Environ. Sci. Technol. 2001, 35, 3553-3559
Lead Immobilization Using Phosphoric Acid in a Smelter-Contaminated Urban Soil J O H N Y A N G , * ,† D A V I D E . M O S B Y , ‡ STAN W. CASTEEL,† AND ROBERT W. BLANCHAR† Department of Geological Sciences, Veterinary Medical Diagnostic Laboratory, and Department of Soil and Atmospheric Sciences, University of Missouri, Columbia, Missouri 65211, and Missouri Department of Natural Resources, Jefferson City, Missouri 65102
Transformation of soil lead (Pb) to pyromorphite, a lead phosphate, may be a cost-effective remedial strategy for immobilizing soil Pb and reducing Pb bioavailability. Soil treatment using phosphoric acid (H3PO4) was assessed for its efficacy to reduce Pb solubility and bioaccessibility. Soil containing 4360 mg of Pb kg-1, collected from a smeltercontaminated site in Joplin, MO, was reacted with 1250, 2500, 5000, and 10 000 mg of P kg-1 as H3PO4. The reaction was followed by measurements of Pb bioaccessibility, solubility products, and microprobe analyses. Soluble Pb concentration in the soil decreased with increasing H3PO4 addition. Adding 10 000 mg of P kg-1 reduced bioaccessible Pb by 60%. The logarithm of bioaccessible Pb decreased as a linear function of increasing H3PO4 addition with an R2 of 0.989. A higher soil/solution ratio was required to extract bioaccessible Pb after the treatment. Microprobe analyses showed that the Pb particles contained P and Cl after the reaction, and the spectra generated by the wavelengthdispersive spectrometer were similar to those of synthetic chloropyromorphite. Lead solubility in the P-treated soil was less than predicted for hydroxypyromorphite [Pb5(PO4)3OH] and greater than predicted for chloropyromorphite [Pb5(PO4)3Cl]. The P treatment caused ∼23% redistribution of soil Pb from the clay and silt size fractions to the sand fraction. Soil treatment with H3PO4 resulted in the formation of a compound similar to chloropyromorphite and reduced bioaccessibility of soil Pb, which may have a potential as an in situ technique for Pb-contaminated soil remediation.
Introduction Ingestion of lead (Pb)-contaminated soil has been identified as a threat to human health, especially to children’s health in urban areas (1). In Jasper County, Missouri, ∼2600 residential properties have been contaminated with >800 mg of Pb kg-1 by a former Pb smelter and require remedial action (2). Surveys conducted by the Missouri Department of Health in 1994 and the City of Joplin Health Department in 1995 showed that 14% of the children under 7 years of age living in the historic smelting area had blood Pb levels >100 * Corresponding author phone: (573) 884-1453; fax: (573) 8825458; e-mail:
[email protected]. † University of Missouri. ‡ Missouri Department of Natural Resourcs. 10.1021/es001770d CCC: $20.00 Published on Web 07/27/2001
2001 American Chemical Society
µg L-1 and required intervention by the Center for Disease Control; the blood Pb levels in children were directly related to Pb concentrations in soil (3, 4). Current remedial action is to excavate contaminated soils and replace them with uncontaminated soils at an estimated cost of nearly $30 million (2). A cost-effective remedial alternative that safeguards human health and the environment from the Pb contamination is needed. The hazard of soil Pb to human health is proportional to its bioavailability, which is defined as the ability of soil Pb in an oral dose to be absorbed into the systemic circulation (5). Lead bioavailability is assumed to largely depend on the mineral species in which soil Pb is incorporated and their dissolution in the gastrointestinal tract (6, 7). It is believed that conversion of soil Pb to species that bind Pb in stable forms could reduce Pb solubility and bioavailability. Transformation of soil Pb to minerals having low solubility would be a potential cost-effective remedial strategy for reducing the health and environment risk. Conversion of soil Pb to pyromorphite, a lead phosphate [Pb5(PO4)3(OH, Cl, F...)], could immobilize soil Pb and reduce its bioavailability. Pyromorphite is much less soluble than most lead minerals (e.g., PbCO3 and PbO) in the gastrointestinal tract and is chemically and biologically stable in the surface soil environment. Formation of pyromorphite involves dissolution of Pb solids and precipitation of pyromorphite. The rate of pyromorphite precipitation is kinetically rapid and controlled by availability of soluble Pb and P as shown in
