintuck fine sandy loam soil (coarse-loamy, siliceous, the environment (Scheckel et al., 2013; Dermatas et al., 2008). superactive, nonacid mesic Typic Udifluvents) was collected Yet, potential issues of P leaching from Pb-contaminated soils from the Big River floodplain near DeSoto, MO (38°5¢13¢¢ N, treated with P amendments have only been lightly discussed or 90°40¢28¢¢ W). Vegetative cover at the site was predominantly mentioned by studies investigating the feasibility of P treatments tall fescue ( Schreb; Kentucky 31). A (Basta and McGowen, 2004; Cao et al., 2002; Chen et al., 2006; Festuca arundinacea hand-held X-ray fluorescence spectrometer (Thermo Fisher) Dermatas et al., 2008; Tang et al., 2009; Yang and Tang, 2007). was used to target surface soil concentrations of >1500 mg Previous research has demonstrated that substantial leaching of kg-1 Pb (Table 1). Samples were collected at a depth of 0 to P from P-treated soils occurs in acidic and alkaline soils under a 15 cm from several locations within a 100-m2 area. Soils were variety of experimental conditions, demonstrating the potential bulked and mechanically mixed to create a single stockpile of importance of research focused on P loss from alluvial soils soil. Undisturbed core samples (7.5 cm by 7.5 cm, diameter by (Dermatas et al., 2008; Kilgour et al., 2008; Stanforth and Qiu, height) used to quantify soil bulk were collected within 2001). the sample area using an Uhland core sampler. In addition to considering P fate and transport after P treatment of Pb-contaminated soils, it is important to confirm pyromorphite Initial Soil Sample Characterization formations as an indicator of reduced Pb bioavailability in the soil (Scheckel et al., 2003; Scheckel et al., 2013). Numerous After air drying and hand mixing, the bulk soil stockpile was techniques have been used to confirm pyromorphite formation, sieved to <2 mm for use in all experimental trials. Ten composite including selective sequential extraction procedures, in vitro physiologically based extraction tests, energy-dispersive X-ray Table 1. Selected properties of untreated bulk stockpile, data represent the arithmetic mean of 10 samples. spectroscopy, and scanning electron microscopy (Ryan et al., 2001; Cao et al., 2003; Scheckel et al., 2003, 2005; Davis et al., Soil property† Result 1993; Yang et al., 2001). However, selective sequential extraction USDA classification Typic Udifluvent and the physiologically based extraction tests are known to Textural class Silt loam artificially create pyromorphites during the digestion of the Bulk density, g cm-3 1.2 ± 0.0‡ -1 22.5 ± 0.2 analyses (Scheckel et al., 2003, 2005), and visual confirmation of CEC NH4OAc, cmol kg -1 16.0 ± 0.1 pyromorphites using scanning electron microscopy and energy CEC NH4Cl, cmol kg dispersive X-ray spectroscopy has been shown to be of limited Percent base saturation 92.4 ± 0.5 utility due to the similarity of hexagonal pyromorphite crystals pH water 7.8 ± 0.0 pH (0.01 mol L-1 CaCl ) 7.6 ± 0.0 to a variety of crystalline soil components (Scheckel and Ryan, 2 -1 1.7 ± 0.1 2003). Consequently, advanced synchrotron spectroscopic BaCl2–extractable acidity, cmol kg techniques are necessary to confirm pyromorphite formation TOC, g kg-1 21.0 ± 0.0 in an exacting and nondestructive manner (Cotter-Howells et TN, g kg-1 2.0 ± 0.1 al., 1994; Ryan et al., 2001; Scheckel and Ryan, 2002; Scheckel Mehlich 3–extractable elements, mg kg-1 and Ryan, 2003; Scheckel and Ryan, 2004). X-ray absorption Al 528 ± 4 spectroscopy (XAS), in combination with advanced statistical Ca 2572 ± 11 models, is frequently used to identify different metals species in Cu 25.2 ± 0.1 soil environments, and XAS is particularly useful when studying Fe 263 ± 1 Pb-contaminated soils amended with P (Manceau et al., 2002). K 53.4 ± 0.1 The objectives of this study were (i) to determine the Mg 611 ± 2 relationship between concentrations of P and metals eluviated Mn 100 ± 1 from three treatment classes of P-treated, Pb-contaminated Na 60 ± 2 soils during simulated rainfall events conducted using P 32 ± 1 unvegetated soils at 6 mo after treatment and vegetated soils Zn 226 ± 1 at 12 mo after treatment; (ii) to confirm potential reductions Total elemental concentration, mg kg-1 in Pb phytoavailability within the P-treated soils by measuring As 7.3 ± 0.1 the content of tissues from vegetation grown on the Ba 940 ± 11 treatment units; and (iii) to investigate pyromorphite formation Cd 10.6 ± 0.4 as a function of P application. We hypothesize that (i) soils with Cu 72.4 ± 0.3 greater levels of applied P will release commensurately greater Pb 2190 ± 13 levels of P to surface water, overall Pb release will be unaffected Mn 1980 ± 15 by treatment, and vegetation establishment and time elapsed will Zn 634 ± 4 significantly reduce both metals and P transport from the soils; † CEC, cation exchange capacity; TN, total N; TOC, total organic C. (ii) Pb phytoavailability in soil will decrease with increasing P ‡ Values are mean ± SE. 1128 Journal of Environmental Quality samples were collected from the bulk stockpile for