Comparison of Heavy Metal Adsorptions by Thai Kaolin and Ballclay

The adsorption characteristics of heavy metals: cadmium(II), chromium(III), copper(II), nickel(II), lead(II), and zinc(II) ions by kaolin (kaolinite) and ballclay (illite) from Thailand were studied. This research was focussed on the pH, adsorption isotherms of single-metal solutions at 30–60 °C by batch experiments, and on ion selectivityin mixed and binary combination solutions. It was found that, except Ni, metal adsorption increased with increased pH of the solutions and their adsorption followed both Langmuir and Freundlich isotherms. Adsorption of metals in the mixture solutions by kaolin was: Cr > Zn > Cu ≈ Cd ≈ Ni > Pb, and for ballclay was: Cr > Zn > Cu > Cd ≈ Pb > Ni. The adsorption of metals was endothermic, with the exception of Cd, Pb and Zn for kaolin, Cu and Zn for ballclay. Kaolin and ballclay exhibited relatively hard Lewis base adsorption site. The presence of other metals may reduce or promote the adsorption of heavy metals. The presence of Cr³⁺ induced the greatest reduction of metal adsorptiononto kaolin, as did the presence of Cu²⁺ for ballclay.     

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.     

Chemical Characterization of Cow Manure and Poultry Manure after Composting with Privet and Cypress Residues

ABSTRACT

Investigating available nutrients and non-essential elements in manures is important for safe management of animal and plant waste. Therefore, this study was carried out to chemically characterize cow manure (CM) and poultry manure (PM) after co-composting with privet and cypress residues. Results showed that heavy metals concentrations in manures varied as Fe > Zn > Mn > Cu > Ni > Pb > Cd. Addition of privet and cypress residues to both manures altered the extractability of heavy metals after composting. Higher concentrations of heavy metals were observed in manures at 1:0 ratio while lowest was noted in both CM and PM composted with plant residues at 1:2 ratio. Total K, Ca, and Mg significantly increased when CM and PM were co-composted with privet and cypress residues. There was an increase in the P content in co-composted CM with privet residual application whereas a reduction in total P was noticed with the addition of cypress plant residues in both manures. Manures amended with plant waste reduced N content. Both CM and PM retained higher NO₃ content without plant residues.     

Influence of pH on the release and chemical fractionation of heavy metals in sediment from a suburban drainage stream in an arid mine-based oasis

Purpose

The objectives of this study were to explore the influences of pH on the release of Cu, Zn, Cd, Pb, Ni, and Cr in sediments derived from the upstream, middle, and downstream reaches of Dongdagou stream in Gansu Province, Northwest China, and to examine the fractionation changes of heavy metals in the sediments after reaching their release equilibrium under different pH conditions.

Materials and methods

Sediment samples were obtained using a stainless steel grab sampler to collect the uppermost 10 cm of sediment from the channel bed. The pH-dependent release experiment was conducted in the solid-to-liquid ratio of 1:20 at different pH values (2, 4, 6, 8, 10, and 12) at room temperature. The total Cu, Zn, Cd, Pb, Ni, and Cr concentrations in the sediments were digested using an acid digestion mixture (HNO₃ + HF + HClO₄) in an open system. Metal fractionation of selected sediments was obtained using the Tessier sequential extraction procedure. Heavy metal concentrations in the samples were determined using atomic absorption spectrophotometry.

Results and discussion

The mean concentrations of heavy metals in sediments decreased in the following order: Zn (1676.67 mg kg^?1) > Pb (528.65 mg kg^?1) > Cu (391.34 mg kg^?1) > Cr (53.48 mg kg^?1) > Ni (34.27 mg kg^?1) > Cd (11.53 mg kg^?1). Overall, the solubility of Cu, Zn, Cd, Pb, and Ni decreased with increasing pH, and they were strongly released at pH 2. Moreover, the solubility of Cr increased with increasing pH, and its release was highest at pH 12. After reaching the release equilibrium of heavy metals under different pH conditions, the percentages of organic Cu, Zn, Cd, and Fe-Mn oxyhydroxide Pb decreased, compared to their initial fractions. The residual fractions of Ni and Cr were dominant, regardless of pH.

Conclusions

The average concentrations of Cu, Zn, Cd, and Pb in sediments were highly elevated compared with the soil background values in Gansu Province, China. The results of this pH-dependent release experiment showed that the release behaviors of Cu, Zn, Pb, and Cr followed an asymmetric V-shaped pattern, whereas Cd and Ni followed an irregular L-shaped pattern. The changes in the release of heavy metals in sediments were related to their redistribution between chemical fractionations.

