三种植物对铀耐性及土壤中铀吸收积累差异的研究

采用溶液培养结合土壤培养的方法,研究了小白菜、冬苋菜和菠菜对铀的耐性及土壤中铀吸收积累的差异.结果表明:水培条件下(U 50mg/L),与小白菜和冬苋菜相比,菠菜对铀具有较强的耐性;在100mg/kg 土U的条件下,菠菜表现出比小白菜和冬苋菜更高吸收和积累铀的能力,其地上部分铀含量为232mg/kg DW(Dry Weight 干重),而根部铀含量达433mh/kg DW(Dry Weight 干重).菠菜可能对铀污染土壤的植物修复具有潜在的应用价值.     

Comparative analysis of proteomic changes in contrasting flax cultivars upon cadmium exposure

Cadmium (Cd) is classified as a serious pollutant due to its high toxicity, high carcinogenicity, and widespread presence in the environment. Phytoremediation represents an effective low‐cost approach for removing pollutants from contaminated soils, and a crop with significant phytoremediation potential is flax. However, significant differences in Cd accumulation and tolerance were previously found among commercial flax cultivars. Notably, cv. Jitka showed substantially higher tolerance to elevated Cd levels in soil and plant tissues than cv. Tábor. Here, significant changes in the expression of 14 proteins (related to disease/defense, metabolism, protein destination and storage, signal transduction, energy and cell structure) were detected by image and mass spectrometric analysis of two‐dimensionally separated proteins extracted from Cd‐treated cell suspension cultures derived from these contrasting cultivars. Further, two proteins, ferritin and glutamine synthetase (a key enzyme in glutathione biosynthesis), were only up‐regulated by Cd in cv. Jitka, indicating that Cd tolerance mechanisms in this cultivar may include maintenance of low Cd levels at sensitive sites by ferritin and low‐molecular weight thiol peptides binding Cd. The identified changes could facilitate marker‐assisted breeding for Cd tolerance and the development of transgenic flax lines with enhanced Cd tolerance and accumulation capacities for phytoremediating Cd‐contaminated soils.     

Determination of thallium in soils by flame atomic absorption spectrometry

A method is described for the determination of Tl in soils by FAAS, involving extraction of Tl from 5 g of soil by digestion with HClO₄/HNO₃ followed by separation of the extracted Tl into 5 mL of diisopropylether from HBr solution, including Ce(SO₄)₂. Tl in the organic phase is determined by direct aspiration into the spectrophotometer. The percentage relative standard deviation (% RSD) for 5 replicate samples is about 1%. The detection limits (S/N = 3) of this method are 0.001 mg/L for aqueous solution and 0.02 mg/kg DW for soil, when 50 mL of soil solution corresponding to 2.5 g soil are used. The Tl concentration even of unpolluted soils can be determined. The method was shown to be unaffected by the presence of various ions in soil and was able to recover nearly 100% Tl added to soils. The arithmetic mean (range) of 18 Japanese unpolluted surface soils was 0.33 (0.10–0.56)mgTl/kg DW.     

Feasibility study on reducing lead and cadmium absorption by spinach (Spinacia oleracea L.) in a contaminated soil using nanoporous activated carbon

Activated carbons (AC) have been long recognized as prominent absorbents in industries and feature numerous applications in preventing or absorbing the harmful gases and liquids and could be employed for filtration and remediation or even reutilization of chemicals. In order to investigate the capacity of AC in reducing the absorption of heavy metals (HM) including lead (Pb) and cadmium (Cd) and dual complex (Pb?×?Cd) by spinach, a factorial experiment in a completely randomized design with three replications on a pot trial was conducted. Three factors including five levels of AC 0, 5000, 10000, 15000, 20000?mg/kg soil, one concentration level of Pb 4,000?mg/kg soil and one concentration level of cadmium Cd 8?mg/kg soil were tested. The index of heavy metal concentration was calculated in leaf, stem and root and their corresponding dry weights. Results illustrated that in contaminated soils, plants with AC exhibited a superior reduction of absorption of HM vis-à-vis the plants without AC. The foremost result regarding the impact of AC on reducing the concentration of Pb and Cd was observed in 20,000 level of AC. This reveals that AC declined the soil contamination and lessened the accumulation of HM into the shoots and roots. Results suggest that the application of AC may be an eligible solution for decreasing the translocation of HM into the plants.     

