Critical evaluation of desorption phenomena of heavy metals from natural sediments

In natural sediments, the majority of heavy metal ions are generally associated with the solid phase. To become bioavailable, the metal ions must desorb from the solid. Numerous studies of heavy metals in sediments have suggested that sorption and desorption exhibit hysteresis (i.e., the two processes are not reversible), while other studies have suggested that desorption hysteresis does not exist. In this study, sorption/desorption hysteresis of lead (Pb) and cadmium (Cd) was evaluated over the following range of conditions: (i) desorption induced by replacing the supernatant liquid with contaminant-free electrolyte solution; (ii) desorption induced by lowering the solution pH with mineral acid; and (iii) desorption induced by sequestration with EDTA. Given the importance of dissolved organic and inorganic ligands in regulating heavy metal behavior in nature sediments, sorption/desorption experiments were conducted on both untreated and prewashed sediments. Prewashing treatment increases the sorption potential of Cd but not Pb. Desorption hysteresis is observed in both the untreated and the prewashed sediments using the replaced supernatant method, and the desorption hysteresis appears to increase with aging time. Hysteresis is not observed when desorption is initiated by lowering the solution pH. A large fraction of the sorbed heavy metal ions can be easily desorbed by EDTA; between 0.04 and 1.2 mmol/kg Cd and Pb ions are resistant to desorption.     

Bioremediation process for sediments contaminated by heavy metals: feasibility study on a pilot scale

The core stages of a sediment remediation process--the conditioning of dredged sludge by plants and the solid-bed leaching of heavy metals using microbially produced sulfuric acid--were tested on a pilot scale using a highly polluted river sediment. Conditioning was performed in 50 m3 basins at sludge depths of 1.8 m. During one vegetation period the anoxic sludge turned into a soil-like oxic material and became very permeable to water. Reed canary grass (Phalaris arundinacea) was found to be best suited for conditioning. Bioleaching was carried out in an aerated solid-bed reactor of 2000 L working volume using oxic soil-like sediment supplemented with 2% sulfur. When applying conditioned sediment, the oxidation of easily degradable organic matter by heterotrophic microbes increased the temperature up to 50 degrees C in the early leaching phase, which in turn temporarily inhibited the sulfur-oxidizing bacteria. Nevertheless, most of the metal contaminants were leached within 21 days. Zn, Cd, Mn, Co, and Ni were removed by 61-81%, Cu was reduced by 21%, while Cr and Pb were nearly immobile. A cost-effectiveness assessment of the remediation process indicates it to be a suitable treatment for restoring polluted sediments for beneficial use.     

Role of sediment resuspension in the remobilization of particulate-phase metals from coastal sediments

The release of particulate-phase trace metals due to sediment resuspension has been investigated by combining erosion chamber experiments that apply a range of shear stresses typically encountered in coastal environments with a shear stress record simulated by a hydrodynamic model. Two sites with contrasting sediment chemistry were investigated. Sediment particles enriched in silver, copper, and lead, 4-50 times greater than the bulk surface-sediment content, were the first particles to be eroded. As the shear-stress level was increased in the chamber, the total mass eroded increased, butthe enrichment of these trace metals fell, approaching the bulk-sediment content. From the temporal distribution of shear stress generated by the hydrodynamic model for a site in Boston Harbor, resuspension fluxes were estimated. The erosion threshold of this site is exceeded during spring tides, releasing the particles enriched in trace metals into the water column. Due to the higher trace metal content and the regularity of resuspension, low-energy resuspension events (up to a shear stress of 0.2 N/m(2)) contribute up to 60% of the resuspension metal flux in an average year. The estimated annual quantity of copper and lead resuspended into the water column is higher than estimates of the total riverine flux for these metals. These results indicate that sediment resuspension is a very important mechanism for releasing metals into the water column and provide new insight into the chemical and physical processes controlling the long-term fate of trace metals in contaminated sediments.     

