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1.
The influence of some complexing agents of (poly)aminopolycarboxylic acids (diethylenetriaminopentaacetic acid (DTPA), ethylenediaminotetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) on the sorption of Cu2+ by crystal and amorphous (hydr)oxides of Fe(III), Al(III), and Mn(IV) that are widespread mineral components of soils was studied. The obtained results are considered in terms of complex-formation in the solution and on the sorbent’s surface. The effect of the complexing agents on the metal sorption (mobilization/immobilization) is determined by (1) the stability, structure, and sorption capability of compexonates formed in the solution; (2) the acidity, and (3) the nature of the sorbent. The desorption effect on Cu2+ cations was found to change in the following sequence of complexing agents: EDTA > DTPA ? NTA > IDA. The high-dentate complexing agents (EDTA, DTPA) had the greatest impact on ?u2+ cations bound with crystalline (hydr)oxides of Fe, Al, and Mn. The low denticity of the complexing agents (IDA, NTA) and binding of ?u2+ with amorphous sorbents leads to the weakening of desorption. The decrease in acidity promoted the mobilization of the metal under the influence of complexing agents; the increase in acidity caused its immobilization. The growth in the mobility of heavy metals bound with soil (hydr)oxides of Fe, Al, and Mn due to the complexing agents entering the surface and ground water is considered a factor of ecological risk.  相似文献   

2.
Persistent organic pollutants (POPs) continue to receive widespread attention as harmful contaminants in the global environment. Increasingly, there have been concerns regarding adverse effects on marine wildlife due to the potential of POPs to induce adverse health effects, including the disruption of endocrine systems. Marine water samples within one kilometer of the coastline of Singapore were analysed to determine prevalent concentrations of a range of persistent organic pollutants (POPs). Samples were collected from 0.5 m and mid-depth (approximately 14 m depth) at twenty-two locations. POPs analysed are classed as USEPA priority pollutants, and included: sixteen polycyclic aromatic hydrocarbons (PAHs); eight polychlorinated biphenyls (PCBs); and twelve organochlorine pesticides (OCPs). Total PAH concentrations varied from 88.44 to 1419.57 ng l-1 at the surface, and 129.78 to 940.41 ng l-1 at mid-depth. Total OCP concentrations varied between 4.90 ng l-1 to 22.04 ng l-1 at surface, and 4.09 to 18.05 ng l-1 at mid-depth. Total PCB concentrations varied from 0.22 ng l-1 to 20.41 ng l-1 at surface and 0.4 to 10.79 ng l-1 at mid-depth. In general, the distribution profile shows that the surface concentrations of POPs are higher than at mid depth. Concentrations of PAHs were considered higher than reported levels for several other countries, whereas levels of OCPs and PCBs are generally lower than reported levels for other Asian countries.  相似文献   

3.
Mercury is emitted from soil and water surfaces, but few actual direct flux measurements have been reported. During June, 1994 we performed the first micrometeorological measurements of Hg vapor fluxes over a boreal forest lake. Using highly precise methods with multiple replicate samplers, we measured concentration gradients of Hg vapor, CO2 and H2O over the lake surface. Mercury was readily emitted from the lake surface, and we found no evidence of Hg dry deposition to the lake. Emission rates over the lake averaged 8.5 ng m2 h?1, and appeared to be weakly influenced by water temperature and solar radiation. These fluxes were somewhat higher than those previously measured using surface chambers at this site.  相似文献   

4.
The Esk estuary is approximately 10 km from the marine outfall fromBritish Nuclear Fuels plc (BNFL) Sellafield Site and saltmarshes here havereceived significant quantities of radionuclides as reported in many studiessince 1975. These studies have concentrated on the inventory ofradionuclides in the estuary, but they have not addressed the continualreworking of radionuclides from these deposits. A detailed investigation ofboth the concentration of 137Cs in the surface 10 cm and gammaair-kerma dose rates has been made where 120 determinations were made in agrid over 14600 m2 of saltmarsh. The surface microtopographyis shown to be important for the continuing deposition of contaminatedsediments to the saltmarsh surface. This study has concentrated on thedevelopment and the possible application of sediment traps made fromAstroturf (an artificial grass). They were deployed at three sites whichwere representative of the major saltmarsh units in the estuary. The trapswere used to investigate the mobile sediments during a single tide, for aweek, and for a month. The Astroturf provided a reasonable analogue for thesaltmarsh surface and was arranged such that the radionuclide concentrationof the trapped sediment was measured directly by gamma spectrometry. Sediment deposition rates of between 30 and 240 g m-2d-1 were determined for the study sites, and these wereconsistent with earlier studies. Measurement of the radionuclideconcentration of the deposited sediment showed the addition of between 90and 750 Bq 317Cs m-2 d-1 and 200and 1400 Bq 241Am m-2 d-1. At thedepositional sites over the saltmarsh this would represent an annualaddition of about 90 kBq m-2 of 137Cs and 180kBq m-2 of 241Am.  相似文献   