5Pb2+ + 3H2PO4- + Cl- S Pb5(PO4)3Cl(s) + 6H+ log K ) -25.05 (1) If sufficient soluble P is provided, dissolution of Pb solids would be a limiting factor for pyromorphite formation. Dissolution of soil Pb has been shown to increase with decreasing pH (8). Neutralization of protons (H+) generated during pyromorphite precipitation shown in eq 1 could favor the reaction toward pyromorphite formation. Thus, initially acidifying soil followed by gradually increasing soil pH would enhance the transformation of soil Pb to pyromorphite. Reduction of Pb concentration in aqueous and soil solutions through addition of hydroxyapatite or phosphate rocks has been reported (9-12). Formation of pyromorphite from soil Pb or various Pb species [e.g., cerrusite (PbCO3), anglesite (PbSO4), galena (PbS), and goethite-adsorbed Pb] that were reacted with phosphate minerals has been also confirmed (1, 8, 11, 13-18). Reduction of Pb bioavailability in smelter-contaminated soils treated with triple superphosphate or phosphate rock plus manganese oxide and the formation of “pyromorphite-like minerals” were observed (19). However, application of hydroxyapatite or phosphate rocks to calcareous soil could restrict the transformation of soil Pb toward pyromorphite because dissolution of Pbbearing solids and availability of soluble P are limited. It is believed that adding H3PO4 to calcareous soil would lower soil pH to facilitate dissolution of soil Pb and increase activity of soluble P to enhance pyromorphite formation. Applications of H3PO4 to various industrial wastes has been shown to stabilize and reduce leaching of heavy metals (20-22). This study was conducted to assess the efficacy of H3PO4 treatment for reducing Pb solubility and bioaccessibility in a calcareous smelter-contaminated urban soil. Objectives were to (i) measure soil Pb bioaccessibility during the treatment periods; (ii) determine the Pb solubility products VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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at the end of the reaction; and (iii) identify solid-phase Pb species formed after the reaction.
Materials and Methods Soil Materials and Characterization. Soil was collected from a Pb-contaminated residential site, ∼0.25 mi from a former Pb smelter in northwest Joplin, MO. The soil was air-dried, passed through a 250 µm sieve, composited, and thoroughly mixed. Clay, silt, and sand contents, pH, cation exchange capacity (CEC), neutralizable acidity (NA), total carbon and nitrogen, and available phosphorus of the soil were determined by the Missouri Soil Characterization Laboratory following standard USDA procedures (23). Soil particle size fractions were obtained as described by Whittig and Allardice (24). Soil or fractions of soil were digested with 3:2 HNO3: HClO4 as described by Blanchar et al. (25) and metals measured by emission-induced coupled plasma spectrometry (ICP). Montana Soil 2710, from the National Institute of Standards and Technology (NIST), was included for quality control. Solid Pb species were analyzed by microprobe analysis as described by Link et al. (26). Mineralogy was qualitatively characterized by X-ray diffraction (XRD). The pH buffering capacity of the soil was determined by adding 0, 1250, 2500, and 5000 mg of P kg-1 as H3PO4 to the soil at a 1:1 soil/solution ratio and measuring the pH after 1, 2, 7, 14, 35, and 60 days. Phosphate adsorption by the soil was measured by adding H3PO4 ranging from 0 to 2500 mg of P kg-1 to the soil at a 1:10 soil/solution ratio. The suspensions were shaken at room temperature at 50 rpm, sampled at 1, 2, 4, 8, and 16 days after the addition, filtered through Whatman 0.2 µm filter paper, and analyzed for P and Pb. Treatments. Duplicate treatments were prepared by adding H3PO4 at a rate of 0, 1250, 2500, and 5000 mg of P kg-1 plus KCl at 500 mg of Cl kg-1 to 750 g of soil. Potassium chloride was added to provide Cl source for formation of chloropyromorphite. Materials were evenly applied to soils in plastic containers, thoroughly mixed, adjusted to field capacity moisture (20% gravimetric water