Assessing the feasibility of land application of fly ash, sewage sludge and their mixtures

Advances in Environmental Research 8 (2003) 77–91

Assessing the feasibility of land application of fly ash, sewage sludge and their mixtures夞 K.S. Sajwana,*, S. Paramasivama, A.K. Alvab, D.C. Adrianoc, P.S. Hoodad a

Center for Marine, Environmental Sciences Biotechnology Research, Savannah State University, P.O. Box 20600, Savannah, GA 31404, USA b USDA-ARS-PWA, Vegetable and Forage Crops Research, 24106 N. Bunn Road, Prosser, WA 99350, USA c Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken, SC 29802, USA d Center for Earth and Environmental Science Research, Kingston University, Kingston upon Thames, Surrey KT1 2EE, UK Received 28 January 2002; accepted 5 August 2002

Abstract Land disposal of fly ash (FA) and sewage sludge (SS) is a major problem due largely to their potentially harmful constituents. Combined use of FA and SS however may help reduce the associated pollution potential. In this paper we summarize the results of several case studies designed to assess the feasibility of land application of FA with and without SS. A wide range of application rates was tested under laboratory, greenhouse and field conditions. The leaching of metals from soil columns amended with moderate rates of FA applications (8–16 Mg hay1) generally had no significant impact on the metal content of leachate or their downward migration in the soil. The application of FA or SS at a much high rate (74.1 Mg hay1) significantly increased both leaching and downward migration of metals. The use of 1:1 FAqSS mixture at 148.2 Mg hay1 reduced metal leaching compared to the combined metal quantities leached when FA or SS applied at 74.1 Mg hay1. The results indicate that combined use of FA and SS at a rational rate of application should not cause any significant effect on drainage water quality. Plant studies conducted using FA and SS mixtures indicated that these materials could be beneficial for biomass production, without contributing significant metal uptake or leaching. The application of FA as high as 560 Mg hay1 in a long-term field trial had no detectable deterioration in soil or groundwater quality and no substantial increases in plant uptake of metals and other trace elements were observed. Low to moderate rates of FA and SS therefore could be successfully used as soil amendments, particularly so when used as a mixture. 䊚 2002 Elsevier Science Ltd. All rights reserved. Keywords: Biomass; Fly ash; Groundwater; Leaching; Metals; Sewage sludge

1. Introduction Public interest in recycling of coal combustion byproducts and municipal by-products continues to increase. In the USA, coal-fired electric utilities supply 夞 Contribution of the Center for Marine, Environmental Sciences and Biotechnology Research, Savannah State University, P.O. Box 20600, Savannah, GA 31404, USA. *Corresponding author. Tel.: q1-912-356-2315; fax: q1912-352-3571. E-mail address: [email protected] (K.S. Sajwan).

annually more than half of the nation’s electricity (Am. Coal Ash Assoc., 1997). Approximately 90% of the 890=106 Mg (metric tons) of coal produced in the US in the late 1990s was used by the electric utilities (Stewart, 1999). To achieve the national goal of energy independence, the amount of coal consumption is expected to increase. The increased use of coal for power generation could result in increased release of potentially toxic organic and inorganic contaminants into the environment (Davis and Boegly, 1981). The annual amount of coal combustion by-products by electric power utilities in the USA is estimated to be

1093-0191/03/$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1093-0191(02)00137-5

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approximately 100=106 Mg; 65% of this amount is fly ash (FA, Am. Coal Ash Assoc., 1997). Since FA and other coal residues contain a variety of potentially hazardous substances, their irrational disposal and management could cause considerable environmental impacts. Coal residue, especially FA application to agricultural land does not supply crop requirements for essential plant nutrients such as N and P. However, it could supply sufficient K, Ca, S, B, Mo and a possible number of other essential micronutrients such as Zn. Alkaline FA would also be effective in neutralizing soil acidity. FA also contains variable amounts of certain trace elements (e.g. Cd, Cr, Pb, Ni, B, Mo and Se), which may limit its potential use for land application (Adriano et al., 1980). Sewage sludge (SS), also known as biosolids, is one of the major solid organic wastes produced by the wastewater treatment plants in cities around the globe. Municipal sewage treatment plants in North America process more than 6=106 dry tons of sewage per day (Naylor and Loehr, 1982). The application of sludge on agricultural land is a common practice around the world, including the USA. Land application of wastewater or ‘reclaimed water’, sludge, and municipal solid waste has been shown to benefit crop production and improve soil quality (McCalla and Peterson, 1977; Page and Chang, 1994; NRC, 1996; Basta, 1995, 2000). However, to realize these benefits, land application of SS must be conducted in an environmentally sustainable manner (CAST, 1976; Chaney et al., 1976). Unlike FA, SS characteristically contains high levels of the major plant nutrients, N and P, and is enriched in organic matter. Benefits from sludge application on croplands, however, have to be weighed against the potential hazards associated with certain sludge-borne constituents (e.g. heavy metals, organic contaminants). Retention of sludge-borne heavy metals in soils and their accumulation in plant tissues have caused concerns about their extensive use on cropland (CAST, 1976; Chaney et al., 1976). Furthermore, SS tends to increase acidity of the soils as a result of proton release from organic matter decomposition and mineralization of NHq 4 yN. Increased soil acidity could cause greater solubility of metals and consequently their enhanced plant availability and leaching potential, particularly in soils with poor buffering capacity (Hooda and Alloway, 1993). Public concerns associated with some municipal byproducts were legislated by the Water Quality Act of 1972 (Logan and Chaney, 1983) that mandated development of technologies to treat, dispose, and recycle nutrients in wastewaters and solid wastes in an environmentally sound manner. With the implementation of the Water Quality Act of 1972 (Public Law 92–500), the production of SS has increased tremendously over the

