Pb-Zn交互作用对红壤微生物生物量的影响

A laboratory incubation experiment was conducted to evaluate the effects of lead and zinc applied alone or in various combinations on the size of microbial biomass in a red soil. Treatments included the application of lead at six different levels i. e., 0 (background), 100, 200, 300, 450 and 600 g g^-1 soil along with each of the four levels of zinc (0, 50, 150 or 250 g g^-1 soil). Application of lead or zinc alone to soil significantly (P < 0. 001) affected the soil microbial biomass. The microbial biomass carbon (C_mic), biomass nitrogen (N_mic) and biomass phosphorus (P_mic) decreased sharply in soils contaminated with lead or zinc. Combined application of lead and zinc resulted in a greater biocidal effect on soil microbial biomass, which was significantly higher (P < 0. 001) than that when either lead or zinc was applied alone. Consistent increase in the biomass C: N and decline in the biomass C:P ratios were also observed with the increased metal (Pb and Zn) toxicity in the soil.     

Microbial Activity Indices： Sensitive Soil Quality Indicators for Trace Metal Stress

Physicochemical properties, total and DTPA （diethylenetriaminepentaacetic acid）-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon （C） content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractable metals were correlated positively and significantly with total metals, CEC, and organic C （except for DTPA-extractable Cd）, while they were negatively and highly significantly correlated with pH, totall Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C mineralization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some “linked” microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.     

微生物活性指标: 重金属污染下的土壤质量敏感指标

Physicochemical properties, total and DTPA (diethylenetriaminepentaacetic acid)-extractable Cu, Zn, Pb and Cd contents, microbial biomass carbon (C) content and the organic C mineralization rate of the soils in a long-term trace metal-contaminated paddy region of Guangdong, China were determined to assess the sensitivity of microbial indices to moderately metal-contaminated paddy soils. The mean contents of total Cu, Zn, Pb and Cd were 251, 250, 171, and 2.4 mg kg^-1 respectively. DTPA-extractablc metals were correlated positively and significantly with total metals, CEC, and organic C (except for DTPA-extractable Cd), while they were negatively and highly significantly correlated with pH, total Fe and Mn. Metal stress resulted in relatively low ratios of microbial biomass C to organic C and in remarkable inhibition of the microbial metabolic quotient and C minera]ization rate, which eventually led to increases in soil organic C and C/N. Moreover, microbial respiratory activity showed a stronger correlation to DTPA-extractable metals than to total metal content. Likewise, in the acid paddy soils some "linked" microbial activity indices, such as metabolic quotient and ratios of basal respiration to organic C, especially during initial incubation, were found to be more sensitive indicators of soil trace metal contamination than microbial biomass C or basal respiration alone.     

长期重金属胁迫下的土壤微生物特征: 沈阳张士污灌区的案例研究

Soil samples were collected from Zhangshi Wastewater Irrigation Area in the suburb of Shenyang City, China, an area with a 30-year irrigation history with heavy metal-containing wastewater. The chemical properties and microbial characteristics of the soils were examined to evaluate the present situation of heavy metal pollution and to assess the soil microbial characteristics under long-term heavy metal stress. In light of the National Environmental Quality Standards of China, the soil in the test area was heavily polluted by Cd and to a lesser degree by Zn and Cu, even though wastewater irrigation ceased in 1993. Soil metabolic quotient （qCO2） had a significant positive correlation, while soil microbial quotient （qM） had a negative correlation with content of soil heavy metals. Soil microbial biomass carbon （MBC） had significantly negative correlation with Cd, but soil substrate~induced respiration （SIR）, dehydrogenase activity （DHA）, cellulase activity, and culturable microbial populations had no persistent correlations with soil heavy metal content. Soil nutrients, except for phosphorous, showed positive effects on soil microbial characteristics, which to a certain degree obscured the adverse effects of soil heavy metals. Soil Cd contributed more to the soil microbial characteristics, but qM and qCO2 were more sensitive and showed persistent responses to heavy metals stress. It could be concluded that qM and qCO2 can be used as bioindicators of heavy metal pollution in soils.     

