Heavy Metal Polluted Soils: Effect on Plants and Bioremediation Methods
TL;DR: Combining both microorganisms and plants is an approach to bioremediation that ensures a more efficient clean-up of heavy metal polluted soils as discussed by the authors, however, success of this approach largely depends on the species of organisms involved in the process.
Abstract: Soils polluted with heavy metals have become common across the globe due to increase in geologic and anthropogenic activities. Plants growing on these soils show a reduction in growth, performance, and yield. Bioremediation is an effective method of treating heavy metal polluted soils. It is a widely accepted method that is mostly carried out in situ; hence it is suitable for the establishment/reestablishment of crops on treated soils. Microorganisms and plants employ different mechanisms for the bioremediation of polluted soils. Using plants for the treatment of polluted soils is a more common approach in the bioremediation of heavy metal polluted soils. Combining both microorganisms and plants is an approach to bioremediation that ensures a more efficient clean-up of heavy metal polluted soils. However, success of this approach largely depends on the species of organisms involved in the process.
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TL;DR: The physiological and biochemical effects of each heavy metal bioaccumulation in humans and the level of gravity and disquieting factor of the disease are shown.
1,185 citations
Cites background from "Heavy Metal Polluted Soils: Effect ..."
...The more acidic the soil, the less elemental elements have been found as these become more soluble and leach lower in the ground where the roots do not reach causing nutrient deficiency to the plants [2, 23]....
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Journal Article•
TL;DR: This work found significant variation in Arabidopsis thaliana ecotypes in accumulation and tolerance of Pb, and screened ethyl methanesulfonate-mutagenized M2 populations and identified several Pb-accumulating mutants.
Abstract: In addition to the often-cited advantages of using Arabidopsis thaliana as a model system in plant biological research (1), Arabidopsis has many additional characteristics that make it an attractive experimental organism for studying lea d (Pb) accumulation and tolerance in plants. These include its fortuitous familial relationship to many known metal hyperaccumulators (Brassicaceae), as well as similar Pbaccumulation patterns to most other plants. Using nutrient-agar plates, hydroponic culture, and Pb-contaminated soils as growth media, we found significant variation in Arabidopsis thaliana ecotypes in accumulation and tolerance of Pb. In addition, we have found that Pb accumulation is not obligatorily linked with Pb tolerance, suggesti ng that different genetic factors control these two processes. We also screened ethyl methanesulfonate-mutagenized M2 populations and identified several Pb-accumulating mutants. Current characterization of these mutants indicates that their phenotypes are likely due to alteration of general metal ion uptake or translocation processes since these mutants also accumulate many other metals in shoots. We expect that further characterization of the ecotypes and mutants will shed light on the basic genetic and physiological underpinnings of plant-based Pb remediation. 7. Aromatic nitroreduction of acifluorfen in soils, rhizospheres, and pure cultures of rhizobacteria. Zablotowicz, R. M., Locke, M. A., and Hoagland, R. E. Phytoremediation of soil and water contaminants. Washington, DC : American Chemical Society, 1997. p. 38-53. NAL Call #: QD1.A45-no.664 Abstract: Reduction of nitroaromatic compounds to their corresponding amino derivatives is one of several pathways in the degradation of nitroxenobiotics. Our studies with the nitrodiphenyl ether herbicide acifluorfen showed rapid metabolism to am inoacifluorfen followed by incorporation into unextractable soil components in both soil and rhizosphere suspensions. Aminoacifluorfen was formed more rapidly in rhizospheres compared to soil, which can be attributed to higher microbial populations, espec ially of Gram-negative bacteria. We identified several strains of Pseudomonas fluorescens that possess nitroreductase activity capable of converting acifluorfen to aminoacifluorfen. Factors affecting acifluorfen nitroreductase activity in pure cultures an d cell-free extracts, and other catabolic transformations of acifluorfen, ether bond cleavage, are discussed. Plant rhizospheres should be conducive for aromatic nitroreduction. Nitroreduction by rhizobacteria is an important catabolic pathway for the ini tial degradation of various nitroherbicides and other