Comparative Effects of Biochar,Slag and Ferrous–Mn Ore on Lead and Cadmium Immobilization in Soil

A variety of remediation approaches have been applied to the heavy metals-contaminated soils, however, the immobilization of metals in co-contaminated soils still not cleared. Therefore, an incubation study was conducted to evaluate the instantaneous effects of different concentrations of biochar (BC), slag (SL) and Fe–Mn ore (FMO) on immobilization of Pb and Cd through the Toxicity Characteristic Leaching Procedure (TCLP) by following the the European Community Bureau of Reference (BCR), CaCl₂ and NH₄NO₃. The sequential extraction of BCR showed decrease in acid soluble fractions, while the residual proportions of Pb and Cd were enhanced with increasing concentrations of SL and BC. Addition of BC significantly lowered the extractable fractions of both metals by TCLP, NH₄NO₃ and CaCl₂ as compared to SL and FMO. Among all amendments, BC incorporation into co-contaminated soil offered promising results for Pb and Cd immobilization. Overall, all amendments showed positive and long-term impact on the reclamation of co-contaminated soil with heavy metals and could deserve advance monitoring studies on a field scale.     

Efficiency of C3 and C4 Plant Derived-Biochar for Cd Mobility,Nutrient Cycling and Microbial Biomass in Contaminated Soil

Biochar is considered a novel soil amendment to reduce metal mobility, but its influence on soil chemical and biochemical properties is not fully understood. In the present study, biochar derived from rice straw (RSB), rice hull (RHB), and maize stover (MSB) was used to evaluate comparative efficiency on Cd mobility and soil biochemical properties. Ammonium nitrate extractable Cd significantly decreased among all the applied biochar types and application rates. The European Community Bureau of Reference (BCR) technique showed significant decrease in acid-soluble Cd by 24%–32%, 19%–23%, and 22%–27% for RSB, RHB, and MSB, respectively at the 1.5% and 3% rate. However, the concentration of Cd in the residual increased by 38%, 35% and 36% for RSB, RHB and MSB, respectively at a 3% application rate. Soil microbial biomass (C and N) and inorganic nitrogen forms (NH₄ and NO₃) significantly increased among all biochar applications. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization, increasing soil nutrient availability, and enhancing soil microbial biomass.     

Heavy Metal Contamination of Arable Soil and Corn Plant in the Vicinity of a Zinc Smelting Factory and Stabilization by Liming

The heavy metal contamination in soils and cultivated corn plants affected by zinc smelting activities in the vicinity of a zinc smelting factory in Korea was studied. Soils and corn plants were sampled at the harvesting stage and analyzed for cadmium (Cd) and zinc (Zn) concentration, as well as Cd and Zn fraction and other chemical properties of soils. Cd and Zn were highly accumulated in the surface soils (0–20 cm), at levels higher than the Korean warning criteria (Cd, 1.5; Zn, 300 mg kg⁻¹), with corresponding mean values of 1.7 and 407 mg kg⁻¹, respectively, but these metals decreased significantly with increasing soil depth and distance from the factory, implying that contaminants may come from the factory through aerosol dynamics (Hong et al., Kor J Environ Agr 26(3):204–209, 2007a; Environ Contam Toxicol 52:496–502, 2007b) and not from geological sources. The leaf part had higher Cd and Zn concentrations, with values of 9.5 and 1733 mg kg⁻¹, compared to the stem (1.6 and 547 mg kg⁻¹) and grain (0.18 and 61 mg kg⁻¹) parts, respectively. Cd and Zn were higher in the oxidizable fraction, at 38.5% and 46.9% of the total Cd (2.6 mg kg⁻¹) and Zn (407 mg kg⁻¹), but the exchangeable + acidic fraction of Cd and Zn as the bioavailable phases was low, 0.2 and 50 mg kg⁻¹, respectively. To study the reduction of plant Cd and Zn uptake by liming, radish (Raphanus sativa L.) was cultivated in one representative field among the sites investigated, and Ca(OH)₂ was applied at rates of 0, 2, 4, and 8 mg ha⁻¹. Plant Cd and Zn concentrations and NH₄OAc extractable Cd and Zn concentrations of soil decreased significantly with increasing Ca(OH)₂ rate, since it markedly increases the cation exchange capacity of soil induced by increased pH. As a result, liming in this kind of soil could be an effective countermeasure in reducing the phytoextractability of Cd and Zn.     

