The biological and physico-chemical uptake of radiocesium by particulate matter of natural origin (Baltic Sea)

The kinetics of radiocesium (¹³⁷Cs) uptake by natural suspended matter collected from coastal waters in the southern Baltic has been studied under laboratory conditions. The uptake of radiocesium from seawater by the suspended matter took place immediately after introduction of the isotope and attained equilibrium within a few hours. Summer and winter suspended matter displayed equal K_d values, indicating similar sorption characteristics of radiocesium. The amounts of radiocesium sorbed from sea water were proportional to the suspended matter concentration studied,i.e. up to 312 mg dry wt dm^–3. The relative uptake of radiocesium by live and dead plankton appeared to be the same. The desorption of radiocesium from dead plankton proceeded more rapidly and more intensively than sorption. There are no significant differences between the K_d values for plankton determined in laboratory experiments and those found for plankton populations under field conditions.     

Experimental investigation of plant uptake of caesium from soils amended with clinoptilolite and calcium carbonate

Radioactive caesium (137Cs), from the Chernobyl accident of 1986, has unexpectedly remained in a bioavailable form in upland, sheep-grazing soils of Great Britain. As a potential remedial measure, clinoptilolite was tested in a greenhouse pot experiment for its effectiveness in selectively taking up Cs from two British soils; a lowland loam (Denbigh 1 brown earth) and an upland peat (Crowdy 2 series)Rye-grass, (Lolium perenne, Arno variety) that was grown on 10% (by weight) clinoptilolite-treated soils containing up to 40 mg kg-1 added Cs, resulted in grass leaf tissue Cs concentrations below 30 mg Cs kg-1 grass in all cases. Where no clinoptilolite had been added Cs in grass leaf-tissue reached 1860 mg kg-1 (grown on peat) and 150 mg kg-1 (grown on loam) at added Cs levels of 40 mg kg-1 soil. The addition of calcium carbonate (as ground limestone) to the Cs-treated, clinoptilolite-free peat soil enhanced the grass concentration of Cs by approximately 5 times, but this effect was not observed with the concentration of Cs in grass grown from loam soils with the same treatments. Compositions of clinoptilolite grains subsequently separated from the experimental soils ranged from 7.5 to 9.0 mg Cs kg-1 for the control soils (no added Cs). Soils treated with 40 mg Cs kg-1 gave Cs concentrations in clinoptilolite of 155-170 mg kg-1 (separated from loam) and 347-354 mg kg-1 (separated from peat).     

黏土矿物中重金属离子的吸附规律及竞争吸附

采用等温吸附法,研究了重金属铜、铅、镉、镍在膨润土中的吸附特征,发现膨润土对铜、铅的吸附明显强于镉、镍,吸附强度大小顺序为Pb2 >Cu2 >Ni2 >Cd2 。Langmuir和Freundlich方程对这4种金属离子等温吸附的拟合均呈极显著关系。Pb2 、Cd2 、Ni2 分别与Cu2 的双组分竞争吸附表明,黏土矿物对4种离子具有"选择性吸附"。在Pb2 、Ni2 、Cd2 的存在条件下,黏土矿物对Cu2 的吸附产生不同程度的下降;100mg/LCu2 对Pb2 的影响不大,但可完全抑制Ni2 、Cd2 的吸附。建立了IAS和LCA模型来预测Pb2 与Cu2 的双组分竞争吸附,并对LCA模型进行修正,提出了更符合实际情况的竞争吸附模型。文章最后用LCA修正模型对Pb2 与Cu2 的双组分竞争吸附进行了模拟。     

Effect of cations,including heavy metals,on cadmium uptake by Lemna polyrhiza L.

