A Laboratory Study on Revegetation and Metal Uptake in Native Plant Species from Neutral Mine Tailings

Lygeum spartum, Zygophyllum fabago and Piptatherum miliaceum are typical plant species that grow in mine tailings in semiarid Mediterranean areas. The aim of this work was to investigate metal uptake of these species growing on neutral mine tailings under controlled conditions and their response to fertilizer additions. A neutral mine tailing (pH of soil solution of 7.1–7.2) with high total metal concentrations (9,100 and 5,200 mg kg^?1 Zn and Pb, respectively) from Southern Spain was used. Soluble Zn and Pb were low (0.5 and <0.1 mg l^?1, respectively) but the major cations and anions reached relatively high levels (e.g. 2,600 and 1,400 mg l^?1 Cl and Na). Fertilization caused a significant increase of the plant weight for the three species and decreased metal accumulation with the exception of Cd. Roots accumulated much higher metal concentrations for the three plants than shoots, except Cd in L. spartum. Shoot concentrations for the three plants were 3–14 mg kg^?1 Cd, 150–300 mg kg^?1 Zn, 4–11 mg kg^?1 Cu, and 1–10 mg kg^?1 As, and 6–110 mg kg^?1 Pb. The results indicate that neutral pH mine tailings present a suitable substrate for establishment of these native plants species and fertilizer favors this establishment. Metal accumulation in plants is relatively low despite high total soil concentrations.     

Effects of Soil Amendments on Growth and Metal Uptake by Ocimum gratissimum Grown in Cd/Zn-Contaminated Soil

Hydroponic and pot experiments were conducted to assess the uptake of heavy metals (Cd and Zn) by a common crop plant, African basil, Ocimum gratissimum. In addition, the effects of soil amendments, hydroxyapatite (HA) and cow manure on plant growth and metal accumulations were compared. In the hydroponic study, plants were exposed to various concentrations of Cd (2.5 and 5 mg L^?1) and Zn (10 and 20 mg L^?1) for 15 days. O. gratissimum was shown to be a Cd accumulator more than a Zn accumulator. Cadmium concentration in its shoots exceeded 100 mg kg^?1. In the pot experiments, soils from a heavily Cd-contaminated site (Cd 67.9 mg kg^?1 and Zn 2,886.8 mg kg^?1) were treated with cow manure and HA at the rates of 10% and 20% (w/w), and 0.75 and 1.5% (w/w), respectively. Plants were grown in the greenhouse for 3 months. The addition of cow manure resulted in the highest biomass production and the lowest accumulations of Cd in plant parts, while HA was more efficient than cow manure in reducing Zn uptake. Leaves of African basil showed a decreased Cd concentration from 1.5 to 0.3 mg kg^?1 (cow manure) and decreased Zn concentration from 69.3 to 34 mg kg^?1 (HA). This clearly demonstrates the efficiency of HA and cow manure in reducing metal content in leaves of plants grown on high metal-contaminated soil to acceptable or close to acceptable values (0.2 mg kg^?1 for Cd, 99.4 mg kg^?1 for Zn).     

Bioremediation of Co-contamination of Crude Oil and Heavy Metals in Soil by Phytoremediation Using Chromolaena odorata (L) King & H.E. Robinson

The capability of Chromolaena odorata (L) to grow in the presence of different concentrations of three heavy metals in crude oil-contaminated soil and its capability to remediate the contaminated soil was investigated using pot experiments. C. odorata plants were transplanted into contaminated soil containing 50,000 mg kg^?1 crude oil and between 100 and 2,000 mg kg^?1 of cadmium, nickel, and zinc and watered weekly with water containing 5% NPK fertilizer for 180 days. C. odorata did not show any growth inhibition in 50,000 mg kg^?1 crude oil. Plants in experiments containing 2,000 mg kg^?1 Cd showed little adverse effect compared to those in Zn-treated soil. Plants in 1,000 and 2,000 mg kg^?1 Ni experiments showed more adverse effects. After 180 days, reduction in heavy metals were: 100 mg kg^?1 experiments, Zn (35%), Cd (33%), and Ni (23%); 500 mg kg^?1, Zn (37%), Cd (41%), and Ni (25%); 1,000 mg kg^?1, Zn (65%), Cd (55%), and Ni (44%); and 2,000 mg kg^?1, Zn (63%), Cd (62%), and Ni (47%). The results showed that the plants accumulated more of the Zn than Cd and Ni. Accumulation of Zn and Cd was highest in the 2,000 mg kg^?1 experiments and Ni in the 500 mg kg^?1 experiments. Crude oil was reduced by 82% in the experiments that did not contain heavy metals and by up to 80% in the heavy metal-treated soil. The control experiments showed a reduction of up to 47% in crude oil concentration, which was attributed to microbial action and natural attenuation. These results show that C. odorata (L) has the capability of thriving and phytoaccumulating heavy metals in contaminated soils while facilitating the removal of the contaminant crude oil. It also shows that the plant??s capability to mediate the removal of crude oil in contaminated soil is not significantly affected by the concentrations of metals in the soil.     

