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80-423: Phytoremediation is proposed as a cost-effective plant-based approach of environmental remediation that takes advantage of the ability of plants to concentrate elements and compounds from the environment and to detoxify various compounds without causing additional pollution. The concentrating effect results from the ability of certain plants called hyperaccumulators to bioaccumulate chemicals. The remediation effect

160-516: A Superfund to remediate abandoned sites, or to litigate to force corporations to remediate their contaminated sites. Other countries have other mechanisms and commonly sites are rezoned to "higher" uses such as high density housing, to give the land a higher value so that after deducting cleanup costs there is still an incentive for a developer to purchase the land, clean it up, redevelop it and sell it on, often as apartments (home units). There are several tools for mapping these sites and which allow

240-458: A jail sentence for the polluter. Penalties must be significant as otherwise fines are treated as a normal expense of doing business. Compliance must be cheaper than to have continuous breaches. Assessment should be made of the risks of operations, transporting contaminated material, disposal of waste which may be contaminated including workers' clothes, and a formal emergency response plan should be developed. Every worker and visitor entering

320-407: A micro-organism or may be transferred from one plant to another variety better adapted to the environmental conditions at the cleanup site. For example, genes encoding a nitroreductase from a bacterium were inserted into tobacco and showed faster removal of TNT and enhanced resistance to the toxic effects of TNT. Researchers have also discovered a mechanism in plants that allows them to grow even when

400-450: A chemical free technology. Air microbubbles generated in water without adding any surfactant could be used to clean oil contaminated sediments. This technology holds promise over the use of chemicals (mainly surfactant) for traditional washing of oil contaminated sediments. In preparation for any significant remediation there should be extensive community consultation. The proponent should both present information to and seek information from

480-571: A concentration of 93% and bioaccumulation factor of 5.6, lead , mercury , zinc with a bioaccumulation factor of 3.6, and arsenic at a concentration of 22%. Black soldier fly larvae (BSFL) have also been used to monitor the degradation and reduction of anthropogenic oil contamination in the environment. Entomoremediation is considered viable as an accessible low-energy, low-carbon, and highly renewable method for environmental decontamination. Cleaning of oil contaminated sediments with self collapsing air microbubbles have been recently explored as

560-403: A considerable amount of contaminants from the soil. Phytoextraction has been growing rapidly in popularity worldwide for the last twenty years or so. Typically, phytoextraction is used for heavy metals or other inorganics. At the time of disposal, contaminants are typically concentrated in the much smaller volume of the plant matter than in the initially contaminated soil or sediment. After harvest,

640-414: A faster rate than would larger particles. Most field applications of nanoremediation have used nano zero-valent iron (nZVI), which may be emulsified or mixed with another metal to enhance dispersion. That nanoparticles are highly reactive can mean that they rapidly clump together or react with soil particles or other material in the environment, limiting their dispersal to target contaminants. Some of

720-446: A lower level of the contaminant will remain in the soil, so the growth/harvest cycle must usually be repeated through several crops to achieve a significant cleanup. After the process, the soil is remediated. Of course many pollutants kill plants, so phytoremediation is not a panacea. For example, chromium is toxic to most higher plants at concentrations above 100 μM·kg−1 dry weight. Mining of these extracted metals through phytomining

800-518: A more cost effective solution. Phytoremediation may be applied to polluted soil or static water environment. This technology has been increasingly investigated and employed at sites with soils contaminated heavy metals like with cadmium , lead , aluminum , arsenic and antimony . These metals can cause oxidative stress in plants, destroy cell membrane integrity, interfere with nutrient uptake, inhibit photosynthesis and decrease plant chlorophyll . Phytoremediation has been used successfully in

880-622: A polluted area of 20,000 m in Bakar , Croatia based on solidification/stabilization with ImmoCem is currently in progress. After three years of intensive research by the Croatian government, the EU funded the immobilization project in Bakar. The area is contaminated with large amounts of TPH , PAH , and metals. For the immobilization, the contractor chose to use the mix-in-plant procedure. Subsoil Subsoil

