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Other Detoxification Mechanisms in Plants

When organic contaminants are present at a given site along with heavy metals, other problems arise. Current research has identified the need to study other detoxification mechanisms too (Lyubenova et al. 2007). Shimabukuro was first to describe a three-phase cascade responsible for the metabolism of herbicides and organic xenobiotics that involved (1) activation of the xenobiotics, (2) detoxification and (3) excretion, a process analogous to animal hepatic metabolism (Schr der and Collins 2002). Activation may be catalysed by esterases, P450 monooxygenases (in membrane fractions of cells) and peroxidases (cytosolic). The second phase is detoxification sensu stricto, and is catalysed by glutathione and glycosyl transferases. It makes the compound under consideration less toxic through substitution and conjugation via reactions with sugars, amino acids and glutathione, which can be transferred to the activated xenobiotic according to the structure of the molecule and its active site...

Detox Industries Inc Detox Process Abstract

The DETOX process is primarily an in situ biodegradation process. The technology consists of two key elements (1) nonpathogenic and nongenetically engineered microorganisms that can biologically destroy refractory and nonrefractory organic chemicals and (2) controlled introduction of water, nutrients, oxygen, microorganisms, soil conditioners, pH adjusters, and surfactants into all types of soils. The process destroys such refractory chemicals as polychlorinated biphenyls (PCBs) pen-tachlorophenol (PCP) polynuclear aromatic hydrocarbons (PAHs) benzene, toluene, ethyl-benzene, and xylene (BTEX) creosote phenolics and pesticides. DETOX also destroys less refractory chemicals, such as unrefined and refined petroleum hydrocarbons. The process is applicable to sludges, sediments, and liquids and to in situ soil remediation. The DETOX process operates most effectively at soil temperatures between 60 and 95 F (16 and 35 C). The bioremediation process stops at soil temperatures below 32 F (0...

Enviro Source Technologies Super Detox Process Abstract

EnviroSource Technologies, formerly EnviroSource Treatment and Disposal Services, Inc., has developed the Super Detox stabilization process for the treatment of electric arc furnace dust (EAF dust). This dust is generated during steel production. The Super Detox process is specifically designed for low-zinc wastes EAF dusts (less than 15 zinc by weight). Super Detox technology stabilizes the ash by multiple reaction mechanisms, including oxidation reduction, metals insolubilization, silicate polymerization and substitution, and pozzolanic bonding and solidification. The technology is commercially available. EnviroSource Technologies claims the following advantages of the Super Detox system Information published by EnviroSource Technologies, formerly EnviroSource Treatment and Disposal Services, Inc., in 1991 stated that Super Detox technology costs would range from 110 to 145 per ton of electric arc furnace dust. This estimate included all processing services, including capital...

In Understanding Heavy Metal Detoxification Mechanisms

The analysis of total soluble protein in response to heavy metal stress provides valuable information about cytosolic soluble proteins related to the toxicity response to particular heavy metals. However, such an approach does not allow for exploration of the mechanisms and proteins associated with heavy metal transport, sequestration, and deposition detoxification processes. It is therefore necessary to investigate the responses of specific tissues and subcellular compartments that are directly involved in heavy metals translocation, transformation, extrusion, and sequestration within cells, such as the xylem, cell wall, plasma membrane, vacuole, and apoplast (Hall 2002). To understand the function of organelles in heavy metal detoxification processes, it is important to analyze the subcellular proteome with advanced proteomic technologies.

National Renewable Energy Laboratory Solar Detoxification of Water Abstract

Researchers at the National Renewable Energy Laboratory (NREL) in cooperation with Sandia National Laboratories are exploring applications of solar detoxification to the remediation of contaminated groundwater. This technology is an adaption of photocatalytic destruction using ultraviolet lamps. In solar detoxification, a photocatalyst (titanium dioxide) is used that generates hydroxyl radicals at approximately ambient temperatures when exposed to near-ultraviolet light. These hydroxyl radicals react with organic contaminants to form carbon dioxide, water, and dilute concentrations of simple mineral acids (i.e., hydrochloric acid). Research indicates that titanium dioxide can also reduce metal ions in solution, in some cases forming insoluble metal hydroxides and salts. The technology is not currently commercially available. Researchers claim the following advantages of solar detoxification Halide-saturated hydrocarbons such as carbon tetrachloride degrade very slowly, if at all, when...

Heavy Metal Detoxification and Tolerance in Higher Plants

Potential cellular mechanisms for metal detoxification and tolerance in higher plants are summarized as (1) restriction of metal movement to roots by mycorrhizas, (2) binding to cell wall and root exudates, (3) reduced influx across plasma membrane, (4) active efflux into apoplast, (5) chelation in cytosol by various ligands, (6) repair and protection of plasma membrane under stress conditions, and (7) transport of and accumulation of metals in vacuole (Hall 2002). Hyperaccumulator or accumulator plants and their related PGPR are main topic in metal detoxification. PGPR and arbuscular mycorrhizal fungi (AMF) develop plant growth and development in heavy metal polluted soil via helping root growth and branching. PGPR and AMF are able to lessen the toxicity of heavy metals either by declining the bioavailability of toxic heavy metals or raising bioavailability of nontoxic heavy metals. PGPR and AMF can alter chemical properties in the rhizosphere and stimulate metal accumulation (Denton...

Cadmium Metal Detoxification and Hyperaccumulators

Varma (eds.), Detoxification of Heavy Metals, Soil Biology 30, 181 internal detoxification (Basic et al. 2005 Shah and Nongkynrih 2007 Roelofs et al. 2008). Therefore, it should be kept in mind that metal hyperaccumulation and metal tolerance are not equivalent. There is little evidence linking hyperaccumulation with metal tolerance disposal (Jiang et al. 2005), yet under controlled conditions, Roosen et al. (2003) and Casio (2004) have found a decrease in hyperaccumulator biomass production with increasing Cd concentration in solution and shoots. This suggests that metal hyperaccumulation though presupposes tolerance of plants toward metals is not necessarily associated with tolerance to the metal burden in the soil. The stress responses of plants to environmental pollutant Cd are widely studied since 1980. This chapter focuses primarily on the accumulation and detoxification of Cd metal in plants and gives an overview of plants that have potential as Cd...

Isolated Enzymes for the Transformation and Detoxification of Organic Pollutants

Center for Bioremediation and Detoxification, The Pennsylvania State University, University Park, Pennsylvania One strategy for overcoming the limitations to the use of microorganisms in the detoxification of organic-polluted sites (and particularly the processes underlined in point 6 ) is the use of cell-free enzyme preparations a review of research aimed at developing the use of isolated enzymes in solid, liquid, and hazardous waste treatment has been published (9). These authors examined the potential application of several enzymes according to categories of specific waste types (e.g., phenols and related compounds, pulp and paper wastes, pesticides, food processing wastes, solid waste and sludge treatment, and heavy metals).

Initial Steps of Intracellular Copper Detoxification

Information concerning the role of MT and PC in detoxification of Cu excess is contradictory and sometimes mutually exclusive (Sch fer et al. 1997 Gonzalez-Mendoza et al. 2007 Guo et al. 2008). We studied the involvement of MT and PC in Cu detoxification in Brassica napus L. plants grown in the presence of 10, 50, and 150 p.M CuSO4 for 10 days The correlation analysis was performed for tested indices. The analysis of the bulk of information obtained for roots showed that the coefficients of correlation between Cu concentration ( Cu ) and the level of mRNA were equal to +0.971 for MT1 and +0.966 for MT2 gene, for leaves, r +0.986 for MT2 gene. These data make very probable that the transcription levels of these genes were tightly connected with Cu concentration in the symplast of corresponding organs. In spite of the complex type of dependence between Cu and the level of PCS mRNA, the coefficients of correlation for each of the branches of this dependence were rather high r +0.957 and...

Metal Accumulation and Detoxification by Cyanobacteria

Microbes can detoxify metals by valence transformation, extracellular chemical precipitation or volatization. Such microbes combat high concentration of heavy metals by inactivation of metals, alternation of the site of inhibition, impermeability of the metals and, other bypass mechanism (Bellivean and Treyors 1989).

Phytoremediation Detoxification of Explosives by Plants

Activation or transformation generally involves oxidation or hydrolysis or reduction type of reactions, where functional groups such as hydroxyl (-OH) and carboxyl (-COOH) are added to the contaminant with enzymatic involvement of cytochrome P450 monooxygenases, esterases, reductases, dehalogenases, and dehydrogenases. The products of phase I (activation) are more hydrophilic and sometimes more toxic than the parent compound. In the phase II (conjugation), the activated contaminant undergoes deactivation by the formation of covalent linkages with endogenous hydrophilic molecules such as glucose, malonate, glutathione (GSH), or carboxylic acids using glucosyltransferase-, glutathione-S-transferase-, and acyltransferase-mediated reactions that result in water soluble conjugates that are less toxic compared to the parent compound. Phase III (compartmenta-tion) involves exporting conjugates to either the vacuole or apoplast using ABC transporters or multidrug and toxic compound extrusion...

Detoxification

The most important role of microorganisms in the transformation of pollutants at aqueous-solid phase interfaces is their ability to bring about detoxification (i. e., the change in a molecule that renders it less harmful to one or more susceptible species). Detoxification results in inactivation, with the toxicologically active substance being converted to an inactive product. Because toxicological activity is associated with many chemical entities, substituents, and modes of action, detoxifications similarly include a large array of different types of reactions. A simple way of demonstrating detoxification is to measure the effect of environmental samples on the behavior, growth, or viability of susceptible species. Detoxification is advantageous to the microorganisms carrying out transformations at interfaces if the concentration of the chemical is in a range which suppresses these species. Several processes may result in detoxification, such as hydrolysis, hydroxylation,...

