| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Institute of Soil Science and Plant Cultivation, Pulawy, Poland
b Virginia Tech., Blacksburg, VA 24061
c USDA, Beltsville, MD 20705
* Corresponding author (ts{at}iung.pulawy.pl)
Received for publication September 12, 2006.
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Local authorities in Silesia realized in the early 1990s that a demonstration project was necessary to encourage the proper utilization of biosolids. This was the basis for establishing the Biosolids Subpart of the Silesia Project which addressed the use of biosolids in the reclamation of mining and smelting dumps (Stuczynski et al., 1996). In the 1990s metal waste sites in the Silesia region were known to contain more than 87 million t of waste and this amount was increasing by approximately 400000 t per year (Pistelok et al., 1995).
It was evident that a simple solution for stabilizing these sites would involve establishing permanent vegetative cover on the waste piles to reduce leaching or erosion of toxic elements, as well as to keep metallic fugitive dust from being dispersed. The reclamation of smelter waste sites which was performed within the framework of the Silesia Project was a joint effort of local government, industry, and international research institutions/agencies, including the U.S. Environmental Protection Agency (USEPA), the Center for Research and Control of the Environment (OBIKS), Virginia Polytechnic Institute, and the Institute of Soil Science and Plant Cultivation (IUNG). The main objective of the Silesia Project was the development of guidelines concerning all aspects of biosolids use for the reclamation of degraded lands and waste sites (Stuczynski and Chaney, 1997). Biological aspects related to reclamation of metal waste with the use of biosolids are discussed in this report.
A traditional strategy for the reclamation of wastelands and degraded lands is based on top soiling methods followed by the intensive use of fertilizers and the planting of various grass mixtures (Williamson and Johnson, 1981). There were also successful attempts to revegetate mining waste areas through the application of only mineral fertilizers and the direct planting of grasses (Patrzalek and Strzyszcz, 1980). In the end, however, these solutions were not found to be cost effective and sometimes were technically difficult. Moreover, they were not evaluated for use on extremely toxic smelter wastes. The primary limitation with topsoiling is the lack of quality soil material. Often, the available soil material is of poor quality with respect to its content of nitrogen, phosphorus, potassium, other nutrients, organic matter, and its adverse physical properties. Further, annual fertilization is necessary if one does not remediate the phytotoxicity and include legumes in the revegetation mixture.
More recently, however, successful application of biosolids or composts has been demonstrated for extremely contaminated soils (Oyler, 1988; Vangronsveld et al., 1995; Li et al., 2000; Brown et al., 2003; Clemente et al., 2005). Such treatments provide large amounts of organic matter which may significantly enlarge metals sorption capacity of soil (Beckett et al., 1979; Adriano, 2001). Furthermore, organic materials favor plant growth by improvement of soil fertility (introduction of nutrients such as nitrogen or phosphorus), soil microbiology, or physical properties (water retention) of often barren and abandoned heavily contaminated soils. Some researchers indicate the role of inorganic components of composts or biosolids such as Fe or Mn oxides in improvement of metals immobilization (Chaney et al., 2001; Hettiarachchi et al., 2003). Combining organic and lime amendments is a common approach in stabilization of metals (Li et al., 2000; Clemente et al., 2005). Liming increases soil pH to reduce metal solubility (Siebielec and Chaney, 2006), but in many cases is not successful as a single treatment (Li et al., 2000). However, pH increase due to lime application increases metals adsorption on biosolid or compost components such as organic matter and Fe oxides (Basta et al., 2005). Technology of so-called tailor-made composts is based on combining biosolids, lime-rich by-products, and other materials into one product—such an approach allows one to limit the number of remediation treatments without reducing its effectiveness (Chaney et al., 2000; Li et al., 2000; Brown et al., 2003).