past three decades. Dramatic changes in land application of SS have occurred during the last 25 years. Land application of SS increased from 20 to 54% of the total SS produced in the USA from 1972 to 1995, respectively (WEF, 1997). The traditional methods of organic waste disposal (landfilling, incineration, ocean dumping) are being restricted or outlawed due to air and water quality concerns. Thus disposal of ever increasing amounts of SS and FA in an environmentally sustainable manner has become a major challenge. Combined use of FA and SS for land application could prove a beneficial means of their disposal. Because of the contrasting chemical properties and nutrient contents of FA and SS, land application of both products as mixture can improve soil quality and crop production. This could help alleviate waste disposal and management problems associated with land application of SS or FA. In addition to these two by-products, there are several by-products used and disposed as land application. In this paper we present several case studies designed to assess the feasibility of land application of FA and SS. Using the finding of these studies together with our previous work on the subject, we aim to evaluate the overall feasibility of land disposal of FA, SS and FAq SS mixtures. The evaluations are made on the basis of leaching, plant uptake and downward migration of metals added to the soils through the use of these amendments as well as their effects on biomass production and groundwater quality. 2. Materials and methods 2.1. Soils and amendments Four different FA materials (FA1, FA2, FA3 and FA4) and one source of SS were used in the case studies reported here. FA materials were collected from the various coal-fired power stations (Table 1), and the SS was obtained from Berkeley County Water and Sewer Treatment Plant (Goose Creek, South Carolina). Selected properties of the amendments are presented in Table 1. The case studies are based on three soils collected from Florida and South Carolina (Table 2). These were a Candler fine sandy soil (sandy, hyperthermic, uncoated, Typic Quartzipsamments), an Orangeburg loamy sand (fine loamy, siliceous, thermic Typic Paledult), and a Congaree silt loam (fine silty, mixed, thermic Fluventic Dystrochrepts). Selected properties of these soils are presented in Table 2. 2.2. Soil, plant and water analyses Soil pH, electrical conductivity (EC), organic matter, cation exchange capacity (CEC) and texture were deter-

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Table 1 Selected properties of FA and SS used

pH P K Ca Mg Mn Fe B Cu Zn Pb Cd Ni Cr Location

FA1

FA2

FA3

FA4

SS

8.0 nd nd nd nd 10.0 66 000.0 nd 43.0 12.0 19.0 9.0 111.0 106.0 Tampa, FL

8.0 nd nd nd nd 111.0 1200.0 nd 48.0 208.0 82.0 20.0 56.0 115.0 Tampa, FL

12.1 1268.0 1447.0 5654.0 214.0 93.0 121.0 57.0 82.0 84.0 199.0 0.9 26.0 106.0 Augusta, GA

8.1 200.0 506.0 4102.0 218.0 13.0 199.0 25.0 19.0 6.0 1.3 0.3 2.3 3.7 Beech Island, SC

5.7 3597.0 6020.0 2308.0 872.0 110.0 619.0 0.5 71.0 81.0 29.0 3.5 25.0 23.0 Charleston, SC

All elemental concentrations in mg kgy1, (on dry wt. basis) determined on Mehlich-3 extraction test. nd, not determined.

mined using standard laboratory procedures. Elemental composition of the soils, FA and SS was determined on the basis of either Mehlich-3 or Mehlich-1 extracts, which were subsequently analyzed for a wide range of nutrients and other elements by inductively coupled plasma optical emission spectroscopy (ICP-OES; Plasma 40, Perkin-Elmer Inc., Norwalk, CT). Harvested plant tissues from the greenhouse and field studies were rinsed in four successive deionized water baths, oven-dried to 70 8C for 72 h, weighed and ground to 841 mm. The ground plant samples were wet-ashed in a nitric–perchloric acid mixture (Council of Soil Testing and Plant Analysis, 1980), and analyzed for various elements, including heavy metals. Soil samples were collected at the time of harvest, air-dried, sieved to pass through a 2-mm sieve, and extracted with Mehlich-3 or Mehlich-1 extractant. The soil extracts were analyzed for various elements, including heavy metals. 2.3. Leaching column studies Plexiglass columns, 32 cm long and 7 cm inner diameter, were used to study the transport of metals from soils amended with various amendments. A Whatman No. 42 filter paper was placed at the bottom of the leaching column and the soils (air-dried -2 mm fraction) were packed to a height of 30 cm to attain a bulk density of 1.5 g cmy3. Three replicate columns were used for each treatment. Appropriate quantities of the amendments were mixed with the top 2.5 cm soil and repacked to attain the same bulk density as above. The amended soil columns were saturated with distilled water and excess water was allowed to drain overnight. A Whatman No. 42 filter paper was placed on top of each soil column and, deionized water was applied at a

constant rate of 1.5 ml miny1, using a peristaltic pump to facilitate leaching. Leachate was collected in half pore volume (220 ml) fractions and analyzed for Fe, Mn, Cu, Se, Zn, Cr and Pb. The quantity of metals leached was calculated using the concentrations of each metal and the volume of leachate fraction. The leaching potential for individual metals represents the cumulative amount of metal leached in all the leachate fractions. When the ionic strength of all the treatments approached that of the non-treated control, water additions were terminated. The soil from each column was divided into three sections at 10 cm increments (0–10, 10–20 and 20–30 cm depth sections), and analyzed for pH and Mehlich-3 extractable metals (Fe, Mn, Cu, Se, Cr and Pb). The leaching column studies were conducted using two sets of experiments. The first experiment compared two sources of FA (FA1 and FA2) obtained from two different electric power plants in Tampa, FL (Table 1). Table 2 Selected properties of the soils used in this study Soil

Sand, g kgy1 Silt, g kgy1 Clay, g kgy1 pH Organic matter, g kgy1 CEC, cmol kgy1 Texture Vegetation Location a

Candler

Congaree

Orangeburg

967 8 25 7.0 13.0 2.2 Fine sand Citrus Polk, FL

920 30 50 5.4 11.0 2.4 Fine sand Naturala Aiken, SC

860 100 40 5.1 18.5 3.9 Loamy sand Natural Aiken, SC

Natural vegetation includes oak, pine and sweet gum.