     

Adsorption isotherms of some heavy metals under conditions of their competitive adsorption onto highly calcareous soils of southern Iran

Recently, application of sewage sludge or effluents resulted in raising the concentrations of some heavy metals in some agricultural soils of Iran. Experiments were conducted to evaluate the competitive adsorption of lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) on six calcareous soils. Adsorption characteristics were evaluated by equilibration of 1 g of each soil sample with 20 ml of 0, 10, 20, 30, 40, 50, 100, or 200 mg L^?1 of their nitrate solutions and 0.01 M NaNO₃ as background electrolyte. Furthermore, solid/liquid distribution coefficients (K_d) of studied metals, as an index of soil capacity to resist a change of the soil solution concentration, were calculated. Results indicated that amounts of adsorbed Pb, Cu, Zn, and Cd increased with increase in their concentrations in the contact solutions, but this trend was more pronounced for Pb and Cu than the others. For all studied soils and metals, Langmuir equation described the adsorption behavior fairly well. Furthermore, Langmuir and Freundlich equation parameters were positively correlated to cation exchange capacity (CEC) and smectite contents; whereas, they were negatively correlated to sand content. Considering K_d values, the selectivity sequence of the metal adsorption was Pb > Cu > Zn > Cd. Therefore, the risk of leaching and also plant uptake of Zn and Cd will be higher as compared to those of the other elements.     

The transfer of heavy metals to barley plants from soils amended with sewage sludge with different heavy metal burdens

Purpose

Our main aim objective was to evaluate the transfer of Cd, Cr, Cu, Ni, Pb and Zn to barley (Hordeum vulgare) grown in various soils previously amended with two sewage sludges containing different concentrations of heavy metals. This allowed us to examine the transfer of heavv metals to barley roots and shoots and the occurrence of restriction mechanisms as function of soil type and for different heavy metal concentration scenarios.

Material and methods

A greenhouse experiment was performed to evaluate the transfer of heavy metals to barley grown in 36 agricultural soils from different parts of Spain previously amended with a single dose (equivalent to 50 t dry weight ha^?1) of two sewage sludges with contrasting levels of heavy metals (common and spiked sludge: CS and SS).

Results and discussion

In soils amended with CS, heavy metals were transferred to roots in the order (mean values of the bio-concentration ratio in roots, BCF_Roots, in brackets): Cu (2.4)?~?Ni (2.3)?>?Cd (2.1)?>?Zn (1.8)?>?Cr (0.7)?~?Pb (0.6); similar values were found for the soils amended with SS. The mean values of the soil-to-shoot ratio were: Cd (0.44)?~?Zn (0.39)?~?Cu (0.39)?>?Cr (0.20)?>?Ni (0.09)?>?Pb (0.01) for CS-amended soils; Zn (0.24)?>?Cu (0.15)?~?Cd (0.14)?>?Ni (0.05)?~?Cr (0.03)?>?Pb (0.006) for SS-amended soils. Heavy metals were transferred from roots to shoots in the following order (mean values of the ratio concentration of heavy metals in shoots to roots in brackets): Cr (0.33)?>?Zn (0.24)?~?Cd (0.22)?>?Cu (0.19)?>?Ni (0.04)?>?Pb (0.02) for CS-amended soils; Zn (0.14)?>?Cd (0.09)?~?Cu (0.08)?>?Cr (0.05)?>?Ni (0.02)?~?Pb (0.010) for SS-amended soils.

Conclusions

Soils weakly restricted the mobility of heavy metals to roots, plant physiology restricted the transfer of heavy metals from roots to shoots, observing further restriction at high heavy metal loadings, and the transfer of Cd, Cu and Zn from soils to shoots was greater than for Cr, Ni and Pb. Stepwise multiple linear regressions revealed that soils with high sand content allowed greater soil-plant transfer of Cr, Cu, Pb and Zn. For Cd and Ni, soils with low pH and soil organic C, respectively, posed the highest risk.     

Heavy metal distribution in different soil aggregate size classes from restored brackish marsh,oil exploitation zone,and tidal mud flat of the Yellow River Delta

Purpose

Heavy metal distribution in soils is affected by soil aggregate fractionation. This study aimed to demons trate the aggregate-associated heavy metal concentrations and fractionations in “sandy,” “normal,” and “mud” soils from the restored brackish tidal marsh, oil exploitation zone, and tidal mudflat of the Yellow River Delta (YRD), China.