5.
Sulfur dioxide (SO2), prevalent in the modern urban environment of industrial countries, attacks calcite (CaCO3)in marble. As a result, a gypsum (CaSO4·2H2O) crust is produced at rain-sheltered surfaces while areas exposed to rain experience accelerated erosion. We have investigated theeffect of certain surfactants as protective agents against SO2 attack. We report that the anions oxalate (C2O4 -2) and oleate (C17H33COO-) from solutions of their highly soluble alkali salt species areable to replace carbonate (CO3 -2) in calcite producingless reactive substrate of oxalate and oleate of calcium. Experiments to measure the protection obtained by these treatments were carried out in the laboratory and field conditions at nearly 1ppm and 10 ppb SO2 concentrations, respectively. We found that these treatments provided significantprotection to marble exposed in sheltered areas, up to 30% reduction of reaction rate by treatment with 2 × 10-4M sodium oleate and up to 14% by a 2 × 10-3 M with potassium oxalate solutions, but become ineffective over long term exposure when applied to surfaces exposed to rain.Carrara marble was used in the reported study. Ion chromatographywas the analytical tool, which allowed precise measurements of ionic concentrations of these salts, the amount of their uptakeby marble, and the thickness of the gypsum crust. X-ray diffraction allowed determination of the new minerals formed at the marble surface by the treatment with surfactants.  相似文献   

6.
The comparison of immobilisation efficiency of various phosphate stabilisation agents for heavy metals in sewage sludge collected from an urban wastewater treatment plant Domale-Kamnik (Slovenia) is reported. The sewage sludge, containing high total concentrations of Zn (2698 ± 8.1 mg kg-1), Ni (1513 ± 5.7 mg kg-1), Cr (1118 ± 3.0 mg kg-1) and Cu (712 ± 2.2 mg kg-1), was mixed with various types of phosphates: highly soluble Ca(H2PO4)2, synthetic hydroxyapatite, with a solubility between Ca(H2PO4)2 and rock apatite, and bone-meal as an alternative low-cost source of poorly crystalline phosphate, in order to reduce metal mobility. The amounts of stabilising agents added to 1 g of the sludge ranged from 0.05 to 1 g. Water and acetic acid extractions were used for the determinationof water-soluble and potentially bioavailable metal fractions in the sewage sludge and its mixtures with various stabilisation agents.  相似文献   

7.
植物基固沙剂是以植物材料提取物为主成分的环保型固沙剂，为研究其应用于沙质耕地是否具有可行性，以3种植物基固沙剂(刺槐型、亚麻型和向日葵型)和沙土为研究对象，喷施等量清水处理为CK,开展不同用量植物基固沙剂对沙土形成的固结层抗压、抗风蚀及其植物种子萌发、幼苗生长的比较试验研究。结果表明：(1)刺槐型、亚麻型、向日葵型固沙剂喷施于风沙土地表，均可形成1～14 mm厚度固结层，其平均抗压强度较CK分别提高206.21%,147.51%,72.74%。(2)3种植物基固沙剂均具有显著的固沙效果，随用量增加土壤抗风蚀能力均显著增强，在5 g/m2用量下风蚀量最低，较CK分别减少65.92%,58.33%和69.55%。(3)刺槐型、亚麻型固沙剂对小麦种子萌发及芽生长有促进作用，向日葵型固沙剂有抑制作用，且随用量增加抑制效果明显，在3 g/m2用量时种子发芽受到显著抑制，发芽率较CK降低62.50%;在4 g/m2用量时，根系萌蘖受到显著抑制；在2 g/m2用量时，芽生长受到显著抑制。(4)固结层对幼苗破土有一...  相似文献   

8.
Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×105 viable propagules g-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.  相似文献   

