Immobilization of Zinc and Cadmium in Polluted Soils by Polynuclear Al13 and Al-Montmorillonite

We investigated the suitability of two aluminum-based binding agents, polynuclear Al₁₃ and Al-coated montmorillonite (Al-mont-morillonite), for the immobilization of heavy metals in two contaminated agricultural soils: a loamy luvisol from an arable site in Rafz, Canton Zürich, Switzerland, and a sandy podsol from Szopienice, Upper Silesia, Poland. Both soils were polluted by lead, zinc, and cadmium: the soil from Szopienice by the emissions of a nearby zinc-lead smelter, and the soil from Rafz by sewage sludge applications. While the samples from Szopienice exhibited extremely high loads of these metals, the samples from Rafz were only moderately contaminated. The samples from both soils were slightly acidic. The Rafz soil contained 2.5% organic matter, that from Szopienice only 1.5%. Destruction of the organic matter in the Szopienice samples by H₂O₂ led to a significant release of Zn and Cd into solution. This indicated that organic matter is an important factor for the immobilization of heavy metals in this soil. The treatment of the Szopienice samples with 8?mmol Al₁₃ per kg dry soil resulted in a considerable mobilization of the two metals. As the pH of the samples did not decrease, this effect was presumably due to direct interactions between the applied aluminium and organic matter. After destruction of soil organic matter, the two binding agents exhibited an immobilizing effect on Zn, which, however, was weak compared with the binding of the metal by the organic matter prior to its destruction. In the case of the Rafz samples, metal mobilization was observed only for Al₁₃ if applied in high doses (4 and 8?mmol per kg soil), but not for Al-montmorillonite. In this soil, Al-montmorillonite as well as Al₁₃ at low doses (1.2?mmol per kg soil and less) decreased soluble zinc concentrations significantly. The mobilization of metals at high doses of the applied binding agents and the dependence of this effect on the type of soil show that care has to be taken with this remediation method and that the proper doses of applied binding agents can be crucial for the success of metal immobilization in polluted soils.     

The chemical fractionation of soil zinc and its specific and total adsorption by Egyptian alluvial soils

Summary The Zn contents of twenty-nine alluvial soils from Egypt were chemically fractionated into: water soluble+exchangeable, weakly bound to inorganic sites, organically bound, occluded as free oxide material, and residual mainly in the mineral structure. On the average these fractions constituted about 0.01, 1.20, 28.6, 21.5 and 45.5% of the total soil Zn respectively which averaged 76.25 ppm. Significant correlations were obtained between each individual Zn-fraction and some soil variable.Zinc adsorption isotherms were developed for seven soils suspended in dilute ZnCl₂ solution in the presence of either 0.05M CaCl₂ solution (Specific adsorption) or deionized water (Total adsorption). The Langmuir constants (adsorption maximum and bonding energy) were calculated. The average value of specific adsorption maximum was 1.94 mg Zn/g soil and of total adsorption maxima was 11.54 mg Zn/g soil. Correlation analysis showed that CEC, free Fe₂O₃ and clay content were the dominant soil variables contributing towards specific Zn adsorption. The (Zn) (OH)₂ ion concentration products in the solutions when Zn adsorption corresponded to the Langmuir adsorption maxima were 0.92×10^–17 in the specific adsorption treatment, and 1.35×10^–15 in the total adsorption treatment. These values are within the solubility range of Zn (OH)₂ and ZnCO₃. The values of Langmuir bonding energy constants showed that Zn was more strongly adsorbed by low carbonate or carbonate-free soils than by carbonate-rich soils.     

