Availability Of Metals In Soil Research Articles

Fractionation and Characterization of Dissolved Organic Matter Derived from Sewage Sludge and Composted Sludge

Dissolved organic matter (DOM) is an important component affecting the availability of heavy metals in sludge-amended soils. In this study, DOM derived from anaerobically digested dewatered sludge and sludge compost were fractionated by a macroreticular exchange resin, and characterized by Fourier Transform-Infrared spectroscopy (FT-IR) technique to evaluate their potential effects on soil metal mobility. The acid fractions of DOM in sludge and sludge compost respectively were 78% and 73%, which included hydrophilic (HiA) and hydrophobic (HoA) acids. The hydrophobic fraction of DOM increased during composting, with the hydrophobic neutral (HoN) and HoA increasing from <1 to 22% and from 38 to 52%, respectively. The relative amount of each component in the hydrophilic fraction of DOM was as follows: hydrophilic acid (HiA) >> hydrophilic base (HiB) > hydrophilic neutral (HiN). The HiA, HiB, and HiN fraction of the sludge DOM was 1.9, 6.7, and 2.2 times higher than the respective fractions of the sludge compost DOM. The FT-IR spectrum shows that the hydrophobic fraction had considerably higher aromatic acids or aromatic phenols, while the hydrophilic fraction was richer in carboxyl and polyhydroxyl groups. Sludge DOM appeared to have more C-N and C-O ligand character, possibly from organic acid, amino acid, and amines than compost DOM, especially for the HiA, HiB, and HoA fractions. Since the hydrophilic fraction of sewage sludge was higher than that of sludge compost, the addition of sewage sludge would likely have a higher ability in reducing the trace metal adsorption capacity of soils as compared to that of sludge compost.

Optimization of DTPA and calcium chloride extractants for assessing extractable metal fraction in polluted soils

Metal availability in soils is often assessed by means of extraction with chemical solutions, among others the chelating agent DTPA (diethylenetriaminepentaacetic acid) and the non‐buffered salt calcium chloride (CaCl2). The same procedures are used for polluted soils that were originally created to assess the nutrient status of arable soils. We studied the influence of various parameters (type of shaker, shaking time, soil to solution ratio, and concentration of chemical extractant) and modify the DTPA and CaCl2 extraction procedures to make them suitable for the study of polluted soils. The chosen extraction ratio and extractant concentration were the followings: 8 g/20 mL of 0.1 MCaCl2 and 2 g/20 mL of 0.005 M DTPA. The optimized procedures were applied to nine soil samples affected by different sources of pollution (mine works, vehicle emissions, and various industries). Cadmium (Cd) showed the highest extractability with both extractants. Depending on the soil, copper (Cu) and zinc (Zn) (using DPTA) and Cu and manganese (Mn) (using CaCl2) were the followings in the extractable amounts. Cadmium, Cu, and Zn were highly correlated in both extractions and with total contents.

Effect of flood with mine wastes on metal extractability of some soils of the Guadiamar river basin (SW Spain)

The availability of metals in soils affected by the accidental flood of mining wastes in the Guadiamar river (SW Spain) is studied at three sites by sequential extraction and by extraction with CaCl 2 and EDTA solutions. Significant increases in the available fractions of some potentially toxic metals like Pb and Zn, and in some cases Cu, were found by sequential extraction in the first 5 cm of the soils studied. However, beyond this depth, the pattern was variable along the river. At two of the sites the metals in soluble form did not penetrate further than 5 cm into the soil, while at the site closest to the mineworks, the soluble forms of some potentially toxic metals such as Pb, Zn and, to a lesser extent, Cu, were significantly more abundant at depths >5 cm of the affected soils than those of analogous unaffected soils. The results indicate that the environmental hazard of metal availability for plants penetrating further than 10 cm is not likely to be significant, although it varies along the river. Further studies are needed to assess the long-term environmental damage to the area after removal of the wastes.

