THE USE OF THE INTEGRATED SOIL MICROCOSMS TO ASSESS ACCUMULATION OF CAESIUM Cs AND LEAD Pb FROM CONTAMINATED SOILS BY EARTHWORMS Eisenia andrei AND THE SUNFLOWER Helianthus annuus... L
Introduction
Contamination of soil by trace metals
Soils have experienced human-induced impacts earlier than most other natural resources, with around 17,000 identified soil activities in the United States alone and countless more globally (Lynden, 2004) The Food and Agriculture Organization classifies land use into four main categories: farming land, rangelands or grasslands, forests, and general use, which includes urban wastelands, unused areas, and barren land.
In an ecosystem, soil plays four fundamental roles which are (1) a physical structure supporting plants to conduct photosynthesize,
Soil plays a vital role in supporting life within ecosystems by regulating temperature, absorbing, storing, and releasing water to sustain plants during dry periods, and providing essential nutrients for plants, animals, and humans (Buol, 1995) Despite its importance as an essential and non-renewable resource, soil has historically received less attention compared to air and water (Lynden, 2004).
Soil contamination by heavy metals and radionuclides poses a widespread environmental threat, affecting large areas globally These contaminants exist in soil solution, as inorganic or mixed complexes, and as precipitated solids, impacting soil chemistry and health (Smith et al., 1995) Key heavy metal pollutants include lead (Pb), chromium (Cr), zinc (Zn), arsenic (As), and cadmium (Cd), which are commonly found in soil and groundwater in a decreasing order of prevalence (National Research Council).
Heavy metals in soils cannot be biodegraded over time, posing significant environmental and health risks, while organic contaminants and radionuclides are biodegradable and decrease through their half-lives The presence of heavy metals and radionuclides raises concerns about the loss of ecosystem services, reduced agricultural productivity, contamination of the food chain, groundwater pollution, economic losses, and increased health issues in humans and animals Addressing soil contamination by these hazardous substances is crucial for protecting environmental and public health (Dushenkov, 2003; Endo et al., 2012; Adriano et al., 1997).
In the United States, a 1997 report estimated nearly half a million contaminated sites, with over 217,000 requiring cleanup efforts The cleanup market, detailed in Table 1.1, encompasses EPA Superfund sites, Resource Conservation and Recovery Act (RCRA) sites, Department of Defense (DOD), Department of Energy (DOE), State-managed sites, and private party sites, highlighting the extensive scope of environmental remediation activities across various sectors.
Europe has a significant number of potentially contaminated sites, with the United Kingdom alone accounting for 325,000 sites covering approximately 300,000 hectares, of which 33,500 have been identified as contaminated and 21,000 have been remediated Germany identified around 360,000 potential contaminated sites, as reported by the German Federal Ministry for the Environment in 2002 Similarly, Denmark reported 40,000 potential contaminated sites in 2009, and the Netherlands recorded 60,000 such sites in the same year, highlighting the widespread nature of land contamination across Europe In Australia, nearly 80,000 contaminated sites had been identified by 2008, emphasizing the global scale of environmental remediation needs.
Table 1.1 The cleanup market sites in the United States
Cleanup market share in the United States Organic and heavy metal contaminated
Environmental Protection Agency’s (EPA) and
The Resource Conservation and Recovery Act
Department of Defense (DOD) sites
Department of Energy (DOE) sites (4000 (23 listed as Superfund sites)
1.1.3 Sources of heavy metals in soil
Soils naturally contain heavy metals from the pedogenetic process at low toxicity levels (Pierzynski et al., 2000; Kabata-Pendias and Pendias, 2001) However, human activities have significantly increased heavy metal concentrations in both rural and urban areas, reaching levels harmful to humans, animals, plants, and ecosystems The toxicity of heavy metals in the environment is heightened by factors such as increased production rates due to industrial activities, transfer from mining sites to other regions, higher concentrations in waste compared to deposit areas, and increased bioavailability in receiving environments (D'Amore et al., 2005) The total amount of heavy metals in soil can be estimated using simplified equations, as outlined by Alloway (1995) and Lombi and Gerzabek (1998).
M total =(M p +M a +M f +M ag +M ow +M ip )-(M cr +M l )
Where “M” is the heavy metal, “p” is the parent material such as rock, “a” is the atmospheric deposition, “f” is the fertilizer sources, “ag” are the agrochemical
4 sources, “ow” are the organic waste sources, “ip” are other inorganic pollutants, “cr” is crop removal, and “l” is the loss by leaching, volatilization, and so on
Soil acts as a sink for heavy metals through the human activities mentioned above Metals cannot be degraded by microbial or chemical pathways (Kirpichtchikova et al.,
Heavy metals such as lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni) are inorganic hazards known to cause various diseases in humans and harm ecosystems They persist in the environment for long periods, inhibiting the biodegradation of organic contaminants, which exacerbates pollution issues These metals can enter the human body and food chains through direct contact, contaminated soil, polluted groundwater, and food, leading to reduced food quality and security (Wuana and Okieimen, 2011) Their presence poses significant risks to environmental health and human safety worldwide.
Soil pollution occurs due to the introduction of heavy metals and metalloids from various sources such as industrial activities, mining operations, and high-metal waste disposal Contaminants like lead (Pb) from fuel, paints, fertilizers, animal waste, sewage sludge, pesticides, herbicides, and wastewater used in agriculture also contribute significantly to soil contamination Additionally, pollution results from burned coal residues, petrochemical spills, and natural deposition processes, posing serious risks to soil health and environmental safety (Wuana and Okieimen, 2011).