Effects of Plant Residue and Salinity on Fractions of Cadmium and Lead in Three Soils

Bioavailability and mobility of heavy metals (HMs) in soils are determined by their partitioning between solution and solid-phase and their further redistribution among solid-phase components. A study was undertaken to determine the effects of organic matter (OM) and salinity on cadmium (Cd) and lead (Pb) distribution among soil fractions. Three agricultural soils were treated with 20 mg Cd/kg as Cd (NO₃)₂·4H₂O, 150 mg Pb/kg as Pb (NO₃)₂, 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl, and then incubated at 60% water holding capacity (60% WHC) and constant temperature (25°C) for 12 weeks. Various fractions of Cd and Pb were extracted from the soils after 2 and 12 w of incubation using a sequential extraction technique. Results showed that in the early stage of incubation (2 w), added Pb were found mainly in the specifically sorbed (SS) and amorphous Fe oxides (AFeO) fractions and added Cd found in SS and Mn oxides (MnO) fractions. Addition of 2% OM decreased the exchangeable (EXC) Pb fraction almost in all soils, whereas it had a different effect on the EXC Cd fraction depending on soil pH. Addition of NaCl increased the EXC Cd fraction in two soils, but it did not alter Pb fractions. At the end of the incubation period, Pb decreased in the EXC and MnO fractions except in the neutral soil and Cd decreased mainly in the SS fraction.     

Cadmium Uptake by Lettuce (Lactuca sativa L.) as Basis for Derivation of Risk Limits in Soils

The availability and uptake of Cd by lettuce (Lactuca sativa L.) in two common tropical soils (before and after liming) were studied in order to derive human health-based risk soil concentration. Cadmium concentrations ranging from 1 to 12 mg kg^?1 were added to samples from a clayey Oxisol and a sandy-loam Ultisol under glasshouse conditions. After incubation, a soil sample was taken from each pot, the concentration of Cd in the soil was determined, lettuce was grown during 36 d, and the edible parts were harvested and analyzed for Cd. A positive linear correlation was observed between total soil Cd and the Cd concentration in lettuce. The amount of Cd absorbed by lettuce grown in the Ultisol was about twice the amount absorbed in the Oxisol. Liming increased the soil pH and slightly reduced Cd availability and uptake. CaCl₂ extraction was better than DTPA to reflect differences in binding strength of Cd between limed and unlimed soils. Risk Cd concentrations in the Ultisol were lower than in the Oxisol, reflecting the greater degree of uptake from the Ultisol. The derived risk Cd values were dependent on soil type and the exposure scenario.     

Adsorption of Copper and Cadmium by Cu- and Cd-Resistant Bacteria and Their Composites with Soil Colloids and Kaolinite

Abstract

Remediation of toxic metals by bacteria offers a relatively inexpensive and efficient way for the decontamination of soil and associated environments. The present study was carried out to investigate the surface characteristics, adsorption, and remobilization of Cd and Cu on bacteria and their composites with soil colloidal components, which are the most active constituents in soils. The bacterial strain NTG-01 (Enterobacter aerogenes), which was both Cd- and Cu-resistant, was isolated from a heavily Cu-contaminated soil of the mining area in Daye suburb of Hubei Province, China. Batch laboratory experiments with NTG-01 and soil colloids were performed to quantify adsorption of Cu and Cd. The surface area of kaolinite and the soil colloids from an Alfisol and Ultisol increased by 3.0–8.8% after the introduction of the bacteria. In the presence of bacterial cells, the negative charges of soil colloid systems increased and the positive charges decreased, shifting pH from 4.0 to 6.5. Our results demonstrate that bacteria promote the adsorption of Cd and Cu by kaolinite and soil colloid systems. However, the heavy metals bound by the bacterial composites could also be easily released by NH₄NO₃ and EDTA. Caution should be taken when using such bacterial strains in bioremediation of heavy metal-contaminated soils.     