Materials and methods

Soil samples were sieved into the aggregates of >2, 0.25–2, 0.053–0.25, and <0.053 mm to determine the concentrations of exchangeable (F1), carbonate-bound (F2), reducible (F3), organic-bound (F4), and residual fraction (F5) of Cd, Cr, Cu, Ni, Pb, and Zn.

Results and discussion

The 0.25–2 mm aggregates presented the highest concentrations but the lowest mass loadings (4.23–12.18 %) for most metal fractions due to low percentages of 0.25–2 mm aggregates (1.85–3.12 %) in soils. Aggregates <0.053 mm took majority mass loadings of metals in sandy and normal soils (62.04–86.95 %). Most soil aggregates had residual Cr, Cu, Ni, Zn, and reducible Cd, Pb dominated in the total Cd, Cr, Cu, Ni, Pb, and Zn concentrations. Sandy soil contained relatively high F4, especially of Cu (F4) in 0.25–2 mm aggregates (10.22 mg kg^?1), which may relate to significantly high organic carbon contents (23.92 g kg^?1, P?<?0.05). Normal soil had the highest total concentrations of metals, especially of Cu, Ni, and Pb, which was attributed to the high F3 and F5 in the <0.053 mm aggregates. Although mud soil showed low total concentrations of heavy metals, the relatively high concentrations of bioavailable Cd and Cu resulted from the relatively high Cd (F2) and Cu (F2) in the >2 mm aggregates indicated contribution of carbonates to soil aggregation and metal adsorption in tidal mud flat.

Conclusions

Soil type and aggregate distribution were important factors controlling heavy metal concentration and fractionation in YRD wetland soil. Compared with mud soil, normal soil contained increased concentrations of F5 and F3 of metals in the 0.053–0.25 mm aggregate, and sandy soil contained increased concentrations of bioavailable and total Cr, Ni, and Zn with great contribution of mass loadings in the <0.053 mm aggregate. The results of this study suggested that oil exploitation and wetland restoration activities may influence the retention characteristics of heavy metals in tidal soils through variation of soil type and aggregate fractions.

     

Pollution assessment and spatial variation of soil heavy metals in Lixia River Region of Eastern China

Purpose

The effect of soil heavy metals on crops and human health is an important research topic in some fields (Agriculture, Ecology et al.). In this paper, the objective is to understand the pollution status and spatial variability of soil heavy metals in this study area. These results can help decision-makers apportion possible soil heavy metal sources and formulate pollution control policies, effective soil remediation, and management strategies.

Materials and methods

A total of 212 topsoil samples (0–20 cm) were collected and analyzed for eight heavy metals (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) from agricultural areas of Yingbao County in Lixia River Region of Eastern China, by using four indices (pollution index (PI), Nemerow pollution index (PI_N), index of geo-accumulation (I _geo), E _i /risk index (RI)) and cluster analysis to assess pollution level and ecological risk level of soil heavy metals and combining with geostatistics to analyze the concentration change of heavy metals in soils. GS+ software was used to analyze the spatial variation of soil heavy metals, and the semi-variogram model is the main tool to calculate the spatial variability and provide the input parameters for the spatial interpolation of kriging. Arcgis software was used to draw the spatial distribution of soil heavy metals.

Results and discussion

The result indicated that the eight heavy metals in soils of this area had moderate variations, with CVs ranging from 23.51 to 64.37 %. Single pollution index and Nemerow pollution index showed that about 2.7 and 1.36 % of soil sampling sites were moderately polluted by Cd and Zn, respectively. The pollution level of soil heavy metals decreased in the order of Cd?>?Zn?>?Pb?>?As?>?Cu?>?Cr?>?Ni?>?Hg. The I _geo values of heavy metals in this area decreased in the order of Zn?>?Cd?>?As?>?Pb?>?Cu?>?Cr?>?Hg?>?Ni. According to the E _i index, except Cd that was in the moderate ecological risk status, other heavy metals in soils were in the light ecological risk status, and the level of potential ecological risk (RI) of soil sampling sites of the whole area was light.