Arsenic redistribution between sediments and water near a highly contaminated source

Mechanisms controlling arsenic partitioning between sediment, groundwater, porewaters, and surface waters were investigated at the Vineland Chemical Company Superfund site in southern New Jersey. Extensive inorganic and organic arsenic contamination at this site (historical total arsenic > 10 000 microg L(-1) or > 130 microM in groundwater) has spread downstream to the Blackwater Branch, Maurice River, and Union Lake. Stream discharge was measured in the Blackwater Branch, and water samples and sediment cores were obtained from both the stream and the lake. Porewaters and sediments were analyzed for arsenic speciation as well as total arsenic, iron, manganese, and sulfur, and they indicate that geochemical processes controlling mobility of arsenic were different in these two locations. Arsenic partitioning in the Blackwater Branch was consistent with arsenic primarily being controlled by sulfur, whereas in Union Lake, the data were consistent with arsenic being controlled largely by iron. Stream discharge and arsenic concentrations indicate that despite large-scale groundwater extraction and treatment, > 99% of arsenic transport away from the site results from continued discharge of high arsenic groundwater to the stream, rather than remobilization of arsenic in stream sediments. Changing redox conditions would be expected to change arsenic retention on sediments. In sulfur-controlled stream sediments, more oxic conditions could oxidize arsenic-bearing sulfide minerals, thereby releasing arsenic to porewaters and streamwaters; in iron-controlled lake sediments, more reducing conditions could release arsenic from sediments via reductive dissolution of arsenic-bearing iron oxides.     

Release and phase partitioning of metals from anoxic estuarine sediments during periods of simulated resuspension

Periodically, marine sediments are subjected to physical processes which resuspend them into the water column, releasing previously sequestered metals. The role of resuspension energy and duration on release and subsequent redistribution of sediment bound metals was measured experimentally using a particle entrainment simulator. Two metal contaminated anoxic sediments with different physical and chemical characteristics were resuspended for 12 h at energies of 2 and 5 dynes cm(-2). Samples were taken at specified intervals, and the water column pH, Eh and dissolved oxygen levels were monitored continuously. Over time, metal concentrations increased in the particulate (nonfilterable > or = 1 microm) and filterable (< 1 microm) phases of the overlying water. In general, metal enrichment followed the Irving-Williams order of complex stability. Overall, the sediment's chemical and physical composition were major factors in determining the amount of metal released, more so than the level of resuspension energy applied. These results provide insight into how physical and chemical processes interact during sediment resuspension to release sediment bound metals and control their phase distribution in the water column.     

北京地区池塘底泥中重金属分布及其污染评价

目的针对北京地区17家养殖池塘底泥中重金属污染状况进行调查及评价重金属生态风险,为水产养殖环境提供理论依据并指导生产。方法使用原子吸收分光光度法测定底泥中Cu、Zn、Cr、Pb、Cd含量,用原子荧光分光光度法测定底泥中Hg、As含量;采用单项污染指数、综合污染指数法及Hakanson潜在生态风险评价方法对养殖池塘底泥中重金属的污染状况分别进行评价。结果 17家池塘底泥中重金属Cu、Zn、Cr、Pb、Cd、As的平均含量分别为17.85、50.27、33.09、14.50、0.06和1.98mg/kg(均以湿基计),Hg未检出;Zn、Pb、Cd、Hg和As处于安全等级,Cu污染处于警戒线,Cr污染处于轻度污染;底泥中重金属的潜在生态风险顺序依次CdCuPbAsCrZn,潜在生态风险危害程度轻微。结论北京地区17家养殖场池塘底泥中重金属含量的蓄积对养殖水产品质量影响较小,适宜水产养殖。     

Assessment of heavy metals remobilization by fractionation: comparison of leaching tests applied to roadside sediments

The pollution emitted by traffic activities and road maintenance is an area of great interest as contaminants can be transported to roadside sediments and pose a risk to environmental and human health. In the presentwork, deposited pollution in roadside sediments has been assessed by sampling along a highly traveled highway in Barcelona and the surrounding area. The available amounts of the heavy metals was determined by applying different leaching tests and calculating the concentration enrichment ratio (CER) and the environmental concentration guideline values (ECG). To gain information on the heavy metals (HMs) fractionation, the sequential extraction scheme (SES), established by the Standard Measurement and Testing (SM&T), was implemented, and the results were compared with those obtained by single leaching tests. An anthropogenic enhancement of certain metals was observed after considering both the CER and ECG values. However, if only ECG values were considered, an overestimation of the anthropogenically enhanced pollutants was obtained due to disregarding geochemical and particle size variability. CER values provide a more realistic assessment by determining different levels of anthropogenic impact. Thus, CER values suggest a minimum anthropogenic apportion for metals such as Cd, Cr, and Ni, whereas different situations from significant to extreme anthropogenic contribution were observed for Zn, Pb, and Cu. These results have been complemented by other leaching tests that minimize the time-consuming environmental evaluation. In this study, HCI extraction produces suitable results for a quick screening since they correlate well with the corresponding SES: Cu(r2 = 0.798), Pb(r2 = 0.958) and Zn(r2 = 0.901). Mild extractants have been observed to be limited to highly polluted samples due to their low leaching power. The information obtained following this procedure helps to identify hazardous areas that need a remedial strategy.     