Utilization of waste seashells and Camelina sativa oil for biodiesel synthesis

The seafood industry produces over 100 million pounds of seashell waste every year. With landfill space diminishing quickly, ways to recycle waste materials are becoming more sought for. Herein, we utilized waste mussel, clam and oyster shells as heterogeneous catalysts for the transesterification of Camelina sativa oil as a feedstock into biodiesel. Camelina sativa oil provides a reliable solution for biodiesel production because it has high tolerance of cold weather, drought, low-fertility soils and contains approximately 40% oil content. The catalysts from waste seashells were characterized by X-ray powder diffraction and Fourier transform infrared (FTIR) spectroscopy. High biodiesel yields were achieved at a 12:1 (alcohol:oil) molar ratio with 1?wt.% waste seashell catalysts in 2?h at 65°C. Biodiesel was analyzed by ¹H NMR and FTIR spectroscopy and the fuel properties of the biodiesel produced from Camelina sativa oil and waste seashells were compared with American Society for Testing and Materials standards.     

Heavy metal contamination of surface soil around Gebze industrial area, Turkey

An increase in heavy metal pollution in the soils of Gebze (Turkey) due to intense industrialization and urbanization has become a serious environmental problem. There are two large organized industrial zones in Gebze; the Gebze Organized Industrial Zone (GOIZ) and the Dilovas? Organized Industrial Zone (DOIZ). The region hosts several industrial facilities which are the main source for hazardous wastes which include paint, plastic, electric, metal, textile, wood, automotive supply industry, food, cosmetics, packing, machinery, and chemicals. Soil samples were collected from these two industrial zones and analyzed for their metal contents. Results of the analysis show that the soils are characterized by high concentrations of Cd, As, Pb, Zn, Mn, Cu, Cr and Hg. Since concentrations of other elements do not exceed the permissible levels, they are not evaluated. Concentrations are 0.05-176 mg/kg of Cd, 10-1161 mg/kg of Cr, 7.87-725 mg/kg of Cu, 1.50-65.60 mg/kg of As, 17.07-8469 mg/kg of Pb, 1.96-10,000 mg/kg of Mn, 29.5-10,000 mg/kg of Zn, and 9-2721 μg/kg of Hg. Application of factor, cluster and correlation analysis showed that heavy metal contamination in soils originates from industrial activities and heavy traffic which are of anthropogenic origin. Contaminations in soils were classified as geoaccumulation index, enrichment factor, contamination factor, and contamination degree. Integrated pollution index (IPI) values indicate that heavy metal pollution levels of soils collected from industrialization sites are greater than those from distal parts of industrialization. Spreading of hazardous wastes from industrial facilities in the study area via rain or wind is the main source of soil pollution. In addition, traffic-related metal pollution is also observed.     

Variations of antioxidant characteristics and mineral contents in pulp and peel of different apple (Malus domestica Borkh.) cultivars from Pakistan