History and definitions

A molecular paradigm or framework for biomarker development was presented in the 1983 report of the National Research Council on Risk Assessment in the Federal Government.1 This paradigm describes progression along a continuum from exposure to disease that is influenced by the following variables external dose, internal dose, target tissue dose, metabolic activation, detoxification and early and late biological effects (see Chapter 21 by J. Groopman, Figure 1 or Chapter 25 by Greenlee, Figure 1). Recent iterations of this paradigm4 recognize that progression from exposure to disease can also be influenced by preventive interventions and genetic and or environmental susceptibility of exposed individuals.

GSR glutathione conjugate of the pollutant

GSTs represent a family of enzymes with usually broad and overlapping substrate specificities, which facilitate the above reactions of hydrophobic, electrophilic substrates. Our knowledge on plant GSTs in trees has expanded greatly in recent years. Evidence is accumulating on the regulation of gene expression, molecular characteristics, and specific catalytic action of the multiple forms of these enzymes. The majority of the information on plant GSTs concerns enzymes which are involved in the detoxification of a number of herbicides 23, 24 , but evidence is gathering that plant GSTs have a much wider role, and may be involved in general plant stress phenomena 25 . Although the Phase II conjugation system is regarded as a detoxification process of xenobiotics, GSH conjugates are not devoid of biological activity. Therefore, processes reducing the concentration of GSH conjugates in the cytosol are important detoxification steps 23 . Because of their active metal-uptake systems plants...

Heavy Metal Tolerance Mechanisms in Plants

Heavy metals such as Cu and Zn are essential for normal plant growth, although elevated concentrations of both essential and nonessential metals can result in growth inhibition and toxicity symptoms. Some plant species, however, have evolved tolerant races that can survive and thrive on such metalliferous soils, presumably by adapting mechanisms that may also be involved in the general homeostasis of, and constitutive tolerance to, essential metal ions as found in all plants. Plants have a range of potential mechanisms at the cellular level that might be involved in the detoxification and thus tolerance to heavy metal stress. The strategies for avoiding heavy metal buildup are diverse. Extracellularly they include roles for mycorrhizas and for cell wall and extracellular exudates. Tolerance could also involve the plasma membrane, either by reducing the uptake of heavy metals or by stimulating the efflux pumping of metals that have entered the cytosol. Within the protoplast a variety...

Extracellular Avoidance of Metal Buildup 1511 Mycorrhizas

Fig. 1.3 Summary of potential cellular mechanisms available for metal detoxification and tolerance in higher plants. 1. Restriction of metal movement to roots by mycorrhizas. 2. Binding to cell wall and root exudates. 3. Reduced influx across plasma membrane. 4. Active efflux into apoplast. 5. Chelation in cytosol by various ligands. 6. Repair and protection of plasma membrane under stress condition. 7. Transport of PC-Cd complex into the vacuole. 8. Transport and accumulation of metals in vacuole (modified from Marschner 1995) strategies employed by higher plants, namely binding to extracellular materials or sequestration in the vacuolar compartment. Thus in the fungus Pisolithus tinctorius, tolerance to Cu and Zn was achieved by binding to extrahyphal slime (Tam 1995), whereas detoxification of Cd in P. involutus involved binding of Cd to the cell walls and accumulation of Cd in the vacuole (Blaudez et al. 2000).

Biological Soil Remediation Technologies and Applications

A growing public awareness and concern about environmental pollutants fostered collaboration between government and industry for the development of safe and cost-effective alternative approaches for dealing with wastes. Of the technologies that have been investigated, bioremediation has emerged as the most desirable approach for cleaning up many environmental pollutants. Bioremediation is an option that offers the possibility to destroy or render harmless various contaminants using natural biological activity. As such, it uses relatively low-cost, low-technology techniques, which generally have a high public acceptance and can often be carried out on site. By definition, bioremediation is the use of living organisms, primarily microorganisms, to degrade the environmental contaminants into less toxic forms. It uses naturally occurring bacteria and fungi or plants to degrade or detoxify substances hazardous to human health and or the environment. The microorganisms may...

Heavy Metal Tolerance

The entrance through leaves is little and is related to the leaf morphology e.g., downy leaves absorb the heavy metals better from atmosphere. The uptake rate depends on the pH of soil solution, organic matter content and concentrations of other ions in the soil. At higher pH value, the solubility of many metal salts in soil solution declines due to the formation of less soluble compounds, as a result their biological availability in the soil decreases. Adding synthetic chelating agents, such as EGTA and EDTA to the soil polluted with heavy metals enhances the uptake and this characteristic can be used for cleansing the soils polluted with heavy metals. In addition to this other ions present in the soil solution considerably affect the uptake of heavy metals by various plant tissues. There is no particular mechanism known, probably other ions present in the soil solution interact and compete with each other thus leading to less biological availability of metal ions and reduction in...

The Cell Wall and Root Exudates

One related process concerns the role of root exudates in metal tolerance. Root exudates have a variety of roles (Marschner 1995) including that of metal chelators that may enhance the uptake of certain metals. In an investigation into the role of Ni-chelating exudates in Ni-hyperaccumulating plants, it was observed that the Ni-chelating histidine and citrate accumulated in the root exudates of nonhyper-accumulating plants and thus could help to reduce Ni uptake and so play a role in a Ni-detoxification strategy (Salt et al. 2000). Since the range of compounds exuded is wide, other exudates could play a role in tolerance to other metals. The clearest example of a role for root secretions in tolerance is in relation to organic acids and the detoxification of the light metal Al (Ma et al. 2001b). Buckwheat, for example, secretes oxalic acid from the roots in response to Al stress and accumulates nontoxic Al-oxalate in the leaves (Ma et al. 1997) thus, detoxification occurs both...

Soil Pollution by Heavy Metals A Highly Complex Disruption of Ecological Equilibrium

Heavy metal pollution in soils constitutes a highly complex disruption of ecological equilibrium. Soils naturally contain a broad diversity of metallic elements, and each metal may be present at variable concentrations and as different chemical species. While some metals have no biological relevance, others are essential trace elements that become toxic when present beyond a certain concentration level. As metals often occur in ionized forms in the soil, they react with negatively charged soil particles, meaning that both their concentrations and their bioavailabilities are relevant. The result of this situation is that soil biota must permanently regulate their activities in order make essential metals available and take them up in the required concentrations, as well as to exclude or detoxify detrimental forms or concentrations. In particular, soil microorganisms must display extensive physiological adaptivity. Considering the space and time variability of soils, selection pressure...

Variation in DNA repair capacity

In noncancer families, the existence of first degree relatives with cancer constitutes a significant risk factor for an individual.54-57 This is taken as evidence for a role for genetic variation in individual susceptibility in the 95 of the cancer cases that are sporadic. The role of genetic variation in cancer risk has also been directly demonstrated in molecular epidemiology studies, especially in studies of genes responsible for the metabolism and detoxification of chemical carcinogens 58-62 The most significant associations with cancer incidence were noted in studies where the level of exposure to carcinogen was modest and alleles at more than a single locus in a pathway or process were included as potential risk factors.59,60 Recent discussions have focussed on the relative contributions of genetics and exposure to cancer incidence. Some authors have suggested that genetic factors make minor contributions to susceptibility, 63-66 while others suggest that the same data are still...

Amino Acids and Organic Acids

Plants produce a range of ligands for Cd, Cu, Ni, and Zn. Carboxylic acids and amino acids, such as citric acid, malic acid, and histidine (His), are potential lig-ands for heavy metals and, so, could play a role in tolerance and detoxification (Rauser 1999 Clemens 2001 Hall 2002).The Cd-and Zn-citrate complexes are prevalent in leaves, even though malate is more abundant. In the xylem sap moving from roots to leaves, citrate, and His are the principal ligands for Cu, Ni, and Zn. Recently, Salt et al. (1999) identified putative Zn-His complexes in the root of the closely related Zn hyperaccumulator T. caerulescens. Kramer et al. (1996) observed a 36-fold increase in the concentration of free His in the xylem exudates of the

Heavy Metal Resistance Systems in Bacteria

Bacteria have developed several efficient systems for detoxifying metals. These mechanisms can be grouped into five categories (1) intracellular sequestration (2) export (3) reduced permeability (4) extracellular sequestration, and (5) extracellular detoxification (Rough et al. 1995). Almost all known bacterial resistance mechanisms are encoded on plasmids and transposons (Silver and Walderhaug 1992), and it is probably by gene transfer or spontaneous mutation that bacteria acquire their resistance to heavy metals (Osborn et al. 1997).

Organic Acids and Amino Acids

Carboxylic acids and amino acids such as citric, malic, and histidine are potential ligands for heavy metals and so could play a role in tolerance and detoxification (for reviews, see Rauser 1999 Clemens 2001) however, strong evidence for a function in tolerance, such as a clear correlation between amounts of acid produced and exposure to a metal, is not yet existing. For example, a 36-fold increase was reported in the histidine content of the xylem sap on exposure to Ni in the Ni-hyperaccumulating plant Alyssum lesbiacum (Kramer et al. 1996). In addition, supplying histidine to a nonaccumulating species greatly increased both its Ni tolerance and the capacity for Ni transport to the shoot. However, the histidine response may not be a widespread mechanism of Ni tolerance since it was not observed in another Ni hyperaccumulator, Thlaspi goesingense (Persans et al. 1999). A possible role of the histidine in the root exudates as a Ni detoxifying agent has been discussed earlier (see...