突飞猛进的光化蚀刻工艺

介绍了光化蚀刻的由来和传统工艺流程中五种掩膜的制作方法及四种现代的光化蚀刻法流程及其应用范围。指出随着电子技术的不断发展,光化蚀刻这门技术已经拓展到了许多新的领域,形成了一定的生产规模,并且带动了相关企业的发展。     

Pu and 137Cs in the Yangtze River estuary sediments: distribution and source identification

Pu isotopes and (137)Cs were analyzed using sector field ICP-MS and γ spectrometry, respectively, in surface sediment and core sediment samples from the Yangtze River estuary. (239+240)Pu activity and (240)Pu/(239)Pu atom ratios (>0.18) shows a generally increasing trend from land to sea and from north to south in the estuary. This spatial distribution pattern indicates that the Pacific Proving Grounds (PPG) source Pu transported by ocean currents was intensively scavenged into the suspended sediment under favorable conditions, and mixed with riverine sediment as the water circulated in the estuary. This process is the main control for the distribution of Pu in the estuary. Moreover, Pu is also an important indicator for monitoring the changes of environmental radioactivity in the estuary as the river basin is currently the site of extensive human activities and the sea level is rising because of global climate changes. For core sediment samples the maximum peak of (239+240)Pu activity was observed at a depth of 172 cm. The sedimentation rate was estimated on the basis of the Pu maximum deposition peak in 1963-1964 to be 4.1 cm/a. The contributions of the PPG close-in fallout Pu (44%) and the riverine Pu (45%) in Yangtze River estuary sediments are equally important for the total Pu deposition in the estuary, which challenges the current hypothesis that the riverine Pu input was the major source of Pu budget in this area.     

Seven thousand years of records on the mining and utilization of metals from lake sediments in central China

A 268 cm section of sediment core from Liangzhi Lake in Hubei province in central China was used to assess the use and accumulation of metals in the lake in the past 7,000 years. The concentrations of trace metals, including Cu, Pb, Ni, and Zn, and major elements, Ca, Fe, and Mg, in a 14C- dated segment of sediment core were analyzed. Historical trends on the input of metals to Liangzhi Lake from around 5000 BC to the present were recorded in the sediments, representing about 7,000 years of history on the mining and utilization of metals in central China. The concentrations of Cu, Ni, Pb, and Zn increased gradually from about 3000 +/- 328 BC, indicating the start of the Bronze Age in ancient China. During the period 467 +/- 257 to 215 +/- 221 AD, there was a rapid increase in the concentrations of these metals in the sediments, indicating enormous inputs of these metals at that time. This era corresponded to China's Warring States Period (475- 221 BC) and the early Han Dynasty (206 BC-220 AD), during which copper and lead were extensively used in making bronze articles such as vessels, tools, and weapons. From 1880 +/- 35 AD to the early 1900s, there was also a significant increase in the concentrations of metals such as Cu, Ni, and Pb, which probably reflected the metal emissions and utilization during the early period of industrial development and weapon manufacture during the wars in China. The Pb isotopic analysis showed that the surface and subsurface sediments had lower 206Pb/207Pb and 208Pb/ 207Pb ratios than the deeper layers, reflecting the additional input of Pb from mining activities that took place during the Bronze Age era and in modern times. This study provides direct evidence of the environmental impact of the mining and utilization of metals in the last 7,000 years in one of the important regions of Chinese civilization.     