Conclusions

The results of four indices and the analysis of spatial variation indicated that the contents of Cd and Zn were contributed mainly by anthropogenic activities and located in the south-east of this study area. However, the contents of Hg, As, Cu, Pb, Cr, and Ni in soils were primarily influenced by soil parent materials.

     

Assessing the Influence of Different Atmospheric and Soil Mercury Concentrations on Foliar Mercury Concentrations in a Controlled Environment

This study vividly presents results from a seasonal particulate matter measurement campaign conducted at world’s largest ship-breaking yard i.e., Alang-Sosiya (Gujarat, India) at six locations and a reference station at Gopnath which is 30 km south of this ship-breaking yard. The collected suspended particulate matter (SPM) 24-h samples were critically analyzed for heavy metals (Pb, Cd, Co, Ni, Cr, Mn, Fe, Cu, Zn). The average concentration of SPM within the ship-breaking yard during the investigation was 287.5 ± 20.4 μg m^?3 and at reference station it was 111.13 ± 5.81 μg m^?3. These values are found to be in excess of the permitted national standards. The levels of heavy metals at Alang-Sosiya are very high as compared to US EPA and WHO guidelines. The mean concentrations of all metals are in the order: Fe >>Zn >Cu > Mn > Cd >Pb > Co >Ni >Cr. The results on enrichment factors (EF) suggest that most of the metals in the ship-breaking yard exhibit EF values of near or above 100 which must have been comprehensively affected by ship-breaking activities. Metal data was used to evaluate the role of spatial factors on their distribution characteristics. Thereafter, factor analysis was carried out to identify the main components liable for the variance of the data set.     

Heavy Metal Accumulation in Soil Amended with Roadside Pond Sediment and Uptake by Rice (Oryza sativa L.)

The effect of addition of roadside pond sediments on heavy metal contents of flooded rice paddies was studied to investigate the yield of rice and uptake of heavy metal by rice straw and grain. Sequential extraction of heavy metals on sediments shows that the percentage contribution of metals in the labile fraction follows the order lead (Pb, 48%) > copper (Cu, 42%) > zinc (Zn, 31%) > cadmium (Cd, 16%) > chromium (Cr, 9%) > nickel (Ni, 6%). The risk assessment code (RAC) for pond sediment revealed that Cr and Ni were found in the low-risk zone, Zn and Cd in the medium-risk zone, and Cu and Pb in the high-risk zone. However, though the heavy metal concentration in rice grain does not exceed the range acceptable for human consumption, it still represents a significant additional source of heavy metals in the diet. The addition of pond sediment significantly increased the rice yield over control. Therefore, pond sediment would be a valuable resource for agriculture if it is properly used.     

Adsorption of Heavy Metals on Mixed Fe-Al Oxides in the Absence or Presence of Organic Ligands

A study was carried out on the adsorption of Co²⁺, Cu²⁺, Pb²⁺, and Zn²⁺ ions on mixed Fe-Al oxides inthe absence or presence of increasing concentrations of oxalate or tartrate. Mixed Fe-Al oxides were prepared by precipitating at pH 5.5 mixtures of Fe and Al ions at initial Fe/Al molar ratios (R) of 0, 1, 2, 4, 10 and ∞ (R0, R1, R2, R4, R10 and R∞).The oxides aged 7 days at 20 °C or 30 days at 50 °C showed different chemical composition and physico-chemical and mineralogical properties. All the mixed Fe-Al oxides showed presence of poorly crystalline materials (ferrihydrite) even after prolonged aging. The heavy metals wereselectively adsorbed on the oxides. For all the precipitates aged7 days at 20 °C, the selectivity sequence wasPb²⁺> Cu²⁺ > Zn²⁺ > Co²⁺, but the pH at which 50% ofeach cation was adsorbed (pH₅₀) was different from sample tosample. It was found that usually the greater the amounts of Fe in Fe-Al gels the lower the pH₅₀ for each metal, but the adsorption of a heavy metal was not linearly related to Fe content. The pH₅₀ usually did not change significantly when the oxides were aged 30 days at 50 °C. Competitive adsorption of Cu and Zn on ferrihydrite (R∞) showed thatCu strongly prevented Zn adsorption even at an initial Zn/Cu molar ratio of 8, whereas Cu sorption was not inhibited. In thepresence of oxalate (OX) or tartrate (TR) (organic ligand/Pb molar ratio (r_L) from 0 to 7) the quantities of Pb adsorbedon the Fe-Al oxides usually increased with increasing r_L. The adsorption increase of Pb was particularly high on the oxidesricher in Fe (R4-R∞), but a significant increase was also observed on R0-R2 samples. The adsorption of Pb on the oxides hasbeen influenced not only by the presence and concentration of organic ligands but also by the sequence of addition of Pb and tartrate on the sorbents. It has been ascertained that on each oxide the greater amounts of Pb were adsorbed when tartrate wasadded before Pb and usually according to the following sequence: Tr before Pb > Pb before Tr > Pb + Tr > Pb.     

