Fraction Distributions of Lead,Cadmium, Copper,and Zinc in Metal‐Contaminated Soil before and after Extraction with Disodium Ethylenediaminetetraacetic Acid

Abstract: The fraction distributions of heavy metals have attracted more attention because of the relationship between the toxicity and their speciation. Heavy‐metal fraction distributions in soil contaminated with mine tailings (soil A) and in soil irrigated with mine wastewater (soil B), before and after treatment with disodium ethylenediaminetetraacetic acid (EDTA), were analyzed with Tessier's sequential extraction procedures. The total contents of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) exceeded the maximum permissible levels by 5.1, 33.3, 3.1, and 8.0 times in soil A and by 2.6, 12.0, 0.2, and 1.9 times in soil B, respectively. The results showed that both soils had high levels of heavy‐metal pollution. Although the fractions were found in different distribution before extraction, the residual fraction was found to be the predominant fraction of the four heavy metals. There was a small amount of exchangeable fraction of heavy metals in both contaminated soils. Furthermore, in this study, the extraction efficiencies of Pb, Cd, and Cu were higher than those of Zn. After extraction, the concentrations of exchangeable Pb, Cd, Cu, and Zn increased 84.7 mg·kg^?1, 0.3 mg·kg^?1, 4.1 mg·kg^?1, and 39.9 mg·kg^?1 in soil A and 48.7 mg·kg^?1, 0.6 mg·kg^?1, 2.7 mg·kg^?1, and 44.1 mg·kg^?1 in soil B, respectively. The concentrations of carbonate, iron and manganese oxides, organic matter, and residue of heavy metals decreased. This implies that EDTA increased metal mobility and bioavailability and may lead to groundwater contamination.     

Sequential and Selective Extraction of Copper in Different Soil Phases and Plant Parts from Former Industrialized Area

Copper (Cu) is an essential trace element for all living organisms; however, excess amounts in soil, plants, and food have negative impacts on the environment and human health. The aim of this study was to determine Cu levels in different chemical phases of soils and the relationship between Cu levels in soil phases and concentrations in plants. Soils and plants grown in these soils from an industrialized area in Turkey were analyzed using a selective and four-stage sequential extraction procedure. Copper levels in exchangeable fractions were found up to 658 mg kg^?1 while total levels were in the range of 133–5609 mg kg^?1. Copper concentrations in plant parts (roots and stem) were in the range of 2.6–240 mg kg^?1. The exchangeable forms of Cu were in the range of 3–22% of total Cu concentrations. The relationships were observed between soil Cu and Rumex plant Cu, and soil Cu and root of Brassicasea plant Cu.     

Chemical Fractionation of Trace Elements in Biosolid‐Amended Soils and Correlation with Trace Elements in Crop Tissue

Abstract

A previous study indicated that agricultural biosolid applications increased the concentration of EPA₃₀₅₀‐digestible trace elements in soils on Pennsylvania production farms but could not indicate potential trace‐element environmental availability. This study was conducted to determine if biosolid application had altered the distribution of trace‐elements among operationally defined soil fractions and the relationship of trace element concentrations in soil and crop tissues. Biosolid‐amended and unamended soils from production farms in Pennsylvania were extracted using a modified Bureau Communautaire de Référence (BCR) sequential fractionation technique and analyzed for chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn). Trace‐element concentrations in crop tissues (soybean silage, sudangrass, corn grain, alfalfa hay, and orchardgrass hay) from the same farms were also determined. Fractionation results indicated that the proportion of Cr, Cu, Ni, Pb, and Zn that is potentially bioavailable is quite small in unamended soils. Biosolid applications significantly (P≤0.1) increased concentrations of Cu in all soil fractions (average increase over unamended soil=1.14, 8.27, 6.04, and 5.84 mg kg^?1 for the exchangeable, reducible, oxidizable, and residual fractions, respectively), Ni (0.41, 1.65 mg kg^?1 for the reducible and residual fractions, respectively), Pb (5.12 and 1.49 mg kg^?1 for the reducible and residual fractions, respectively), and Zn (8.28, 7.12, 4.44, and 8.98 mg kg^?1 for the exchangeable, reducible, oxidizable, and residual fractions, respectively) but did not significantly increase Cr in any soil fraction. Concentrations of Cu in all soil fractions were significantly (P≤0.01) correlated with concentrations of Cu in orchardgrass tissue (r=0.70, 0.66, 0.76, and 0.69 for the exchangeable, reducible, oxidizable, and residual soil fractions, respectively). Concentrations of exchangeable and reducible Zn were significantly correlated with Zn in sudangrass tissue (r=0.81 and 0.67), and reducible Zn was significantly correlated with Zn concentrations in orchardgrass tissue (r=0.65). Application of biosolids had little effect on bioavailability of Cr, Ni, or Pb, whereas higher loadings of Cu and Zn led to a shift toward the more labile soil fractions. Loadings of Cu and Zn were much smaller than cumulative loadings permitted under U.S. Environmental Protection Agency (USEPA) Part 503 regulations. Chemical soil fractionation was able to detect increases in labile soil Cu and Zn that relate to increased phytoavailability.     

