Evaluation of the Chemcatcher and DGT passive samplers for monitoring metals with highly fluctuating water concentrations

Passive sampling devices accumulate chemicals continuously from water and can provide time weighted average (TWA) concentrations of pollutants over the exposure period. Hence, they offer a number of advantages over other conventional monitoring techniques such as spot or grab sampling. The diffusive gradient in thin film (DGT) and the Chemcatcher passive samplers can be used to provide TWA concentrations of labile metals, but the approaches to their calibration differ. DGT uses diffusion coefficients of metals in the hydrogel layer, whereas Chemcatcher uses metal specific uptake rates, with both sets of values obtained under controlled laboratory conditions with constant aqueous metal concentrations. However, little is known of how such samplers respond to fluctuating concentrations. We evaluated the responsiveness of these two passive sampling devices to rapidly changing concentrations of Cd, Cu, Ni, Pb and Zn in natural freshwater, over a relatively short deployment time. Maximum metal concentrations in water were varied between 70 and 140 microg L(-1). Experiments were carried out in a tank with a rotating carousel system and filled with Meuse river water, allowing a degree of control over experimental conditions while using natural river water. Fluctuating concentrations were obtained by stepwise addition of standard solutions of the metals. The reliability and accuracy of the TWA concentrations measured by the samplers were assessed by comparison with concentrations of the metals in spot samples of water taken regularly over the deployment period. The spot samples of water were either unfiltered (total), filtered (0.45 microm) or ultrafiltered (5 kDa). Predictive speciation modelling using the visual MINTEQ programme was also undertaken. There was reasonable agreement between the TWA concentrations of Cd and Ni obtained with Chemcatcher and DGT and the total Cd and Ni concentrations measured in repeated unfiltered spot samples. For elements (i.e. Cu, Pb, Zn) that associate to a significant degree with suspended solids, colloids or dissolved organic carbon, or form complexes with large organic ligands, optimum agreement was with the filtered or ultrafiltered fractions and with the predicted inorganic and inorganic-fulvic acid associated fractions. While Chemcatcher-based TWA concentration ranges for Cu and Zn were in best agreement with the total filtered fraction, there was lack of agreement for Pb. The combined use of DGT devices with open pore (OP) and restricted pore (RP) gels allowed the labile fraction of metal associated with large organic ligands or DOC to be differentiated and quantified, since this is available to DGT OP but unable to diffuse into the DGT RP. This evaluation of the two sampling devices clearly demonstrated their ability to react reliably to transient peaks in concentration of metal pollutants in water and indicated where future efforts are needed to improve calibration data. Such samplers may prove valuable in responding to the monitoring requirements of the European Union's Water Framework Directive.     

Monitoring of (bio)available labile metal fraction in a drinking water treatment plant by diffusive gradients in thin films

A performance study of diffusive gradients in thin films (DGT) and inductively coupled plasma optical emission spectrometry (ICP-OES) was applied for the monitoring of the labile fraction of metals Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, in Sant Joan Despí Drinking Water Treatment Plant located in the South of Barcelona’s Metropolitan Area (Spain). The DWTP monitoring protocol was optimized by working for 1 day of deployment (24 h) with the DGT device in contact with both treated and river water matrixes. Additionally, it was demonstrated that an increase in the deployment time of 1 week did not decrease the evaluated concentrations of the studied metals. The quality parameters of the DGT device and ICP-OES determination, such as limit of quantification, accuracy expressed as relative error (%) and reproducibility expressed as relative standard deviation, were evaluated. Good results were obtained for all the metals in ultrapure water; limits of quantification ranged from 1.5 μg L^− 1 for cadmium to 28 μg L^− 1 for zinc when deployment time of 24 h was used and from 0.2 μg L^− 1 for cadmium to 4 μg L^− 1 for zinc when this time was increased by 1 week. Accuracy and precisions lower than or equal to 10% were obtained at a parametric concentration value of the metals regulated in the European Drinking Water Guidelines (98/83/EC). DGT deployment was tested in river and treated water, and good results were obtained for Cd, Ni, Co and Zn, whereas for the other metals, a continuous control of their metallic labile fractions was monitored. Therefore, DGT device allows the continuous monitoring of the labile metal species in a drinking water treatment plant.     