Kinetics of metal fixation in soils: measurement and modeling by isotopic dilution

The bioavailability of metal contaminants in soils varies widely, depending on soil characteristics and the source of the contaminant. As a consequence, site-specific risk assessment requires accurate prediction of the bioavailable (or labile) fraction of soil metal. Moreover, metals in soil are subject to time-dependent processes, which affect their bioavailability and thereby complicate the prediction of future risk. The aim of the present study was to describe the development of simple, readily applicable models for the time-dependent changes in lability of Cd and Zn in soils. We present data showing the time-dependent behavior of radiolabile and soil solution concentrations of Cd and Zn during an incubation study over a period of 813 d in 23 diverse soils. The data are used to parameterize candidate models of metal fixation in soils designed to be readily applicable and therefore relevant to risk assessment. We conclude that the final extent of metal fixation increases with pH and generally is greater for Zn than for Cd; however, the rate of fixation is independent of pH and equivalent to a half-time to equilibrium of 29 and 89 d for Cd and Zn, respectively. It is possible that longer-term processes occur, especially for Zn, but these could not be detected in the present study.     

Biochemical evaluation of urban soils (in case of Kemerovo)

The study has revealed common changes in the chemical composition of soils in the town of Kemerovo. Under urban conditions, there is a reduction in pH, an increase in the carbonate properties of soil mineral part and in the content of exchange cations (Ca2+, K+, Na+) in the soil absorptive complex, a decrease in the level of gross elements (N, P, K), as well as accumulation of heavy metals (Pb, Cd, Zn, Ni, Mn, Co, Fe, Cr) and sulfates. The above changes are determined by the level of a technogenic load; and they are more pronounced in the soils located along the main roads, particularly in the districts (Kirovsky, Rudnichnyi, and Zavodskoy) with heavy traffic of freight transport.     

Kinetics of zinc and cadmium release in freshly contaminated soils

The kinetics of metal release from the solid phase to solution was measured on two sets of 14 freshly contaminated soils with diverse properties. From measurements of metal concentrations in extracted soil pore water, the amount accumulated from the soil by diffusive gradients in thin-film (DGT) devices, and the distribution coefficient for labile metal, Kdl, estimated by isotopic exchange, we calculated the response time, Tc, of the soil-solution system to the removal of metal by DGT and the rate constant for release from the solid phase, k(-1). Resupply was so fast for Zn that Tc (and k(-1)) could be measured only in three of the soils, with either a silty or a sandy loam texture and low to intermediate pH (4.84-5.66). In only six clay soils was resupply of Cd too fast to measure. The generally slower release rates of Cd compared to Zn may reflect the 100-fold lower concentration of Cd, which allowed a greater proportion of it to occupy stronger binding sites with slower release rates. The rate constants derived indicate that supply from the solid phase to solution will not limit uptake of Cd or Zn by plants in clay soils, but it could be a factor in sandy or silty soils with a low pH. These findings suggest that risk assessment of clay soils could be undertaken using measurements of metals in soil solution. However, devices such as DGT, which respond to the kinetics of supply, are necessary to assess available metal in low pH, sandy, and silty soils.     

Impact of metal pools and soil properties on metal accumulation in Folsomia candida (Collembola)

Soil-dwelling organisms are exposed to metals in different ways. Evidence exists for predominant pore water uptake of metals by soft-bodied oligochaete species. In the present research, uptake kinetics of metals and the metalloid As by the semi-soft-bodied springtail Folsomia candida were studied, for which uptake via the pore water is less obvious. Springtails were exposed in 16 field soils and in metal-spiked artificial Organization for Economic Cooperation and Development (Paris, France) soil (OECD soil). Subsequently, accumulation parameters were statistically related to soil metal pools and soil properties. In Cd-spiked OECD soil, internal Cd levels were linearly related to external Cd concentrations, whereas the springtails maintained fixed internal levels of Cu and Zn regardless of spiked concentrations. In the field soils, all body concentrations of the elements As, Cr, and Ni were below detection limit. The essential metals Cu and Zn were presumably regulated, and no influence of soil characteristics could be demonstrated. For Cd and Pb, accumulation patterns were correlated mainly to solid-phase soil characteristics. The presence of these explanatory variables in the multiple correlations suggests that an uptake mechanism that is solely determined by pore water concentrations should not be taken as a universally applicable principle in risk assessments of metals for soil invertebrates. Cadmium in OECD soils was more available for uptake than in the field soils. The difference remained when extractability was taken into account. The results suggest that experiments in OECD soil cannot be used directly in risk assessment for nonessential metals (at least for F. candida), although a reduction of uncertainties in metal risk assessment can be reached by consistent use of body residues rather than external concentrations.     