content) with deionized water, and incubated at room temperature for 60 days. An additional 5000 mg of P kg-1 treatment was incubated at 55 °C to evaluate whether a higher temperature facilitates the transformation reaction. During the incubation, soils dried from field capacity to air-dry moisture content, and then deionized water was added to adjust soil moisture to field capacity to simulate natural wet-dry cycles. The soils were sampled, 20 g each, at 5, 10, 20, 40, and 60 days during the incubation period. At the end of the incubation, the soils were oven-dried, passed through a 250 µm sieve, and saved for the analyses. After 40 days of incubation, a 10 000 mg of P kg-1 treatment was created by adding an additional 5000 mg of P kg-1 as NaH2PO4 to a 5000 mg of P kg-1 treatment. The pH of this treatment was adjusted to 6.5 by adding CaO. An additional amount of P was applied to further enhance the transformation processes. Analytical Procedures. Lead bioaccessibility (in vitro) is an estimate of Pb bioavailability (in vivo), which simulates Pb dissolution under gastrointestinal conditions using a chemical extraction. In this study, a modified physiologically based extraction test (PBET) (5) using 0.011 M HCl (pH 2) solution was selected for extracting bioaccessible Pb. The extraction at a 1:100 soil/solution ratio resulted in a final solution pH of 2.5. Soil, 0.40 g, was placed in a 60-mL Nalgene bottle, 40 mL of 0.011 M HCl was added, and then the bottle was rotated at 30 rpm at 37 °C for 60 min. The solution was taken up in a 10-mL plastic syringe and immediately passed through a Whatman 0.2 µm filter paper. The filtrates were analyzed for pH, electric conductance (EC), Pb [by atomic 3554
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absorption spectrophotometry (AA) in a 0.1% La solution], and P [using the molybdenum blue method (27)]. To ensure quality of the results, the soils were analyzed with eight measurements per treatment. Standard solutions with the same matrix as the samples were run before and after sample measurements. Instrument stability was checked with blank and internal standards at 10 sample intervals. Measurements of Pb, P, pH, and EC in the 0.01 N HCl extracts were used to calculate solubility products of soil Pb on the basis of the following assumptions:
total Pb ) Pb2+ + PbOH+ + PbCl+ + PbH2PO4+
(2)
total P ) H3PO4 + H2PO4- + HPO42- + PO43- +
CaH2PO4+ (3)
EC and pH measurements were used to estimate ionic strength, activity coefficient, and H+ activity in the solution as described by Lindsay (28). The activity of each aqueous Pb or P species described in eqs 2 and 3 was calculated using the stability constant of each species (29). Then the solubility products of lead phosphates in the treated soils were estimated. Lead distributions in clay, silt, and sand fractions were determined after ultrasonic dispersion and separation by centrifuge (24). Each soil fraction was digested with 1 M HNO3 at 100 °C for 1 h and Pb measured by AA in a 0.1% La solution. Solid Pb speciation was done by microprobe analysis. Soils were mounted on 10-mm-diameter Al stubs with double-sided sticky tape and then carbon-coated. Microprobe analysis was performed on an AMRAY-1600T microprobe with operating parameters of 10 keV, 30 mA emission current, and 40 nA beam current. A low kiloelectronvolt level was selected to allow the electron beam to penetrate only 1 µm in depth, which reduced interferences of the minerals surrounding the Pb particles. Backscattering (BS) electron was initially used to identify particles with a high atomic number, and then energy dispersive spectroscopy (EDS) was used to determine whether the particles contain Pb. Particles containing Pb were scanned from 1.9 to 3.1 keV with 200 channel wavelength dispersive spectroscopy (WDS) to determine the elemental composition of the particles. The scanning range covered P, Pb, S, and Cl elements. WDS instead of EDS was used to determine the composition because of overlaps of the Pb, Cl, and S peaks in the EDS spectrum. Morphology of the particles was observed with scanning electron microscopy (SEM). Chloropyromophite was synthesized from PbCl2 and NH4H2PO4 as described by Wazer (30), characterized by XRD, and included in the microprobe analyses for quality control.