Chicken-manure-derived biochar reduced bioavailability of copper in a contaminated soil

Purpose

Copper (Cu) contamination has been increasing in land ecosystems due to economic development activities. Excessive amount of Cu in soils is toxic to both plants and microorganisms. Biochar (BC) is known to immobilize soil Cu. The objectives of this research were to investigate the effects of chicken-manure-derived BC (CMB) on Cu immobilization, and growth of native metallophyte Oenothera picensis in a Cu-contaminated soil.

Materials and methods

A Cu-contaminated sandy soil (338 mg Cu kg^?1) was spiked and equilibrated with additional Cu (0, 100, and 500 mg Cu kg^?1). The spiked soil was then amended with CMB (0, 5, and 10 % w/w) and incubated for 2 weeks. The metallophyte was grown on these treatments under greenhouse conditions for 3 months. Pore water solutions were collected from the plant pots every 30 days. After the harvest, soil and pore water pH, soil Cu fractions, pore water Cu concentration, soil microbial activity, plant biomass weight, and Cu concentration in plant parts were determined.

Results and discussion

The CMB increased the pH of soils and soil pore water, and probably also soil major nutrients. It reduced the exchangeable fraction of Cu but increased its organic matter and residual fractions. At the same time, it decreased the Cu concentration in the soil pore water. The CMB increased basal respiration and dehydrogenase activity. The CMB application produced up to three and seven times more root and shoot biomass, respectively. In addition, shoots accumulated lesser Cu than control but roots did more. Plants survived in soil that was spiked with 500 mg Cu kg^?1, only when CMB dose was 10 %.

Conclusions

The CMB affected the Cu uptake in plant by altering the mobility, bioavailability, and spatial distribution of Cu in soils. The increase in available nutrients and decrease in Cu toxicity facilitated plant growth. The increased microbial activity probably also promoted the plant growth and reduced the Cu bioavailability. Therefore, CMB can be used to remediate Cu-contaminated soils.

     

DISTRIBUTION AND PHYTOAVAILABILITY PREDICTION OF ZINC IN AGRICULTURAL CALCAREOUS SOILS

The extractability and distributions of zinc (Zn) were evaluated in calcareous agricultural soils from South-West Iran. Both single [diethylenetriaminepentaacetic acid (DTPA)] and sequential extraction procedures (Singh scheme) were applied to 20 representative soils. The DTPA extractable zinc levels were low (on average 3.34%). The sequential extraction procedures were also utilized for the study of zinc phytoavailability in maize plants (Zea mays L.) in a greenhouse experiment. The Singh scheme was significantly better than DTPA plus soil properties in phytoavailability prediction of zinc in soils. Significant correlations were found between the amounts of DTPA extractable zinc and the iron (Fe) oxides-bound (AFe and CFe) and residual fractions extracted by the Singh procedure. Zinc concentrations in plant samples (mean value of 27.49 mg kg^?1) were poorly correlated with the different extracted soil fractions (single and sequential). The Singh procedure provided better predictions of zinc uptake by plants than DTPA extraction method.     