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This experiment was conducted with the Candler sandy soil (Table 2). Each FA was applied at 3 rates: 0, 3 and 6 g FA per column, equivalent to 0, 8 and 16 Mg FA hay1. The leaching experiment continued until the ionic strength of all the treatments became similar to the non-treated control, which took 5 pore volume. The second experiment compared leaching of various elements from soils amended with varying rates of FAq SS (1:1) mixture or with a single application of either FA or SS. FA used in this study was FA3 (Table 1). This study was conducted on two soils: the Orangeburg loamy sand and the Candler sandy soil (Table 2). The treatments comprised of a 1:1 FAqSS mixture (dry weight basis) applied either at 0, 10.9, 21.8, 43.6 or 65.4 g per column, equivalent to 0, 24.7, 49.4, 98.8 and 148.2 Mg hay1. To compare quantities of metals leached from the highest mixture application rate with that from separate application of each of the amendments, two additional treatments of 74.1 Mg hay1 either FA or SS were also included. The soil columns were leached with deionized water as described previously. Leachate was collected in a half pore volume fraction (220 ml) for a total of 7 fractions when the ionic strength of all the treatments became similar to the non-treated control. 2.4. Greenhouse studies This study was conducted using the Ap horizon (0– 15 cm) of the Orangeburg loamy sand (Table 1) and six rates of FAqSS application, mixed in various ratios. The alkaline FA (FA-3) and SS were used to make the various treatment mixtures. The treatments consisted of four FAqSS mixtures (1:4, 2:4, 3:4 and 4:4) and six application rates (0, 124, 247, 371, 494 and 988 Mg hay1). These rates were applied to the soil (-2 mm fraction) on the dry-weight basis to make a final weight of 6 kg, thoroughly blended, and each treatment was replicated 4 times. The bottom of each 7-kg polyethylene pot was lined with gravel, and then filled with 6 kg treated soil. Pots were incubated for 8 weeks at the field capacity moisture content and then seeded with ten Sorghum vulgaris seeds. After 2 weeks, the seedlings were thinned to five plants per pot and grown for 10 weeks. The pots were watered daily to maintain moisture content at field capacity throughout the growing period. The day and night temperatures of the greenhouse were maintained at 30"3 and 24"3 8C, respectively, to represent the typical ambient temperatures. No artificial lighting was used, as the natural day length of approximately 15 h during the course of the study was considered adequate. The above ground portion of each plant was harvested 10 weeks after planting, by clipping above the first node, and processed for biomass production and chemical analysis. At the time of harvest, soil samples were

collected and processed for various chemical analyses as described previously. 2.5. Field studies The FA (FA4) used in this study was slightly alkaline (Table 1) and the field soil was Congaree silt loam (Table 2). This experiment was conducted as a Latin Square design with 4 levels of FA application (0, 280, 560 and 1120 Mg hay1 on dry weight basis). Each treatment plot was 46.5 m2 in size and was separated by 3.6 m spacing between each plot. FA was applied in treatment plots, rototilled and seeded with centipede grass (Eremochloa ophiroides). All plots received N at the rate of 24 N kg hay1 at every 6 weeks interval for 3 times during spring and early summer months, which coincides with active growth period. Soil samples were taken throughout the 4-year duration of this study using an auger for shallow sampling and a drill rig for deeper sampling to study the effect of high rates of FA application on metal distribution and transport in the soil profile. Collected soil samples were air-dried to constant weight prior to pass through a 2-mm sieve and analyzed for pH, EC and Mehlich-1 extractable nutrients and other elements. Groundwater samples were obtained periodically from pre-installed groundwater monitoring wells. Water from groundwater monitoring wells was pumped out (at least four well volumes) and samples were collected once the pH and EC of well water was stabilized. These samples were preserved in an ice chest until they were transported to the laboratory and filtered through 0.45 mm filter, acidified and analyzed for various elements using ICP-OES. Plant biomass was determined by harvesting the whole plot approximately 2 cm from the ground periodically throughout the 4-year study period and measuring the dried (70 8C for 72 h) plant biomass. Sub samples of the ground plant tissues were wet-ashed in a nitric–perchloric acid mixture as described previously and analyzed for various elements. 3. Results and discussion 3.1. Leaching column studies Leaching of heavy metals underneath of landfills, out-side storage of SS and FA by-products or when they are applied to agricultural soils could contaminate surface or groundwater sources (Carlson and Adriano, 1993; Alva et al., 1999a,b; Ghuman et al., 1999). The heavy metal contents in FA and SS vary considerably depending on the origin and source of these materials. The presence of an organic amendment with FA, however, may help to bind the metals by chelation, adsorption or precipitation, and therefore could minimize the

K.S. Sajwan et al. / Advances in Environmental Research 8 (2003) 77–91

Fig. 1. Iron leaching from the Candler sand: a comparison of two different types of FA sources. The error bar at each data point represents the standard error of the mean.

leaching potential of metals (Herdt and Duvall, 1975; Logan and Traina, 1993). We conducted several leaching column studies designed to evaluate the leaching of metals from two sources of FA as well as when applied as FAqSS mixtures, FA or SS. The distribution and potential downward migration of metals following a series of leaching events were also assessed. 3.1.1. Two sources of FA: leaching trend and concentration of metals The concentration of Fe in the leachate from FA amended treatments was 3–4-fold greater for FA-1 than for FA-2, particularly in the first four-leachate fractions (Fig. 1). Application of FA-2 at both rates did not substantially increase the Fe concentration compared to those for the unamended control. The highest concentration of Fe in the leachate (5 mg ly1 ) was well below that generally found in shallow groundwater, i.e. 30– 7400 mg ly1 (Deverell et al., 1984). The addition of FA from both sources increased the Mn concentration for the first two-leachate fractions (Fig. 2). The Mn concentration decreased substantially in the subsequent fractions from the soil amended with either FA source and was somewhat similar to the concentration of Mn in leachate from the unamended soil. The concentration of Mn in the leachate was in the range of 0.1–1.9 mg ly1. These concentrations were within the range found in shallow groundwater, i.e. 0.3– 2.5 mg ly1 (Deverell et al., 1984). The concentrations of Zn in the first two-leachate fractions were much greater in the FA amended soil as compared to the unamended control (Fig. 3). The highest concentration of Zn in the subsequent leachate was approximately 0.3 mg ly1. For the majority of samples, concentrations of Zn in the leachate for both FA sources were similar to those of the unamended soil.

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Fig. 2. Comparison of Mn leaching from the Candler fine sand when amended with two rates of FA from two different sources. The error bars as in Fig. 1.

Both FA sources (FA1 and FA2) used in this leaching study were low-alkaline in reaction (pH 8) and are not expected to cause significant changes in leachate pH as observed in other studies (Rai et al., 1987; Twardowska, 1999). A neutral to alkaline pH range favours metal retention by adsorption and precipitation, with consequential control on their leaching as seen in this study (Figs. 1–3). The Cu concentrations in the leachate varied from 110 to 300 mg ly1 (data not presented) with the mean concentration range of 191–204 mg Cu ly1 for the various treatments (Table 3). Although these values are much greater than those reported for shallow groundwater, i.e. 1–14 mg ly1 (Deverell et al., 1984; Tanji and Valoppi, 1989), the concentrations did not exceed the maximum contamination level (MCL) for drinking water, i.e. 300 mg Cu ly1 (Rubenstein and Segal, 1993).

Fig. 3. Comparison of Zn leaching from the Candler fine sand when amended with two rates of FA from two different sources. The error bars as in Fig. 1.

