Heavy Metals

Modeling of Adsorption by Soils Constant Capacitance Model

Constant Capacitance Model Arsenic

The constant capacitance model is a chemical surface complexation model that was developed to describe ion adsorption at the oxide-solution interface Schindler et al ., 1976 Stumm, Kummert, and Sigg, 1980 . As is characteristic of surface complexation models, this chemical model explicitly defines surface species, chemical reactions, equilibrium constants, mass balances, charge balance, and electrostatic potentials The reactive surface site is defined as SOH, an average reactive surface...

Nonlinear Behavior of Heavy Metals in Soils Mobility and Bioavailability

747 Cargo Door

Transport Retention First-Order and Freundlich Second-Order and Multiple Reaction Second-Order Models Transport in Layered Concluding The dynamics of heavy metals and their transport in the soil profile play a significant role in their bioavailability and leaching losses beyond the root-zone . The primary emphasis in this chapter is on different approaches that describe the dynamics of heavy metals in the soil system. Such knowledge is necessary because these approaches provide direct...

References

M ., Shennan C . , Zazoski J . , and Burau R . G . 1990 . Selenomethionine uptake by wheat seedlings . Agron. J., 82 1127-1130. Adriano D C . 2001. Trace elements in the terrestrial environment. Springer, New York Anderson T. A, Guthrie E . A ., and Walton B . T., 1993. Bioremediation in the rhizosphere . Environ. Sci. Technol., 27 2630-2636 . Alexander M . 2000 . Aging, bioavailability and overestimation of risk from environmental pollutants . Environ. Sci. Technol. 34 4259-4265 ....

Chromium Wetland Soil Redox Chemistry Sorption and reduction of Cr6

Wetland Redox

In the natural environment, Cr exists mainly in two stable oxidation states tri-valent Cr and hexavalent Cr In terms of toxicity, mobility, and bioavailability, Cr3+ and Cr6+ differ remarkably from each other (Bartlett and James, 1988 Calder 1988 Holdway, 1988 Nieboer and Shaw, 1988 Wong and Trevors, 1988 Yassi and Nieboer, 1988). Cr6+, generally in the forms of chromate and dichromate, is toxic and very soluble in water (Xu and Jaffe, 2006) . In a flooded soil or anoxic sediment, microbial...

Adsorption Desorption Reactions

Adsorption is the accumulation of a chemical species at the solid-solution interface to form a two-dimensional molecular surface . Adsorption reactions on soil surfaces often control the concentration of As and Se in soil solution Arsenic adsorption is significantly positively correlated with the clay, Al and Fe oxide, organic carbon, and inorganic carbon content of soils (Wauchope, 1975 Livesey and Huang, 1981 Elkhatib, Bennett, and Wright, 1984 Yang et al , 2002) Selenium adsorption is also...

Metal Uptake by Wetland Plants

Wetland plants influence heavy metal uptake transport and mobility. Wetland plants can alter the redox condition, pH, and organic matter content of sediments and thus affect the chemical speciation and mobility of metals Metals may be mobilized or immobilized, depending on numerous factors, thus making it difficult to predict actual plant effects on metal mobility for a given set of conditions Wetland plants play an important role in heavy metal removal in wetlands Uptake rates and the...

Heavy Metals Transformation in Wetlands

Metal Metal Organic and Clay Redox and pH Conditions Effects on Metal Chromium Wetland Soil Redox Chemistry Sorption and Reduction of Sedimentation Metal Uptake by Wetland Heavy Metal Localization, Translocation, and Distribution in Wetland Heavy Metal Translocation and Heavy Metal Release by Wetland Plants 233 Toxicological Plant-Sediment

Redox and pH Conditions Effects on Metal Transformation

Metal cycling in wetlands is very dependent on pH. Soil redox conditions (or Eh status) also govern the oxidation and reduction of some trace metals found in wetlands . Trace metals are present in various oxidation states for example, Cr can exist in several oxidation states from Cr0 (the metallic form) to Cr6+. The most stable oxidation states of Cr in the environment are Cr3+ and Cr6+. In addition to the elemental metallic form, which is extensively used in alloys, Cr has three important...

Inorganic Chemistry of As and Se in Soil Solution

The dominant inorganic As solution species are As(III) (arsenite) and As(V) (arsenate), while Se(IV) (selenite) and Se(VI) (selenate) are the dominant inorganic Se species in soil solution (Adriano, 1986). For both elements, toxicity depends on the oxidation state, with the lower redox state considered more toxic that is, arsenite is more toxic than arsenate (Penrose, 1974) and selenite is more toxic than selenate (Harr, 1978) . At most natural pHs, arsenite is present in solution predominantly...