The influence of compost addition on heavy metal distribution between operationally defined geochemical fractions and on metal accumulation in plant

Purpose

Metal distribution patterns among geochemical fractions are informative for metal phytoavailability. Compost added to polluted soils may adsorb metals on the less phytoavailable fractions. A bioassay experiment was conducted to establish possible correlations between metal concentrations in different soil fractions and metal contents in edible plant parts and to investigate the influence of different compost loads on heavy metal availability to plants.

Materials and methods

Chinese cabbage plants were grown in pots with sandy and clayey soils and soils mixed with different doses of biosolid compost spiked with soluble heavy metal salts (Cd, Cu, and Pb). The metals’ distribution pattern in the soil and mixed samples was determined by sequential extraction procedure (modified BCR protocol). The studied fractions, from most to least bioavailable, were water-extractable (WE), exchangeable-adsorbed (EXC), associated with carbonates and acetic acid-soluble forms (CARB), occluded by reducible (hydro)oxides of Fe and Mn (RO), and associated with organic matter (OM) and a residual fraction (RES). Metal concentrations in soil extracts and in the digested plant tissue were measured by ICP-AES.

Results and discussion

The highest compost doses (72 and 115 Mg ha^?1) enhanced cabbage yield significantly. No excessive phytoaccumulation of metals was observed in plants grown in the clayey soil or its mixtures with compost. The compost dose of 72 Mg ha^?1 was optimal in decreasing Cu accumulation by plants grown in sandy soil, and 28.8 Mg ha^?1 was found to be effective in reducing Cd and Pb uptake. Metals were accumulated in plants primarily from the WE, EXC, and CARB fractions, whereas other fractions decreased phytoaccumulation. Compost addition suppressed heavy metal mobility, but different fractions were active in pollutant sorption, depending on soil type and metal.

Conclusions

Compost addition increased metal proportions in the RO and OM fractions, reducing metal phytoavailability. This is especially important for sandy soils with low adsorption ability and higher vulnerability to metal pollution than clayey soils. A compost dose of 20% v/v (or 28.8 Mg ha^?1) effectively reduced plant accumulation of Cd and Pb. We propose using the first three steps of the modified BCR protocol as a three-step sequential-extraction procedure for the most phytoavailable fractions of heavy metal: WE, EXC, and CARB.     

Pine Bark Amendment to Promote Sustainability in Cu-Polluted Acid Soils: Effects on <Emphasis Type="Italic">Lolium perenne</Emphasis> Growth and Cu Uptake

The establishment of a complementary grass cover on vineyard soils can promote sustainability of the affected environment. In this work, we used an acid vineyard soil with total Cu concentration 188 mg kg^?1 to study the influence of pine bark amendment on Lolium perenne growth and Cu uptake. The results indicate that the pine bark amendment did not cause a significant increase in the mass of the shoots of Lolium perenne, but favored the root biomass: 0.034 g for control and 0.061 g for soil samples amended with 48 g kg^?1 of pine bark. Moreover, the pine bark amendment decreased Cu concentration in both, shoots (50 mg kg^?1 for control soil and 29 mg kg^?1 for soil amended with 48 g kg^?1 pine bark) and roots (250 mg kg^?1 for control soil and 64 mg kg^?1 for soil amended with 48 g kg^?1 pine bark). The main factor responsible for these results was a significant decrease of the most mobile fractions of Cu in the soil. Those fractions were extracted using ammonium acetate, ammonium chloride, sodium salt of ethylene-diamine-tetraacetic acid (EDTA-Na), and diethylene-triamine-pentaacetic acid (DTPA).     

Distribution of Forms of Copper and their Association with Soil Properties and Uptake in Major Soil Orders in Semi-arid Soils of Punjab,India

