Field test of in situ soil amendments at the Tar Creek National Priorities List Superfund site

A range of soil amendments including diammonium phosphate fertilizer (DAP), municipal biosolids (BS), biosolids compost, and Al- and Fe-based water treatment residuals were tested on Pb-, Zn-, and Cd-contaminated yard soils and tailings at the Tar Creek NPL site in Oklahoma to determine if amendments could restore a vegetative cover and reduce metal availability in situ. For the yard soils, all amendments reduced bioaccessible (assessed with a physiologic-based extraction method) Pb, with reductions ranging from 35% (BS+Al, DAP 0.5%, DAP+Compost+Al) to 57% (Compost+Al). Plant Zn (Cynadon dactylon L.) and NH4 NO3-extractable Cd and Zn were also reduced by a number of amendments. For the tailings, all amendments excluding BS reduced bioaccessible Pb, with the largest reductions observed in the DAP 3% and DAP3%+BS treatments (75 and 84%). Plant growth was suppressed in all treatments that contained DAP for the first season, with the highest growth in the treatments that included compost and biosolids. In the second year, growth was vigorous for all treatments. Plant Zn and Cd and extractable metal concentration were also reduced. A number of treatments were identified that reduced bioaccessible Pb and sustained a healthy plant with reduced metal concentrations. For the yard soil, Compost+Al was the most effective treatment tested. For the tailings, BS+DAP 1% was the most effective treatment tested. These results indicate that in situ amendments offer a remedial alternative for the Tar Creek site.     

Cottongrass effects on trace elements in submersed mine tailings

Phytostabilization may limit the leakage of metals and As from submersed mine tailings, thus treatment of acid mine drainage with lime could be reduced. Tall cottongrass (Eriophorum angustifolium Honckeny) and white cottongrass (E. scheuchzeri Hoppe) were planted in pots with unlimed (pH 5.0) and limed (pH 10.9) tailings (containing sulfides) amended with sewage sludge (SS) or a bioashsewage sludge mixture (ASM). Effects of the amendments on plant growth and plant element uptake were studied. Also, effects of plant growth on elements (Cd, Cu, Pb, Zn, and As), pH, electrical conductivity (EC), and concentrations of SO4(2-), in the drainage water as well as dissolved oxygen in tailings, were measured. Both plant species grew better and the shoot element concentrations of white cottongrass were lower in SS than in ASM. Metal concentrations were lowest in drainage water from limed tailings, and plant establishment had little effect on metal release, except for an increase in Zn levels, even though SO4(2-) levels were increased. In unlimed tailings, plant growth increased SO4(2-) levels slightly; however, pH was increased and metal concentrations were low. Thus, metals were stabilized by plant uptake and high pH. Amendments or plants did not affect As levels in the drainage water from unlimed tailings. Thus, to reduce the use of lime for stabilizing metals, phytostabilization with tall cottongrass and white cottongrass on tailings is a sound possibility.     

Metal bioavailability and speciation in a wetland tailings repository amended with biosolids compost,wood ash,and sulfate

Lead poisoning of waterfowl from direct ingestion of wetland mine tailings has been reported at the Coeur d'Alene River basin in Idaho. A greenhouse study was conducted to evaluate the effects of surface applications of amendments on lead bioavailability in the tailings. Treatments included sediment only, and sediment with three different surface amendments: (i) biosolids compost plus wood ash, (ii) compost + wood ash + a low SO4(2-) addition as K2SO4, and (iii) compost + wood ash + a high SO4(2-) addition. Measured variables included growth and tissue Pb, Zn, and Cd concentration of arrowhead (Sagittaria latifolia Willd.) and cattail (Typha latifolia L.) and soil pH, redox potential (Eh), pore water Pb, Pb speciation by X-ray absorption spectroscopy, and in vitro Pb bioavailability. The compost + ash amendment alleviated phytotoxicity for both plant species. Bioavailability of Pb as measured by a rapid in vitro extract decreased by 24 to 34% (over control) in the tailings directly below the amendment layer in the compost + SO4 treatments. The ratio of acid volatile sulfide (AVS) to simultaneously extracted metals (SEM) also indicated a reduction in Pb bioavailability (1:40 control, 1:20 compost, 1:8 compost + low SO4, and 1:3 compost + high SO4). Extended X-ray adsorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopy data indicated that lead sulfide was greater after 99 d in the treatments that included additions of sulfate. These results indicated that, under reducing conditions, surface amendments of compost + wood ash (with or without sulfate) decreased the bioavailability of Pb in metal-contaminated mine tailings.     