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960-417: A remediation project. The use of incremental health risk is based on carcinogenic and other (e.g., mutagenic , teratogenic ) effects and often involves value judgements about the acceptable projected rate of increase in cancer . In some jurisdictions this is 1 in 1,000,000 but in other jurisdictions the acceptable projected rate of increase is 1 in 100,000. A relatively small incremental health risk from

1040-728: A section of the tree trunk for later laboratory analysis, often by using an increment borer . Phytoscreening may lead to more optimized site investigations and reduce contaminated site cleanup costs. Environmental remediation Environmental remediation is the cleanup of hazardous substances dealing with the removal, treatment and containment of pollution or contaminants from environmental media such as soil , groundwater , sediment . Remediation may be required by regulations before development of land revitalization projects. Developers who agree to voluntary cleanup may be offered incentives under state or municipal programs like New York State's Brownfield Cleanup Program. If remediation

1120-459: A single project is not of much comfort if the area already has a relatively high health risk from other operations like incinerators or other emissions, or if other projects exist at the same time causing a greater cumulative risk or an unacceptably high total risk. An analogy often used by remediators is to compare the risk of the remediation on nearby residents to the risks of death through car accidents or tobacco smoking . Standards are set for

1200-422: A transformation pathway has been proposed. Phytostimulation (or rhizodegradation) is the enhancement of soil microbial activity for the degradation of organic contaminants, typically by organisms that associate with roots . This process occurs within the rhizosphere , which is the layer of soil that surrounds the roots. Plants release carbohydrates and acids that stimulate microorganism activity which results in

1280-443: Is a conceivable way of recovering the material. Hyperaccumulating plants are often metallophyte . Induced or assisted phytoextraction is a process where a conditioning fluid containing a chelator or another agent is added to soil to increase metal solubility or mobilization so that the plants can absorb them more easily. While such additives can increase metal uptake by plants, they can also lead to large amounts of available metals in

1360-473: Is a controversial step as: Often corporations which do voluntary testing of their sites are protected from the reports to environmental agencies becoming public under Freedom of Information Acts , however a "Freedom of Information" inquiry will often produce other documents that are not protected or will produce references to the reports. In the US there has been a mechanism for taxing polluting industries to form

1440-414: Is a technology for soil remediation. During the process a desorber volatilizes the contaminants (e.g. oil, mercury or hydrocarbon) to separate them from especially soil or sludge. After that the contaminants can either be collected or destroyed in an offgas treatment system. Excavation processes can be as simple as hauling the contaminated soil to a regulated landfill , but can also involve aerating

1520-583: Is a variant of bioremediation in which insects decontaminate soils. Entomoremediation techniques engage microorganisms , collembolans , ants , flies , beetles , and termites . It is dependent on saprophytic insect larvae, resistant to adverse environmental conditions and able to bioaccumulate toxic heavy metal contaminants. Hermetia illucens (black soldier fly - BSF) is an important entomoremediation participant. H. illucens has been observed to reduce polluted substrate dry weight by 49%. H. illucens larvae have been observed to accumulate cadmium at

1600-449: Is also successful when utilized as the initial step in a multi-faceted remedial approach utilizing SEAR then In situ Oxidation, bioremediation enhancement or soil vapor extraction (SVE). Pump and treat involves pumping out contaminated groundwater with the use of a submersible or vacuum pump , and allowing the extracted groundwater to be purified by slowly proceeding through a series of vessels that contain materials designed to adsorb

1680-450: Is also used for the mining of metals such as copper(II) compounds. The roots take up substances from the soil or water and concentrate them above ground in the plant biomass Organisms that can uptake high amounts of contaminants are called hyperaccumulators . Phytoextraction can also be performed by plants (e.g. Populus and Salix ) that take up lower levels of pollutants, but due to their high growth rate and biomass production, may remove