Distribution, movement and plant availability of trace metals in soils amended with sewage sludge composts: application to low metal loadings

Three soils, representative of various physico–chemical properties, an acid soil from a granitic arena with a sandy texture, a calcareous soil with a sandy silty texture and a clayey and silty one, were used in a lysimetric experiment to evaluate the ecotoxicological risks associated with the disposal of sewage sludge composts (SSC) containing trace metal contents below the recommended limit values established by the French legislation. A crop of colza ( Brassica napus) was grown on the amended soils. Based on the results from this experiment, SSC application enhanced the nutritional levels of the soils and stimulated the growth of plants. Chemical fractionation of composts and amended soils was performed using a sequential extraction technique. The pattern of metal distribution in the five fractions gave a good prediction of the trace metal behaviour in soils. Among the metals studied, Zn was the one that moved most readily in the soils (except in the calcareous soil) since compost application increased the proportion of the most labile forms of Zn and especially its pH 4.7 acid-soluble forms in the amended soils. The migration of Cu and Pb within the profiles of amended soils was significantly influenced by the release of soluble organics from the amended layers during the sludge–soil equilibration period. However, leachates were very little affected by SSC application as metal redistribution took place in deep layers of these amended soils. The movement of Pb within the profiles of the amended soils was not pH dependent whereas the mobility and plant availability of Cu and Zn increased as soil pH decreased. The sequence of trace metal concentrations in all plant parts was: Zn⪢Cu>Pb. Colza leaves were the organs of accumulation of trace metals and nutrients (except Na). Zn contents in leaves were governed by SSC loading rates. Principal component analysis performed on the ‘total’ metal and nutrient concentrations in plants showed on the one hand that no deficiency in nutrients caused by interactions with trace metals arose in the plant organs and on the other hand that the nutrient and trace metal contents in plants were more influenced by soil nature than compost application.

Availability of heavy metals in compost-amended soil

Composted municipal wastes can be applied to cropland to supply nutrients and improve soil physical properties, but farmers are concerned about heavy metal availability. Three municipal composts were applied at 0, 25, 50 and 100 × 10 6 g ha −1 in 1994 to an unlimed and limed (pH 6.5) Dyke clay (clayey, mixed, mesic Typic Rhodudults), and burley tobacco ( Nicotiana tabacum L.) was planted in 1994 and 1995. The composts were municipal solid waste (MSWC), wastewater biosolids (WBC) and co-composted municipal solid waste/wastewater biosolids (COC). Leaf samples were collected three times in each year and analyzed for heavy metal concentration. Soil samples were collected three times in each year, extracted with DTPA and extracts were analyzed for heavy metal concentration. With the exception of Cd in 1994 cured burley leaves, Cd, Ni, and Pb concentrations were generally undetectable for all treatments in both years. When leaf Cu and Zn concentrations in cured leaves from COC and WBC in 1994 were regressed against amounts of Cu and Zn applied with respective compost treatments, mean leaf Cu and Zn were significantly higher in COC (215 mg Cu kg −1 and 738 mg Zn kg −1) than in WBC (173 mg Cu kg −1 and 499 mg Zn kg −1) treatments. Because compost Cu and Zn concentrations in MSWC (53 mg Cu kg −1 and 96 mg Zn kg −1) were much lower than in other composts, cured leaf Cu and Zn in MSWC treatments were not compared with cured leaf Cu and Zn in COC or WBC treatments. DTPA-extractable Zn, Pb, Cd and Cu concentrations increased with increasing soil pH at the 100 × 10 6 g ha −1 rates of COC addition in September, 1994. Higher metal composts were associated with higher metal extractability than were lower metal composts: when equal rates of metal addition to soil from different composts were compared, DTPA-extractable Cu and Pb concentrations in September 1994, were significantly higher in COC than in WBC treatments, and DTPA-extractable Cd concentration was significantly lower in MSWC treatments than in COC or WBC treatments.

In Situ Measurements of Solution Concentrations and Fluxes of Trace Metals in Soils Using DGT

Assessments of the availability of toxic or nutrient metals in soils need to consider solution speciation, mobility, and the kinetics of exchange between solution and solid phase. The newly developed technique of diffusive gradients in thin films (DGT) accumulates metals in a well-defined geometry that allows quantification of their supply from the solid phase. DGT was used to measure potential maximum fluxes of available metals in old arable and ex-woodland soils variously treated with sewage sludge with and without metal amendments. The flux increased with increas ing sludge application. The results suggest that for Zn and Cd there are two separate pools of metal associated with the solid phase. In untreated soils or those with 100 m3 ha-1 yr-1 sludge treatments, Zn and Cd appear to have higher resupply rate constants from the solid phase than in soils with 300 m3 ha-1 yr-1 sludge treatments (assuming the ratio of labile solid-phase metal to soil solution metal does not change). However, the actual rate...