Antioxidative Defense Mechanism

Recent reports suggest that though antioxidative defense system is not directly involved in heavy metal detoxification, yet ROS play important role as intermediate signaling molecules to regulate the expression of genes for plant's defense system (Orozco-Cardenas et al. 2001 Vranova et al. 2002).

Other Metal Binding Proteins

Metal-binding proteins and peptides in plants can enhance metal tolerance or accu-mulation.These metal-binding peptides or proteins should be preferentially metal specific so that only toxic metals like Cd, Hg, and Pb are sequestered rather than essential ones like Zn and Cu. Ryu et al. (2003) isolated and characterized a novel Cu-binding protein (BP) in the Asian periwinkle Littorina brevicula, which is highly resistant to a wide range of heavy metal concentrations and has its metal-binding protein(s) induced in the presence of Cd. They found that Cu-BP contained an equal amount of Zn in non-exposed physiological conditions following purification by Sephacryl S-100 chromatography. However, Zn is replaced by Cu at the binding site upon the addition of excess Cu (100 mol L-1 CuCl2) to the cytosol or after a long period (60 d) of exposure of plants to the metal ion (150 g L-1 CuCl2). The molecular weight of the purified protein was determined as 11.38 kDa using MALDI-TOF MS analyses....

Mineralogical Conditions

Their minerals act as sinks for sulfate, barium, strontium, and lead in oxidizing sulfidic wastes, and their precipitation controls the amount of sulfate, barium, strontium, and lead in AMD solutions (Lottermoser 2007). Secondary hydrous sulfates may redissolve in water and release their ions back into solution or may dehydrate to less hydrous or anhydrous compositions. Also, the hydrous Fe2+ sulfates may oxidize to Fe2+-Fe3+ or Fe3+ sulfate salts. The newly formed secondary minerals are more stable and resistant to redissolution compared to their precursors. Secondary mineral possess large surface areas and adsorb or coprecipitate significant quantities of trace elements, including metals and metalloids. The precipitates effectively immobilize elements in acid mine waters and hence provide an important natural attenuation and detoxification mechanism in mine waters (Lottermoser 2007).

Photo Catalytic Oxidation

Fig. 3.3 Schematic of the mechanism involved in photocatalytic oxidation TiO2 has been used as the catalyst to suit a wide range of industrial applications, including water treatment. In recent years, photocatalytic detoxification of volatile organic compounds is generally more efficient in the gas-phase than in aqueous phase Fig. 3.3 Schematic of the mechanism involved in photocatalytic oxidation TiO2 has been used as the catalyst to suit a wide range of industrial applications, including water treatment. In recent years, photocatalytic detoxification of volatile organic compounds is generally more efficient in the gas-phase than in aqueous phase

Estimated 105 Upper Bound Human Cancer Risk 106 Levels for 246TCP

The pretreatment of rats with 2,4,5- or 2,4,6-TCP by gavage at doses up to 400 mg kg day for 14 days had no effect on ethyl -nitrophenylphosphonothionate detoxification (Carlson 1978). 2,4,5-TCP but not 2,4,6-TCP at 400 mg kg day decreased microsomal NADPH-reductase activity and cytochrome P-450 activity.

Role of smokingrelated DNA adducts in lung cancer

DNA adducts represent the biologically effective dose, defined as the amount of carcinogen bound to DNA in either target tissue or a surrogate tissue taking into account the individual differences in absorption and metabolism of a carcinogen to its DNA reactive intermediate(s), detoxification of the reactive intermediates, and repair of DNA damage. DNA adduct formation is generally accepted as one of the key events in tumor initiation during chemical carcinogenesis.19 The biological potential of a given DNA adduct depends on its mutagenic potential, ability to be repaired, location within a target gene, and the nature of the target gene.20 For example, formation of BPDE-dG adducts in mutational hot spots of the p53 tumor suppressor gene in lung cancer patients substantiates the association between tobacco carcinogen-induced DNA damage and lung cancer.21 Total DNA adduct levels, and in some cases specific adducts, have been correlated with in vitro muta

Mechanism of Animal Remediation

4.2.3.2 Detoxification As we know, some hazardous heavy metals exercise a detrimental influence on cells by binding to vital proteins, interfering with cellular activities, and inhibiting regulation of cells. Luckily, hyperaccumulator plants have evolved their own mechanisms to protect themselves from negative heavy metal stress. Several important detoxification mechanisms are explained as follows 1. Chelation Chelation plays a crucial role not only in the accumulation and transportation of heavy metals but also in the detoxification phase. Usually chelators have ligands (most commonly histidine and citrate) and can bind metal ions. Combined metal ions appear uncharged and inert when reacting with other substances, by which way heavy metals' damage toward cell are reduced significantly. is quite effective in controlling the distribution and concentration of metal ions. To compartmentalize the vacuole is to arrest and imprison hazardous metal ions, constricting them into a limited...

Role of Pahdna adducts in human carcinogenesis

Determined levels of PAH adducts were generally within the range from 1 to 10, and not higher than 40 adducts per 108 nucleotides.23 Typical statistically significant differences between the exposed and control groups were from 1.5- to 3-fold.23 All studies detected a considerable adduct level variability in subjects belonging to the same experimental group. This suggests a strong effect of individual genetic susceptibility factors. These factors include pathways of absorption, activation, distribution, and detoxification of carcinogens, DNA repair capacity, and various lifestyle and dietary effects. Therefore, a recent trend in research on molecular epidemiology of DNA adducts has been to correlate DNA damage in populations with genotype or phenotype of xenobiotic metabolism and DNA repair genes, e.g., CYP1A1, GSTM1, NAT2, XP genes, and XRCC1.

Future Perspectives

Every year around 1,000-1,500 new chemicals are manufactured with perhaps 60,000 chemicals in daily use. Most of these are organic chemicals and pesticides. These compounds due to their extensive use as chemical intermediates are resulting in amassing higher concentration in the environment as recalcitrant. If their concentration is not checked in the environment, every pollutant that was released to the environment would still be here to haunt us. Fortunately, there are many reactions that check their concentrations such as chemical hydrolysis, photo degradation, volatilization, sorption, and most important and economic process bioremediation. Over the last few years, a number of companies have been established already to develop and commercialize biodegradation technologies. Existence of such companies now has become economically justifiable, because of burgeoning costs of traditional treatment technologies, increasing public resistance to such traditional technologies, accompanied...

Soil Bacterial Community

However, if plants can elicit different mechanisms of Se detoxification in soil microbes, even a direct microbial Se volatilization cannot be ruled out as a further mechanism of microbial Se detoxification (Frankenberger and Karlson, 1994 Lin et al ., 2000 Lin and Terry, 2003) .

Role of Arbuscular Mycorrhiza

Observed dilution, such a mechanism may be Cu entrapping or filtering resulting in retaining the great part of Cu excess in the mycelium and, as a consequence, in observed decrease in the Cu content within the plant and its translocation from roots to shoots. It is quite possible that the main reason for this effect is a high CEC value of AMF mycelium (toward Cu), which exceeds markedly CEC of colonized plant roots. In this connection, the data concerning the involvement of insoluble glyco-protein, glomalin, in Cu detoxification are of a great interest. In the experiments performed in vitro, this protein could sequester up to 28 mg Cu g of protein (Gonzalez-Chavez et al. 2004). For the appraisal of the cell wall protective role, the fact (established with monoclonal antibody MAb32B11) that glomalin is mainly located in the cell walls of AMF hyphae is of especial importance (Purin and Rillig 2008 Ferrol et al. 2009). At the same time, data concerning changes in the cell wall...

Molecular Mechanisms of Metal Homeostasis and Tolerance

Heavy metals such as Cu and Zn (essentials) or Cd (non-essential) can be toxic to plants above a certain threshold. Plants have evolved a regulated network of uptake and distribution enabling an effective protection to the metabolic processes. In general, factors influencing the metal uptake and distribution in plants include (1) mobilization from the soil, (2) uptake and sequestration by metal-complex formation and deposition in vacuoles for detoxification within roots, (3) metal translocation to shoots via xylem, and (4) distribution and sequestration in aboveground organs and tissues (Clemens et al., 2002). A further defensive line against HM effects is a series of antioxidant mechanisms against ROS produced by excess of metal ions. These include enzymes and reducing metabolites (Foyer and Noctor, 2005). Metallothioneins are characterized as low molecular weight, cysteine-rich, metal-binding proteins and may play a role in their intracellular sequestration (Cobbett and Goldsbrough,...

Biomass Production and Biochemical Responses of Cd Hyperaccumulator Plants Toward Elevated Cd Levels

A study on the ROS metabolism during Cd hyperaccumulation at 400-600 mmol L CdCl2 by Zhang and Qiu (2007) in hyperaccumulator plant Sedum alfredii suggested that the accumulation of ROS induced by Cd treatment might be involved in Cd hyperaccumulation. Similar to published work of Shah et al. 2001 and Olmos et al. 2003, Cd enhanced superoxide anion generation and H2O2 accumulation. The group concluded that the ROS scavenging enzyme peroxidase plays an important role in S. alfredii during the process of Cd hyperaccumulation. ROS accumulated at a certain concentration could function as a signal mediating adaptive response to Cd stress such as enhancing the expression of genes responsible for encoding antioxi-dant enzymes, namely, CAT1 (catalase), cAPX (sscorbate peroxidase), and GR1 (glutathione reductase). Studies on the effect of cadmium on molybdate containing hydroxylases in Phragmites australis suggested activation of aldehyde oxidase and xanthine dehydrogenase enzyme so as to...