Variations of phenolics, antioxidant activity, and mineral contents in peel and pulp of five apple (Malus domestica Borkh.) cultivars from Pakistan, namely Red Delicious, Golden Delicious, Kashmiri Amri, Kala Kulu and Sky Spur were appraised. The mean extract yield of antioxidant components obtained with 80:20 methanol-water (v/v), was found to be 22.1 g/100 g for peel and 14.2 g/100 g for pulp on a dry weight basis. The amounts of total phenolics and total flavonoids in peel and pulp of different cultivars of apple ranged from 1,907.5-2,587.9 mg gallic acid equivalent/100 g DW and 1,214.3-1,816.4 mg catechin equivalent/100 g DW and 1,185.2-1,475.5 mg GAE/100 g DW and 711.8-999.3 mg CE/100 g DW, respectively. The inhibition of linoleic acid peroxidation and DPPH scavenging activity of the extracts varied from 71.7-84.9 and 66.6-80.8% in peel, and 43.9-52.8 and 42.9-51.1% in pulp, respectively. Reducing power of the tested fruit part extracts at concentration 12.5 mg/mL ranged from 2.54-2.89 and 1.37-1.73, respectively. With regard to minerals analysis, both fruit parts showed the amount of K to be the highest, followed by Mg, Ca, Fe, Na and Zn. The results revealed that peel of the tested apple cultivars in this study had superior antioxidant capacity and mineral concentration than the pulp, indicating significant variations between the parts tested. Thus, consumption of apple fruits along with peel might be recommended to gaining better nutritive benefits.     

Polychlorinated biphenyls,dibenzo-p-dioxins and dibenzofurans in soil samples from airport areas of Croatia

Levels and patterns of polychlorinated biphenyls (PCBs) were studied in surface soil samples collected in the coastal part of Croatia within and surrounding four different airports and in the vicinity of two partially devastated electrical transformer stations. The compounds accumulated from air-dried soil samples by multiple ultrasonic extraction with an n-hexane?:?acetone 1?:?1 mixture were analysed by capillary gas chromatography with electron capture and ion-trap detection. PCBs were quantified against a standard Aroclor 1242/Aroclor 1260 mixture and a standard mixture of 17 individual PCB congeners (IUPAC No.: 28, 52, 60, 74, 101, 105, 114, 118, 123, 138, 153, 156, 157, 167, 170, 180, and 189). The mass fractions of total PCBs in 18 soil samples collected within the airport premises ranged from 3 to 41?327?µg/kg dry weight (dw) (median: 533?µg/kg?dw), and those in 21 samples collected at a distance ranging from several metres to 5?km away from the airport fence, from <1 to 39?µg/kg?dw (median: 5?µg/kg?dw). The highest PCB levels were determined in soils along the airport aprons where the aircrafts were serviced and refuelled. The PCB pattern was very similar to technical Aroclor 1260 in all airport soils. The PCB pattern in 22 soils collected in the vicinity of electrical transformer stations was dominated by congeners contained in Aroclor 1242. These soils contained 7 to >400?µg/kg?dw of total PCBs. One highly PCB-contaminated airport soil sample was analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). With an international toxic equivalent (I-TEQ) of 9.7?ng/kg?dw, the airport soil contamination was within values typical for urban and rural areas, and the congener patterns gave no clear indication for PCBs as the only source of PCDDs/PCDFs.     

Dynamics of Phloridzin and Related Compounds in Four Cultivars of Apple Trees during the Vegetation Period