Results and Discussion Soil Characterization. The soil was a calcareous silt loam with relatively high carbon and low P contents (Table 1). The soil contained 4361 mg of Pb kg-1 and 4680 mg of Zn kg-1. Relatively high Pb and low P levels in the soil were suited for H3PO4 treatment. XRD analysis indicated that quartz, illite, and kaolinite were major minerals in the 50 µm fraction. The presence of dolomite contributes to high C content and alkaline conditions of the soil. Lead concentrations in the soil fractions increased as particle size decreased. However, when the amount of each fraction is considered, 18% of total Pb was associated with clay, 60% with silt, and 22% with sand. The Pb distributions in the size fractions were consistent with a site contaminated by the airborne particles. Cerrusite (PbCO3) and lead oxides, illite > kaolinite a
Pb Distribution in Soil Fractions (mg kg-1) silt 4953 ( 98
sand
3483 ( 137
Mineral Components
Data represent an average of triplicates with a standard deviation.
b
Cation exchange capacity and neutralizable acidity, respectively.
FIGURE 2. Soluble P concentrations in a 1:10 soil/solution ratio as a function of H3PO4 addition and time. FIGURE 1. Effect of H3PO4 addition and time on the pH of 1:1 soil/ solution suspensions. in untreated soil. The Pb species and the particle sizes were similar to those reported by Casteel et al. (31) and Roy F. Weston, Inc. (32) in residential soils collected from similar sites in Jasper County. Cerrusite and lead oxides are both relatively soluble in acid, and the treatment of the soil using H3PO4 would favor their dissolution and the transformation to less soluble forms. Soil pH was significantly reduced with increasing amounts of added H3PO4 followed by a gradual pH increase with time (Figure 1). Addition of 5000 mg of P kg-1 initially lowered the soil pH by 3 units from 7.22 to 4.34, but the pH gradually increased to 5.53 after 60 days. Increased pH over time may be due to dissolution of dolomite present in the soil. Initial low pH induced by H3PO4 would favor dissolution of soil Pb, and the gradual pH increase would favor pyromorphite formation. Addition of H3PO4 to the soil increased soluble P in solution, which then decreased with time (Figure 2). Decreased P concentration could result from P reaction with Fe, Al, Ca, and Zn compounds in soil and as well as precipitations of lead phosphates. Formation of calcium phosphates, tertiary metal phosphates, and apatite family minerals were observed in the reaction of calcium-based
industrial wastes with soluble P (20-22). The rate of P decline was initially high and decreased with time. The maximum amount of P adsorbed by the soil was estimated to be ∼4000 mg kg-1 after 60 days, on the basis of the solid solution model described by Blanchar and Stearman (33). The maximum amount of H3PO4 added (5000 mg of P kg-1) was based on the P adsorption maximum and provided 7.6 mol of P/mol of Pb. Soluble Pb in solutions used for assessing P adsorption was also measured. Data presented in Figure 3 showed that soluble Pb was significantly reduced as H3PO4 addition increased. The reduction was greater at 2 weeks than at 1 week. However, the reductions with time appeared to be attenuated by increasing H3PO4. This might reflect a higher dissolution rate of Pb-bearing solids induced by the acidity of higher H3PO4 addition and rapid precipitation of lead phosphates. Data also suggest that reductions of soluble Pb could be achieved at a lower H3PO4 rate with a longer incubation time. The reduction of soluble Pb over time in untreated soil may result as more stable Pb precipitates form or as Pb is adsorbed by clay minerals. Bioaccessible Pb. Increasing amounts of added H3PO4 and elevating temperature significantly decreased bioaccessible Pb in the soil; however, the reductions with incubation time were not significantly different during the 60 days VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Bioaccessible Pb Concentrations as a Function of Time and Amount of H3PO4 Added to Soil P addition (mg of P kg-1) 0 1250 2500 5000 5000 at 55 °C 10000 a