Ecosystem function in alluvial tailings after biosolids and lime addition

Municipal biosolids and agricultural limestone were incorporated into the surface of alluvial highly acidic, metal-contaminated mine tailings in Leadville, CO, in 1998. Amended sites were seeded and a plant cover was subsequently established. A range of chemical and biological parameters were measured over time to determine if treatment was sufficient to restore ecosystem function. An uncontaminated upstream control (UUC), a contaminated vegetated area (CVA), and soils collected from the tailings deposits before amendment addition were used for comparison. Standard soil extracts showed decreases in extractable Pb, Zn, and Cd in the amended soils. Increased CO2 evolution, reduced N2O, and elevated NO3- in the amended tailings indicated an active microbial community. Levels of CO2 and NO3- were elevated in comparison with the CVA and UUC. Ryegrass (Lolium perenne L.) and earthworm (Eisenia foetida) survival and metal uptake values were similar in amended tailings to a laboratory control soil. Ryegrass and worms in unamended tailings died. Field plant diversity was lower in amended areas than in CVA or UUC, with a higher percentage of the vegetative cover consisting of grasses. Small mammal analysis showed a low potential for elevated body Cd and Pb in the amended tailings. A re-entrainment study using fathead minnows (Pimephales promelas) showed no danger for resuspended amended tailings, as survival of fish was similar to the laboratory control. Data suggest that ecosystem function has been restored to the amended tailings, but that these systems are not yet in equilibrium.     

Germination,Growth, and Nodulation of Sesbania rostrata Grown in Pb/Zn Mine Tailings

Sesbania rostrata in pure and amended Pb/Zn tailings. About 90% of seeds of S. rostrata germinated in pure Pb/Zn tailings, which contained high concentrations of Pb, Zn, Cu, and Cd. Although seedling growth suffered from the adverse environment of Pb/Zn tailings, they became established on tailings stands, in the greenhouse, as well as on the actual tailings dam, and completed their life cycle in 4 months. Dry matter production and nitrogen accumulation was 3200 kg/ha and 69.4 kg/ha, respectively in the actual tailings dam. Applying inorganic fertilizer to Pb/Zn tailings led to no obvious improvement in growth and nodulation of S. rostrata, while tailings amended by river sediment or domestic refuse rich in organic matter improved the growth and nodulation of the species. Azorhizobium caulinodans survived and formed N-fixing stem and root nodules in S. rostrata grown in pure Pb/Zn tailings with a nodule biomass exceeding 300 mg fresh matter per plant.     

In situ soil treatments to reduce the phyto- and bioavailability of lead, zinc, and cadmium

A study was established near a former Zn and Pb smelter to test the ability of soil amendments to reduce the availability of Pb, Zn, and Cd in situ. Soil collected from the field was amended in the lab with P added as 1% P-H3PO4, biosolids compost added at 10% (referred to hereafter as "compost"), and a high-Fe by-product (referred to hereafter as "Fe") + P-triple superphosphate (TSP) (2.5% Fe + 1% P-TSP) and incubated under laboratory conditions at a constant soil pH. Changes in Pb bioavailability were measured with an in vitro test and a feeding study with weanling rats. Field-amended and incubated soils using these plus additional treatments were evaluated using the in vitro extraction and tall fescue (Festuca arundinacea Schreb. cv. Kentucky-31) metal concentration. Reductions were observed across all parameters but were not consistent. In the feeding study, the 1% P-H3PO4 and compost treatments resulted in a decrease of 26% in rat tissue Pb concentration compared with the control soil. The 2.5% Fe + 1% P-TSP showed a 39% decrease. The 1% P-H3PO4 treatment caused the greatest reduction in in vitro extractable Pb from field samples (pH 2.2) with a measured reduction of 66%, while the compost treatment had a 39% reduction and the 2.5% Fe + 1% P-TSP treatment a 50% reduction. The in vitro extraction (pH 1.5) run on field samples showed no reduction in the compost or Fe treatments. The 1% P-H3PO4 treatment was the most effective at reducing plant Pb, Zn, and Cd.     