Remediation of a Sandy Soil Contaminated with Cadmium,Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract

This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg^?1 of soil), nickel (Ni) (50 and 100 mg Ni kg^?1 of soil), zinc (Zn) (250 and 400 mg Zn kg^?1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg^?1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.     

Potential of Borago officinalis, Sinapis alba L. and Phacelia boratus for Phytoextraction of Cd and Pb from Soil

Heavy metal phytoextraction is a soil remediation technique, which makes use of plants in removing contamination from soil. The plants must thus be tolerant to heavy metals, adaptable to soil and climate characteristics, and able to take up large amounts of heavy metals. Most of the high biomass productive plants such as, maize, oat and sunflower are plants, which do not grow in cold climates or need intensive care. In this study three “weed” plants, Borago officinalis; Sinapis alba L. and Phacelia boratus were investigated for their ability to tolerate and accumulate high amounts of Cd and Pb. Pot experiments were performed with soil containing Cd and Pb at concentrations of up to 180 mg kg^?1 and 2,400 mg kg^?1 respectively. All three plants showed high levels of tolerance. Borago officinalis; and Sinapis alba L. accumulated 109 mg kg^?1 and 123 mg kg^?1 Cd, respectively at the highest Cd spiked soil concentration. Phacelia boratus reached a Cd concentration of 42 mg kg^?1 at a Cd soil concentration of 100 mg kg^?1. In the case of Pb, B. officinalis and S. alba L. displayed Pb concentrations of 25 mg kg^?1 and 29 mg kg^?1, respectively at the highest Pb spiked soil concentration. Although the Pb uptake in P. boratus reached up to 57 mg kg^?1 at a Pb spiked soil concentration of 1,200 mg kg^?1, it is not suitable for phytoextraction because of its too low biomass.     

Trace Element Concentrations in Saltmarsh Soils Strongly Affected by Wastes from Metal Sulphide Mining Areas

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L^?1 and maximum Zn 0.553 mg L^?1) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg^?1 of Mn, 62,280 mg kg^?1 of Zn, 16,845 mg kg^?1 of Pb, 77 mg kg^?1 of Cd, 418 mg kg^?1 of Cu and 725 mg kg^?1 of As), and soluble metals in the pore water reached 38.7 mg L^?1 for Zn, 3.15 mg L^?1 for Pb, 48.0 mg L^?1 for Mn, 0.61 mg L^?1 for Cd and 0.29 mg L^?1 for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility.     

Heavy Metal Pollution in Soils Around the Abandoned Mine Sites of the Iberian Pyrite Belt (Southwest Spain)

This paper investigates the pollution load of selected trace elements in 32 soil samples collected around 21 different mining areas of the Iberian Pyrite Belt (Southwest Spain), integrating chemical data with soil parameters to help understand the partitioning and mobility of pollutants. The minesoils are depleted in acid neutralising minerals and show limiting physicochemical properties, including low pH values and very high anomalies of potentially hazardous metals. The total concentrations of As (up to 1,560 mg kg^?1) and certain heavy metals (up to 2,874 mg kg^?1 Cu, 6,500 mg kg^?1 Pb, 6,890 mg kg^?1 Zn, 62 mg kg^?1 Hg and 22 mg kg^?1 Cd) are two orders of magnitude above the soil background values. The close association of Cd and Zn with the carbonate content in lime-amended minesoils suggests metal immobilisation through adsorption and/or co-precipitation mechanisms, after acid neutralisation, whereas As and Pb are similarly partitioned into the soil and mostly associated with iron oxy-hydroxides.     