Determination of chemical availability of cadmium and zinc in soils using inert soil moisture samplers

A rapid method for extracting soil solutions using porous plastic soil-moisture samplers was combined with a cation resin equilibration based speciation technique to look at the chemical availability of metals in soil. Industrially polluted, metal sulphate amended and sewage sludge treated soils were used in our study. Cadmium sulphate amended and industrially contaminated soils all had > 65% of the total soil solution Cd present as free Cd 2+. However, increasing total soil Cd concentrations by adding CdSO 4 resulted in smaller total soil solution Cd. Consequently, the free Cd 2+ concentrations in soil solutions extracted from these soils were smaller than in the same soil contaminated by sewage sludge addition. Amendment with ZnSO 4 gave much greater concentrations of free Zn 2+ in soil solutions compared with the same soil after long-term Zn contamination via sewage sludge additions. Our results demonstrate the difficulty in comparing total soil solution and free metal ion concentrations for soils from different areas with different physiochemical properties and sources of contamination. However, when comparing the same Woburn soil, Cd was much less available as Cd 2+ in soil solution from the CdSO 4 amended soils compared with soil contaminated by about 36 years of sewage sludge additions. In contrast, much more Zn was available in soil solution as free Zn 2+ in the ZnSO 4 amended soils compared with the sewage sludge treated soils.

Long‐Term Effects of Biosolids Applications on Heavy Metal Bioavailability in Agricultural Soils

Concerns exist over the long-term availability of trace metals in biosolids-amended soils. The objective of this study was to quantify extractable forms of trace metals in biosolids-amended, continuously cultivated soils after cessation of sewage sludge applications and to determine their bioavailability to romaine lettuce (Lactuca saliva L.). Trace metals in surface soils from two biosolids-amended sites were speciated into increasingly stable chemical fractions using a series of sequential extractions that were operationally defined as exchangeable (Exch), specifically adsorbed (SA), Fe-Mn oxide and acid replaceable (Ox/AR), residual organic (R-Org), and residual inorganic (R-In). Romaine lettuce was grown on the soils to determine heavy metal bioavailability. In control and biosolids-amended soils, 60 to 75% of Cd was found in the more easily extracted Exch and SA forms, but the percentage was significantly greater in the biosolids-amended soils. Biosolids applications also increased the percentages of Ni and Zn in the Exch and SA fractions. Biosolids applications had little effect on the Exch and SA fractions of Cr and Pb. Greater than 75% of Cr, Cu, Ni, Pb, and Zn were found in the relatively stable Ox/AR, R-Org, and R-In fractions of control and biosolids-amended soils. Concentrations of Cd, Ni, and Zn in aboveground lettuce tissue, and to a lesser extent, Cu and Cr, were significantly increased by biosolids applications, but Pb uptake was not affected. Cadmium, Cr, and Cu concentrations in lettuce were highly correlated (P < 0.001) to metal concentrations in one or more of the Exch, SA, and Ox/AR soil chemical fractions. Results of this study show that 15 yr after biosolids applications, the relative bioavailability of biosolids-applied heavy metals was Cd >> Zn ≥ Ni > Cu >> Cr > Pb.