As shown in Table 1, some of the biosolids from the Silesia region do not meet required Polish standards for agricultural use: 500, 2500, 500, and 10 mg kg–1 for Pb, Zn, Cr, and Cd content, respectively (Ministry of Environment, 2002). Therefore utilization to treat metal-contaminated wastes seems to be the only potential use of such materials until they are improved by industrial pretreatment. Taking these arguments into account, it is reasonable to assume that sludge would be a feasible, and possibly quite effective, alternative to traditional topsoiling techniques. The main objective of the demonstration project was to develop and implement techniques for safe use of biosolids which would meet all respective ecological, sanitary, and hygienic standards. There was a general consensus that clear and concise sets of procedures and guidelines needed to be developed before implementation of this reclamation technology. Such regulations and guidelines must take into consideration practical aspects of biosolids disposal, not just thresholds. The necessary protocols would include: (i) establish adequate methodologies for sampling the area designated for treatment; (ii) determine the extent of necessary site monitoring after treatment; (iii) implement innovative techniques for treating slopes; and (iv) establish safe buffers to protect surface waters and drinking water supply facilities.
|
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
The reclamation treatments for both sites took place in summer 1994. The wastes were treated by application of municipal biosolids at the rate 300 dry t ha–1 (dry matter basis) combined with the incorporation of lime in an oxide and carbonate form at the rate of 1.5 and 30 t, respectively. The incorporation of materials used for stabilization was done by a chisel plow to a depth of 15 to 20 cm. To achieve a better mixing the plots were plowed three times using the chisel plow, first along the longer axis, followed by two passes at 30 to 40° relative to the first one. The fields were then seeded with mixture of grasses with a rate 150 kg ha–1. The mixture consisted of the following local cultivars: Festuca rubra L. cv. Atra, Poa pratensis L. cv. Alicja, Festuca arundinacea Schreb. cv. SZD, and Festuca ovina L. cv. Sima at amounts equal to 35, 35, 15, and 15% of the total rate, respectively.
Since such a reclamation treatment of a Doerschel field failed due to high metal toxicity and salinity of the material, a different approach was required for the Doerschel site in a subsequent season (1995). It involved the use of a 30 cm by-product lime cap which was lined over the top of the waste surface. This capping operation was followed by incorporation of biosolids at a rate of 300 t ha–1 (dry matter basis). The field was then re-seeded with the same mixture of grasses.
The by-product lime was obtained from the sedimentation pond of a ground water treatment facility where calcium hydroxide was used to precipitate metals from water. Biosolids were obtained from the municipal waste water treatment plant in Katowice as cake from the centrifuge dewatering process. The biosolids contained 50% organic matter and 25 g N, 20 g P, 32 g K and 24 g Fe per kg of biosolids dry matter.
Weather conditions might be an important factor affecting growth of plants under chemical stress. Yearly total precipitation in the area of the experiment was 776, 709, 784, 933, 744, 759, and 832 mm in years from 1994 to 1999, respectively (IMGW, 1999). Mean daily temperatures for January and July calculated using the last 30 years of data are –1.5 and 18°C, respectively (Gorski and Zaliwski, 2002).
Both the Welz and Doerschel sites were sampled in a 10 by 10 m grid in subsequent years (1995–1999). Samples were taken from 0- to 15-cm depth. The total number of samples collected each year within the Welz field was 48 whereas for the Doerschel field it was 55.
Samples taken from each grid point consisted of five 100-g subsamples collected within 0.5-m radius. This material was thoroughly mixed to achieve better homogeneity, placed in a plastic bag and transferred to laboratory where the material was subdivided into two portions: one to be dried before chemical analysis and the second stored fresh in the refrigerator at 4°C for enzyme activity testing.
Pot Study
A pot study was performed to measure the resistance of grasses to high metal mobility and salinity. A number of cultivars and species were tested in three replications on Welz waste material treated with 10% w/w of Katowice biosolids on a dry matter basis in two separate series: low salinity material and high salinity material. High salinity material refers to Welz waste which was amended with 2% w/w of Na2SO4 to mimic electrical conductivity (EC) conditions which may occur in the field. Low salinity smelter waste refers to Welz material not treated with Na2SO4. Controls in the pot experiment consisted of material not treated with biosolids which was phytotoxic and nutrient deficient; thus the control plants died shortly after germination.
The study was performed in 2-kg pots in a greenhouse with controlled temperature and light. Pots were watered with deionized water as needed. Plants were harvested after 60 d of growth. Yield was recorded and macronutrients and trace metals content in shoot dry matter were analyzed after harvest.