Comparison of single and competitive metal adsorption by pepper stem biochar

Carbon-based sorbents have been proven to be cost-effective in removing pollutants from wastewater. Biochar from plant residue and agricultural waste is an emerging treatment technology. However, there is a limited number of studies on the effects of various biochar sources on metal adsorption. The aim of this study was using batch experiment to evaluate the adsorption of heavy metals in single- and multi-metal conditions onto pepper stem biochar. The maximum adsorption capacities (mg g^?1) of metals by pepper stem biochar were in the order of Pb (131) ? Cr (76) > Cd (67) > Cu (48) > Zn (31) in the single-metal adsorption isotherm and Pb (91) ? Cu (39) > Cr (29) > Zn (20) > Cd (13) in the multi-metal adsorption isotherm. Lead was the most retained cation, whereas Cr and Cd could be easily exchanged and substituted by other metals (Pb or Cu). For pepper stem biochar, the Langmuir model provided a slightly better fit than the Freundlich model. Results from the batch experiments show that competitive adsorption among metals increases the mobility of these metals. Particularly, Cd adsorption capacity in multi-metal conditions was significantly reduced. Overall, the results suggested that competitive adsorption studies are necessary for obtaining an accurate estimation of the metal retention capacity of pepper stem biochar in natural environments.     

Anthropogenic environmental impact in the Mediterranean coastal area of Koper/Capodistria,Slovenia

Purpose

Heavy metal content in soils could be a consequence of geogenic and different anthropogenic sources. In ancient times, soils in the Mediterranean region were affected by agriculture and viticulture, whereas more recently, industry and traffic might contribute more to their pollution. The aim of the study is to determine the extent of multisource heavy metal pollution in soils within the Koper area.

Materials and methods

Along the northern Adriatic Sea coast, around the port city of Koper/Capodistria, 24 topsoil samples were collected; sets of six samples representing four possible pollution sources: intensive agriculture, viticulture, port activities and industry. The parent material of the soil is mainly derived from the Eocene flysch weathered marls and calcarenites and the soil types are eutric. The chemical composition of the samples was determined by ICP-ES for oxides and several minor elements and by ICP-MS for heavy metals. The mineral composition of the selected samples was checked using X-ray powder diffraction. Different statistical analyses were performed on the normally distributed data.

Results and discussion

The mean concentrations of all samples are: Cr 215 mg kg^?1, Ni 81 mg kg^?1, Zn 67 mg kg^?1, Cu 44 mg kg^?1 and Pb and Co 18 mg kg^?1. The ANOVA showed significant differences only in CaO, C/TOT, P₂O₅, Co and Pb between those locations within reach of the different contamination sources. The observed average values of heavy metals are well below Slovenia’s Directive limit for Cu, Pb and Zn, close to but not above it for Co and above the action value for Cr and Ni. According to Igeo, soils from all the sampling locations are uncontaminated with Co, Ni and Pb, and uncontaminated to moderately contaminated with Cu and Zn at one port location, and with Cr at all locations.

Conclusions

The very high Cr and Ni levels could still be geogenic because soils developed on Eocene flysch rocks are enriched in both metals. Cr and Ni are not correlated because of their different levels of sorption and retention in carbonate soils. Cr was retained and concentrated in the sand fraction but Ni has been mobilised in solution. The only serious threat to the environment seems to be an illegal waste dumping area near the port.     