9.
"秸秆降解生防菌强化技术"(BS)近年在我国北方冬季温室栽培中广泛使用, 具改良土壤、减轻病害、改善品质、提高产量等多方面的效果。为探讨应用该技术后对黄瓜连作土壤中微生物区系的影响, 本研究采用平板培养计数与末端标记限制性片段长度多态性(T-RFLP)分析相结合的方法, 检测了黄瓜连作土壤中真菌、细菌、放线菌以及生防菌和病原菌的数量动态。结果表明, BS处理土壤后, 在连作第2茬时, 土壤中真菌群体总量比第1茬显著减少; 细菌总量比第1茬显著增加。细菌与真菌数量比值(B/F值)在连作两茬时明显升高, 土壤表现为"细菌型"; 连茬土壤中两种生防菌的含量保持相对稳定; 枯萎病原菌数量在连作两茬时与其他处理和对照相比有所降低, 但不显著; 处理后土壤细菌多样性在第2茬时显著升高, 并能促进TRF139等有益菌群增殖, 抑制TRF341和TRF501等有害菌群增殖。BS处理土壤能明显提高连作黄瓜的产量并降低根结线虫的病情指数, 在第3茬时产量比对照增加25.9%, 病情指数比对照减少71.4%。生防菌与秸秆配合使用对黄瓜连作土壤微生物的数量和群落结构影响显著, 在一定的连作茬数内能够保证生防菌有效定殖, 抑制病原菌数量增长, 提高土壤微生物多样性, 使土壤微环境达到相对健康的状态。  相似文献   

10.
This paper reports on the effect of activating agents such as the impregnation ratio of phosphoric acid (1:1–1:5) at constant activation temperature on the performance of porous activated carbon from waste residues (maize tassel). The variation in the impregnation ratio of the produced activated carbon (AC) from 1:1 to 1:5 enabled the preparation of a high surface area (1,263 m2/g) and a large pore volume (1.592 cm3/g) of AC produced from maize tassel (MT) using a convectional chemical activating agent (phosphoric acid). Impregnation ratios (IR) of the precursors were varied between 1:1 and 1:5 in which it was found that the ratio of 1:4 was optimal based on the high surface area, while 1:5 has the optimal pore volume value for the produced activated carbon.  相似文献   

11.
As for the reactions by oxidizing agents of humic acids and for the products obtained by the said reactions, a number of investigations (1) have been made with regard to the study of the chemical structure of humic acids and with the use of the products of decomposition. The authors (2) have observed that A-or B-types of soil humic acids could be separated into three or four fundamental composing fractions by using Al2O3 column.  相似文献   

12.
Two consecutive years of investigation on soil surface features, surface runoff and soil detachment within 1-m2 microplots on 40% slope highlighted the effects of land-use change, vegetation cover and biological activity on the water pathways in Northern Vietnam. Three replicate plots were set up on each of five land-uses: cassava (CAS), grass fodder of Bracharia ruziziensis (BRA), a 3-year old fallow (FAL), tree stands of Acacia mangium and Venicia montana (FOR), and a fallow with regrowth of Eucalyptus regularly cut (EUC). The second year, two of the microplots under FAL and EUC were treated with herbicide (FALh, EUCh), one of them was burnt (FALh+b, EUCh+b). The highest yearly surface runoff coefficient of 16%, and soil detachment rate of 700 g m− 2 yr− 1 in average with a maximum of 1305 g m− 2 yr− 1 have been recorded under CAS. On FALh and FALh+b, runoff ratios were 8.7 and 13.5%, respectively and detachment rates were 86 and 389 g m− 2. On FAL and BRA the yearly runoff ratio varied from 5.9 to 9.8% but the detachment rate was limited at 24 to 35 g m− 2. FOR and EUC annual runoff was ≤ 3.1% and annual soil detachment ≤ 71 g m− 2. These values were very low compared to the values reported on steep slopes in Laos within similar climate and vegetation cover.The runoff and detachment rates underlined the importance of rainfall intensities, soil physical properties, soil surface features, soil vegetation cover and biological activity. The annual surface runoff was highly correlated to the soil surface crusting. CAS and BRA plots were prone to crusting especially after weeding at the onset of the rainy season, when the soil surface was still uncovered. Soil bioturbation (earthworm casting activity) was the second factor that explains local variation of surface runoff and soil detachment. The continuous production of earthworms casts on soil surface, especially on FOR and EUC microplots, induced a marked surface roughness and reduced the surface runoff. The production of casts was very limited in FAL and completely absent in CAS microplots. So it is evident that our results confirm the deleterious effects of cassava on soil and water conservation.  相似文献   