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.     

APPLICATION OF INCREASING LEVELS OF ZINC TO SOIL REDUCED ACCUMULATION OF CADMIUM IN LUPIN GRAIN

Yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (L. angustifolius L.) are grown as grain legumes in rotation with spring wheat (Triticum aestivum L.) on acidic sandy soils of south-western Australia. Yellow lupin can accumulate significantly larger cadmium (Cd) concentrations in grain than narrow-leafed lupin. A glasshouse experiment was undertaken to test whether adding increasing zinc (Zn) levels to soil increased Zn uptake by yellow lupin reducing accumulation of Cd in yellow lupin grain. Two cultivars of yellow lupin (cv. ‘Motiv’ and ‘Teo’) and 1 cultivar of narrow-leafed lupin (cv. ‘Gungurru’) were used. The soil was Zn deficient for grain production of both yellow and narrow-leafed lupin, but had low levels of native soil Cd (total Cd <0.05 mg kg^?1) so 1.6 mg Cd pot^?1, as a solution of cadmium chloride (CdCl₂·H₂O), was added and mixed through the soil. Eight Zn levels (0–3.2 mg Zn pot^?1), as solutions of zinc sulfate (ZnSO₄·7H₂O), were added and evenly mixed through the soil. Yellow lupin accumulated 0.16 mg Cd kg^?1 in grain when no Zn was applied, which decreased as increasing Zn levels were applied to soil, with ～0.06 mg Cd kg^?1 in grain when the largest level of Zn (3.2 mg Zn pot^?1) was applied. Low Cd concentrations (<0.016 mg Cd kg^?1) were measured in narrow-leafed lupin grain regardless of the Zn treatment. When no Zn was applied, yellow lupin produced ～2.3 times more grain than narrow-leafed lupin, indicating yellow lupin was better at acquiring and using indigenous Zn from soil for grain production. Yellow lupin required about half as much applied Zn as narrow-leafed lupin to produce 90% of the maximum grain yield, ～0.8 mg pot^?1 Zn compared with ～1.5 mg Zn pot^?1. Zn concentration in whole shoots of young plants (eight leaf growth stage) related to 90% of the maximum grain yield (critical prognostic concentration) was (mg Zn kg^?1) 25 for both yellow lupin cultivars and 19 for the narrow-leafed lupin cultivar. Critical Zn concentration in grain related to 90% of maximum grain yield was (mg Zn kg^?1) 24 for both yellow lupin cultivars compared with 20 for the narrow-leafed lupin cultivar.     

Arsenic and heavy metal accumulation by Athyrium yokoscense from contaminated soils

Abstract

Athyrium yokoscense, a type of fern that grows vigorously in mining areas in Japan, is well known as a Cd hyperaccumulator as well as a Cu, Pb and Zn tolerant plant. However, no information is available on As accumulation of A. yokoscense, although it often grows on soils containing high levels of both heavy metals and As. In this study, young ferns collected from a mine area were grown in media containing As-spiked soils or mine soil in a greenhouse for 21 weeks. Athyrium yokosense was highly tolerant to arsenate and survived in soils containing up to 500 mg As (V) kg^?1. The addition of 100 mg As (V) kg^?1 resulted in the highest fern biomass (1.95 g plant^?1) among As-spiked soils. Although the As concentration of the fern was lower than other As hyperaccumulators, such as Pteris vittata, A. yokoscense could hyperaccumulate As in mature and old fronds. Arsenic was accumulated most efficiently in old fronds (922 mg kg^?1) in the media containing 5 mg As (III) kg^?1. Moreover, higher As accumulation was found in the roots of the ferns, with a range from 506 to 2,192 mg kg^?1. In addition, in the mine soil with elevated concentrations of As and heavy metals, A. yokoscense not only hyperaccumulated As (242 mg As kg^?1 in old fronds), but also accumulated Cd, Pb, Cu and Zn at concentrations much higher than those reported for other terrestrial plants. Athyrium yokoscense accumulated Cd mostly in fronds in high concentrations, up to 1095 mg kg^?1, while it accumulated Cu, Zn and Pb mainly in the roots and the concentrations were 375, 2040 and 1165 mg kg^?1, respectively.     