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The concentration of Se in the leachate exceeded 100 mg Se ly1 only for the 220 and 440 ml pore volume leachate fractions (leaching pattern data not shown). The mean concentration of Se varied from 84 to 104 mg Se ly1 for the various treatments (Table 3). These concentrations are greater than its MCL (50 mg Se ly1) for drinking water standards (Rubenstein and Segal, 1993). However, Se concentrations as high as 400 mg Se ly1 have been reported in freshwaters (Cannon, 1974). The concentration of Cr in the leachate was very low (in the range of 23–69 mg Cr ly1) and was not influenced by the FA application. The observed Cr concentrations in the leachate were lower than its MCL (100 mg Cr ly1) for drinking water (Rubenstein and Segal, 1993). Similarly, the source and rates of FA application did not influence the quantity of Pb in the leachate (Table 3). 3.1.2. Two sources of FA: cumulative metal leaching Cumulative quantities of Fe, Mn, Cu, Se, Zn, Cr, Pb in 5 pore volume of the leachate are shown in Table 3. The cumulative leaching of Fe, Mn, Zn and Se were numerically greater from soil columns amended with 16 Mg hay1 FA compared to either 8 Mg hay1 FA or no FA amendment. The cumulative leaching of Cu, Pb, and Se, were somewhat greater from the soil amended with FA-2 than that with FA-1. The opposite trend was observed for Fe and Mn leaching. The source or rates of FA amendment compared to the unamended soil did not affect the cumulative leaching of Cr. The effect of FA source on the cumulative leaching of Fe, Zn and Pb was not evident even though the two FA sources significantly varied in terms of their metal contents (Table 1). This was due to the fact that both FA sources were low-alkaline in reaction, which in turn probably allowed only limited solubility of most of the FA-borne metals, as observed in other studies (Rai et al., 1987; Twardowska, 1999). 3.1.3. Two sources of FA: metal distribution and downward migration To understand the metal distribution and downward migration, the soil columns were sectioned into 3 depths

Fig. 4. Mehlich-3 extractable Zn and soil pH in the Candler soil columns amended with 16 Mg hay1 of FA. The Zn and pH values were measured after the columns were leached with 2320 ml of deionized water. The error bars as in Fig. 1.

of 10 cm increments, and analyzed for pH and Mehlich3 extractable metals. The soil pH values and Mehlich-3 extractable Zn, Fe and Mn only for the 16 Mg hay1 FA treatment, as example results, are discussed here. The pH values of the soil amended with FA-1 were approximately 6.0 across the three depths and were not significantly affected by the amendment (Fig. 4). However, pH of the FA-2 amended soil was approximately 7.0 for the top 0–10 cm soil depth, which was significantly greater compared to the other two soil depths (Fig. 4). The pH value of the FA-2 amended soil ranged between 6.8 and 7.2, which was broadly similar to the original soil pH. The FA-1 amended soil pH decreased by about a unit. Soil pH may decrease or may not change when amended with low-alkaline FA since the chemical reactions of FA in soils are dictated by the gypsum equilibrium (Twardowska, 1999). Soilyleachate pH, however, is expected to increase when soil is amended with highalkaline FA since the FA–soil reaction is governed by the carbonate equilibria. The type of FA used therefore governs the changes in pH for a given soil and thereby

Table 3 Total quantities (mg) of elements recovered in 2320 ml from the Candler fine sand amended with FA Treatmenty FA source

Application rate (Mg hay1)

Fe

Mn

Cu

Se

Zn

Cr

Pb

Control FA-1

0 8 16

3778 4094 4290

461 924 988

444 466 447

198 194 201

176 214 245

35 30 38

136 121 134

FA-2

8 16

3431 3916

664 692

474 477

206 241

215 223

38 34

139 141

Source: Alva et al. (1999a).

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Fig. 5. Mehlich-3 extractable Mn and Fe as affected by FA application. The soil, experimental and other details are the same as in Fig. 4.

Fig. 6. Comparison of Fe leaching from two soils amended with various rates of FAqSS mixtures (1:1 ratio), FA or SS.

determine the bioavailability and mobility of various elements and chemical composition of the leachate (Twardowska, 1999). The magnitude of change in soil pH following FA application, however, would depend upon the rate of FA application and the buffering capacity of the soil. The downward migration and distribution of Zn in the soil columns at the various depths after a series of leaching events was not significantly affected. Although the Zn content of FA-2 was 17-fold greater than that of FA-1 (Table 1), the distribution of Zn in the soil profile was in the range of 21.2–22.6 mg kgy1, regardless of the FA used (Fig. 4). Therefore, the downward transport of Zn from both sources of FA is negligible even in a sandy soil, with little metal retention capacity (Table 2). Similarly, the downward migration and distribution of Fe and Mn in the soil columns when leaching ceased was not significantly affected by the FA application (Fig. 5). It is important to note that the amount of Fe in FA-1 was almost 55 times greater than that of FA-2 (Table 1) and the amount of Mn in FA-2 was approximately 11 times greater than that of FA-1. However, the difference of Fe and Mn contents between the two FA sources used in this study had no effect on the contents of Mehlich-3 extractable Fe and Mn in the soil. The Fe contents in the soil profile was in the range of 63.4– 66.5 mg kgy1 while the distribution of Mn was in the range of 13.0–15.4 mg kgy1, irrespective of the FA source used (Fig. 5).

pared to the Orangeburg loamy sand (Fig. 6). In the former case, a slight increase in Fe concentration, however, was found for the 148.2 Mg hay1 FAqSS mixture and 74.1 Mg hay1 SS application. For the Orangeburg loamy sand, Fe concentration in the leachate rapidly increased after the fourth leachate fraction for the SS application and for the highest rate of FAqSS mixture application. The Fe concentration peaked to 1.72 mg ly1 in the sixth leachate fraction from the Orangeburg loamy sand, which received the SS application (74.1 Mg hay1). The concentrations of Mn in all leachate fractions from the Candler fine sand followed the similar trend like Fe and were generally -2 mg ly1, irrespective of the type or rate of amendment application (Fig. 7). In the Orangeburg loamy sand, little Mn was seen in the

3.2. Comparison of FA and SS mixture vs. FA or SS application 3.2.1. Leaching trend and concentration of metal The concentrations of Fe in all leachate fractions from the Candler sand were considerably lower com-

Fig. 7. Comparison of Mn leaching from two soils, experimental and other details as in Fig. 6.