Distribution of zinc fractions and their transformation in submerged rice soils

Distribution of different forms of Zn in 16 acid alluvial rice growing soils of West Bengal (India) and their transformation on submergence were studied. The results showed that more than 84% of total Zn occurred in the relatively inactive clay lattice-bound form while a smaller fractionviz. 1.1, 1.6, 11.1 and 2.0 per cent of the total occurred as water-soluble plus exchangeable, organic complexed, amorphous sesquioxide-bound and crystalline sesquioxide bound forms, respectively. All these four Zn forms showed significant negative correlations with soil pH (r=−0.48^**, −0.39^*, −0.61^** and −0.67^**, respectively), while the latter two Zn forms showed significant positive correlations with Fe₂O₃ (0.68^** and 0.88^***) and Al₂O₃ (0.89^*** and 0.75^***) content of the soils. The different Zn forms were found to have positive and significant correlations amongst each other, suggesting the existence of a dynamic equilibrium of these forms in soil. Submergence caused an increase in the amorphous sesquioxide-bound form of Zn and a decrease in each of the other three forms. The magnitude of such decreases in water-soluble plus exchangeable and crystalline sesquioxide-bound forms was found to be correlated negatively with initial pH values of the soils and positively with the increase in the amorphous sesquioxide-bound form, indicating their adsorption on the surface of the freshly formed hydrated oxides of Fe, which view was supported by the existence of significant positive correlation between the increase in the amorphous sesquioxide-bound form of Zn and that in AlCl₃-extractable iron. The existence of a positive correlation between the decrease in crystalline sesquioxide-bound Zn and that in Fe₂O₃ content in soil suggested that on waterlogging the soil Zn occluded in the cry talline sesquioxide was released as a result of reduction of Fe₂O₃.     

可降解螯合剂对镉胁迫下籽粒苋根系形态及生理生化特征的影响

采用盆栽试验研究了可降解螯合剂EDDS和NTA对镉胁迫下籽粒苋(Amaranthus hybridus L.)根系形态及生理生化特征的影响。结果表明:当螯合剂施入10 mg/kg的镉污染土壤后,籽粒苋根系生物量和总长等根系形态指标与对照无显著差异,过氧化物酶(POD)、过氧化氢酶(CAT)活性、谷胱甘肽(GSH)和可溶性蛋白含量显著上升。当螯合剂施入100 mg/kg的镉污染土壤后,籽粒苋根系生物量、总长、表面积、体积及侧根数比对照显著减少了12.30%—23.98%、17.01%—24.90%、41.87%—57.93%、16.46%—32.94%和23.48%—53.35%;EDDS的施入使籽粒苋根系POD、CAT活性、GSH和可溶性蛋白含量显著升高;而NTA施入后,根系中的POD活性比对照降低了4.12%—35.95%,并且CAT活性和可溶性蛋白含量在2 mmol/kg NTA处理下分别显著降低了14.66%—15.79%和26.81%—30.48%;EDDS和NTA施入后,GSH含量比对照显著升高了14.73%—65.65%和28.05%—84.10%。当镉处理浓度分别为10 mg/kg和100 mg/kg时,螯合剂的施入显著增强了籽粒苋根系对镉的吸收,比对照分别增加了40.76%—103.10%和15.03%—49.49%。因此,EDDS和NTA施入镉污染土壤后,通过影响籽粒苋根系形态和生理生化过程以响应重金属镉的胁迫。     

Extracellular complexation of Cd in the Hartig net and cytosolic Zn sequestration in the fungal mantle of Picea abies – Hebeloma crustuliniforme ectomycorrhizas

Compartmentation of heavy metals on or within mycorrhizal fungi may serve as a protective function for the roots of forest trees growing in soils containing elevated concentrations of metals such as Cd and Zn. In this paper we present the first quantitative measurements by X‐ray microanalysis of heavy metals in high‐pressure frozen and cryosectioned ectomycorrhizal fungal hyphae. We used this technique to analyse the main sites of Cd and Zn in fungal cells of mantle and Hartig net hyphae and in cortical root cells of symbiotic Picea abies – Hebeloma crustuliniforme associations to gain new insights into the mechanisms of detoxification of these two metals in Norway spruce seedlings. The mycorrhizal seedlings were exposed in growth pouches to either 1 mM Cd or 2 mM Zn for 5 weeks. The microanalytical data revealed that two distinct Cd‐ and Zn‐binding mechanisms are involved in cellular compartmentation of Cd and Zn in the mycobiont. Whereas extracellular complexation of Cd occurred predominantly in the Hartig net hyphae, both extracellular complexation and cytosolic sequestration of Zn occurred in the fungal tissue. The vacuoles were presumed not to be a significant pool for Cd and Zn storage. Cadmium was almost exclusively localized in the cell walls of the Hartig net (up to 161 mmol kg ^{? 1} DW) compared with significantly lower concentrations in the cell walls of mantle hyphae (22 mmol kg ^{? 1} DW) and in the cell walls of cortical cells (15 mmol kg ^{? 1} DW). This suggests that the apoplast of the Hartig net is a primary accumulation site for Cd. Zinc accumulated mainly in the cell walls of the mantle hyphae (111 mmol kg ^{? 1} DW), the Hartig net hyphae (130 mmol kg ^{? 1} DW) and the cortical cells (152 mmol kg ^{? 1} DW). In addition, Zn occurred in high concentrations in the cytoplasm of the fungal mantle hyphae (up to 164 mmol kg ^{? 1} DW) suggesting that both the cell walls and the cytoplasm of fungal tissue are the main accumulation sites for Zn in P. abies resulting in decreased Zn transfer from the fungus to the root.     

