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Contaminant Fate (contaminant + fate)
Selected AbstractsA MATLAB toolbox for solving acid-base chemistry problems in environmental engineering applicationsCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 4 2005Chetan T. Goudar Abstract A MATLAB toolbox incorporating several computer programs has been developed in an attempt to automate laborious calculations in acid-base chemistry. Such calculations are routinely used in several environmental engineering applications including the design of wastewater treatment systems and for predicting contaminant fate and transport in the subsurface. The computer programs presented in this study do not replace student thinking involved in formulating the problem solving strategy but are merely tools that simplify the actual problem solving process. They encompass a wide variety of acid-base chemistry topics including equilibrium constant calculations, construction of distribution diagrams for mono and multiprotic systems, ionic strength and activity coefficient calculations, and buffer index calculations. All programs are characterized by an intuitive graphical user interface where the user supplies input information. Program outputs are either numerical or graphical depending upon the nature of the problem. The application of this approach to solving actual acid-base chemistry problems is illustrated by computing the pH and equilibrium composition of a 0.1 M Na2CO3 system at 30°C using several programs in the toolbox. As these programs simplify lengthy computations such as ionization fraction and activity coefficient calculations, it is hoped they will help bring more complicated problems to the environmental engineering classroom and enhance student understanding of important concepts that are applicable to real-world systems. The programs are available free of charge for academic use from the authors. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 257,265, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20051 [source] Community responses to contaminants: Using basic ecological principles to predict ecotoxicological effectsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2009William H. Clements Abstract Community ecotoxicology is defined as the study of the effects of contaminants on patterns of species abundance, diversity, community composition, and species interactions. Recent discoveries that species diversity is positively associated with ecosystem stability, recovery, and services have made a community-level perspective on ecotoxicology more important than ever. Community ecotoxicology must explicitly consider both present and impending global change and shift from a purely descriptive to a more predictive science. Greater consideration of the ecological factors and threshold responses that determine community resistance and resilience should improve our ability to predict how and when communities will respond to, and recover from, xenobiotics. A better understanding of pollution-induced community tolerance, and of the costs of this tolerance, should facilitate identifying contaminant-impacted communities, thus forecasting the ecological consequences of contaminant exposure and determining the restoration effectiveness. Given the vast complexity of community ecotoxicology, simplifying assumptions, such as the possibility that the approximately 100,000 registered chemicals could be reduced to a more manageable number of contaminant classes with similar modes of action, must be identified and validated. In addition to providing a framework for predicting contaminant fate and effects, food-web ecology can help to identify communities that are sensitive to contaminants, contaminants that are particularly insidious to communities, and species that are crucial for transmitting adverse effects across trophic levels. Integration of basic ecological principles into the design and implementation of ecotoxicological research is essential for predicting contaminant effects within the context of rapidly changing, global environmental conditions. [source] Concentrations and partitioning of polychlorinated biphenyls in the surface waters of the southern Baltic Sea,seasonal effectsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2006Kilian E.C. Smith Abstract In the marine environment, the partitioning of hydrophobic organic contaminants, such as polychlorinated biphenyls (PCBs), between the dissolved and suspended matter phases in the water column plays a fundamental role in determining contaminant fate (e.g., air,water exchange or food-chain uptake). Despite the pronounced seasonality in physical, chemical, and biological conditions in temperate marine ecosystems, little is known about the seasonality in organic contaminant partitioning behavior. Surface water from the western Baltic Sea was sampled regularly during an 18-month period between February 2003 and July 2004. The concentrations of seven PCB congeners were determined in the dissolved and particulate organic carbon (POC) phases. An inverse relationship was found between KPOC (i.e., the ratio between the POC-normalized PCB concentration [pg/kg POC] and the dissolved concentration [pg/L]) and temperature. The decrease in the water temperature of 20°C between summer and winter resulted in an increase in KPOC by a factor of approximately five. The POC-normalized PCB concentrations were higher in winter than in summer by a factor of 9 to 20. This reflected the higher KPOC and somewhat greater PCB concentrations in the dissolved phase, and it could have consequences for bioaccumulation of these chemicals in aquatic food webs. The results demonstrate a clear seasonality in contaminant partitioning in the temperate marine environment that should be accounted for when interpreting field data or modeling contaminant fate. [source] A dynamic mass budget for toxaphene in North AmericaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2002Matthew MacLeod Abstract A continental-scale dynamic mass budget for toxaphene in North America is presented, based on available information on physicochemical properties, usage patterns, and reported environmental concentrations and using the Berkeley-Trent North American mass balance contaminant fate model (BETR North America). The model describes contaminant fate in 24 ecological regions of North America, including advective transport between regions in the atmosphere, freshwater, and near-shore coastal water. The dynamic mass budget accounts for environmental partitioning, transport, and degradation of the estimated 534 million kg of toxaphene that were used in North America as an insecticide and piscicide between 1945 and 2000. Satisfactory agreement exists between model results and current and historically reported concentrations of toxaphene in air, water, soil, and sediments throughout North America. An estimated 15 million kg of toxaphene are believed to remain in active circulation in the North American environment in the year 2000, with the majority in soils in the southern United States and Mexico, where historic usage was highest. Approximately 70% of total toxaphene deposition from the atmosphere to the Great Lakes is attributed to sources outside the Great Lakes Basin, and an estimated total of 3.9 million kg of toxaphene have been transported to this region from other parts of the continent. The toxaphene mass budget presented here is believed to be the first reported continental-scalemultimedia mass budget for any contaminant. [source] Revisiting a Classification Scheme for U.S.