determination A total of 16 test beds were prepared, and each treatment level of general soil properties before P treatment. Analyses were was replicated in quadruplicate. -1 performed, including pHwater, pHsalt (0.01 mol L CaCl2), particle Rainfall simulation studies were completed using the rainfall size distribution, extractable Al, titratable acidity, pH 7 buffered simulation tower at the University of Missouri using deionized, and unbuffered cation exchange capacity, organic C, Mehlich 3 reverse osmosis (DIRO) water (Regmi and Thompson, 2000). P, and total N content, following procedures recommended by Briefly, the 1-m × 1-m laboratory-scale simulator operates under the USDA–NRCS (Soil Survey Staff, 2009). Total elemental a positive displacement principle to provide a mean droplet analysis of the soils (As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, and Zn) diameter of 2.6 mm. Adjustable stands used to hold the RFS test was determined using the HNO3 digestion procedure (USEPA beds were set to 2% slope for all experiments. Soils were exposed Method 3050B; USEPA, 1996) and inductively coupled to simulated rainfall for 1.5 h at an average rate of 5 cm h-1. A plasma– spectrometry (Table 1). storm of this intensity is predicted to occur at approximately 15-yr intervals in DeSoto, MO (Huff and Angel, 1992). All Phosphate Treatment of Soils effluents from the V trough of the test beds were collected in Based on previous research (Ma et al., 1993, 1995; Xu and preweighed, 3.8-L, high-density polyethylene buckets; a shield Schwartz, 1994; Ruby et al., 1994; Zhang et al., 1998), soil was was used to prevent simulated rainfall from directly entering the amended with triple superphosphate (TSP) [Ca(H2PO4)2] at four sampling containers. Sediments deposited in the trough were molar ratios of P to Pb (P:Pb): 0:1 (control), 4:1, 8:1, and 16:1. Four collected for analysis. did not emanate from drainage replicates of each treatment level were created by placing 108 kg tubes located within the sand substrate, thus eliminating the of air-dried soil (1.5% moisture by mass) from the bulk stockpile need to collect subsurface drainage waters. into 70-gallon polyethylene tanks. The soils were then treated After the first RFS, the test beds were planted withF. with granulated TSP (Bonide Products, Inc.) as an equivalently arundinacea to simulate pastures observed in the Big River split application on two separate dates. The initial application was floodplain. The tall fescue was watered once a week with a volume used to induce acidification. The second application, 40 d later, of DIRO equal to one half of the soil volume in the test beds (i.e., was performed to achieve the desired P:Pb molar ratios for each 8 L per test bed per week). Air temperature was kept constant at treatment (Melamed et al., 2002). On each application date, one 25°C. At 30 d after the first RFS, all vegetation above the top lip quarter of the total TSP mass required to achieve the desired of the test beds was removed for metals analysis. Tissue samples molar ratio was added to the soil and thoroughly mixed into the were also collected 180 d after the first RFS and analyzed. soils with a power auger, and then the process was repeated (Yang To gauge the impact of time and vegetative cover on the et al., 2001). Treated soils were moistened with deionized water to erosion of soil and the loss of associated contaminants from the field capacity and allowed to react for 60 d (deionized water was test beds, a second RFS test was conducted 180 d after the first added to maintain field capacity throughout the reaction period). simulation. At the conclusion of the second RFS, composite After the reaction period, soils were amended with hydrated soil samples were collected and analyzed for available P using

[Ca(OH)2] to achieve a soil pH of 6.5 to 7.5, thereby simulating Mehlich 3 analyses. normal agronomic conditions and enhancing pyromorphite formation (Chappell and Scheckel, 2007). The control treatment Effluent Water Sample Processing was not limed because native pHwater was approximately pH 7.8 Effluents collected during a given RFS test period were (Table 1). After liming, all treatment soils were kept moist for 90 weighed to determine the combined total mass of the water, d in a greenhouse at approximately 25°C. eroded sediment, and bucket. Samples were then thoroughly mixed for 5 min at 1000 rpm using a stir plate and stir bar. Rainfall Simulations and Vegetation Establishment Aliquots of solution and suspended sediments for total metals Rainfall simulation (RFS) test beds (50 cm × 30 cm × 25 cm, and total P analyses were collected using a Geotech GeoPump length × width × depth) were fabricated using 16-gauge sheet peristaltic pump and Masterflex Platinum Silicone L/S 15 tubing (Supplemental Fig. S1). An adjustable V-notch was attached by submerging the tubing into a continuously stirred sample. to the front of the RFS test beds to channel surface runoff to a Samples for dissolved metals and dissolved orthophosphate collection point. Perforated, 1.27-cm schedule 40 PVC pipe was analysis were collected by attaching a Geotech Dispos-a-filter (a used to construct a subsurface drainage collection point with 0.45-µm, high-capacity, in-line filter) to the peristaltic pump and two ports located on the exterior of the drainage box below the tubing. Samples for total and dissolved metals were immediately