Cations, including calcium, magnesium, potassium, sodium, copper, iron, nickel and zinc, inhibited (up to 40%) extracellular binding and intracellular uptake of cadmium by Lemna polyrhiza in solution culture. Test plants showed a high capacity of extracellular cadmium binding which was competitively inhibited by copper, nickel and zinc; however, calcium, magnesium and potassium caused non-competitive inhibition. Iron and sodium increased K _m and decreased V _max, thereby causing mixed inhibition of extracellular binding. Intracellular cadmium uptake displayed Michaelis-Menten kinetics. It was competitively inhibited by calcium, magnesium, iron, nickel and zinc. Monovalent cations (sodium and potassium) caused non-competitive and copper caused mixed inhibition of intracellular cadmium uptake. Thus, high levels of cations and metals in the external environment should be expected to lower the cadmium accumulation efficiency of L. polyrhiza.     

沸石对土壤养分生物有效性和土壤化学性质的影响研究

在花岗岩发育的赤红壤上进行的天然沸石混施化肥的盆栽试验研究结果表明,沸石提高了土壤养分的生物有效性,显著促进玉米的生长,增加玉米的生物量和提高了玉米对N,P,K的吸收量,15N示踪技术表明,沸石处理可以显著提高氮肥的利用率,两造玉米最高的氮肥利用率分别比对照提高28．8％和60．0％,土壤的分析结果表明,沸石处理也可提高土壤阳离子交换量,盐基饱和度和土壤pH值。     

Enhanced phytoextraction: II. Effect of EDTA and citric acid on heavy metal uptake by Helianthus annuus from a calcareous soil

High biomass producing plant species, such as Helianthus annuus, have potential for removing large amounts of trace metals by harvesting the aboveground biomass if sufficient metal concentrations in their biomass can be achieved However, the low bioavailability of heavy metals in soils and the limited translocation of heavy metals to the shoots by most high biomass producing plant species limit the efficiency of the phytoextraction process. Amendment of a contaminated soil with ethylene diamine tetraacetic acid (EDTA) or citric acid increases soluble heavy metal concentrations, potentially rendering them more available for plant uptake. This article discusses the effects of EDTA and citric acid on the uptake of heavy metals and translocation to aboveground harvestable plant parts in Helianthus annuus. EDTA was included in the research for comparison purposes in our quest for less persistent alternatives, suitable for enhanced phytoextraction. Plants were grown in a calcareous soil moderately contaminated with Cu, Pb, Zn, and Cd and treated with increasing concentrations of EDTA (0.1, 1, 3, 5, 7, and 10 mmol kg(-1) soil) or citric acid (0.01, 0.05, 0.25, 0.442, and 0.5 mol kg(-1) soil). Heavy metal concentrations in harvested shoots increased with EDTA concentration but the actual amount of phytoextracted heavy metals decreased at high EDTA concentrations, due to severe growth depression. Helianthus annuus suffered heavy metal stress due to the significantly increased bioavailable metal fraction in the soil. The rapid mineralization of citric acid and the high buffering capacity of the soil made citric acid inefficient in increasing the phytoextracted amounts of heavy metals. Treatments that did not exceed the buffering capacity of the soil (< 0.442 mol kg(-1) soil) did not result in any significant increase in shoot heavy metal concentrations. Treatments with high concentrations resulted in a dissolution of the carbonates and compaction of the soil. These physicochemical changes caused growth depression of Helianthus annuus. EDTA and citric acid added before sowing of Helianthus annuus did not appear to be efficient amendments when phytoextraction of heavy metals from calcareous soils is considered.     

Influence of clay mineral type and organic matter content on the uptake of239Pu and241Am by plants