The Ecotoxicological Approaches to Toxicodynamics

Most of the work on the individual tolerance concept has focused on organic chemicals. One of the reasons may be that for metals a CBR on a whole body basis has only limited applicability. Due to compartmentalization of metals in the body and the presence of regulation and detoxification mechanisms, it is unlikely that the total body residue is simply related to toxicity (see, e.g., Lock and Janssen 2001 Vijver et al. 2004). The biotic ligand models (BLMs) assume a critical level of metal accumulation at the biotic ligand and do not include a time aspect, although more TD-like approaches have been suggested (Paquin et al. 2002b).

Intracellular Storage

One of the enzymes in streptomycetes that is known to require nickel at its active center is nickel-dependent superoxide dismutase (NiSOD). SOD is involved in ROS detoxification, making this special enzyme interesting for two reasons. Overexpression of SOD has been shown to lead to heavy metal tolerance in yeast, and the expression level of NiSOD in resistant strains was investigated to see whether NiSOD plays a protective role under in situ conditions in contaminated soil (Schmidt et al. 2007). In addition, NiSOD itself is interesting, since the enzyme is structurally different from other SODs (Schmidt et al. 2009b). The nickel-resistant strains provide a source for biochemical characterization, since nickel in the medium increases SOD expression, and so highly expressed enzymes can be purified.

Research and Development Potential

In addition to improved biomass pretreatment methods to increase the yield from enzymatic hydrolysis, new crops are also being investigated which either through breeding or genetic manipulation demonstrate, for example, a higher yield per hectare, a reduced lignin content, or in comparison with hemicellulose a greater cellulose content. In the future hydrolysis, inhibitors should either be avoidable via gentler pretreatment processes or separated as much as possible via detoxification prior to the hydrolysis. improved detoxification processes

Intracellular Sequestration

Intracellular sequestration or bioaccumulation of metals intracellularly (Acheampong et al. 2009) necessitates metal-binding proteins within the cytosol of resistant strains. For plants and yeasts, e.g., Schizosaccharomyces pombe and Saccharomyces cerevisiae, two types of cystein-rich, metal-binding peptides, the phytochelatins ((g-GluCys)nGly where n 2-11) and the metallothioneins (small peptides of up to 100 amino acid residues of high cystein content) store certain essential trace metals and detoxify excessive concentrations of metals (Van de Weghe and Ow 2001 Hall 2002 Shanker et al. 2005 Yang et al. 2005 Pal and Rai 2010 Xu et al. 2010). In contrast, bacterial cells have only recently been reported to express metallothioneins, like the cyanobacterial SmtA and BmtA (Blindauer et al. 2002). The chromium-reducing Streptomyces sp. MC1 accumulated Cr(III) after reduction. Analysis of these metal deposits supported the idea of storage by chromium binding proteins (Polti et al. 2010)....

Children S Susceptibility

Komori 1990 Vieira et al. 1996 NRC 1993). Whether differences in xenobiotic metabolism make the child more or less susceptible also depend on whether the relevant enzymes are involved in activation of the parent compound to its toxic form or in detoxification. There may also be differences in excretion, particularly in the newborn who has a low glomerular filtration rate and has not developed efficient tubular secretion and resorption capacities (Altman and Dittmer 1974 West et al. 1948 NRC 1993). Children and adults may differ in their capacity to repair damage from chemical insults. Children also have a longer lifetime in which to express damage from chemicals this potential is particularly relevant to cancer.

Role of Phytochelatins PCs in Metal Tolerance

The key to understanding accumulation is identification and characterization of corresponding ligands. One recurrent mechanism for heavy metal detoxification is chelation by ligand. A number of chelation ligands such as PCs, glutathione (GSH) and metallothionines (MTs) ligands have now been recognized in plants. The role of PCs in detoxification of metals in plants is an area of interest for this research group and is the basis of these studies. In view of the importance of GSH as building blocks for PCs preliminary experiments were carried out in order to investigate GSH interaction with metal ions 56 . The observations of these studies could provide a foundation in the understanding of the role of PCs in metal detoxification.

Metal Speciation in Metallophytes

It is now generally accepted by environmental chemists, nutritionists and toxicologists that the knowledge of the total elemental concentrations of a sample does not suffice to assess the environmental hazard, essentiality and bioavailability of elements as these could be present in a variety of forms 85-87 . Information regarding both the total content and the chemical forms of species present in a complex matrix is thus required in order to have a true reflection of potential toxicity, bioavailability, bioaccumulation and transport of a particular element. It is thus important in our research studies not only to know the total concentration of metals accumulated in metallophytes but also to know the nature of various metals species present in different parts of the plant. A comprehensive knowledge of chemical forms of metals that plants accumulate is essential as this could shed some light on the processes involved and in detoxification mechanisms metallophytes employ.

Mechanisms to Prevent Cells from Heavy Metal Toxicity

In natural systems, low molecular weight organic acids (LMWOAs) are involved in a wide range of different processes, from nutrient mobilization, mineral weathering and metal detoxification to wood-decay processes and plant pathogenesis because of their dual acidifying and chelating abilities (Landeweert et al. 2001).

Childrens Susceptibility

Are proportionately larger (Altman and Dittmer 1974 Fomon 1966 Fomon et al. 1982 Owen and Brozek 1966 Widdowson and Dickerson 1964). The infant also has an immature blood-brain barrier (Adinolfi 1985 Johanson 1980) and probably an immature blood-testis barrier (Setchell and Waites 1975). Many xenobiotic-metabolizing enzymes have distinctive developmental patterns, and at various stages of growth and development, levels of particular enzymes may be higher or lower than those of adults sometimes unique enzymes may exist at particular developmental stages (Komori 1990 Leeder and Kearns 1997 NRC 1993 Vieira et al. 1996). Whether differences in xenobiotic metabolism make the child more or less susceptible also depends on whether the relevant enzymes are involved in activation of the parent compound to its toxic form or in detoxification. There may also be differences in excretion, particularly in the newborn who has a low glomerular filtration rate and has not developed efficient tubular...

Populations That Are Unusually Susceptible

A susceptible population will exhibit a different or enhanced response to CDFs than will most persons exposed to the same level of CDFs in the environment. Reasons include genetic make-up, developmental stage, age, health and nutritional status (including dietary habits that may increase susceptibility, such as inconsistent diets or nutritional deficiencies), and substance exposure history (including smoking). These parameters result in decreased function of the detoxification and excretory processes (mainly hepatic, renal, and respiratory) or the pre-existing compromised function of target organs (including effects or clearance rates and any resulting end-product metabolites). For these reasons the elderly with declining organ function and the youngest of the population with immature and developing organs will generally be more vulnerable to toxic substances than healthy adults. Populations who are at greater risk due to their unusually high exposure are discussed in Section 5.6,...

Resistance or Tolerance to Metals in Plants

In the case of biotransformation, the metal toxicity in plants can be decreased by chemical reduction of the element and or by its incorporation into organic compounds (Salt et al., 1998). Intraspecific and intravarietal differences exist regarding to tolerance to Cr excess that can be controlled by different genes, through diverse biochemical pathways (Samantaray et al., 1998). In the root system of certain plant species Cr also can be reduced chemically from Cr6+ to Cr3+, as part of a detoxification mechanism (Shanker et al., 2005). Inside plant cells, the metals in excess, together with those not used in the metabolism, need to be stored to prevent its toxicity (Briat and Lebrun, 1999). Several potential storage mechanisms, at the cellular level, can be involved in the detoxification and tolerance to metal stress (Cobbett and Goldsbrough, 2002). Moreover, some plant species are capable to accumulate great amounts of metals in the aerial part, while others accumulate them in the...

Interactions With Other Substances

Factors interfering with Phase II conjugation reactions would inhibit the detoxification of chlorophenols. The results of recent experimentation indicate that the polycyclic aromatic hydrocarbon (PAH), 3-methylcholanthrene (3-MC), stimulates the glucuronidation of phenolic substrates through the induction of glucuronylsyltransferase (Jansen et al. 1992 Wishart 1978a, 1978b). The enzymes induced have a spectrophotometric peak of 448 nanometers (cytochrome P-448) and are characteristically distinct from the phenobarbital-type induced enzymes that have an absorbance maximum at 450 nanometers. These findings suggest that other toxic and or carcinogenic PAHs, such as benzo(a)pyrene, can significantly enhance the metabolism of phenols. The relationship between PAH particulate and solid material, commonly associated with incinerators and hazardous waste sites, and chlorophenol metabolism has not been studied. In general, the ability of another chemical to affect the toxicity of chlorophenols...

Biomarkers and liver cancer prevention

Several approaches can be considered for the prevention of liver cancer. A first approach is vaccination against HBV. Unfortunately, many people living in high-risk areas for liver cancer acquire the HBV infection before age three. Thus, an immunization program for total population protection would have to occur over several generations, provided that mutant strains of HBV do not arise, thereby eliminating the utility of current vaccines. Despite these problems, vaccination programs for HBV have been implemented in many areas of Africa and Asia. A second approach for cancer prevention would be the elimination of aflatoxin exposures. Primary prevention of aflatoxin exposures could be accomplished through large expenditures of resources for proper crop storage and handling however, this approach is not economically feasible in many areas of the world. Secondary prevention measures using chemopreventive agents, which block the activation and enhance the detoxification of AFB1 are being...