Accelerated weathering of biosolid-amended copper mine tailings

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.     

Vertical distribution and speciation of trace metals in weathering flotation residues of a zinc/lead sulfide mine

Sulfide-bearing mine tailings are a serious environmental problem around the world. In this study, the vertical distribution and speciation of Zn and Pb in the fine-grained flotation residues of a former sulfide ore mine in Germany were investigated to assess the inorganic weathering processes that effect the environmental risk arising from this site. Total metal contents were determined by X-ray fluorescence spectroscopy (XRF). Mobilizable fractions of Zn, Pb, Fe, and Mn were quantified by sequential chemical extractions (SCE). Furthermore, the speciation of Zn was analyzed by Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) to identify the residual Zn species. The variations in pH and inorganic C content show an acidification of the topsoil to pH 5.5. EXAFS results confirm that Zn is mainly bound in sphalerite in the subsoil and weathering reactions lead to a redistribution of Zn in the topsoil. A loss of 35% Zn and S from the topsoil compared with the parent material with 10 g kg-1 Zn and neutral pH has been observed. If acidification proceeds it will lead to a significant release of Zn, S, and Pb to the ground water. In contrast to Zn, Pb is enriched in the mobile fraction of the topsoil by more than a factor of two compared with the subsoil which contains a total of 2 g kg-1 Pb. Thus, the high bioavailability of Pb and the potential for Pb uptake by plants and animals currently represent the most severe threat for environmental health.     

Compost and calcium surface treatment effects on subsoil chemistry in acidic minespoil columns

Surface incorporation of a liming agent in combination with compost or biosolids is a proven way to revegetate acidic minespoils, but little is known about the effect of the surface amendments on subsoil chemistry. We conducted a greenhouse column experiment to investigate how different surface amendments affected plant growth and subsoil chemistry in highly acidic minespoil material. Columns were filled with shale minespoil material (pH approximately 2.5), amended with CaCO3, CaSO4 x 2H2O (gypsum), and two rates of compost, and seeded with birdsfoot trefoil (Lotus corniculatus L.) and 'Kentucky 31' tall fescue (Festuca arundinacea Schreb.). We measured leachate and plant growth over a 170-d period with extensive irrigation. Without CaCO3, plants could only grow at the high compost rate (68.8 g kg(-1)), even though the soil pH in those treatments was below 3.5, indicating the capability of natural organic matter to detoxify Al(3+) by forming Al-organic matter complexes. Compost had no effect on the subsoil. When CaCO3 or gypsum was added to the surface, extractable Ca increased in the subsoil, but there was no relevant increase in subsoil pH. Even in the first 5 cm of subsoil material, extractable Al did not decrease very much, possibly because a jurbanite-like solid phase controlled subsoil Al(3+) activities. During the reclamation of highly acidic minespoil material one should therefore not expect significant effects of the surface treatment on the untreated subsoil. A sufficient root zone would have to be achieved by incorporating the liming agent down to the desired rooting depth.     

Effect of liming on the distribution of heavy metals in untreated industrial sewage sludge produced in Pakistan for the cultivation of <Emphasis Type="Italic">Sorghum bicolor</Emphasis> (L.)