基于小白菜Cd吸收推算土壤Cd安全阈值

Cadmium(Cd), a common toxic heavy metal in soil, has relatively high bioavailability, which seriously threatens agricultural products. In this study, 8 different soils with contrasting soil properties were collected from different regions in China to investigate the Cd transfer coefficient from soil to Chinese cabbage(Brassica chinensis L.) and the threshold levels of Cd in soils for production of Chinese cabbage according to the food safety standard for Cd. Exogenous Cd(0–4 mg kg~(-1)) was added to the soils and equilibrated for 2 weeks before Chinese cabbage was grown under greenhouse conditions. The influence of soil properties on the relationship between soil and cabbage Cd concentrations was investigated. The results showed that Cd concentration in the edible part of Chinese cabbage increased linearly with soil Cd concentration in 5 soils, but showed a curvilinear pattern with a plateau at the highest dose of exogenous Cd in the other 3 soils. The Cd transfer coefficient from soil to plant varied significantly among the different soils and decreased with increasing soil p H from 4.7 to 7.5. However, further increase in soil pH to 8.0 resulted in a significant decrease in the Cd transfer coefficient. According to the measured Cd transfer coefficient and by reference to the National Food Safety Standards of China, the safety threshold of Cd concentration in soil was predicted to be between 0.12 and 1.7 mg kg~(-1) for the tested soils. The predicted threshold values were higher than the current soil quality standard for Cd in 5 soils, but lower than the standard in the other 3 soils. Regression analysis showed a significant positive relationship between the predicted soil Cd safety threshold value and soil p H in combination with soil organic matter or clay content.     

利用PCR-DGGE技术研究长期自然恢复、种植作物和裸地条件下黑土土壤细菌群落结构变化

Soil microbial biomass and community structures are commonly used as indicators for soil quality and fertility. A investigation was performed to study the effects of long-term natural restoration, cropping, and bare fallow managements on the soil microbial biomass and bacterial community structures in depths of 0--10, 20--30, and 40--50 cm in a black soil (Mollisol). Microbial biomass was estimated from chloroform fumigation-extraction, and bacterial community structures were determined by analysis of 16S rDNA using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Experimental results showed that microbial biomass significantly declined with soil depth in the managements of restoration and cropping, but not in the bare fallow. DGGE profiles indicated that the band number in top 0--10 cm soils was less than that in depth of 20--30 or 40--50 cm. These suggested that the microbial population was high but the bacterial community structure was simple in the topsoil. Cluster and principle component analysis based on DGGE banding patterns showed that the bacterial community structure was affected by soil depth more primarily than by managements, and the succession of bacterial community as increase of soil depth has a similar tendency in the three managements. Fourteen predominating DGGE bands were excised and sequenced, in which 6 bands were identified as the taxa of Verrucomicrobia, 2 bands as Actinobacteria, 2 bands as α-Proteobacteria, and the other 4 bands as δ-Proteobacteria, Acidobacteria, Nitrospira, and unclassified bacteria. In addition, the sequences of 11 DGGE bands were closely related to uncultured bacteria. Thus, the bacterial community structure in black soil was stable, and the predominating bacterial groups were uncultured.     

森林土壤重金属的分布和迁移: 一种高密度采样方法的应用

The vertical distribution and migration of Cu, Zn, Pb, and Cd in two forest soil profiles near an industrial emission source were investigated using a high resolution sampling method together with reference element Ti. One-meter soil profile was sectioned horizontally at 2 cm intervals in the first 40 cm, 5 cm intervals in the next 40 cm, and 10 cm intervals in the last 20 cm. The migration distance and rate of heavy metals in the soil profiles were calculated according to their relative concentrations in the profiles, as calibrated by the reference element Ti. The enrichment of heavy metals appeared in the uppermost layer of the forest soil, and the soil heavy metal concentrations decreased down the profile until reaching their background values. The calculated average migration rates of Cd, Cu, Pb, and Zn were 0.70, 0.33, 0.37, and 0.76 cm year^-1, respectively, which were comparable to other methods. A simulation model was proposed, which could well describe the distribution of Cu, Zn, Pb, and Cd in natural forest soils.     