碳酸钙对水稻吸收重金属(Pb、Cd、Zn)和As的影响

选用重金属(Pb、Cd、Zn)和As复合污染土壤进行水稻盆栽试验,结果表明,碳酸钙的添加显著提高了土壤pH值,显著降低了土壤中交换态Pb、Cd、Zn和As的含量,与对照相比,交换态Pb、Cd、Zn和As含量分别最多降低了98.35%,93.72%,98.52%和69.48%。碳酸钙对水稻根、稻谷干重和总生物量没有显著影响,添加量过高时显著降低了水稻分蘖数和茎叶干重,说明过量施用碳酸钙对水稻生长会产生负面作用。因为碳酸钙的添加,水稻植株各部位重金属Zn含量显著降低,糙米中Zn含量最多减少了34.95%;根、谷壳中Pb、Cd含量显著降低,但糙米中含量却未显著降低;水稻各部位As含量均没有显著降低。参照《食品中污染物限量》(GB2762—2012),试验糙米中Pb、Cd、无机As含量均未达到限量标准。显然,碳酸钙的添加降低了Pb、Cd、Zn的生物有效性(水稻根系对Pb、Cd、Zn的吸收累积减少),但并未有效地抑制Pb、Cd向糙米转运;碳酸钙显著降低了土壤的交换态As含量,但并未使土壤中As的生物有效性明显降低(水稻植株各部位的As含量并未显著减少)。     

Phytoextraction potential of soils highly polluted with cadmium using the cadmium/zinc hyperaccumulator Sedum plumbizincicola

Abstract

A three-crop repeated phytoextraction experiment was conducted using four soils (S1–S4) highly polluted with cadmium (Cd) and two enhanced phytoextraction pot experiments using the most polluted soil (S4) to investigate the feasibility of Cd removal from highly polluted soils using the Cd/zinc (Zn)-hyperaccumulator Sedum plumbizincicola. Shoot biomass showed no significant difference during the repeated phytoextraction experiment on the four test soils and shoot Cd content showed a decreasing trend with the three consecutive crops in soils S1, S2, and S3 but not in soil S4. The Cd removal rates in soils S1, S2, S3, and S4 were 84.5, 81.6, 45.3, and 32.4%, respectively. Rice straw application increased Cd extraction efficiency by 42.6% but the addition of ethylenediaminedisuccinic acid, biochar or nitrogen had no effect on Cd remediation. Shoot Cd content increased significantly (1.57 and 1.71 times, respectively) at low (S₀-1) and high (S₀-2) sulfur addition rates. Soil extractable-Cd in S₀-1 after the experiment showed no significant difference from the control but was 2.43 times higher in S₀-2 than in the control. These results indicate that S. plumbizincicola shows good prospects for the phytoextraction of Cd from highly polluted soils and that the process can be enhanced by adding straw and/or sulfur to the soil.     