V-notch. All surfaces of the test beds were painted using Pb-free preserved using a 10% (v/v) HNO3 solution (Ricca Chemical latex paint, and all test beds were cleaned with a dilute HNO3 Co.). Samples for total P were preserved using 1:1 H2SO4 sample (1% by volume) and rinsed in triplicate with deionized water. preservation ampules (EaglePicher Scientific). All water samples The RFS beds were filled with screened and washed were stored in 250-mL, high-density polyethylene containers, medium-grade (0.08–0.3 mm) sand (Quikrete) to a depth of certified I-CHEM clean (Nalgene Corp.), at 4°C. 10 cm, completely covering the PVC drainage tubing. The The remaining bulk effluent samples and sediments removed sand was covered with landscape fabric to prevent intrusion from the trough were filtered through preweighed Fisher of the treatment soil into the sand. Soil from the four P:Pb Scientific Q2 Fine Porosity Filter Paper (particle retention, 1–5 treatment levels was placed into individual test beds to a depth µm). Soil plus filter papers were dried at 70°C for 48 h, and the of approximately 10 cm in two separate 5-cm lifts and compacted mass of filter paper plus soil was measured. The mass of total P to a field bulk density of 1.2 g cm-3 (Table 1) at each lift. Soils and total metals lost per unit area to erosive flows was calculated were moistened to facilitate uniform and homogeneous packing. (Table 2) by multiplying the concentration of a contaminant by Journal of Environmental Quality 1129 the volume of runoff collected and dividing by the surface area of Fisher’s LSD method was used to evaluate differences between the RFS test bed. the means (SAS Institute, 2013). Treatments included phosphate application rate (0:1, 4:1, 8:1, and 16:1 P:Pb) and vegetative Sediment, Water, and Plant Tissues Analyses cover with grass (grass cover and no grass cover). Statistical Unfiltered water samples collected for total and dissolved differences were tested at a = 0.05. metals were digested by placing 5 mL of sample and 1 mL X-ray Absorption Near-Edge Structure Spectroscopy of HNO3 into a 50-mL quartz reaction vessel and heating the sealed high-pressure vessel assembly in a PerkinElmer Lead LIII-edge (13, 035 eV) X-ray absorption spectra (XAS) Multiwave Digestion System. After cooling, digested samples were collected at the Materials Research Collaborative Access were transferred to a storage container and diluted to a final Team’s beamline 10-ID, Sector 10 at the Advanced Photon volume of 50 mL (2% HNO3 matrix). Total P and dissolved Source at the Argonne National Laboratory, Argonne, IL. The ortho-P samples were processed using the procedures described electron storage ring was operated in top-up mode at 7 GeV. in USEPA Method 365.1 (USEPA, 2007b). Spectra were collected in fluorescence mode with either a Lytle Total and dissolved metals contents of digested water samples or a -state drift detector at room temperature. The were quantified with a PerkinElmer Sciex Elan DRCe inductively samples were prepared as thin pellets using an IR pellet press, coupled plasma–mass spectrometer using the quantitative and samples were secured to sample holders using Kapton tape. analysis mode. Multipoint standard curves were developed for For each sample, 15 to 17 scans were collected using the Lytle analytes of interest, and rhodium (0.01 mg L-1) and bismuth detector or four to five scans using the solid-state detector and (0.01 mg L-1) were used as internal standards. Where multiple averaged. Before averaging the data, the spectra were inspected masses were monitored, masses were selected for reporting based to ensure that beam-induced damaged had not occurred during on least interference. Lead was reported as the sum of three analysis. Data were analyzed using the Athena software program masses (206Pb + 207Pb + 208Pb). Digested water samples for total (Ravel and Newville, 2005). Sample spectra were compared with P and dissolved orthophosphate were analyzed colorimetrically synthesized minerals and specimens acquired from the using a Lachat QuikChem 8500 Series 2 FIA System following Smithsonian National Museum of Natural History. All minerals USEPA Method 365.1 (USEPA, 2007b). were verified with X-ray diffraction before use as reference Harvested grass tissue samples were rinsed with DIRO for 1 materials. min to remove soil particles, and tissue samples were oven-dried Soil Pb speciation was determined by comparison of Pb at 70°C for 48 h before digestion by USEPA Method 3052 (with standards to the field samples via linear combination fitting