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1760-515: Is an effective remediation technology for soil. "Multi Phase Extraction" (MPE) is also an effective remediation technology when soil and groundwater are to be remediated coincidentally. SVE and MPE utilize different technologies to treat the off-gas volatile organic compounds (VOCs) generated after vacuum removal of air and vapors (and VOCs) from the subsurface and include granular activated carbon (most commonly used historically), thermal and/or catalytic oxidation and vapor condensation. Generally, carbon

1840-631: Is done by removal the waste materials are simply transported off-site for disposal at another location. The waste material can also be contained by physical barriers like slurry walls . The use of slurry walls is well-established in the construction industry. The application of (low) pressure grouting , used to mitigate soil liquefaction risks in San Francisco and other earthquake zones, has achieved mixed results in field tests to create barriers, and site-specific results depend upon many variable conditions that can greatly impact outcomes. Remedial action

1920-617: Is generally subject to an array of regulatory requirements, and may also be based on assessments of human health and ecological risks where no legislative standards exist, or where standards are advisory. In the United States , the most comprehensive set of Preliminary Remediation Goals (PRGs) is from the Environmental Protection Agency (EPA) Regional Screening Levels (RSLs). A set of standards used in Europe exists and

2000-501: Is known as Phase I metabolism, similar to the way that the human liver increases the polarity of drugs and foreign compounds ( drug metabolism ). Whereas in the human liver enzymes such as cytochrome P450s are responsible for the initial reactions, in plants enzymes such as peroxidases, phenoloxidases, esterases and nitroreductases carry out the same role. In the second stage of phytotransformation, known as Phase II metabolism, plant biomolecules such as glucose and amino acids are added to

2080-512: Is likely to come in contact is of particular importance for barriers constructed from fluids which are supposed to set in-situ. EPA emphasizes this compatibility in its guidance documents, noting that thorough characterization of the waste, leachate, barrier material chemistry, site geochemistry, and compatibility testing of the barrier material with the likely disposal site chemical environment are all required." These guidelines are for all materials - experimental and traditional. Thermal desorption

2160-742: Is often called the Dutch standards . The European Union (EU) is rapidly moving towards Europe-wide standards, although most of the industrialised nations in Europe have their own standards at present. In Canada , most standards for remediation are set by the provinces individually, but the Canadian Council of Ministers of the Environment provides guidance at a federal level in the form of the Canadian Environmental Quality Guidelines and

2240-455: Is quite different. Toxic heavy metals cannot be degraded, but organic pollutants can be, and are generally the major targets for phytoremediation. Several field trials confirmed the feasibility of using plants for environmental cleanup . Soil remediation is an expensive and complicated process. Traditional methods involve removal of the contaminated soil followed by treatment and return of the treated soil. Phytoremediation could in principle be

2320-438: Is the depth where these weathering products accumulate. The accumulation of clay minerals, iron, aluminum, and organic compounds is called illuviation . Whereas the topsoil tends to be the depth of greatest physical, chemical, and biological activity, the subsoil is the depth of most deposition. Due to physical, chemical, and biological activity, the subsoil generally has a soil structure . The presence of structure distinguishes

2400-414: Is the impact on local traffic, schools, playing fields, and other public facilities due to the increased population. Dioxins from Union Carbide used in the production of now-banned pesticide 2,4,5-Trichlorophenoxyacetic acid and defoliant Agent Orange polluted Homebush Bay . Remediation was completed in 2010, but fishing will continue to be banned for decades. An EU contract for immobilization of

2480-581: Is the layer of soil under the topsoil on the surface of the ground. Like topsoil, it is composed of a variable mixture of small particles such as sand , silt and clay , but with a much lower percentage of organic matter and humus . The subsoil is labeled the B Horizon in most soil mapping systems. Because it has less organic matter than topsoil , subsoil soil colour is mainly derived from iron oxides. Iron oxides and clay minerals form due to weathering . Rainfall moves these weathering products downward as solutes and colloids by rainfall. The subsoil