Improvement of activity and stability of Rhizomucor miehei lipase by immobilization on nanoporous aluminium oxide and potassium sulfate microcrystals and their applications in the synthesis of aroma esters

In this study, Rhizomucor miehei lipase (RML) was immobilized on the hexagonally-ordered nanoporous aluminium oxide membranes (RML-Al₂O₃-NP) by adsorption and as protein-coated microcrystals (RML-PCMCs) by simultaneously precipitating RML on micron-sized potassium sulfate crystals (K₂SO₄) in pre-chilled acetone. The hydrolytic activities of immobilized lipase preparations were investigated in terms of p-nitrophenyl palmitate hydrolysis and their esterification activities were examined for the synthesis of some aroma esters such as butyl acetate, isoamyl acetate, hexyl acetate, heptyl acetate, and geranyl acetate. The immobilization yields were 33.8 and 25.1%, respectively for RML immobilized on Al₂O₃-NP membranes and potassium sulfate crystals. The catalytic efficiency ratios of RML-Al₂O₃-NP and RML-PCMCs were 2.3- and 3.9-fold higher than that of the free lipase, respectively in terms of hydrolytic activity. The free lipase was stabilized as 4.1- and 10.5-fold, respectively at 40 and 50?°C when immobilized on Al₂O₃-NP. The corresponding stabilization factors were 4.6- and 12.8-fold higher for RML-PCMCs. RML-Al₂O₃-NP and RML-PCMCs maintained 84 and 86% of their initial hydrolytic activities, respectively after 10 reuses. Of the synthesized aroma esters, the highest yield was obtained for the geranyl acetate. After 4?h reaction time, no geraniol was detected in the preparative-scale (196?g/L) synthesis of geranyl acetate for both the immobilized lipases when the initial geraniol amount, vinyl acetate amount, RML-PCMCs amount, and reaction temperature values were 1?mmol, 3?mmol, 100?mg (or 300?mg RML-Al₂O₃-NP), and 50?°C, respectively. These results show that the immobilization of R. miehei lipase by adsorption on nanoporous aluminium oxide and as protein-coated microcrystals leads to the obtention of highly stable, catalytically more active, and reusable lipase preparations.     

Predictability of the Zn and Cd phytoextraction efficiency of a Salix smithiana clone by DGT and conventional bioavailability assays

Aims

Phytomanagement of metal-polluted soils requires information on plant responses to metal availability in soil, but the predictability of metal accumulation in plant shoots and/or roots may be limited by metal toxicity and inherent shortfalls of the bioavailability assays.

Methods

We measured the uptake of Cd and Zn in a Salix smithiana clone grown in a pot experiment on soils with different characteristics and metal availabilities, determined by conventional soil single extractions (0.05 M Na₂-EDTA and 1 M NH₄NO₃), soil solution obtained by centrifugation, and diffusive gradients in thin films (DGT). The Cd and Zn phytoavailability after a 2-year phytoextraction by willow was assessed by metal accumulation in the straw of the following barley culture.

Results

The phytoextraction efficiency was largest on a moderately polluted acid soil. Biomass and shoot Zn concentrations of S. smithiana were better predicted by DGT-measured Zn concentrations in soil solution (C _DGT) than by Zn concentrations in the soil solution and extractable soil fractions. The weaker correlation for Cd in shoots may be related to relative Cd enrichment in the plant tissues. The metal accumulation in barley straw was unaffected or increased after a 2-year phytoextraction.

Conclusions

The shoot Zn and Cd removal of the tested Salix clone can be predicted by C _DGT concentrations and is highest on either calcareous or moderately polluted acid soils. Single extraction with NH₄NO₃ and the C _DGT value of Cd were not able to predict shoot Cd removal on the tested soils. Only shoot removal of Zn was predicted fairly well by the C _DGT value.     