The recycling of sewage sludge on agriculture land represents an alternative, advantageous, disposal of this waste material. The aim of the present study was to evaluate the feasibility of using industrial sewage sludge, produced in Pakistan, as a fertiliser. Agricultural soil amended with 25% (w/w) sewage sludge with or without lime treatment was used for growing a variety of sorghum (PARC-SS-1). The mobility of the heavy metals (HMs) (Cd, Cu, Cr, Ni, Pb and Zn) and metalloid (As) in the untreated industrial waste water sewage sludge (UIWS) samples were assessed by applying a modified BCR (Community Bureau of Reference) sequential extraction procedure. The single extraction procedure comprised of the application of mild extractant (CaCl₂) and water for the estimation of the proportion of easily soluble metal fractions. The precision and accuracy of BCR was evaluated by using a certified reference material of soil amended with sewage sludge BCR 483. The plant available metal contents, as extracted by the deionised water and 0.01 M CaCl₂ solution and exchangeable fraction of BCR sequential, decreased with lime application in the range of 10–44% for As, Cr, Ni, Pb and Zn, except in the cases of Cd and Cu, where their mobility was increased by 10% and 24%, respectively. Sludge amendment enhanced the dry weight yield of sorghum and the increase was more obvious after liming up to 25%. The uptake of HMs were lower in test samples (3.2–21.8%), except for Cu and Cd, which was higher (4%), while they were below the permissible limit of these metals. The present experiment demonstrates that liming was important in factors facilitating the growth of sorghum in sludge-amended soil.     

Source-separated municipal solid waste compost application to Swiss chard and basil

A growth room experiment was conducted to evaluate the bioavailability of Cu, Mn, Zn, Ca, Fe, K, Mg, P, S, As, B, Cd, Co, Cr, Hg, Mo, Na, Ni, Pb, and Se from a sandy loam soil amended with source-separated municipal solid waste (SSMSW) compost. Basil (Ocimum basilicum L.) and Swiss chard (Beta vulgaris L.) were amended with 0, 20, 40, and 60% SSMSW compost to soil (by volume) mixture. Soils and compost were sequentially extracted to fractionate Cu, Pb, and Zn into exchangeable (EXCH), iron- and manganese-oxide-bound (FeMnOX), organic-matter (OM), and structurally bound (SB) forms. Overall, in both species, the proportion of Cu, Pb, and Zn levels in different fractions followed the sequence: SB > OM > FeMnOX > EXCH for Cu; FeMnOX = SB > OM > EXCH for Pb; and FeMnOX > SB = EXCH > OM for Zn. Application of SSMSW compost increased soil pH and electrical conductivity (EC), and increased the concentration of Cu, Pb, and Zn in all fractions, but not EXCH Pb. Basil yields were greatest in the 20% treatment, but Swiss chard yields were greater in all compost-amended soils relative to the unamended soil. Basil plants in 20 or 40% compost treatments reached flowering earlier than plants from other treatments. Additions of SSMSW compost to soil altered basil essential oil, but basil oil was free of metals. The results from this study suggest that mature SSMSW compost with concentrations of Cu, Pb, Mo, and Zn of 311, 223, 17, and 767 mg/kg, respectively, could be used as a soil conditioner without phytotoxic effects on agricultural crops and without increasing the normal range of Cu, Pb, and Zn in crop tissue. However, the long-term effect of the accumulation of heavy metals in soils needs to be carefully considered.     

Adsorption of cadmium on biosolids-amended soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.     

Influence of water treatment residuals on phosphorus solubility and leaching

Laboratory and greenhouse studies compared the ability of water treatment residuals (WTRs) to alter P solubility and leaching in Immokalee sandy soil (sandy, siliceous, hyperthermic Arenic Alaquod) amended with biosolids and triple superphosphate (TSP). Aluminum sulfate (Al-WTR) and ferric sulfate (Fe-WTR) coagulation residuals, a lime softening residual (Ca-WTR) produced during hardness removal, and pure hematite were examined. In equilibration studies, the ability to reduce soluble P followed the order Al-WTR > Ca-WTR = Fe-WTR > hematite. Differences in the P-fixing capacity of the sesquioxide-dominated materials (Al-WTR, Fe-WTR, hematite) were attributed to their varying reactive Fe- and Al-hydrous oxide contents as measured by oxalate extraction. Leachate P was monitored from greenhouse columns where bahiagrass (Paspalum notatum Flugge) was grown on Immokalee soil amended with biosolids or TSP at an equivalent rate of 224 kg P ha(-1) and WTRs at 2.5% (56 Mg ha(-1)). In the absence of WTRs, 21% of TSP and 11% of Largo cake biosolids total phosphorus (PT) leached over 4 mo. With co-applied WTRs, losses from TSP columns were reduced to 3.5% (Fe-WTR), 2.5% (Ca-WTR), and <1% (Al-WTR) of applied P. For the Largo biosolids treatments all WTRs retarded downward P flux such that leachate P was not statistically different than for control (soil only) columns. The phosphorus saturation index (PSI = [Pox]/ [Al(ox) + Fe(ox)], where Pox, Al, and Fe(ox) are oxalate-extractable P, Al, and Fe, respectively) based on a simple oxalate extraction of the WTR and biosolids is potentially useful for determining WTR application rates for controlled reduction of P in drainage when biosolids are applied to low P-sorbing soils.     