nitroaromatic compounds in soils under Reduction of nitroaromatic compounds to their corresponding amino derivatives is one of several pathways in the degradation of nitroxenobiotics. Our studies with the nitrodiphenyl ether herbicide acifluorfen showed rapid metabolism to am inoacifluorfen followed by incorporation into unextractable soil components in both soil and rhizosphere suspensions. Aminoacifluorfen was formed more rapidly in rhizospheres compared to soil, which can be attributed to higher microbial populations, espec ially of Gram-negative bacteria. We identified several strains of Pseudomonas fluorescens that possess nitroreductase activity capable of converting acifluorfen to aminoacifluorfen. Factors affecting acifluorfen nitroreductase activity in pure cultures an d cell-free extracts, and other catabolic transformations of acifluorfen, ether bond cleavage, are discussed. Plant rhizospheres should be conducive for aromatic nitroreduction. Nitroreduction by rhizobacteria is an important catabolic pathway for the ini tial degradation of various nitroherbicides and other nitroaromatic compounds in soils under phytoremediation management. 8. Ascorbate: a biomarker of herbicide stress in wetland plants. Lytle, T. F. and Lytle, J. S. Phytoremediation of soil and water contaminants. Washington, DC : American Chemical Society, 1997. p. 106-113. NAL Call #: QD1.A45-no.664 Abstract: In laboratory exposures of wetland plants to low herbicide levels (<0.1 micrograms/mL), some plants showed increased total ascorbic acid suggesting a stimulatory effect on ascorbic acid synthesis occurred; at higher herbicide conce ntrations (greater than or equal to 0.1 micrograms/mL) a notable decline in total ascorbic acid and increase in the oxidized form, dehydroascorbic acid occurred. Vigna luteola and Sesbania vesicaria were exposed for 7 and 21 days respectively to atrazine (0.05 to 1 microgram/mL); Spartina alterniflora 28 days at 0.1 micrograms/mL trifluralin; Hibiscus moscheutos 14 days at 0.1 and 1 microgram/mL metolachlor in fresh and brackish water. The greatest increase following low dosage occurred with S. alterniflo ra, increasing from <600 micrograms/g wet wt. total ascorbic acid to >1000 micrograms/g. Ascorbic acid may be a promising biomarker of estuarine plants exposed to herbicide runoff; stimulation of ascorbic acid synthesis may enable some wetland plant s used in phytoremediation to cope with low levels of these compounds. In laboratory exposures of wetland plants to low herbicide levels (<0.1 micrograms/mL), some plants showed increased total ascorbic acid suggesting a stimulatory effect on ascorbic acid synthesis occurred; at higher herbicide conce ntrations (greater than or equal to 0.1 micrograms/mL) a notable decline in total ascorbic acid and increase in the oxidized form, dehydroascorbic acid occurred. Vigna luteola and Sesbania vesicaria were exposed for 7 and 21 days respectively to atrazine (0.05 to 1 microgram/mL); Spartina alterniflora 28 days at 0.1 micrograms/mL trifluralin; Hibiscus moscheutos 14 days at 0.1 and 1 microgram/mL metolachlor in fresh and brackish water. The greatest increase following low dosage occurred with S. alterniflo ra, increasing from <600 micrograms/g wet wt. total ascorbic acid to >1000 micrograms/g. Ascorbic acid may be a promising biomarker of estuarine plants exposed to herbicide runoff; stimulation of ascorbic acid synthesis may enable some wetland plant s used in phytoremediation to cope with low levels of these compounds. 9. Atmospheric nitrogenous compounds and ozone--is NO(x) fixation by plants a possible solution. Wellburn, A. R. New phytol. 139: 1 pp. 5-9. (May 1998). NAL Call #: 450-N42 Descriptors: ozoneair-pollution nitrogen-dioxide nitric-oxide air-quality tolerancebioremediationacclimatizationnutrient-sources nutrient-uptake plantscultivarsgenetic-variation literature-reviews 10. Atrazine degradation in pesticide-contaminated soils: phytoremediation potential. Kruger, E. L., Anhalt, J. C., Sorenson, D., Nelson, B., Chouhy, A. L., Anderson, T. A., and Coats, J. R. Phytoremediation of soil and water contaminants. Washington, DC : American Chemical Society, 1997. p. 54-64. NAL Call #: QD1.A45-no. 664 Abstract: Studies were conducted in the laboratory to determine the fate of atrazine in pesticide-contaminated soils from agrochemical dealer sites. No significant differences in atrazine concentrations occurred in soils treated with atrazine i ndividually or combinations with metolachlor and trifluralin. In a screening study carried out in soils from four agrochemical dealer sites, rapid mineralization of atrazine occurred in three out of eight soils tested, with the greatest amount occurring i n Bravo rhizosphere soil (35% of the applied