Plant Availability of Heavy Metals in Soils Previously Amended with Heavy Applications of Sewage Sludge

Plant uptake is one of the major pathways by which sludge-borne potentially toxic metals enter the food chain. This study examined the accumulation of Cd, Cu, Ni, Pb and Zn in wheat, carrots and spinach grown on soils from 13 sites previously amended with sewage sludge. Winter wheat, carrots and spinach were grown consecutively under field like conditions. The results showed that plant availability of heavy metals differed widely among the crop species. The accumulation of Cd, Ni and Zn in the plants showed the greatest increases compared to their background levels. The Cu and Pb accumulation in the plants grown on sludge-amended soils showed only small increases compared to those grown on uncontaminated soils. Multiple regression analysis of various soil properties showed that the surest way to control the accumulation of metals in food plants is by controlling their concentrations in the soils. Furthermore, soils with a non-acidic pH and a clayey texture tended to achieve better control of metal accumulation in food plants compared to those with an acidic reaction and a coarse texture. Metal concentrations in the plants generally correlated well with those extracted from soils in 0·005 M DTPA, 0·05 M EDTA-(Na)2, 1 M NH4NO3 and 0·05 M CaCl2. The EDTA, however, proved to be a more reliable and consistent test in predicting the accumulation of metals in the plants. The results also showed that liming soils to pH 7 effectively reduced the metal contents in carrots and spinach, but liming to pH 6·5 had little effect on metal concentrations in wheat grain. © 1997 SCI.

Plant Availability of Heavy Metals in Soils Previously Amended with Heavy Applications of Sewage Sludge

Plant uptake is one of the major pathways by which sludge-borne potentially toxic metals enter the food chain. This study examined the accumulation of Cd, Cu, Ni, Pb and Zn in wheat, carrots and spinach grown on soils from 13 sites previously amended with sewage sludge. Winter wheat, carrots and spinach were grown consecutively under field like conditions. The results showed that plant availability of heavy metals differed widely among the crop species. The accumulation of Cd, Ni and Zn in the plants showed the greatest increases compared to their background levels. The Cu and Pb accumulation in the plants grown on sludge-amended soils showed only small increases compared to those grown on uncontaminated soils. Multiple regression analysis of various soil properties showed that the surest way to control the accumulation of metals in food plants is by controlling their concentrations in the soils. Furthermore, soils with a non-acidic pH and a clayey texture tended to achieve better control of metal accumulation in food plants compared to those with an acidic reaction and a coarse texture. Metal concentrations in the plants generally correlated well with those extracted from soils in 0·005 M DTPA, 0·05 M EDTA-(Na)2, 1 M NH4NO3 and 0·05 M CaCl2. The EDTA, however, proved to be a more reliable and consistent test in predicting the accumulation of metals in the plants. The results also showed that liming soils to pH 7 effectively reduced the metal contents in carrots and spinach, but liming to pH 6·5 had little effect on metal concentrations in wheat grain. © 1997 SCI.

Mehlich‐1‐ and DTPA‐extractable lead in soils in relation to soil properties

Mehlich‐1 and DTPA extractants are frequently used to predict metal availability in soils. Metal extractability by the acid or chelate extractant reflects the metal characteristics and metal‐soil interactions. In this study, samples of eight topsoils from the southeastern United States were incubated with added lead (Pb) at the rate of 40 mg#lbkg‐1. After five months in the greenhouse, Mehlich‐1 and DTPA extractants were employed to extract Pb in both metal‐amended and natural soils. For the natural soils, Pb concentration in the DTPA extractant was always higher than that in the Mehlich‐1 extractant. This indicates that the DTPA chelate extractant is able to dissolve some Pb in soils which is not solubilized by protons. The negative correlation found between Mehlich‐1‐extractable Pb and soil clay content might result from two mechanisms: i) strong association between Pb and soil surfaces, or ii) readsorption of Pb during extraction. None of the correlations between DTPA‐extractable Pb and soil properties was significant, suggesting that the DTPA‐extractable Pb is not heavily dependent on soil properties. The DTPA extractant showed a high ability to solubilize Pb in the natural soils possibly due to a high affinity of Pb for soil organic matter.