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Fig. 8. Comparison of Zn leaching from two soils, experimental and other details as in Fig. 6.

first leachate fraction, regardless of the amendment or application rate. However, the concentration increased sharply in the second leachate and peaked in the third leachate for all treatments and subsequently decreased rapidly to below 4 mg Mn ly1 regardless of the treatment. The maximum leachate concentration of Mn (27 mg Mn ly1) from the Orangeburg loamy sand occurred from the highest rate of FAqSS mixture application (148.2 Mg hay1). The corresponding concentration for the Candler sand was 1.68 mg Mn ly1. The leachate Mn concentration increased with the rate of application for the second through fourth leachate fractions. For Candler fine sand, Mn leachate concentrations were in the range of 0.01–1.68 mg ly1, which are similar to

those found in shallow groundwater, i.e. 0.3–2.5 mg ly1 (Deverell et al., 1984). However, leachate Mn concentrations from the Orangeburg loamy sand were in the range of 0.09–26.74 mg Mn ly1, which are greater compared to those generally found in shallow groundwater. The leachate Zn concentration from the Candler sand was in the range of 23.5–44.5 mg Zn ly1 for the first leachate fraction (Fig. 8). However, the concentration increased sharply in the second fraction. This was followed by a sharp decrease to the fifth leachate fraction before being stabilizing in the range of 11.7 and 39.4 mg Zn ly1 across the treatments. The maximum Zn concentration for the Candler fine sand was 104 mg Zn ly1 that occurred from the highest rate of FAqSS mixture application (148.2 Mg hay1 ). The corresponding concentration for the Orangeburg loamy sand was 34.5 mg Zn ly1. The Zn concentration in the Orangeburg loamy leachate increased concurrently with the rate of amendments for the second through fourth leachate fractions (Fig. 8). Overall, the leachate Zn concentrations were in the range of 12–105 and 4–35 mg Zn ly1 for the Candler sand and the Orangeburg loamy sand, respectively. The observed concentrations were many fold greater than that generally found in natural irrigation water (up to 500 mg Zn ly1) (Zeng-Sang, 1992) and in shallow groundwater (Deverell et al., 1984). The greater Zn concentrations from the Candler fine sand compared to the Orange loamy sand are probably a reflection of the differences in the mechanism of metal retention–release and the original Zn content in the soils. The average leachate Cu concentration across the treatments for the Candler sand was 587 mg Cu ly1

Table 4 Comparison of total quantities of metals (mg) in 1540 ml of leachate from the Candler fine sand and the Orangeburg loamy sand amended with FA and SS mixture and FA or SS Treatments (Mg hay1)

Cr

Zn

Cd

Cu

Pb

Ni

Candler fine sand 24.7 (FAqSS) 49.4 (FAqSS) 98.8 (FAqSS) 148.2 (FAqSS) 74.1 (FA) 74.1 (SS)

286 293 335 259 235 271

310 236 259 331 190 346

93 87 104 66 62 76

513 603 949 1518 492 1349

1082 924 1140 831 988 1070

281 288 293 232 269 258

74 88 134 262 105 265

289 396 655 1053 383 618

Orangeburg loamy sand 24.7 (FAqSS) 49.4 (FAqSS) 98.8 (FAqSS) 148.2 (FAqSS) 74.1 (FA) 74.1 (SS)

203 219 241 166 163 200

85 87 100 109 92 126

63 99 106 95 85 101

43 38 45 41 39 60

483 613 812 686 671 909

174 217 268 224 216 277

38 65 345 930 57 1383

3000 5125 10 192 12 561 5166 11 144

Source: Alva et al. (1999b).

Fe

Mn

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(calculated from Table 4), which is many times greater compared to the mean concentration found in fresh water or in shallow groundwater (Bowen, 1979; ZengSang, 1992). However, the Orangeburg loamy sand leachate concentrations (25–38 mg Cu ly1, calculated from Table 4) only slightly exceeded the mean concentration range reported for fresh water or shallow groundwater, i.e. 0.2–30 mg ly1 (Bowen, 1979; Zeng-Sang, 1992). While the Candler sand leachate Cu concentration exceeded its MCL for drinking water (300 mg Cu ly1), the leachate concentrations from the Orangeburg loamy sand remained below the MCL level (Rubenstein and Segal, 1993). Elevated leachate concentrations of Zn and Cu from the Candler sand amended with FAqSS are at least partly due to its larger Zn and Cu contents, possibly because of the fungicide use in citrus cultivation (Table 2). This is supported by its greater contents of Mehlich3 extractable Zn and Cu compared to the Orangeburg soil. The leachate concentrations of Cr and Cd were 182 mg? Cr ly1 ?and 53 mg Cd ly1 for the Candler sand, and 129 mg Cr ly1 and 59 mg Cd ly1 for the Orangeburg soil when averaged across the treatments and leachate fractions (Table 4). These values were greater than the critical upper limits (100 mg Cr ly1 and 5 mg Cd ly1, respectively) set for drinking water (Rubenstein and Segal, 1993). Similarly, Pb in the leachate increased substantially with the FAqSS mixture application rate of 98.8 Mg hay1 compared to 24.7 Mg hay1. However, the leachate concentrations significantly decreased for the highest rate of FAqSS mixture (Table 4), indicating the mixture was acting as a source as well as sink for Pb. 3.2.2. Cumulative metal leaching In the Orangeburg loamy sand, leaching of most elements except Cu, increased concurrently with the rate of FAqSS mixture application up to 98.8 Mg hay1 (Table 4). A further increase in FAqSS application rate to 148.2 Mg hay1 had little effect on the leaching of most metals. The amount of Cu in the leachate was the lowest compared to the other metals and the rate of amendment application had little or no effect on the amount of Cu leached from this soil (Table 4). The quantities of metals leached from the FAqSS mixture application rate of 148.2 Mg hay1 were lower than the combined quantities of the metals leached from the soil columns, which received 74.1 Mg hay1 of either FA or SS. The leaching of most metals from the Candler sand was greater, except Mn, compared to that from the Orangeburg loamy sand for any given rate or source of amendment application (Table 4). This is clearly because of the greater leaching potential for most metals from the coarse textured sand compared to the medium

85

Fig. 9. Soil pH in the Candler sand soil columns amended with various rates of FAqSS mixture (1:1) or 74.1 Mg hay1 of either FA or SS. The pH measurements were made after the columns were leached with 1760 ml of deionized water. The error bars as in Fig. 1.