Profiles of semi-arid-zone soils in Punjab, northwestern India, were investigated for different forms of copper (Cu), including total Cu, diethylenetriaminepentaacetic acid (DTPA)–extractable Cu, soil solution plus exchangeable Cu, Cu adsorbed onto inorganic sites, Cu bound by organic sites, and Cu adsorbed onto oxide surfaces. When all soils were considered, total Cu content ranged from 7 to 37 mg kg^?1, while DTPA-extractable and soil solution plus exchangeable Cu contents ranged from 0.30 to 3.26 mg kg^?1 and from 0.02 to 0.43 mg kg^?1, respectively. Copper adsorbed onto inorganic sites ranged from 0.62 to 2.6 mg kg^?1 and that onto oxide surfaces ranged from 2.0 to 13.2 mg kg^?1. The Cu bound by organic sites ranged from 1.2 to 12.2 mg kg^?1. The magnitudes of different forms of Cu in soils did not exhibit any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Cu. The content of all forms of Cu was generally greater in the fine-textured Alfisols and Inceptisols than coarse-textured Entisols. Soil solution plus exchangeable Cu, Cu held onto organic sites, and and Cu adsorbed onto inorganic sites (crystalline) had significant positive correlations with organic carbon and silt contents.The DTPA Cu was positively correlated with organic carbon, silt, and clay contents. Total Cu content strongly correlated with silt and clay contents of soils. Among the forms, Cu held on the organic site, water soluble + exchangeable Cu, and Cu adsorbed onto oxide surface were positively correlated with DTPA-extractable Cu. The DTPA-extractable Cu and soil solution plus exchangeable Cu seems to be good indices of Cu availability in soils and can be used for correction of Cu deficiency in the soils of the region. The uptake of Cu was greater in fine-textured Inceptisols and Alfisols than coarse-textured Entisols. Among the different forms only DTPA-extractable Cu was positively correlated with total uptake of Cu.     

Organic Amendment Effects on the Transformation and Fractionation of Aluminum in Acidic Sandy Soil

Addition of organic amendments can alleviate the level of aluminum (Al) phytotoxicity in acid soils by affecting the nature and quantity of Al species. This study evaluated the transformation of Al in an acidic sandy Alaquod soil amended with composts (10 and 50 g kg^?1 soil of yard waste, yard + municipal waste, GreenEdge^®, and synthetic humic acid) based on soil Al fractionation by single and sequential extractions. Though the organic compost amendments increased total Al in soil, they alleviated Al potential toxicity in acidic soil by increasing soil pH and converting exchangeable Al to organically bound and other noncrystalline fractions, stressing the benefits of amending composts to improve acid soil fertility. The single‐extraction method appears to be more reliable for exchangeable Al than sequential extraction because of the use of nonbuffered pH extract solution.     

Ibuprofen Sorption to Coastal Plain Soils

Ibuprofen is commonly detected in onsite wastewater systems. Such onsite systems are abundant in coastal plain areas, globally. Coastal plain soils have unique mineralogy. Rapid subsurface transport may occur in coastal plain soils due to their characteristic permeable soils and seasonally high water tables. Laboratory batch sorption studies were conducted on Norfolk, Goldsboro, and Lynchburg, three archetypical coastal plain soils, with varying physicochemical properties, to evaluate ibuprofen sorption. Sorption distribution coefficients (K_D values) across all three soils ranged from 0.63 to 1.26 L kg^?1. Sorption of ibuprofen to Norfolk and Goldsboro soils was able to be modeled using a Freundlich isotherm; however, the Lynchburg soil, was not, likely due to soil heterogeneity. In general, sorption of ibuprofen was influenced by soil organic carbon content.     

Relationship Between Extractable Metals in Acid Soils and Metals Taken Up by Tea Plants

Abstract

The accumulation of heavy metals in plants is related to concentrations andchemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate‐bound, organic matter‐bound, oxides‐bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mgCukg^?1, 0.03 to 1.09 mg Cd kg^?1, 3.43 to 31.2 mg Pb kg^?1, and 31.0 to 132.0 mg Zn kg^?1. The concentrations of exchangeable and carbonate‐bound fractions of the metals depended mainly on the pH, and those of organic matter‐bound, oxides‐bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L^?1 CaCl₂, NH₄OAc, and DTPA‐TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long‐term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.     