Summary The uptake of²³⁹Pu and²⁴¹Am from different clay mineral-organic matter-sand mixtures simulating contrasting soil types was examined in growth chamber experiments. The mixtures represented various combinations of organic matter (0, 5 and 10%), kaolinite (11 type) and montomorillonite (21 type) clay minerals, each at the levels of 5, 10 and 25%, and purified quartz sand (as filler).Results indicated a marked reduction in uptake of both²³⁹Pu and²⁴¹Am with increase in organic matter as well as clay content of the mixtures. The Pu Concentration Ratios (CRs) ranged from (2.5–7.0)×10^–3 in the case of kaolinite-organic matter mixtures, and from (0.9–5.5)×10^–3 in the case of montmorillonite-organic matter mixtures. The corresponding values of Am Concentration Ratios (CRs) obtained were (1.9–725.4)×10^–3 in the case of kaolinite-organic matter mixtures, and between (0.7–3.5)×10^–3 for the montmorillonite-organic matter mixtures.Reduction in the uptake of²⁴¹Am with increasing clay content was more pronounced in the montmorillonite clay-organic matter mixtures as compared to that in the case of kaolinite-organic matter mixtures. While similar qualitative reduction in²³⁹Pu CRs with increasing clay content was observed, the reduction was less marked than in the case of²⁴¹Am. The values for Am CRs were higher than the corresponding Pu CRs in kaolinite based mixtures whereas in the case of montmorillonite-organic matter mixtures Pu CRs exceeded the Am CRs.Increasing organic matter content and its interaction with both kaolinite and montmorillonite clay minerals were found to be equally effective in reducing the uptake of²³⁹Pu as well as²⁴¹Am by plants.     

Studies on the removal of heavy metals from sludges by leaching and uptake by plants

Sewage sludges from 19 Polish municipal treatment plants were investigated. Lysimeter leaching experiments on sludges and on sludge-quartz sand mixtures were made. A variety of plants was sowed in the lysimeters and the leachates were collected. Harvested plants as well as leachates were analysed for Pb, Cu, Cd, Ni, Zn and Cr concentration. Removal coefficients were established to characterize the mobility of these metals from the sludges. The high values of the correlation coefficient for cadmium and nickel suggested that water solubility of metal salts is mainly responsible for their mobility.     

Bioavailability and mobility of heavy metals in soil in vicinity of a coal mine from Huaibei,China

This study investigated the concentrations of Co, Cr, Cu, Mn, Ni, Pb and Zn in surface soil and corn cob samples collected from agricultural fields near a coal mine from Huaibei, China. Meanwhile, the mobility and availability of heavy metals in soil samples were evaluated by a modified three-step The European Community Bureau of Reference (BCR) sequential extraction procedure. The total concentrations of metals in soil pose no ecological threats to the local plants. Transfer factors of essential metals, Cu and Zn, as well as those of non-essential metal Pb, were higher than those of the remained metals. The results of BCR fractionation analysis revealed that the acid soluble, reducible and oxidizable fractions of the Mn, Pb and Zn were higher than those of the residual fraction, suggesting that these elements may be more bioavailable. The pH and organic matter contents of soil were significant parameters affecting speciation of metals in soil samples. Hierarchical cluster analysis indicated significant correlations between metal levels in corn grains and more available (acid soluble and reducible) fractions in soil, indicating that heavy metals in the first two fractions were more available for corn crops. The elevated mobility and bioavailability of Pb in soil are of great concern in the study area.     

Effect of soil nitrogen,carbon and moisture on methane uptake by dry tropical forest soils

Methane uptake was measured for two consecutive years for four forest and one savanna sites in a seasonally dry tropical region of India. The soils were nutrient-poor and well drained. These sites differed in vegetational cover and physico-chemical features of the soil. There were significant differences in CH₄ consumption rates during the two years (mean 0.43 and 0.49 mg m^-2 h^-1), and at different sites (mean 0.36 to 0.57 mg m^-2 h^-1). The mean uptake rate was higher (P < 0.05) in dry seasons than in the rainy season at all the sites. There was a significant season and site interaction, indicating that the effect of different seasons differed across the sites. There was a positive relation between soil moisture and CH₄ uptake rates during summer (the driest period) and a negative relation during the rest of the year. The results suggested that seasonally dry tropical forests are a strong sink for CH₄, and C and N status of soils regulates the strength of the sink in the long term.     