textured sand (Table 2). Similar to the Orangeburg loamy sand, the total amounts of metals leached from the Candler sand amended with 74.1 Mg hay1 each of FA and SS (applied separately) was greater when compared to those from a single application of 148.2 Mg hay1 of 1:1 mixture of FAqSS. This trend was consistent across the two soils used, and clearly shows that the highest rate of FAqSS mixture application increased the metal binding capacity of the soils. This is consistent with earlier findings, which showed increased metal retention and reduced metal uptake from soils amended with SS at 150 Mg hay1 when compared with a lower rate of 50 Mg hay1 (Hooda and Alloway, 1993, 1998). Such effects of a large application of organic amendments on metal mobility or retention, however, could diminish with time when the amendment decomposes in the soil (Hooda and Alloway, 1994). It has been generally accepted that the reaction of the soil system (soil pH along with redox) mainly governs solubility and mobility of various elements in the soil system (Lindsay, 1979). Amending soils with varying amounts of either FA, SS or FAqSS mixture may modify pH of the soil, which, in turn, could affect the leaching potential. This depends on the composition of the FA and SS materials and the buffering capacity of the soil. Soils used in this study had contrasting pH values (Candlers7.0; Orangeburgs5.1) where as pH of the FA is 12.1 and SS is 5.7. The resulting changes in soil pH as shown for the Candler sand (Fig. 9) together with other complexes formed or binding sites created due to the interaction among soil–FA–SS are expected to modify metal solubility, with consequential effect on leaching.

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Fig. 10. Mehlich-3 extractable Fe, the soil and other details as in Fig. 9.

Fig. 11. Mehlich-3 extractable Mn, the soil and other details as in Fig. 9.

3.2.3. Downward migration and distribution metals Soil pH and the distribution of Zn, Fe, and Mn, only for the Candler sand, as example results, are presented here. For a given soil depth the application of FAqSS mixture had no significant effect on soil pH, which ranged between 6.3 and 6.7 across the mixture application rates (Fig. 9). The soil pH values, however, were significantly affected when the soil was amended with SS alone. The soil pH was greater in the 10–20 cm depth samples compared to the top (0–10 cm) or the bottom (20–30 cm) depth across all rates of the FAq SS mixture applied (Fig. 9). The pH values of the FAq SS amended soils were significantly lower than that of the soil, which received 74.1 Mg hay1 of FA as the sole amendment (Fig. 9). Therefore, mixing SS with FA decreased the pH compared to the application of FA alone. In contrast, the application of SS alone lowered the soil pH considerably through the entire soil column depth compared to the application of FA. The concentration of Mehlich-3 extractable Fe in the top 10 cm increased with the FAqSS mixture application rate (Fig. 10), with only a marginal effect below this depth. The concentration of Fe increased in the top 10 cm soil following the FA or SS application, the effect however was less pronounced compared to the mixture application. This effect was also seen in the lower depths, though not as prominent as for the top layer, which indicates downward migration of Fe in the soil profile. The extractable Fe varied significantly across the depths in the columns, which received application of either FA or SS. The concentration and distribution of Mn in the soil columns at the end of leaching was significantly affected (Fig. 11) across the depths. This effect was clearly evident at the highest FAqSS (1:1) mixture application rate. The profile of Mehlich-3 extractable Mn when FA

(74.1 Mg hay1) was applied show significant differences across the depths, indicating both the increase in its content and downward migration. No such effect was apparent with the SS application (Fig. 11), although the SS had somewhat larger Mn content (Table 1) compared to the FA (FA-3). The Mehlich-3 extractable Zn in the top 10 cm of the soil column increased with the FAqSS application (Fig. 12). The two lower depths, however, had similar extractable Zn concentrations for all FAqSS application rates. In contrast, the concentration of Zn decreased consistently with the depth when either FA or SS was applied. These differences in Zn concentration across the depths were significant, indicating its significant downward migration and accumulation. The Zn concentration in the top 10 cm SS amended soil was extremely

Fig. 12. Mehlich-3 extractable Zn, the soil and other details as in Fig. 9.

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high compared to the other depths and the FA amended soil (Fig. 12) even though Zn content in both the FA (FA-3) and SS amendments were similar (Table 1). This is probably because of the differences in Zn retention and release when the amendments are applied separately or as their mixture. The results clearly show that the application of FAqSS mixture generally helped control the downward migration of metals when compared with separate application of either FA or SS (Figs. 10–12). 3.3. Plant biomass and metal uptake—greenhouse studies

87

Table 5 Biomass production as influenced by FAqSS mixture application (Sajwan et al., 1995) Application rate (Mg ha#1) 0 124 247 371 494 988

FA:SS ratio 1:4 2:4 Biomass (g poty1)a

3:4

2.93 34.58 29.38 17.06 14.43 7.89

2.99 37.26 35.60 25.18 19.30 17.92

Ac Aa Aa Ab Ab Bc

3.08 37.74 36.60 26.72 16.99 10.46

Ad Aa Aa Ab Ac Ac

4:4 Ad Aa Aa Ab Acb Ac

3.11 36.65 36.04 27.87 21.58 13.80

Ad Aa Aa Aba Acb Abc

a

Historically, the use of FA in agriculture has been based on its liming potential and supply of essential elements such as Ca, B, S and Mo (Martens, 1971; Page et al., 1979). However, the use of FA as an agricultural amendment can be enhanced by blending it with potentially acid-forming organic by-products such as SS, poultry and cattle manure which are significantly rich in N and P (Adriano et al., 1980). Moreover, the alkalinity of FA should promote the neutralization of acidic organic by-products, thereby minimizing the bioavailability of potentially toxic trace elements such as heavy metals. This section summarizes greenhouse studies conducted to evaluate the effect of FAqSS mixtures on the growth and nutrient uptake by Sorghum vulgaris var. Sudanese Hitchc, ‘sorgrass’—a sorghum-Sudan grass hybrid. 3.3.1. Effect of FAqSS mixtures on plant biomass production There is no clear guidance with regard to the application rate of FA, SS or manure as soil amendments. The application rates, however, are generally expected to be within 10–50 Mg hay1 per application. The FAq SS mixture application rates many times greater than the typical rates were also included, which might be suitable for highly disturbed soils as a single application. The application of 124 or 247 Mg hay1 of FAqSS mixture increased plant biomass by approximately 10fold for all FAqSS mixture ratios compared to the control soil, which received no nutrients or manure application (Table 5). The mixture rates higher than 247 Mg hay1 resulted in substantial reduction in plant biomass. For example, compared to the application rate of 124 Mg hay1 the plant biomass was reduced by 77, 72, 52 and 62% when the mixture was applied at 988 Mg hay1 in the 1:4, 2:4, 3:4 and 4:4 FA:SS ratios, respectively. Results of other preliminary work indicated that the application of the alkaline FA (pH 12.1) alone at 124 Mg hay1 resulted in substantial reduction in plant biomass yield (data not shown). The same preliminary work also showed similar yield reductions when plants were grown on soil amended with SS alone. Further-