Emission and Control Characteristics for Incineration of Sedum Plumbizincicola Biomass in a Laboratory-Scale Entrained Flow Tube Furnace

Experiments were conducted to investigate and control pollutant emission from incineration of Sedum plumbizincicola plants on a laboratory scale using an entrained flow tube furnace. Without control technologies, the flue gas contained 0.101 mg Nm^?3 of Cd, 46.4 mg Nm^?3 of Zn, 553 mg Nm^?3 of NOx, 131 pg Nm^?3 of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/Fs) and 35.4 mg Nm^?3 of polycyclic aromatic hydrocarbons (PAHs). In pollutants control experiments. Al₂O₃, CaO, and kaolin were compared as adsorbents and activated carbon was used as an end-of-pipe method for the capture of pollutants. Kaolin, the most effective of the three adsorbents, removed 91.2% of the Cd in flue gas. While 97.6% of the Cd and 99.6% of the PAHs were removed by activated carbon. Incineration may therefore be regarded as a viable option for the safe disposal of the biomass of the zinc and cadmium hyperaccumulator species S. plumbizincicola.     

淹水条件下控释氮肥对污染红壤中重金属有效性的影响

采用淹水培养方法研究了不同氮水平(100、200和400 mg/kg,分别记为1、2、3)下普通尿素(PU)、硫包膜尿素(SCU)、树脂包膜尿素(PCU)和硫加树脂双层包膜尿素(SPCU)对污染红壤中Cd、Pb、Cu、Zn有效性的影响.结果表明,不同包膜尿素对土壤pH值和水溶性SO42-含量有较大影响.各施氮处理红壤pH值随着施氮量的增加(除5d时PU和60 d时SCU)而增加,不同包膜尿素对土壤中水溶性SO42-含量有较大影响,在同一施氮水平下不同包膜尿素处理间土壤pH值和土壤中水溶性SO42-含量差异较大.60 d培养期间PU、SCU、PCU和SPCU处理pH值比对照分别升高0.17-0.38、0.08-0.27、0.07-0.36和0.10-0.21;水溶性SO42-含量PU、SCU和PCU处理比对照分别升高39.5％-157.3％、40.9％-94.5％和7.55％-55.8％,而SPCU处理降低5.67％-90.7％.不同尿素类型和氮肥的施用量对红壤Cd、Pb、Cu和Zn有效性的影响均存在显著差异.60 d培养期间红壤有效态Cd含量以树脂包膜尿素100 mg N/kg下最低,其有效态Cd含量比对照显著降低20.7％-69.8％;有效态Pb、Cu和Zn含量以普通尿素400 mg N/kg下最低,其有效态Pb、Cu和Zn含量比对照分别显著降低17.0％-54.2％、18.5％-34.6％和15.6％-59.5％.随施氮量提高,PU处理有效态Cd含量先升高后降低,有效态Pb、Cu和Zn含量逐渐降低;SCU处理有效态Pb含量逐渐降低,有效态Cd、Cu和Zn含量变化规律不一致;PCU处理有效态Cd含量逐渐升高,有效态Pb、Cu和Zn含量变化规律不一致;SPCU处理有效态Cd、Pb、Cu和Zn含量逐渐降低.有效态Pb和Zn含量与pH值和水溶性SO42-含量呈显著负相关,有效态Cd与水溶性SO42-含量呈显著正相关.在多重金属污染红壤中,可考虑不同控释氮肥的配合使用,降低土壤中重金属的有效性.     

Phytoextraction of Cd and Zn from agricultural soils by Salix ssp. and intercropping of Salix caprea and Arabidopsis halleri

Contamination of agricultural topsoils with Cd above guideline values is of concern in many countries throughout the world. Extraction of metals from contaminated soils using high-biomass, metal-accumulating Salix sp. has been proposed as a low-cost, gentle remediation strategy, but reasonable phytoextraction rates remain to be demonstrated. In an outdoor pot experiment we assessed the phytoextraction potential for Cd and Zn of four willow species (Salix caprea, S. fragilis, S. × smithiana, S. × dasyclados) and intercropping of S. caprea with the hyperaccumulator Arabidopsis halleri on three moderately contaminated, agricultural soils. Large concentrations of Cd (250 mg kg⁻¹) and Zn (3,300 mg kg⁻¹) were determined in leaves of Salix × smithiana grown on a soil containing 13.4 mg kg⁻¹ Cd and 955 mg kg⁻¹ Zn, resulting in bioaccumulation factors of 27 (Cd) and 3 (Zn). Total removal of up to 20% Cd and 5% Zn after three vegetation periods were shown for Salix × smithiana closely followed by S. caprea, S. fragilis and S. × dasyclados. While total Cd concentrations in soils were reduced by up to 20%, 1 M NH₄NO₃-extractable metal concentrations did not significantly decrease within 3 years. Intercropping of S. caprea and A. halleri partly increased total removal of Zn, but did not enhance total Cd extraction compared to single plantings of S. caprea after two vegetation periods.     