HNO3 and HF) (USEPA, 2012) and total metals analysis by (LCF). Linear combination fitting refers to the process of inductively coupled plasma–mass spectroscopy. selecting a multiple component fitting function with a least- squares algorithm that minimizes the sum of the squares of Statistical Analyses for Rainfall Simulation and Metals residuals. A fit range of -20 to 50 eV was used for the X-ray Content of Grass Tissue absorption near-edge structure (XANES) portion of the XAS A one-way ANOVA was used to analyze the RFS data using spectra and up to four variables. The best fitting scenarios are c2 the statistical analysis software SAS 9.3 (SAS Institute, 2013). determined by the smallest residual error ( ) and the sum of all component fractions being close to 1. The first derivative Table 2. Mass of P and Pb lost during the first and second rainfall of the XANES spectra was used in the LCF analysis. This was simulation experiments. done to exploit the subtle changes that exist in the Pb-L3 line Rainfall simulation and P loss‡§ Pb loss shape. Fitting the additional peaks and shoulder features in treatment class† the first derivative spectra provides for a more robust fit of -1 —————— k g h a —————— the data and greater confidence in the LCF results. Detailed RFS1-UAC 0.18a,A 1.54a,A descriptions of the fitting procedure are described elsewhere RFS1–4:1 0.76ab,ABC 1.81ab,AB (Manceau et al., 2002). The reference samples used in the RFS1–8:1 1.75b,C 2.76ab,C LCF model were plumboferrite (PbFe O ), plumbonacrite RFS1–16:1 6.01c,D 2.45b,BC 4 7 [Pb O(OH) (CO ) ] chloropyromorphite [Pb (PO ) Cl], RFS2-UAC 0.09a,AB 0.004a,D 5 2 3 3 , 5 4 3 Pb sorbed to complex (Ca5Pb (PO ) (OH) ], RFS2–4:1 0.17b,AB 0.004a,D 5 4 6 2 PbS, hydrocerussite [Pb (CO ) (OH) ], anglesite (PbSO ), RFS2–8:1 0.25c,AB 0.007a,D 3 3 2 2 4 plumbomagnetite (PbFe O ), litharge (PbO), Pb hydroxide RFS2:16:1 0.38d,AB 0.005a,D 2 4 [Pb(OH)2], Pb sorbed to humic , goethite, and kaolinite. † 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. Results and Discussion ‡ Values represent the arithmetic mean of four replicates per treatment Effluent Water Chemistry from Unvegetated level. Within a column, mean values followed by different lowercase and Vegetated Soils letters are significantly different within a given rainfall simulation experiment (1 or 2) as determined using a one-way ANOVA and Unvegetated control and P-treated soils were exposed to RFS Fisher’s LSD means separation test (a= 0.05). after P application and a 6-mo reaction period to capture water § Within a column, mean values followed by different uppercase letters quality and soils data that could approximate field conditions are significantly different between the rainfall simulation experiments as determined using a one-way ANOVA and the Fisher’s LSD means for a P-treated, Pb-contaminated soil. Total and dissolved P separation test (a= 0.05). concentrations in effluent from the 16:1 P:Pb phosphorus 1130 Journal of Environmental Quality 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 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 –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 Fig. 1. Effluent chemistry data from the first rainfall simulation including (a) total P and dissolved orthophosphate and (b) total introduced during the P treatment regimen described above. and dissolved Pb. Values followed by different lowercase letters The total volume of runoff effluents and the mass of eroded are significantly different between treatment classes for dissolved sediments were not significantly different among the treatments orthophosphate (a) and dissolved Pb (b) determined using a one-way ANOVA and Fisher’s LSD means separation test (a = 0.05). Values (Supplemental Table S1). However, the overall mass of P and followed by different uppercase letters are significantly different total Pb lost via runoff increased significantly for the two highest between treatment classes for total P (a) and total Pb (b) determined treatment classes (8:1 and 16:1 P:Pb ratios) (Table 2). Total P using a one-way ANOVA and Fisher’s LSD means separation test (a = loss at the 16:1 P:Pb ratio treatment (6.01 kg ha-1) was 33 times 0.05). Error bars represent SE. greater than P loss from unamended soils, which parallels trends dissolved Pb were observed between the vegetated treatments, reported for effluent P concentrations. These results are up to dissolved P concentration remained significantly greater for the two orders of magnitude greater than results reported from 16:1 P:Pb treatment. Interestingly, no significant difference in other P transport studies using RFS (Blanco-Canqui et al., 2004; dissolved P concentration was observed between the control Sharpley and Kleinman, 2003; Schroeder et al., 2004). However, and the 4:1 P:Pb treatment, and total P concentrations of the final Mehlich 3–extractable P concentrations of the P-treated effluents from these treatments are within the range observed for - soils from the current study (4:1 P:Pb, 481 mg kg 1; 8:1 P:Pb, agricultural watersheds of Missouri (Udawatta et al., 2004). - - 947 mg kg 1; and 16:1 P:Pb, 2074 mg kg 1) are an order of Overall, the total mass of soil (Supplemental Table S1) and magnitude greater than the above-mentioned agronomic studies. elements (Table 2) transported during