磷改良剂对中度和高度含碳酸盐的菜园土壤中Cd和Pb环境有效性和植物有效性的影响

The behaviour of metals mainly depends on soil p H, carbonate contents and contamination level, which should be considered for the management of contaminated soils. In this study, kitchen garden topsoils(0–25 cm) were sampled from the area around three smelters in France, with different Cd and Pb contamination levels. Effect of a phosphate amendment(a mixture of diammonium phosphate and hydroxyapatite) on the environmental availability and phytoavailability of Cd and Pb was evaluated by different chemical extractions and cultivating lettuce(Lactuca sativa L.), respectively. Changes in the distribution of Cd and Pb were found in most contaminated soils after phosphate amendment. An increase of Cd and Pb in the residual phase was highlighted in almost all carbonated contaminated soils, whereas a decrease of Pb in the exchangeable, water and acid-soluble phase was observed in most contaminated soils with the lowest carbonate contents. The concentrations of extractable Cd and Pb using calcium chloride and acetic and citric acids generally decreased after the soil amendment. Lettuces grown on amended soils were acceptable for human consumption as regard to Pb concentration. In contrast, some lettuces were unacceptable for human consumption, since the concentrations of Cd in the leaves were higher than the European legislation limit. Surprisingly, in carbonated soils with very low concentration of Cd, the Cd concentrations in lettuce reached up to the European legislation limit, making the lettuce unacceptable for human consumption.Our study highlighted the fact that the total metal concentration in soils does not always allow to predict the metal accumulation in the edible parts of vegetables in order to make a judgement about their acceptability or unacceptability for human consumption.     

一株在微生物燃料电池中可以利用喹啉发电的产电假单胞杆菌Q1的产电特性研究

A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.     

4种湿地植物根系泌氧由根诱导的pH,Eh和Fe(II)变化和根际土壤中铅和锌的组分研究

A rhizobox experiment was conducted to compare iron (Fe) oxidation and changes of pH, redox potential (Eh) and fractions of zinc (Zn) and lead (Pb) in rhizosphere and non-rhizosphere soils of four emergent-rooted wetland plants (Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris and Veronica serpyllifolia) with different radial oxygen loss (ROL) from roots. The results indicated that all these wetland plants decreased pH and concentration of Fe(Ⅱ) but increased the Eh in the rhizosphere soils. Pb and Zn were transformed from unstable fractions to more stable fractions in the rhizosphere soils, so decreasing their potential metal mobility factors (MF). Among the four plants, E. macrophyllus, with the highest ROL and root biomass, possessed the greatest ability in formation of Fe plaque and in the reduction of heavy metal MFs in the rhizosphere soil. Wetland plants, with higher ROLs and root biomass, may thus be effective in decreasing potential long-term heavy metal bioavailabilities.     

Use of the BCR three-step sequential extraction procedure for the study of the partitioning of Cd, Pb and Zn in various soil samples

A slightly modified three-step sequential extraction procedure proposed by the Community Bureau of Reference (BCR) for analysis of sediments was successfully applied to soil samples. Contaminated soil samples from the lead and zinc mining area in the Mezica valley (Slovenia) and natural soils from a non-industrial area were analysed. The total concentrations of Cd, Pb and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS). Total metal concentrations in natural soils ranged from 0.3 to 2.6 mg kg^-1 for Cd, from 20 to 45 mg kg^-1 for Pb and from 70 to 140 mg kg^-1 for Zn, while these concentrations ranged from 0.5 to 35 mg kg^-1 for Cd, from 200 to 10000 mg kg^-1 for Pb and from 140 to 1500 mg kg^-1 for Zn in soils from contaminated areas. The results of the partitioning study applying the slightly modified BCR three-step extraction procedure indicate that Cd, Pb and Zn in natural soils prevails mostly in sparingly soluble fractions. Cd in natural soils is bound mainly to Fe and Mn oxides and hydroxides, Pb to organic matter, sulphides and silicates, while Zn is predominantly bound to silicates. In contaminated soils, Cd, Pb and Zn are distributed between the easily and sparingly soluble fractions. Due to the high total Cd, Pb and Zn concentrations in contaminated soil close to the smelter, ! and their high proportions in the easily soluble fraction (80% of Cd, 50% of Pb and 70% of Zn), the soil around smelters represents an environmental hazard.     

Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan,India

Use of wastewater for irrigating agricultural crops is on the rise, particularly in the developing countries. The present study was undertaken to assess the long-term effect of irrigation with zinc smelter effluent on important soil properties including heavy metal status. Metal concentration in the edible parts of the crops grown on smelter effluent-irrigated soils was also measured. For this purpose, the agricultural lands which have been receiving the zinc smelter effluent irrigation for about five decades at Debari, Udaipur, India were selected. The adjacent tubewell water-irrigated fields were selected as reference. Long-term irrigation with smelter effluent resulted into significant buildup of ethylenediaminetetraacetic acid extractable Zn (57.7 fold), Cu (4.51 fold), Fe (3.35 fold), Mn (1.77 fold), Ni (1.20 fold), Pb (45.1 fold), and Cd (79.2 fold) in soils over tubewell water-irrigated fields. Total Zn, Cu, Mn, Ni, Pb, and Cd content in effluent-irrigated soils was also increased by 27.0, 1.60, 1.40, 1.30, 26.2, and 167 fold, respectively. Risk assessment indicated a very high to moderate potential ecological risk due to Cd, Pb, and Zn in soils close to the immediate vicinity of the smelter plant. Cadmium and Pb concentrations in edible parts of almost all the crops grown on effluent-irrigated soils were above the safe limit of CODEX commission. On an average, soil pH dropped by 0.31 units due to smelter effluent irrigation. Smelter effluent irrigation resulted into significant increase in soil organic carbon, electrical conductivity, and CaCO₃ content. On an average, there was decrease in available N (21.0%) and P (20.8%) content in effluent-irrigated soils over the tubewell water-irrigated ones. An increase in available K (102%) and S (26.0 fold) was recorded in effluent-irrigated soils. Long-term irrigation with zinc smelter effluent resulted into reduced microbial activities in soil as evidenced from the level of microbial biomass carbon and dehydrogenase activity. In view of the buildup of heavy metals and subsequent imbalance in essential plant nutrients in smelter effluent-irrigated soils, appropriate remediation-cum-fertilization strategy needs to be adopted for better soil health and plant nutrition.     

Soybean nodulation and nitrogen fixation on soil previously amended with sewage sludge

Summary A greenhouse study was conducted to examine the residual effects of sewage sludge on soybean Glycine max (L.) Merr., nodulation, and N fixation. Nodulating and nonnodulating isolines of Clark soybean were grown to the R2 stage in soils (Typic Paleudults) obtained from plots where heat-treated sludge had been applied in 1976 at rates equal to 0, 56,112, and 224 Mg ha^–1 high (7.0) and low (6.2) soil pH regimes were established by CaCO₃ additions. Sludge and soil pH treatments resulted in clearly defined differences in metal uptake by soybean shoots. Plant Zn, Cd, and Ni concentrations were greater on pH 6.2, sludge-amended soil than on the pH 7.0, amended soil. At low soil pH, soybean Zn and Cd concentrations, respectively, increased from 41 and 0.19 mg kg^–1 (control) to 120 and 0.58 mg kg^–1 at the 224 Mg hat sludge rate. At the high soil pH and 224 hg hat sludge rate, Zn and Cd concentrations were 45 and 0.15 mg kg^–1, respectively.Symbiotic N fixation provided 90% of the total N accumulation. Total N accumulation, shoot N concentration, dry matter, and N fixation by nodulating soybeans exhibited a significant linear increase with sludge rate. Total N accumulation, dry matter, and N fixation were significantly greater at high soil pH. For high and low soil pH, respectively, N fixation increased from 422 and 382 mg N per plant (control) to 614 and 518 mg N per plant at the 224 Mg ha^–1 sludge rate. While soybean nodulation also increased linearly on sludge-amended soil, a significant rate times pH interaction for nodule number indicated that nodulation was less strongly enhanced by sludge at low soil pH.     

Heavy‐Metal Inhibition of Nitrification in Selected Iowa Soils Treated with Stay‐N 2000

Abstract

Heavy‐metal inhibition of nitrification in soils treated with reformulated nitrapyrin was investigated. Clarion and Okoboji soils were treated with ammonium sulfate [(NH₄)₂SO₄] and a nitrification inhibitor. Copper(II) (Cu), Zinc(II) (Zn), Cadmium(II) (Cd), or Lead(II) (Pb) were added to each soil. A first‐order equation was used to calculate the maximum nitrification rate (K _max), duration of lag period (t′), period of maximum nitrification (Δt), and the termination period of nitrification (t _s). In the Clarion soil, the K _max decreased from 12 mg kg^?1 d^?1 without the nitrification inhibitor to 4, 0.25, 0.86, and 0.27 mg kg^?1 d^?1, respectively, when the inhibitor and Cu, Zn, Pb, or Cd were applied. In the Okoboji soil, K _max decreased from 22 mg kg^?1 d^?1 with no inhibitor to 6, 3, 4, and 2 mg kg^?1 d^?1, respectively, when an inhibitor and Cu, Zn, Pb, or Cd were added. The t′ varied from 8 to 25 d in the Clarion soil and from 5 to 25 d in the Okoboji soil, due to addition of Cu, Zn, Pb, or Cd and the inhibitor.     