对水污染源在线监测设备系统集成的思考

简述了水污染源在线监测设备系统集成的必要性,分析了目前系统集成中存在的问题,以及应采取的对策。按照国家有关规范要求,对现场端的在线监测设备进行科学的综合布局,并从采水、配水、预处理、控制、分析、数据采集与传输、辅助等构成单元,提出了有关水污染源在线监测设备系统集成的方案。     

可伸缩延长气体采样装置在应急监测中的应用

提出了一种可伸缩延长气体采样装置,并将其与现场气体监测仪器配套使用。初步考察了延长采样装置中Teflon采样管长度对现场监测结果可能产生的影响,并对监测站实验室楼顶废气排出筒气体进行了实际样品监测。结果表明,该装置可有效提高现场应急监测的安全防护保障效果,增加可监测区域范围,使现场应急监测工作能够为突发性环境污染事件的处置提供更多技术支持。     

Measurement of environmental pollutants using passive sampling devices--a commentary on the current state of the art

Passive sampling devices have been used since the 1970s to measure time-weighted average (TWA) or equilibrium concentrations of pollutants in various environmental matrices (e.g. air, soils and sediments and water). In recent years the popularity of using such samplers has increased and the technology in now well established for the measurement of atmospheric pollutants. This sector has a long experience of using passive samplers in the short- and long-term assessment of air quality in the local environment and on a global scale (e.g. within the United Nations Stockholm Convention on the trans-boundary movement of persistent organic pollutants (POPs) where large networks of samplers on a continental scale have been established). In comparison, the use of passive samplers for monitoring the aquatic environment has been slower to take off. There has, however, been a recent research drive to develop devices for measuring the wide range of pollutants that can be found in environmental waters (e.g. ground, surface, and marine). It is now being recognised that passive samplers can play a valuable role in monitoring water quality within a legislative framework such as the European Union's Water Framework Directive (WFD). The data from these devices can be used alongside the results obtained from conventional spot or bottle sampling to improve risk assessments and to inform decisions on undertaking potentially expensive remedial actions. Such monitoring techniques may have uses within the European Registration, Evaluation, Authorisation & restriction of CHemicals (REACH) Directive and the forthcoming European Marine Strategy Directive. It is expected that the aquatic monitoring sector will follow a transition similar to that which occurred in air monitoring where data obtained from passive samplers can use used within a legal framework. There has also been increased interest in extending the role of passive samplers to both the measurement of equilibrium concentrations and investigating the movement and release of the dissolved fraction of various pollutants in the pore water of sediments and soils.     

Chemcatcher and DGT passive sampling devices for regulatory monitoring of trace metals in surface water

This work aimed to evaluate whether the performance of passive sampling devices in measuring time-weighted average (TWA) concentrations supports their application in regulatory monitoring of trace metals in surface waters, such as for the European Union's Water Framework Directive (WFD). The ability of the Chemcatcher and the diffusive gradient in thin film (DGT) device sampler to provide comparable TWA concentrations of Cd, Cu, Ni, Pb and Zn was tested through consecutive and overlapping deployments (7-28 days) in the River Meuse (The Netherlands). In order to evaluate the consistency of these TWA labile metal concentrations, these were assessed against total and filtered concentrations measured at relatively high frequencies by two teams using standard monitoring procedures, and metal species predicted by equilibrium speciation modeling using Visual MINTEQ. For Cd and Zn, the concentrations obtained with filtered water samples and the passive sampling devices were generally similar. The samplers consistently underestimated filtered concentrations of Cu and Ni, in agreement with their respective predicted speciation. For Pb, a small labile fraction was mainly responsible for low sampler accumulation and hence high measurement uncertainty. While only the high frequency of spot sampling procedures enabled the observation of higher Cd concentrations during the first 14 days, consecutive DGT deployments were able to detect it and provide a reasonable estimate of ambient concentrations. The range of concentrations measured by spot and passive sampling, for exposures up to 28 days, demonstrated that both modes of monitoring were equally reliable. Passive sampling provides information that cannot be obtained by a realistic spot sampling frequency and this may impact on the ability to detect trends and assess monitoring data against environmental quality standards when concentrations fluctuate.     