the second RFS were Differences in P loss among these studies and the current study significantly less than those lost during the first RFS (Table 2). are likely attributable to methods used for the RFS, including The reduction in mass lost is especially pronounced for Pb at air drying, sieving, and thorough mechanical mixing of soils, as the 8:1 P:Pb treatment (RFS1 = 2.76 kg ha-1; RFS2 = 0.007 kg well as greater quantities of P applied and the use of DIRO water ha-1) and for P at the 16:1 P:Pb treatment (RFS1 = 6.01 kg ha-1; rather than natural rainfall. RFS2 = 0.38 kg ha-1). Although the establishment of vegetation A second RFS experiment was conducted 1 yr after P and the increased reaction time reduced total P and Pb loss in application and the establishment of tall fescue. Concentrations the second RFS, P loss continued to positively correlate with P of total and dissolved P and Pb dramatically decreased during application. For example, P losses from the 16:1 P:Pb treatment the second RFS study (Fig. 2). Total Pb concentrations in runoff were 4.2- and 2.2-fold greater than the control and 4:1 P:Pb effluents were reduced by up to three orders of magnitude, and treatments, respectively. total P concentration was reduced by one order of magnitude, The effluent water chemistry results from the first and second when compared with results from the first RFS. Total P RFS illustrate the benefits of establishing vegetation on P-treated, concentrations in runoff effluents were significantly different heavy metals–contaminated soils as a means to reduce total between the treatments, with the greatest concentration Pb and P transport to surface water resources. Implementation corresponding to the 16:1 P:Pb treatment. Dissolved Pb and P of specific best management practices (e.g., the installation of concentrations were reduced by nearly one half relative to the vegetative buffer strips, riparian offsets, and exclusions on the use first RFS experiment. Although no significant differences in Journal of Environmental Quality 1131 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. 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 and animals associated with the formation of pyromorphite minerals in soil Fig. 2. Effluent chemistry data from the second rainfall simulation, after P treatment of Pb-contaminated soils (Brown et al., 2004; including (a) total P and dissolved orthophosphate and (b) total Hettiarachchi et al., 2001; Cao et al., 2002). 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 X-ray Absorption Near-Edge Spectra and Linear ANOVA and Fisher’s LSD means separation test (a = 0.05). Values Combination Fitting Analysis followed by different uppercase letters are significantly different between treatment classes for total P (a) and total Pb (b) determined Background Pb Mineralogy using a one-way ANOVA and Fisher’s LSD means separation test (a = 0.05). Error bars represent SE. Results from the XANES analysis and linear combination fitting of standards to fit the XANES spectra are shown in Fig. of the P-based technology near sensitive aquatic areas) should be 4 for the unamended soil and selected P-treated soils collected considered before application. Furthermore, the data strongly from RFS test beds after the second runoff experiment. The support the need for optimized P applications that minimally LCF fits were developed using reference spectra (Supplemental alter surface runoff chemistry and reduce Pb phytoavailability. Fig. S3) and eliminating insignificant component reference The 4:1 P:Pb molar ratio treatment resulted in the least P loss spectra until the best statistical fit was acquired. In general, LCF among soils receiving P application, and Pb transport from results are accurate to ±5%; thus, results with <10% weight the 4:1 P:Pb treatment was not significantly greater than from contribution should be interpreted with caution even though unamended soils. However, the RFS studies did not provide a these components improve the overall error within the fitting measure of Pb phytoavailability reduction, which necessitated process (Scheinost et al., 2002). investigations of Pb uptake by plants and pyromorphite The predominant Pb species present in unamended soils formation that are described in subsequent sections. samples collected from the field were plumbonacrite (38%) and plumboferrite (62%), both of which are more soluble than Influence of P Treatment on Pb Uptake by Tall Fescue pyromorphite (Krivovichev and Burns, 2000; Ostergren et al., Tall fescue established on the different P treatments and 1999). These findings are reasonable because the source of Pb control soil was harvested and analyzed for Pb content at 30 contamination to the floodplain of the Big River is attributed to and 180 d after establishment. Overall, the results indicate a crushed PbS ores known to weather to Pb carbonate compounds significant reduction of plant bioavailable Pb in contaminated such as plumbonacrite (Moles et al., 2004; Hillier et al., 2001; soils treated with TSP (Fig. 3). Importantly, the use of the 4:1 Cotter-Howells et al., 1994), a