卡诺拉油沉淀物质分析方法

综述了卡诺拉油沉淀物质常用的分析原理、方法。     

Photochemical behaviour of hydrolysed keratin

An investigation into the influence of UV irradiation on keratin hydrolysates was carried out using UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and fluorescence spectroscopy. It was found that the absorption of keratin hydrolysates in solution increased during irradiation of the sample, most notably between 250-280 and 320-410 nm. The increase in absorbance in the region 320-410 was because of the new photoproducts formed during UV irradiation of keratin hydrolysates. The fluorescence of keratin hydrolysates was observed at 328 nm after excitation at 270 nm. UV irradiation caused fluorescence fading at 328 nm, and after 60 min of irradiation, a new broad weak band of fluorescence, attributable to new photoproducts, emerged in the UV wavelength region with emission maximum between 400 and 500 nm. FTIR spectroscopy results showed degradation of keratin under UV irradiation. A slight increase in oxidized sulphur species was also observed. The results obtained suggest that UV irradiation can be used as modifying agent for preparation of keratin hydrolysates for cosmetic applications.     

Photochemical degradation of PCBs in snow

This work represents the first laboratory study known to the authors describing photochemical behavior of persistent organic pollutants in snow at environmentally relevant concentrations. The snow samples were prepared by shock freezing of the corresponding aqueous solutions in liquid nitrogen and were UV-irradiated in a photochemical cold chamber reactor at -25 degrees C, in which simultaneous monitoring of snow-air exchange processeswas also possible. The main photodegradation pathway of two model snow contaminants, PCB-7 and PCB-153 (c approximately 100 ng kg(-1)), was found to be reductive dehalogenation. Possible involvement of the water molecules of snow in this reaction has been excluded by performing the photolyses in D2O snow. Instead, trace amounts of volatile organic compounds have been proposed to be the major source of hydrogen atom in the reduction, and this hypothesis was confirmed by the experiments with deuterated organic cocontaminants, such as d6-ethanol or d8-tetrahydrofuran. It is argued that bimolecular photoreduction of PCBs was more efficient or feasible than any other phototransformations under the experimental conditions used, including the coupling reactions. The photodegradation of PCBs, however, competed with a desorption process responsible for the pollutant loss from the snow samples, especially in case of lower molecular-mass congeners. Organic compounds, apparently largely located or photoproduced on the surface of snow crystals, had a predisposition to be released to the air but, at the same time, to react with other species in the gas phase. It is concluded that physicochemical properties of the contaminants and trace co-contaminants, their location and local concentrations in the matrix, and the wavelength and intensity of radiation are the most important factors in the evaluation of organic contaminants' lifetime in snow. Based on the results, it has been estimated that the average lifetime of PCBs in surface snow, connected exclusively to the photoreductive dechlorination process, is 1-2 orders of magnitude longer than that in surface waters when subjected to the equivalent solar radiation. However, in case that the concentration of the hydrogen peroxide in natural snow is sufficient, the photoinduced oxidation process could succeed the photoreductive dechlorination and evaporative fluxes as the major sink.     

Photochemical Grafting of Vinyl Monomers onto Starch

A general study of the UV light-induced grafting of vinyl monomers upon potato starch is reported. A large variety of monomers with hydrophilic and hydrophobic properties and of initiators of free radicals was used. The best conditions of the grafting reaction were determined and several parameters were investigated: temperature, oxygen, initiator concentration, additives. Percentage of grafting-time conversion curves, percentage of homopolymer, rate of grafting were obtained. For a given monomer, the most efficient photoinitiator can be selected.     

Photochemical Treatment to Improve Storability of Fresh Strawberries

We investigated the effect of pre-storage exposure to shortwave ultra-violet (UV-C) light on the decay and quality of fresh strawberries. Fresh strawberries (cv. Kent, 25% to 50% red) were exposed to UV-C at doses of 0.25 and 1.0 kJ/m² and stored at 4 °C or 13 °C. UV treatment controlled the decay caused by Botrytis cinerea at both temperatures and extended the shelf-life of the fruits by 4 to 5 d. UV-treated fruits had a lower respiration rate, higher titratable acidity and anthocyanin content, and were firmer than the untreated fruits. The percentage of free sugars increased faster in UV-treated fruits at the beginning of the storage period. A lower electrical conductivity in fruits treated with 0.25 kJ/m² suggests a slower rate of senescence compared to the control. A higher electrical conductivity observed with 1.0 kJ/m²suggests damage to the fruits. Overall, UV treatment at 0.25 kJ/m² appears to slow down the ripening and senescence of strawberry fruits stored at 4 °C.