atrazine after 9 weeks). Suppression of atrazine mineralization in the Bravo rhizosphere soil did not occur with the addition of high concentrations of herbicide mixtures, but instead was increased. Plants had a positive impact on dissipation of aged Studies were conducted in the laboratory to determine the fate of atrazine in pesticide-contaminated soils from agrochemical dealer sites. No significant differences in atrazine concentrations occurred in soils treated with atrazine i ndividually or combinations with metolachlor and trifluralin. In a screening study carried out in soils from four agrochemical dealer sites, rapid mineralization of atrazine occurred in three out of eight soils tested, with the greatest amount occurring i n Bravo rhizosphere soil (35% of the applied atrazine after 9 weeks). Suppression of atrazine mineralization in the Bravo rhizosphere soil did not occur with the addition of high concentrations of herbicide mixtures, but instead was increased. Plants had a positive impact on dissipation of aged atrazine in soil, with significantly less atrazine extractable from Kochia-vegetated soils than from nonvegetated soils. 11. Bacterial inoculants of forage grasses that enhance degradation of 2-chlorobenzoic acid in soil. Siciliano, S. D. and Germida, J. J. Environ toxicol chem. 16: 6 pp. 1098-1104. (June 1997). NAL Call #: QH545.A1E58 Descriptors: polluted-soils bioremediationAbstract: Biological remediation of contaminated soil is an effective method of reducing risk to human and ecosystem health. Bacteria and plants might be used to enhance remediation of soil pollutants in situ. This study assessed the potential of bacteria (12 isolates), plants (16 forage grasses), and plant-bacteria associations (selected pairings) to remediate 2-chlorobenzoic acid (2CBA)-contaminated soil. Initially, grass viability was assessed in 2CBA-contaminated soil. Soil was contaminated wi th 2CBA, forage grasses were grown under growth chamber conditions for 42 or 60 d, and the 2CBA concentration in soil was determined by gas chromatography. Only five of 16 forage grasses grew in 2CBA-treated (816 mg/kg) soil. Growth of Bromus inermis had no effect on 2CBA concentration, whereas Agropyron intermedium, B. biebersteinii, A. riparum, and Elymus dauricus decreased 2CBA relative to nonplanted control soil by 32 to 42%. The 12 bacteria isolates were screened for their ability to promote the germ ination of the five grasses in 2CBA-contaminated soil. Inoculation of A. riparum with Pseudomonas aeruginos
1,049 citations
TL;DR: The sources of toxic heavy metals are discussed, the groups of microorganisms with biosorbent potential for heavy metal removal are described and the use of microbial biosorbents is eco-friendly and cost effective.
Abstract: Persistent heavy metal pollution poses a major threat to all life forms in the environment due to its toxic effects. These metals are very reactive at low concentrations and can accumulate in the food web, causing severe public health concerns. Remediation using conventional physical and chemical methods is uneconomical and generates large volumes of chemical waste. Bioremediation of hazardous metals has received considerable and growing interest over the years. The use of microbial biosorbents is eco-friendly and cost effective; hence, it is an efficient alternative for the remediation of heavy metal contaminated environments. Microbes have various mechanisms of metal sequestration that hold greater metal biosorption capacities. The goal of microbial biosorption is to remove and/or recover metals and metalloids from solutions, using living or dead biomass and their components. This review discusses the sources of toxic heavy metals and describes the groups of microorganisms with biosorbent potential for heavy metal removal.
1,035 citations
Cites background from "Heavy Metal Polluted Soils: Effect ..."
...Zinc Brass manufacturing, mining, oil refinery, plumbing Ataxia, depression, gastrointestinal irritation, hematuria, icterus, impotence, kidney and liver failure, lethargy, macular degeneration, metal fume fever, prostate cancer, seizures, vomiting Affects photosynthesis, inhibits growth rate, reduced chlorophyll content, germination rate and plant biomass Death, decrease in biomass, inhibits growth [25,41]...
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...Nickel Electroplating, non-ferrous metal, paints, porcelain enameling Cardiovascular diseases, chest pain, dermatitis, dizziness, dry cough and shortness of breath, headache, kidney diseases, lung and nasal cancer, nausea Decrease chlorophyll content, inhibit enzyme activities and growth, reduced nutrient uptake Disrupt cell membrane, inhibit enzyme activities, oxidative stress [24,25,36]...