Apple trees (Malus domestica Borgh) are a rich source of dihydrochalcones, phenolic acids and flavonoids. Considering the increasing demand for these phytochemicals with health-benefitting properties, the objective of this study was to evaluate the profile of the main bioactive compounds—phloridzin, phloretin, chlorogenic acid and rutin—in apple tree bark, leaves, flower buds and twigs. The variety in the phenolic profiles of four apple tree cultivars was monitored during the vegetation period from March to September using chromatography analysis. Phloridzin, the major glycoside of interest, reached the highest values in the bark of all the tested cultivars in May (up to 91.7 ± 4.4 mg g⁻¹ of the dried weight (DW), cv. ‘Opal’). In the leaves, the highest levels of phloridzin were found in cv. ‘Opal’ in May (82.5 ± 22.0 mg g⁻¹ of DW); in twigs, the highest levels were found in cv. ‘Rozela’ in September (52.4 ± 12.1 mg g⁻¹ of DW). In the flower buds, the content of phloridzin was similar to that in the twigs. Aglycone phloretin was found only in the leaves in relatively low concentrations (max. value 2.8 ± 1.4 mg g⁻¹ of DW). The highest values of rutin were found in the leaves of all the tested cultivars (10.5 ± 2.9 mg g⁻¹ of DW, cv. ‘Opal’ in September); the concentrations in the bark and twigs were much lower. The highest content of chlorogenic acid was found in flower buds (3.3 ± 1.0 mg g⁻¹ of DW, cv. ‘Rozela’). Whole apple fruits harvested in September were rich in chlorogenic acid and phloridzin. The statistical evaluation by Scheffe’s test confirmed the significant difference of cv. ‘Rozela’ from the other tested cultivars. In conclusion, apple tree bark, twigs, and leaves were found to be important renewable resources of bioactive phenolics, especially phloridzin and rutin. The simple availability of waste plant material can therefore be used as a rich source of phenolic compounds for cosmetics, nutraceuticals, and food supplement preparation.     

Anthocyanins profile,total phenolics and antioxidant activity of two Romanian red grape varieties: Fetească neagră and Băbească neagră (<Emphasis Type="Italic">Vitis vinifera</Emphasis>)

The phenolic composition of Feteasc? neagr?and B?beasc? neagr? grapes from Dealul Bujorului vineyard (south-east Romania) was studied using the spectrophotometric and high-performance liquid chromatographic (HPLC) methods. The results revealed significant differences between these cultivars. Total anthocyanins ranged from 0.22–5.98 mg g^?1 DW berries in B?beasc? neagr? grapes to 0.54–18.54 mg g^?1 DW berries in Feteasc? neagr?. Both cultivars were characterised by an interesting anthocyanin profile for winemaking with a prevalence of malvidin-3-glucoside. The skins and seeds both had small amounts of flavonoids. In contrast with B?beasc? neagr?, Feteasc? neagr? had more flavonoids in the seeds (69 %) than in the skins. Statistically significant correlations were observed between antioxidant activity and total anthocyanin content in both varieties. The antioxidant activity was also found to be highly correlated to the total phenolic compounds content.     

Determination of oleanolic acid, ursolic acid and amygdalin in the flower of Eriobotrya japonica Lindl. by HPLC

Simple and accurate HPLC methods were developed for the determination of oleanolic acid (OA), ursolic acid (UA) and amygdalin in loquat (Eriobotrya japonica Lindl.) flower, which is commonly used for the treatment of various diseases as a traditional Chinese medicine. HPLC assay was performed on a reversed-phase C(18) column and all three compounds were detected at 210 nm with a flow rate of 1.0 mL/min. The mobile phase consisted of methanol (A) and 0.03 mol/L phosphate buffer (pH 2.8) (B) with a ratio of 88:12 (A:B, v/v) for simultaneous detection of OA and UA, and 25:75 (A:B, v/v) for detection of amygdalin. The established methods showed good precision and accuracy with overall intra-day and inter-day variation of 0.99-3.55 and 1.05-4.05%, respectively, and overall recoveries of 97.37-99.32% for the three compounds. Application of these methods to determine the OA, UA and amygdalin contents in loquat flower showed that cultivar had a minor effect on the contents of all three compounds, with average amounts of 0.38-0.51 mg OA/g dry weight (DW), 2.15-2.68 mg UA/g DW and 1.23-1.56 mg amygdalin/g DW among five loquat cultivars tested. However, developmental stages and flower tissues showed significant effect on the contents of all three bioactive components.     

