Characterizing exposure to chemicals from soil vapor intrusion using a two-compartment model

Though several different models have been developed for sub-surface migration, little attention has been given to the effect of subsurface transport on the indoor environment. Existing methods generally assume that a house is one well-mixed compartment. A two-compartment model was developed to better characterize this exposure pathway; the model treats the house as two well-mixed compartments, one for the basement and one for the remainder of the house. A field study was completed to quantify parameters associated with the two-compartment model, such as soil gas intrusion rates and basement to ground floor air exchange rates. Two residential test houses in Paulsboro, New Jersey were selected for this study. All experiments were completed using sulfur hexafluoride (SF₆) as a tracer gas. Soil gas intrusion rates were found to be highly dependent on the soil gas to basement pressure difference, varying from 0.001 m³ m⁻² h⁻¹ for a pressure drop of –0.2 Pa to 0.011 m³ m⁻² h⁻¹ for a pressure drop of –6.0 Pa. Basement ventilation rates ranged from 0.17 to 0.75 air changes per hour (ACH) for basement to ambient pressure differences ranging from –1.1 to –7.6 Pa (relative to ambient). Application of experimental results in conjunction with the two-compartment model indicate that exposures are highly dependent on gas intrusion rates, basement ventilation rate, and fraction of time spent in the basement. These results can also be significantly different when compared with the simple well-mixed house assumption.     

Detection of methylquinoline transformation products in microcosm experiments and in tar oil contaminated groundwater using LC-NMR

N-heterocyclic compounds are known pollutants at tar oil contaminated sites. Here we report the degradation of methyl-, and hydroxy-methyl-substituted quinolines under nitrate-, sulfate- and iron-reducing conditions in microcosms with aquifer material of a former coke manufacturing site. Comparison of degradation potential and rate under different redox conditions revealed highest degradation activities under sulfate-reducing conditions, the prevailing conditions in the field. Metabolites of methylquinolines, with the exception of 2-methylquinolines, were formed in high amounts in the microcosms and could be identified by ¹H NMR spectroscopy as 2(1H)-quinolinone analogues. 4-Methyl-, 6-methyl-, and 7-methyl-3,4-dihydro-2(1H)-quinolinone, the hydrogenated metabolites in the degradation of quinoline compounds, were identified by high resolution LC-MS. Metabolites of methylquinolines showed persistence, although for the first time a transformation of 4-methylquinoline and its metabolite 4-methyl-2(1H)-quinolinone is described. The relevance of the identified metabolites is supported by the detection of a broad spectrum of them in groundwater of the field site using LC-NMR technique. LC-NMR allowed the differentiation of isomers and identification without reference compounds. A variety of methylated 2(1H)-quinolinones, as well as methyl-3,4-dihydro-2(1H)-quinolinone isomers were not identified before in groundwater.     

Assessing the aerobic biodegradability of 14 hydrocarbons in two soils using a simple microcosm/respiration method.

The aerobic biodegradability of 14 hydrocarbons in two soils was determined using a simple microcosm/respirometric method based on oxygen consumption. Biodegradability was assessed indirectly by measuring the depletion of oxygen over time in the headspace of microcosms containing soil and test chemicals. The microcosms consisted of small glass vials fitted with valves that allowed headspace gas samples to be collected, essentially resulting in a sealed system. Respiration data from control microcosms were obtained from identically treated microcosms with no test chemical. Control data were necessarily included in all calculations of percent of theoretical oxygen demand (%ThOD) for any given test chemical. Two experiments were performed to verify this simple biodegradation test method. First, an experiment was performed in which disappearance of n-tetradecane from the microcosms was measured directly by standard soil extraction and analytical techniques while simultaneously performing this simple respirometric method based on %ThOD with the same test chemical. Second, the method was compared to a well-established radiochemical technique using 14C-phenanthrene. Results of both comparisons showed that the method is both accurate and reliable. The consistent manner with which the data were produced in two different soils show that the method is also very reproducible. The method described here provides a simple and inexpensive method for determining the aerobic biodegradability of organic compounds in soils.     

Verification of a three-dimensional transport model using tetroon data from project state

During August 1978, The Environmental Protection Agency (EPA) conducted a major field study at the Cumberland Steam Plant of the Tennessee Valley Authority. This study, known as the Tennessee Plume Study, was conducted as part of the EPA Sulfur Transport and Transformation in the Environment (STATE) Project. The field experiments included the release and tracking of tetroons from Cumberland during numerous intervals within the period of the study. On 15 August, 10 tetroons were released, traveling distances ranging from less than 25 km to in excess of 200 km. The tetroon position data were compared with three-dimensional (3-D) kinematic trajectory predictions from a 3-D regional-scale dynamic model. The average directional error was 7° where the maximum error was 14° and an error of less than 2° prevailed for 2 trajectories. The average displacement error was 9 % of the observed path of the tetroon, with the maximum being 30% and an error of 3% or less prevailing for 4 trajectories.     