Means followed by similar letters, upper case across FA:SS ratio comparison and lower case across annual application rate comparison, are not significantly different (P-0.05) according to Duncan’s Multiple Range Test.

more, application of SS at rates higher than 124 Mg hay1 caused severe phytotoxicity, including plant mortality (date not shown). Excessive mineral salts and B content in the SS amended soil were found to be the major contributory factors for the observed plant mortality and biomass reduction (Mass, 1990; Menon et al., 1993). It would therefore appear that the use of SS or FA alone has the potential to restrict plant growth, possibly by modifying soil pH and soil-nutrient supply. However, the use of FAqSS mixture could provide beneficial effects on crop production (Table 5), particularly when applied at a suitable application rate. The findings also showed that it is beneficial to use FAqSS mixtures compared to FA or SS, and the mixture should not be applied at rates greater than 247 Mg hay1 even when designed as a single application. 3.3.2. Effect of FAqSS mixtures on plant tissue and soil metal content The contents of Fe, Mn, B, Cu and Zn in the plant tissue at the time of harvest are presented in Table 6. These results revealed that B was the only element that consistently increased across the treatment combinations. The plant uptake of other elements had a variable response to the FAqSS mixture ratios and application rates (Table 6). One of the possible reasons for the decreased biomass yields when the mixture applied above 247 Mg hay1 (Table 5) may have been the accumulation of phytotoxic level of B and mineral salts. The regression analysis (not presented here) carried out between biomass vs. B in the plants and biomass production vs. salt content measured by EC and total dissolved salt in the soil confirmed the negative relationship between these factors. This is consistent with other reports of similar observations with regard to the possible phytotoxic effect of B and soluble salts from

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88

Table 6 Metal contents (mg kgy1) in Sudan grass grown on FAqSS mixture amended soils Application

Plant tissue concentrationa

Ratio Rate Mn (Mg hay1)

Fe

B

Cu

Zn

1:4

0 124 247 371 494 988

303 513 421 318 267 133

c a b c c d

51 83 62 56 60 64

c a b bc b b

8 11 14 15 19 25

c bc bc bc ab a

3 14 15 14 15 17

b a a a a a

27 113 174 176 154 99

c b a a a b

2:4

0 124 247 371 494 988

298 375 352 300 253 159

bc a ab bc c d

96 105 112 94 110 112

a a a a a a

10 20 25 27 33 45

d c bc bc b a

3 13 14 14 16 13

c 27 c b 99 b b 103 b b 136 a a 131 a b 98 b

3:4

0 124 247 371 494 988

355 305 320 311 287 201

a ab ab ab b c

61 99 91 84 85 96

c a b b b a

1 13 17 25 30 49

e d cd bc b a

6 12 12 14 14 14

b a a a a a

24 95 108 144 149 122

e d c a a b

4:4

0 124 247 371 494 988

378 259 279 270 251 192

a 46 c b 87 b b 82 b b 88 b bc 117 a c 116 a

1 6 8 21 22 25

c b b a a a

3 12 12 14 14 15

c b b a a a

29 80 102 117 114 136

e d bcd ab abc a

a Similar letters after a mean indicate no significant difference (P-0.05) between treatment means within a column and within selected treatment mixture according to Duncan’s Multiple Range Test.

FA and biosolids (Menon et al., 1993; Adriano et al., 2002). The concentrations of Mn, Fe, Cu and Zn in the plant tissue showed some variations, with no particular trend (Table 6). The concentrations, however, were within their normal ranges. Other trace elements such as Cd, Se, As, and Pb in the plants and soil extracts were below the detection limits of the ICP-OES, and therefore are not reported here. The contents of Mehlich-3 extractable Mn, Fe and B increased with increasing FAqSS application rates and mixture ratios but that of Cu and Zn was largely unaffected (Sajwan et al., 1995). 3.4. Potential benefits of FA application to turf grass— field studies This section summarizes the results obtained from a 4-year field study conducted in Beech Island, South Carolina, to evaluate potential benefits of applying a single application of high rates of FA (FA4, Table 1)

for the turf grass culture of centipede grass (Eremochloa ophiroides). This study evaluated, soil physical properties, plant uptake, soil and leachate composition, and the quality of the underlying groundwater as influenced by the FA application. The FA application had no apparent effect on bulk density or temperature of the soil in spite of the apparent darkening of the soil color at the high rates. The FA application evidently enhanced the water holding capacity of the soil by approximately 5% compared to the unamended control (Adriano and Weber, 2001). The increase in the water holding capacity though became statistically significant only when the application rate was 0560 Mg hay1. 3.4.1. Plant tissue composition Elemental composition of the plant tissue was significantly impacted by the FA application when compared with the control (Table 7). The results showed that the FA application had no effect on plant tissue contents of K, Ca, Fe, Ni, Cu, Cd, Pb, Cr, Sb and Hg (Adriano et al., 2002). However, the concentration of B, Mo, As, Se increased significantly by the FA application (Table 7). On the other hand, the plant tissue concentrations of Mn, Zn were significantly decreased. The FA application probably increased the retention of these two metals, with consequential reduction in their bioavailability. A comparison of plant uptake data for the 4-year study period (3-year data shown in Table 7) showed that plant contents of K, Ca, Mg, Fe, Cd, Cr, Ni, Pb, Ag, Sb, Al and Zn showed no significant change over time (Adriano et al., 2002). However, P, Mo, As and Cu contents in plant tissues increased with time. B and Se contents decreased after peaking in the 2nd year (Table 7), and Mn in the plant tissue decreased with time but this decrease was not significant. 3.4.2. Soil chemical properties and elemental contents The soil pH increased with the rate of FA application. Most of the increase in pH was observed for the 0–15 cm depth (4.9 for the control treatment to 6.5 for the highest rate of FA) during the first year. Although some increases for the next depth increment (15–30 cm) were later observed in the subsequent years, no further increases in soil pH were discernible below this depth. The EC values of the soil extracts increased with the FA application rate (data not shown). The largest value (0.20 dS my1) was measured in samples collected from the 0–15 cm depth in plots, which received 1120 Mg hay1 FA during the first year after the application. The EC values of soil samples collected during the 3rd year of this study were almost 7-fold lower than the values of the 2nd year. By the beginning of the 4th year, any effect of FA application on soil salinity (EC)