Zinc and Cadmium Toxicity to Alfalfa and Its Microsymbiont

AbstractThe availability of heavy metals in soil depends on their speciation in solution and chemical activities of free metals. To examine the sensitivity of alfalfa (Glycine max L.), its microsymbiont, and the process of N2 fixation to Zn2+ and Cd2+ activities, a growth chamber study was conducted. Nutrient solution was used with the chelator, EGTA, to buffer Zn2+ and Cd2+ activities. The activities of Zn2+ and Cd2+ ranged from pZn2+ = 8.0 to 5.0 and pCd2+ = 10.5 to 8.0 mol L−1. Plants grown in pZn2+ = 5.25 and 5.0; and pCd2+ = 8.75 and 8.65 were stunted and chlorotic with interveinal necrosis. In these treatments, shoot concentrations of Zn and Cd averaged about 300 and 50 mg kg−1, respectively. This resulted in a 20 and 90% yield reduction for plants grown in pZn2+ = 5.25 and 5.0, respectively. Yield reduction was 50 and 75% for pCd2+ = 8.75 and 8.65, respectively. Plants supplied with mineral N had about 40% greater shoot yield than plants inoculated with rhizobia. No nodulation occurred at pZn2+ = 5.0, but at pZn2+ = 5.25 and pCd2+ = 8.75 and 8.65, there was a delay in nodulation. All nodules formed were mostly effective in N2 fixation. Enumeration of viable cells showed a significant decline of total cell counts from 105.5 cell mL−1 in the control to 105.1 and 104.8 at the highest Zn2+ and Cd2+ activities, respectively. At the activities studied, Cd was more toxic to rhizobia than Zn. However, at the highest activities, toxicity of metals were so severe that root development was inhibited and in some cases resulted in plant death. These results suggest that toxicity of Zn and Cd was greater to plants than to rhizobia.

Dispersal and mobility of heavy metals in relation to tree survival in an aerially contaminated woodland soil

Nearly a century of metal deposition adjacent to a metal refinery in Prescot, north-west England has led to highly elevated metal levels in soils at a dominantly Acer pseudoplatanus woodland, but with incongruously and perplexingly few detrimental effects on trees. Dispersal and speciation of Cu, Cd, Zn, Pb and Ni in soil was found to be extremely variable, but spatial patterns of metals were inter-related and also related to soil pH and soil organic matter. These soil variables were all generally higher in soil directly beneath trees than in soil between trees, and were particularly high beneath the spreading canopy of Aesculus hippocastanum. It is argued that this heterogeneous dispersal and availability of metals in soils may explain the survival of mature trees and the successful establishment of seedlings within the woodland. Differing speciation and mobility has allowed high disappearance rates of metals since recent closure of the refinery, which may result in soil recovery at a faster rate than previously thought.

Trace and Toxic Metals in Wetlands-A Review.

The mobility and plant availability of many trace and toxic metals in wetland soils is often substantially different from upland soils. Oxidation-reduction (redox) and associated pH changes that occur in soils as a result of flooding or drainage can affect the retention and release of metals by clay minerals, organic matter, iron oxides, and, for coastal wetlands, sulfides. Except where a flooded soil or sediment becomes strongly acid upon drainage and oxidation, as sometimes occurs, the processes immobilizing metals tend to be complimentary such that large-scale metal releases from contaminated soils and sediments do not occur with changing redox conditions. Metals tend to be retained more strongly in wetland soils compared with upland soils.

The plant availability and DTPA extractability of trace metals in sludge-amended soils

The DTPA extractability of trace metals and their bioaccumulation by ryegrass ( Lolium perenne L.), grown on two soils treated with sewage sludge, were investigated in a greenhouse pot experiment over a period of 1 year following sludge application. The experiments were carried out at ambient temperatures of 15°C and 25°C. The sludge application resulted in elevated concentrations of Cd, Cu, Ni, Pb, and Zn in ryegrass. The plants grown at 25°C accumulated significantly higher levels of all the metals than those grown at 15°C. A trend towards increasing plant metal accumulation over successive harvests was observed for all the metals except Cu. This appeared to be caused by the progressive decline in pH and organic matter status. The DTPA extraction data generally supported the results of plant metal concentrations for a given harvest or temperature; however, it was not consistent in predicting the changing metal uptake behaviour by the ryegrass over the residual period.