bioaccessible Pba (mg kg-1) after incubation for 20 days 40 days 60 days
5 days
10 days
1513 ( 78 1357 ( 56 1275 ( 23 1169 ( 64 975 ( 34
1375 ( 66 1121 ( 71 1060 ( 50 807 ( 41
1557 ( 45 1312 ( 62 1210 ( 39 935 ( 23 822 ( 38
1499 ( 73 1304 ( 50 1192 ( 45 911 ( 38 854 ( 60
70 days
1645 ( 102
1789 ( 84
890 ( 37 701 ( 41
564 ( 23
400 days
597 ( 12
Average of four measurements for each treatment.
FIGURE 3. Soluble Pb concentrations in a 1:10 soil/solution ratio as a function of H3PO4 addition and time.
FIGURE 4. Lead concentrations in 0.011 M HCl extracts from untreated soil and soil treated with 10 000 mg of P kg-1 as H3PO4 after 60 days of incubation.
(Table 2). Logarithms of mean bioaccessible Pb at room temperature were a linear function of the amount of H3PO4 added as shown in
log(bioaccessible Pb) ) 3.17 - 0.0000376 (H3PO4) R2 ) 0.989 (4) The soil averaged 1563 mg kg-1 of bioaccessible Pb, 36% of total Pb, before treatment and 15% after treatment with 10 000 mg of P kg-1. Bioaccessible Pb was reduced 39% (percentage of initial mean minus treatment mean over initial mean) by the addition of 5000 mg of P kg-1, which was similar to the 25-35% reductions reported by Hettiarachchi et al. (19) when similar soils were treated with 5000 mg of P kg-1 using triple superphosphate or phosphate rock. Hettiarachchi et al. (19) also reported that the bioavailability reductions did not vary significantly over time. Bioaccessible Pb values were consistently lower when the reaction was carried out at 55 °C than when the reaction was carried out at room temperature. In the 5000 mg of P kg-1 treatment at 55 °C mean bioaccessible Pb was 885 mg of Pb kg-1 during the 60 days and was 956 mg of Pb kg-1 at room temperature. Reductions in Pb bioaccessibility due to increased temperature indicate that higher temperature would favor transformation of soil Pb to nonbioaccessible forms. The data in Table 2 indicate that bioaccessible Pb was partially transformed to nonbioaccessible forms. Incomplete transformation may be attributed to incomplete dissolution of Pb-bearing solids during the reaction. Dissolution of soil Pb has been considered to be the factor controlling Pb transformation by H3PO4 and is largely dependent on soil pH, Pb mineralogy, and the degree of Pb encapsulation in soil minerals (6-8). Although addition of H3PO4 to the soil reduced pH and should accelerate dissolution of soil Pb, the dissolution rate might decrease over time due to attenuation 3556
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FIGURE 5. Total Pb in soil fractions of untreated soil and soil treated with 10 000 mg of P kg-1 as H3PO4 after 60 days of incubation. of acidity caused by dissolution of dolomite and soil pH buffering. As a result, the Pb species that were relatively nonlabile would be incompletely dissolved. High Zn and Fe in the soil were reported to potentially inhibit the formation of pyromorphite (35), which may also partially account for incomplete transformation of soil Pb. Lead bioaccessibility is also a function of Pb dissolution during the extraction processes and is controlled by geochemical factors such as Pb mineralogy, the degree of encapsulation, and dissolution kinetics (6, 7). It has been suggested that newly formed Pb species, which have relatively high solubility compared with their aged forms, may interact with organic ligands during the extracting processes and contribute to higher Pb bio-
FIGURE 6. WDS patterns for Pb particles in untreated soil and H3PO4-treated soils after 60 days of incubation.