Environmental concerns of desalinating seawater using reverse osmosis

This Critical Review on environmental concerns of desalination plants suggests that planning and monitoring stages are critical aspects of successful management and operation of plants. The site for the desalination plants should be selected carefully and should be away from residential areas particularly for forward planning for possible future expansions. The concerning issues identified are noise pollution, visual pollution, reduction in recreational fishing and swimming areas, emission of materials into the atmosphere, the brine discharge and types of disposal methods used are the main cause of pollution. The reverse osmosis (RO) method is the preferred option in modern times especially when fossil fuels are becoming expensive. The RO has other positives such as better efficiency (30-50%) when compared with distillation type plants (10-30%). However, the RO membranes are susceptible to fouling and scaling and as such they need to be cleaned with chemicals regularly that may be toxic to receiving waters. The input and output water in desalination plants have to be pre and post treated, respectively. This involves treating for pH, coagulants, Cl, Cu, organics, CO(2), H(2)S and hypoxia. The by-product of the plant is mainly brine with concentration at times twice that of seawater. This discharge also includes traces of various chemicals used in cleaning including any anticorrosion products used in the plant and has to be treated to acceptable levels of each chemical before discharge but acceptable levels vary depending on receiving waters and state regulations. The discharge of the brine is usually done by a long pipe far into the sea or at the coastline. Either way the high density of the discharge reaches the bottom layers of receiving waters and may affect marine life particularly at the bottom layers or boundaries. The longer term effects of such discharge concentrate has not been documented but it is possible that small traces of toxic substances used in the cleaning of RO membranes may be harmful to marine life and ecosystem. The plants require saline water and thus the construction of input and discharge output piping is vital. The piping are often lengthy and underground as it is in Tugun (QLD, Australia), passing below the ground. Leakage of the concentrate via cracks in rocks to aquifers is a concern and therefore appropriate monitoring quality is needed. Leakage monitoring devices ought to be attached to such piping during installation. The initial environment impact assessment should identify key parameters for monitoring during discharge processes and should recommend ongoing monitoring with devices attached to structures installed during construction of plants.     

基于REST+RIA架构的水环境监测点位管理系统

针对目前水环境点位管理中系统化、规范化和标准化方面存在的问题,提出采用REST+RIA的软件架构,引入CA认证技术和GIS技术构建水环境点位管理系统,满足点位管理业务复杂性的要求.结合关键技术对系统的逻辑架构、部署方案、点位管理的业务流程进行了分析和介绍.     

湖南省生态环境遥感监测平台建设思考

简述了国内外遥感监测平台的发展现状,基于湖南省生态环境遥感监测现状进行了分析,指出遥感监测平台存在遥感监测与评估技术缺乏、监测能力薄弱以及监测网络建设不完善等问题。从平台建设架构出发,构建了数据平台,对卫星遥感数据、地面调查/监测资料、无人机航测数据进行管理、存储、分析等;业务平台,主要围绕水、气、土壤等整个生态环境监测体系开展相应的监测和管理,还可针对重点区域,环境督察等业务进行拓展;展示平台,主要是通过各种终端设备和硬件对各类业务进行可视化。提出发射独立高分遥感卫星、深化遥感监测应用研究、加强各部门协同合作等建议,以期为湖南省生态环境遥感监测平台建设与发展提供参考。     