Sample Analysis
Waste samples were air-dried and sieved through an 8-mm mesh before analysis. Using such a mesh was decided for maintaining physical characteristics as closely as possible to those found in the field. This was essential for realistic determination of metal solubility. Soil pH was measured (Ion Analyzer Mat 3201) using a combined glass electrode in a slurry with a 1:2 v/v soil/water ratio. Organic matter was measured by a loss on ignition in a muffle oven at 480°C within 16 h. Electrical conductivity was measured in filtrates of a 1:5 soil/water slurry at 25°C (Conductivity meter Radelkis OK-102/1). Available P was measured colorimetrically (Beckman DU-68 spectrophotometer) after extraction with 0.4 M calcium lactate.
Total metal contents were analyzed by atomic absorption spectrometry (AAS; PerkinElmer 1100B) after hot aqua regia sample digestion protocol (digestion in mixture of concentrated nitric and hydrochloric acids, followed by refluxing in 3 M hydrochloric acid) (McGrath and Cunliffe, 1985).
Analysis of metals solubility was by extraction in deionized water (1:2 soil/water ratio, shaken for 2 h at room temperature).
Dried plant material was prepared for analyses by ashing in a muffle oven at 480°C for 16 h, followed by digestion in concentrated HNO3 and refluxing with 3 M HCl. Element concentrations in filtrates were measured by AAS.
The revegetation effort to stabilize smelter toxic waste sites was supported by studying biological activities to assess sustainability of the new ecosystems established on reclaimed fields. Activity measurements followed standard protocols (Tabatabai, 1994) and included a range of enzymes: alkaline phosphatase, acid phosphatase, urease, and arylsulfatase. For urease, this procedure was slightly modified—the activity was measured as the amount of ammonia produced and not by measurement of the urea remaining. Determination of dehydrogenase was conducted as described by Casida et al. (1964). Glucose-induced respiration was measured as described by Anderson and Domsch (1973) to characterize fungal and bacterial contributions to overall biological activity. Total respiration was measured during 10-d incubations by CO2 absorption with 1 N NaOH traps and titration with 0.5 N HCl at the end of the incubation period.
Feeding Trial
Feeding studies were also conducted to look at the ecotoxicology and food chain risk aspect associated with the revegetation of metal wastes in Silesia. A feeding study was conducted with young calves (Bos taurus L., Holstein-Friesian breed) to measure the extent of metal transfer from Pb-, Cd-, and Zn-contaminated hay which was harvested from smelter waste reclaimed with lime and biosolids. The feeding trial was conducted at the Grabow IUNG experimental station in 1997, 2 yr after remediation treatment. Twenty calves of similar weight (40–45 kg), age, and genetic characteristics were assigned to four types of diet:
Cadmium and Zn were added to the hay in the form of a chloride solution mixed with feed just before consumption. The group fed Cd-amended control hay feed vs. the Cd+Zn-amended hay group should reflect the role of Zn-Cd interactions in Cd absorption by animals and retention in tissues and in organs. The addition of these metal-salt amendments was to test the contrast between the bioavailability of Cd which is naturally absorbed by plants in a high-metal soil environment with Cd salts added to diets and to assess the role of Zn-Cd interactions in Cd retention within animals consuming the plant biomass. All calves were fed control hay and a protein concentrate for 2 wk before treatment to ensure that all animals had the same nutritional background.
The study was terminated after 96 d; samples from different tissues and organs were collected for analysis of Cd, Pb, Zn, Fe, and Cu by cross-section sampling to represent the whole organ. Elements were analyzed by AAS after drying, ashing in a furnace at 450°C, and dissolving in 1 N HCl.
|
RESULTS AND DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Regardless of the fact that the toxicity of Welz waste was very high, the treatment used allowed the establishment of plant cover over more than 80% of the area tested. This means that the adaptation capabilities of the selected plant species were considerable. At the same time, when tested on Doerschel waste the same approach failed because of high concentrations of soluble metals and salinity (Table 3).