Agriculture has historically been the first human influence on soil, involving the addition of essential nutrients to support plant growth, including macronutrients like nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, and trace elements such as cobalt, copper, iron, manganese, molybdenum, nickel, and zinc To enhance crop development, additional copper and manganese are often applied to soils, especially for cereal and root crops Intensive agriculture relies heavily on fertilizers enriched with nitrogen, phosphorus, and potassium, but these fertilizers can contain toxic heavy metal impurities like cadmium and lead, which may accumulate in soils over time, posing environmental risks.
Many widely used pesticides in agriculture and horticulture contain high concentrations of heavy metals, posing potential health and environmental risks For instance, about 10% of the insecticides and fungicides approved in the UK are chemical formulations that include heavy metals, highlighting the need for careful regulation and monitoring of these substances.
Copper-containing fungicidal sprays such as Bordeaux mixture (copper sulphate) and copper oxychloride have been widely used in agriculture, with historical use of lead arsenate as an insecticide in fruit orchards Additionally, arsenic-based substances were commonly employed in New Zealand and Australia to control cattle ticks and banana pests CCA compounds (copper, chromium, and arsenic) have traditionally been used for timber preservation However, many contaminated sites now exceed environmental quality guidelines for these elements, raising concerns about human health risks from trace metals, especially when such sites are repurposed for agriculture or other uses.
The widespread use of biosolids, such as livestock manure, municipal waste, composts, and sewage sludge, on landfills can significantly increase soil concentrations of heavy metals like arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), selenium (Se), molybdenum (Mo), zinc (Zn), thallium (Tl), and antimony (Sb) (Basta et al., 2005) Manures from poultry, cattle, and pigs are commonly applied as solid or liquid fertilizers on crops and pastures, but they can introduce contaminants such as copper and zinc—used to promote growth—as well as arsenic compounds found in poultry health chemicals These substances can lead to heavy metal contamination in soils and may accumulate over time with repeated manure application, posing ongoing environmental risks (Sumner, 2000; Chaney and Oliver).
Sewage sludge from wastewater treatment is commonly recycled as fertilizer in agriculture worldwide, with approximately 2.8 million dry tons reused or disposed of annually in the United States In Europe, over 30% of sewage sludge is applied to agricultural land, highlighting its widespread use (Silveira et al., 2003) Australia also reuses significant quantities, with more than 175,000 tons of biosolids used for crop production However, the application of sewage sludge can increase the concentration of heavy metals in soils, raising environmental concerns (McLaughlin et al., 2000) Additionally, composting biosolids derived from sawdust, straw, and garden wastes may pose risks to soil health due to potential contamination when frequently applied.
Biosolid application can introduce heavy metals such as cadmium (Cd), nickel (Ni), and zinc (Zn) into the soil, posing environmental risks Under specific conditions, these metals can leach from the soil into groundwater, potentially contaminating water sources Studies from New Zealand have shown increasing levels of Cd, Ni, and Zn in leachates resulting from biosolids applied to soils, highlighting the importance of careful management to prevent heavy metal contamination (Canet et al., 1998; Keller et al., 2002; McLaren et al.).
Caesium
Caesium is a soft, ductile, and silvery white alkaline metal known for its low melting point, becoming liquid just above room temperature It possesses a single oxidation state (+1) and features unique properties such as a low boiling point, high vapor pressure, and high density compared to other stable alkaline metals These characteristics make caesium notable in various scientific and industrial applications.
Caesium is significantly more reactive than other alkali metals, producing a reddish-violet flame when exposed to air and forming caesium oxides Like its alkali metal counterparts, cesium reacts vigorously with water, resulting in the formation of caesium hydroxide and hydrogen gas Most caesium salts and compounds are soluble in water, although caesium alkyl and aryl compounds are exceptions to this solubility.
Isotopes of Cs range from 114 Cs to 145 Cs The shortest half life is about 0.57 seconds
Cesium isotopes, particularly 135 Cs, have notably long half-lives, with 135 Cs lasting approximately 3 million years, making it highly persistent in the environment (Helmers, 1996) Among the cesium isotopes, 137 Cs and 134 Cs are widely utilized in various applications due to their high fission yields—specifically, 137 Cs is produced at a rate of six atoms per 100 fission events (WHO, 1983a)—and their relatively long half-lives of about 30.2 years for 137 Cs and 2.1 years for 134 Cs This combination of high production rates and extended half-lives underscores their importance in nuclear science and environmental monitoring.
137Cs and 134 Cs respectively) Stable Cs and radiocaesium have the same chemical properties (ATSDR, 2004)
Cesium-133 (133Cs) is a naturally stable isotope found in minerals and is present at low concentrations in the Earth's crust, such as approximately 1 mg/kg in granites and 4 mg/kg in sedimentary rocks The primary commercial source of cesium is pollucite, a mineral containing 5-32% Cs2O, with about two-thirds of global supply produced in Canada Environmental sources of cesium predominantly include dust and erosion, while mining activities of pollucite ores and industrial processes in electronics and energy sectors also contribute to its presence Additionally, cesium can be found in fly ash from coal burning and waste incineration, further impacting its environmental distribution.
Concerns about radiocaesium (¹³⁷Cs and ¹³⁴Cs) persist, with greater focus on its radioactive form rather than the stable isotope The average concentration of ¹³⁷Cs in U.S soils is approximately 620 mCi/km², according to Holmgren et al (1993) Both ¹³⁴Cs and ¹³⁷Cs have been released into the environment since 1945 due to nuclear weapon testing, nuclear waste disposal, and nuclear facility accidents (Avery, 1996), highlighting the ongoing impact of nuclear activities on environmental radioactivity.
During the 1950s and 1960s, atmospheric wet and dry depositions contributed up to 1.5x10^18 Bq of radiocaesium, primarily originating from nuclear weapons testing Atmospheric fallout was the main source of food chain contamination through vegetation deposition, impacting environmental safety and public health (Holmgren et al., 1993; Meriwether et al., 1988) By the end of 1986, remediation strategies focused on land contaminated by such radioactive deposition to mitigate long-term environmental and health risks.