Heavy metal distribution and chemical speciation in tailings and soils around a Pb-Zn mine in Spain

Soil pollution by lead, zinc, cadmium and copper was characterized in the mine tailings and surrounding soils (arable and pasture lands) of an old Spanish Pb-Zn mine. Sixty soil samples were analyzed, determining the total metal concentration by acid digestion and the chemical fractionation of Pb and Zn by the modified BCR sequential extraction method. Samples belonging to mine waste areas showed the highest values, with mean concentrations of 28,453.50 mg kg(-1) for Pb, 7000.44 mg kg(-1) for Zn, 20.57 mg kg(-1) for Cd and 308.48 mg kg(-1) for Cu. High concentrations of Pb, Zn and Cd were found in many of the samples taken from surrounding arable and pasture lands, indicating a certain extent of spreading of heavy metal pollution. Acidic drainage and wind transport of dust were proposed as the main effects causing the dispersion of pollution. Sequential extraction showed that most of the Pb was associated with non-residual fractions, mainly in reducible form, in all the collected samples. Zn appeared mainly associated with the acid-extractable form in mine tailing samples, while the residual form was the predominant one in samples belonging to surrounding areas. Comparison of our results with several criteria reported in the literature for risk assessment in soils polluted by heavy metals showed the need to treat the mine tailings dumped in the mine area.     

In situ accumulation of copper, chromium, nickel, and zinc in soils used for long-term waste water reclamation

We studied the long-term in situ accumulation of Cu, Cr, Ni, and Zn in the soil profile of a large-scale effluent recharge basin after 24 yr of operation in a wastewater reclamation plant using the Soil Aquifer System approach in the Coastal Plain of Israel. The objective was to quantify metals accumulation in the basin's soil profile, clarify retention mechanisms, and calculate material balances and metal removal efficiency as the metal loads increase. Effluent recharge led to measurable accumulation, relative to the pristine soil, of Ni and Zn in the 0- to 4-m soil profile, with concentration increases of 0.3 to 1.3 mg kg(-1) and 2.9 to 6.4 mg kg(-1), respectively. Copper accumulated only in the 0- to 1-m top soil layer, with concentration increase of 0.28 to 0.76 mg kg(-1). Chromium concentration increased by 3.1 to 7.3 mg kg(-1) in the 0- to 1-m horizon and 0.9 to 2.3 mg kg(-1) at deeper horizons. Sequential selective extraction showed Cu tended to be preferentially retained by Fe oxides and organic matter (OM), Cr by OM, Ni by OM, and carbonate and Zn by carbonate. The average total retained amounts of Cu, Cr, Ni, and Zn were 0.7 +/- 1.0, 13.6 +/- 4.8, 4.3 +/- 3.6, and 28.7 +/- 5.4 g per a representative unit soil slab (1 m(2) x 4 m) of the basin, respectively. This amounts to 3.6 +/- 4.9%, 79.5 +/- 28.0%, 8.0 +/- 6.9%, and 9.3 +/- 1.8% of the Cu, Cr, Ni, and Zn loads, respectively, applied during 24 yr of effluent recharge (total of approximately 1880 m effluent load). The low long-term overall removal efficiency of the metals from the recharged effluent in the top horizon may be due to the metals' low concentrations in the recharged effluent and the low adsorption affinity and retention capacity of the sandy soil toward them. This leads to attainment of a quasi-equilibrium and a steady state in element distribution between the recharged effluent solution and the soil after few years of recharge and relatively small cumulative effluent loadings.     