Synergistic mixture effects

Lichtenstein et al. (1973) provided an early example of synergistic combination effects between insecticides and herbicides, with insect lethality as the endpoint. They found that photosystem II-inhibiting herbicides, such as atrazine, simazine, or monuron, increased the lethal effects of the insecticides parathion and DDT in various insects. Conversely, some insecticides seem to enhance the plant-damaging effects of certain herbicides (Kwon and Penner 1995). These interactions have been explained in terms of competition for cytochrome P450 mixed-function oxygenases, which resulted in inhibitions of detoxification reactions leading to elevated levels of the herbicides and therefore prolonged activity. Similar types of interaction were described for the effect of the fungicide prochloraz on the adverse effects of lambda-cyhalothrin in the honey bee Apis mellifera (Pilling et al. 1995). Bocquene et al. (1995) studied acetylcholinesterase inhibition with mixtures of organophosphates and...

Cell Wall and Microsomal Proteomics

The plasma membrane is the first living barrier to free inward diffusion of heavy metals into the cell, and it is considered to be the initial site of heavy metal toxicity in plant root cells. Knowledge regarding the mechanisms controlling the entrance and translocation of metals from the root to the shoot is still rudimentary, however. Identifying the genes encoding membrane proteins associated with metal entrance and translocation is key to understanding heavy metal detoxification processes in plant cells. Analysis of the microsomal and or plasma membrane proteomes, which contain a number of proteins involved in heavy metal detoxification, including receptors, channel proteins, transporters, and membrane-associated signaling proteins, represents one potential analytical strategy for the comprehensive identification of membrane proteins associated with responses to specific heavy metals. However, a number of factors make extracting and purifying plasma membrane proteins a difficult...

Identification of Data Needs

Mechanistic studies indicated that cultured hepatocytes ameliorated the adverse developmental effects associated with in vitro 4-CP exposure (Oglesby et al. 1992). This finding is apparently attributable to increased rates of detoxification in the hepatocyte cell cultures. In addition, results from mammalian embryo assay indicate that monochlorophenols are not potent developmental toxicants or teratogens (Mayura et al. 1991). In vivo studies involving exposure around the implantation period may help corroborate these in vitro data. Studies on developmental effects of postnatal exposure will also be useful.

Mechanical Processing of Cyanide Waste

Conversion of cyanide to cyanogenic chloride. This compound is then hydrolyzed into cyanate (Akcil 2003). Although chemical and physical treatments provide more rapid detoxification and are less susceptible to environmental upsets (Akcil and Mudder 2003), biological alternatives are more economical and good for ecological balance.

Regulatorysafety Aspects And Ongoing Monitoring Programmes

The monitoring of BFRs throughout the food chain is conducted or sponsored by numerous entities including governments, industry, environmental groups, and academia and has occurred to some extent in most developed countries. BFRs have been analysed in several on-going biomonitoring programs including the third round of a WHO-coordinated human exposure study (2000-2003) 227 and the National Health and Nutrition Examination Survey (NHANES, 2001-2002) conducted in the USA 228 . Environmental non-profit organizations, such as the World Wide Fund for Nature (WWF, www.panda.org detox) and Greenpeace (www.greenpeace.org.uk), have sponsored studies to investigate levels of BFRs (PBDEs, HBCDs, and TBBP-A) in humans, foods, wildlife, and

Types and Classifications

Both bacteria and fungi are particularly important with respect to biochemical transformations and have a critical role in influencing the fate and mitigation of many organic pollutants. Accordingly, a large subdivision of bacteria includes the actinomycetes, which are often treated as a separate group of microorganisms because of their unique characteristics. In the following discussion, a broad overview of bacteria, actinomycetes, and fungi is presented in order to examine their significance with respect to detoxification and biodegradation. The importance of solid phase microflora is illustrated by their numbers and biomass. The relative estimates of the abundances of solid phase microbes in the aqueous-solid phase environment of bacteria, actinomycetes and fungi are 108, 107,and 106 number g solid phase,respectively 2,40-45 . It is obvious that very large populations can be sustained in on solid particles. In addition, the groups are very diverse, so that large numbers of...

Microbial Metabolism of Cyanide and Nitriles

Nitrile compounds are abundant in the natural environment and are synthesized by plants and microbes as intermediates in chemical biosynthesis and degradation (Legras et al. 1990) . The widespread occurrence of nitrile compounds in nature may explain the prevalence of nitrilases in prokaryotes and eukaryotes. Nitrile-metabolizing enzymes are found in a wide variety of bacterial, fungal and plant species. Nitrilases and nitrile hydratases transform both aliphatic and aromatic nitriles to the corresponding acid or amide, respectively, but exhibit less substrate specificity than cyanide hydratase and cyanidase. In bacteria, nitriles may be formed during the detoxification of endogenous and exogenous cyanide. Bacteria produce cyanide in a process termed cyanogenesis, in which HCN and CO. are synthesized from glycine by the enzyme HCN synthase. Bacteria that are exposed to actively producing cyanide may protect themselves from cyanide toxicity using cyanide-degrading enzymes, which may...

Phyto RhizoRemediation

A method used to extract, sequester, or detoxify pollutants with the help of plants. A number of plants which have extensive fibrous roots such as common grasses, corn, wheat, soyabean, peas and beans were studied for their rhizoremediation potential (Glick 2003). Several trees of family Salicaceae (poplar and willow) which can grow fast and possess a deep rooting ability were planted to bioremediate soil polluted with 20,000 mg kg gasoline and diesel compounds to a depth of 3 m (Trapp et al. 2001). However, there use for bioremediation, per se, was restricted and localized and for low hydrocarbon contamination.

Biological Interactions

Biological uptake of most synthetic organic contaminants occurs by simple passive diffusion across a cell membrane. Accordingly, the octanol-water partition coefficient of the contaminant (Kow) is often a good predictor of its tendency to bioaccumulate.7 Membrane carriers are not involved, and the biological effect of the contaminant is often characterized by narcosis. In contrast, metals generally exist in the environment in polar, hydrophilic forms (Table 2), which are strongly hydrated and are unable to traverse biological membranes by simple diffusion. Membrane transport occurs by facilitated transport, usually passive (i.e., not against a concentration gradient), and necessarily involving either membrane carriers or channels9 with few exceptions (e.g., some organometallics and neutral metal complexes, such as CH3HgCl and HgCl20, respectively), the octanol-water partitioning coefficient of the metal forms has no bearing on the relative facility with which they cross biological...

Heavy Metal Resistant Marine Bacteria from Coastal Waters

Since presence of metal resistant bacterial isolates in the environment directly suggests metal contamination, unusual rise in the number of mercury resistant bacteria along the Indian coast indicates significant mercury contamination. Several heavy metal resistant marine bacteria from coastal waters of India were isolated and evaluated for their ability to transform efflux heavy metals viz. mercury, cadmium and lead. Interestingly, these marine bacteria were highly resistant to mercury and were capable of growing at 25 ppm or higher levels of mercury indicating their potential for detoxification not only of Hg, but also Cd and Pb along with polychlorinated biphenyls (Ramaiah and De 2003 De et al. 2006, 2007, 2008).These metal tolerant bacteria removed mercury by means of volatilization and were successful to detoxify mercury amended waters. Mercury resistant marine, Pseudomonas aeruginosa strain CH07 resists lead by EPS - entrapment mechanism which was clearly revealed by SEM-EDX...

Some useful definitions

It is obvious to anyone that life has evolved in the presence of metals, some of which - the essential trace metals - have become incorporated into metabolic processes crucial to the survival, growth and reproduction of organisms. As a consequence, organisms have developed various mechanisms for the uptake and excretion, regulation and detoxification of essential metals, mechanisms which - in many cases - are functioning also for non-essential metals. In their summary statement on the Essentiality of Metals , Janssen and Muyssen (2001) point out that an element is considered essential when storage, i.e. binding of metals in various types of complexes for long-term storage in a detoxified form Rainbow (2002) reviewed the current literature with regard to metal accumulation in aquatic invertebrates. Aquatic invertebrates take up and accumulate metals whether essential or not, resulting in a great variability of subsequent body concentrations across metals and taxa. Accumulated metals...

Biotechnological Applications

The understanding of dehalogenation reactions catalyzed by microorganisms through fundamental studies has provided a basis for developing industrial and environmental applications (20). The technological applications of microbial dehalogenation can be classified into two broad categories the commercial generation of halogenated synthetic intermediates or synthesis of novel halocompounds and the detoxification and degradation of haloge-nated compounds in the environment. (177,178). Bioremediation has been developed and used to transform or mineralize haloge-nated contaminants into less harmful metabolites that can be integrated into biogeochemi-cal cycles. Numerous examples of bioremediation of contaminated soil and contaminated waters exist in the literature (20 Chapter 19). Many are described for bioreactors and others for in situ applications. There have been a number of successes using bioaugmentation in the field with chlorinated compounds where microbial populations capable of...

Gen etic Engin eering of Marin e Bacteria for Bioremediation of Metals

Detoxify mercury contaminated marine sites. Introducing genes responsible for resistance to multiple heavy metals into a marine bacterium makes it resistant to multiple heavy metals and may be used to bioremediate sites contaminated with multiple heavy metals. Marine bacteria can be genetically engineered to express high amount of metal binding groups viz. carboxyl, hydroxyl, sulphate, phosphoric, amine for biosorption of high amount of toxic metals either on cell surface or microbial products such as EPS and biosurfactants. Modification of bacterial isolates which can over produce EPS and biosurfactants may be a good strategy for bioremediation of significant amount of heavy metals. Microbial enzymes can be modified to increase their kinetics to reductively precipitate heavy metal ions or increase efficiency of enzyme to effectively detoxify metals such as mercury.

