Degradation of 2,4-dinitrotoluene by persulfate activated with zero-valent iron

The oxidation of 2,4-dinitrotoluene (DNT) by persulfate (S₂O₈²⁻) activated with zero-valent iron (Fe^o) was studied through a series of batch experiments. The mechanism for Fe^o activation was investigated by comparing with Fe²⁺, and the effects of persulfate-to-iron ratio and pre-reduction on DNT oxidation were examined. DNT was stable in the presence of persulfate and transformed only when Fe^o was added. Most DNT was degraded oxidatively by Fe^o-activated persulfate, whereas direct reduction of DNT by Fe^o was unimportant. The rate of DNT degradation increased with higher Fe^o dose, presumably due to increasing activation of persulfate by Fe^o and Fe²⁺. In contrast to the Fe^o-persulfate system, where complete oxidation DNT was achieved, only ≤ 20% of DNT was degraded and the reaction was terminated rapidly when Fe^o was replaced with equimolar Fe²⁺. This indicates that Fe^o is more effective than Fe²⁺ as activating agent and potentially more suitable for environmental applications. The reduction products of DNT were more rapidly oxidized by persulfate than DNT, suggesting that converting the nitro groups of NACs to amino groups prior to oxidation can greatly enhance their oxidation. This suggests that a sequential Fe^o reduction-persulfate oxidation process may be an effective strategy to promote NAC degradation.     

Selenium toxicity in soils,plants and animals in some parts of Punjab,India

Pockets of seleniferous soils have been identified in north eastern parts of Punjab, India, by examining the Se content of soils, irrigation water, plants and animal tissues. Toxic sites ranging from 4 ‐ 16 ha were sporadically distributed in the study area and occupied more than 100 ha. In the seleniferous areas, the selenium content of surface (2.12 ± 1.13 mg kg^‐1) and sub surface (1.16±0.51mg kg^‐1) layers of soils was 4–5 times higher than that of nonseleniferous areas. It seems that the deposition of seleniferous materials transported by seasonal rivulets from higher reaches of the Siwalik hills and use of underground water for frequently irrigating crops like lowland rice lead to the development of seleniferous pockets in the study area.     

天然沉积粉质土压缩特性研究

采用自由活塞薄壁取土器自地表至深度70m取得不扰动原状粉质土样,通过一系列物理力学试验,对比分析了天然沉积粉质土与天然沉积粘性土的异同。明确了位于塑性图A线下方的粉质土的重塑压缩性状可以用孔隙指数进行归一化,其孔隙指数和固结压力的关系与基于塑性图中位于A线上方的粘性土试验数据提出的固有压缩曲线一致。但是,天然沉积粉质土的天然沉积状态线位于普通粘性土的天然沉积压缩线的上方。结果表明,天然沉积粉质土比天然沉积粘性土有更高位的结构,灵敏度更高,更易于受到取样扰动的影响。     

Arsenic,Sb and Bi contamination of soils,plants, waters and sediments in the vicinity of the Dalsung Cu-W mine in Korea

The diagnosis of lead poisoning in horses living on farmland in the vicinity of a battery recycling plant was based on clinical signs as well as on laboratory findings. Chemical analysis of six surface soils (0-15 cm) and herbage samples taken at different distances to the recycling plant showed very high total lead levels in the closest sites to the facility and a clear decrease with distance. Total lead levels in soil samples ranged from 127 to 5657 mg kg(-1), with more than 70% of lead extractable by EDTA in the most polluted soils. Lead levels in the aerial part of herbage samples were in the range of 113-4741 mg kg(-1). A water washing pre-treatment of the vegetal samples considerably diminished the concentration of lead, suggesting that airborne lead particles from the facility emissions were fixed on the shoots. The analysis of samples taken from six dead horses showed lead concentrations, expressed as mg kg(-1) (d.w.), as follows: blood: 0.20-0.89; liver: 2.5-15; kidney: 1.70-6.75. Lead intake levels, estimated according to the ingestion rate of Grammineae forage, illustrates that the apported lead through the ingestion of vegetation growing in the closest sites to the recycling plant was approximately 99.5 mg Pb/kg body weight/day surpassing the fatal dosage for horses of 2.4 mg Pb/kg body weight/day reported by Hammond and Aronson, Ann NY Acad Sci, 1964; 111: 595-611.     