9 density higher than 3700 kBq/m 2 was banned from agricultural production (Fesenko and Howard, 2012)
Radiocaesium fallout from nuclear accidents such as Chernobyl in Ukraine (1986) and Fukushima Dai-ichi in Japan (2011) has caused widespread environmental contamination The Chernobyl disaster contaminated approximately 6% of Europe with 137Cs levels exceeding 20 kBq/m², with higher contamination levels above 40 kBq/m² found in 2% of the region and 0.03% reaching 1480 kBq/m² (Mench et al., 2000; MEXT, 2011a; Bruno et al., 2000).
Furthermore, radiocaesium exists in buried radioactive waste materials (Mench et al.,
2000, Iskandar, 1992, Meriwether et al., 1988) Caesium in wastes is considered as intermediate in solubility
Stable Cs ( 133 Cs) occurs in soils through mining, milling, coal and burning of wastes
Studies have shown that bottom ash from municipal solid waste incinerators contains varying levels of cesium-133, with concentrations ranging from 0.44 to 2.01 mg/kg in the United States and 3 to 23 mg/kg in Spain (Fernandez et al., 1992) Additionally, stable cesium has been detected in both soil and sediment samples at one of the eight National Priorities List (NPL) hazardous waste sites in the United States, indicating environmental contamination concerns (HazDat., 2003).
Radiocaesium contamination in soils originates primarily from nuclear weapons testing and nuclear plant accidents Specifically, underground and surface nuclear tests have introduced radiocaesium into the environment, with approximately 1,400 underground nuclear tests conducted worldwide according to the Agency for Toxic Substances and Disease Registry (1993) Major nuclear accidents such as Chernobyl and Fukushima Dai-ichi have also contributed significantly to radiocaesium deposition in affected regions.
Small releases of 137Cs and 134Cs can occur from nuclear plant operations due to the storage and use of radioactive cesium, as documented by Radiation (1996) At the Idaho National Engineering and Environmental Laboratory (INEEL), researchers found 137Cs levels ranging from 1.6×10^-8 to 3.4×10^-7 Ci/m² at a transuranic waste storage site, highlighting ongoing contamination risks (DOE, 1998a) Several years after the Chernobyl disaster, the average concentration of 137Cs and 134Cs in the top 0-8 cm soil layer near the Chernobyl nuclear power plant underscored the long-term environmental impacts of radioactive fallout.
10 accident was 8.6x10 -5 Ci/m 2 and 1.9x10 -5 Ci/m 2 respectively (Mikhaylovskaya et al.,
Nuclear accidents at Chernobyl, Ukraine, in 1986 and Fukushima, Japan, caused significant environmental concerns, with ecological damage observed within a 30 km radius of the reactors The Chernobyl disaster exposed over 260,000 km² to radiation levels exceeding 1 Ci/km² of Cesium-137, resulting in an additional 4.3 mSv of radiation exposure—equivalent to a 0.1% increase in cancer mortality risk in Ukraine (Dushenkov, 2003; Endo et al.).
Radiocaesium was detected in UK milk during the 1960s and 1980s, aligning with peak nuclear weapons testing in 1964 and the Chernobyl nuclear accident in 1986 (Adriano et al., 1997; Department of the Environment, 1994).
The Fukushima Dai-ichi nuclear disaster on March 11, 2011, caused extensive environmental damage both onsite and globally Radioactive contaminants such as iodine-131 and cesium-137 were detected in agricultural, marine, and animal products, leading to significant negative impacts on producers and consumers worldwide.
In 2012, Japan established maps covering over 2,000 locations within 100 km of the Fukushima Dai-ichi nuclear power plant, highlighting areas contaminated with cesium (MEXT, 2011a) Additionally, radioactive contamination from the Fukushima incident was detected in neighboring countries, including Korea (Kim et al., 2012) and Vietnam (Long et al., 2012), indicating the extensive regional impact of nuclear fallout (Figure 1.2 and 1.3).
Figure 1.2 Dependence of the integrated activity concentration of radionuclides during March and April 2011 on the distance from Fukushima
Figure 1.3 Comparison between Third Airbone Monitoring Results and Map of Cs-134 Concentration
(source: MEXT (Ministry of education, culture, sports, science and technology, Japan, 2011a)
1.2.4 The Chemical behavior of Cs in soils
In soil, the mobility of Cs is very low (from 0.11 to 0.29 cm/ year (Schuller et al.,
Cesium (Cs) primarily exists within the top 20 cm of soil and is rarely found below 40 cm depth When present, Cs can either be absorbed by soil particles—particularly clay minerals—remain mobile within the soil solution, or be taken up and accumulated by plants and microorganisms These interactions influence the environmental mobility and bioavailability of Cs in contaminated soils (Korobova et al., 1998; Takenaka et al., 1998; Bunzl et al., 1989; Beckmann and Faas, 1992; Bunzl et al., 1994).
Lead
Lead is a naturally occurring metal found in the Earth's crust, with its concentration in surface soils worldwide ranging from 10 to 67 mg/kg It predominantly exists in compound form, such as with sulfur in PbS and PbSO4 or with oxygen in PbCO3 In nature, lead has four stable isotopes: 208Pb (51-53%), 206Pb (23.5-27%), 207Pb (20.5-23%), and 204Pb (1.35-1.5%), which are important for understanding its environmental cycling and sources.
Lead is produced in smaller quantities than metals like iron, copper, aluminum, and zinc In the United States, approximately 50% of lead is primarily used for battery manufacturing Other significant applications of lead include soldering, bearings, cable coverings, ammunition, plumbing, pigments, and caulking Lead is often combined with metals such as antimony, calcium, tin, silver, strontium, and tellurium, especially in the production of maintenance-free storage batteries, anodes, electroplating, chemical installations, nuclear shielding, sleeve bearings, printing, and high-precision castings These diverse applications highlight the essential role of lead across various industries.