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2560-404: Is the possibility of decreasing anaerobic contaminant destruction natural attenuation where existing conditions enhance anaerobic bacteria which normally live in the soil prefer a reducing environment . In general, aerobic activity is much faster than anaerobic and overall destruction rates are typically greater when aerobic activity can be successfully promoted. The injection of gases into

2640-486: Is the removal of substances from soil or water with release into the air, sometimes as a result of phytotransformation to more volatile and/or less polluting substances. In this process, contaminants are taken up by the plant and through transpiration, evaporate into the atmosphere. This is the most studied form of phytovolatilization, where volatilization occurs at the stem and leaves of the plant, however indirect phytovolatilization occurs when contaminants are volatilized from

2720-455: Is then captured and pumped out by extraction wells for further treatment at the surface. Then the water after treatment is discharged into surface water or re-injected into groundwater. In geologic formations that allow delivery of hydrocarbon mitigation agents or specialty surfactants, this approach provides a cost-effective and permanent solution to sites that have been previously unsuccessful utilizing other remedial approaches. This technology

2800-467: Is used for low (below 500 ppmV) VOC concentration vapor streams, oxidation is used for moderate (up to 4,000 ppmV) VOC concentration streams, and vapor condensation is used for high (over 4,000 ppmV) VOC concentration vapor streams. Below is a brief summary of each technology. Using nano-sized reactive agents to degrade or immobilize contaminants is termed nanoremediation . In soil or groundwater nanoremediation, nanoparticles are brought into contact with

2880-601: The Canada-Wide Standards|Canada-Wide Standard for Petroleum Hydrocarbons in Soil . Once a site is suspected of being contaminated there is a need to assess the contamination. Often the assessment begins with preparation of a Phase I Environmental Site Assessment . The historical use of the site and the materials used and produced on site will guide the assessment strategy and type of sampling and chemical analysis to be done. Often nearby sites owned by

2960-447: The root mats of meadow grasses are effective at demobilising radiosource materials especially with certain combinations of other agricultural practices. Vidal also find that the particular grass mix makes a significant difference. Phytodegradation (also called phytotransformation) uses plants or microorganisms to degrade organic pollutants in the soil or within the body of the plant. The organic compounds are broken down by enzymes that

3040-462: The EPA; however, the EPA traditionally has been more cautious about negative externalities that may or may not arise from the introduction of these species. One of their concerns is that the toxic chemicals would lead to the microbe's gene degradation, which would then be passed on to other harmful bacteria, creating more issues, if the pathogens evolve the ability to feed off of pollutants. Entomoremediation

3120-526: The USA. Contaminants can be removed from a site or controlled. One option for control are barrier walls, which can be temporary to prevent contamination during treatment and removal, or more permanent. Techniques to construct barrier walls are deep soil mixing , jet grouting , low pressure grouting with cement and chemicals, freezing and slurry walls. Barrier walls must be constructed of impermeable materials and resistant to deterioration from contact with waste, for

3200-446: The biodegradation of the organic contaminants. This means that the microorganisms are able to digest and break down the toxic substances into harmless form. Phytostimulation has been shown to be effective in degrading petroleum hydrocarbons, PCBs, and PAHs. Phytostimulation can also involve aquatic plants supporting active populations of microbial degraders, as in the stimulation of atrazine degradation by hornwort . Phytovolatilization

3280-496: The case of organic pollutants, such as pesticides , explosives , solvents , industrial chemicals, and other xenobiotic substances, certain plants, such as Cannas , render these substances non-toxic by their metabolism . In other cases, microorganisms living in association with plant roots may metabolize these substances in soil or water. These complex and recalcitrant compounds cannot be broken down to basic molecules (water, carbon-dioxide, etc.) by plant molecules, and, hence,

