Comparative distribution, sourcing, and chemical behavior of PCDD/Fs and PCBs in an estuary environment

PCDD/F and PCB field data (1041 samples) in five media (dissolved, suspended sediment, bed sediment, catfish, and blue crab) were studied to explore dual contaminant patterns in the Houston Ship Channel, Texas, USA. PCDD/Fs showed greater concentration than PCBs in suspended sediments while PCBs were higher in apparent dissolved (truly dissolved + DOC-associated), fish, and crab. PCDD/Fs at nearly all locations contributed more strongly to dioxin-like toxicity. The fraction of PCB TEQ was, however, enriched in biotic over abiotic media due in large part to the presence of PCB 126, which was mostly undetected in water and sediment and yet exhibited a BAF three times greater than 2,3,7,8-TCDD. Dissolved-suspended sediment and suspended-bed sediment relationships showed that (1) observed apparent dissolved concentration differences (as fraction of total water were mean 10% PCDD/Fs and 63% PCBs) can reasonably be explained by a four-phase partition model (truly dissolved, DOC-associated, suspended OC, and suspended BC) for PCBs but not for PCDD/Fs and (2) the contaminants behaved similarly in bed to suspended sediment concentration ratios (C_bed/C_susp) upstream of a major confluence but not downstream. PCA-cluster analysis pointed to the possibility that suspended sediment PCB contamination originates from resuspended bed sediment while PCDD/Fs in suspended sediment originates more probably from other sediment sources such as upstream wash load or air deposition. Finally, examinations of a congener marker ratio (PCB 209/206) seemed to indicate that a source of pure PCB 209 may exist in bed sediment near Patrick Bayou though the source was not completely localized.     

Estimation of transport parameters of phenolic compounds and inorganic contaminants through composite landfill liners using one-dimensional mass transport model

One-dimensional (1D) advection–dispersion transport modeling was conducted as a conceptual approach for the estimation of the transport parameters of fourteen different phenolic compounds (phenol, 2-CP, 2-MP, 3-MP, 4-MP, 2-NP, 4-NP, 2,4-DNP, 2,4-DCP, 2,6-DCP, 2,4,5-TCP, 2,4,6-TCP, 2,3,4,6-TeCP, PCP) and three different inorganic contaminants (Cu, Zn, Fe) migrating downward through the several liner systems. Four identical pilot-scale landfill reactors (0.25 m³) with different composite liners (R1: 0.10 + 0.10 m of compacted clay liner (CCL), L_e = 0.20 m, k_e = 1 × 10⁻⁸ m/s, R2: 0.002-m-thick damaged high-density polyethylene (HDPE) geomembrane overlying 0.10 + 0.10 m of CCL, L_e = 0.20 m, k_e = 1 × 10⁻⁸ m/s, R3: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick bentonite layer encapsulated between 0.10 + 0.10 m CCL, L_e = 0.22 m, k_e = 1 × 10⁻⁸ m/s, R4: 0.002-m-thick damaged HDPE geomembrane overlying a 0.02-m-thick zeolite layer encapsulated between 0.10 + 0.10 m CCL, L_e = 0.22 m, k_e = 4.24 × 10⁻⁷ m/s) were simultaneously run for a period of about 540 days to investigate the nature of diffusive and advective transport of the selected organic and inorganic contaminants. The results of 1D transport model showed that the highest molecular diffusion coefficients, ranging from 4.77 × 10⁻¹⁰ to 10.67 × 10⁻¹⁰ m²/s, were estimated for phenol (R4), 2-MP (R1), 2,4-DNP (R2), 2,4-DCP (R1), 2,6-DCP (R2), 2,4,5-TCP (R2) and 2,3,4,6-TeCP (R1). For all reactors, dispersion coefficients of Cu, ranging from 3.47 × 10⁻⁶ m²/s to 5.37 × 10⁻² m²/s, was determined to be higher than others obtained for Zn and Fe. Average molecular diffusion coefficients of phenolic compounds were estimated to be about 5.64 × 10⁻¹⁰ m²/s, 5.37 × 10⁻¹⁰ m²/s, 2.69 × 10⁻¹⁰ m²/s and 3.29 × 10⁻¹⁰ m²/s for R1, R2, R3 and R4 systems, respectively. The findings of this study clearly indicated that about 35–50% of transport of phenolic compounds to the groundwater is believed to be prevented with the use of zeolite and bentonite materials in landfill liner systems.     