Anthropogenic Heavy Metal Pollution in the Surficial Sediments of the Keratsini Harbor, Saronikos Gulf, Greece

The contents of ten elements [Cd, Pb, W, Zn, Mn, As, Se, Cr, Cu, and organic carbon (C_org)] have been determined in the surficial sediments of Keratsini harbor, Saronikos Gulf, Greece. The contamination of the sediments was assessed on the basis of geoaccumulation index and to corresponding sediment quality guidelines (SQGs) effects range low/effects range median. The results revealed highly elevated Cd, Pb, W, Zn, As, Se, Cr, Cu, and C_org values (Cd, 190–1,763 mg kg^?1; Pb, 521–1,263 mg kg^?1; W, 38–100 mg kg^?1; Zn, 409–6,725 mg kg^?1; Mn, 95–1,101 mg kg^?1; As, not detectable–1,813 mg kg^?1; Se, not detectable–58 mg kg^?1; Cr, 264–860 mg kg^?1; Cu, 195–518 mg kg^?1; and C_org, 0.69–4.41%). The enrichment of metals in the sediments results from the contribution of the central Athens sewage outfall through which the waste of the Attica basin ends up in Keratsini harbor as well as from industrial and ship contaminants.     

Cd, Ni, Pb, and Zn Concentrations in Forest Vegetation and Soils in Maine

Bioaccumulation of trace metals in plant tissues can present a health risk to wildlife, and potentially to humans. The Passamaquoddy tribe in Maine was concerned about health risks of cadmium (Cd) because of a health advisory for moose liver and kidney consumption due to high Cd levels. This study found relatively low to moderate concentrations of Cd, nickel (Ni), lead (Pb), and zinc (Zn) concentrations in four common terrestrial moose browse species, associated forest soils, and two species of aquatic vegetation on Passamaquoddy tribal land in eastern Maine. Terrestrial plant tissue concentrations ranged from 0.1 to 1.97, 0.65 to 7.08, 0.29 to 2.0, and 42 to 431 mg kg^?1 for Cd, Ni, Pb and Zn, respectively. Deciduous species, particularly aspen and birch, may be a more significant source of Cd and Zn to wildlife compared to coniferous or aquatic species. Aquatic plant tissue concentrations ranged from 0.11 to 0.14, 0.46 to 1.01, 0.8 to 0.9, and 22 to 41 mg kg^?1 for Cd, Ni, Pb and Zn, respectively. Total O horizon concentration means for coniferous and deciduous were 0.50 and 1.00, 4.27 and 4.11, 55 and 21, and 55 and 167 mg kg^?1 for Cd, Ni, Pb and Zn, respectively. The study provides baseline vegetation and soil trace metal concentrations for a remote region in Maine impacted by non-point sources.     

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.     

Heavy Metal Concentration Survey in Soils and Plants of the Les Malines Mining District (Southern France): Implications for Soil Restoration

Mining activities generate spoils and effluents with extremely high metal concentrations of heavy metals that might have adverse effects on ecosystems and human health. Therefore, information on soil and plant metal concentrations is needed to assess the severity of the pollution and develop a strategy for soil reclamation such as phytoremediation. Here, we studied soils and vegetation in three heavily contaminated sites with potential toxic metals and metalloids (Zn, Pb, Cd, As, TI) in the mining district of Les Malines in the Languedoc region (southern France). Extremely high concentrations were found at different places such as the Les Aviniéres tailing basins (up to 160,000 mg kg^?C1 Zn, 90,000 mg kg^?C1 Pb, 9,700 mg kg^?C1 of As and 245 mg kg^?C1 of Tl) near a former furnace. Metal contamination extended several kilometres away from the mine sites probably because of the transport of toxic mining residues by wind and water. Spontaneous vegetation growing on the three mine sites was highly diversified and included 116 plant species. The vegetation cover consisted of species also found in non-contaminated soils, some of which have been shown to be metal-tolerant ecotypes (Festuca arvernensis, Koeleria vallesiana and Armeria arenaria) and several Zn, Cd and Tl hyperaccumulators such as Anthyllis vulneraria, Thlaspi caerulescens, Iberis intermedia and Silene latifolia. This latter species was highlighted as a new thallium hyperaccumulator, accumulating nearly 1,500 mg kg^?C1. These species represent a patrimonial interest for their potential use for the phytoremediation of toxic metal-polluted areas.     