Fluorine sorption by soils developed from various parent materials in Galicia (NW Spain)

Fluorine is a phytotoxic element that can reach the soil from various industrial activities. Fluorine sorption by soil is crucial to protect water and food chain from fluorine pollution. In Galicia (NW Spain), various activities emit fluorine into the atmosphere, mainly ceramic industries and an aluminium smelter. This study, aiming to investigate fluorine sorption by Galician soils, was conducted on natural soil horizons representative of the area. Most soils were acid and rich in organic matter and showed strong fluorine sorption. The lowest sorptions were exhibited by a near-neutral serpentinite-derived soil (1001 mg kg(-1)) and the B horizons of soils developed from quartz schist (989 mg kg(-1)), and the highest by the A horizons of amphibolite-derived soils (1783 mg kg(-1)). In soils developed from quartz schist, biotitic schist and amphibolite, A horizons sorbed more fluoride than the corresponding B horizons (average 1621 and 1324 mg kg(-1), respectively), while the opposite is true in granite-derived soils (average 1644 and 1324 mg kg(-1), respectively). In the A horizons, the F sorption significantly correlated to soil pH (r=-0.79), pH in NaF (r=0.83) and oxalate Al (r=0.81). In the B horizons, sorption correlated to soil pH (r=-0.78), oxalate Fe (r=0.71) and organic C (r=0.66). F sorption can be described by both the Langmuir and Freundlich equations. The concentration of free fluoride in the equilibrium solutions increased above pH 6.     

Physicochemical profile studies of soil along the banks of Ubu river in Ekwusigo and Nnewi local government areas of Anambra State of Nigeria

A physicochemical profile study on the soil along the banks of the Ubu river that runs across Ekwusigo and Nnewi Local Government Areas (LGA) of Anambra State of Nigeria was investigated for possible evidence of industrial waste disposal by the various large to medium scale industrial activities taking place within the two LGAs. When compared with soil samples from Uzoakwa Ihiala (pH 5.44) with little or no industrial activities, the soil along the banks of the course of the river were found to be more acidic with mean pH values that are lower than 4.7. Similarity in mean sulphate (7.01 mg/kg), phosphate (12.95 mg/kg) and chloride (242 mg/kg) contents was observed between the soils from the banks at Nnewi with those of the Uzoakwa Ihiala that was used as control. This was attributed to contributions from domestic sources rather than from industrial sources, and partly to the similarity of their soil chemistry that may be indigenous to both areas. Electrical conductivity values (55 -74 microS/cm) show that the ionic content of the soil is lower than those of the control (129 microS/cm). This may have been explained by the higher extractible Ca (175.73 mg/kg), K (34.32 mg/kg), and Mg (1.94 mg/kg) recorded for the control. The abundance of the metals extractible from the soils of the river banks follow the sequence Ca>K>Na>Fe. Results for the digested soil samples show that Fe is the most abundant metal in the soil with mean values that are close to 13,000 mg/kg, but is much lower than the mean value of 39,210 mg/kg recorded for the control. Both bank and control samples can be characterized as ferrous. The relative abundance of metal ions observed in the digested soil samples from the river banks follow the sequence Fe>Al>Ca>Na>K>Zn>Cr. Values of 4,565 mg/kg and 300 mg/kg were recorded for total hydrocarbon content and lead respectively for soils around Cento Group, indicating that there were industrial waste disposal or spillages on soil around the area, which was not observed in other areas.     