TABLE 3. Lead Solubility Products Estimated in Soil Treated with 10 000 mg of P kg-1 after 60 Days of Incubation -log K Pb species
standarda
calculated
Pb5(PO4)3Cl 5pPb + 3pH2PO4 + pCl - 6pH
25.02
21.04
Pb5(PO4)3OH 5pPb + 3pH2PO4 - 7pH
4.14
16.57
Pb3(PO4)2 3pPb + 2pH2PO4 - 4pH
5.26
11.16
a
Data from Lindsay (28, 29).
accessibility (34). Reductions of Pb bioaccessibility at 70 days when the soils were oven-dried may suggest that the drying process increased crystallization of newly formed lead phosphates. The bioavailability of soil Pb is associated with the solubility and dissolution rate of soil Pb in the gastrointestinal tract. A number of physiological factors in the gastrointestinal tract such as the soil/fluid ratio, stomach content, and stomach emptying time may affect the Pb dissolution. The
effect of the soil/solution ratio on Pb bioaccessibility measured in 0.011 M HCl, before and after the P treatment, was assessed. Data shown in Figure 4 indicated that addition of 10 000 mg of P kg-1 to the soil decreased bioaccessible Pb and a higher soil/solution ratio was required for Pb extraction from the P-treated soils. The highest bioaccessible Pb was measured at the 1:100 ratio in the untreated soil and at the 1:200 ratio in the P-treated soil. At a 1:50 soil/solution ratio, bioaccessible Pb was below the detection limit in the P-treated soil, whereas 3 mg of Pb L-1 was measured in the untreated soil. Measured Pb concentrations at the 1:100 ratio were consistent with Pb bioaccessibility shown in Table 2. Data indicate that Pb bioaccessibility is sensitive to solution volume, and a higher soil/solution ratio or large volume of stomach fluid is required for Pb extraction due to lower Pb extractability by the P treatment, suggesting that ingestion of soil Pb at a low volume of stomach fluid would result in less dissolution of soil Pb and have less potential to be absorbed. Distributions of Pb in Soil Fractions. The H3PO4 treatments also caused redistribution of soil Pb among soil fractions. In 10 000 mg of P kg-1 treated soil, the Pb concentration in the sand fraction increased from 3483 to 6136 mg kg-1, whereas the Pb in the clay and the silt decreased VOL. 35, NO. 17, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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which shows that one particle was an individual solid and the other was attached to a soil grain. This study demonstrates that H3PO4 treatment of smeltercontaminated soil effectively reduced Pb bioaccessibility and solubility and has the potential to lower the bioavailability of soil Pb. The treatment resulted in the formation of a compound similar to chloropyromorphite in chemical composition, although slightly more soluble and without the crystal form expected. Results suggest that H3PO4 treatment should be further considered as a cost-effective remedial strategy for in situ immobilization of soil Pb.
Acknowledgments This research was funded by the U.S. Environmental Protection Agency Region VII and the Missouri Department of Natural Resources. Although the research described in this paper has been undertaken by the U.S. EPA and MDNR, it has not been subjected to the agency’s required peer and policy review and therefore does not necessarily reflect the views of the agencies and no official endorsement should be inferred.