Metal Pollution (Cd,Pb, Zn,and As) in Agricultural Soils and Soybean,Glycine max,in Southern China

Crops produced on metal-polluted agricultural soils may lead to chronic toxicity to humans via the food chain. To assess metal pollution in agricultural soils and soybean in southern China, 30 soybean grain samples and 17 soybean-field soil samples were collected from 17 sites in southern China, and metal concentrations of samples were analyzed by graphite furnace atomic absorption spectrophotometer. The integrated pollution index was used to evaluate if the samples were contaminated by Cd, Pb, Zn and As. Results showed that Cd concentration of 12 samples, Pb concentration of 2 samples, Zn concentration of 2 samples, and As concentrations of 2 samples were above the maximum permissible levels in soils. The integrated pollution index indicated that 11 of 17 soil samples were polluted by metals. Metal concentrations in soybean grain samples ranged from 0.11 to 0.91 mg kg^?1 for Cd; 0.34 to 2.83 mg kg^?1 for Pb; 42 to 88 mg kg^?1 for Zn; and 0.26 to 5.07 mg kg^?1 for As, which means all 30 soybean grain samples were polluted by Pb, Pb/Cd, Cd/Pb/As or Pb/As. Taken together, our study provides evidence that metal pollution is an important concern in agricultural soils and soybeans in southern China.     

Combined Amendments of Nano-hydroxyapatite Immobilized Cadmium in Contaminated Soil-Potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) System

The toxicity of cadmium (Cd) has posed major public health concern in crops grown in the Cd-contaminated soils. The effects of five amendments, nano-hydroxyapatite (n-HA) and it combined with lime, zeolite, bone mill and fly ash on Cd immobilization in soils and uptake in potatoes, were investigated in a contaminated soil by pot experiments. The result showed that the applications of combined amendments significantly decreased the bioavailable Cd concentrations extracted by TCLP, DTPA–TEA and MgCl₂ in the contaminated soils, and changed the soluble and exchangeable and specifically sorbed fractions to oxide-bound and organic-bound fractions. Compared to the control group, the concentrations of Cd in the potato tubers grown in n-HA, n-HA?+?Fly ash, n-HA?+?Lime, n-HA?+?Bone mill and n-HA?+?Zeolite soil were reduced 17.4%, 20.7%, 15.2%, 32.6% and 39.1%, respectively. Nano-hydroxyapatite combined amendments was more effective in reducing bioavailable Cd concentrations and Cd accumulations in potatoes, especially for n-HA?+?Z.     

Phytoremediation of heavy-metal-polluted soils: Screening for new accumulator plants in Angouran mine (Iran) and evaluation of removal ability

Heavy metal pollution is a worldwide problem. Phytoremediation is an effective and low-cost interesting technology. This study was conducted in a dried waste pool of a lead and zinc mine in Angouran (Iran) to find accumulator plant(s). Concentrations of heavy metals were determined both in the soil and the plants that were grown in the mine and out of mine. The concentration of total Cu, Fe, Zn, Pb and Ni in the mine area were higher than the control soil. The results showed that five dominant vegetations namely Amaranthus retroflexus, Polygonum aviculare, Gundelia tournefortii, Noea mucronata and Scariola orientalis accumulated heavy metals. Based on the results, it was concluded that N. mucronata is the best accumulator for Pb, Zn, Cu, Cd and Ni, but the best Fe accumulator is A. retroflexus. Phytoremediation ability of N. mucronata was evaluated in experimental pots. The study showed that the amounts of heavy metals were decreased in polluted soils during experiments. The accumulation of metals in the root, leave and shoot portions of N. mucronata varied significantly but all the concentrations were more than natural soils. The results indicated that N. mucronata is an effective accumulator plant for phytoremediation of heavy-metals-polluted soils.     