Toxicity of aluminium in natural waters controlled by type rather than quantity of natural organic matter

Extension of the conditions under which Al toxicity is tested is required. Environmentally representative preparation of waters is used in investigating roles of alginate (AA) and humic acids (HA) in partitioning of Al (0.5 mg L^− 1), subsequent uptake and accumulation by and toxicity to Lymnaea stagnalis. HA and AA did not alter precipitation of Al(OH)₃, but altered subsequent behaviour of Al. High (40 mg L^− 1) HA concentrations, and to a lesser extent AA, prevented settling and availability for benthic grazing but made deposited Al more likely to be ingested. HA detoxified but AA increased toxicity relative to Al alone. Low concentration (4 mg L^− 1) AA and HA do not change partitioning but increase uptake; they both detoxify, but AA less than HA. The study shows OC:Al ratio is critical in predicting Al behaviour in natural waters, also uptake is mediated by snail behaviour, not solely a function of concentration and form of Al. Therefore, predicting Al behaviour will be subject to errors in determining relevant water composition and response of biota to the new speciation. However, with respect to toxicity, rather than other aspects of Al behaviour, different ratios of HA and Al are insignificant compared to whether AA is present rather than HA.     

Phytotoxicity and uptake of nitroglycerin in a natural sandy loam soil

Nitroglycerin (NG) is widely used for the production of explosives and solid propellants, and is a soil contaminant of concern at some military training ranges. NG phytotoxicity data reported in the literature cannot be applied directly to development of ecotoxicological benchmarks for plant exposures in soil because they were determined in studies using hydroponic media, cell cultures, and transgenic plants. Toxicities of NG in the present studies were evaluated for alfalfa (Medicago sativa), barnyard grass (Echinochloa crusgalli), and ryegrass (Lolium perenne) exposed to NG in Sassafras sandy loam soil. Uptake and degradation of NG were also evaluated in ryegrass. The median effective concentration values for shoot growth ranged from 40 to 231 mg kg^− 1 in studies with NG freshly amended in soil, and from 23 to 185 mg kg^− 1 in studies with NG weathered-and-aged in soil. Weathering-and-aging NG in soil did not significantly affect the toxicity based on 95% confidence intervals for either seedling emergence or plant growth endpoints. Uptake studies revealed that NG was not accumulated in ryegrass but was transformed into dinitroglycerin in the soil and roots, and was subsequently translocated into the ryegrass shoots. The highest bioconcentration factors for dinitroglycerin of 685 and 40 were determined for roots and shoots, respectively. Results of these studies will improve our understanding of toxicity and bioconcentration of NG in terrestrial plants and will contribute to ecological risk assessment of NG-contaminated sites.     

Sorption behavior of potential organic wastewater indicators with soils

Soil-aquifer treatment is a wastewater treatment and reclamation option to facilitate beneficial water reuse. The fate of wastewater originated micropollutants in the soil-aquifer system is important to understand. In the study the sorption behavior of potential wastewater indicators such as two antiepileptic drugs (carbamazepine, primidone), one sulfonamide (sulfamethoxazole), and one corrosion inhibitor (benzotriazole) were determined with three natural soils (Lufa 2.2, Euro Soil 5, and Wulpen sand) that differed in pH, organic carbon content and particle size distribution. As aqueous phase a 0.01 M CaCl₂ solution as well as the effluent of a municipal wastewater treatment plant was used. Affinities of all analytes to the soil increased from Wulpen sand, over Lufa 2.2 to Euro Soil 5, indicating that the organic carbon contents might be crucial for sorption. Isotherms were well described by the Freundlich model. Sorption was mainly close to linear (n = 0.93-1.07) for most target compounds and soils. Desorption gave rise to a small hysteresis only for Euro Soil 5 which was likely artificial, due to slow desorption kinetics beyond 24 h used in the experiment. All sorption studies confirmed that Carbamazepine, Benzotriazole and Primidone are appropriate to be used as wastewater indicator substances based on their low sorption affinity to soils, while the suitability of Sulfamethoxazole is limited due to the formation of non-extractable residues, especially at lower pH values.     