Bioavailability of Selenium

The concentration and speciation of Se in soil are governed by several physical and chemical factors, including pH, redox status, mineralogical composition, and adsorbing surface (Dhillon and Dhillon, 1999) . In poorly aerated, acidic, organic-rich soils under strong reducing conditions, Se primarily occurs as insoluble elemental (Se0) and selenide (Se2-) forms, while in oxidizing environments such as aerobic soils, Se is present as soluble selenite (Se4+) and selenate (Se6+) species, the...

Bioavailability of Heavy Metals

The total metal content of contaminated soil can indicate the extent of contamination but is not a good indicator of metal availability to organisms or their phytotoxicity To predict the extent of the adverse effects of metals in soil and in organisms and the probability with which adverse effects occur, it is necessary to determine the fraction of contaminants that are active in organisms Bioavailability can be defined as the fraction of a substance that will exert an effect on an organism and...

Methylation and Volatilization Reactions

Methylation reactions involve the addition or substitution of methyl groups, -CH3, to substrates . Methylated compounds of As that can form in soils include monomethylarsenic acid (CH3AsO3H2), dimethylarsenic acid ((CH3)2AsO2H), trimethylarsine oxide, ((CH3)3AsO), and the methylarsines monomethylarsine (CH3AsH2), dimethylarsine, ((CH3)2AsH), and trimethylarsine ((CH3)3As). The various arsine compounds, including arsine (AsH3), are volatile and tend to escape to the atmosphere (Gao, Tanji, and...

Heavy Metals Mail

Heavy metals in wetlands have both natural and anthropogenic sources . Man-made sources include atmospheric deposition, runoff from adjacent uplands, and wastewater discharge from municipalities and industries . Once within a wetland, the ability of a heavy metal to be transported depends on its chemical properties, which influence availability and toxicity. The species of metal (or metal speciation) also determines behavior in wetland environments . Valence, sorption to sediments, complexation...

The Case of Selenium

Selenium (Se), whose chemical and physical properties are intermediate between metals and nonmetals, has been recognized as an essential nutrient for animals, humans, and microorganisms However, it has also been found to be toxic at levels just above those required for health, and the range between its essentiality and its toxicity is quite narrow (Wilber, 1980) . In nature, Se is widely, but unevenly, distributed in the earth's crust. Growing health and environmental concerns about Se exposure...

Nonequilibrium Transport of Heavy Metals in Soils Physical and Chemical Processes

Equilibrium Solute Physical Preferential Matrix Physical Nonequilibrium Chemical Kinetic Ion Kinetic Adsorption and Irreversible Mulitreaction Multiprocess Nonequilibrium Transport 57 Significance to Site Soil contamination of heavy metals from mining, industrial, agricultural, and geological sources poses serious environmental risk around the world because of its high toxicity to human health as well as the ecosystem . The transport of toxic metals in the vadose zone and aquifers may lead to...

Metal Dynamics in Soil

Various metals, including heavy metals and metalloids, are common contaminants in soil and can reach critical levels in terms of human health, food safety, soil fertility, and ecological risks (Sharma and Agrawal, 2005) . The presence of metals in soil is due to natural processes, for example the formation of soil, and anthropogenic activities such as the use of sludge or municipal compost, pesticides, and fertilizers, industrial manufacturing processes, residues from metalliferous mines and...

Colloid Associated Transport and Metal Speciation at Reclaimed Mine Sites Following Biosolid Application

Miller CONTENTS Case Soil Monolith Bulk Soil Colloid Fractionation and In Situ Colloid Metal Concentrations in Bulk Adsorption Metal Elution in Virginia Reclaimed Spoil Biosolid Metal Elution in Kentucky Reclaimed Biosolid Metal Concluding Remarks 144 The unsaturated soil zone (McCarthy and Zachara, 1989) is often assumed to act as a buffer for groundwater contaminants due to potential immobilization by sorption onto the soil matrix (Levin et al ., 2002). However,...

Determining Dissolved Elements in Soils and Water

Soil samples are analyzed on air-dried, < 2-mm soil by methods described in the Soil Survey Investigations Report (SSIR) No 42 (USDA NRCS, 2004) Alphanumeric codes in parentheses next to each method represent specific standard operating procedures . Particle-size analysis is performed by the sieve and pipette method (3A1) . Cation exchange capacity (CEC) is conducted by NH4OAc buffered at pH 7.0 (5A8b) . Total carbon (C) content is determined by dry combustion (6A2f), and the CaCO3 equivalent...