The Halophyte Influence on Metal Speciation

And chemical characteristics (Nigam et al., 2000), participating in nutrient uptake and in heavy metal detoxification (Ma et al., 2001). It is known that some of these organic compounds exudated by roots are acids such as citric, malic, oxalic and succinic acids (Dakora and Phillips, 2002). A previous study (Duarte et al., 2007) focused on the role of a specific organic acid (citric acid) detected on root exudates from H. portulacoides individuals when exposed to cadmium and nickel. There are also bibliographic references that indicate the increase of the citric acid among some salt marsh plants, such as Juncus maritimus (Mucha et al., 2005). While for nickel the application of this chelator showed no advantage to phytoremediative processes, it was very useful for Cd treatment. In the presence of citric acid, Cd uptake was enhanced and, most importantly, the translocation to the higher parts of the plant also increased, when citric acid was applied at a concentration similar to the...

Cyanoremediation A Green Clean Technology

The main cyanobacterial strain viz sps. of Anabena, Nostoc, Phormidium, Aphanocapsa, Oscillatoria, Lgngbya, Spirulina, Aulosira, Anasystis appears to be promiring bioremediators for the effluent rich in nitrates and phosphates. Cyanobacteria metabolize organic compounds through ring hydroxylation. The cyanobacteria produce siderophores which may be responsible for absorption of metal ions into organism. The metal accumulating algal biomass can either be disposed off or incinerated for metal recovery. It was also studied that cyanobacteria accelerate transformation and degradation of certain polycyclic aromatic hydrocarbons, organo phosphorous, in water by the sun light. Thus algal detoxification, and degradation of environmental pollutants could help in controlling the pollution of the aquatic and terrestrial habitats. Keywords Cyanobacteria Remediation Bioremediation Detoxification Biomonitoring Pollution

Priming and Reductive Dechlorination

The persistence of PCBs in river and harbor sediments and contaminated soils worldwide has become a focus for environmental regulation because PCBs accumulate in fauna and flora and are potentially toxic to wildlife and humans. The discovery that microbial PCB dechlorination was occurring in situ in freshwater and estuarine sediments 371, 451, 454 raised hopes for natural restoration because dechlorination is expected to detoxify the PCBs and at the same time make them more degradable and less persistent 34, 59 . Microbial dechlorination of PCBs has had a major impact at some locations such as the Hudson River 2,371,451 ,but it has had a much smaller impact at other locations such as the Housatonic River (Pittsfield, MA) 453 . An effective method for stimulating or priming the activity of indigenous PCB-dechlorinating microbes would have great potential for accelerating natural restoration at the latter sites.

Transgenic Plants for Remediation of Phenolic Compounds

Transgenic technology also exploits other in vitro plant-based experimental systems that are available to the phytoremediation researcher, mainly cell suspensions and hairy roots that have widely been applied in numerous studies focus on the identification of plant capabilties to tolerate, assimilate, detoxify, metabolize, and store a wide variety of organic and heavy metal pollutants (Doran, 2009). produce large amounts of enzyme for the degradation and detoxification of environmental pollutants (Sakamoto et al., 2008).

Application of PGPR Pseudomonas for Nickel Removal

Restoration of the heavy metal polluted soils is a priority direction in many countries. Soil phytoremediation and protection of agricultural crops from heavy metals are actual problems of modern biotechnology. Bacteria are actively involved in global cycles of metals circulation in biosphere. Heavy metal contamination in soil leads to dynamic instability of certain groups of microorganisms in soil 42 , and predominance of phytopathogens decreases the efficiency of metabolism in plants and plant-associated microorganisms and as a result, impairs phytoremediation. Hence, PGPR resistant to heavy metals can be used to optimize phytoremediation 43 . Microorganisms possess different mechanisms of resistance to heavy metal divalent cations. The efflux of heavy metals from cells realizes with help of transmembrane protein complexes 44, 45 , cation diffusion facilitators 46 , specific ATPase 47 . The mechanism of resistance via efflux provides detoxification only cytoplasm of bacterial cell,...

Proteomic Studies in Response to Heavy Metal Toxicity

To unravel the role of vacuolar transporters in Cd-detoxification processes, Schneider et al. (2009) used iTRAQ to identify a number of membrane proteins, including transporters such as the cation proton exchanger (CAX1), in the barley leaf tonoplast proteome. Comparative proteomic approaches, including both gel-based (2D-DIGE) and gel-free (iTRAQ) techniques, were used to investigate Cd-responsive proteins in Brassica juncea roots, and these experiments revealed that only 12 of the differentially expressed proteins were identified by both approaches (Alvarez et al. 2009). As expected, membrane proteins as well as low abundance proteins were primarily identified by the iTRAQ method however, 2D-DIGE analysis identified many differentially expressed posttranslationally modified proteins, suggesting that each approach has its own strengths and thus should be used in a complementary manner.

Plant Mechanisms for the Removal of Dyes

To either completely degrade the dye or to transform it into products which are non toxic and can be safely released into the ecosystem. Because plants are static and live in a competitive and sometimes hostile environment, they have evolved mechanisms that protect them from environmental abiotic stress, including the detoxification of xenobiotic compounds (Page and Schwitzguebel, 2009). Plant mechanism is diverse and can be used to treat compounds not degradable by bacteria. Different aromatic compounds such as derivatives of sulfonated anthraquinones occur naturally in several plant genera and thus these plants are likely to possess enzymes that can accept these aromatic compounds as substrates and process them (Aubert and Schwitzguebel, 2004). An important step in the removal of sulfonated anthraquinones appears to be involving the action of dioxygenases adding oxygen across the double bond bearing the sulfonate group leading to its elimination (Schwitzguebel et al., 2002). Plant...

Metabolism of Hazardous Phenolic Compounds in Plants

Phyto Degradation

It has generally been accepted that several enzyme systems, not necessarily physiologically connected, form a metabolic cascade for the detoxification, breakdown and final storage of organic xenobiotics (Schr der et al., 2008). Detoxification mechanisms described for phenolic compounds, resemble more the reactions in the animal liver than the bacterial metabolism, following the green liver model proposed for the metabolism of other organic pollutants by Sandermann (1994). This network of reactions can be subdivided into three distinct phases tranformation (phase I), conjugation (phase II) and compartmentation (phase III). Recently, the last phase has been categorized into two independent phases, one confined to transport and storage in the vacuole, and a second one involving final reactions, such as cell wall binding or excretion (Schr der et al., 2007 Abhilash et al., 2009). The first metabolic step is the transformation of the initial substrate and generally includes several...

Transgenics for Cyanide Remedy

Phytodegradation of cyanide can be optimized by selecting or engineering plant species with higher activities of the enzymes thought to be involved and rate-limiting in cyanide detoxification. There are some examples of promising transgenic approaches which have been used in other cases. For example, the expression of bacterial enzymes in plants involved in reductive transformation of TNT (tetranitrate reductase or nitroreductase) resulted in enhanced plant tolerance and degradation of TNT (Hanninket al. 2001 French et al. 1999). Also, the constitutive expression of a mammalian cytochrome P450 in tobacco resulted in an up to 640-fold higher ability to metabolize TCE (Doty et al. 2000). Similar approach can be applied for cyanide detoxification. After decades of accumulating evidence for the existence and importance of various enzyme complexes involved in cyanide detoxification, the ability to model these systems in three dimensions will be an approaching reality. As described in...

Microbial Interactions with Metals

Microorganisms have coevolved along with metals and minerals that constitute the earth crust (Hazen 2008). This long term coexistence (from 3.6 billion years ago) have allowed natural microbial flora to developed strategies to interact and modify these metals and metal bearing minerals sometimes to their benefit (in various metabolic reactions or just for detoxification) or as part of other secondary consequences. Bioremediation of metal pollution strongly relies on complex interplay of biological, chemical and physical processes, particularly, the mechanistic understanding of interrelated microbial processes, chemical reactions and contaminants mobility. Microorganisms exist in complex biogeochemical matrices within soil and subsurface environments. Their interaction with metals is subjected to several environmental factors like solution chemistry, sorptive reactive surface, availability of organic ligands and reductants (Tabak et al. 2005). Microorganisms interact with toxic metals...

Factors Affecting Uptake and Transport

Plant uptake (Taiz and Zeiger 2002) although in some cases it can also prevent uptake. Furthermore, plants extrude H+ via ATPases, which replace cations at soil CEC sites, making metal cations more bioavailable (Taiz and Zeiger 2002). This strategy can be very useful in detoxification of cyanide-metal complex.

Phytoremediation of Heavy Metal Polluted Soil

Into the surface biomass, and (3) produce a large quantity of plant biomass. In addition, remediative plants must have mechanism(s) to detoxify and or tolerate high metal concentrations accumulated in their shoots. In the natural setting, certain plants that have the potential of uptaking heavy metals have been identified. Indian mustard (B. juncea) is a high biomass, rapidly growing plant that has an ability to accumulate Ni and Cd in its shoots. It is a promising plant for phytoremediation (Terry et al. 1992).

Pesticide Oil Degradation and Remediation by Cyanobacteria

Cyanobacteria metabolize organic compounds through ring hydroxtlation. This has been demonstrated in Aulosira fertilissima and Nostoc sp. which were able to degrade, detoxify and use the pesticide as the sole phosphorous source through the production of phosphate solubilizing enzyme (Subramanian et al. 1994). It was also found that cyanobacteria accelerated transformation and degradation of certain polycyclic aromatic hydrocarbons, organophosphorous compound in water by the sunlight. Thus algal detoxification of environmental pollutant could help in controlling the pollution of the aquatic and terrestrial habitat.