The effect of vegetation on pesticide dissipation from ponded treatment wetlands: quantification using a simple model

Field data shows that plants accelerate pesticide dissipation from aquatic systems by increasing sedimentation, biofilm contact and photolysis. In this study, a graphical model was constructed and calibrated with site-specific and supplementary data to describe the loss of two pesticides, endosulfan and fluometuron, from a vegetated and a non-vegetated pond. In the model, the major processes responsible for endosulfan dissipation were alkaline hydrolysis and sedimentation, with the former process being reduced by vegetation and the latter enhanced. Fluometuron dissipation resulted primarily from biofilm reaction and photolysis, both of which were increased by vegetation. Here, greater photolysis under vegetation arose from faster sedimentation and increased light penetration, despite shading. Management options for employing constructed wetlands to polish pesticide-contaminated agricultural runoff are discussed. The lack of easily fulfilled sub-models and data describing the effect of aquatic vegetation on water chemistry and sedimentation is also highlighted.     

The fate of isoproturon in a freshwater microcosm with Lemna minor as a model organism

Degradation, bioaccumulation and volatile loss of the 14C-labeled phenylurea herbicide isoproturon (IPU) was examined in a freshwater microcosm with the free floating macrophyte species Lemna minor during a 21-day exposure time. Isoproturon volatilisation was very low with 0.13+/-0.01% of the initially applied herbicide. Only a minor amount of the herbicide was completely metabolised, presumably by rhizosphere microorganisms and released as 14CO2. In total, about 9% isoproturon was removed from the aquatic medium during 21 days. The major portion of the pesticide was removed by bioaccumulation of Lemna minor (5.0+/-0.8%) and the bioconcentration factor (BCF) based on freshweight was 15.8+/-0.2. However, this study indicated a high persistence of IPU in freshwater ecosystems and a potential hazard due to bioaccumulation in non-target species. The novel experimental system of this study, developed for easy use and multiple sampling abilities, enabled quantitatively studying the fate of isoproturon and showed high reproducibility with a mean average (14)C-recovery rate of 97.1+/-0.7%.     

A mathematical model of drift deposition from a bifurcated cooling tower plume

Cooling tower drift deposition modeling has been extended by including the centrifugal force induced by plume bifurcation as a mechanism for droplet removal from the plume. The model is capable of predicting the trajectory of a single droplet from the stage of strong interaction with the vortex field soon after droplet emission at the tower top through the stage of droplet evaporation after breakaway from the plume. Applications showed the droplet to follow a helical trajectory within the plume, with breakaway and ground impact depending upon plume rise, ambient wind, evaporation and vortex strength.     

Development of a novel mathematical model using a group contribution method for prediction of ionic liquid toxicities

A new mathematical model has been developed that expresses the toxicities (EC₅₀ values) of a wide variety of ionic liquids (ILs) towards the freshwater flea Daphnia magna by means of a quantitative structure-activity relationship (QSAR). The data were analyzed using summed contributions from the cations, their alkyl substituents and anions. The model employed multiple linear regression analysis with polynomial model using the MATLAB software. The model predicted IL toxicities with R² = 0.974 and standard error of estimate of 0.028. This model affords a practical, cost-effective and convenient alternative to experimental ecotoxicological assessment of many ILs.     

Direct coupling of a genome-scale microbial in silico model and a groundwater reactive transport model

The activity of microorganisms often plays an important role in dynamic natural attenuation or engineered bioremediation of subsurface contaminants, such as chlorinated solvents, metals, and radionuclides. To evaluate and/or design bioremediated systems, quantitative reactive transport models are needed. State-of-the-art reactive transport models often ignore the microbial effects or simulate the microbial effects with static growth yield and constant reaction rate parameters over simulated conditions, while in reality microorganisms can dynamically modify their functionality (such as utilization of alternative respiratory pathways) in response to spatial and temporal variations in environmental conditions. Constraint-based genome-scale microbial in silico models, using genomic data and multiple-pathway reaction networks, have been shown to be able to simulate transient metabolism of some well studied microorganisms and identify growth rate, substrate uptake rates, and byproduct rates under different growth conditions. These rates can be identified and used to replace specific microbially-mediated reaction rates in a reactive transport model using local geochemical conditions as constraints. We previously demonstrated the potential utility of integrating a constraint-based microbial metabolism model with a reactive transport simulator as applied to bioremediation of uranium in groundwater. However, that work relied on an indirect coupling approach that was effective for initial demonstration but may not be extensible to more complex problems that are of significant interest (e.g., communities of microbial species and multiple constraining variables). Here, we extend that work by presenting and demonstrating a method of directly integrating a reactive transport model (FORTRAN code) with constraint-based in silico models solved with IBM ILOG CPLEX linear optimizer base system (C library). The models were integrated with BABEL, a language interoperability tool. The modeling system is designed in such a way that constraint-based models targeting different microorganisms or competing organism communities can be easily plugged into the system. Constraint-based modeling is very costly given the size of a genome-scale reaction network. To save computation time, a binary tree is traversed to examine the concentration and solution pool generated during the simulation in order to decide whether the constraint-based model should be called. We also show preliminary results from the integrated model including a comparison of the direct and indirect coupling approaches and evaluated the ability of the approach to simulate field experiment.     