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3360-437: The community should be engaged (at proponent expense if a fee is required). Minutes of meetings including questions asked and the answers to them and copies of presentations by the proponent should be available both on the internet and at a local library (even a school library) or community centre. Incremental health risk is the increased risk that a receptor (normally a human being living nearby) will face from (the lack of)

3440-402: The community. The proponent needs to learn about "sensitive" (future) uses like childcare, schools, hospitals, and playgrounds as well as community concerns and interests information. Consultation should be open, on a group basis so that each member of the community is informed about issues they may not have individually thought about. An independent chairperson acceptable to both the proponent and

3520-501: The compounds used which vary in viscosity, gel time and density: "The selection of subsurface barriers for any given site which needs remediation, and the selection of a particular barrier technology must be done, however, by means of the Superfund Process, with special emphasis on the remedial investigation and feasibility study portions. The chemical compatibility of the material with the wastes, leachates and geology with which it

3600-627: The contaminant through either in situ injection or a pump-and-treat process. The nanomaterials then degrade organic contaminants through redox reactions or adsorb to and immobilize metals such as lead or arsenic . In commercial settings, this technology has been dominantly applied to groundwater remediation , with research into wastewater treatment . Research is also investigating how nanoparticles may be applied to cleanup of soil and gases. Nanomaterials are highly reactive because of their high surface area per unit mass, and due to this reactivity nanomaterials may react with target contaminants at

3680-495: The contaminants from the groundwater. For petroleum-contaminated sites this material is usually activated carbon in granular form. Chemical reagents such as flocculants followed by sand filters may also be used to decrease the contamination of groundwater. Air stripping is a method that can be effective for volatile pollutants such as BTEX compounds found in gasoline. For most biodegradable materials like BTEX , MTBE and most hydrocarbons, bioreactors can be used to clean

3760-442: The contaminated water to non-detectable levels. With fluidized bed bioreactors it is possible to achieve very low discharge concentrations which will meet or exceed discharge requirements for most pollutants. Depending on geology and soil type, pump and treat may be a good method to quickly reduce high concentrations of pollutants. It is more difficult to reach sufficiently low concentrations to satisfy remediation standards, due to

3840-587: The degradation of the target pollutants. Broad categories of bioremediation include biostimulation , bioaugmentation , and natural recovery ( natural attenuation ). Bioremediation is either done on the contaminated site (in situ) or after the removal of contaminated soils at another more controlled site (ex situ). In the past, it has been difficult to turn to bioremediation as an implemented policy solution, as lack of adequate production of remediating microbes led to little options for implementation. Those that manufacture microbes for bioremediation must be approved by

3920-523: The dissolved oxygen content of the groundwater to support microbial degradation of the compound (especially petroleum) by direct injection of oxygen into the subsurface, or the direct injection of a slurry that slowly releases oxygen over time (typically magnesium peroxide or calcium oxy-hydroxide). Solidification and stabilization work has a reasonably good track record but also a set of serious deficiencies related to durability of solutions and potential long-term effects. In addition CO 2 emissions due to

4000-450: The emission is emanating from an area zoned industrial does not mean that in a nearby residential area there should be permitted any exceedances of the appropriate residential standards. Monitoring for compliance against each standards is critical to ensure that exceedances are detected and reported both to authorities and the local community. Enforcement is necessary to ensure that continued or significant breaches result in fines or even

4080-546: The equilibrium of absorption / desorption processes in the soil. However, pump and treat is typically not the best form of remediation. It is expensive to treat the groundwater, and typically is a very slow process to clean up a release with pump and treat. It is best suited to control the hydraulic gradient and keep a release from spreading further. Better options of in-situ treatment often include air sparge/soil vapor extraction (AS/SVE) or dual phase extraction/multiphase extraction (DPE/MPE). Other methods include trying to increase