Metal Accumulation by Woody Species on Contaminated Sites in the North of France

Metal accumulation was investigated in a range of woody species that were planted on Cd-, Zn- and Pb- polluted sites in North of France. The study is unique in that we directly compare a large number of woody species (25). The highest accumulation of Zn and Cd was found in the Salicaceae family members with up to 950 mg Zn kg^?1 dry weight (DW) and 44 mg Cd kg^?1 DW in leaves of Populus tremula × Populus tremuloides. Zn content was positively correlated with Cd content, both in leaves and stems. Pb concentration was generally low and was species-independent. Oak and birch species accumulated more Mn as compared to other woody species. A seasonal variation in metal accumulation could be found. Although soil compositions and metal bioavailabilities differed amongst the experimental sites chosen in this study, variation of metal concentrations within a given species was small. High bioconcentration factors for poplar and willow suggested the high potential of these species over other woody species for metal accumulation. Taken together, these data suggest that poplar and willow species are good candidates for phytoremediation programmes.     

Heavy Metal Content in Lettuce Plants Grown in Biosolids Compost

The objective of this work was to evaluate the affects of the application of composted biosolids on the accumulation of heavy metals (Cd, Cu, Ni, Pb and Zn) in lettuce leaves. Pots containing different proportions (0 to 100%) of composted biosolids were used to grow lettuce plants under greenhouse conditions. Dry and fresh weight, leaf area and Cd, Cu, Ni, Pb and Zn uptake were determined after harvest. It was found that the dry and fresh matter productions of the plants were significantly lower in the control treatment. The addition of composted biosolids caused a 20 and 40% increase in biomass accumulation. Cd and Pb concentrations in leaves were below detection limits (0.05 mg kg^?1) in all treatments. Zn concentration in leaves increases as compost proportion decreases, ranging from 57.2 to 80.4 mg kg^?1. Composted biosolids application increased the Cu and Ni plant concentrations, ranging from 5.1 to 9.8 mg Cu kg^?1 and 2.3 to 3.7 mg Ni kg^?1. In all treatments the proportions of heavy metals in plants were below the international standards of toxicity. The results allow us to suggest that, in short-term applications, composted biosolids could be used as soil amendment for lettuce production, without toxic effects in the chemical composition of the plant.     

Toxicity and binding of copper,zinc, and cadmium by the blue-green alga,Chroococcus paris

The toxic effects and accumulation of the heavy metals, Cd, Cu, and Zn by the sheath forming blue-green alga Chroococcus paris were investigated. All three of the metals were bound rapidly. Approximately 90% of the total amount of the added metal was bound within 1 min. Further significant binding occurred at a slower rate. The maximum metal binding capacity, as determined by filtration studies, was determined to be 53, 120, and 65 mg g^?1 dry algal weight for Cd, Cu, and Zn, respectively. Binding curves for the metals followed the Langmuir adsorption isotherm model. The amount of metal bound increased with increasing pH. Metal binding increased significantly when pH was increased from 4 to 7. Nearly all of the metal was found to be rapidly EDTA extractable. Metals were found to be increasingly toxic to growing cultures in the order, Zn, Cd, and Cu. All of the metals studied exhibited toxic effects at concentrations greater than 1.0 mg L^?1. The lowest concentrations used which showed detectable toxicity were 0.1 mg L^?1 for Cu and >0.4 mg L^?1 for Cd and Zn.     