A simple model for the dispersion of pollutants from a road tunnel portal

The dispersion of pollutants from a roadway tunnel portal is mainly determined by the interaction between the ambient wind and the jet stream from the tunnel portal. In principal, Eulerian microscale models by solving the conservation equations for mass, momentum, and energy, are thus able to simulate effects such as buoyancy etc. properly. However, for engineering applications such models need too much CPU time, and are not easy to handle by non-scientific personnel. Only a few dispersion models, applicable for regulatory purposes, have so far appeared in the literature. These models are either empirical models not always applicable for different sites, or they do not capture important physical effects like buoyancy phenomena. Here, a rather simple model is presented, which takes into account most of the important processes considered to govern the dispersion of a jet stream from portals. These are the exit velocity, the buoyancy, the influence of ambient wind direction fluctuations on the position of the jet stream, and traffic induced turbulence. Although the model contains some heuristic elements, it was successfully tested against tracer experiments taken near a motorway tunnel portal in Austria. The model requires relatively little CPU time. Current limitations of the model include the neglect of terrain, building, and vehicle effects on the dispersion, and the neglect of the horizontal dispersion arising from entrainment of ambient air in the jet stream. The latter could lead to an underestimation of plume spreads for higher wind speeds. The validation of the model will be the focus of future research. The experimental data set is also available for the scientific community.     

Study on transformation and enrichment behavior of selenium in particulate matter in combustion flame

An ethylene/air inverse diffusion flame (IDF) burner was employed to generate a stable flame, and selenium was introduced into the combustion flame in vapor phase under different air-fuel ratio (A/F) with SO2 additive. At different height above burner (HAB) along the flame edge, selenium of different speciation (gaseous selenium and particulate selenium) was sampled via the U.S. EPA method 29, and the samples were determined by hydride generation atomic fluorescence spectrometry (HG-AFS), in order to study the mechanism of transformation and enrichment behavior of selenium during the combustion process. The results showed that selenium presented in vapor phase, crossing the flame into air, which means gaseous phase is the main form of selenium during combustion process. Both gaseous selenium and particulate selenium increased with elevated temperature from 820K to 1650K, suggesting that higher temperature is beneficial to the release of selenium. Low concentration of sulfur dioxide would increase the concentration of particulate selenium and gaseous selenium, and accelerate the release of selenium.

Implications: The enrichment behavior of selenium and its transformation in combustion flame were studied. The results showed that gaseous selenium is found in higher quantity in compared to particulate selenium during combustion. Higher temperature and air–fuel ratio will cause an increase in the formation of selenium. While the presence of sulfur dioxide in a range of 0–200 ppm will promote the release of selenium, higher sulfur dioxide level in a range of 200–350 ppm will have a reverse effect.     

有机磷通过弱透水层的迁移转化规律研究

在地下水超量开采区,上层劣质潜水可以越过弱透水层补给承压水.有机磷能否随水迁移进入深层地下水构成水质污染是极为关注的问题.采用施压条件下将一定浓度的有机磷溶液渗透通过粘性土柱的模拟实验,对有机磷在饱和粘性土层中降解转化的各种因子及其影响机制进行分析,探讨有机磷在弱透水层环境中的降解转化和迁移的规律.结果表明:(1)粘性...     

The mathematical modelling of total nitrogencontamination transport via groundwater from asugar factory in Eskisehir, Turkey

In this study, mathematical modelling of the total nitrogen contamination transport in a porous medium was evaluated in order to determine the potential groundwater pollution caused by a sugar factory in the Eskisehir region of Turkey. Analytical solutions of mathematical modelling were performed to show graphically the distributions of contaminant concentrations. Multiflow computer programming was used to determine the distribution of contaminant concentrations with respect to time and distance. The distribution distance of contaminant concentrations was determined at any time interval. From this study, the potential pollution of groundwater can be effectively estimated. Prediction of pollution by means of the model will help to form the future predictions of water resource management.     