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TL;DR: The toxic effects of heavy metal pollution and the mechanisms used by microbes and plants for environmental remediation are discussed and the importance of modern biotechnological techniques and approaches in improving the ability of microbial enzymes to effectively degrade heavy metals at a faster rate is emphasized.
Abstract: Environmental pollution from hazardous waste materials, organic pollutants and heavy metals, has adversely affected the natural ecosystem to the detriment of man. These pollutants arise from anthropogenic sources as well as natural disasters such as hurricanes and volcanic eruptions. Toxic metals could accumulate in agricultural soils and get into the food chain, thereby becoming a major threat to food security. Conventional and physical methods are expensive and not effective in areas with low metal toxicity. Bioremediation is therefore an eco-friendly and efficient method of reclaiming environments contaminated with heavy metals by making use of the inherent biological mechanisms of microorganisms and plants to eradicate hazardous contaminants. This review discusses the toxic effects of heavy metal pollution and the mechanisms used by microbes and plants for environmental remediation. It also emphasized the importance of modern biotechnological techniques and approaches in improving the ability of microbial enzymes to effectively degrade heavy metals at a faster rate, highlighting recent advances in microbial bioremediation and phytoremediation for the removal of heavy metals from the environment as well as future prospects and limitations. However, strict adherence to biosafety regulations must be followed in the use of biotechnological methods to ensure safety of the environment.
631 citations
Cites background or methods from "Heavy Metal Polluted Soils: Effect ..."
...Sulphate-reducing bacteria such as Desulfovibrio desulfuricans have the ability to convert sulphate to hydrogen sulphate which then reacts with heavy metals such as Cd and Zn to form insoluble forms of these metal sulphides [7]....
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...Moreover, high metal toxicity inhibits cytoplasmic enzymes in plant cells and causes damage to cell structures due to oxidative stress [7,51] which consequently affects plant growth and metabolism....
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...This leads to base damage through formation of reactive oxygen species (ROS) which includes oxygen radicals (superoxide and hydroxyl) [7] and non-radical derivatives of molecular oxygen (O2) such as hydrogen peroxide (H2O2), as well as breakage of the DNA molecule [5,6]....
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...[10] who were able to save 50–65% of cost, when bioremediation was used for the treatment of one acre of Pb-polluted soil compared with the use of conventional methods such as excavation and landfill [7]....
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...Asteraceae Berkheya coddii Ni [108] Asteraceae Helianthus annuus Pb, Cd, Zn [101,109] Brassicaceae Alyssum bertolonii Ni [110] Brassicaceae Alyssum murale Ni [111] Brassicaceae Arabidopsis halleri Zn, Cd [112] Brassicaceae Arabidopsis halleri Cd Cd [113] Caryophyllaceae Minuartia verna Zn, Cd, Pb [114] Crassulaceae Sedum alfredii Pb [7,115] Euphorbiaceae Euphorbia cheiradenia Cu, Fe, Pb, Zn [1] Fabaceae Astragalus racemosus Se [116] Fabaceae Medicago sativa Pb [7] Poaceae Spartina argentinensis Cr [117] Pteridaceae Pteris vittata As [118–120] Pteridaceae Pteris vittata Hg [121] Violaceae Viola boashanensis Pb, Zn, Cd [122]...
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TL;DR: In this review, the recent literature on the biological functions of K, its uptake, its translocation, and its role in plant abiotic stress tolerance are summarized.
Abstract: Among the plant nutrients, potassium (K) is one of the vital elements required for plant growth and physiology. Potassium is not only a constituent of the plant structure but it also has a regulatory function in several biochemical processes related to protein synthesis, carbohydrate metabolism, and enzyme activation. Several physiological processes depend on K, such as stomatal regulation and photosynthesis. In recent decades, K was found to provide abiotic stress tolerance. Under salt stress, K helps to maintain ion homeostasis and to regulate the osmotic balance. Under drought stress conditions, K regulates stomatal opening and helps plants adapt to water deficits. Many reports support the notion that K enhances antioxidant defense in plants and therefore protects them from oxidative stress under various environmental adversities. In addition, this element provides some cellular signaling alone or in association with other signaling molecules and phytohormones. Although considerable progress has been made in understanding K-induced abiotic stress tolerance in plants, the exact molecular mechanisms of these protections are still under investigation. In this review, we summarized the recent literature on the biological functions of K, its uptake, its translocation, and its role in plant abiotic stress tolerance.