The distribution and influence of heavy metals in mangrove forests of the Tamshui Estuary in Taiwan

Abstract The Tamshui estuary area is one of the few locations in Taiwan where mangroves are still growing. Heavy metals are generally carried by the water of the Tamshui river and accumulate in the estuary soil. Their accumulation is closely related to the frequency and duration of tidal flood. The concentration of heavy metals in Kandelia candel showed a sequential decline from roots to stems, leaves, and seedlings. There was a correlation between the amount of extractable heavy metals in soils and that in the tissues in Phragmites communis, while in Kandelia candel the correlation varied largely with the habitats except for the roots. The availability of heavy metals in mangrove soil may decrease due to the flooding which subsequently reduces their uptake in plant tissues. Sequential extractions of mangrove soil Indicated that the labile fraction contained a relatively small proportion of the total amount under the mangrove estuary environment. The tolerance of Kandelia candel seedlings to copper and zinc was much higher than that of rice plants (Oryza sativa). The value of 50% inhibition concentration (IC50) of root development in Kandelia candel was estimated at 3.8 mg liter-1 for Cu and 46.33 mg liter-1 for Zn. For comparison, the correspecting values of the IC50 in rice was 0.39 mg liter-1 for Cu and 9.63 mg liter-1 for Zn. Field studies and greenhouse experiments have revealed that Kandelia candel can adapt to areas polluted with heavy metals partly because of its tolerance and partly because of the low availability of heavy metals in mangrove soil.

Long term availability of metals in sludge amended acid soils

Abstract Nicotiana tabacum L. was grown to maturity in 1984 at two research sites in Maryland which were amended with municipal sludge materials representing a variety of wastewater treatment technologies in 1972, 1976 and 1978. Four sludges from Washington, D.C. and Annapolis, MD were applied at rates equal to 0, 56, 112 and 224 Mg ha‐1. A high‐metal sludge from Chicago was applied at rates equal to 50 and 100 Mg ha‐1 in 1978. Composite leaf samples of cured tobacco and Ap horizon soil samples were analyzed for Zn, Cu, Mn, Fe, Pb, Ni and Cd. Available soil metals were estimated using three procedures: DTPA (pH 7.3), Double Acid and Mehlich 3. DTPA and Double Acid produced significant correlation coefficients (r) for Zn, Cu, Mn, Ni and Cd when compared with plant metal contents; however, none of the extractants produced significant r values for Fe or Pb. All sludge sources resulted in significant increases in DTPA soil Zn, Cu, Ni and Cd with increased application rates; however, plant levels were affected...

Effects of soil texture on respiration and metal solubility in heating oil-amended soils

A comparison of oil transformations in soils of varying texture but similar fertility could reveal the effects of soil texture on oil decomposition. Differences in soil surface area may also cause differential responses to added metals in soils of diverse textures. The purpose of this experiment was to determine the effect of three different soil textures on rates of soil respiration and soil metal availability and content, following amendment with two types of heating oils.

Copper(II) and iron(III) complexation by soil humic acids: An IR and ESR study

The reactivity of soil humic acids toward added Cu 2+ and Fe 3+ ions, the type of complexes formed and their water- and HCl-stability have been studied by infrared and electron spin resonance spectroscopy. Two principal classes of binding site are available on humic acids for complexation of Cu 2+ and Fe 3+ ions: (a) one involving weak surface sites, able to bind the metal ions in complexes which are water-stable but easily disrupted by proton exchange; (b) another involving functional groups able to form highly stable, inner-sphere complexes resistant to extensive proton exchange. Iron ions compete favorably with copper ions in occupying the most stable sites. These results are applicable to problems of metal ion retention and availability in soil, including their depletion from arable and forest soils because of the acid rain.

Heavy metal species, mobility and availability in soils

AbstractThe ecological effects of heavy metals in soils are closely related to the content and speciation of the elements in the solid and liquid phases of soils. Methods for the determination of metal species in both phases are described and critically evaluated. In connection with the possible binding mechanisms of heavy metals in soils the concept of specific and non‐specific adsorption is discussed. Recent results indicate that the adsorption of heavy metals on soil particles is not only restricted to the formation of surface complexes but can also take place in the interior of minerals. Diffusion processes of heavy metals into soil minerals are described for goethite. In order to assess metal mobility and availability in soils, the concentration and speciation of metals in the soil solution or in comparable aeqeous equilibrium solutions of soil samples and the transfer of metals from solid pools to the liquid phase and vice versa have to be assessed. Methods for the determination of the amount of plant available heavy metals are described and the associated problems discussed.