-Mexico Alluvial Basin-Fill AquifersGROUND WATER, Issue 5 2005Barry J. Hibbs Intermontane basins in the Trans-Pecos region of westernmost Texas and northern Chihuahua, Mexico, are target areas for disposal of interstate municipal sludge and have been identified as possible disposal sites for low-level radioactive waste. Understanding ground water movement within and between these basins is needed to assess potential contaminant fate and movement. Four associated basin aquifers are evaluated and classified; the Red Light Draw Aquifer, the Northwest Eagle Flat Aquifer, the Southeast Eagle Flat Aquifer, and the El Cuervo Aquifer. Encompassed on all but one side by mountains and local divides, the Red Light Draw Aquifer has the Rio Grande as an outlet for both surface drainage and ground water discharge. The river juxtaposed against its southern edge, the basin is classified as a topographically open, through-flowing basin. The Northwest Eagle Flat Aquifer is classified as a topographically closed and drained basin because surface drainage is to the interior of the basin and ground water discharge occurs by interbasin ground water flow. Mountains and ground water divides encompass this basin aquifer on all sides; yet, depth to ground water in the interior of the basin is commonly >500 feet. Negligible ground water discharge within the basin indicates that ground water discharges from the basin by vertical flow and underflow to a surrounding basin or basins. The most likely mode of discharge is by vertical, cross-formational flow to underlying Permian rocks that are more porous and permeable and subsequent flow along regional flowpaths beneath local ground water divides. The Southeast Eagle Flat Aquifer is classified as a topographically open and drained basin because surface drainage and ground water discharge are to the adjacent Wildhorse Flat area. Opposite the Eagle Flat and Red Light Draw aquifers is the El Cuervo Aquifer of northern Chihuahua, Mexico. The El Cuervo Aquifer has interior drainage to Laguna El Cuervo, which is a phreatic playa that also serves as a focal point of ground water discharge. Our evidence suggests that El Cuervo Aquifer may lose a smaller portion of its discharge by interbasin ground water flow to Indian Hot Springs, near the Rio Grande. Thus, El Cuervo Aquifer is a topographically closed basin that is either partially drained if a component of its ground water discharge reaches Indian Hot Springs or undrained if all its natural ground water discharge is to Laguna El Cuervo. [source] Performing contaminant mass balances for remedy assessmentsREMEDIATION, Issue 2 2009James T. Gibbs Contaminant mass-balance assessments are useful tools to help quantify various mass transport and removal mechanisms that may be active in a remedial system setting. This article presents the basics of performing a mass balance and illustrates the utility of using the information derived to support project management decisions. It is important to understand the partitioning of contaminant mass into various environmental media and physical forms, as well as the relationships among the partitions. Contaminant partitioning tends toward an equilibrium state, so natural or engineered mass transfer into or out of one partition will affect the others. Mass balances are exercises that quantify, to the extent possible, the contaminant mass in the various environmental partitions and the transfer and transformation processes that affect contaminant distribution. Understanding mass partitioning and transfer mechanisms helps remediation practitioners to engineer and optimize those mechanisms that contribute to risk reduction at a contaminated site. Such knowledge can inform risk managers when natural mechanisms may dominate engineered approaches and help identify uncertainties in contaminant fate and transport. © 2009 Wiley Periodicals, Inc. [source] Biokinetic models for representing the complete inhibition of microbial activity at high substrate concentrationsBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2001Gunaseelan Alagappan Abstract This paper reintroduces the Wayman and Tseng model for representing substrate inhibition effects on specific growth rate by further documenting its potential predictive capabilities. It also introduces a modification to this model in which an Andrews inhibition function is used in place of the Monod noninhibitory substrate function. This modification better represents the relationship between specific growth rate and substrate concentration for those substrates that show Andrews type inhibition at lower substrate concentrations, rather than the Monod type noninhibitory behavior described in the model of Wayman and Tseng. Results from nonlinear, least squares regression analysis are used to evaluate the ability of these models to empirically represent experimental data (both new and from the literature). The statistical goodness of fit is evaluated by comparing the regression results against those obtained using other empirical models. Finally, possible mechanisms of toxicity responsible for the observed inhibition trends are used to further justify use of these empirical models. The dominant mechanism considered to be relevant for conceptually explaining complete inhibition at high concentrations of solvents is the deterioration of cell membrane integrity. Literature citations are used to support this argument. This work should lead to improvements in the mathematical modeling of contaminant fate and transport in the environment and in the simulation of microbial growth and organic compound biodegradation in engineered systems. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 75: 393,405, 2001. [source] | |||||||||||||