Root-zone modeling of heavy metal uptake and leaching in the presence of organic ligands

We present a mechanistic model which describes root uptake and leaching of heavy metals in the plant root zone, accounting for solution- and surface-complexation, (kinetic) mineral dissolution, heavy metal diffusion towards the root, root uptake, root exudation, ligand degradation and convective-dispersive transport of the soluble species. The model was used to simulate the influence of EDTA addition on Cu transport and plant uptake and the effect of oxalate exudation by roots on Cu transport and bioavailability using parameter values from the literature. In the simulations we assumed that free Cu²⁺ is the bioavailable form. Under slightly acidic conditions (pH 6) the model predicted that EDTA stabilizes Cu while at a slightly alkaline pH (pH 7.5), EDTA mobilizes Cu. The addition of EDTA approximately halved the cumulative Cu uptake after 360 days at pH 4.5, and reduced the uptake by a factor of 100 and 1000 at pH 6 and 7.5, respectively. Although the total dissolved concentration was increased, plant uptake was reduced by the formation of bio-inavailable complexes. The exudation of oxalate resulted in a decrease of the Cu concentration breaking through below the root zone, due to sorption of Cu-oxalate. In the presence of dissolved organic carbon (DOC), the exudation of oxalate increased Cu leaching considerably at pH 6 and 7.5. In the absence of DOC, the exudation of oxalate reduced Cu uptake due to the formation and adsorption of Cu-oxalate on goethite surface sites. Exudation of oxalate in the presence of DOC resulted in a further decrease of Cu uptake. Oxalate gradually takes over from DOC in binding Cu due to simultaneous production of oxalate and leaching of DOC. The simulations show that addition or exudation of ligands does not necessarily increase the solubility, transport and bioavailability of metals. Depending on the conditions (mainly the pH), also reduced transport and uptake can be observed, either by formation of ternary surface complexes or reduction of free metal concentration. The model can be easily extended to include further processes.     

Effect of land-use change and methane mixing ratio on methane uptake from United Kingdom soil

Methane (CH₄) is a trace gas 30 times more radiatively active than carbon dioxide and, apart from a recent decrease, its atmospheric concentration has been increasing at a rate of ～ 1%per annum since 1945. The increase results from an imbalance between CH₄ production and consumption. Here we assess the impact that changes in land use and increasing atmospheric CH₄ mixing ratios have had on CH4 uptake rates by soil in the UK since before the Iron age. This has been achieved by making retrospective analyses of CH₄ uptake in UK soils under four different conditions of land use and CH₄ mixing ratio. The calculations indicate that 54% of the current CH₄ uptake by UK soils is the result of increased CH₄ mixing ratio but that land-use change has caused a reduction of ～ 37 kt CH4 y^?1 in the potential sink strength of UK soils for CH₄. The results are discussed with respect to the compilation of greenhouse gas inventories.     

Effect of soil compaction on root growth and uptake of phosphorus

Summary Zea mays L. andLolium rigidum Gaud. were grown for 18 and 33 days respectively in pots containing three layers of soil each weighing 1 kg. The top and bottom layers were 100 mm deep and they had a bulk density of 1200 kg m^–3, while the central layer of soil was compacted to one of 12 bulk densities between 1200 and 1750 kg m^–3. The soil was labelled with³²P and³³P so that the contribution of the different layers of soil to the phosphorus content of the plant tops could be determined. Soil water potential was maintained between –20 and –100 kPa.Total dry weight of the plant tops and total root length were slightly affected by compaction of the soil, but root distribution was greatly altered. Compaction decreased root length in the compacted soil but increased root length in the overlying soil. Where bulk density was 1550 kg m^–3, root length in the compacted soil was about 0.5 of the maximum. At that density, the penetrometer resistance of the soil was 1.25 and 5.0 MPa and air porosity was 0.05 and 0.14 at water potentials of –20 and –100 kPa respectively, and daytime oxygen concentrations in the soil atmosphere at time of harvest were about 0.1 m³m^–3. Roots failed to grow completely through the compacted layer of soil at bulk densities 1550 kg m^–3. No differences were detected in the abilities of the two species to penetrate compacted soil.Ryegrass absorbed about twice as much phosphorus from uncompacted soil per unit length of root as did maize. Uptake of phosphorus from each layer of soil was related to the length of root in that layer, but differences in uptake between layers existed. Phosphorus uptake per unit length of root was higher from compacted than from uncompacted soil, particularly in the case of ryegrass at bulk densities of 1300–1500 kg m^–3.     