Literature Cited FIGURE 7. SEM photographs of Pb particles shown in Figure 6 from soil treated with 10 000 mg of P kg-1. by 48 and 27%, respectively (Figure 5). The total amounts of Pb in clay, silt, and sand fractions of untreated soil were 17, 59, and 24%, respectively. In the H3PO4-treated soil, Pb in the sand fraction increased to 46% of total Pb. The redistribution of soil Pb may result from precipitation of larger individual lead phosphates or formation of fine precipitates on the surface of sand sized particles. Solubility Products. Measurements of Pb, P, pH, and EC in 0.011 M HCl extracts of soil treated with 10 000 mg of P kg-1 were used to estimate solubility products of the Pb species formed. The calculated solubility constants of the Pb solids were greater than that of Pb3(PO4)2 and hydroxypyromorphite and less than that of chloropyromorphite (Table 3). The solution was undersaturated with respect to hydroxypyromorphite and Pb3(PO4)2 and supersaturated with respect to chloropyromorphite. Isomorphic substitution into the apatite family minerals results in mixtures described as tertiary metal phosphates [e.g., Pb5(PO4)3Cl, Ca3(PO4)2] or as ideal solid solutions [e.g., (Pb2, Ca)(PO4)2] that were reported as solid phases controlling for Pb2+, Ca2+, and Zn2+ in the Ca-based industrial wastes reacted with soluble P (21). Formation of poorly crystalline chloropyromorphite or substituted mixtures may explain Pb solubility in the treated soil. Solid Speciation of Pb. Microprobe analysis was used to examine Pb solids in untreated and P-treated soils to verify whether pyromorphites were formed. Microprobe analysis by WDS illustrated that in P-treated soils those particles containing Pb also contained P and Cl, whereas in untreated soil Pb occurred in particles with no P and Cl (Figure 6). The WDS patterns in P-treated soils were similar to those of a synthetic chloropyromorphite standard. The analyses suggest that chloropyromorphite or a “chloropyromorphite-like mineral” might be formed after the P treatment. SEM analysis showed that “chloropyromorphite-like minerals” were heterogeneously distributed in the sample, ∼10-50 µm in size, and not in the classic five-sided columnar structure of chloropyromorphite. SEM images of Pb particles were similar in all P-treated soils and are represented by two particles from the 10 000 mg of P kg-1 treatment shown in Figure 7, 3558
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(1) Cotter-Howells, J.; Thomtom, I. Environ. Geochem. Health 1991, 13 (2), 127-135. (2) Record of decision residential yard and mine waste yard soils operable units 2 and 3, Oronogo-Duenweg Mining Belt Site, Jasper County, Missouri: 1996; U.S. Environmental Protection Agency Region VII, Kansas City, KS, 1996. (3) Lead and cadmium exposure study in Jasper County Superfund site, Jasper County, Missouri: 1994; Missouri Department of Health, Jefferson City, MO, 1994. (4) Report to Jasper County EPA Superfund Citizen’s Task Force: 1995. City of Joplin Health Department, Joplin, MO, 1995. (5) Ruby, M. V.; Davis, A.; Schoof, R.; Eberle, S.; Sellstone, C. M. Environ. Sci. Technol. 1996, 30, 422-430. (6) Ruby, M. V.; Davis, A.; Kempton, J. H.; Drexler, J. W.; Bergstrom, P. D. Environ. Sci. Technol. 