Guidance on choosing a measuring instrument for indoor particle pollution studies

The possibility of acquiring real-time concentration data is leading many indoor air quality and health researchers to the use of particle measuring instruments instead of the classic filtration approach. This paper summarizes a checklist of characteristics that have to be considered on the selection of such instruments and checks the compliance of three air monitoring devices suitable for environmental exposure researches. An evaluation table with desirable instrument technical, economic, and logistics characteristics was summarized in a checklist, and spec sheets of three air monitoring devices suitable for environmental exposure researches were checked. Technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. Only one instrument was in comply with it. A popular air monitoring device among environmental exposure researchers was checked and it failed the accuracy check. When selecting a particle measuring instrument, technical, economic, and logistics aspects have to be considered. Suitability, measurement range, accuracy, resolution, and robustness are indispensable metrological characteristics. When selecting an instrument for a study, a lack of information on the quality of results is a strong indication that it should not be considered, as study's response may be compromised.     

Moisture monitoring in waste disposal surface barriers

Surface barriers for waste disposal sites should preventwaste water and gas emission into the environment. It isnecessary to assess their proper operation by monitoring thewater regime of the containment. A set of three new water contentmeasuring devices has been developed that provide an economicalsolution for monitoring the moisture distribution and waterdynamic. They will give an early warning service if the barriersystem is at risk of being damaged. The cryo soil moisture sensor`LUMBRICUS' is an in situ self-calibrating absolute water contentmeasuring device. It measures moisture profiles at spot locationsdown to 2.5 m depth with an accuracy of better than 1.5% and adepth resolution of 0.03 m. The sensor inherently measuresdensity changes and initial cracks of shrinking materials likeclay minerals. The large area soil moisture sensor `TAUPE' is amoisture sensitive electric cable network to be buried in themineral barrier material of the cover. A report will be givenwith results and experiences on an exemplary installation at theWaste Disposal Facility Karlsruhe-West. 800 m² of the barrierconstruction have been continuously monitored since December1997. Volumetric water content differences of 1.5% have beendetected and localised within 4 m. This device is alreadyinstalled in two other waste disposal sites. A modified `TAUPE'was constructed for the control of tunnels and river dams aswell. Thin sheet moisture sensor `FORMI' is specifically designedfor moisture measurements in liners like bentonite, textile andplastic. Due to its flexibility it follows the curvature of theliner. The sensor measures independently from neighbouringmaterials and can be matched to a wide range of differentthickness of the material. The sensors are patented in several countries.     

Assessing the removal of inorganic colloids and Cryptosporidium parvum from drinking water

A new batch device that simulates the conditions in water and wastewater treatment plants and enables the study of low-concentration feeds is described. The application of this apparatus to the monitoring of the concentration of inorganic and/or biological contaminants is demonstrated, using kaolin particles and Cryptosporidium parvum oocysts, respectively. The rate of inorganic particle attachment to the static medium is found to be directly proportional to the initial influent concentration. On the other hand, Cryptosporidium parvum removal is found to be more effective in the presence of additional (kaolin) particles, and this is attributed to electrostatic interactions between oppositely charged layers on the absorbing medium. Accordingly, the addition of humic materials is found to inhibit the removal process, possibly by neutralizing the positive charge on the kaolin particles. The relevance of these results to existing water purification processes in general and to risk assessment of microbiological contamination in particular is discussed.     