Lead (Pb) released into soil, groundwater, and surface water primarily exists as ionic Pb (Pb(II)), Pb oxides and hydroxides, and Pb metal oxyanion complexes Among these, Pb(II) and lead-hydroxy complexes are recognized as the most stable forms, with Pb(OH)2 being the most thermodynamically stable solid in soil environments Under increasing sulfide presence and reducing conditions, PbS formation becomes prominent Additionally, organolead compounds such as tetramethyl lead can form under anaerobic conditions through microbial alkylation processes, highlighting the diverse chemical transformations of lead in environmental systems.
Lead phosphates, and Pb carbonates are formed when the pH is greater than 6, and Pb (hydro) oxides are predominant insoluble forms (Raskin and Ensley, 2000)
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
1993) The form of Pb is affected by pH, salinity, sorption and biotransformation processes In acidic environments, Pb present as PbSO4, PbCl4, ionic, Pb hydroxide Pb(OH)2 (U.S EPA, 1979)
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
Lead (Pb) contamination in soils primarily originates from anthropogenic sources, including mining, smelting activities, manure and sewage sludge application in agriculture, and vehicle exhaust emissions Historically, lead arsenate (PbHAsO4) has been used in orchards to control insect pests, leading to elevated lead concentrations in orchard soils These sources contribute significantly to soil pollution, impacting environmental health and requiring ongoing monitoring and assessment.
The worldwide average concentration of lead (Pb) in uncontaminated soils is approximately 17 mg/kg (Nriagu, 1978) In the early 20th century, the rise of internal combustion engines increased demand for high-octane petrol to improve engine performance and prevent uneven combustion To address this, lead alkyls such as tetraethyl and tetramethyllead were discovered in the 1920s as effective additives Consequently, the first leaded petrol was introduced and began to be widely sold by 1923, becoming the standard fuel for many years.
Research by Warren and Delavault (1960) highlighted that soils and vegetation near roads exhibit unusually high levels of lead (Pb) and petrol fumes, emphasizing the environmental impact of vehicular emissions Cannon and Bowles (1962) discovered that Pb was present in grass within 152 meters downwind of roads in Denver, Colorado, demonstrating a clear relationship between lead concentration and distance from traffic sources Additionally, they identified a contamination zone approximately 15 meters on both sides of roads with elevated lead levels compared to local background levels, indicating widespread global contamination resulting from the use of leaded petrol.
502 Bad GatewayUnable to reach the origin service The service may be down or it may not be responding to traffic from cloudflared
Atmospheric deposition of lead (Pb) varies significantly across different regions, with remote and countryside areas experiencing values between 3.1 to 31 mg/m²/year, while industrial and suburban locations receive higher deposits ranging from 27 to 140 mg/m²/year In specific regions, such as the South Pole, atmospheric Pb deposition is about 0.4 g/ha/year, whereas northwestern Canada and northern Michigan, USA, experience deposition levels of 7.2 g/ha/year and 6.3 g/ha/year, respectively (Sposito and Page, 1984) The reduction or phased-out use of lead in petrol by many countries has led to a subsequent decrease in soil Pb content over time (Jones et al., 1991; Jones and Johnston, 1991).
1.3.4 The chemical behavior of Pb in soil
Remediation of contaminated soils
Remediation aims to identify the most effective solution to reduce contaminant concentrations or their bioavailability to levels that are safe for human health and the environment When dealing with heavy metals in soils, the physical and chemical properties of the metals play a crucial role in selecting appropriate treatment methods (Martin and Ruby, 2004) Site-specific information, including physical characteristics, contaminant type, level, and distribution, is essential for proposing effective remediation strategies The target metal concentration is determined based on soil quality standards or risk assessments tailored to the site Remediation objectives may focus on reducing total metal concentrations, leachable metals, or both to ensure environmental safety and compliance.
Remediation methods are classified into various categories based on hazard-technologies, including gentle in situ techniques, harsh in situ soil restrictive measures, and harsh soil destructive measures (Gupta et al., 2000) The USEPA categorizes methods into source control (both in situ and ex situ) and containment remedies like vertical engineered barriers, caps, and liners (USEPA, 2007) Another classification divides remediation into five types: isolation, immobilization, toxicity reduction, physical separation, and extraction (GWRTAC, 1997) Factors influencing the selection of remediation techniques include cost, long-term effectiveness, commercial viability, acceptance, applicability to high concentrations, ability to handle mixed wastes, reduction of toxicity, mobility control, and mass removal (Wuana and Okieimen, 2011) Overall, remediation methods can be grouped into physical techniques involving containment or removal, chemical techniques that modify contaminant mobility and exposure, and biological techniques which utilize natural or biochemical processes to detoxify or stabilize pollutants.
20 either elevate mobility and then release metals for extraction or reduce the availability (Knox et al., 2001)
1.4.1 Remediation of heavy metals in soils
Current methods for remediating heavy metal-contaminated soils include immobilization (solidification/stabilization and vitrification), soil washing, and phytoremediation (Wuana and Okieimen, 2011) Immobilization techniques can be performed in situ, where amendments are added directly to contaminated soils without excavation, offering advantages such as low cost, simplicity, and minimal waste generation; however, they are only temporary solutions and may require ongoing monitoring due to potential pollutant reactivation Ex situ immobilization involves removing soils for treatment, enabling rapid and straightforward application but can be invasive, produce significant waste, and increase long-term operation costs Soil washing is effective in removing contaminants but can lead to secondary waste issues, while phytoremediation utilizes plants to extract or stabilize heavy metals, providing an eco-friendly approach with limited environmental disturbance Each method has specific benefits and limitations, making their selection dependent on contamination levels, site conditions, and long-term remediation goals.