13.
ABSTRACT

We studied the bioactive compound of the fungus Simplicillium chinense strain Snef5, isolated from its culture filtrate. Following purification by chromatography, the structure of the secondary metabolite, identified as 2,6-pyridinedicarboxylic acid, was determined by spectroscopic methods (IR, 1H, and 13C NMR) and scanning electron microscopy (SEM). The metabolite exhibited antimicrobial activity against M. incognita with an LD50 of 0.229?mg/ml. The light microscope was used to observe the surface and internal cellular micro-structure of the nematodes. The results of the microscopy indicated that the anatomy of the J2 of M. incognita was disrupted following exposure to 2,6-pyridinedicarboxylic acid. This is the first report on the activity of 2,6-pyridinedicarboxylic acid of S. chinense metabolites on the root knot nematode. It showed a high level of nematicidal activity. Our data on the inhibitory effects of 2,6-pyridinedicarboxylic acid suggest that secondary metabolites from Snef5 have potential use as novel biological control agents.  相似文献   

14.
The efficiency of As(III) oxidation by MnO2, and retention of oxidation products varies with system pH. Maximum retention by hydrous Mn(IV) oxide occurs at pH < 5, declining at higher pH to about half total As at pH 10. The adsorption capacities of pyrolusite and cryptomelane at pH ～6.5 for As(V) species were 10 and 25 mmol kg?1, respectively. HMO surface saturation (～10 mmol kg?1) was reached with equilibrium As(V) levels of 5 to 8 × 10?6 M but this was supplemented at higher levels by an absorption process where uptake increased linearly with concentration (e.g., 68 mmol kg?1 with 2 × 10?5 M As(V)). Added As(III) was avidly oxidized and most product retained at pH 3. At higher pH increasing amounts of As(III) remained unoxidized due to initial reactions apparently blocking access to internal pores. Added Na+ reduced the amount of As retained by the HMO, with the phosphate salt having a significant effect. Extraction studies confirmed that most As could be released by exposure to reducing agents or chelating agents (EDTA). The environmental significance of the results has been considered.  相似文献   

15.
ABSTRACT

Arbuscular mycorrhizae (AM) are the symbiotic fungi that predominate in the roots and soils of agricultural crop plants. The most recognized beneficial effect of these fungi is to enhance host plant uptake of relatively immobile nutrients, in particular phosphorus (P), and several micronutrients. The AM fungi absorb inorganic P either from the soluble P pools in the soil, or from insoluble forms such as rock phosphates as well as from insoluble organic sources. Recent studies show that mycorrhizal fungi would have access to rock phosphate through localized alterations of pH and/or by the production of organic acid anions that may act as chelating agents. The AM colonization also improves plant N nutrition. Generally mycorrhizal symbiosis more influences on nitrogen (N) uptake and translocation if ammonium (NH4 +) rather than nitrate (NO3 ?) is the nitrogen source. However, under drought stress the role of mycorrhizae in NO3 ? transport to the root surface may be significant as the NO3 ? mobility is severely restricted due to its low concentration and diffusion rate under such circumstances. However, as yet little is known about the mechanism of N uptake by the AM fungi. Uptake of micronutrients is also influenced by mycorrhizal colonization.  相似文献   

16.
Differences in soil phosphorus (P) contents measured by various techniques may have implications for agronomic and environmental testing. Reduced-tillage systems combined with surface manure application increase the potential risk of nutrient losses by surface runoff. A field trial was conducted to evaluate the effect of livestock slurry on nutrient accumulation at the surface layer of an acidic soil rich in organic matter with excess P levels and loamy texture. Two reduced-tillage systems, no tillage (NT) and minimum tillage (MT), and four different fertilizer treatments were assessed. The amounts of P extracted by anion-exchange resin (AER) and by Mehlich 3 (M3) were compared; in addition, differences between two determination methods of P contents extracted by Mehlich 3, namely molybdic acid colorimetric standard procedure (M3-COL) and inductively coupled plasma–mass spectroscopy (M3-ICP), were evaluated. Ninety-six soil samples were taken from the 0- to 5-cm surface layer in three successive dates after increasing manure addition. Colorimetric Mehlich 3 P ranged from 49 to 431 mg dm–3. The ranks of mean extractable soil P concentrations were AER < M3-COL < M3-ICP. The linear correlation coefficient between M3-COL and M3-ICP was highly significant (R2 = 0.89; P < 0.01), but a two-straight-lines model or a quadratic relationship were more adequate for describing the dependence between the two determination procedures after M3 extraction. Relative and absolute differences between M3-COL and M3-ICP showed a tendency to increase as organic carbon content increased. Phosphorus content extracted by AER and M3-COL or M3-ICP reported a significant but much less predictable relationship with R2 values of 0.27 and 0.21 (n = 96), respectively. The P in the surface layer accumulated more under NT than under MT.  相似文献   