Measurements of dissolved methylmercury in natural waters using diffusive gradients in thin film (DGT)

A diffusive gradient in thin films (DGT) technique for measuring methylmercury (MeHg) concentrations in natural waters was developed using 3-mercaptopropyl-functionalized silica gel to preconcentrate the methylmercury. The new resin was characterized and calibrated. Methylmercury is efficiently accumulated at a pH range of 3-9. Basic performance tests of the new DGT device confirmed the applicability of Fick's first law for such DGT measurements. The diffusion coefficient of methylmercury in polyacrylamide gel was 5 x 10(-6) cm(2) s(-1). Methylmercury concentrations determined by DGT deployed for different time periods in the field are statistically not different from results obtained through direct measurements. The DGT technique represents therefore an alternative in situ sampling method for methylmercury. The detection limit of the overall method is 1 pg of MeHg, which correspond to approximately 30 pg L(-1) of MeHg in a water sample, when deploying a typical DGT device for 24 hours. Lower MeHg concentrations are measurable using longer deployment times or thinner diffusive gel layers.     

野外无人值守森林实时监控与报警系统研究

随着中国森林的过度砍伐，森林面积急剧减少，对植被的保护刻不容缓。但由于人力物力有限，无法对大量的野生植被进行实时巡视，造成大量野生植被的滥砍滥伐。采用数字摄像头作为采集终端，利用太阳能电池作为可移动电源，结合 GPS 和 GSM的智能控制板，实现植被状况的前端智能判断与实时监控。     

Changes in water quality in agricultural catchments after deployment of wastewater treatment plant

Insufficient wastewater remediation in small communities and nonpoint source pollution are the key factors in determining the water quality of small streams in an agricultural landscape. Despite the current extensive construction of municipal wastewater treatment facilities in small communities, the level of organic substances and nutrients in the recipient catchments has not decreased in many areas. This paper analyzes the changes in the water quality of the small streams after the deployment of wastewater treatment plants that were designed to address sources of pollution from small municipalities. The analysis is based on the results from a water quality monitoring network in the small watersheds in the Czech Republic. Five rural catchments with one dominant municipal pollution source, where a wastewater treatment plant was deployed during the monitoring period, were selected according to a predefined set of criteria, from a series of 317 profiles. Basic water quality indicators were selected for the assessment: O₂, BOD-5, COD, TOC, conductivity, NH₄-N, NO₂-N, NO₃-N, PT, and PO₄-P. Results of the analysis showed that the simple deployment of the water treatment facilities at these streams often did not lead to a reduction of contamination in the streams. The expected post-deployment changes, namely, a significant and permanent reduction of stream contamination, occurred only in one catchment, whereas in the remainder of the catchments, only marginal changes or even increased concentrations of the contaminants were detected. As the critical factors that determined the efficiency of wastewater treatment were studied, the need for the consideration of the local conditions during the design of the facility, particularly regarding the size of the catchments, initial level of contamination, proper system of operation, and process optimization of the treatment facility, emerged as the important factor.     

一种基于游弋图像的水域监视鸟瞰图成像系统

针对各类水域污染日趋严重而传统水质监测方式离散、范围受限等不足,构建了基于游弋图像的水域鸟瞰图成像系统,实现大范围实时、连续监控。使用偏振设备消除水面反光,得到清晰的水面图像。设计了摄像机内外参标定的方法,在线获得状态参数;提出了自适应空洞填补的策略,消除了由透视图映射至鸟瞰图时产生的图像空洞;结合GPS信息和图像特征配准技术,获取了由船载摄像机视频序列拼合成的鸟瞰全景图像。该方法具有分辨率高、实时性强、监测范围广和使用成本低等优势。     

Possible way to substantial improvement of early warning system in the International Odra (Oder) River Basin