In immobilization technology, various amendments such as clay, cement, zeolites, minerals, phosphates, organic composts, and microbes are commonly used to enhance stability (GWRTAC, 1997; Finžgar et al., 2006) Recently, industrial residues like red mud have gained attention for their potential in immobilization processes due to their mineralogical properties (Boisson et al., 1999; Lombi et al., 2002; Anoduadi et al.).
Sure! Here's a coherent, SEO-friendly paragraph synthesized from the provided content:"Low-cost amendments such as 2009 amendments and termitaria (Anoduadi et al., 2009) are effective in stabilizing heavy metals in contaminated soils Their primary function is to enhance metal stability through processes like sorption, precipitation, and complexation (Hashimoto et al., 2009) However, the detailed mechanisms behind these stabilization processes remain unclear due to the complex soil matrix and current limitations in analytical techniques (Wang et al., 2009)."
Solidification techniques utilize binding agents to immobilize contaminants, forming a stable solid product while minimizing external accessibility through chemical reactions, encapsulation, and reduction of surface area or permeability Stabilization, also known as fixation, involves reagents that chemically react with heavy metals in contaminated soils to produce more stable and less mobile compounds, enhancing environmental safety (Evanko and Dzombak, 1997).
Table 1.2 Organic amendments for heavy metal immobilization
Bark saw dust (from timber industry)
Xylogen (from paper mill wastewater)
Chitosan (from crab meat canning industry)
Poultry manure (from poultry farm)
Cattle manure (from cattle farm)
Rice hulls (from rice processing)
Table 1.3 Inorganic amendments for heavy metal immobilization
Phosphate salt (from fertilizer plant)
Fly ash (from thermal power plant)
Slag (from thermal power plant)
Portland cement (from cement plant)
Cd, Cu, Ni, Pb, Zn
Cd, Pb, Cu, Zn, Cr
Vitrification treatment involves applying high temperatures to contaminated sites to produce stable vitreous (glass-like) materials, effectively immobilizing pollutants This process not only stabilizes heavy metals such as lead (Pb), cadmium (Cd), and chromium (Cr), but also destroys and volatilizes organic contaminants, ensuring thorough decontamination It is particularly effective for reclaiming soils contaminated with hazardous materials like asbestos and asbestos-containing substances Additionally, volatile metals released during vitrification must be carefully collected for proper treatment or disposal, ensuring environmental safety and compliance.
Vitrification can be applied in situ and ex situ with a large range of organic and inorganic contaminants In situ is preference because of lower cost and energy requirement (USEPA, 1992)
Ex situ treatment involves processes such as excavation, pretreatment, mixing, feeding, melting, heating, gas collection and treatment, and casting of the melted product, with energy consumption for melting being a significant cost factor Waste generated during the process can be recycled and reused, enhancing sustainability (Smith et al., 1995) In situ applications utilize electrical current to generate heat for melting contaminated soils, with a single four-electrode system capable of treating up to 1,000 tons of soil at depths of 20 feet, processing 3 to 6 tons per hour To optimize melting efficiency, additives like flaked graphite and glass grit are required when soils are excessively alkaline or dry, due to high Na2O and K2O content (Buelt and Thompson, 1992).
Soil washing is an effective volume reduction and waste minimization technique that can be performed either in situ or ex situ This process involves separating contaminant-laden soil particles from bulk soil using chemical agents like acids and chelators to recover contaminants such as heavy metals The addition of acids, alkalis, complexes, solvents, and surfactants enhances the solubility of heavy metals, allowing their removal into the aqueous phase Removed contaminants can be further treated through chemical sorption, ion exchange, thermal methods, or biological procedures, or they may be disposed of in hazardous waste landfills The cleaned soil can subsequently be recycled, reused in construction, or disposed of as non-hazardous waste, making soil washing a versatile solution for contaminated site remediation.
Soil washing can achieve an efficiency rate of over 70-80%, making it a cost-effective solution for sandy and granular soils However, its effectiveness drops to less than 30-35% when dealing with clay and silt soils, due to the strong binding of heavy metals to soil particles To improve treatment outcomes, extractants with high potential for dissolving heavy metals while preserving soil properties are essential, with organic acids and chelating agents being recommended Natural low molecular weight organic acids such as oxalic, citric, formic, acetic, malic, succinic, malonic, maleic, lactic, aconitic, and fumaric acids are commonly used in this context.
Low Molecular Weight Organic Acids (LMWOAs) are effective in dissolving heavy metals, offering a potential solution for metal remediation However, certain commonly used chelators, including citric acid, tartaric acid, and EDTA, have not yet been proven suitable for full-scale applications due to limitations in efficacy or environmental concerns (Naidu and Harter, 1998; Ke et al., 2006; Peters, 1999; Tejowulan and Hendershot, 1998; Sun et al., 2001).
1.4.2 Remediation of radionuclides in soils
Current techniques for remediating radionuclide-contaminated soils include physical methods, agricultural countermeasures, and phytoremediation Physical approaches often involve soil removal combined with dispersing and chelating agents, but these are limited by high labor, equipment costs, and potential ecological disturbance Additionally, transporting contaminated soil can spread pollutants and harm ecosystems The use of chemical agents may also pose environmental risks Alternative strategies to mitigate contamination include surface soil removal, soil ploughing, harvesting contaminated plant parts, and applying detergents or cleaning agents to reduce radionuclide levels.