Heavy Metal Translocation and Distribution

Wetland plants can accumulate heavy metals in their leaves and stems when they translocate metals from root tissue to aerial tissue . Many wetland plants accumulated higher concentrations of heavy metals in roots than in shoots (Taylor and Crowder, 1983 Ye et al ., 1997a,b Cheng et al ., 2002 Stoltz and Greger, 2002 Deng, Ye, and Wong, 2004, 2006) . The pattern of metal distribution in wetland plants is suitable to restrict metals transported from roots to shoots However, the degree of upward...

Toxicological Effects

Heavy metals accumulated in wetland plant tissues can cause toxic effects, especially when translocated to above-ground tissues Effects can be measured at the biochemical and cellular level, but most studies of effects have focused on growth as the response to the toxicant Some studies focused on plant growth, showing their responses to heavy metals When exposed to higher metal concentrations, plants showed a significant reduction in root elongation, height of seedling, leaf number, leaf area,...

Plant Sediment Relationships

Wetland sediments are generally considered a sink for metals . A number of studies have analyzed the correlations between metal uptake by wetland plants and metal concentrations in sediment Most studies reported poor correlations between them (Campbell et al., 1985 Jackson and Kalff, 1993 Cardwell, Hawker, and Greenway, 2002) . The bioavailability of the metals is low compared to terrestrial systems with oxidized soils . Different forms of metals have different availabilities water-soluble...

Can Water Lily Uptake Chromium And Copper

James . 1988. Mobility and bioavailability of chromium in soils . In Nriagu, J . O ., and E . Nieboer (Eds . ) Chromium in the natural and human environments . John Wiley & Sons, New York . pp . 267-304. Batty, L . C ., A .J .M . Baker, and B . D . Wheeler. 2002 . Aluminium and phosphate uptake by Phragmites australis The role of Fe, Mn, and Al root plaques . Ann. Bot. 89 443-449 Batty, L . C ., A .J .M . Baker, B. D . Wheeler, and C . D . Curtis . 2000. The...

Epiaquic Moisture Regime

Frequently flooded soils are semi-terrestrial and or semi-aquatic soils with aquic or epiaquic moisture regimes . They are influenced by various aquatic sources, including groundwater, static water, return seepage, and flood water. In general, large variations in flooding frequency as well as in flood water characteristics have been observed . As a result, sedimentation rates of substances also reveal a large variation according to the site-specific conditions . Frequently flooded soils such as...

Heavy Metals Forms in Biosolids Soils and Biosolid Amended Soils

Biosolids Benefits and Problems of Biosolids Use in Legislation on Biosolids in Agricultural Heavy Metals in Soils and Forms of Heavy Metals in Methods of Determination of Heavy Metal Single Chemical Sequential Chemical Forms of Heavy Metals in Heavy Metal Fractions in Biosolid-Amended Effect of Biosolids on Forms of Heavy Metals 284 Concluding

Forms of Heavy Metals in Soils

The sources of HMs in soils are both natural and anthropogenic The natural sources are the parent materials of soils derived from the weathering of rocks In igneous rocks, HMs are found as components of primary minerals, in the structure of which are entering with isomorphous substitution, occurring during the period of crystallization of the rocks between ions that differs in electric charge by up to one unit and in size up to 15 (Krauskopf, 1967) HMs described in Directive 278 86 of the EU...

Heavy Metal Fractions in Biosolid Amended Soils

The application of biosolids to soils causes alterations in some soil properties, which in turn may lead to the redistribution of HMs between various fractions and thus change their availability to plants . The soil properties that appear to be affected by the application of biosolids are pH and redox potential, the organic matter content, the concentration of minerals in the soil solution and ionic strength, the concentration of essential elements to plant growth, and the concentration of...

Davidson 1976 Adsorption Freundlich Retardation

0 50 100 150 200 250 300 350 400 450 500 Time, Hours with Consecutive Irreversible Reaction 0 50 100 150 200 250 300 350 400 450 500 Time, Hours Experimental results of As(V) concentration in soil solution for Olivier soil versus time for all Co's . Dashed curves were obtained using second-order model (SOM) with concurrent (top figure) and consecutive (bottom figure) irreversible reactions . A major source of soil heterogeneity is soil stratifications or layering. The phenomenon of...

NRCS Technique Estimation of Runoff Water

Rainfall is the primary source of water that runs off the surfaces of small agricultural watersheds The main factors affecting the volume of rainfall that runs off are the kind of soil and the type of vegetation in the watershed (USDA SCS, 1991) . The runoff equation can be written as follows where Q runoff (inches), R rainfall (inches), and S potential maximum retention (inches) after runoff begins The potential maximum retention (S) can range from zero on a smooth and impervious surface to...