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4160-518: The excavated material in the case of volatile organic compounds (VOCs) . Recent advancements in bioaugmentation and biostimulation of the excavated material have also proven to be able to remediate semi-volatile organic compounds (SVOCs) onsite. If the contamination affects a river or bay bottom, then dredging of bay mud or other silty clays containing contaminants (including sewage sludge with harmful microorganisms ) may be conducted. Recently, ExSitu Chemical oxidation has also been utilized in

4240-573: The groundwater may also cause contamination to spread faster than normal depending on the hydrogeology of the site. In these cases, injections downgradient of groundwater flow may provide adequate microbial destruction of contaminants prior to exposure to surface waters or drinking water supply wells. Migration of metal contaminants must also be considered whenever modifying subsurface oxidation-reduction potential. Certain metals are more soluble in oxidizing environments while others are more mobile in reducing environments. Soil vapor extraction (SVE)

4320-441: The heavy metal pollutant into a less toxic form. Stabilization results in reduced erosion, runoff, leaching, in addition to reducing the bioavailability of the contaminant. An example application of phytostabilization is using a vegetative cap to stabilize and contain mine tailings . Some soil amendments decrease radiosource mobility – while at some concentrations the same amendments will increase mobility. Vidal et al. 2000 find

4400-494: The important challenges currently limiting nanoremediation technologies include identifying coatings or other formulations that increase dispersal of the nanoparticle agents to better reach target contaminants while limiting any potential toxicity to bioremediation agents, wildlife, or people. Bioremediation is a process that treats a polluted area either by altering environmental conditions to stimulate growth of microorganisms or through natural microorganism activity, resulting in

4480-421: The levels of dust, noise, odour, emissions to air and groundwater, and discharge to sewers or waterways of all chemicals of concern or chemicals likely to be produced during the remediation by processing of the contaminants. These are compared against both natural background levels in the area and standards for areas zoned as nearby areas are zoned and against standards used in other recent remediations. Just because

4560-468: The lifespan of the barrier wall. It wasn't until the use of newer polymer and chemical grouts in the 1950s and 1960s that Federal agencies of the US government recognized the need to establish a minimum project life of 50 years in real world applications. The Department of Energy is one US government agency that sponsors research to formulate, test and determine use applications for innovative polymer grouts used in waste containment barriers. Portland cement

4640-399: The physiology of the plant. Even cultivars within the same species have varying abilities to accumulate pollutants. A range of processes mediated by plants or algae are tested in treating environmental problems.: Phytoextraction (or phytoaccumulation or phytosequestration ) exploits the ability of plants or algae to remove contaminants from soil or water into harvestable plant biomass. It

4720-474: The plant roots secrete and these molecules are then taken up by the plant and released through transpiration. This process works best with organic contaminants like herbicides, trichloroethylene , and methyl tert -butyl ether . Phytotransformation results in the chemical modification of environmental substances as a direct result of plant metabolism , often resulting in their inactivation, degradation (phytodegradation), or immobilization (phytostabilization). In

4800-499: The plant. This ensures that the xenobiotic is safely stored, and does not affect the functioning of the plant. However, preliminary studies have shown that these plants can be toxic to small animals (such as snails), and, hence, plants involved in phytotransformation may need to be maintained in a closed enclosure. Hence, the plants reduce toxicity (with exceptions) and sequester the xenobiotics in phytotransformation. Trinitrotoluene phytotransformation has been extensively researched and

4880-445: The polarized xenobiotic to further increase the polarity (known as conjugation). This is again similar to the processes occurring in the human liver where glucuronidation (addition of glucose molecules by the UGT class of enzymes, e.g. UGT1A1 ) and glutathione addition reactions occur on reactive centres of the xenobiotic. Phase I and II reactions serve to increase the polarity and reduce