Heavy‐Metal Contamination of Soil and Vegetables in Wastewater‐Irrigated Agricultural Soil in a Suburban Area of Hanoi,Vietnam

The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serve as sources of water for irrigating vegetable farms. The purposes of this study were to identify the impact of wastewater irrigation on the level of heavy metals in the soils and vegetables and to predict their potential mobility and bioavailability. Soil samples were collected from different distances from the canal. The average concentrations of the heavy metals in the soil were in the order zinc (Zn; 204 mg kg^?1) > copper (Cu; 196 mg kg^?1) > chromium (Cr; 175 mg kg^?1) > lead (Pb; 131 mg kg^?1) > nickel (Ni; 60 mg kg^?1) > cadmium (Cd; 4 mg kg^?1). The concentrations of all heavy metals in the study site were much greater than the background level in that area and exceeded the permissible levels of the Vietnamese standards for Cd, Cu, and Pb. The concentrations of Zn, Ni, and Pb in the surface soil decreased with distance from the canal. The results of selective sequential extraction indicated that dominant fractions were oxide, organic, and residual for Ni, Pb, and Zn; organic and oxide for Cr; oxide for Cd; and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order of Cd > Ni > Cr > Pb > Cu > Zn and in the order of Cd > Ni > Cr > Zn > Cu > Pb for the ethylenediaminetetraaceitc acid (EDTA) treatment. The EDTA treatment gave greater leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were fully released from the exchangeable fraction, and some heavy metals were fully released from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the vegetables exceeded the Vietnamese standards. The transfer coefficients for the metals were in the order of Zn > Ni > Cu > Cd = Cr > Pb.     

Cadmium accumulation in Crassocephalum crepidioides (Benth.) S. Moore (Compositae) in heavy-metal polluted soils and Cd-added conditions in hydroponic and pot cultures

Abstract

We have identified Crassocephalum crepidioides (Benth.) S. Moore (Compositae) as a cadmium (Cd)-accumulator plant in a heavy-metal polluted environment. In soil polluted with Cd, 5.7–17.5 mg kg^?1 Cd, concentrations in the above-ground plant tissues were measured as 14.6–78.6 mg kg^?1 with transfer factors in the above-ground plant tissues (concentration in above-ground tissues/soil concentration) of 1.5–6.0. No other toxic heavy metals or plant micronutrients were found to have accumulated into the above-ground plant tissues. In a hydroponic culture with 1 µmol L^?1 Cd added to Hoagland's nutrient solution, Cd concentration in the above-ground plant tissues was 121.0 mg kg^?1, with a transfer factor of more than 1000. In a pot culture carried out for 9 weeks in a greenhouse, the highest Cd concentration in the above-ground plant tissues, 121.2 mg kg^?1, was found in a treatment with 5 mg kg^?1 Cd, whereas the highest Cd content in an above-ground plant tissue, 106.1 µg, was found in a treatment with 2 mg kg^?1 Cd. These results clearly showed that C. crepidioides is a Cd accumulator. In all samples, the Cd concentration in the above-ground plant tissues was higher than that in the roots. The results obtained in the present study show that this plant has a strong potential for use in phytoremediation in farm fields contaminated with Cd.     

Assessing the depletion of soil P following sequential extractions with Mehlich-3 and Olsen solutions

We analyzed in soils with contrasting cultivation histories the depletion of P following sequential extractions with soil testing solutions. Soil samples were collected in three experiments in eastern Canada (L’Acadie, Lévis, and Normandin) and P was sequentially extracted 16 times, once daily, using Mehlich-3 (M3) or Olsen (Ol) solution. The cumulative amount of P extracted was 252 mg P_M3 kg^?1 and 77 mg kg^?1 P_Ol for L’Acadie, 212 mg P_M3 kg^?1 and 66 mg P_Ol kg^?1 for Lévis, and 424 mg P_M3 kg^?1 and 83 mg P_Ol kg^?1 for Normandin. The depletion of P was described by a logarithmic function (Y = a ln (N) + b) for P_M3, and a power function (Y = αN^β) for P_Ol. The inorganic P pool decreased in the three soils. The organic P pool did not decrease possibly because soil testing solutions did not directly extract P from this pool. This study demonstrated that laboratory soil testing analysis using M3 or Ol solution principally target P from the inorganic pool, suggesting that P fertilizer recommendations to mineral soils relying on these methods do not account for the potential of the organic P pool to contribute to soil P availability.     