Agriculture-based countermeasures are among the most effective methods to reduce radiation exposure in humans through contaminated crops, utilizing mineral and chemical absorbents or K- and Ca-containing fertilizers Natural or synthetic amendments, such as zeolite, enhance the soil's ability to immobilize radionuclides by increasing the soil-liquid distribution coefficient (Kd) for radiocaesium, thereby decreasing its uptake by plants Chemical agents like ammonium-ferric-hexacyano-ferrate (AFCF) effectively reduce radiocaesium levels in soils; for example, applying 10 to 100 g/cm² AFCF can lower radiocaesium accumulation in ryegrass grown on sandy soil without impacting plant growth Additionally, the application of potassium and calcium fertilizers has been shown to decrease the absorption of radiocaesium and radiostrontium in crops, providing a practical approach to mitigate radiological risks in agriculture.
Bioremediation is considered an energy saving and cost effective solution which includes soil fungi, mycorrhizae and phytoextraction application (Zhu and Shaw,
2000) Stable Cs accumulation was found in 18 fungal species (Clint et al., 1991) Radioceasium immobilization by soil fungi was discovered by Dighton et al (1991)
Mycorrhizae, a vital group of soil fungi, play a significant role in mitigating groundwater pollution by blocking radionuclides in the topsoil layer, thus reducing environmental contamination (Dighton et al., 1991) The potential of mycorrhizae to improve radionuclide-contaminated soils is promising, but further research is needed to fully understand their effectiveness and mechanisms (Zhu and Shaw, 2000).
1.4.3 Phytoremediation of heavy metals and radionuclides
Phytoremediation, also known as green remediation, botanoremediation, agroremediation, or vegetative remediation, is an in situ strategy that utilizes vegetation, associated microbiota, soil amendments, and agronomic techniques to effectively remove, contain, or neutralize environmental contaminants This eco-friendly approach offers a sustainable solution for cleaning up contaminated sites by harnessing the natural abilities of plants and microorganisms.
Sunflowers for phytoremediation of trace metals in soils
There is a wealth of evidence that several species of plants can tolerate heavy metal and other chemicals for example Indian mustard (Brassica juncea), Corn (Zea mays
L.) or sunflower (Helianthus annuus L.).Therefore these plants can be used for phytoremediation
Sunflower (Helianthus annuus L.) is a vital environmental cleanup crop known for its oil production and ornamental value It effectively remediates chemical and radiological contaminated soils and water, significantly reducing heavy metal concentrations such as Cd, Cr, Cu, Mn, Ni, and Pb within just one hour of application (Eapen et al., 2007) Combined with Indian mustard (Brassica rapa), sunflowers have been used to remediate heavy metal and radionuclide-contaminated sites in the USA, including lead contamination in Connecticut from 1997 to 2000, highlighting their effectiveness in environmental detoxification efforts.
Pb contaminated soil (75-3,450 mg/kg) at the Daimler Chysler car manufacturing company In one season, with sunflower and Indian Mustard application, the level of
Sunflowers have proven effective in phytoremediation, as they can reduce soil lead (Pb) levels to 900 mg/kg and accumulate uranium (U) ranging from 764 to 1669 mg/kg, making them suitable for cleaning contaminated sites At US Army sites in Aberdeen, Maryland, sunflowers were specifically used to remediate uranium-contaminated soil containing 47 mg/kg of U Multiple studies (Salt et al., 1998; Jovanovia et al., 2001) confirm that sunflowers effectively absorb uranium from polluted soils The combined application of sunflowers and Indian Mustard for soil remediation costs approximately $40-50 USD per cubic yard, offering an affordable solution for contaminated land cleanup.
Compared to traditional excavation and landfill disposal, my methods can save over US$1.1 million in the USA, offering a cost-effective solution for waste management (Singh et al., 2007) Sunflowers are highly efficient in decontaminating heavy metals and radionuclides, with studies by Dushenkov et al (1995), Salt et al (1998), and Jovanovic et al (2001) demonstrating their effectiveness The roots of sunflowers can significantly reduce levels of contaminants such as cadmium (Cd) and chromium (Cr), making them a sustainable choice for environmental remediation.
Sunflowers are considered a promising candidate for phytoremediation due to their high biomass production, which enhances the removal of heavy metals and radionuclides from contaminated soils Unlike hyperaccumulators that often grow slowly and produce low biomass, sunflowers exhibit fast growth, high biomass, and remarkable tolerance and accumulation capabilities for metals such as Cu, Mn, Ni, Pb, Sr, U (VI), and Zn, making them effective for soil remediation in polluted environments.
Source: http://homeopathtyler.wordpress.com
Earthworms for remediation of heavy metals and radionuclides
Using earthworms (vermiremediation technology) for soil heavy metal decontamination is also an innovative and effective solution According to Hand
Vermiremediation is a cost-effective and easy-to-perform technology for cleaning soils contaminated with chemicals, costing less than twice as much as mechanical excavation—approximately $500 to $1,000 per hectare compared to $10,000 to $15,000 per hectare This eco-friendly remediation method is effective because it significantly increases earthworm populations, which enhance soil detoxification processes; notable improvements can be observed in just three days.
Earthworms can rapidly establish populations in polluted land, with 0.2 to 1.0 million individuals developing over 30 months in one hectare, highlighting their potential for bioremediation (Sinha et al., 2008) They exhibit high tolerance to soil toxicants, accumulating heavy metals and organic pollutants, which aids in detoxifying contaminated soils (Ireland, 1979; Contreras-Ramos et al., 2006) Additionally, earthworms play a crucial role in biosolids treatment by inhibiting pathogens like Salmonella, thereby improving biosafety standards (Shakir Hanna and Weaver, 2002) Their ability to bioaccumulate heavy metals is especially effective when metals cannot easily cross cell membranes, making them valuable for contaminant removal Furthermore, earthworm vermicasts contain enzymes such as amylase, cellulase, and chitinase that break down organic matter and release essential nutrients, promoting healthy plant growth (Sinha et al., 2008).