无黏性管涌型土的BP神经网络判别法研究

运用基于Matlab的神经网络工具箱(NNT)建立无黏性管涌型土的预测模型,并分别以试验数据为研究对象,运用BP神经网络模型对该段土样的渗透破坏形式进行预测。预测结果与规范及试验所得结果相同,说明了基于Matlab的BP神经网络运用于无黏性管涌型土预测的可行性和应用价值。     

Study on the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chloro-phenoxyacetic sodium (MCPA sodium) in natural agriculture-soils of Fuzhou, China using capillary electrophoresis

A new method of analyzing trace 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2-methy-4-chloro-lphenoxyacetic sodium (MCPA sodium) in soils by capillary electrophoresis (CE) has been developed in this study. The optimum analytical conditions including chemical component and concentration of buffer solution, pH, separation voltage and sample injection time were studied in detail. Under the optimum conditions, 2,4-D and MCPA sodium in soils can be speedy separated and determined within 20 min with detection limits of 0.15 µg/g (2,4-D) and 0.25 µg/g (MCPA sodium) , a RSD (n = 6) < 5% and a recovery > 89%.With the help of analytical method developed in this study, the degradations of 2,4-D and MCPA sodium in natural agriculture-soils of Fuzhou were studied. The experimental results indicated that the degradations of 2,4-D and MCPA sodium follow first-order kinetics with degradation constants of 0.1509 day^-1 (2,4-D) and 0.2722 day^-1 (MCPA sodium) respectively. The degradation half-life were calculated to be 4.6 days (2,4-D) and 2.6 days (MCPA sodium) at 27 °C, implied that 2,4-D and MCPA sodium can be speedy degraded in natural agriculture-soils of Fuzhou, China.     

水泥稳定天然碎石土强度影响因素分析研究

通过分析天然碎石土的化学成分、水泥类型以及水泥剂量、水泥稳定天然碎石土的含水量以及干密度、拌合方法、施工过程以及养生条件、压实度等因素对水泥稳定天然碎石土强度的影响,得出水泥稳定天然碎石土做基层的水泥剂量要求,含水量的控制以及压实度的要求。     

Erosion of arable soils in Britain

Changing perspectives on erosion problems on British arable soils are reviewed. Current agricultural practices are increasing the magnitude and extent of soil erosion in Britain and other parts of Europe. Current trends in soil erosion research are examined, in particular recent field survey developments and the potential value of radar‐satellite based monitoring of erosive weather systems. More attention should be devoted to assessing levels of erosion on British arable soils and to the implications of current erosion rates on the long‐term ability of soil to act as a medium for sustained crop yield. Proposed strategies for soil conservation include avoiding cultivation of steep slopes, increasing soil organic content, reducing soil compaction, investigating and remedying sub‐soil compaction, developing a mature crop cover before convective storms occur in early summer and reducing cultivations to a minimum.     

Quantifying heavy metal inputs to agricultural soils in England and Wales

Heavy metal inputs to agricultural soils in England and Wales were estimated from major sources, including atmospheric deposition, biosolids, livestock manures, inorganic fertilisers and lime, industrial by‐product ‘wastes’ and composts (year 2000). Across the whole agricultural land area, atmospheric deposition was the main source of most metals ranging from 25 to 85% of total inputs. Livestock manures and biosolids were also important sources representing 37 and 8% of total zinc (Zn) inputs, 40 and 17% for copper (Cu), and 10 and 4% for cadmium, respectively. The highest heavy metal input rates on a field basis were generally from biosolids, although Zn and Cu inputs from pig manures were equivalent to 46–52% of biosolids inputs (both applied at a rate of 250 kg/ha total N). The study provided baseline information to develop and focus policies limiting heavy metal inputs to and accumulation in topsoils.     

Assessment of fly ash-aided phytostabilisation of highly contaminated soils after an 8-year field trial Part 2. Influence on plants