地下水中多环芳烃迁移转化研究

吸附和生物降解是受污染地下水中多环芳烃(PAHs)归宿的主要途径.论述了PAHs在含水层中吸附过程的特征、影响因素与研究方法,并比较各种研究方法的优缺点;分析了PAHs在含水层中生物降解过程机制以及研究进展;介绍了PAHs在地下水中迁移、转化数学模型与数值模拟的研究开发状况;指出了PAHs与固相介质的吸附机制和竞争吸附行为、高分子量PAHs的生物降解途径和机制及共存PAHs或与其他污染物在地下水中的迁移、转化、归宿与修复技术是深入研究的方向.     

Description of sorbing tracers transport in fractured media using the lattice model approach

The transport of contaminants in fractured media is a complex phenomenon with a great environmental impact. It has been described with several models, most of them based on complex partial differential equations, that are difficult to apply when equilibrium and nonequilibrium dynamics are considered in complex boundaries. With the aim of overcoming this limitation, a combination of two lattice Bathnagar, Gross and Krook (BGK) models, derived from the lattice Boltzmann model, is proposed in this paper. The fractured medium is assumed to be a single fissure in a porous rock matrix. The proposed approach permits us to deal with two processes with different length scales: advection–dispersion in the fissure and diffusion within the rock matrix. In addition to the mentioned phenomena, sorption reactions are also considered. The combined model has been tested using the experimental breakthrough curves obtained by Garnier et al. (Garnier, J.M., Crampon, N., Préaux, C., Porel, G., Vreulx, M., 1985. Traçage par ¹³C, ²H, I⁻ et uranine dans la nappe de la craie sénonienne en écoulement radial convergent (Béthune, France). J. Hidrol. 78, 379–392.) giving acceptable results. A study on the influence of the lattice BGK models parameters controlling sorption and matrix diffusion on the breakthrough curves shape is included.     

Uptake kinetics and interaction of selenium species in tomato (Solanum lycopersicum L.) seedlings

Environmental Science and Pollution Research - Selenite and selenate are two main selenium (Se) forms absorbed by plants. The comparative effects of selenite and/or selenate on Se uptake and...     

Description of sorbing tracers transport in fractured media using the lattice model approach

The transport of contaminants in fractured media is a complex phenomenon with a great environmental impact. It has been described with several models, most of them based on complex partial differential equations, that are difficult to apply when equilibrium and nonequilibrium dynamics are considered in complex boundaries. With the aim of overcoming this limitation, a combination of two lattice Bathnagar, Gross and Krook (BGK) models, derived from the lattice Boltzmann model, is proposed in this paper. The fractured medium is assumed to be a single fissure in a porous rock matrix. The proposed approach permits us to deal with two processes with different length scales: advection-dispersion in the fissure and diffusion within the rock matrix. In addition to the mentioned phenomena, sorption reactions are also considered. The combined model has been tested using the experimental breakthrough curves obtained by Garnier et al. (Garnier, J.M., Crampon, N., Préaux, C., Porel, G., Vreulx, M., 1985. Tra?age par 13C, 2H, I- et uranine dans la nappe de la craie sénonienne en écoulement radial convergent (Béthune, France). J. Hidrol. 78, 379-392.) giving acceptable results. A study on the influence of the lattice BGK models parameters controlling sorption and matrix diffusion on the breakthrough curves shape is included.     

Difference between selenite and selenate in selenium transformation and the regulation of cadmium accumulation in Brassica chinensis

Environmental Science and Pollution Research - Se can regulate Cd accumulation and translocation in plants; however, such effects can be controversial because of the differences in plant species...     

Simulation of resuspended sediments resulting from dredging operations by a numerical flocculent transport model

Environmental remediations such as dredging operations cause contaminated sediments from the bottom of water bodies to become suspended into the water column. These resuspended particles are significant water quality concerns and cause adverse effects to aquatic organisms. In this paper, we present a vertically integrated two-dimensional flocculent sediment transport model to better model concentration changes of resuspended bottom sediments. The flocculent transport model has been applied to the Savannah River cutterhead dredge field study involving the resuspension of bottom sediments. The results showed that the model predictions correlate reasonably well with field data. These comparisons suggest that the flocculent sediment transport model can be used to predict the concentration profiles of a plume of toxic compounds resulting from cutterhead dredge operation.     

利用数学模拟方法分析硝化MBR系统中SMP转换过程

为深入了解膜生物反应器(MBR)中微生物代谢产物(SMP)的生成降解以及利用情况,研究了以NH4Cl为惟一能源物质的硝化MBR反应器中SMP浓度以及分子量(MW)变化情况,并运用活性污泥模型3(ASM3)准确地计算出微生物利用底物相关的溶解性产物(UAP)和微生物死亡相关的溶解性产物(BAP)的量分别是多少,最终证明硝化系统中产生的SMP可作为能源物质被异养菌进一步利用,而且相较于BAP而言UAP更易于被生物降解,得出结论 BAP是SMP中的主要污染成分。