Chemical characterization of heavy-metal contaminated soil in southeast Kansas

A tri-state mining region, including parts of Missouri, Oklahoma, and Kansas, was the site of intense lead and zinc mining and smelting activity until the 1950's. A study was initiated to characterize the heavy-metal contamination of soils in this area. Water-soluble, an index of plantavailable, total, and sequentially extractable metals; organic, and total carbon; and saturated paste pH were determined for mine tailings and soil samples. Mine tailings contained 81 to 89 mg kg^?1 total Cd, 1 150 to 1 370 mg kg^?1 total Pb, and 11 400 to 13 700 mg kg^?1 total Zn. Total concentrations in soil samples were 15 to 86 mg kg^?1 Cd, 35 to 1 620 mg kg^?1 Pb, and 99 to 18 500 mg kg^?1 Zn; and, DTPA extractable concentrations ranged from 0.6 to 10 mg kg^?1 Cd, 7.8 to 68 mg kg^?1 Pb, and 33 to 715 mg kg^?1 Zn. Samples were sequentially extracted to approximate the proportions of the metals in the sulfide, carbonate, organic, sorbed, and exchangeable fractions. For Zn and Cd, concentrations were greatest in the sulfide fraction followed by carbonate, organic, sorbed, and exchangeable. Lead followed the same pattern, except higher concentrations were observed in the sorbed than the organic fractions.     

Mobility of Cd and Zn in polluted and unpolluted Spodosols

Leaching of Cd and Zn in polluted acid, well‐drained soils is a critical pathway for groundwater pollution. Models predicting future groundwater contamination with these metals have rarely been validated at the field scale. Spodosol profiles (pH 3.2–4.5) were sampled in an unpolluted (reference) field and in a field contaminated with Cd and Zn through atmospheric deposition near a zinc smelter. Average metal concentrations in the upper horizons were 0.2 mg Cd kg^?1 and 9 mg Zn kg^?1 in the unpolluted field, and 0.8 mg Cd kg^?1 and 71 mg Zn kg^?1 in the contaminated field. Isotopic dilution was used to measure the labile concentration of Cd and Zn, and the metal transport was modelled using measured sorption parameters that describe the distribution between the labile metal pool (instead of the total metal pool) and the solution phase obtained by centrifugation. Solutions were also collected by wick samplers in two polluted and one unpolluted profile at a depth of 70 cm. Concentrations in these solutions were in the order of 15 µg Cd litre^?1 and 0.8 mg Zn litre^?1 for the polluted profiles, and 1 µg Cd litre^?1 and 0.04 mg Zn litre^?1 for the unpolluted profile. The concentrations in these solutions agreed well with those in soil solutions obtained by centrifugation, which supported the use of the local equilibrium assumption (LEA). Present‐day Cd profiles in the polluted field were calculated with the LEA, based on the emission history of the nearby smelter and taking spatial variability into account. Observed and predicted depth profiles agreed reasonably well, but total Cd concentrations in the topsoil were generally underestimated by the model. This may be attributed to the presence of non‐labile Cd in the atmospheric deposition, which was not accounted for in the retrospective modelling. The large concentrations of non‐labile Zn in the topsoil of the polluted field were also indicative that metals in the atmospheric deposition were (partly) in a sparingly soluble form, and that release of these non‐labile metals is a slow process. The presence of non‐labile metals should be taken into account when evaluating metal mobility or predicting their transport.     

Soil affects on the cadmium and zinc contents of Chinese cabbage in Yunnan Province,China

Chinese cabbage and surface soil samples (0–20 cm) from a periurban market garden in Yunnan Province (P.R. China) were collected to determine variations of cadmium (Cd) and zinc (Zn) contents in Chinese cabbage and the influence of soil factors. Mean Cd content was 0.49 mg kg^?1 dry materials (DM) in Chinese cabbage, ranging between 0.23 and 1.34 mg kg^?1 DM (n = 21 samples). Mean Zn content was 51.2 mg kg^?1 DM, ranging from 34.9 to 157.5 mg kg^?1 DM (n = 21 samples). The soil factors best predicting Chinese cabbage Cd and Zn contents were total and available Cd and Zn contents and cation exchange capacity (CEC). Soil samples and corresponding Chinese cabbage samples were divided into two groups: soils with low pH (<6.5, n = 10) and soils with high pH (>6.5, n = 11). Positive correlation between CEC with pH > 6.5 and Cd and Zn contents in Chinese cabbage were observed. Available trace element contents and CEC explained 77% and 69% of variation of Cd and Zn contents in Chinese cabbage, respectively. AEC (enrichment coefficient related to trace element availability) and BCF (bioaccumulation factors) could be used to understand Cd and Zn accumulation in Chinese cabbage.