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4960-1076: The pollutant involved (for example: more than 1000 mg/kg of dry weight for nickel , copper , cobalt , chromium or lead ; or more than 10,000 mg/kg for zinc or manganese ). This capacity for accumulation is due to hypertolerance , or phytotolerance : the result of adaptative evolution from the plants to hostile environments through many generations. A number of interactions may be affected by metal hyperaccumulation, including protection, interferences with neighbour plants of different species, mutualism (including mycorrhizae , pollen and seed dispersal), commensalism, and biofilm . As plants are able to translocate and accumulate particular types of contaminants, plants can be used as biosensors of subsurface contamination, thereby allowing investigators to quickly delineate contaminant plumes. Chlorinated solvents, such as trichloroethylene , have been observed in tree trunks at concentrations related to groundwater concentrations. To ease field implementation of phytoscreening, standard methods have been developed to extract

5040-427: The pollutant. The plant immobilizes the pollutants by binding them to soil particles making them less available for plant or human uptake. Unlike phytoextraction, phytostabilization focuses mainly on sequestering pollutants in soil near the roots but not in plant tissues. Pollutants become less bioavailable, resulting in reduced exposure. The plants can also excrete a substance that produces a chemical reaction, converting

5120-405: The pollution concentration in the soil is lethal for non-treated plants. Some natural, biodegradable compounds, such as exogenous polyamines , allow the plants to tolerate concentrations of pollutants 500 times higher than untreated plants, and to absorb more pollutants. A plant is said to be a hyperaccumulator if it can concentrate the pollutants in a minimum percentage which varies according to

5200-465: The remediation of contaminated soil. This process involves the excavation of the contaminated area into large bermed areas where they are treated using chemical oxidation methods. This is used in removing non-aqueous phase liquids (NAPLs) from aquifer. This is done by pumping surfactant solution into contaminated aquifer using injection wells which are passed through contaminated zones to the extraction wells. The Surfactant solution containing contaminants

5280-661: The restoration of abandoned metal mine workings, and sites where polychlorinated biphenyls have been dumped during manufacture and mitigation of ongoing coal mine discharges reducing the impact of contaminants in soils, water, or air. Contaminants such as metals, pesticides, solvents, explosives, and crude oil and its derivatives, have been mitigated in phytoremediation projects worldwide. Many plants such as mustard plants , alpine pennycress , hemp , and pigweed have proven to be successful at hyperaccumulating contaminants at toxic waste sites. Not all plants are able to accumulate heavy metals or organics pollutants due to differences in

5360-403: The root zone. Selenium (Se) and Mercury (Hg) are often removed from soil through phytovolatilization. Poplar trees are one of the most successful plants for removing VOCs through this process due to its high transpiration rate. Rhizofiltration is a process that filters water through a mass of roots to remove toxic substances or excess nutrients . The pollutants remain absorbed in or adsorbed to

5440-427: The roots. This process is often used to clean up contaminated groundwater through planting directly in the contaminated site or through removing the contaminated water and providing it to these plants in an off-site location. In either case though, typically plants are first grown in a greenhouse under precise conditions. Biological hydraulic containment occurs when some plants, like poplars, draw water upwards through

5520-517: The same company or which are nearby and have been reclaimed, levelled or filled are also contaminated even where the current land use seems innocuous. For example, a car park may have been levelled by using contaminated waste in the fill . Also important is to consider off site contamination of nearby sites often through decades of emissions to soil , groundwater , and air. Ceiling dust, topsoil , surface and groundwater of nearby properties should also be tested, both before and after any remediation. This

5600-405: The site should have a safety induction personalised to their involvement with the site. Local communities and government often resist the rezoning because of the adverse effects of the remediation and new development on the local amenities. The main impacts during remediation are noise, dust, odour, and incremental health risk. Then there is the noise, dust, and traffic of developments. Then, there