Retention of Cd, Cu, Pb and Zn by Wood Ash, Lime and Fume Dust

Heavy metals are of interest due to their deleterious impacts on both human and ecosystem health. This study investigated the effectiveness of wood ash in immobilizing the heavy metals Pb, Cd, Cu and Zn from aqueous solutions. The effects of initial metal concentrations, solution pH, ash dose and reaction time on metal sorption, as well as the metal sorption mechanisms were studied. To investigate the effect of initial metal concentrations, solutions containing Cd, Zn (25, 50, 75, 100 or 125 mg L^?1), Cu (25, 50, 75, 100, 125, 150 or 175 mg L^?1) or Pb (250, 500, 750, 1000, 1250, or 1500 mg L^?1) were reacted with 10 g L^?1 ash for two hours. For the effect of pH, solutions containing 100 mg L^?1 of Cd, Cu or Zn or 1500 mg L^?1 of Pb were reacted with 15 g L^?1 ash over a pH range of 4 to 7. The wood ash was effective in immobilizing the four metals with a sorption range of 41–100 %. The amounts of metals retained by the ash followed the order of Pb > Cu > Cd > Zn. As expected, absolute metal retention increased with increasing initial metal concentrations, solution pH and ash dose. Metal retention by the ash exhibited a two-phase step: an initial rapid uptake of the metal followed by a period of relatively slow removal of metal from solution. Metal retention by the ash could be described by the Langmuir and Freundlich isotherms, with the latter providing a better fit for the data. Dissolution of calcite /gypsum minerals and precipitation of metal carbonate/sulfate like minerals were probably responsible for metal immobilization by the ash in addition to adsorption.     

Estimating Sorption Affinities of Heavy Metals on Humic Acid and Silica using a Constant Capacitance Model

The adsorption of heavy metals [cadmium (Cd ²⁺), cobalt (Co²⁺), nickel (Ni²⁺), zinc (Zn²⁺), and lead (Pb)] and calcium (Ca²⁺) on humic acid and silica were investigated to understand the adsorptive selectivities of heavy metals on the constituents of soil. The experiments for the adsorption of Cd and Pb were carried out in a 0.1 mol L^?1 (M) sodium nitrate (NaNO₃) background solution, whereas those for the other metals were done in a 0.1 M sodium chloride (NaCl) solution. The adsorptive affinities of the metal ions on the humic acid and silica were ranked by the intrinsic surface complexation constants [K _m ¹(int)] that were calculated approximately from the adsorptive data using a constant capacitance model. The log [K _m ¹(int)] values of the metals were in the order Zn²⁺(?2.29) > Cd²⁺(?2.41) > Co²⁺(?2.74) > Ni²⁺(?2.92) ?> Ca²⁺ (?3.33) for the humic acid and Zn²⁺(?4.23) > Cd²⁺(?4.49) > Ni²⁺(?4.51) ? Co²⁺ (?5.99) > Ca²⁺(?6.37) for silica.     

Heavy Metals in Freshly Deposited Stream Sediments of Rivers Associated with Urbanisation of the Ganga Plain,India

Freshly deposited stream sediments from six urban centres of the Ganga Plain were collected and analysed for heavy metals to obtain a general scenery of sediment quality. The concentrations of heavy metals varied within a wide range for Cr (115–817), Mn (440–1 750), Fe (28 700–61 100), Co (11.7–29.0), Ni (35–538), Cu (33–1 204), Zn (90–1 974), Pb (14–856) and Cd (0.14–114.8) in mg kg^-1. Metal enrichment factors for the stream sediments were <1.5 for Mn, Fe and Co; 1.5–4.1 for Cr, Ni, Cu, Zn and Pb; and 34 for Cd. The anthropogenic source in metals concentrations contributes to 59% Cr, 49% Cu, 52% Zn, 51% Pb and 77% Cd. High positive correlation between concentrations of Cr/Ni, Cr/Cu, Cr/Zn, Ni/Zn, Ni/Cu, Cu/Zn, Cu/Cd, Cu/Pb, Fe/Co, Mn/Co, Zn/Cd, Zn/Pb and Cd/Pb indicate either their common urban origin or their common sink in the stream sediments. The binding capacity of selected metals to sediment carbon and sulphur decreases in order of Zn > Cu > Cr > Ni and Cu > Zn > Cr > Ni, respectively. Stream sediments from Lucknow, Kanpur, Delhi and Agra urban centres have been classified by the proposed Sediment Pollution Index as highly polluted to dangerous sediments. Heavy metal analysis in the <20-μm-fraction of stream sediments appears to be an adequate method for the environmental assessment of urbanisation activities on alluvial rivers. The present study reveals that urban centres act as sources of Cr, Ni, Cu, Zn, Pb and Cd and cause metallic sediment pollution in rivers of the Ganga Plain.     