Fractionation of Cd and Zn in Cd-contaminated soils amended by sugarcane waste products from an ethanol production plant

Purpose

Sugarcane waste products (boiler ash, filter cake, and vinasse) from an ethanol production plant were used as soil amendments by adding 3 % (w/w) in single and/or in combination, with a research focus towards stabilization of cadmium (Cd) and zinc (Zn) in contaminated soils. The objective of this laboratory study was to evaluate the effects of adding these sugarcane waste products on bioavailability of Cd and Zn over time (aging) in Cd- and Zn-contaminated agricultural soils of Thailand.

Materials and methods

Two agricultural contaminated soils of low (<3 mg kg^?1) and high (10–15 mg kg^?1) Cd concentrations were collected from Tak Province, Northwest Thailand. Fourteen treatments were sampled at 2-week intervals for 84 days for metal bioavailability using BCR extraction procedures (proposed by The Standards, Measurements and Testing Programme of the European Union, SM&T) that determined exchangeable (BCR1), reducible (BCR2), oxidizable (BCR3), and residual (BCR4) fractions, and total concentration was determined using aqua regia digestion and microwave digestion.

Results and discussion

Cd was potentially bioavailable, predominantly in exchangeable (BCR1) and reducible (BCR2) fractions, while the higher contribution of Zn was more prevalent in refractory fractions (BCR2 and BCR4). Aging had an influence on fractionation of Cd and Zn, most notably in the first two fractions (BCR1 and BCR2) of BCR sequential extraction, which resulted in reduction of exchangeable Cd during the first few weeks of incubation (T?=?0 to 28 days). At the end of pot experiment, the exchangeable Cd fraction in the low Cd (LCdS) soil was reduced from 2.3 to 4.7 % and 9.4 to 39.9 % in low and high Cd (HCdS)-contaminated soils, respectively, as compared to nonamended soils.

Conclusions

The observed reduction in exchangeable Cd (BCR1) in the amended soils at the 3 % (w/w) application rate, the low total metal concentrations, and the significant amount of essential plant nutrients (N, P, and K) within these waste products highlight the benefits of amending metal-rich soils with them.     

Bioavailability,fractionation of pb and Zn in the rhizosphere of sunflower in chelators-amended contaminated soil

Assisted phytoremediation procedures have been widely employed as soil removal instrument of heavy metals from contaminated soils. Rhizosphere processes have a major impact on pb and Zn availability and its fractions in soils. The present study evaluates the effects of EDTA, citric acid (CA) and poultry manure extract (PME) on bioavailability and fractionation of pb, Zn in both the rhizosphere of sunflower (Helianthus annuus L.) and bulk soil. EDTA and CA were added to soils at the rates of 0, 0.5 and 1 mmol kg^?1 soil and PME at 0, 0.5 and 1 g kg^?1 soil as factorial in a completely randomized pattern with three replicates in greenhouse condition. Results showed that chelator application had a significant impact (p < 0.05) on pb, Zn extraction by different extractants and its fractions in soils. The order of concentrations of pb, Zn present in different fractions in soil treated by chelators was: oxides-bounded fraction > residual fraction > OM-bounded fraction > carbonate-bounded fraction > exchangeable fraction. Biochemical soil characteristics in the sunflower rhizosphere change resulting from its roots contributing to pb, Zn decline in mobile soil fractions, and change in soil pb, Zn fractions that are generally regarded as more stable.     

Metal Uptake in Plants and Health Risk Assessments in Metal‐Contaminated Smelter Soils

Metal pollution is an important concern because of its potential to affect human health. Metals such as lead and cadmium can enter soil via the food chain and exceed normal limits, producing harmful effects. In this study, six common garden and residential plant species were grown in soils from Spelter, WV, USA, contaminated with a variety of metals including lead (Pb), zinc (Zn), cadmium (Cd), and copper (Cu). Plant species included radish, carrot, chicory, spinach, lettuce, and clover. Metal concentrations in plant tissues were compared with metal concentration in soil by a multi‐step chemical extraction. The largest accumulation of Pb (126 mg kg⁻¹) and Zn (1493 mg kg⁻¹) was seen in radish roots, with Cd (40 mg kg⁻¹) having the largest accumulation in carrot roots. Comparisons of plant availability with soil chemical extractions indicated that the combined soluble and exchangeable fractions could estimate available Zn and Cd for all six plant species. For Pb and Cu, however, the comparisons indicate that these two elements were not readily available in Spelter soils. A health risk assessment was carried out for residents at Spelter on the basis of edible tissue concentrations and publicly available consumption data. Uptake of Cd by carrot roots was about five times more than the regulatory limits for men, eight times more for women, and 12 times more for children. On the basis of the results, carrot and lettuce grown in these soils have the potential to cause toxicological problems in men, women, and young children resulting from Cd and Zn accumulation. Copyright © 2013 John Wiley & Sons, Ltd.     