The Use of Hydroponics and Plant Tissue Culture Technologies for Dye Degradation

Plant species (Rheum rabarbarum, Rumex acetosa, Rumex hydrolapatum and Apium graveolens), in hydroponic solutions for the removal of sulfonated anthraquinones. Many plant species have the capacity to absorb large quantities of water form hydroponic solutions. The water absorption capacity of a plant is a factor that should be taken into consideration while performing studies in hydroponic solutions because it reflects the overall health of a plant. Lower water absorption capacity for the plant Rumex acetosa in hydroponic solution indicated that the plant was not in optimum health under hydroponic conditions and thus the metabolism and transpiration was probably reduced as compared to soil grown plants. Though difficult, it is quite possible to grow adult terrestrial plants such as Rhubarb and common sorrel under hydroponic conditions (Aubert and Schwitzguebel, 2004). But, research that has been involving the cultivation and experimentation with plants in such systems also portrays...

Bioremediation of Cyanide and Nitrile Contaminated Sites

In situ application of microbes in removal of hazardous compounds to remediate the contaminated soil water is gaining importance in as it is cost-effective and ecof-riendly and requires lesser energy input. The bacterium or consortium of bacteria that are involved in the degradation of the hazardous compound occur naturally at the site. Cyanide can be degraded into simpler substances by microorganisms in the wastewater, piles and in the soil. Many bacterial and fungal species are capable of decomposing nitriles and highly toxic cyanides. The biological treatment methods do not depend on the supply of electricity or other energy sources. The bacterial detoxification is found to be safer, quicker, and cost effective than the chemical treatment for the handling of cyanide and nitrile wastes.

Metal Sequestration with Plants

The determining factor in the successful phytoremediation is the ability to cultivate a high biomass yielding hyperaccumulators in soil with high metal content 2 . Genetic modification of some plants to enhance their phytoextraction capabilities has been tried. Such modifications aimed at converting slow-growing, low-biomass hyperaccumulators into fast-growing, high-biomass species 40 . Enhanced tolerance to metals was observed in transgenic plants containing gene related to phytochelatins (metal inducible cysteine-rich peptides, a natural plant internal chelant for heavy metal detoxification) 37, 41, 42 . However, public concern about the introduction of transgenic plants turned out to be the main obstacle to allow such approach. Instead of gene-modification approaches, the conventional plant breeding approaches with the emphasis on the search of natural hyperaccumulators are opt to be accepted 43, 44 . The most feasible strategy to develop a low-cost, environment-friendly...

Heavy Metal Effects on Transcriptomics of ECM Fungi

Detoxification mechanisms in the mycobiont are probably achieved via several physiological processes rather than through a single mechanism (Hartley et al. 1997). This is seen in studies with EST (expressed sequence tags) data of Cd-treated mycelium of Paxillus involutus (Jacob et al. 2004) and microarrays of

Intracellular Accumulation

The assimilation of metals by bacteria plays an important role in detoxification. Sigg (1987) presented a probable scenario for intracellular accumulation. Extracellular ligands or ligands attached to the cell wall are thought to bind toxic metals. These ligands transport the complexed metals through the cell wall in a slow transport step. The metals are released inside the cell, incorporated into biochemical pathways, or trapped in an inactive form via complexation with another high-affinity ligand. Cadmium is accumulated by a large number of organisms. Research by Macaskie et al. (1987) on Citrobacter suggests that it is accumulated as cell-bound cadmium phosphate. This is presumably a detoxification mechanism and is similar to the accumulation of lead as PbHPO4 by a different Citrobacter sp., as suggested by Aickin et al. (1979). The ability of certain bacterial cells to accumulate metals intra-cellularly has been exploited in mining practices, particularly in the management of...

Molecular Mechanisms and Genetic Basis of Heavy Metal Toxicity and Tolerance in Plants

Abstract Heavy metal pollutants are mainly derived from growing number of anthropogenic sources. As the environmental pollution with heavy metals increases, some new technologies are being developed, one of these being phytoremediation. Hyperaccumulator plant varieties can be achieved by using methods of genetic engineering. An uptake of excessive amounts of heavy metals by plants from soil solution leads to range of interactions at cellular level which produce toxic effects on cell metabolism in terms of enzyme activity, protein structure, mineral nutrition, water balance, respiration and ATP content, photosynthesis, growth and morphogenesis and formation of reactive oxygen species (ROS).On the basis of accumulation of heavy metals plants are divided into three main types (i) the accumulator plants, (ii) the indicator plants, and (iii) the excluder plants. Generally, the accumulation of heavy metals in plant organ is in series root leaves stem inflorescence seed. Most of plants...

Toxicokinetics and toxicodynamics

At present for many ecotoxicological applications, regarding the organism as a 1-compartment model is a good initial choice for whole body residues, and probably also for mixture TK. There are, of course, several situations where such simplicity will not apply and where more elaborate PBTK modeling may be required. These include larger organisms where internal redistribution is not fast enough to make a 1-compartment model reasonable, species with known tissues for handling and detoxification of chemicals where these are likely to interact, and also situations where the kinetics of receptor interactions or the accumulation of internal damage may need to be modeled explicitly as additional state variables. However, it is generally advisable to start with the simple 1-compartment model, and build more complex models when needed (in view of the limited data available). For single metals, there is growing evidence in aquatic ecotoxicology that advocates the concept of biodynamic modeling...

Phytoremediation of Toxins

Phytovolatilization involves the uptake of contaminants from polluted soil and their transformation into volatile compounds and their extraction into the atmosphere by transpiration. This technique is relatively less useful for removal of heavy metals as the pollutant must (i) be taken up by plants through roots, (ii) pass through the xylem to the leaves (iii) be converted into some volatilable compounds, and (iv) volatilize to the atmosphere (Mueller et al. 1999). Despite these limitations, this technique has been reported to be useful for the removal of mercury from the polluted soils by transgenic tobacco plants carrying bacterial mercury detoxification genes merA and merB (Rugh et al. 1996, 1998 Bizily et al. 1999, 2000). The genes (merA) encodes the enzyme mercuric ion reductase that reduces ionic mercury (Hg+) to the less toxic volatile Hg(0) using NADPH reducing equivalents. In this process, the mercuric ion is transformed into methylmercury (CH3Hg+) and phenylmercuric acetate...

Soil Sediment Continuum

Several processes take place near the sediment-water interface (Lerman 1978). There is considerable debate on the distinction between soils and sediments (Blum 2005). Sediment pollution is caused by natural and anthropogenic influence. According to Gross (1978), human activities have significantly altered sediment characteristics. Industrial effluents and urban wastes are sources of pollutants in waters and sediments. Heavy metals in floodplain soils and sediment remediation including detoxification mechanisms involving plants are gaining considerable global attention (Rinklebe et al. 2007). The metal detoxification in plants is complex and usually involves a combination of several mechanisms, both limiting the metal circulation within plant organisms and preventing damages caused by a metal-induced oxidative stress (see below).

Ex Situ and In Situ Methods of Phytoremediation 19911 Ex Situ Methods

Here, the contaminated soil is treated on- or offsite, and then returned to its original site. Conventional ex situ methods applied to remediate polluted soils include excavation, detoxification, and or destruction of the contaminant physically or chemically, meaning that the contaminant undergoes stabilization, solidification, immobilization, incineration or destruction.

Uptake and Transport of Cyanide By Plants

Phytoremediation, may provide opportunity to remediate cyanide and iron cyanide contamination, provided that these compounds can be transported and assimilated by plants after passive or active uptake. Translocation from root to shoot requires a membrane transport step from root symplast into xylem apoplast. The impermeable suberin layer in the cell wall of the root endodermis (Casparian strip) prevents toxic substances from flowing straight from the soil solution or root apoplast into the root xylem (Taiz and Zeiger 2002). Organic pollutants pass the membrane between root symplast and xylem apoplast via simple diffusion. When pollutants are sequestered in tissues, they are often bound by chelators or form conjugates. Chelators that are involved in metal sequestration include the tripeptide GSH (y - glu-cys-gly) and its oligomers, the phytochelatins (PCs) (Pickering et al. 2000). After chelation, an ABC-type transporter can actively transport the metal-chelate complex to the vacuole,...

Microorganisms and Metal Contamination

Microbes can, in principle, solubilize metals, thereby increasing their bioavailability, or immobilize them and reduce their bioavailability. Nonradioactive As, Cd, Cu, Hg, Pb and Zn and radioactive Sr, Cs and U are the most environmentally important metallic pollutants. Although organic molecules can be degraded, toxic metals can only be remediated by removal from soil. Microorganisms can detoxify metals by valence transformation, extracellular chemical precipitation, or volatilization. In fact, some microorganisms can enzymatically reduce a variety of metals in metabolic processes 12 . Some bacteria gain energy for growth by coupling the oxidation of simple organic acids and alcohols, hydrogen, or aromatic compounds, to the reduction of Fe(III) or Mn(IV). The reduction of the toxic selenate and selenite to the insoluble and much less toxic elemental selenium may be exploited to enhance removal of these anions from contaminated sites 13, 14, 15,16, 17 . The more toxic form of...

The Structural and Functional Characteristics of Asiatic Desert Halophytes for Phytostabilization of Polluted Sites

Abstract Phytoremediation, the use of plants to extract, sequester, and or detoxify pollutants through biological processes is an effective, in situ, non-intrusive, low-cost, ecologically friendly, socially accepted technology to remediate polluted soils. Crystalline to fibrillar wax formations, appressed to surfaces of guard cells appear to originate from guard cells in the vicinity of the stomatal aperture. Formations may arise from evaporation of plant water at the interface between stomatal antechambers and substomatal cavities, leaving salt ions behind to precipitate. Many questions remain unanswered regarding their ecological and physiological significance as well as their occurrence and prevalence in both time and space. Such functions would be of considerable adaptive value in the light of their possible relationships to the impact of pollutants. An attempt has been made here to address these questions by analysing the morphology of salt glands and intracellular salt crystals...