Trace element concentrations in soil, corn leaves, and grain after cessation of biosolids applications

From 1974 to 1984, 543 Mg ha(-1) of biosolids were applied to portions of a land-reclamation site in Fulton County, IL. Soil organic C increased to 5.1% then decreased significantly (p < 0.01) to 3.8% following cessation of biosolids applications (1985-1997). Metal concentrations in amended soils (1995-1997) were not significantly different (p > 0.05) (Ni and Zn) or were significantly lower (p < 0.05) (6.4% for Cd and 8.4% for Cu) than concentrations from 1985-1987. For the same biosolids-amended fields, metal concentrations in corn (Zea mays L.) either remained the same (p > 0.05, grain Cu and Zn) or decreased (p < 0.05, grain Cd and Ni, leaf Cd, Cu, Ni, Zn) for plants grown in 1995-1997 compared with plants grown immediately following termination of biosolids applications (1985-1987). Biosolids application increased (p < 0.05) Cd and Zn concentrations in grain compared with unamended fields (0.01 to 0.10 mg kg(-1) for Cd and 23 to 28 mg kg(-1) for Zn) but had no effect (p > 0.05) on grain Ni concentrations. Biosolids reduced (p < 0.05) Cu concentration in grain compared with grain from unamended fields (1.9 to 1.5 mg kg(-1)). Biosolids increased (p < 0.05) Cd, Ni, and Zn concentrations in leaves compared with unamended fields (0.3 to 5.6 mg kg(-1) for Cd, 0.2 to 0.5 mg kg(-1) for Ni, and 32 to 87 mg kg(-1) for Zn), but had no significant effect (p > 0.05) on leaf Cu concentrations. Based on results from this field study, USEPA's Part 503 risk model overpredicted transfer of these metals from biosolids-amended soil to corn.     

Migration of trace elements from pyrite tailings in carbonate soils

In the carbonate soils contaminated by a toxic spill from a pyrite mine (Aznalcóllar, southern Spain), a study was made of a thin layer (thickness = 4 mm) of polluted soil located between the pyrite tailings and the underlying soil. This layer, reddish-yellow in color due to a high Fe content, formed when sulfates (from the oxidation of sulfides) infiltrated the soil, causing acidification (to pH 5.6 as opposed to 8.0 of unaffected soil) and pollution (in Zn, Cu, As, Pb, Co, Cd, Sb, Bi, Tl, and In). The less mobile elements (As, Bi, In, Pb, Sb, and Tl) concentrated in the uppermost part of the reddish-yellow layer, with concentration decreasing downward. The more mobile elements (Co, Cd, Zn, and Cu) tended to precipitate where the pH was basic, toward the bottom of the layer or in the upper part of the underlying soil. The greatest accumulations occurred within the first 6 mm in overall soil depth, and were negligible below 15 mm. In addition, the acidity of the solution from the tailings degraded the minerals of the clay fraction of the soils, both the phyllosilicates as well as the carbonates. Also, within the reddish-yellow layer, gypsum formed autigenically, together with complex salts of sulfates of Fe, Al, Zn, Ca, and Mn, jarosite, and oxihydroxides of Fe.     

Chemical immobilization of lead, zinc, and cadmium in smelter-contaminated soils using biosolids and rock phosphate