State of the Art Report on Mathematical Methods for Groundwater Pollution Source Identification

The reliable assessment of hazards or risks arising from groundwater contamination problems and the design of efficient and effective techniques to mitigate these problems require the capability to predict the behavior of chemical contaminants in flowing water. Most attempts at quantifying contaminant transport have relied on a solution of some form of a well-known governing equation referred to as advection-dispersion-reaction equation. To choose an appropriate remediation strategy, knowledge of the contaminant release source and time release history becomes pertinent. As additional contaminated sites are being detected, it is almost impossible to perform exhaustive drilling, testing, and chemical fingerprint analysis every time. Moreover, chemical fingerprinting and site records are not sufficient to allow a unique solution for the timing of source releases. The purpose of this paper is to present and review mathematical methods that have been developed during the past 15 years to identify the contaminant source location and recover the time release history.     

International cooperation around the North Sea basin

During the past 25 years, the management of marine ecosystems has evolved significantly. Due to the increased use of the sea and the increased awareness of adverse impacts of certain human activities in and around the sea, which has been a common good for a long time—‘Mare Liberum’—an international and integrated approach has become increasingly important to regulate the use of our common seas. From the late 1960s onwards, intergovernmental meetings have taken place in order to tackle the problems of international pollution of seas and oceans. One reason for this attention was the Torrey Canyon accident in 1967, which triggered the start of the Bonn Agreement in 1969 for coordinating the combat mission against oil and chemical spills in the North Sea. After the 1972 United Nations Conference on the Human Environment in Stockholm, with the involvement of the European Union, the International Council for Exploration of the Sea (ICES) and Non-Governmental Organizations (NGOs), other regional and global Conventions, as well as the North Sea Ministerial Conferences were established. These continuous international efforts have resulted in a considerable reduction of the input of certain contaminants and of nutrients (in particular phosphate) into the marine environment. However, not all problems have yet been solve. The North Sea Ministers agreed at the Conference in Esbjerg (1995) to aim at a reduction of the input of all hazardous substances within one generation, in order to reach the goal of negligible risks of pollution. Furthermore, there is a general aim to minimize adverse effects of disturbing activities. The challenge, now and in the future, is to find a balance between economic development and environmental protection of our international marine waters aiming at a sustainable development of the marine resources by employing scientifically based measures and, in situations where there are reasonable grounds for concern but no conclusive links between cause and problem, applying the precautionary principle with respect to pollution and disturbing activities.     

特别选题:环境微界面过程与污染控制序

长期以来,人们主要关注的是污染物的均相环境过程,这一点在大气污染化学和水污染化学的研究中尤其明显。然而近年来,人们开始关注环境中的非均相反应过程,从相对微观的尺度思考和探索环境的微界面问题,并从不同的视角不断认识和揭示这一过程在环境污染及其控制中的作用和意义。1997年,由荷兰科学家L.K.Koopal教授发起设立了Interfaces Against Pollution两年一次的系列国际会议,形成了全球范围内有关科学研究组织和科学家探讨和交流环境界面问题的重要平台。中国科学院生态环境研究中心汤鸿霄院士在我国首次提出环境微界面的概念,并于2003年主编了《环境科学学报》之“环境微界面过程研究论文专辑”,为该专辑作序并发表了“环境纳米污染物与微界面水质过程”的研究论文,对环境纳米微界面问题给出了全面和准确的内涵,进而开启了我国在此方面的系统性研究工作。基于汤鸿霄院士提出的环境微界面内涵和思想,2006年中国科学院生态环境研究中心组织了“环境微界面过程与污染控制”创新研究群体,得到国家自然科学基金委员会的资助。群体的研究目标是深入探索污染物在环境微界面的转移转化机制与控制原理,力争在复杂条件下微界面的定量化表征、污染物在环境微界面的转移转化规律及复合效应、基于微界面原理的环境过程调控等方面取得科学与技术突破。该研究群体的建立及深入开展相关的研究工作,将有力推动我国环境微界面理论和技术的研究进展,也将不断培养本研究方向的专业化高级人才。在过去的2年里,该研究群体在不同环境微界面特征及过程表达、污染物在典型介质和界面变化行为的原位观测、水/气/土/生物微界面上污染物的转移转化规律、基于微界面过程的水、气、固等环境的污染控制等方面取得预期研究进展。本专栏所组织的稿件,即试图从不同角度反映我们所关注的环境微界面研究领域,并通过前期研究所获得的一些具体的科学数据和结果,对环境微界面过程给出进一步的认识。然而,由于本群体的研究工作还不够深入,这样一个专栏所发表的内容不论是对环境微界面的概念与内涵,还是在探索与创新上,都还是初步的和不成熟的。或者说,本专栏所反映的只是一个有待发展和完善的科学思路。由于本专栏作者水平有限,这些论文定有不少谬误之处,敬请读者批评指正。 衷心感谢《环境科学学报》编辑部为我们提供这样一个重要的平台和机会,感谢他们为本专栏组稿、编辑和出版所做出的辛苦努力！     

Variation in PAH inputs and microbial community in surface sediments of Hamilton Harbour: implications to remediation and monitoring