High rates of nitrogen cycling in volcanic soils from Chilean grasslands

There are over one million hectares of pasture in Chile, and 80% and 50% of the country's milk and meat comes from 72% of this area, situated in the lake region of southern Chile. The soils are volcanic and a major characteristic is that they have very high organic matter (OM) contents with the potential to support plant growth with only moderate levels of added nitrogen (N). To understand better the potential fertility of these soils in order to maximise production and minimise losses of N, we undertook studies using the stable isotope of N ((15)N) to resolve the rates of the main internal N cycling processes in three soils representing the two main volcanic soil types: Osorno and Chiloé (Andisol) and Cudico (Ultisol). We also assessed the longer-term potential of these soils to sustain N release using anaerobic incubation. Gross rates (μg N g(-1) day(-1)) of mineralisation were 27.9, 27.1 and 15.5 and rates of immobilisation were 5.9, 12.0 and 6.3 for Osorno, Chiloé and Cudico, respectively, implying high rates of net mineralisation in these soils. This was confirmed by anaerobic incubation which gave potential seasonal net mineralisation indices of 1225, 1059 and 450 kg N ha(-1) in the top 10 cm soil layers of the three soils. However, plant production may still benefit from added N, as the release of N from organic sources may not be closely synchronised with crop demand. The low rates of nitrification that we found with these acidic soils suggest that the more mobile N (viz. nitrate-N) would be in limited supply and plants would have to compete for the less mobile ammonium-N with the soil microbial biomass. Nitrogen was mineralised in appreciable amounts even down to 60 cm depth, so that leaching could become significant, particularly if the soils were limed, which could enhance nitrification and N mobility through the soil profile.     

成都市农业土壤重金属污染特征初步研究

对成都市农业土壤中七种重金属元素Pb、Hg、Cr、As、Cu、Zn和Cd进行了测定和研究,并进行了潜在生态风险评价。结果表明,成都市农业土壤重金属元素含量分别为:Pb 77.27mg/kg,Hg 0.31 mg/kg,Cr 59.50 mg/kg,As 11.27 mg/kg,Cu 42.52 mg/kg,Zn 227.00 mg/kg,Cd0.36 mg/kg;重金属潜在的生态危害因子表明,Hg和Cd达到中等生态危害程度,Pb、As、Cu、Zn、Cr达到轻微生态危害;多种重金属的生态系统的潜在生态风险指数(RI)表明,成都市农业土壤生态危害级别为中等生态危害。     

Distribution and Assessment of Heavy Metals in Trifolium dubium (Little Hop Clover) and the Impact of Soil Quality

Trifolium dubium is an edible plant that is utilized in traditional medicine for its anti-inflammatory and wound-healing properties. In this study, T. dubium was assessed to determine the elemental uptake by the plant as a function of soil characteristics. Across 10 geographic locations in KwaZulu-Natal, South Africa, the concentration of elements in T. dubium were found to be (descending order) Ca?>?Mg?>?Fe?>?Zn?>?Mn?>?Se?>?Ni?>?Cr?>?Cu?>?Co?>?Pb?>?Cd?>?As. The site had an influence on elemental uptake by the plant; however, accumulation or exclusion of elements from soil was controlled to meet physiological requirements. Soil chemical characteristics showed T. dubium grew in slightly acidic soils (pH – 6.15 to 6.68). The findings of this study show T. dubium to contain adequate concentrations of essential elements with undetectable levels of toxic metals, making the herb safe for human consumption and for use in traditional medicine. The plant can also contribute to poor communities by ameliorating food insecurity.     

Determination of cadmium by flow injection-chemical vapor generation-atomic absorption spectrometry

A method was developed for the generation of a "cold vapor" of cadmium by means of flow injection-chemical vapor generation from aqueous samples, the determination being conducted with an atomic absorption spectrometer (Pyrex glass T-cell). Several gas-liquid separator designs, atomizer designs, and the effect of several reagents previously reported as sensitivity enhancers (including cobalt, nickel, thiourea and didodecyl-dimethylammonium bromide) were investigated. The limit of detection, calculated as the concentration giving a signal equal to three times the standard deviation of the blank, was 16 ng L(-1), and the relative standard deviation was 1.4% for a concentration of 2 microg L(-1) and 3.8% for 0.1 microg L(-1). The addition of nickel and thiourea to the samples provided improved tolerance to the interference of coexisting ions. Two NIST certified reference materials, Montana Soil and Apple Leaves (respectively containing 41.7+/-0.25 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd) were accurately analyzed. The interference of lead was overcome by coprecipitation with barium sulfate, and the experimental values obtained were 41+/-1 mg kg(-1) Cd and 0.013+/-0.002 mg kg(-1) Cd, respectively.     