Heavy metal levels in earthworms of a forest ecosystem influenced by traffic and air pollution

Soils of a forest ecosystem in Berlin (West) are highly polluted by Pb and less polluted by Cd and Cu. Pb levels in earthworm species depend primarily on soil type and only secondarily on the distance from a highway crossing the forest. The dominating species Lumbricus rubellus and Dendrobaena octaedra show different body burdens especially of Cd. Liming the forest soils decreases the Pb concentrations significantly. Only in D. octaedra has body weight been found to be related to Pb; Pb has been increased from 50 mg kg^–1 in small to 250 mg kg^–1 in large specimens; Cu has been regulated at a more or less constant absolute level (about 0.4 pg per specimen). This species obviously regulates or accumulates the three metals in different ways. Centipedes as predators of earthworms in the sites show markedly less pollution of Pb and Cd (about 2.5 and 0.6 mg kg^–1) than the worms, but higher concentrations of the essential Cu (about 40 mg kg^–1). The use of earthworms as indicators of heavy metal pollution should take into account the biology of the various species, the soil type, the type and amount of organic matter as well as chemical parameters such as pH value or basic anions.     

Plant Availability and Uptake of Lead, Zinc, and Cadmium in Soils Contaminated with Anti-corrosion Paint from Pylons in Comparison to Heavy Metal Contaminated Urban Soils

Red lead (Pb₃O₄) has been used extensively in the past as an anti-corrosion paint for the protection of steel constructions. Prominent examples being some of the 200,000 high-voltage pylons in Germany which have been treated with red lead anti-corrosion paints until about 1970. Through weathering and maintenance work, paint compounds and particles are deposited on the soils beneath these constructions. In the present study, six such “pylon soils” were investigated in order to characterize the plant availability and plant uptake of Pb, Cd, and Zn. For comparison, three urban soils with similar levels of heavy metal contamination were included. One phase extractions with 1 M NH₄NO₃, sequential extractions (seven steps), and extractions at different soil pH were used to evaluate the heavy metal binding forms in the soil and availability to plants. Greenhouse experiments were conducted to determine heavy metal uptake by Lolium multiflorum and Lactuca sativa var. crispa in untreated and limed red lead paint contaminated soils. Concentrations of Pb and Zn in the pylon soils were elevated with maximum values of 783 mg Pb kg⁻¹ and 635 Zn mg kg⁻¹ while the soil Cd content was similar to nearby reference soils. The pylon soils were characterized by exceptionally high proportions of NH₄NO₃-extractable Pb reaching up to 17% of total Pb. Even if the relatively low pH of the soils is considered (pH 4.3–4.9), this appears to be a specific feature of the red lead contamination since similarly contaminated urban soils have to be acidified to pH 2.5 to achieve a similarly high Pb extractability. The Pb content in L. multiflorum shoots reached maximum values of 73 mg kg⁻¹ after a cultivation time of 4 weeks in pylon soil. Lime amendment reduced the plant uptake of Pb and Zn significantly by up to 91%. But L. sativa var. crispa cultivated on soils limed to neutral pH still contained critical Pb concentrations (up to 0.6 mg kg⁻¹ fresh weight). Possible mechanisms for the exceptionally high plant availability of soil Pb derived from red lead paint are discussed.     

Regenwürmer als Bioindikatoren für Schwermetallbelastungen von Böden unter Freilandbedingungen

The use of earthworms in monitoring soil pollution by heavy metals Total heavy metal contents (HNO₃-soluble) and exchangeable fractions (Ca(NO₃)₂-soluble) of Pb, Zn and Cd were measured in soils, litter layers and earthworms (dry masses) from forest, arable and pasture sites in a transect of the main wind direction and varying distances (1.5, 5.4, 11.4, 15.6 km) to a lead smelter near Bad Ems, Germany. Additionally, cast materials of Lumbricus terrestris-individuals were collected from the surface of the pasture sites. In the observed area total soil contents of Pb and Cd exceeded the C-level and total contents of Zn the B-level of the “Netherland-list”. Heavy metal contents in soils and earthworms decreased with increasing distance to the smelter. Pb showed the best correlation. Correlation between total contents of Pb and Cd in soils and earthworms were significant (rs = 0.66; p < 0.05 and rs = 0.67; p < 0.01, respectively). The uptake of heavy metals by Lumbricus rubellus, L. terrestris and Aporrectodea caliginosa was metal specific rather than species specific with factors of accumulation being <1 (Pb), 2.7–7.6 (Zn) and 19.5–85.5 (Cd). The heavy metal contents of the observed cast materials signified the different transfer of elements from soil material via earthworm individuals to the faeces. In the cast materials the amounts of Pb were high and the amounts of Zn and Cd were low. This indicates a high accumulation rate for Zn and especially for Cd in the tissues of the observed earthworm individuals. The present data support the necessity of ecotoxicological threshold levels.     