poorly crystalline precursor P:Pb molar ratio treatment resulted in a >50% reduction in to hydrocerussite [Pb3(CO3)2(OH)2] and cerussite (PbCO3) plant bioavailable Pb, which was significantly (a = 0.05) less (Krivovichev and Burns, 2000). The presence of plumboferrite than Pb content of plant tissues collected from unamended in the control sample data is consistent with soil Pb mineral (i.e., control) soils. No significant differences in Pb content assemblages near Leadville, CO, where Pb associated with Fe were observed in tissues harvested from the 4:1 and 8:1 P:Pb constitutes >50% by mass of Pb species present (Ostergren treatments. However, plant tissues harvested from the 16:1 P:Pb et al., 1999; Davis et al., 1993). Manganese and Fe-Pb oxides treatment contained significantly less Pb relative to all other at the Leadville, CO site occur as discrete grains, coatings on

1132 Journal of Environmental Quality 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 Fig. 4. First derivative of normalized X-ray absorption near-edge spectroscopy spectra of untreated soils and select treated soils. The distribution of Pb species abundance was observed (Fig. 5b). solid curve represents the raw sample data, and the dotted curve The LCF model indicated that soluble plumbonacrite was represents fit results from a linear combination of the reference absent within soils treated with the 16:1 P:Pb molar ratio, and spectra. Labels represent the rainfall simulation and the treatment class (1–4, rainfall simulation 1, 4:1 P:Pb treatment class; RFS2–4, plumboferrite remained the predominant (>40%) Pb species in rainfall simulation 2, 4:1 P:Pb treatment class, etc.). all treatments. Chloropyromorphite formation increased from 29 to 32% of the Pb species present at the 4:1 P:Pb treatment non-Pb minerals, and alteration rinds on Fe particles level, which is identical to the amount of chloropyromorphite (Davis et al., 1993). Model system investigations suggest that formed in samples receiving greater P application (8:1 and Pb associated with Fe oxides may also be bound as adsorption 16:1 P:Pb molar ratios). Similar to LCF results of XANES complexes (Ford et al., 1997). However, including spectra of from samples collected after the first RFS, the amount of the Pb sorbed to a suite of minerals (e.g., goethite) did not improve Pb sorbed to hydroxyapatite species (29%) was greatest in LCF models developed for the unamended soil studied here. 16:1 P:Pb treatment soil. Interestingly, the proportions of the Noteworthy are the substantial differences in Pb species Pb-hydroxyapatite within soils collected after the second RFS found in the alluvial, heavy metals–contaminated soil we study are consistently less than within samples collected after the studied and residential soil from southwestern Missouri that first RFS study, and the species is completely absent from the 4:1 was contaminated by a Pb smelter (Scheckel and Ryan, 2004; P:Pb molar ratio treated soil. The reduction in the proportion Scheckel et al., 2005). The Pb species in the alluvial soil were of Pb-hydroxyapatite corresponds with increased proportions predominantly plumbonacrite and plumboferrite, whereas the of chloropyromorphite and plumboferrite within the P-treated residential soil contained mostly PbS, anglesite, and Pb sorbed soils, suggesting that the Pb sorbed to hydroxyapatite may be to organic matter (21, 32, and 37%, respectively). The lack of transforming to thermodynamically stable Pb minerals over time PbS and the enhanced association of Pb with Fe oxides in the Although P treatment of the Pb-contaminated soils resulted in alluvial soil studied is consistent with previous studies of Big comparable proportions of pyromorphite formation in our work River sediments showing little presence of PbS 20 nautical km and that of Scheckel and Ryan (2004), differences in the initial Pb downstream from the Desloge Tailings Pile in Desloge, MO and species present within the alluvial soil and smelter-contaminated an increased presence of Pb in Fe-rich particles (Wronkiewicz et soil result in some dissimilar mineral transformations after P al., 2006); for reference, the Desloge Tailings Pile is approximately application. Where XANES analyses of the P-treated alluvial soil 50 nautical km upstream from our sampling location. Although demonstrated greater to complete dissolution of plumbonacrite, the nature of the association between Pb- and Fe-rich materials partial dissolution of plumboferrite, and enhanced formation has not been characterized in previous studies in southeastern of Pb sorbed to hydroxyapatite with increased P application, Missouri, the soils most likely contain Pb as plumboferrite Scheckel and Ryan (2004) report the complete transformation precipitates and, to a lesser extent, Pb adsorption complexes. of PbS and partial transformation of anglesite (PbSO4) with Pb Species Transformations after Phosphate Treatment marked increases in the relative abundance of cerussite and After the first RFS experiment (i.e., a 6-mo reaction period), inner-sphere complexes in soils treated with TSP compared