Chemical immobilization, an in situ remediation method where inexpensive chemicals are used to reduce contaminant solubility in contaminated soil, has gained attention. We investigated the effectiveness of lime-stabilized biosolid (LSB), N-Viro Soil (NV), rock phosphate (RP), and anaerobic biosolid (AB) to reduce extractability and plant and gastrointestinal (GI) bioavailability in three Cd-, Pb-, and Zn-contaminated soils from smelter sites. Treated (100 g kg(-1) soil) and control soils were incubated at 27 degrees C and -0.033 MPa (0.33 bar) water content for 90 d. The effect of soil treatment on metal extractability was evaluated by sequential extraction, on phytoavailability by a lettuce bioassay (Lactuca sativa L.), on human GI availability of Pb from soil ingestion by the Physiologically Based Extraction Test. The largest reductions in metal extractability and phytoavailability were from alkaline organic treatments (LSB and NV). Phytotoxic Zn [1188 mg Zn kg(-1) extracted with 0.5 M Ca(NO3)2] in Blackwell soil (disturbed soil) was reduced by LSB, NV, and RP to 166, 25, and 784 mg Zn kg(-1), respectively. Rock phosphate was the only treatment that reduced GI-available Pb in both gastric and intestinal solutions, 23 and 92%, respectively. Alkaline organic treatments (LSB, NV) decreases Cd transmission through the food chain pathway, whereas rock phosphate decreases risk from exposure to Pb via the soil ingestion pathway. Alkaline organic treatments can reduce human exposure to Cd and Pb by reducing Zn phytotoxicity and revegetation of contaminated sites.     

Response of soil microbiological activities to cadmium,lead, and zinc salt amendments

Heavy metal pollution of soil has been recognized as a major factor impeding soil microbial processes. From this perspective, we studied responses of the soil biological activities to metal stress simulated by soil amendment with Zn, Pb, and Cd chlorides. The amounts of heavy metal salts added to five metal-polluted soils and four nonpolluted soils were selected to match the total metal concentrations typically found in polluted soils of the Silesia region of Poland. From the perspective of soil quality, metal mobility in amended soils could not be described by simple functions of pH or organic matter. Reaction of Pb with the soil caused strong immobilization with less than 1% of the Pb amendment recovered by 0.01 M CaCl2 extractions. Immobilization of Cd was also significant, whereas immobilization of the Zn amendment was much weaker than that of Cd or Pb. The Zn amendment had substantial inhibitory effect on soil dehydrogenase, acid and alkaline phosphatase, arylsulfatase, urease, and nitrification potential. Generally, Cd and Pb had limited or stimulatory effect on most of these biological activities, with an exception of Pb strongly inhibiting soil urease. The effect of the metal amendments on biological activities could not be satisfactorily accounted for by metal toxicity because no strong relationship was observed between extractable metal content and the degree of inhibition. The Zn amendment had a significant effect on soil pH, resulting in confounding effects of pH and Zn toxicity on activities. Metal amendment experiments seem to be of limited utility for meaningful assessment of metal contamination effects on soil quality.     

Recovery and distribution of biosolids-derived trace metals in a clay loam soil

The long-term mobility of trace metals has been cited as a potential hazard by critics of EPA 503 rule governing the land application of biosolids. The objectives of this study were to assess the accumulation of Cu, Ni, Cd, and Zn within the soil profile; the distribution of exchangeable, specifically adsorbed, organic, and oxide fractions of each metal; and mass balance of Cu, Ni, and Zn 17 yr after a single biosolids application. Biosolids were applied to 1.5- x 2.3-m confined plots of a Davidson clay loam (fine, kaolinitic, thermic Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha(-1). The highest biosolids application supplied 4.5, 750, 43, and 600 kg ha(-1) of Cd, Cu, Ni, and Zn, respectively. Soils were sampled to a depth of 0.9 m and sectioned into 5-cm increments after separating the Ap horizon. Total (EPA-3050B), bioavailable (Mehlich-I), sequential extraction, and dispersible clay analyses were performed on samples from the control, 126 Mg ha(-1), and 210 Mg ha(-1) treatments. Trace metals are still concentrated in the top 0.2 m with slight enrichment down to 0.3 m. More than 85% of applied Cu, Ni, and Zn are still found in the topsoil where biosolids was incorporated and 95% or more of the applied metals were accounted for with mass balance calculations. Mehlich-I results showed a slight increase in metal concentration down to 0.35 m. Biosolids application increased the concentrations of trace metals in all the extracted fractions. The major portions of Cu, Zn, and Ni are associated with the metal-oxides fraction. Dispersible clay content and water-soluble metal contents were low and except for water-soluble Zn they were not affected by biosolids application. Results from this study showed that 17 yr after biosolids application there was negligible movement of trace metals through the soil profile and consequently there is little risk of contamination of ground water at this site.