Effects of cadmium and simulated acid rain on ammonification and nitrification in soil

A perfusion technique was used to study the effects of 1) simulated acid rain on the mineralization and nitrification of glycine (NH₂-N) or ammonium sulfate (NH₄-N) by adjusting the pH of the perfusates to 3.0, 2.5, or 2.0 with H₂SO₄; and 2) 0, 50, 100, 500, and 1,000μg Cd/g dry weight of soil on the mineralization and nitrification of NH₂-N, both in soil adjusted with H₂SO₄ to pH 3.0 and in soil not exposed to acidity. Ammonification was relatively insensitive to both Cd and acidity, occurring even in soil exposed to pH 2.0 or 1,000 ppm Cd. Nitrification was more sensitive, being retarded in NH₂-N-supplemented soils exposed to pH 2.5 and inhibited in soil exposed to pH 2.O. In NH₄-N-supplemented soils, nitrification was retarded at pH 3.0 and inhibited at pH 2.5. This retardation and inhibition occurred despite the increase in the pH of the perfusates to a noninhibitory level. Nitrification was retarded at 500 ppm Cd and to a greater extent at 1,000 ppm Cd, where nitrite accumulated. The combined effect of exposure to Cd and H₂SO₄ at pH 3.0 was additive rather than synergistic, and even with 1,000 ppm Cd at pH 3.0 some nitrification eventually occurred.     

Heavy metals in urban soils of central Jordan: should we worry about their environmental risks?

Forty soil samples collected from central Jordan were analyzed by atomic absorption spectrophotometry for Pb, Cd, Zn, Cr, and Hg. The samples were also investigated for mineralogy using X-ray, electron, and optical microscopes. Sequential extraction procedures were used to predict the percentages of the Pb, Zn, Cd, and Cr present in each of the soil geochemical phases. The clay mineral assemblage encountered in the analyzed samples is composed of kaolinite, smectite, illite, and illite/smectite mixed-layer. The nonclay minerals of the sand-sized fraction are composed mainly of quartz and calcite as major minerals with pyroxene, biotite, and feldspars as minor minerals. The enrichment factors of the measured heavy metals Pb, Cd, Zn, Cr, and Hg in the clay fraction (<2 microm) of the collected samples are 3.1, 16.6, 1.5, 0.9, and 4.5, respectively. According to the index of geoaccumulation, the soils of the study area are considered to be moderately contaminated with respect to Cd, uncontaminated to moderately contaminated with respect to Pb, Hg, and Zn, and uncontaminated with respect to Cr. The measured metals correlated positively with the determined physicochemical factors such as pH, clay content, organic matter content, and carbonate content. The relatively high concentrations of Cd, Pb, and Hg in the soils of the study area are related to anthropogenic sources such as cement industry, fertilizers, and vehicle exhausts. It was found that Pb, Zn, and Cr are associated mainly with the residual phases and are relatively immobile. On the other hand Cd is enriched in the carbonate phase of the analyzed soil samples. It is possible to suggest the sequence of mobility for Pb, Zn, Cd, and Cr in the analyzed soil samples as the following: Cd>Pb>Cr>Zn.     

Microbial Toxicity of Cd and Hg in Different Soils Related to Total and Water-Soluble Contents

Microbial toxicity tests with Cd and Hg and up to 18 soil samples were combined with sorption and solubility measurements. The data ought to indicate to what extent toxic effects of the metals are influenced by sorption and the other factors that may alter their biocidal action. The microbial reduction of Fe(III) oxides to Fe²⁺ions was used as a parameter of microbial activity to calculate the total amounts of Cd and Hg that cause 10, 50, and 90% inhibition [effective doses (ED)₁₀, ED₅₀, ED₉₀]. The corresponding solution concentrations [effective concentrations: (EC)₁₀, EC₅₀, EC₉₀] were derived from Freundlich adsorption isotherms. The very large variability in ED values in different soils (ED₁₀: Cd, 5–95 mg/kg; Hg, 0.125–125 mg/kg) can be related to the sorption and solubility behavior of the metals. Nevertheless, the EC values of both metals also indicate a considerable variation (EC₁₀: Cd, 0.01–1.13 mg/liter; Hg, <0.001–0.041 mg/liter). The influence of soluble soilborne substances on metal speciation is the main reason for their varying toxic potential in different soil solutions. The strong and complex influence of soil properties on the toxicity of heavy metals in soils indicates that both chemical and biological methods of soil analysis are needed to assess the risks of soil contamination adequately.     