Solubilization and Plant Uptake of Zinc and Cadmium from Soils Treated with Elemental Sulfur

In growth chamber experiments we studied the potential use of elemental sulfur (S₈) as an acidifying agent to enhance the uptake of Cd and Zn from three different polluted soils by candidate phytoremediation plants (Brassica juncea, Helianthus annuus, Salix viminalis). Two of the three soils were calcareous, the other slightly acidic. One of the calcareous soils had been contaminated by dust emissions from a nearby brass smelter. The pollution of the other two soils had resulted from sewage sludge applications.

Sulfur was added to soils in quantities of 20 to 400 mmol sulfur kg^-1 soil. Plants were grown under fluorescent light in 1.5 l ($OS 13 cm) pots for 28 d.

Within 700 h soil pH decreased significantly in all soils, depending on S₈ dosage. In the acid soil, pH decreased from pH 6.5 to about 4 at the highest treatment level, while pH in one of the calcareous soils dropped even below pH 4. The effect was smaller in the second calcareous soil.

NaNO₃-extractable Cd and Zn increased up to 26-and 13-fold, respectively, in the acid soil, while in the calcareous soils, maximum increases were 9-and 11-fold, respectively.

Increased NaNO₃-extractable concentrations translated well into shoot concentrations (dry matter) in plants. Shoot Zn concentrations in H. annuus, for example, increased from 930 in the controls to 4300 mg kg^-1 in the highest S₈ treatment. However, effects observed in the plants were generally smaller than in the soils. In addition, in some variants growth was negatively affected, resulting in reduced metal removal from the soils.     

Zinc phytoavailability after remediation in soils contaminated by sphalerite-containing pyritic sludge

Zinc can be toxic to plants growing on soils in areas of the Guadiamar River valley (southwestern Spain) affected by the spillage of pyritic sludge in April 1998. The shoots and the soil around the roots of two wild plants (viz. Amaranthus blitoides S. Wats., November 2000; and Xanthium strumarium L., June 2001) growing in the sludge-affected areas were sampled with the purpose of relating Zn phytoavailability to soil properties. The soils were calcareous and non-calcareous Entisols and Inceptisols which, after remediation, contained ploughed-in residual sludge and unevenly distributed industrial lime. Chemical extracts from the soils suggested that much of the sphalerite (ZnS) originally present in the sludge had weathered and Zn was partly bound to carbonates and Fe oxides, the total Zn concentration ranging from 37 to 2407 mg kg ^–1. To identify the soil properties that influenced Zn phytoavailability under controlled conditions, the soil samples (n=63) were homogenized and oilseed rape (Brassica napus var. Karola) was pot-grown on them in a growth chamber. The concentrations of Zn in oilseed rape shoots and roots were below phytotoxic levels, with mean ± standard deviation values of 142 ± 128 and 244 ± 328 mg kg ^–1 dry matter, respectively. Citrate/bicarbonate-extractable Zn in soil (Zn _cb) was found to be the best predictor for the Zn concentration in both shoots and roots. Also, the Zn _cb/Olsen P ratio exhibited a high predictive power for Zn in shoots as the likely result of the Zn-P interaction in soil. The shoot Zn concentration in the wild plants, generally lay below phytotoxic levels (the mean ± standard deviation values were 261 ± 255 and 200 ± 228 mg kg ^–1 dry matter for Amaranthus blitoides and Xanthium strumarium, respectively) and was not correlated with soil properties – by exception, there was slight correlation between the Zn concentration in Amaranthus blitoides and Zn _cb/Olsen P. Such a lack of correlation can be ascribed to the local small-scale soil heterogeneity caused by remediation practices. The Zn concentration in wild plants growing on CaCO ₃-poor soils was weakly correlated with Zn _cb/Olsen P; no similar correlation was found in CaCO ₃-rich soils, however. The wild plants growing on CaCO ₃-poor and CaCO ₃-rich soils differed little in Zn concentration; this suggests that further addition of lime to reduce Zn phytoavailability may be unjustified.     