5680-404: The soil beyond what the plants are able to translocate, causing potential leaching into the subsoil or groundwater. Examples of plants that are known to accumulate the following contaminants: Phytostabilization reduces the mobility of substances in the environment, for example, by limiting the leaching of substances from the soil . It focuses on the long term stabilization and containment of

5760-501: The soil into the roots and out through the plant, which decreases the movement of soluble contaminants downwards, deeper into the site and into the groundwater. Phytodesalination uses halophytes (plants adapted to saline soil) to extract salt from the soil to improve its fertility. Breeding programs and genetic engineering are powerful methods for enhancing natural phytoremediation capabilities, or for introducing new capabilities into plants. Genes for phytoremediation may originate from

5840-421: The subsoil from the underlying substratum. Due to human activity, the topsoil and subsoil in many environments have been mixed. Below the subsoil is the soil substratum (or C horizon). Clay-based subsoil has been the primary source of material for adobe , cob , rammed earth , wattle and daub , and other earthen construction methods for millennia. Coarse sand , the other ingredient in most of these materials,

5920-728: The surface as well as extraction of contaminated groundwater and treatment at the surface. In-situ methods seek to treat the contamination without removing the soils or groundwater. Various technologies have been developed for remediation of oil-contaminated soil/sediments. Traditional remediation approaches consist of soil excavation and disposal to landfill and groundwater "pump and treat". In-situ technologies include but are not limited to: solidification and stabilization , soil vapor extraction , permeable reactive barriers, monitored natural attenuation, bioremediation - phytoremediation , chemical oxidation, steam-enhanced extraction and in situ thermal desorption and have been used extensively in

6000-461: The term phytotransformation represents a change in chemical structure without complete breakdown of the compound. The term "Green Liver" is used to describe phytotransformation, as plants behave analogously to the human liver when dealing with these xenobiotic compounds (foreign compound/pollutant). After uptake of the xenobiotics, plant enzymes increase the polarity of the xenobiotics by adding functional groups such as hydroxyl groups (-OH). This

6080-408: The toxicity of the compounds, although many exceptions to the rule are seen. The increased polarity also allows for easy transport of the xenobiotic along aqueous channels. In the final stage of phytotransformation (Phase III metabolism), a sequestration of the xenobiotic occurs within the plant. The xenobiotics polymerize in a lignin -like manner and develop a complex structure that is sequestered in

6160-459: The use of cement are also becoming a major obstacle to its widespread use in solidification/stabilization projects. Stabilization/solidification (S/S) is a remediation and treatment technology that relies on the reaction between a binder and soil to stop/prevent or reduce the mobility of contaminants. Conventional S/S is an established remediation technology for contaminated soils and treatment technology for hazardous wastes in many countries in

6240-869: The user to view additional information. One such tool is TOXMAP , a Geographic Information System (GIS) from the Division of Specialized Information Services of the United States National Library of Medicine (NLM) that uses maps of the United States to help users visually explore data from the United States Environmental Protection Agency 's (EPA) Superfund and Toxics Release Inventory programs. Remediation technologies are many and varied but can generally be categorized into ex-situ and in-situ methods. Ex-situ methods involve excavation of affected soils and subsequent treatment at

6320-616: The world. However, the uptake of S/S technologies has been relatively modest, and a number of barriers have been identified including: New in situ oxidation technologies have become popular for remediation of a wide range of soil and groundwater contaminants. Remediation by chemical oxidation involves the injection of strong oxidants such as hydrogen peroxide , ozone gas, potassium permanganate or persulfates. Oxygen gas or ambient air can also be injected to promote growth of aerobic bacteria which accelerate natural attenuation of organic contaminants. One disadvantage of this approach

6400-399: Was used in the past, however cracking and poor performance under wet-dry conditions at arid sites need improved materials to remedy. Sites that need remediation have variable humidity, moisture and soil conditions. Field implementation remains challenging: different environmental and site conditions require different materials and the placement technologies are specific to the characteristics of

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