with control and P-treated soils were analyzed using XANES to unamended control samples. quantify Pb species present in our experimental soils. The Journal of Environmental Quality 1133 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 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 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 Pb forms within the two studies. Li et al. (2014) spiked (a) first rainfall simulation and (b) second rainfall simulation. RFS1–4, rainfall an uncontaminated soil with Pb dissolved in solution, simulation 1, 4:1 P:Pb treatment class; RFS2–4, rainfall simulation 2, 4:1 P:Pb which likely adsorbed to cation exchange sites, whereas treatment class, etc. UAC, unamended control. Error bars represent SE. the soils we studied contained Pb primarily within Factors Potentially Limiting Pyromorphite Formation the minerals plumbonacrite and plumboferrite. Thus, it is plausible that the dissolution of plumbonacrite and The kinetics of Pb species transformation to pyromorphite is plumboferrite or the transformation of metastable Pb phosphate dependent on soil pH, and the transformation is favored under minerals (Baker et al., 2014) are rate-limiting steps controlling acidic to weak acidic conditions (Xu and Schwartz, 1994; Zhang pyromorphite formation. and Ryan, 1999). Other studies have not reported data for soil pH Alternatively, the plateau in chloropyromorphite formation alteration on the addition of acidic P amendments (e.g., H PO 3 4 observed in our data and other studies may be attributable to and TSP), but the very high stoichiometric ratios of P:Pb used reductions in P available for reaction. Dissolved P concentration by Scheckel and Ryan (2004) suggest that soil acidification and was noted to decrease between RFS studies 1 and 2, which is favorable kinetic conditions for the formation of pyromorphites likely due to the complexation of P with Al, Ca, Fe, and Mn in must have been present in the system. However, even under the soil solution; P sorption to metal oxides and hydroxyapatite; and most favorable stoichiometric and kinetic conditions created by plant uptake. Aluminum and Fe oxides are known to have a great Scheckel and Ryan (2004), the maximum level of pyromorphite affinity for P, and the metal oxides may be sorbing P on release formation achieved peaked at 45% when using a 1% H PO 3 4 into soil solution (Cao et al., 2002). Additionally, Hashimoto et treatment. After treatment with TSP, the lowest values for al. (2007) reports that soils with abundant Al and Fe hydroxides pH of the 4:1, 8:1, and 16:1 P:Pb molar ratio treatment water tend to increase their ability to sorb anions at acidic pH conditions classes studied here were pH 6.90, 6.08, and 5.43, respectively, where mineral surface functional groups are positively charged. compared with a control pH of 7.8 (Table 1). These acidic and Consequently, the creation of acidic pH soil conditions that weakly acidic pH values place them within the range where kinetically favor the formation of pyromorphite may also induce transformation to pyromorphite is kinetically favorable (Xu and the sorption of P to protonated Al and Fe hydroxides surfaces, Schwartz, 1994; Zhang and Ryan, 1999; Scheckel et al., 2003). as described by Hashimoto et al. (2009). The most acidic pH Accordingly, there must be other factors limiting the formation measured in this study was in soil from the 16:1 P:Pb treatment of pyromorphite in soils. at 60 d after treatment (pH = 5.43), which is within a range Studies (Hashimoto et al., 2009; Scheckel and Ryan, 2004) water favorable for pyromorphite formation as well as Al and Fe oxide have suggested that greater organic matter levels in treated soils

1134 Journal of Environmental Quality protonation (Xu and Schwartz, 1994; Zhang and Ryan, 1999; not necessarily represent the views of the US Fish and Wildlife Service, Hashimoto et al., 2009). the State of Missouri, the USEPA, or the funding agencies/sources. The marked increase in Pb sorbed to hydroxyapatite species formation in conjunction with the observed plateau References of chloropyromorphite formation (Fig. 5) has been observed Arnich, N., M.C. Lanhers, F. Laurensot, R. Podor, A. Montiel, and D. previously (Ma et al., 1993; Ma et al., 1994; Ma et al., 1995). Burnel. 2003. In vitro and in vivo studies of lead immobilization by synthetic hydroxyapatite. Environ. Pollut. 124:139–149. doi:10.1016/ Hydroxyapatite is known to selectively remove Pb from solution S0269-7491(02)00416-5 in the presence of aqueous metallic cations such as Al, Cd, Cu, 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 Fe, Ni, or Zn (Ma et al., 1994; Xu and Schwartz, 1994; Laperche micro-X-ray diffraction investigation of lead speciation after the addition of et al., 1996). Thus, an abundance of dissolved metallic cations different phosphorus amendments to a smelter-contaminated soil. J. Environ. in conjunction with the presence of hydroxyapatite may also Qual. 43:488–497. doi:10.2134/jeq2013.07.0281 Basta, N.T., and S.L. McGowen. 