Earthworms are highly effective for remediating heavy metals and radionuclides in soil due to their constant contact with the soil throughout their life cycle and their ability to inhabit various soil types and horizons They can survive in contaminated soils, and their body concentrations serve as indicators of contaminant bioavailability Earthworms directly uptake contaminants through their skin and ingest soil as a primary food source, facilitating the accumulation of pollutants Their sufficient biomass allows for accurate measurement of contaminant levels, and their physiology and metal metabolism are well understood, enabling reliable assessments Additionally, earthworms can enhance the mobility and bioavailability of heavy metals to plants, contributing to ecological remediation processes (Lanno et al., 2004; Wen et al., 2004b).
Earthworms have the ability to absorb heavy metals, pesticides, and organic contaminants such as PAHs (polycyclic aromatic hydrocarbons), playing a crucial role in soil contaminant dynamics (Contreras-Ramos et al., 2006; Sinha et al., 2008) The bioaccumulation factor (BAF), defined as the ratio of contaminant concentration in worms to that in soil, serves as an important tool for assessing the bioavailability of these pollutants in soil environments (Fründ et al., 2011).
The bioaccumulation of earthworms is affected by biotic and abiotic factors In the soil, the accumulation depends on the concentration and physicochemical
Studies have shown a significant correlation between soil metal concentrations—specifically Cd, Zn, Pb, and Cu—and their accumulation in earthworms (Aporrectodea tuberculata and L rubellus), with Neuhauser et al (1995) noting this relationship in soils amended with sewage sludge The strength of these correlations varies, with R² values of 0.72 for Cd, 0.65 for Cu, and lower values for other metals, indicating differing bioavailability levels (Tischer, 2009) The chemical form of contaminants influences their bioaccumulation; for example, lead in salt form is more readily absorbed than aged contaminated lead Additionally, soil conditions such as pH and redox potential significantly impact metal speciation and bioavailability (Alberti et al., 1996) Microcompartment distribution within the soil—covering roots, organic matter, minerals, aggregates, and soil water—also plays a crucial role in determining the extent of metal accumulation in organisms (Ernst et al., 2008; Morgan and Morgan).
Earthworms passively accumulate contaminants, including heavy metals and radionuclides, through their body wall, mouth, and intestinal wall, primarily driven by diffusion based on concentration gradients between pore water and their tissues (Jager et al., 2003) Their contamination levels are influenced by both behavioral factors such as avoidance, feeding habits, habitat preferences, and spatial mobility, as well as physiological processes including cellular uptake, regulation, binding protein interactions, granule formation, and excretion mechanisms (Fründ et al., 2011).
Earthworms significantly influence both abiotic and biotic soil properties, impacting soil health and contamination remediation Their burrowing activity enhances soil aeration by creating channels and breaking down particles, which promotes greater microbial exposure and facilitates the degradation of contaminants Additionally, earthworms consume and digest organic matter containing pollutants, converting it into smaller, more manageable forms for microbial action On the biotic side, earthworm excretion enriches the soil by increasing microbial populations such as bacteria, fungi, and actinomycetes, due to the presence of nutrients like urine, mucus, glucose, and other organic compounds (Sinha et al., 2009).
Earthworms can change the bioavailability of pollutants as a result of stimulation of the soil microbial population, alteration of soil pH and dissolved organic carbon
Earthworm casts enhance soil health by increasing microbial biomass, including bacteria, actinomycetes, and fungi, which can lead to greater metal availability for plants (Went et al., 2004) Microbial populations play a key role in degrading metal-binding organic matter, releasing metals into the soil solution and improving metal sequestration and speciation within earthworm tissues (Sizmur and Hodson, 2009) This process highlights the important function of earthworms and soil microbes in metal cycling and soil fertility.
Earthworm activities significantly enhance soil aeration, organic matter content, and water availability, contributing to improved soil health (Tiunov and Scheu, 1999) They can alter soil pH levels, with some studies indicating that earthworms decrease soil pH and increase metal availability through this pH reduction (El-Gharmali, 2002; Kizilkaya, 2004; Yu et al., 2005) Conversely, other research suggests that earthworms elevate soil pH by excreting mucus, which also results in increased metal availability (Schrader, 1994; Ma et al., 2002).
Changes in soil dissolved organic carbon (DOC) significantly affect the availability of heavy metals, as DOC readily forms complexes with metals in the soil solution and facilitates their extraction from the soil surface Earthworms contribute to this process by producing humic acid, which enhances metal bioavailability through the formation of organo-metal compounds Additionally, earthworm-derived organic chelating materials can increase plant uptake of heavy metals, linking biological activity to improved phytoextraction of contaminated soils.
Earthworms accumulate heavy metals, such as lead (Pb), zinc (Zn), and cadmium (Cd), primarily in the chloragogenous tissue surrounding the posterior alimentary canal They maintain these metals through two main mechanisms: first, by binding insoluble metals with phosphate-rich granules called chloragosomes, which facilitate the sequestration of Pb and Zn; second, by binding metals to low molecular weight, sulfur-donating ligands known as metallothioneins, which effectively detoxify metals like Cd and Pb Studies have confirmed the presence of Cd-metallothioneins and Pb-metallothioneins in earthworm tissues, highlighting their role in heavy metal detoxification.
L terrestris and D rubidus respectively by Ireland (1979) (Ireland, 1979) Earthworm metallothionein isoform 1 wMT-1 is responsible for essential heavy metals such as Zn
33 and Cu at non toxic concentration wMT-2 responses for non essential metals and essential metals (Zn) at a higher toxic threshold level (Morgan and Morgan, 1989, Sturzenbaum et al., 2001)
Eisenia andrei was selected for this study due to its ease of cultivation under laboratory conditions and its well-documented chemical toxicity profile, as extensively reported in previous research (Lee et al., 2008).