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89

Table 7 Concentration of various elements in plants grown on FA amended soil Year

Application rate (Mg ha#1)

Plant tissue concentration B (mg kgy1)

Mn (mg kgy1)

Zn (mg kgy1)

Mo (mg kgy1)

Se (mg kgy1)

As (mg kgy1) nd nd nd nd

1994

0 280 560 1120

4.7 12.8 12.7 20.8

c b b a

306.0 178.5 136.5 132.4

a b c c

57.9 41.4 38.7 39.5

a b b b

0.5 8.7 7.3 8.9

b a a a

nd nd nd nd

1995

0 280 560 1120

14.5 21.6 24.0 29.3

c ab a a

337.8 155.0 125.7 112.6

a b c c

57.8 43.3 36.2 36.6

a b b b

0.4 7.4 13.5 13.9

c b a a

145.0 1916.0 4264.0 6467.0

d c b a

214.0 c 787.0 b 1501.0 a 1875.0 a

1996

0 280 560 1120

10.8 22.3 13.7 13.8

b a b b

264.6 104.3 99.8 100.7

a b b b

59.2 44.0 41.0 43.8

a b b b

4.5 18.0 28.7 35.6

c b a a

134.0 1154.0 2325.0 3986.0

d c b a

726.0 1489.0 2775.0 4073.0

d c b a

Source: Adriano et al. (2002). nd, not determined.

had completely dissipated regardless of soil depth (Adriano et al., 2002). 3.4.3. Extractable elements in relation to their contents in plant tissue Double acid (Mehlich-1) extractable elemental concentrations in the soil were determined prior to planting as well as every year throughout the study period. The data showed that the increased contents of extractable Ca and Mo, in the 0–15 cm depth, with the FA application, which are consistent with their plant contents. The apparent increase in the extractable Mg (0– 15 cm) with the ash application contradicts its decreased plant concentration. The observed decrease in extractable Mn (0–15 cm) with the FA application, however, is consistent with its decline in plant tissue. The FA application increased extractable contents of K, Cu, Fe, Cd, Cr and Ni in the topsoil; however, no such increases in their plant contents were seen. On the other hand, the decreased contents of extractable P and B did not correspond to their increasing trends in the plant tissues with time. 3.4.4. Quality of underlying groundwater Groundwater samples were monitored for various chemical parameters to study the effect of FA application on groundwater quality. Among the parameters measured throughout the study period for groundwater samples, only EC exhibited a discernible trend with FA application rate and time. There were no detectable changes caused by FA application with respect to pH and potential inorganic contaminants (Ag, Al, As, B, Cd, Cr, Cu, Ni, Pb, Fe, Mn, Zn, Mo, Hg, As, Se). The data from this field study suggested that there was no significant impact on growth and biomass

production of centipede grass even though the alteration in soil pH was significant. Also the data indicated that there was no detectable deterioration of soil or ground water quality in terms of their chemical composition and no substantial accumulation of metals and other elements in the harvested plants occurred. This longterm field study indicated that high application rates of FA on turf farms could be a viable venue for the disposal of this by-product. 4. General discussion and conclusions The case studies represented three specific categories (leaching column study, 10-week long greenhouse plant uptake study, and a 4-year field study) and included a wide range of FA and municipal SS application rates individually or as mixtures to evaluate their potential role in agriculture. There were considerable benefits in terms of both physical and chemical properties of the soils when large amounts of these amendments as mixtures or separately were compared. The physical benefits of the soil include improved soil structure due to the addition of silt-size FA particles that promoted better aeration, percolation, and water retention capacity (Adriano and Weber, 2001). Chemical benefits would be ensured from the presence and supply of essential plant nutrients for crop growth and biomass production or by modifying soil pH. It should be noted that the modification of soil pH could adversely affect soil-nutrient supply as well. Increased application rates of these amendments (either alone or as mixtures) resulted in increased leaching of essential nutrient elements and metals from the column studies. However, the quantities of cumulative leaching of the essential nutrients and metals from the soil

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amended with 1:1 FAqSS mixture were substantially lower than the combined quantities leached from soil columns, which were amended with either FA or SS. This clearly showed the benefit of using FAqSS mixture rather than using them separately. The concentration of most metals in the leachate following application of low to moderate rates of FAqSS mixtures generally did not exceed the Environmental Protection Agency stipulated maximum contaminant level for most metals. Results of greenhouse and long-term field study demonstrated that plant establishment, subsequent growth and biomass production were not affected significantly up to ;280 Mg hay1, irrespective of the amendments applied either alone or as FAqSS mixture across the ratios investigated. This was true irrespective of the grass species (‘Sudan-sorghum’ grass or ‘Turf-grass) used. However, it is difficult to generalize this trend without extensive studies with wide spectrum of naturally abundant grasses. It should be stressed here that some of the high rates of FA, SS or FAqSS mixture used in the case studies would not be considered logical even as a single application but may be appropriate for highly disturbed soils, such as those affected by mining activities. Plant tissues of ‘Turf grass’ accumulated nutrients and other elements such as Cd, Se, As and Pb in the field experiment with FA application. However, the accumulation of these elements in ‘Sudan-sorghum grass’ was not significant in the greenhouse studies when the FAqSS mixtures were applied. Addition of FA could potentially create some unfavorable effects on plant growth due to high pH, accumulation of toxic trace metals (Cd, Cr, Zn, etc.) and increase in soluble salts concentrations (Cervelli et al., 1987; Pitchel and Hayes, 1990). This was at least partially supported by the increased accumulation of Se, As and Mo in Turf grass with increasing rate of FA application in the field study. Since the Turf grass used in this study is not generally used as animal feed, these elements would not be carried through the food chain. The increased accumulation of B in plant tissue, observed both in the greenhouse and field studies following the use of FAq SS mixture was considered as the possible reason for the reduction in biomass production. Overall, the case studies showed that a mixture of FAqSS (1:1) as a soil amendment could provide benefits in terms of soil fertility without any significant risk of soil, water or plants being contaminated, particularly when applied at a reasonable rate of application. Acknowledgments This research was performed under the auspices of contract number DE-FG09-96SR18558, US Department of Energy and Environmental Protection Agency. The authors express their gratitude to Dr Tracy Punshon for

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