Evaluation of different phosphate amendments on availability of metals in contaminated soil

A pot trial was conducted to assess the efficiency of P-induced metal immobilization in soils. Natural hydroxyapatite (HA), phosphate rock (PR), triple-superphosphate (TSP), and diammonium phosphate (DAP) were evaluated for their ability to reduce cadmium (Cd), lead (Pb), and zinc (Zn) bioavailability in an artificially metal-contaminated soil with three addition levels: T0 (without metals added), T1 (Cd/Pb/Zn:0.6/100/66 mgkg(-1)), and T2 (Cd/Pb/Zn: 1.5/300/200 mgkg(-1)). Phosphate compounds were applied at 2500 mg P(2)O(5) kg(-1) soil for each metal level with five treatments: CK (control), TSP, DAP, PR, and HA, respectively. The immobilization and bioavailability of Cd, Pb, and Zn were determined by plant (Brassica campestris L.) uptake, scanning electron microscope (SEM), and sequential extraction. The results showed that HA was superior to all other materials for reducing Pb, Zn, and Cd uptake in shoot with reductions of 34.6-53.3% for Pb, 31.2-47.3% for Zn, and 39.1-42.4% for Cd, respectively, as compared with the control treatment. The mechanisms of Pb immobilization in the soil and the decreased Pb translocation from the plant root to shoot induced by added phosphate were identified with scanning electron microscope (SEM) equipped with energy dispersive X-ray elemental spectrometry (EDS). Sequential extraction results indicated that the phosphate amendments converted significant amounts of the soil Pb, Zn, and Cd from exchangeable (EX), organic bound (OC), carbonate bound (CB), amorphous Fe and Al oxides-bound (OX) (non-residual (RES) fractions) to RES fraction. In general, the effect of different phosphates on plant uptake of Pb, Zn, and Cd followed the order: HA>PR>DAP>TSP. The results suggested that HA and PR amendments could significantly reduce the bioavailability and increase the geochemical stability of soil Pb, Zn, and Cd in contaminated soils.     

Sewage sludge applied to agricultural soil: Ecotoxicological effects on representative soil organisms

Application of sewage sludge to agricultural lands is a current practice in EU. European legislation permits its use when concentrations of metals in soil do not increase above the maximum permissible limits. In order to assess the fate and the effects on representative soil organisms of sewage sludge amendments on agricultural lands, a soil microcosm (multi-species soil system—MS 3) experiment was performed. The MS 3 columns were filled with spiked soil at three different doses: 30, 60 and 120 t ha^?1 fresh wt. Seed plants (Triticum aestivum, Vicia sativa and Brassica rapa) and earthworms (Eisenia fetida) were introduced into the systems. After a 21-d exposure period, a statistically significant increase for Cd, Cu, Zn and Hg concentrations was found for the soils treated with the highest application rate. Dose-related increase was observed for nickel concentrations in leachates. Plants and earthworm metal body burden offer much more information than metal concentrations and help to understand the potential for metal accumulation. Bioaccumulation factor (BAF_plant?soil) presented a different behavior among species and large differences for BAF_{earthworm?soil}, from control or sewage-amended soil, for Cd and Hg were found. B. rapa seed germination was reduced. Statistically significant decrease in fresh biomass was observed for T. aestivum and V. sativa at the highest application rate, whereas B. rapa biomass decreased at any application rate. Enzymatic activities (dehydrogenase and phosphatase) as well as respiration rate on soil microorganisms were enlarged.     