Lourenço et al (2011) demonstrated that contaminated soils with heavy metals and radionuclides, such as uranium mining residues, pose risks to the survival and health of epigeic Eisenia andrei populations, with tissue effects correlating to metal accumulation Natal-da-Luz et al (2011) found that organic matter increases reduce metal bioavailability in sludge and freshly spiked soils contaminated with chromium, copper, nickel, and zinc Saxe et al (2001) developed a model linking Eisenia andrei’s body concentrations of cadmium, copper, lead, and zinc to soil pH, metals, and organic carbon levels, highlighting the use of earthworms as effective biomonitors for predicting metal contamination in soils.
Use of toxicity tests for environmental risk assessment of contaminated soils
For effective soil toxicity testing, it is ideal to include all ecological and commercial organisms related to the soil environment; however, this is impractical, so selected test species are used to best estimate ecosystem risk These test organisms must be representative of the specific environment and sensitive to contaminants to ensure accurate results Standardized toxicity testing protocols have been developed by organizations such as OECD, ISO, ASTM, and EPA, facilitating consistent assessment methods Toxicity data can be obtained through biochemical and other biological endpoints to evaluate contaminant impacts on soil health effectively.
Source: http://www.thegardenforums.org
34 physiological, reproductive, behavioral effects, lethality, reproduction, and growth (Stephenson et al., 2002)
Earthworm toxicity tests are the most popular Two major tests based on mortality and production of Eisenia sp have been standardized by OCED (OECD, 2004a)
Avoidance, weight loss, and chemical bioaccumulation can also be used to estimate the toxicity of chemicals in the terrestrial environment (Domínguez, 2008)
Plants serve as vital indicators of soil quality and health To assess soil toxicity, various methods have been evaluated, focusing on endpoints such as plant survival, growth (including height, length, or biomass), seed germination, and seedling development Additionally, biochemical markers like specific enzyme activities and respiration rates (both total and dark respiration) are used to determine contaminant effects, following standardized protocols like OECD (2006a).
Microbial toxicity tests are essential tools for assessing soil quality by evaluating the health and functionality of soil microorganisms These tests focus on key microbial activities such as soil respiration, nitrogen mineralization, and the activity of crucial soil enzymes—including dehydrogenases, β-glucosidases, ureases, phosphatases, arylsulphatases, cellulases, and phenol oxidases—that are vital for organic matter decomposition and nutrient cycling in terrestrial ecosystems (Dick et al., 1996).
The bioluminescence assay using Vibrio fischeri (Microtox) is a reliable method for assessing soil leachate toxicity due to the bacterium's sensitivity to heavy metals and other contaminants This marine bacterium emits light, and changes in luminescence are measured with a photometer over time to determine toxicity levels Thanks to its fast metabolism, the assay provides quick and accurate results, making it a widely accepted, sensitive, and precise tool for environmental toxicity testing.
Integrated soil microcosms
Single species toxicity tests often fall short in accurately predicting the overall environmental impact of toxicants under field conditions (Edwards, 2002) In contrast, integrated soil microcosms (ISM) that include multiple species offer a more comprehensive understanding of how toxicants interact with biological communities, effectively simulating real-world scenarios These microcosms can provide valuable data on the interactive effects of toxicants on soil health and biological activity, aiding in more accurate risk assessments Additionally, various types of microcosms are widely used in ecotoxicological studies due to their ease of operation, cost-effectiveness, and ability to be controlled under laboratory settings with multiple replicates, making them a practical tool for environmental toxicity testing (Chen and Edwards, 2001).
The integrated soil microcosm (ISM) is constructed as a plastic or PVC/HDPE cylinder containing approximately 1 kg of sieved, homogenized field soil mixed with indigenous soil organisms, including earthworms and plants (Edwards, 2002) Ion exchange resins are placed at the bottom, separated by a glass wool layer, to collect leachates and prevent root intrusion Irrigation occurs two to three times a week at 40-60% of field water holding capacity, with leachates collected weekly by adding excess water for analysis A funnel can be used to replace the ion exchange layer during studies on pesticide fate and leaching, and collected leachates are stored in a plastic container for further examination (Edwards, 2002).
Figure 1.6 Main components of an integrated soil microcosm (ISM)
36 testing the toxicity of environmental pollutants there are few published studies on the use of ISMs to evaluate bioremediation of trace metal pollutants.
Aims of the project
This project focused on assessing the effectiveness of bioremediation strategies for removing cesium (Cs) and lead (Pb) from contaminated soils using specific biota The study aimed to determine the potential of selected microorganisms and plants to immobilize or extract these hazardous metals By evaluating different bioremediation methods, the research sought to identify the most efficient approach for restoring soil health The findings contribute valuable insights into sustainable remediation techniques for Cs and Pb contamination, supporting environmental cleanup efforts and soil safety.
1 The accumulation of Cs from soil contaminated with Cs only by sunflowers with and without earthworms
2 The accumulation of Pb from contaminated soil by sunflowers with and without earthworms
3 The accumulation of Cs and Pb from soil contaminated with a mixture of these metals by sunflowers with and without earthworms
4 The effects of Cs and Pb as individual metal contaminants and a mixture of
Pb and Cs on plants and earthworms in contaminated soil
5 The fate of Cs and Pb in the soil profile through their mobility, leaching and effects on soil pH, conductivity and organic matter
This study introduces innovative approaches by utilizing Eisenia andrei earthworms and the dwarf sunflower, Helianthus annuus, in combination for enhanced phytoremediation The research also explores the combined application of cesium (Cs) and lead (Pb) contaminants as a mixture, aiming to assess their collective impact on soil remediation processes Additionally, the use of integrated soil microcosms provides a controlled environment to better understand the interactions between biotic and abiotic factors, thereby advancing sustainable strategies for soil detoxification and environmental remediation.