Phytoextraction of cadmium and zinc by Salix from soil historically amended with sewage sludge

Short rotation coppice (SRC) such as Salix spp. can be grown as an energy crop and offers some potential for economic and practical phytoextraction of marginally contaminated arable soil. This study tested various soil amendments intended to increase soil metal availability to Salix, investigated the distribution of metal between different tree fractions and assessed the viability of phytoextraction using SRC on arable soils. Several Salix genotypes were grown in field trials over 4 years. Cd and Zn concentrations were generally ranked in the order leaves > bark > wood. Metal concentrations in wood increased towards the top of the willow stems, whereas concentrations in leaves showed the opposite trend. None of the amendments significantly increased uptake of Zn by willow. However, in response to a range of soil HCl treatments, mean Cd concentrations in stems and leaves were 112% and 130% of control values. Data from the current experiment, and previous studies, were combined to develop a predictive model of Cd and Zn stem uptake by Salix. The minimum biological concentration factor (BCF) required to achieve a prescribed soil metal target was also calculated based on typical proportions of bioavailable Cd in sludge-amended soils for a 25-year Salix rotation. The best Salix genotypes investigated achieved less than 20% of the uptake rate required to remove one third of the soil Cd content (equivalent to the average isotopically exchangeable Cd fraction in soils at the study site).     

Acute effects of Cu on oxygen consumption and 96 hr-LC50 values in the freshwater fish Tilapia sparrmani (Teleostei: Cichlidae) in Mooi River hard water,South Africa

The median lethal copper (Cu) concentration (96 hr-LC₅₀) values for acute Cu toxicity for Tilapia sparrmanii (live mass: 30 ± 8g) in Mooi River hard water of dolomitic origin at 20 °C, pH 7.9, was 68.1 μmol l^?1. At this 96 hr-LC₅₀ value the specific oxygen consumption rate (∈ O₂) decreased by 44.2 (± 2.1) % from a non-exposed value of 6.6 (±0.32) mmol O₂ kg^?1 hr^?1 to 3.63 (±0.23) mmol O₂ kg ^?1 hr^?1. At 46.4 μmol Cu l^?1, 100% of the exposed T. sparrmanii were still alive after 96 hours, but the ∈ O₂ decreased by a mean value of 1.65 (± 0.16) mmol O₂ kg^?1 fish hr^?1 or 25% (± 2.4). Contrary to Pb and Cd, Cu as CuCl₂ 2H₂O was not precipitated in hard water four days after it was dissolved. Thus T. sparrmanii and other cichlids are shown to be more than an order of magnitude more resistant to Cu as a toxicant than most salmonids.     

Adsorption,Bioavailability, and Toxicity of Cadmium to Soil Microorganisms

The influence of adsorption on cadmium toxicity to soil microorganisms in soils was quantified as a function of solution and sorbent characteristics. The influence of adsorption on cadmium toxicity to soil microorganisms was assessed indirectly through the relative change in microbial hydrolysis of fluorescein diacetate (FDA) as a function of total Cd concentration and sorbent characteristics. The sequence of relative percentage of FDA hydrolysis was reference smectite (RS) > untreated Vertisol (UV) > dithionate-citrate-bicarbonate (DCB)-treated Vertisol (DV) > H₂O₂-treated Vertisol (HV) in suspensions containing the same total Cd concentrations. The correlation between the percentage of FDA hydrolysis and activity of Cd²⁺ _(aq) illustrates that RS has a higher capacity of Cd adsorption. The microbial activity of RS was higher and the toxicity was lower than that of other soil samples. The HV had lower capacity of Cd adsorption so that its FDA hydrolysis was low and the Cd toxicity was high.