Effect of simultaneous establishment of Sedum alfredii and Zea mays on heavy metal accumulation in plants

Land application of biosolids to improve agricultural productivity is a cost-effective approach for resource recovery. Unfortunately, municipal biosolids often contain high concentrations of heavy metals, including zinc and copper. In this study, a co-cropping technique was investigated using a known zinc hyperaccumulator, Sedum alfredii with a grain crop, Zea mays. After a 3-mo growth trial, the results indicate that when Z. mays is co-cropped with S. alfredii, heavy metals accumulated in the grains were significantly reduced when compared to monoculture cropping. Co-cropping improved the growth of both plant species. In addition, the biosolids maintained stable pH, N-P-K concentrations, germination potential, and water content after the plant treatment, regardless of the plant species used in the trial. In conclusion, co-cropping with hyperaccumulators may be an effective approach to reducing the risk of contaminant uptake in edible crops.     

Comparative study on EUF and other methods of soil analysis for the determination of available potassium in soils from Northern Greece

Summary Twenty-one representative soils from Northern Greece could be grouped into three categories based on the EUF-K curves which displayed marked differences in the magnitude of K release by the soils employed. The cumulative K desorption by EUF within 35 min and the cumulative K-uptake values of ryegrass (10 cuts) were found to be correlated (r=0.87***). Although this correlation is rather close, the K dynamics of a soil can be better characterized by the course of the K-desorption curves. Because the quotient EUF-K-80°C/EUF-K-20°C can give information on the course of K desorption it is therefore sufficient in routine investigations to know the EUF-K-20°C contents and the numerical values of the quotients EUF-K-80°C/EUF-K-20°C.The EUF procedure does not only indicate the close relationship between K extracted and K uptake by plants, but it can also provide information on other nutrients in the same soil sample. With this extra information it was possible to explain why in some of the analysed soils K uptake was low despite high K availability, the reason being that P availability was not optimal in one of the experimental soils and that the Mn concentration of the soil solution was too high in another. At equal K availability the K uptake was also dependent on the amount of EUF-extractable N.     

Deposition of radiocesium to the soil by stemflow,throughfall and leaf-fall from beech trees

The amount of Chernobyl-derived¹³⁷Cs transferred to the soil by stemflow, throughfall (precipitation under the tree crown), and leaffall from three beeches was investigated as a function of time in the growing seasons of 1991 and 1992. Up to 70 Bq/week was deposited with the stemflow, mainly in dissolved form (<0.45 µm)=" rather=" than=" in=" particulate=" form=" (=">0.45 µm). The ratio of dissolved radiocesium to particulate radiocesium was about 10 in the stemflow. It varied considerably with time, but since these variations followed the same pattern for all three trees, they indicated a common cause to be responsible for the fractionation of radiocesium (e.g. meteorological conditions for bark weathering). A significant correlation was observed for the amount of dissolved¹³⁷Cs (in Bq) and the amount of stemflow (in liters). The¹³⁷Cs concentration in the stemflow (in Bq/1), however, decreased with increasing stemflow intensity (in Bq/week). For particulate radiocesium such correlations were not detected. Up to 5 Bq/m² per week was deposited with the throughfall from the canopy, mainly in particulate form (ratio dissolved radiocesium to particulate radiocesium = 0.34). The mean total annual amounts of¹³⁷Cs deposited to the ground (dissolved+particulate) for the three trees were: stemflow: 1991 600 Bq; 1992 460 Bq; throughfall: 1991 and 1992 100 Bq/m² each; leaffall: 1992 10 Bq/m². The data indicate that at present a substantial amount of the radiocesium in the leaves derives already from root uptake.Dedicated to Professor W. Jacobi on the occasion of his 65th birthday     