Methyl jasmonate influence on silymarin production and plant stress responses in Silybum marianum hairy root cultures in a bioreactor

In this article our aim was to evaluate mass cultivation of S. marianum hairy roots in a bioreactor to produce silymarin. The effects of methyl jasmonate (MJ) elicitation on the accumulation of silymarin and the extent of the MJ-induced oxidative damage were investigated in bioreactor hairy root cultures of S. marianum. The growth rate of the bioreactor hairy root cultures was higher than that of those in a shake flask after 3 weeks. Silymarin accumulation was increased from 0.13?mg?g?1 DW in non-treated hairy roots to 0.22?mg?g?1 DW in hairy roots 72?h after 100?μM?MJ treatment. Guaiacol peroxidase and ascorbate peroxidase were activated by MJ?72?h after treatment, being 3.2- and 1.3-fold higher, respectively, than that of the control. An increase in enzymatic activity suggests increased scavenging of reactive oxygen species, indicating the tolerance to MJ stress. These results suggest that MJ elicitation is beneficial for silymarin production using bioreactor hairy root cultures.     

Oxalate distribution in soils under rhubarb (Rheum rhaponticum)

Oxalate in soils may enhance phosphate availability, promote mineral dissolution, and increase the mobility of aluminium and heavy metal cations by complexation. Rhubarb (Rheum rhaponticum L.) has very high content of oxalate in leaves and petioles, and therefore the topsoil under rhubarb might have elevated contents of oxalate. Soil samples were collected at depths of 0–2.5 and 2.5–5?cm from 10?cm sections along 100?cm transects from rhubarb plants at four locations in Denmark, and from seven layers in a soil profile to 80?cm depth at one location. Oxalate was extracted from the soil with 0.2?M phosphate at pH 2 by reciprocal shaking for 24?h and then determined by a new fast capillary zone electrophoresis method with 300?mM KH₂PO₄ and 0.30?mM TTAB electrolyte adjusted to pH 7, developed and tested to analyse high-ionic-strength soil extracts. Rhubarb increases the oxalate content in soil under the leaves slightly. The average content of oxalate in the upper 0–5?cm soil was 444?µmol/kg at the Kaldred site, and 111–333?µmol/kg at the three other locations. In the soil profile, the content of oxalate decreased from 500?µmol/kg in 0–5?cm depth to 110?µmol/kg at 75–80?cm depth. No significant seasonal changes in oxalate contents were observed, while an annual variation of 100?µmol/kg could be observed at 0–2.5?cm depth. During plant decay in autumn, a slight increase in oxalate content was observed at 30?cm soil depth. In conclusion, the role of oxalate in weathering and metal transport appears to be limited in soils under rhubarb. Oxalate might stimulate microbiological growth and phosphate mobilisation in the rhizosphere, but concentrations observed are too low to impose any toxic effects to organisms.     

Persistence of Metal Residues in Sewage Sludge Treated Soils Over Seventeen Years

Abstract

Results from two long-term sewage sludge experiments conducted on different soil types are presented. Sewage sludges highly contaminated with Cr, Cu, Ni or Zn and a relatively uncontaminated sludge were applied at both sites at the same rates and metal contents in 1968. The Cr-rich sludge also had a high Cd content. Plot soils were sampled in 1972, 1976 or 1977, 1981 and 1985 and total and extractable metal contents determined. Metals added in sewage sludge may change their form but persist in soils in an extractable and plant available form for many years. There is little difference in soil extractable contents or plant uptake of Cu and Zn whether sludge is applied as one single application or as its equivalent in four separate annual applications of one quarter the amount. The percentages of the total chromium contents extractable by both EDTA and acetic acid were small and this was reflected in a low uptake of this element by pasture herbage species (<0.3 mg Cr/kg DM).