Immobilization of heavy metals in soils using inorganic amendments in a greenhouse study

The effect of red mud (10 g kg^–1), a by‐product of the alumina industry, zeolite (20 g kg^–1), a naturally‐occurring hydrous aluminosilicate, and lime (3 g kg^–1) on metal lability in soil and uptake by fescue (Festuca rubra L.) (FEST) and amaranthus (Amaranthus hybridus L.) (AMA) was investigated in four different soils from Austria. The soil collection locations were Untertiefenbach (UNT), Weyersdorf (WEY), Reisenberg (REI), and Arnoldstein (ARN). The latter was collected in the vicinity of a former Pb‐Zn smelter and was highly polluted with Pb (12300 mg kg^–1), Zn (2713 mg kg^–1), and Cd (19.7 mg kg^–1) by long‐term deposition. The other soils were spiked with Zn (700 mg kg^–1), Cu (250 mg kg^–1), Ni (100 mg kg^–1), V (100 mg kg^–1), and Cd (7 mg kg^–1) salts in 1987. The two plant species were cultivated for 15 months. Ammonium nitrate (1 M) extraction was used in a soil : solution ratio of 1:2.5 to assess the influence of the amendments on the labile metal pools. The reduction of metal extractability due to red mud was 70 % (Cd), 89 % (Zn), and 74 % (Ni) in the sandy soil (WEY). Plant uptake in this treatment was reduced by 38 to 87 % (Cd), 50 to 81 % (Zn), and 66 to 87 % (Ni) when compared to the control. Sequential extraction revealed relative enrichments of Fe‐oxide‐associated metal fractions at the expense of exchangeable metal fractions. Red mud was the only amendment that decreased lability in soil and plant uptake of Zn, Cd, and Ni consistently. Possible drawbacks of red mud application (e.g., As and Cr concentration) remain to be evaluated.     

Bioavailability and Accumulation of Cadmium and Zinc by Sedum plumbizincicola after Liming of an Agricultural Soil Subjected to Acid Mine Drainage

A glasshouse pot experiment was conducted to study the effects of liming on plant growth and zinc (Zn) and cadmium (Cd) accumulation by Sedum plumbizincicola in a heavy-metal-contaminated acidified paddy soil. Lime application significantly increased the soil pH, which reached a maximum of 5.53 after addition of 4.0 g kg^?1 lime to soil, about 1.4 units more than that of the control. Sedum plumbizincicola grew larger after lime application but aboveground biomass did not increase significantly with increasing soil pH. Liming significantly reduced shoot Zn and Cd concentrations and uptake except at the lowest lime application rate (0.5 g kg^?1 lime to soil). This indicates that S. plumbizincicola can grow well in acidic soil at a soil pH of 4.15, and application of lime did not increase plant heavy-metal extraction. Consequently, it is promising to use this plant for Cd and Zn phytoextraction from agricultural soils polluted with acid and metals.     

Bioavailability of zinc and lead from a contaminated soil amended with pine bark-goat manure compost

The distribution in soil and plant uptake of zinc (Zn) and lead (Pb) as influenced by pine bark-goat manure (PBG) compost additions were investigated from the soils artificially contaminated with Zn or Pb ions using maize (Zea mays L.) as a test crop. Soils were amended with four rates of pine bark-goat manure compost (0, 50, 100, and 200 tons ha^?1) and four rates (0, 300, 600 and 1200 mg kg^?1) of Zn or Pb. Maize was planted and grown for 42 days. At harvest, plants samples were analyzed for Zn and Pb concentration. Soils samples were analyzed for pH, extractable and diethylene triamine pentaacetic acid (DTPA) extractable Zn and Pb. Extractable Zn and Pb was lower in PBG compost amended soils than in unamended soils and steadily declined with increasing amount of compost applied. The extractable fraction for Zn dropped by 62.2, 65.0 and 44.6% for 300, 600 and 1200 mg Zn kg^?1, respectively when 200 t ha^?1 of PBG compost was applied. Metal uptake by maize plants were directly related to the rate of applied heavy metal ions with greater concentrations of metals ions found where metal ions were added to non-amended soils.