|
|
As previously mentioned, the originally designed biosolids/lime treatment (300 t ha–1 of biosolids plus 30 and 1.5 t ha–1 of carbonate and oxide lime, respectively) did not result in plant establishment on the highly phytotoxic Doerschel waste. Adverse physical properties of the Doerschel material, particularly high compaction and sedimentation, also contributed to the total inhibition of plant growth. Lime and biosolids at the rates used were not effective for the establishment of vegetation, although their incorporation reduced metal solubility which should decrease metal leaching from these piles (Table 3). We should emphasize that changes in pH and Cd and Zn solubility in both Doerschel and Welz materials during the first year after reclamation—as affected by biosolids and lime application—were smaller than expected. Evidently, liming was not effective for pH and metal solubility control with these materials. This may be due to limited solubility and/or occlusion with Fe or other metal oxides that were present in solutions at very high concentrations. Laboratory experiments with these wastes demonstrated that high rates of calcium carbonate did not result in substantial increases of pH (Stuczynski et al., 2000), nor did they result in a reduction of Cd and Zn solubility. On the other hand, calcium oxide reduced metal mobility to ppb levels although this effect may be temporary since the calcium oxide buffering system changes with time into calcium carbonate via CO2 absorption. This seems very likely since the addition of calcium oxide along with calcium carbonate to smelter plots did not affect the initial pH or metal solubility to any great extent after the first year of biosolids application.
The retreatment of Doerschel waste by using a less toxic waste cap was successful. A 15-cm cap of waste lime which subsequently received 300 t of biosolids created growing conditions suitable for a tolerant grass seed mix. This type of treatment resulted in an 80 to 90% ground cover success rate with little evidence of metal toxicity in the vegetation. On-site evaluation indicated that the roots penetrated to the lime/waste interface, but not more than 2 cm into the underlying toxic material. With time, it was observed that a number of perennial herbaceous and woody species had invaded the plots from the surrounding area. This supports our observation that the chemistry of toxic metal waste materials has thus been sufficiently stabilized by the use of lime and biosolids to support long-term plant growth.
Assessment of metal solubility in subsequent years (1996–1999) showed substantial decreases of Zn, Cd, and Pb solubility as measured by water extraction. This was partly an effect of pH increase due to dissolution of originally applied limestone (Welz) or introduction of additional lime (Doerschel). However, significant immobilization of metals was mainly an effect of progressive adsorption and occlusion of metals in the presence of organic matter and Fe oxides—such reduced mobility of metals over time has been reported (Bruemmer et al., 1988).
Selection of Grass Cultivars—Pot Study
The data shown in Tables 4 and 5 characterize the metal uptake by different grass cultivars grown on smelter waste in a pot study. The first set of pot study experiments depicts metal uptake in grasses grown on low-salinity smelter waste while the second set contains data characterizing metal uptake in grass cultivars grown on high-salinity smelter waste. As these data demonstrate, cultivars have different abilities tolerate the smelter wastes and to accumulate metals. Eleven grass cultivars which we tested in pot experiments seemed to be useful for revegetation purposes and demonstrated different degrees of adaptation to chemical stress (Table 4, 5). Comparing the low and high salinity series, most of the cultivars that survived in high-salt pots accumulated more Zn and Pb than in low-salinity series. No regular trend was observed for Cd.
|
|
None of the studied cultivars showed an Fe deficiency, even though the waste on which they were cultivated contained extremely high concentrations of Zn. Iron deficiency is a common symptom of plants grown in Zn-contaminated soils due to reduced Fe uptake under a presence of excessive amounts of Zn in a soil solution (Chaney, 1993). The lack of Fe deficiency in the studied environment can be explained by the fact that the smelter waste reclaimed with biosolids contained large amounts of Fe. It is also very likely that the interaction between organic matter present in biosolids and Fe oxides reduces Zn concentration in soil solution. This interaction forms a specific sorption for metals because both constituents have a significant sorption potential (Sposito, 1986; Li et al., 2000; Sparks, 2001; Basta et al., 2005).
Results of both field and pot studies allow us to recommend a mixture of the most metal/salt-tolerant species. Such a selection of cultivars may be needed for different types of waste.
Biological Activities of Revegetated Waste
The revegetation effort to stabilize smelter toxic waste sites was supported by studying biological activities to assess sustainability of these newly established ecosystems. Measurements showed substantial activity of most enzymes (Table 6). However, significant spatial variability was observed in this system similar to that of biomass and other indicators shown in Fig. 1. The spatial structure was highly correlated to the distribution of organic matter—this was confirmed by developed multivariate regression equations (Table 7). This indicates that the biological activity is driven by the distribution of biosolids applied and incorporated into the surface of the waste material. Stimulating effect of organic matter on microbial or biochemical activity is a common phenomenon both in traditionally fertilized soils (Beck et al., 1995; Siebielec et al., 2006) and those treated with biosolids (Frankenberger et al., 1983; Johansson et al., 1999; Emmerling et al., 2000). Microbial/biochemical parameters have not been commonly used as indicators of remediation effectiveness of heavily metal-contaminated soils. Hinojosa et al. (2004) used soil enzymes and microbial measurements (respiration, N mineralization, nitrification) to study activity of soils contaminated by the Aznalcollar toxic spill. The study revealed limited effectiveness of soil restoration by removal of top layer and liming. Experiments with soils from this region, testing various organic and inorganic amendments, showed a strong beneficial effect of municipal waste compost on soil activity (Perez de Mora et al., 2004).