1992, 26, 1242-1248. (7) Davis, A.; Drexler, J. W.; Ruby, M. V.; Nicholson, A. Environ. Sci. Technol. 1993, 27, 1415-1425. (8) Zhang, P. C.; Ryan, J. A.; Yang, J. Environ. Sci. Technol. 1998, 32, 2763-2768. (9) Nriagu, J. O. Geochim. Cosmochim. Acta 1974, 38, 887-898. (10) Xu, Y.; Schwartz, F. W. J. Contam. Hydrol. 1994, 15, 187-206. (11) Ma, Q. Y.; Traina, S. J.; Logan, T. J.; Ryan, J. A. Environ. Sci. Technol. 1993, 27, 1803-1810. (12) Ma, Q. Y.; Logan, T. J.; Traina S. J. Environ. Sci. Technol. 1995, 29, 1118-1126. (13) Ruby, M. V.; Davis, A.; Nicholson, A. Environ. Sci. Technol. 1994, 28, 646-654. (14) Laperche, V.; Traina, S. J.; Gaddam, P.; Logan, T. J. Environ. Sci. Technol. 1996, 30, 3321-3326. (15) Zhang, P. C.; Ryan, J. A. Environ. Sci. Technol. 1999, 33, 625630. (16) Zhang, P. C.; Ryan, J. A. Environ. Sci. Technol. 1998, 32, 33183324. (17) Zhang, P. C.; Ryan, J. A. Environ. Sci. Technol. 1999, 33, 618624. (18) Zhang, P. C.; Ryan, J. A.; Bryndzia, L. T. Environ. Sci. Technol. 1997, 31, 2673-2678. (19) Hettiarachchi, G. M.; Pierzynski, G. M.; Ransom, M. D. Environ. Sci. Technol. 2000, 34, 4614-4619. (20) Eighmy, T. T.; Crannell, B. S.; Butler, L.; Cartledge, F. K.; Emery, E. F.; Oblas, D.; Krzanowski, J. E.; Eusden, J. D., Jr.; Shaw, E. L.; Francis, C. A. Environ. Sci. Technol. 1997, 31, 3330-3338. (21) Crannell, B. S.; Eighmy, T. T.; Krzanowski, J. E.; Eusden, J. D., Jr.; Shaw, E. L.; Francis, C. A. Waste Manag. 2000, 20, 135-148. (22) Eighmy, T. T.; Crannell, B. S.; Krzanowski, J. E.; Butler, L.; Cartledge, F. K.; Emery, E. F.; Eusden, J. D., Jr.; Shaw, E. L.; Francis, C. A. Waste Manag. 1998, 18, 513-524. (23) Agricultural. Handbook 463; Soil Survey Staff; U.S. Department of Agriculture: Washington, DC, 1975. (24) Whittig, L. D.; Allardice, W. R. Methods of Soil Analysis, Part I. Physical and Mineralogical Methods: Agronomy. Monograph no 9, 2nd ed.; Agronomy Society of American, Madison, WI, 1986; p 336-342
(25) Blanchar, R. W.; Rehm, G.; Caldwell, A. C. Soil Sci. Soc. Am. Proc. 1968, 29, 71-72. (26) Link, T. E.; Ruby, M. V.; Davis, A.; Bicholson, A. D. Environ. Sci. Technol. 1994, 28, 985-988. (27) Murphy, J.; Riley, H. P. Anal. Chem. Acta 1968, 27, 31-36. (28) Lindsay, W. L. Chemical Equilibria in Soils; Wiley: New York, 1986; pp 12-18. (29) Lindsay, W. L. Chemical Equilibria in Soil; Wiley: New York, 1986; pp 330-331. (30) Wazer, J. R. Van. Phosphorus and Its Compounds, Vol. I, Chemistry; 1958; p 867. (31) Casteel, S. W.; Weiss, C. P.; Bratitin, W. B. Report to U.S. Environmental Protection Agency; Document Control 04800030-0155; U.S. Environmental Protection Agency: Washington, DC, 1996.
(32) Roy F. Weston Inc., Final Phase II Bioavailability StudiessSample Preparation and Analysis; Document Control 04800-030-0126; U.S. Environmental Protection Agency, Washington, DC, 1995. (33) Blanchar, R. W.; Stearman, G. K. Soil Sci. Soc. Am. J. 1985, 49, 578-583. (34) Sauve, S.; McBride, M. Environ. Sci. Technol. 1998, 32, 388393. (35) Ma, L. Q. J. Environ. Qual. 1996, 25, 1420-1429.
Received for review October 16, 2000. Revised manuscript received June 13, 2001. Accepted June 18, 2001. ES001770D
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