407 citations
References
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Book•
01 Jan 1984
TL;DR: The Biosphere The Anthroposphere Soils and Soil Processes Weathering Processes Pedogenic Processes Soil Constituents Trace Elements Minerals Organic Matter Organisms in Soils Trace Elements in Plants.
Abstract: Chapter 1 The Biosphere Chapter 2 The Anthroposphere Introduction Air Pollution Water Pollution Soil Plants Chapter 3 Soils and Soil Processes Introduction Weathering Processes Pedogenic Processes Chapter 4 Soil Constituents Introduction Trace Elements Minerals Organic Matter Organisms in Soils Chapter 5 Trace Elements in Plants Introduction Absorption Translocation Availability Essentiality and Deficiency Toxicity and Tolerance Speciation Interaction Chapter 6 Elements of Group 1 (Previously Group Ia) Introduction Lithium Rubidium Cesium Chapter 7 Elements of Group 2 (Previously Group IIa) Beryllium Strontium Barium Radium Chapter 8 Elements of Group 3 (Previously Group IIIb) Scandium Yttrium Lanthanides Actinides Chapter 9 Elements of Group 4 (Previously Group IVb) Titanium Zirconium Hafnium Chapter 10 Elements of Group 5 (Previously Group Vb) Vanadium Niobium Tantalum Chapter 11 Elements of Group 6 (Previously Group VIb) Chromium Molybdenum Tungsten Chapter 12 Elements of Group 7 (Previously Group VIIb) Manganese Technetium Rhenium Chapter 13 Elements of Group 8 (Previously Part of Group VIII) Iron Ruthenium Osmium Chapter 14 Elements of Group 9 (Previously Part of Group VIII) Cobalt Rhodium Iridium Chapter 15 Elements of Group 10 (Previously Part of Group VIII) Nickel Palladium Platinum Chapter 16 Elements of Group 11 (Previously Group Ib) Copper Silver Gold Chapter 17 Trace Elements of Group 12 (Previously of Group IIb) Zinc Cadmium Mercury Chapter 18 Elements of Group 13 (Previously Group IIIa) Boron Aluminum Gallium Indium Thallium Chapter 19 Elements of Group I4 (Previously Group IVa) Silicon Germanium Tin Lead Chapter 20 Elements of Group 15 (Previously Group Va) Arsenic Antimony Bismuth Chapter 21 Elements of Group 16 (Previously Group VIa) Selenium Tellurium Polonium Chapter 22 Elements of Group 17 (Previously Group VIIa) Fluorine Chlorine Bromine Iodine
9,739 citations
01 Jan 1980
TL;DR: In this paper, the essential roles of arsenic, fluorine, nickel, silicon, tin and vanadium have in recent years been established in animal nutrition, and they are known as trace elements, minor elements or micro-nutrients.
Abstract: Fifteen or more elements present in rocks and soils normally in very small amounts are essential for plant and/or animal nutrition. By the nature of their low abundance in natural uncontaminated earth materials or plants, they are known as trace elements, minor elements or micro-nutrients. Boron, copper, iron, manganese, molybdenum, silicon, vanadium and zinc are required by plants; copper, cobalt, iodine, iron, manganese, molybdenum, selenium and zinc by animals. In addition essential roles of arsenic, fluorine, nickel, silicon, tin and vanadium have in recent years been established in animal nutrition.
3,339 citations
"Heavy Metal Polluted Soils: Effect ..." refers background in this paper
...reduced photosynthetic activities, plant mineral nutrition, and reduced activity of some enzymes [34]....
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01 Jan 1989
TL;DR: Phytochemical studies suggest that hyperaccumulation is closely linked to the mechanism of metal tolerance involved in the successful colonization of metalliferous and otherwise phytotoxic soils.