Solubility of Trace Elements and Heavy Metals from Stabilized Sewage Sludge by Fly Ash

Stabilized sewage sludge (SS) by fly ash (FA) and alkaline mine tailing as artificial soil, to be applied on the ecological rehabilitation at mining junkyard, offers a potential viable utilization of the industrial by-product, as well as solves the shortage of soil resource in mine area. In this study, trace element and heavy metal soil solution concentrations arising from fly ash, sewage sludge, mine tailing, and artificial soil mixtures were investigated in a laboratory incubation. It was found that total Cd, Pb, and Zn contents in artificial soils were significantly lower than the control standards for pollutants in sludges from agricultural use (GB 4284-84). Soil solution Cd and Pb concentrations were obviously reduced by mixing sewage sludge with alkaline fly ash. Initial soil solution Cd, Pb, and Zn concentrations in artificial soils were 1.773–14.672, 4.05–24.95, and 133–608 μg L⁻¹, respectively, and after 35-days incubation, soil solution Cd, Pb, and Zn concentrations gradually decreased and were approaching control levels by the end of the experiment, and finial soil solution were decreased to 0.037–0.365, 2.12–7.34, and 29–509 μg L⁻¹, respectively.     

Effects of Flooding on Changes in Eh,pH and Speciation of Cadmium and Lead in Contaminated Soil

Artificially contaminated soils (A, B) and naturally contaminated soil (S2) in China were used as the tested soils, and the effect of continuous flooding on the changes of Eh, pH and the speciation of cadmium, lead in contaminated soils was studied in the paper. The results indicated that soil Eh decreased with flooding time, and that soil pH increased with flooding time. The changes of soil pH ceased after 60 days of submergence. The exchangeable Cd and Pb decreased obviously during the flooding process from the results of five-step sequential extraction. The calculations of mobility factor (MF) showed that Cd mobility significantly decreased in artificially contaminated soils (A, B) after the flood. But the change of Pb mobility was not significant after the flood, although a decrease of Pb concentration in the exchangeable fraction (SE) was observed.     

Metal uptake from soils and soil-sediment mixtures by larvae of Tenebrio molitor (L.) (Coleoptera)

Bioassays were performed to evaluate the impact of soil characteristics on Cd, Cu, Pb, and Zn uptake by larvae of Tenebrio molitor. Metal accumulation was determined in 13 natural field soils, one metal-spiked field soil, four soil-sediment mixtures, and Cd- or Zn-spiked OECD artificial soil. Statistical analyses were used to investigate covariation of accumulation patterns with various soil metal pools and soil properties. Body concentrations of Cu and Zn in Zn-spiked OECD soils, field soils, and soil-sediment mixtures mostly remained constant. Considerable variation was noted for all Cd and Pb steady-state body concentrations among field soils and soil-sediment mixtures. For the spiked field soil and in the Cd-spiked OECD soil, body concentrations increased almost linearly with time. For the nonessential metals Cd and Pb, larval body concentrations correlated mainly to the total metal pool of the soil. Cd uptake at similar total Cd concentrations was within the same range among spiked OECD soils, field soils, and mixtures. A comparison of the findings with studies on other soil-inhabiting species shows that metal uptake patterns depend on metal type, soil type, and exposed species. It is suggested that soil organisms can be categorized according to gross divergence in ecophysiological characteristics, determined by, for instance, (non)permeability of the outer integument. These characteristics appear as similarities among multivariate functions as derived for the beetle.     

Soil-solution speciation of Cd as affected by soil characteristics in unpolluted and polluted soils

Total metal content by itself is insufficient as a measure to indicate actual environmental risk. Understanding the mobility of heavy metals in the soil and their speciation in the soil solution is of great importance for accurately assessing environmental risks posed by these metals. In a first explorative study, the effects of general soil characteristics on Cd mobility were evaluated and expressed in the form of empirical formulations. The most important factors influencing mobility of Cd proved to be pH and total soil content. This may indicate that current legislation expressing the requirement for soil sanitation in Flanders (Belgium) as a function of total soil content, organic matter, and clay does not successfully reflect actual risks. Current legal frameworks focusing on total content, therefore, should be amended with criteria that are indicative of metal mobility and availability and are based on physicochemical soil properties. In addition, soil-solution speciation was performed using two independent software packages (Visual Minteq 2.23 and Windermere Humic Aqueous model VI [WHAM VI]). Both programs largely were in agreement in concern to Cd speciation in all 29 soils under study. Depending on soil type, free ion and the organically complexed forms were the most abundant species. Additional inorganic soluble species were sulfates and chlorides. Minor species in solution were in the form of nitrates, hydroxides, and carbonates, the relative importance of which was deemed insignificant in comparison to the four major species.