Conclusion Of The Plant Adaptation

Plants and their associated microbes can remediate cyanide via cyanide uptake, transport, degradation and assimilation in plants. Experiments using free cyanide have shown that many terrestrial and aquatic plants including willow, sorghum, cassava and water hyacinth can remove cyanide from the growing medium. Cyanide uptake in plants can be associated with a very complex physiological mechanism which includes transport and assimilation of cyanide within the plants for catering plant's nitrogen needs. Phytoremediation offers a cost-effective and environment-friendly alternative or complementary technology for conventional remediation methods. Although phytoremediation can work effectively, the underlying biological processes are still largely unknown in many cases. Some important processes that require further study are plant-microbe interactions, detailed cyanide transport, chelation and degradation mechanisms in plants. Collection of this information would be useful in developing...

Examples Of Using Enzymes For Bioremediation

First Munnecke (18,19) then Caldwell and Raushel (198) investigated the feasibility of using an immobilized enzymatic system to detoxify organophosphate pesticides. A parathion hydrolase was immobilized successfully on porous glass or silica beads and showed good operational performance (i.e., high residual activity and long-term stability) (18,19). When applied in a fluidized-bed reactor, the hydrolase was able to remove more than 90 of the parathion from parathion-polluted water. A similar reactor was utilized by Caldwell and Raushel (198) with a phosphodiesterase from Pseudomonas putida adsorbed on trityl agarose. The chemical and kinetic parameters of the immobilized enzyme were comparable to those of the free enzyme. Furthermore, the immobilized system was able to hydrolyze, to an elevated extent ( 90 ), several organophosphate pesticides, including methyl parathion, paraoxon, ethyl parathion, diazinon, and coumaphos (198). There is limited number of papers dealing with the use...

Role of Dissolved Humic Substances in Pollutant Solid Phase Interactions

Organic pollutants may be bound to DHS through abiotic or biological processes whereby the formation of bound residues usually results in detoxification of these pollutants. Therefore, enhancing the binding of xenobiotic chemicals to humic matter can serve as a means to reduce toxicity as well as migration of the toxic compounds 51,52,64,67,166,290 . Binding of a pollutant to DHS, clays, or other materials would be expected to decrease its toxic effects. Binding can reduce the amount of a compound available to the biota and, as the quantity of an available xenobiotic is reduced, toxicity also declines. Below are some possible ways of binding with DHS

Pathways of Heavy Metal Access

Klipp Vningar

Similar to heavy metal uptake by plants, aquatic organisms vary in their metal uptake. They can be grouped into two categories regulators (excluders) and accumulators (non-excluders) 218 . Fig. 28 shows some examples for aquatic organisms and their different strategies for uptake, accumulation, and excretion of heavy metals 219 . Regulators are characterized by their low metal uptake, while accumulators are characterized by their high metal uptake. While regulators are able to control metal accumulations and keep their intracellular metal concentrations within a narrow range over a broad external concentration range of heavy metals, accumulators are capable of adopting a detoxification system with an elevated metal body level even in noncontaminated environments.

Phytoremediation A Potential Tool of Bioremediation

Sebertia Acuminate

May be a lead detoxification Metal hyperaccumulator species, capable of taking up metals in the thousands of ppm, possess additional detoxification mechanisms. Understanding the mechanisms of rhizosphere interaction, uptake, transport and sequestration of metals in hyperaccumulator plants will lead to designing novel transgenic plants with improved remediation traits ( 184 . For example, research has shown that in T. goesingense, a Ni hyperacccumulator, high tolerance was due to Ni complexation by histidine, which rendered the metal inactive 185-186 . Sequestration in the vacuole has been suggested to be responsible for Zn tolerance in the shoots of the Zn-hyperaccumulator T. caerulescens 169, 187 . Cadmium, a potentially toxic metal, has been shown to accumulate in plants where it is detoxified by binding to phytochelatins 188-190 .

Biomarkers of Exposure and Effect

Semiquinones and quinones may be potentially toxic but short-lived metabolites after oral exposure (Juhl et al. 1991 Phornchirasilp et al. 1989b). The extent and type of Phase II detoxification reactions is apparently species- and isomer-related (Bahig et al. 1981 Bray et al. 1952a, 1952b Pekari et al. 1986 Somani and Khalique 1982 Spencer and Williams 1950). Broad-based experimentation to determine dose-effect relationships for hepatic adaptive and toxic effects are needed. Part of this experimentation may involve estimation of the rate constants for the formation of both potentially toxic intermediates and Phase II conjugates. Metabolic studies for determining rate differences in conjugate formation between Methods for Reducing Toxic Effects. The P-448 inducer 3-MC, and possibly other PAHs, apparently increase the Phase II conjugation rates of phenolic substrates (Jansen et al. 1992 Wishart 1978a, 1978b). This observation implies that certain chemicals may decrease the body burden...

Bioremediation of Arsenic from Contaminated Groundwater

Microbial arsenate metabolism was first identified by Green (1918). Green isolated an arsenate reducer, Bacterium arenreducens. and an arsenite oxidizer Bacillus arsenoxydans. The microbiological oxidation of As(III) to As(V) can impact the mobility and speciation of arsenic in the environment. The process has been known for many years and more than 30 strains representing at least nine genera have been reported to be involved, including a-,b-, and g-Proteobacteria Deinocci (i.e., Thermus) and Crenarchaeota (Stolz and Oremland 2003). Physiologically diverse, these include both heterotrophic arsenite oxidizers (HAOs) and the more recently described chemolithoautotrophic arsenite oxidizers (CAOs). Heterotrophic oxidation of As(III) is viewed as a detoxification reaction that converts As(III) encountered on the cell's outer membrane into the less toxic form i.e. As(V), perhaps making it less likely to enter the cell. CAOs couple the oxidation of arsenite (e.g., electron donor) to the...

Transport of Zn Across Membranes 741 Diversity of Zn Transporters

Recently, a zinc-induced facilitator 1 (ZIF1) has been reported to influence the detoxification and accumulation of Zn in Arabidopsis thaliana and to be different from the known Zn transporters, which transport free Zn cation (Haydon and Cobbett 2007). Carboxylic organic acids are effective ligands for chelation of Zn in plant cells. Therefore, ZIF1 is thought to transport low-molecular-mass Zn-ligands, such as organic acids, and or Zn-ligand complexes into the vacuoles. expressed in the meristematic and elongating zones of the main and emerging lateral roots even under normal conditions. MTP3 might be involved in the com-partmentalization and detoxification of Zn together with MTP1 under excess Zn conditions. Indeed, overexpression of MTP3 resulted in high accumulation of Zn in A. thaliana and conferred Zn tolerance compared with the wild-type plants (Arrivault et al. 2006). MTP3 has a short His-rich loop and an N-terminal region different from MTP1 (for sequence alignment, see...

Phytoremediation of Toxic Explosives

Abstract Widespread contamination of the environment by explosives resulting from the manufacture, disposal and testing of munitions is becoming a matter of increasing concern. Most explosives are considered to be a major hazard to biological systems due to their toxic and mutagenic effects. Interest on the bioremediation of lands contaminated with explosives has recently been focused on phytoreme-diation. Unfortunately, whilst plants have many advantages for the remediation of contaminated land and water, they lack the catabolic versatility which enables microorganisms to mineralize such a wide diversity of xenobiotic compounds. This raised the interesting question as to whether the impressive biodegradative capabilities of soil bacteria could be combined with the high biomass and stability of plants to yield an optimal system for in situ bioremediation of explosive residues in soil. During the last few years, plants have been genetically modified to overcome the inherent limitation...

Subcellular Localization of Cu in Elsholtzia splendens

One of the most important principles of heavy metal tolerance and detoxification in plant cells is its selective distribution, which could avoid damaging relatively significant organelles. The cell walls of plants have the capacity to bind metal ions in negatively charged sites (Macfie and Welbourn 2000). Therefore, plant cell walls could be a critical defensive strategy of plants to heavy metal stress (Branquinho et al. 1997). In addition to cell wall compartmentation, transport of Through transmission electron microscope (TEM) and energy-dispersive analysis of X-rays (EDX), the likely location of copper within the cells of Elsholtzia splendens was investigated (Ni et al. 2005). It was found that the majority of copper in Elsholtzia splendens was localized primarily in the vacuolar and cell wall. The study of Lou et al (2004) revealed that most of the increased Cu in the roots was found on the cell walls during the short-time culture (24 h), while copper proportion on the cell walls...

Microbial Methylation and Demethylation for Arsenic Remediation

Arsine Arsenic Ions

Methylation and demethylation may play a significant role in influencing the toxicity and mobility of arsenic in soils and groundwater. As(III) and As(V) methylation may form volatile species leading to the escape of arsenic from water and soil surfaces by volatilization. Though the methylated arsenic species are generally considered less toxic than the inorganic species, the methylation processes do not necessarily contribute to the detoxification mechanism. Recent research has demonstrated that trivalent methylated arsenic species are more effective in destroying DNA. The potency of the DNA damage decreases in the order DMAA (III) MMAA (III) As(III),As(V) MMAA(V) DMAA(V) trimethylarsine oxide TMAO(V) (Dopp et al. 2004 Wang and Zhao 2009).

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