Abstract: This paper reviews the plant geography, ecology, metal tolerance and phytochcmistry of terrestrial higher plants which arc able to accumulate metallic elements in their dry matter to an exceptional degree. The review is limited to the elements Co, Cu, Cr, Pb. Mn. Ni and Zn. Hyperaccumulators of Co, Cu, Cr, Pb and Ni arc here defined as plants containing over 1000 u.g/g (ppm) of any of these elements in the dry matter; for Mn and Zn, the criterion is 10,000 u.g/g (1%). A unifying feature of hypcraccumula ting plants is their general restriction to mineralized soils and specific rock types. Lists of hypcraccumula ting species arc presented for the elements considered. These suggest that the phenomenon is widespread throughout the plant kingdom. For example, 145 hyper-accumulators of nickel are reported: these arc distributed among 6 supcrordcrs, 17 orders, and 22 families and include herbs, shrubs and trees from both the temperate and tropical zones. Although some phylogcnetic relationships emerge, the evolutionary significance of metal hyperaccumulation remains obscure. Phytochemical studies however suggest that hyperaccumulation is closely linked to the mechanism of metal tolerance involved in the successful colonization of metalliferous and otherwise phytotoxic soils. The potentialities of hyperaccumula ting plants in biorccovcry and soil detoxification arc indicated.
2,341 citations
"Heavy Metal Polluted Soils: Effect ..." refers background in this paper
...0% for Zn [97]; (ii) the ratio of shoot to root concentration must be consistently higher than 1 [98]; this indicates the capability to transport metals from roots to shoot and the existence of hypertolerance ability [7]; (iii) the ratio of shoot to root concentration must be higher than 1; this indicates the degree of plant metal uptake [7, 98]....
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TL;DR: In this paper, two basic strategies of plant response are suggested, accumulators and excluders, which do not generally suppress metal uptake but result in internal detoxification, and indicators are seen as a further mode of response where proportional relationships exist between metal levels in the soil, uptake and accumulation in plant parts.
Abstract: Plants colonizing metalliferous soils have evolved physiological mechanisms which enable them to tolerate metal toxicity. These mechanisms do not generally suppress metal uptake but result in internal detoxification. Two basic strategies of plant response are suggested, accumulators and excluders. In the former, metals can be concentrated in plant parts from low or high background levels. By contrast, differential uptake and transport between root and shoot in excluders, lead to more or less constant low shoot levels over a wide range of external concentration. ‘Indicators’ are seen as a further mode of response where proportional relationships exist between metal levels in the soil, uptake and accumulation in plant parts. The physiological properties of accumulator and excluder species are considered in relation to metal tolerance mechanisms.
2,035 citations
"Heavy Metal Polluted Soils: Effect ..." refers background in this paper
...Baker [72] reported that these plants are able to tolerate these metals via 3 mechanisms, namely, (i) exclusion: restriction of metal transport and maintenance of a constant metal concentration in the shoot over a wide range of soil concentrations; (ii) inclusion: metal concentrations in the shoot reflecting those in the soil solution through a linear relationship; and (iii) bioaccumulation: accumulation ofmetals in the shoot and roots of plants at both low and high soil concentrations....
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TL;DR: In this article, a hypothesis is formulated to explain how microorganisms may become affected by gradually increasing soil metal concentrations and this is discussed in relation to defining safe or critical soil metal loadings for soil protection.
Abstract: An increasing body of evidence suggests that microorganisms are far more sensitive to heavy metal stress than soil animals or plants growing on the same soils. Not surprisingly, most studies of heavy metal toxicity to soil microorganisms have concentrated on effects where loss of microbial function can be observed and yet such studies may mask underlying effects on biodiversity within microbial populations and communities. The types of evidence which are available for determining critical metal concentrations or loadings for microbial processes and populations in agricultural soil are assessed, particularly in relation to the agricultural use of sewage sludge. Much of the confusion in deriving critical toxic concentrations of heavy metals in soils arises from comparison of experimental results based on short-term laboratory ecotoxicological studies with results from monitoring of long-term exposures of microbial populations to heavy metals in field experiments. The laboratory studies in effect measure responses to immediate, acute toxicity (disturbance) whereas the monitoring of field experiments measures responses to long-term chronic toxicity (stress) which accumulates gradually. Laboratory ecotoxicological studies are the most easily conducted and by far the most numerous, but are difficult to extrapolate meaningfully to toxic effects likely to occur in the field. Using evidence primarily derived from long-term field experiments, a hypothesis is formulated to explain how microorganisms may become affected by gradually increasing soil metal concentrations and this is discussed in relation to defining “safe” or “critical” soil metal loadings for soil protection.
1,887 citations