Adsorption isotherms of copper and zinc in clay minerals of calcareous soils and their effects on X-ray diffraction

Reactions of elements with the water mineral interface are important and affect their bioavailability and transportation within soil. Effects of metal sorption on X-ray-diffraction (XRD-photographs) of clay minerals have been not studied. Therefore, sorption experiments were done on clay fractions of two calcareous soils using 12 concentrations of 0–2000 mg L^?1 Zn(NO₃)₂ and Cu(NO₃)₂. Langmuir and Freundlich isotherms’ coefficients were determined. After sorption, XRD-diffraction were prepared and compared with those of initial samples. Langmuir (R² = 0.996–0.999 and SE = 0.001–0.002) and Freundlich equation were the best-model for Zn and Cu-sorption, respectively. Sorption energy was higher for Zn than Cu, whereas the maximum concentration of sorbed-Cu was higher than that of Zn. Distribution coefficient (K_d) of Cu were more (threefold) than that of Zn. The K_d values representing the slope of Freundlich isotherms decreased according to linear regression equations (R² = 0.72–0.91) as the equilibrium concentrations of metals increased. No significant differences were observed among XRD-photographs of applied concentrations (some negligible differences were found in position/sharpness of peaks). Dry-XRD-method resulted in omission of intensity peaks at 2θ which may interfere in recognition of clays that show a maximum intensity >1.4 nm in the mentioned 2θ. Zinc can become more leachable especially in Shekarbani-soil-series, whereas, Cu highly adsorb on clay minerals and can show less tendency to transportation.     

Standards for the contents of heavy metals and metalloids in soils

In line with the present-day ecological and toxicological data obtained by Dutch ecologists, heavy metals/metalloids form the following succession according to their hazard degree in soils: Se > Tl > Sb > Cd > V > Hg > Ni > Cu > Cr > As > Ba. This sequence substantially differs from the succession of heavy elements presented in the general toxicological GOST (State Norms and Standards) 17.4.1.02-8, which considers As, Cd, Hg, Se, Pb, and Zn to be strongly hazardous elements, whereas Co, Ni, Mo, Sb, and Cr to be moderately hazardous. As compared to the general toxicological approach, the hazard of lead, zinc, and cobalt is lower in soils, and that of vanadium, antimony, and barium is higher. The new sequence also differs from that of the metal hazard in soils according to the Russian standard on the maximal permissible concentration of mobile metal forms (MPC_mob): Cu > Ni > Co > Cr > Zn. Neither an MPC_mob nor an APC_mob has been adopted for strongly hazardous thallium, selenium, and vanadium in Russia. The content of heavy metals in contaminated soils is very unevenly studied: 11 of them, i.e., Cu, Zn, Pb, Ni, Cd, Cr, As, Mn, Co, Hg, and Se, are better known, while the rest, much worse, although there are dangerous elements (Ba, V, Tl) among them.     

工业废弃地多金属污染土壤组合淋洗修复技术研究

采用批量淋洗实验方法,对比了采用人工螯合剂乙二胺四乙酸二钠盐(EDTA-Na2)和天然有机酸草酸(oxalic acid,OX)对工业废弃地污染土壤中重金属的去除效果,并采用不同浓度草酸和EDTA组合的两步淋洗法研究多金属污染土壤的最佳淋洗方式。结果表明,EDTA淋洗剂对土壤中Zn、Pb、Cu、Ni去除效果较好,而对Cr去除效果较差,实验条件下,EDTA对金属的去除率并未随着浓度增加而增加;相反,草酸对Cr去除效果较好,且去除率随着淋洗剂浓度的增加而增加,而对Zn、Cu、Ni的去除效果随着淋洗剂浓度增加而降低,对Pb的去除率非常低;采用先以0.20 mol L-1草酸提取2 h,再以0.01 mol L-1EDTA提取2 h的两步淋洗法可以达到对多金属同时去除,且对Zn、Cu、Cr、Ni的去除率明显高于单用草酸和EDTA,总去除率分别为Zn 75.21%、Pb 21.30%、Cu 59.81%、Cr 60.72%和Ni 62.10%,更为有意义的是两步淋洗法对非残渣态金属去除效果分别高达Zn 91.93%、Pb 57.75%、Cu 75.33%、Cr 73.94%、Ni 77.99%。利用不同化学淋洗剂对金属去除能力的差异进行组合的多步淋洗法是一种较为高效的去除工业废弃地污染土壤中重金属的化学淋洗修复方法。