Zinc sorption–desorption by sand,silt and clay fractions in calcareous soils of Iran

Zinc sorption–desorption by sand, silt and clay fractions of six representative calcareous soils of Iran were measured. Sand, silt and clay particles were fractionated after dispersion of soils with an ultrasonic probe. Zinc sorption analysis was performed by adding eight rates of Zn from 6 to 120 μmol g^?1. For the desorption experiment, samples retained after the measurement of Zn sorption were resuspended sequentially in 0.01 M NaNO₃ solution and shaken for 24 h. Results indicated that Zn sorption by soil fractions increased in the order clay > silt > sand, and correlated negatively with CaCO₃ content and positively with cation exchange capacity (CEC) and smectite content. Results indicated that for all fractions, the Langmuir equation described the sorption rates fairly well. In contrast to sorption, Zn desorption from soil fractions increased in the order sand > silt > clay, and correlated positively with CaCO₃ content, CEC and smectite content. Results showed that parabolic diffusion and two constant equations adequately described the reaction rates of Zn desorption. In general, for all soils studied, the coarser the particle size, the less Zn sorption and more Zn desorption, and this reflects much higher risk of Zn leaching into groundwater or plant uptake in contaminated soils.     

Properties and available micronutrient status of some soils derived from Abeokuta formation in Nigeria

Available iron, zinc, copper and manganese were determined in six pedons located in upper slope, middle slope and valley bottom soils derived from Abeokuta geological materials in Nigeria. The soils had an average of 639.8 g kg^?1 sand, 241.8 g kg^?1 clay and 118.4 g kg^?1 silt. The fertility status of the soils was low–medium with a strongly acid–neutral reaction, 1.3–15.1 g kg^?1 organic carbon contents, moderate–high exchangeable bases and 1.38 mg kg^?1 available phosphorus. Both Fe (122.50 mg kg^?1) and Mn (111.40 mg kg^?1) occurred at toxic levels, whereas the mean Cu (1.27 mg kg^?1) and Zn (2.56 mg kg^?1) contents were found to be adequate for most crops grown in the region. There were significant positive correlations among the micronutrients and also between soil pH, organic carbon, particle size fractions and micronutrients. The high levels of Fe and Mn were probably due to the presence of oolitic ironstone in the parent material.     

EDTA Leaching of Cu Contaminated Soils Using Ozone/UV for Treatment and Reuse of Washing Solution in a Closed Loop

Ozone and UV irradiation were used for oxidative decomposition of EDTA-Cu complexes in washing solution obtained during multi-step leaching of Cu (344,1?±?36.5 mg kg^?1) contaminated vineyard soil with EDTA as a chelant. The released Cu was absorbed from the washing solution on a commercial mixture of metal absorbing minerals, and the treated washing solution then reused for removal of soil residual Cu-EDTA complexes in a closed-loop process. Six consecutive leaching steps (6?×?2.5 mmol kg^?1 of EDTA) removed 38.8 % of Cu from soils, and reduced Cu soil mobility, determined using the toxicity characteristic leaching test (TCLP), by 28.5%. The final washing solution obtained after soil remediation was colourless, with a pH close to neutral (7.5?±?0.2) and with low concentrations of Cu and EDTA (0.51?±?0.22 mg L^?1 and 0.083 mM, respectively). The proposed remediation method has therefore potential not just to recycle and save process water, but also not to produce toxic wastewaters. Soil treatment did not substantially alter the soil properties determined by pedological analysis, and had relatively little impact on soil hydraulic conductivity and soil water sorption capacity.