17.
Synthetic chelating agents such as EDTA form strong complexes with heavy metals and therefore have the potential to remobilize metals from sediments and aquifers. In natural waters EDTA is present almost exclusively in the form of metal-complexes. Therefore, remobilization of metals is always a metal-metal-EDTA exchange reaction. We have investigated, to our knowledge for the first time, the remobilization of metals from the surface of synthetic iron oxides and from a river sediment by different metal-EDTA complexes. The metals are exchanged as follows:MeEDTAdissolved + Meast adsorbed MeastEDTAdissolved + Meadsorbed The order of the remobilization rate of Zn2+ from goethite is CaEDTA > Fe(III)EDTA, reflecting the slow exchange reaction of Fe(III)EDTA. For the remobilization of Pb2+ from goethite, the rate was found to be Fe(III)EDTA > CaEDTA > ZnEDTA. Here, Fe(III)EDTA has surprisingly the fastest exchange rate. Only very limited remobilization of Pb2+ is possible from hydrous ferric oxide at pH 8 due to the very strong adsorption of Pb2+. The order of remobilization of Zn2+ from a natural river sediment was found to be CaEDTA > CuEDTA > Fe(III)EDTA. The remobilization rate of Zn2+ with Fe(III)EDTA is only 12% of the rate with CaEDTA, illustrating the importance of EDTA speciation for assessing remobilization.  相似文献   

18.
In order to promote the transformation of a burnt Mediterranean forest area into a dehesa system, 10 t ha−1 of dry matter of the same sewage sludge in three different forms: fresh, composted and thermally‐dried, were added superficially to field plots of loam and sandy soils located on a 16 per cent slope. This application is equivalent to 13ċ8 t ha−1 of composted sludge, 50 t ha−1 of fresh sludge and 11ċ3 t ha−1 of thermally‐dried sludge. The surface addition of a single application of thermally‐dried sludge resulted in a decrease in runoff and erosion in both kinds of soil. Runoff in thermally‐dried sludge plots was lower than in the control treatment (32 per cent for the loam soil and 26 per cent for the sandy soil). The addition of any type of sludge to both soil types also reduces sediment production. Significant differences between the control and sludge treatments indicate that the rapid development of plant cover and the direct protective effect of sludge on the soil are the main agents that influence soil erosion rates. Results suggest that the surface application of thermally‐dried sludge is the most efficient way to enhance soil infiltration. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

19.
This study assessed the agricultural information needs of root- and tuber-crop farmers in the Atisbo Local Government Area of Oyo State. A simple random sampling technique was used to select respondents. Data were presented using percentages and rankings. The most utilized sources of information on agricultural practices were associations (75.8%), other farmers (70.8%), and extension agents (60.8%). Agricultural information reported as “highly needed” by respondents included marketing procedures, processing and improved planting techniques, and soil management methods. Chi-square test results showed a significant relationship between selected personal characteristics of respondents (gender χ2 = 24.9, p < .05; educational status χ2 = 10.8, p < .05; marital status χ2 = 181.1, p < .05 and household size χ2 = 48.6; p < .05) and information needs.  相似文献   

20.
About 80% of Ethiopia's population is involved in rain‐fed agriculture. Moisture stress coupled with traditional tillage with breaking ard plough, locally known as ‘Maresha ’ are the major limiting factors for agricultural production. Soil erosion, low infiltration and decline agricultural productivity because of conventional tillage implement have been frequently reported. In order to curve this situation and meet the huge food demand of the growing population, different conservation tillage systems have been implemented. However, there is limited information about the impacts of the practices. This review paper therefore aimed at providing adequate information concerning the impacts of the practices on water balance and crop yield. Systematic, best evidence and narrative review techniques were used. Results revealed that the application of conservation tillage had brought significant improvement on water balance and agricultural production. Researchers found over 50% decreased in surface runoff, 9 to 40% improvement in water productivity and good crop transpiration (T = 53 mm season−1), compared to conventional tillage T = 49 mm‐season−1 because of conservation tillage implement. Moreover, doubled grain yield was obtained from ridging, subsoiling and wing plough (1076, 1044 and 1040 kg ha−1, respectively) compared to traditional tillage which resulted in 540 kg ha−1. Improving water balance and agricultural production in rain‐fed agriculture need to reduce evaporation and surface runoff through improving moisture retention and transpiration. This could be achieved by the adoption of conservation tillage which can improve on‐farm water balance, yields and water productivity among smallholder farmers in Ethiopia. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

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