Wagon Train Watershed

The Wagon Train (WT) Watershed has a 315-acre (128-hectare) reservoir located on the Hickman Branch of Salt Creek (Platte River Basin) in Lancaster County, Nebraska (Figure 7.1). The reservoir was constructed primarily as a flood control structure by the U. S. Army Corps of Engineers in 1962. The total drainage area encompasses 9,984 acres (4,042 hectares) of agricultural land . Most of the area (70 ) is cultivated with crops soybean (Glycine willd), corn (Zea mays L .), wheat (Triticum...

Trace Element Biogeochemistry in the Rhizosphere

Wenzel, Eva Oburger, Markus Puschenreiter, and Jakob Santner Biogeochemistry and Bioavailability of Trace Elements as Affected by Rhizosphere Root-Induced Changes in Soil Water Content Affecting Trace Element Bioavailability 149 Root-Induced Changes in Root-Induced Changes in Redox Complexation and Chelation of Trace Elements in Rhizosphere 151 Recent Experimental Evidence for Rhizosphere Effects on Trace Element Solubility and Chemical Alleviation of Trace Element Toxicity in Trace...

Adsorption and Desorption

Ion exchange is the interchange between an ion in solution and another ion in the boundary layer between the solution and a charged soil surface (Sparks, 2003) In soil chemistry, it has been well established for a long time that the major sources of cation exchange in soils are clay minerals, organic matter, and amorphous minerals According to Evans (1989), electropositive charged elements can be bound to negatively charged surfaces of organic matter, clay particles, as well as Fe and Al...

Carbonates and pH

Changes in pH can be induced by varying redox conditions that can affect the mobility of metals indirectly (e .g., Kumpiene et al ., 2009) . During reduction, protons are consumed, whereas during oxidation, acidification tends to occur (Yu et al., 2007 Du Laing et al., 2009). As a consequence, these pH changes might affect the mobility and reaction kinetics of metals . Generally, a higher proton activity reduces the negative surface charge of organic matter, clay particles, and Fe and Al...

Change in Valence State

Metals can directly react to changes in redox conditions . Reduced conditions result in the reduction of Cr (VI) to Cr (III) and the immobilization of chromates (Reddy and DeLaune, 2008) . Conversely, Cr(VI) will be mobilized at high Eh values . Marsh sediments tend to rapidly reduce the very toxic Cr(VI) to the less toxic Cr(III) (Pardue and Patrick, 1995) A reduction of Cu(II) to Cu (I) under slightly alkaline and anaerobic conditions was found when a suitable electron donor was available...

Redox Processes

Redox processes are central to the mobility of many metals and metalloids (e.g., Van den Berg et al ., 2000 Du Laing et al ., 2009) . Van Griethuysen et al . (2005) pointed out that the dynamics of many metals in frequently flooded soils are driven by seasonal redox cycles of S, Fe, and Mn . At the oxic-anoxic interface and in the anoxic layers of flooded soils, redox-driven processes often include the precipitation and dissolution of metals . The kinetics of those processes are of great...

Plant Growth

The chemical form as well as the concentration of Se added to the soil affected plant growth In 2 5 mg Se kg-1 soil, Se6+ induced a significant reduction in both fresh and dry biomass production (Table 4 . 1) . No significant differences in fresh and dry matter production were detected in plants grown in the presence of Se4+. Plants grown in the presence of Se6+ accumulated higher Biomass Production by Brassica juncea at Maturity Biomass Production by Brassica juncea at Maturity Note Numbers...

Modeling of Adsorption by Soils Empirical Models

Adsorption reactions by soils have historically been described using empirical adsorption isotherm equations . The most popular adsorption isotherms are the linear, Freundlich, and Langmuir equations . Typically, these equations are very good at describing experimental data despite their lack of theoretical basis Their popularity stems in part from their simplicity and from the ease of estimation of their adjustable parameters The adsorption isotherm equation is a linear function and is written...

Precipitation Dissolution Reactions

Precipitation and dissolution reactions of As and Se solid phases are processes that may influence the soil solution concentrations of these elements . Under oxidizing conditions, Ca3(AsO4)2 and Mn3(AsO4)2 are the most stable As minerals in alkaline soils, while in acid soils Fe3(AsO4)2, FeAsO4, and AlAsO4 are the least soluble minerals (Sadiq, 1997) . Soils that had been contaminated historically with lead arsenate were found to be supersaturated with Pb3(AsO4)2 and Mn3(AsO4)2 (Hess and...