2004. Evaluation of chemical immobilization explain the limitations on chloropyromorphite formation in treatments for reducing heavy metal transport in a smelter-contaminated soil. this study. However, the plateau in pyromorphite formation Environ. Pollut. 127:73–82. doi:10.1016/S0269-7491(03)00250-1 observed in Fig. 5b combined with the formation and subsequent 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, reduction of the Pb–hydroxyapatite complex over time, as well sediment, , and phosphorus loss. Soil Sci. Soc. Am. J. 68:1670–1678. as the continued dissolution of the plumbonacrite, suggests doi:10.2136/sssaj2004.1670 that Pb–hydroxyapatite formation did not completely inhibit 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. chloropyromorphite development. In fact, the data suggest that Environ. Qual. 33:522–531. doi:10.2134/jeq2004.5220 Pb desorbed from the hydroxyapatite surface with time (35% in Cao, X., L.Q. Ma, M. Chen, S.P. Singh, and W.G. Harris. 2002. Impacts of phosphate amendments on lead at a contaminated site. Environ. Sci. RFS1 to 29% RFS2 at 16:1 P:Pb) resulted in the formation of Technol. 36:5296–5304. doi:10.1021/es020697j small quantities of additional chloropyromorphite. Cao, R.X., L.Q. Ma, M. Chen, S.P. Singh, and W.G. Harris. 2003. Phosphate-induced We speculate that slow dissolution of Pb minerals metal immobilization in a contaminated site. Environ. Pollut. 122:19–28. doi:10.1016/S0269-7491(02)00283-X initially present in the contaminated soil, P sorption and the Chappell, M.A., and K.G. Scheckel. 2007. Pyromorphite formation and stability after formation of aqueous metallic P complexes, and Pb sorption quick lime neutralization in the presence of soil and clay sorbents. Environ. to hydroxyapatite may be limiting pyromorphite formation 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 in the alluvial soils studied. However, we cannot rule out the amendment on metal immobilization in contaminated soils. J. Hazard. Mater. formation and influence of other phosphate minerals and ideal 134:74–79. doi:10.1016/j.jhazmat.2005.10.027 solutions as inconsequential contributors to the limited amount 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 of pyromorphite formed across all treatment classes in this study and EXAFS. Eur. J. Soil Sci. 45:393–402. doi:10.1111/j.1365-2389.1994. (Ma et al., 1994; Eighmy et al., 1997; Crannell et al., 2000; Baker tb00524.x Crannell, B.S., T.T. Eighmy, J.E. Krzanowski, J.D. Eusden, Jr., E.L. Shaw, and C.A. et al., 2014). Francis. 2000. Heavy metal stabilization in municipal solid waste combustion bottom ash using soluble phosphate. Waste Manage. 20:135–148. doi:10.1016/ Conclusions S0956-053X(99)00312-8 Davis, A., J.W. Drexler, M.V. Ruby, and A. Nicholson. 1993. Micromineralogy of mine The overarching goal of this work was to evaluate potential wastes in relation to lead bioavailability, Butte, Montana. Environ. Sci. Technol. water quality challenges and benefits associated with the 27:1415–1425. doi:10.1021/es00044a018 application of P to Pb-contaminated soils with the hopes 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. of identifying a reasonable remediation scenario for alluvial 37:47–56. doi:10.2134/jeq2007.0151 soils. To the best of our knowledge, this is the first reported 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 experiment to use RFS to evaluate P and metals loss from heavy stabilization in municipal solid waste combustion dry scrubber residue using metal–contaminated soils remediated via P application. As soluble phosphate. Environ. Sci. Technol. 31:3330–3338. doi:10.1021/ a consequence of the multiple lines of evidence generated by es970407c Ford, R.G., P.M. Bertsch, and K.J. Farley. 1997. Changes in transition and heavy metal this experiment, including effluent and soil chemistry from the partitioning during hydrous oxide aging. Environ. Sci. Technol. 31:2028– rainfall simulation studies, direct measurement of Pb uptake in 2033. doi:10.1021/es960824+ plants, and speciation via XANES, we conclude that applying Hashimoto, Y., T.J. Smyth, D. Hesterberg, and D.W. Israel. 2007. growth in relation to ionic composition in magnesium-amended acid subsoils: TSP to the alluvial soil at a rate necessary to achieve a 4:1 P:Pb Implications on root citrate ameliorating aluminum constraints. Soil Sci. Plant molar ratio would be a viable remediation strategy. Out of range Nutr. 53:753–763. doi:10.1111/j.1747-0765.2007.00191.x Hashimoto, Y., M. Takaoka, K. Oshita, and H. Tanida. 2009. Incomplete of the full range of P treatments considered, the 4:1 P:Pb molar transformations of Pb to pyromorphite by phosphate induced immobilization ratio treatment offers a great likelihood of success for reducing investigated by X-ray absorption fine structure (XAFS) spectroscopy. soil Pb bioavailability and the lowest likelihood of potentially 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 adverse environmental consequences. of soil lead using phosphorus. J. Environ. Qual. 30:1214–1221. doi:10.2134/ jeq2001.3041214x Acknowledgments Hillier, S., K. Suzuki, and J. Cotter-Howells. 2001. 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