Aided phytostabilisation is a cost-efficient technique to manage metal-contaminated areas, particularly in the presence of extensive pollution. Plant establishment and survival in highly metal-contaminated soils are crucial for phytostabilisation success, as metal toxicity for plants is widely reported. A relevant phytostabilisation solution must limit metal transfer through the food chain. Therefore, this study aimed at evaluating the long-term efficiency of aided phytostabilisation on former agricultural soils highly contaminated by cadmium, lead, and zinc. The influence of afforestation and fly ash amendments on reducing metal phytoavailability was investigated as were their effects on plant development. Before being planted with a tree mix, the site was divided into three plots: a reference plot with no amendment, a plot amended with silico-aluminous fly ash and one with sulfo-calcic fly ash. Unlike Salix alba and Quercus robur, Alnus glutinosa, Acer pseudoplatanus and Robinia pseudoacacia grew well on the site and accumulated, overall, quite low concentrations of metals in their leaves and young twigs. This suggests that these three species have an excluder phenotype for Cd, Zn and Pb. After 8 years, metal availability to A. glutinosa, A. pseudoplatanus and R. pseudoacacia, and translocation to their above-ground parts, strongly decreased in fly ash-amended soils. Such decreases fit well together with the depletion of CaCl₂-extractable metals in amended soils. Although both fly ashes were effective to decrease Cd, Pb and Zn concentrations in above-ground parts of trees, the sulfo-calcic ash was more efficient.     

Toxicity of chlorpyrifos and TCP alone and in combination to Daphnia carinata: the influence of microbial degradation in natural water

The acute toxicity of chlorpyrifos and its principal metabolite 3,5,6-trichloropyridinol (TCP) alone and in combination to a cladoceran, Daphnia carinata, was studied in both cladoceran culture medium and natural water collected from a local suburban stream. TCP was found to be more toxic than its parent chemical chlorpyrifos to Daphnia survival in cladoceran culture medium. However, TCP in natural water was not toxic to D. carinata up to 2 microgL(-1). The LC(50) values for chlorpyrifos, TCP and chlorpyrifos+TCP were 0.24, 0.20 and 0.08 microgL(-1), respectively, in cladoceran culture medium. Although the parent chemicals and their degradation products co-exist in natural waters, the existing guidelines for water quality are based on individual chemicals. The results of this investigation suggest that chlorpyrifos and TCP can interact synergistically, additively or antagonistically, resulting in an increase or decrease in the overall toxicity of the mixture compared to individual compounds. The indigenous microorganisms in natural water could play a significant role in degradation of these compounds thereby influencing their toxicity in receiving waters. This study clearly suggests that the joint action of pesticides and their degradation products should be considered in the development of water quality guidelines. To our knowledge, this is the first study on the interactive effect of chlorpyrifos and TCP to a cladoceran and suggests that these two compounds are non-toxic when present together at concentrations up to 0.12 microgL(-1). However, these compounds together act additively at and above 0.5 microgL(-1) to fresh water invertebrates and therefore pollution with these compounds may adversely affect natural ecosystems.     

Photodegradation of 2,4-dichlorophenoxyacetic acid in various iron-mediated oxidation systems

The oxidation of herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) by different iron-mediated processes, with or without the presence of ultraviolet (at 253.7 nm) and oxalate, was investigated and compared. The initial decay rate and the overall removal percentage were used as the performance indexes. To extensively explore the associated processes, the following combinations or blank systems were investigated: UV radiation only, Fe(2+)/H(2)O(2), Fe(2+)/H(2)O(2)/UV, ferrous oxalate/H(2)O(2), ferrous oxalate/H(2)O(2)/UV, Fe(3+)/H(2)O(2), Fe(3+)/H(2)O(2)/UV, ferrioxalate/H(2)O(2), and ferrioxalate/H(2)O(2)/UV. This study showed that the degradation of 2,4-D by sole UV or dark processes (without UV) is generally slow, except by the conventional Fenton's process (Fe(2+)/H(2)O(2)). However, these slow reactions can be accelerated by exposure to UV irradiation, which can increase the initial 2,4-D decay rate from ten to more than one hundred times. Furthermore, if the reaction is initiated by ferrous oxalate or ferrioxalate instead of Fe(2+) or Fe(3+) ions, the rates can be further improved, because of the higher light sensitivity of the organometallic complexes. These reactions were also found sensitive to the initial hydrogen peroxide concentration. The competition of hydroxyl free radicals by the primary intermediate, 2,4-dichlorophenol, was also observed.     