|
|
Measurements of enzyme activities in reclaimed metal waste produces similar levels of these indicators to that of usable soils from the region (Siebielec et al., 2006). This indicates that the reclamation methods involving amendment of toxic metal materials with biosolids and lime can be an effective way to establish new, fully functioning ecosystems that support plant growth.
Feeding Trial
The data in Table 8 indicate that the Pb and Cd levels found in hay harvested from reclaimed Zn and Pb smelter waste greatly exceeded current allowed thresholds for animal feedstuffs by 20- and 6-fold, respectively (Ministry of Agriculture, 2003).
|
|
As mentioned, no excessive transfer of Pb and Cd to muscles was observed. The maximum permissible levels (MPL) accepted in Poland for Pb and Cd in meat are 0.2 and 0.05 mg kg–1, respectively (Ministry of Healthcare, 2000). The concentration of Pb found in muscles of calves fed with contaminated hay grown on smelter soil was 20 times smaller than MPL, while accumulation of Cd was 40 times smaller as compared to MPL. Moreover, there was no accumulation of muscle Cd in the group fed with CdCl2–amended hay, which suggests that the level of Cd added can be considered as subtoxic.
Cadmium present in naturally contaminated hay accumulated in kidneys and liver, but did not exceed Polish MPL values (1.50 and 0.50 mg kg–1, respectively) (Ministry of Healthcare, 2000). Hay amendment with CdCl2 dramatically enhanced Cd accumulation in these organs; however, the addition of Zn reduced this transfer (Table 9).
The results reported clearly indicate that crop contamination with Pb, Cd, and Zn by natural uptake of these elements has significantly different effects on their transfer to animal tissues than from feedstuff amended with metal salts. This provides strong evidence that studies utilizing metal salt amendments to feed to evaluate the metal accumulation in the animal body should not be used for assessment of exposure thresholds and food safety for naturally produced foodstuffs. It is evident that the interaction between Zn and Cd plays a crucial role in limiting the movement of Cd into the food chain. It is evident from these studies that forage crops grown on Zn-, Cd-, and Pb-contaminated sites reclaimed using lime and biosolids do not pose any identified risk for wildlife and food safety, regardless to the fact that current thresholds for Pb, Cd, and Zn in forage may be exceeded. This lends support to the argument that the existing evaluation criteria for metals in animal feed should be revised.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
For waste characterized by medium salinity such as Welz waste the recommended rate of biosolids should not be higher than 300 dry t ha–1 under average conditions. Waste which demonstrates higher salinity, such as Doerschel waste, must be treated differently. An integral part of a biosolids reclamation project is the selection of grass species and cultivars that are resistant to toxicity and adapted to the local climate. The appropriate selection creates conditions for good coverage of an area and limits the dispersal of toxic elements into the terrestrial ecosystem. The metal concentration in the biomass of selected species also reduces the impact of metals on the health conditions of organisms/animals returning to reclaimed areas.
Studies on biological activities indicate that the reclamation methods used by amending toxic metal materials with biosolids and lime can be an effective way to establish new, fully functioning ecosystems that support plant growth for waste pile stabilization. However, such reclamation sites shall be monitored—the question of how persistent and sustainable such constructed ecosystems are is very crucial for assessment of method effectiveness on a long-term timescale.
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  S. Brown, A. Svendsen, and C. Henry Restoration of High Zinc and Lead Tailings with Municipal Biosolids and Lime: A Field Study J. Environ. Qual., October 29, 2009; 38(6): 2189 - 2197. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Crop Science | |||
| Journal of Natural Resources and Life Sciences Education |
Vadose Zone Journal | ||||
| Soil Science Society of America Journal | Journal of Plant Registrations | The Plant Genome | |||
.