Water ecosystems are threatened by accidental spills of pollution. Rapidity and trueness of information gathering the biological impact of accidental pollution is crucial for the efficiency of the minimisation of possible deterioration of ecosystems and for success in detecting the source of pollution. Due to the randomised occurrence of accidental spills the only way to quickly detect hazardous situations is to perform continuous monitoring of surface water quality. The current situation in the field of early warning in the International Odra (Oder) River basin is not satisfactory. The actual number of monitoring stations and list of routinely continuously monitored parameters are not able to meet the needs of sensitive and rapid detection of biological impact of accidental pollution spills. An effort to change this unfavourable situation was the reason for the offer survey, selection and a model operation of a commercially produced biological monitoring device. This apparatus was located on the border-line profile on the territory of the Czech Republic and represented the first and only one tool of continual biological monitoring of surface water quality in the International Odra (Oder) River Basin. The selected apparatus was the Daphnia Toximeter produced by the firm bbe Moldaenke (Kiel, Germany). This device exploited for rapid detection of changes of biological quality of surface water evaluation of behavioural response of monitoring organisms??daphnids. Five years of model operation proved its suitability for early warning purposes. The apparatus was reliable in function and sensitive enough to detect the deterioration of the biological quality of the river water. The given examples document its applicability not only for detection of accidental spills but also of illegal emissions of pollution, which are very often toxic.     

Antifouling strategies for marine and riverine sensors

Traditionally, water quality has been monitored by sampling and lab based analysis. However, there are disadvantages associated with this method, for example, deterioration of samples with time, limited sampling points, limited temporal monitoring. This has provided impetus for the development of sensors which can be deployed from remote locations over extended deployment periods. However, a major limitation of these systems is their vulnerability to biofouling. This review outlines the research that has been carried out on strategies for the protection of marine and riverine sensors against fouling.     

上海市浅层地下水在线监测技术要点

地下水在线监测技术可以实现地下水水质的高频监测,是未来发展的重要趋势。梳理国内外地下水在线监测技术研究进展,以上海市典型水文地质特征与环境质量状况为例,探讨地下水在线监测点位布设、指标筛选、监测方式及监测井设计等技术要点。首先,优化监测点位布设,对需要开展高频监测的区域或重点风险源开展在线监测,以代表性点位反映总体地下水环境质量状况。其次,综合筛选监测指标,除常规参数外,优先选取水体中的氨氮、高锰酸盐指数等作为在线监测指标,在具有潜在有机污染的区域,选取水中有机物、水中油等作为有机污染指示性指标。应进一步加强指标之间的相关性分析,为指示性指标的确立提供依据。再次,合理确定监测方式,根据取样方式以及污染源风险等级,设置相应的微型站和小型站。最后,优化监测井设计技术方案,进一步研究不同井管材质对地下水中无机或有机污染物的长期吸附(解吸)作用。     

Optimal Expansion of Water Quality Monitoring Network by Fuzzy Optimization Approach

River reaches are frequently classified with respect to various mode of water utilization depending on the quantity and quality of water resources available at different location. Monitoring of water quality in a river system must collect both temporal and spatial information for comparison with respect to the preferred situation of a water body based on different scenarios. Designing a technically sound monitoring network, however, needs to identify a suite of significant planning objectives and consider a series of inherent limitations simultaneously. It would rely on applying an advanced systems analysis technique via an integrated simulation-optimization approach to meet the ultimate goal. This article presents an optimal expansion strategy of water quality monitoring stations for fulfilling a long-term monitoring mission under an uncertain environment. The planning objectives considered in this analysis are to increase the protection degree in the proximity of the river system with higher population density, to enhance the detection capability for lower compliance areas, to promote the detection sensitivity by better deployment and installation of monitoring stations, to reflect the levels of utilization potential of water body at different locations, and to monitor the essential water quality in the upper stream areas of all water intakes. The constraint set contains the limitations of budget, equity implication, and the detection sensitivity in the water environment. A fuzzy multi-objective evaluation framework that reflects the uncertainty embedded in decision making is designed for postulating and analyzing the underlying principles of optimal expansion strategy of monitoring network. The case study being organized in South Taiwan demonstrates a set of more robust and flexible expansion alternatives in terms of spatial priority. Such an approach uniquely indicates the preference order of each candidate site to be expanded step-wise whenever the budget limitation is sensitive in the government agencies.