饱和土体应变局部化的复合体理论

有限元法求解应变局部化问题时经常受到单元尺寸敏感性问题的困扰。为克服这一难题 ,给出一种基于整体坐标的应变局部化的复合体理论 ,通过对剪切带内外土体力学特性进行均一化处理来描述含剪切带土体的宏观力学特性。首先从理论上分析了饱和土体应变局部化的产生条件 ,随后通过复合体理论给出了描述在排水条件和不排水条件下饱和土体应变局部化的本构方程 ,最后对平面应变条件下的饱和密砂试样进行了分析 ,通过与室内平面应变试验结果的对比 ,验证了本文理论的合理性。     

饱和地基中埋置点源荷载的动力Green函数

基于合理的弹性土波动方程 ,应用积分变换方法 ,研究了饱和半空间地基中埋置点源荷载的轴对称Lamb问题解答。借助数值Hankel反演 ,分析了地基表面竖向位移的变化规律 ,并考察了土的渗透性及激振频率对它的影响。本文的结论可应用于地下爆破及地下结构等动力分析 ,对工程实践有指导意义。     

The response of natural displacement ventilation to time-varying heat sources

We examine transients caused by sudden changes in heat load in a naturally ventilated chamber. The space we consider has an isolated heat source, modeled as an ideal plume, and is connected to the exterior via openings at the top and bottom. Pressure differences between the exterior and interior that arise due to the buoyancy in the space drive a natural ventilation flow through the space that generates a two-layer system with buoyant (warm) fluid in the upper layer and ambient fluid in the lower layer. We develop two mathematical models, one assuming perfect mixing of each layer, the other accounting for stratification. We compare both models to small scale laboratory experiments. Neither model is significantly better than the other, and both give good agreement with the experiments.     

Denitrification potential and its relation to organic carbon quality in three coastal wetland soils

Capacity of a wetland to remove nitrate through denitrification is controlled by its physico-chemical and biological characteristics. Understanding these characteristics will help better to guide beneficial use of wetlands in processing nitrate. This study was conducted to determine the relationship between soil organic carbon (SOC) quality and denitrification rate in Louisiana coastal wetlands. Composite soil samples of different depths were collected from three different wetlands along a salinity gradient, namely, bottomland forest swamp (FS), freshwater marsh (FM), and saline marsh (SM) located in the Barataria Basin estuary. Potential denitrification rate (PDR) was measured by acetylene inhibition method and distribution of carbon (C) moieties in organic C was determined by 13C solid-state NMR. Of the three wetlands, the FM soil profile exhibited the highest PDR on both unit weight and unit volume basis as compared to FS and SM. The FM also tended to yield higher amount of N2O as compared to the FS and SM especially at earlier stages of denitrification, suggesting incomplete reduction of NO3(-) at FM and potential for emission of N2O. Saline marsh soil profile had the lowest PDR on the unit volume basis. Increasing incubation concentration from 2 to 10 mg NO3(-)-N L(-1) increased PDR by 2 to 6 fold with the highest increase in the top horizons of FS and SM soils. Regression analysis showed that across these three wetland systems, organic C has significant effect in regulating PDR. Of the compositional C moieties, polysaccharides positively influenced denitrification rate whereas phenolics (likely phenolic adehydes and ketonics) negatively affected denitrification rate in these wetland soils. These results could have significant implication in integrated assessment and management of wetlands for treating nutrient-rich biosolids and wastewaters, non-point source agricultural runoff, and nitrate found in the diverted Mississippi River water used for coastal restoration.     

Contribution of the ozonation pre-treatment to the biodegradation of aqueous solutions of 2,4-dichlorophenol

The effect of ozonation on the biodegradability of 100-ppm aqueous solutions of 2,4-dichlorophenol has been investigated. BOD at 5, 10 and 21 days, BOD/COD and BOD/TOC ratios and the average oxidation state are presented. Biodegradability measured as BOD₅/COD ratio was increased from 0 of the original solution to 0.25 at the moment of removing all the initial compound (corresponding to an ozone dose of 0.12 g L⁻¹, 0.48 for BOD₂₁/COD ratio). To test the effect of this pre-treatment, the biological oxidation of these pre-ozonated solutions was performed in two semi-continuous stirred tank reactors, one with non-acclimated sludge and one with acclimated-to-phenol sludge. The study showed that the TOC content of the pre-treated solution could be removed up to 68% by an aerobic biological treatment as well as co-digested with municipal wastewater (TOC removal up to 82%), with similar operating retention times to a municipal wastewater plant (12-24 h). Kinetic studies based on Monod model have also been carried out. Pseudo-first-order kinetic constants were found to be in the range of 0.5-0.8 L g TVSS⁻¹ h⁻¹.