Variations in concentrations of polycyclic aromatic hydrocarbons (PAHs) and microbial community indicators were investigated in representative highly contaminated and less contaminated surface sediment sites of Hamilton Harbour. Inputs of PAH to the upper 3cm of sediments up to four times the average upper sediment concentrations were observed. Associated PAH fingerprint profiles indicated that the source was consistent with the PAH source to the industrial region of the harbour. Increased PAH loadings were associated with decreased bacterial populations as indicated by phospholipid fatty acid (PLFA) concentrations. However, relatively minor impacts on overall community composition were indicated. Porewater methane concentrations and isotopic data indicated a difference in the occurrence of methane oxidation between the two sites. This study confirms temporally limited transport of contaminants from highly impacted regions as a vector for contaminants within the harbour and the impact on microbial carbon cycling and bed stability.     

Measurement and analysis of non-Fickian dispersion in heterogeneous porous media

Contaminant breakthrough behavior in a variety of heterogeneous porous media was measured in laboratory experiments, and evaluated in terms of both the classical advection-dispersion equation (ADE) and the continuous time random walk (CTRW) framework. Heterogeneity can give rise to non-Fickian transport patterns, which are distinguished by "anomalous" early arrival and late time tails in breakthrough curves. Experiments were conducted in two mid-scale laboratory flow cells packed with clean, sieved sand of specified grain sizes. Three sets of experiments were performed, using a "homogeneous" packing, a randomly heterogeneous packing using sand of two grain sizes, and an exponentially correlated structure using sand of three grain sizes. Concentrations of sodium chloride tracer were monitored at the inflow reservoir and measured at the outflow reservoir. Breakthrough curves were then analyzed by comparison to fitted solutions from the ADE and CTRW formulations. In all three systems, including the "homogeneous" one, subtle yet measurable differences between Fickian and non-Fickian transport were observed. Quantitative analysis demonstrated that the CTRW theory characterized the full shape of the breakthrough curves far more effectively than the ADE.     

Influence of indoor transport and mixing time scales on the performance of sensor systems for characterizing contaminant releases

Optimizing real-time sensor systems to detect and identify relevant characteristics of an indoor contaminant event is a challenging task. The interpretation of incoming sensor data is confounded by uncertainties in building operation, in the forces driving contaminant transport, and in the physical parameters governing transport. In addition, simulation tools used by the sensor interpretation algorithm introduce modeling uncertainties. This paper explores how the time scales inherent in contaminant transport influence the information that can be extracted from real-time sensor data. In particular, we identify three time scales (within room mixing, room-to-room transport, and removal from the building) and study how they affect the ability of a Bayesian Monte Carlo (BMC) sensor interpretation algorithm to identify the release location and release mass from a set of experimental data, recorded in a multi-floor building. The research shows that some limitations in the BMC approach do not depend on details of the models or the algorithmic implementation, but rather on the physics of contaminant transport. These inherent constraints have implications for the design of sensor systems.     

Pesticides in ground water in the united states: Monitoring,modeling, and risks from the U.S. perspective

Abstract

Scientific and regulatory interest in ground water contamination by pesticides increased significantly in 1979. This was prompted by findings of the nematicide 1,2‐dibromo‐3‐chloropropane (DBCP) and the nematicide/insecticide aldicarb (Temik®) in ground water in several states. Since that time, at least 130 pesticides and pesticide metabolites have been detected in ground water in over 150 studies, but detection frequencies are 4–10% nationally. Detection frequencies of pesticides over Health Advisory Levels are generally lower. Screening‐level models and detailed computer simulation models are useful for risk assessments and regulatory decisions. Attenuation Factor, CMLS, PRZM2, GLEAMS, and LEACHM are all useful models.     

Multi-component reactive transport modeling of natural attenuation of an acid groundwater plume at a uranium mill tailings site

Natural attenuation of an acidic plume in the aquifer underneath a uranium mill tailings pond in Wyoming, USA was simulated using the multi-component reactive transport code PHREEQC. A one-dimensional model was constructed for the site and the model included advective-dispersive transport, aqueous speciation of 11 components, and precipitation-dissolution of six minerals. Transport simulation was performed for a reclamation scenario in which the source of acidic seepage will be terminated after 5 years and the plume will then be flushed by uncontaminated upgradient groundwater. Simulations show that successive pH buffer reactions with calcite, Al(OH)3(a), and Fe(OH)3(a) create distinct geochemical zones and most reactions occur at the boundaries of geochemical zones. The complex interplay of physical transport processes and chemical reactions produce multiple concentration waves. For SO4(2-) transport, the concentration waves are related to advection-dispersion, and gypsum precipitation and dissolution. Wave speeds from numerical simulations compare well to an analytical solution for wave propagation.