杀灭土壤中线虫对小麦生长和吸收N、P的影响

盆栽条件下研究了施用杀线剂(克线磷,67mg·kg^-1干土)和干热(105℃,2h)两种杀线措施对小麦生长和N、P养分吸收的影响。杀线剂对土壤中线虫的平均杀灭率约为80%, 干热处理的杀灭率为100%. 在杀线剂处理中,苗期至抽穗期小麦生物量、拔节期至成熟期植株含N量、全生育期植株吸N量以及抽穗和成熟期吸P量均显着低于对照。土壤干热处理后抽穗和成熟期小麦的生物量、含N量及N、P吸收量也比对照显着降低。两种杀线处理植株地上部生物量和N、P吸收量与相应处理全株变化趋势基本一致。但杀灭线虫对植株含P量影响较小。分析杀线虫后小麦生长和养分吸收受抑主要与土壤有机氮的矿化作用减弱、微生物活动产生的植物生长促进物质降低有关     

Effect of Immobilizing Substances and Salinity on Heavy Metals Availability to Wheat Grown on Sewage Sludge-Contaminated Soil

The objective of the investigation was to evaluate the effect of immobilizing substances and NaCl salinity on the availability of heavy metals: Zn, Cd, Cu, Ni, and Pb to wheat (Triticum aestivum L.). In greenhouse pot experiment, a sewage sludge amended soil was treated with the following immobilizing substances: three clay minerals (Na-bentonite, Ca-bentonite and zeolite), iron oxides (goethite and hematite), and phosphate fertilizers (superphosphate and Novaphos). The pots were planted with wheat and were irrigated either with deionized or saline water containing 1600 mg L^?1 NaCl. Wheat was harvested two times for shoot metal concentrations and biomass measurements. Metal species in soil solution were estimated using the software MINEQL+.

The addition of metal immobilizing substances to the soil significantly decreased metal availability to wheat. The largest reduction in metal bioavailability was found for bentonites. The irrigation with saline water (1600 mg L^?1 NaCl) resulted in a significant increase in metal chloride species (MCl⁺ and MCl₂ ⁰). The highest metal complexation with Cl occurred for Cd, which was about 53% of its total soil solution concentration. The total concentration of Cd (Cd_T) in soil solution increased by 1.6–2.8-fold due to saline water. The NaCl salinity caused a significant increase in uptake and shoot concentration of Cd for two harvests and small but significant increase in shoot Pb concentration for the second harvest. It was concluded that the use of bentonites is the most promising for the reduction of heavy metal availability to plants. Saline water containing 1600 mg L^{? 1} NaCl increased the availability of Cd and Pb to wheat and decreased the efficiency of bentonites to immobilize soluble Cd.     

Shading and the capture of localized soil nutrients: nutrient contents,carbohydrates, and root uptake kinetics of a perennial tussock grass

Summary The ability to exploit spatial and temporal heterogeneity in soil resources can be one factor important to the competitive balance of plants. Competition above-ground may limit selective plant responses to below-ground heterogeneity, since mechanisms such as root proliferation and alterations in uptake kinetics are energy-dependent processes. We studied the effect of shading on the ability of the perennial tussock grassAgropyron desertorum to take up nutrients from enriched soil microsites in two consecutive growing seasons. Roots of unshaded plants selectively increased phosphate uptake capacity in enriched soil microsites (mean increases of up to 73%), but shading eliminated this response. There were no changes in ammonium uptake capacity for roots in control and enriched patches for either shaded or unshaded plants. The 9-day shade treatments significantly reduced total nonstructural carbohydrate (TNC) concentrations for roots in 1990, but had no apparent effect on root carbohydrates in 1991 despite dramatic reductions in shoot TNC and fructan concentrations. Enrichment of the soil patches resulted in significantly greater phosphate concentrations in roots of both shaded and unshaded plants, with less dramatic differences for nitrogen and no changes in potassium concentrations. In many respects the shaded plants did surprisingly well, at least in terms of apparent nutrient acquisition. The effects of aboveground competition on nutrient demand, energy requirements, and belowground processes are discussed for plants exploiting soil resource heterogeneity.