Contaminant Dispersion Research Articles

Dispersion of inorganic contaminants in surface water in the vicinity of Potchefstroom

Potchefstroom and the neighbouring cities rely mostly on the Mooi River and Vaal River for their water needs. These rivers flow through the gold mining areas and farms, and are therefore likely to be contaminated with substantial amounts of inorganic pollutants. Water was collected along the rivers network, streams, canals and dams in Potchefstroom and the vicinity. The samples were characterized for geochemical parameters, metals and anions concentrations. The results showed high concentrations of potentially toxic elements such as As (4.53 mg/L – 5.74 mg/L), Cd (0.25 mg/L – 0.7 mg/L), Pb (1.14 mg/L – 5.13 mg/L) and U (0.04 mg/L – 0.11 mg/L) which were predominantly found around the mining areas. Elevated concentrations of anions such SO42- and CN− were detected around mining areas while NO3− was dominant near farms. The relatively high levels of anions and metals in the surface water made it unfit for domestic or agricultural use. The study showed that contaminants in mining and agricultural facilities were potentially mobilised, thus impacting the nearby water systems.

Indicators for environmental dispersion in a two-layer wetland flow with effect of wind

For typical two-layer wetland flows where wind occurs frequently, indicators for flow and contaminant dispersion with wind effect are considered in this paper. Based on the general formulation for porous media flows, the velocity distribution of a fully developed flow through a wetland is illustrated, with that for a single-layer wetland flow under wind recovered as a special case. And the contrary wind of high speed might result in the appearance of an inverse-flow layer. For the more complex case of a two-layer wetland flow under wind, the more simplified method of asymptotic analysis is adopted instead of Aris's method of concentration moments to determine the dispersivity in terms of the longitudinal evolution of the depth-averaged concentration. And it is illustrated with the effect of dimensionless parameters. The velocity profile and environmental dispersivity for the two-layer wetland flow in the absence of wind can be included as a limiting case. Both the direction and the strength of the wind can affect the environmental dispersivity considerably under long-term evolution. Analytical solutions for the mean concentration and the region influenced by the contaminant cloud are derived. And for the instantaneous emission of typical contaminant constituents, the related indicators for water quality assessment, such as the critical length and duration of the influenced region are illustrated. The results show that the critical length and duration of the concentration cloud can change considerably because of the wind and vegetation heterogeneity.

Visual Determination of Potential Dermal and Inhalation Exposure Using Allura Red As an Environmentally Friendly Pesticide Surrogate

Quantifying dermal and inhalation exposure to pesticides is a critical component of the decision-making procedure for risk evaluation. For traditional determination of pesticide exposure, a large amount of organic solvent is inevitably used to extract pesticides from the sampling medium. This paper presents an environmentally benign method for determining potential dermal and inhalation exposure using water-soluble Allura Red as a pesticide surrogate. Only water is used to extract the Allura Red from the sampling medium. More importantly, the operator can attain an immediate visual impression of the exposure patterns. This visual contaminant dispersion can be helpful for the development of measures to improve operational safety through pesticide management. For validation of the method, comparative exposure analyses were carried out with representative lipophilic and hydrophilic pesticides (chlorpyrifos and nitenpyram) under similar application conditions. The results indicate that Allura Red had similar ...

Arsenic in stream waters is bioaccumulated but neither biomagnified through food webs nor biodispersed to land

Human activities such as mining have contributed substantially to the increase of metals in aquatic environments worldwide. These metals are bioaccumulated by aquatic organisms and can be biomagnified along trophic webs. The dispersal of contaminants from water to land has been little investigated, even though most aquatic invertebrates in streams have aerial stages. We used field and laboratory approaches to investigate the effects of arsenic pollution on stream invertebrate assemblages, and its bioaccumulation, biomagnification and trophic transfer from aquatic to terrestrial environments by emergent insects. We conducted the study in an arsenic-impacted stream (40μgL–1 As at the most polluted site) and a reference stream (0.3μgL–1 As). Invertebrate abundance and richness were lowest at the most impacted site. Arsenic in biofilm and in invertebrates increased with the arsenic content in the water. The highest arsenic accumulators were bryophytes (1760μgg–1), followed by the biofilm (449μgg–1) and shredder invertebrates (313μgg–1); predators had the lowest arsenic concentration. Insects emerging from water and spiders along streambanks sampled from the reference and the impacted stream did not differ in their body arsenic concentrations. In the laboratory, the shredder Sericostoma vittatum had reduced feeding rates when exposed to water from the impacted stream in comparison with the reference stream (15.6 vs. 19.0mg leaves mg body mass–1 day–1; p<0.05), but they grew faster in the polluted water (0.16±0.04% day–1vs. 0.05±0.01% day–1, p<0.05). S. vittatum exposed to contaminated stream water accumulated arsenic from food, not through contact with water. We concluded that although arsenic is bioaccumulated, mainly by food ingestion, it is not biomagnified through food webs and is not transported from the aquatic to terrestrial environment when insects leave the stream water.

Characterization and mechanical properties of α-Al2O3 particle reinforced aluminium matrix composites, synthesized via uniball magneto-milling and uniaxial hot pressing

Al-based composite powders containing 2, 4, 7 and 10 volume fraction of α-Al2O3 were prepared using the uniball controlled magneto-milling method and were then uniaxially hot pressed at (600±10)°C under 70MPa for 15min. The resulting composites were greater than 99% theoretical density with enhanced mechanical properties. Detailed characterization was performed using: X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectroscopy, electrical conductivity, compression, ultra-micro indentation testing and pin on drum wear testing at ambient temperature. Microstructure-mechanical property correlations were obtained as functions of α-Al2O3 volume fraction. It was found that controlled milling resulted in an uniform distribution of the hard α-Al2O3 particles within the Al, an acceleration of Al hardening and fracturing, and strain accumulation by the Al matrix. Hardness, strength, wear resistance and electrical resistivity of the monolithic products increased with increasing the volume fraction of α-Al2O3 up to 10vol.%. These were: HV=(1.84±0.26)GPa, maximum compressive strength=(845±33)MPa, compressive yield strength=(515±11) MPa. Outcomes were interpreted in light of the structural defects induced by milling, the presence of α-Al2O3, and dispersion of iron milling contaminants, with additional effects caused by oxygen introduced during the milling and/or the heat treatment.

Pore‐network modeling of particle retention in porous media

Transport and filtration of micron and submicron particles in porous media is important in applications such as water purification, contaminants dispersion, and drilling mud invasion. Existing macroscopic models often fail to be predictive without empirical adjustments and a more fundamental approach may be required. We develop a physically‐representative, 3D pore network model based on a particle tracking method to simulate particle retention and permeability impairment in polydisperse particle systems. The model includes the effect of hydraulic drag, gravity, electrostatic and van der Waals forces, as well as Brownian motion. A converging‐diverging pore throat geometry is used to capture the mechanism of interception. With the analytical solution of fluid velocity within a pore throat, the trajectory of each particle is calculated explicitly. We also incorporate surface roughness and particle–surface interaction to determine particle attachment and detachment. Pore throat structure and conductivity are updated dynamically to account for the effect of deposited particles. Predictions of effluent concentration and macroscopic filtration coefficient are in good agreement with published experimental data. We find that the filtration coefficient is dependent on the relative angle between fluid flow and gravity. Particle deposition by interception is significant for large particle/grain size ratios. Brownian diffusion is the primary cause of retention at low Peclet numbers, especially for small gravity numbers. Particle size distribution is found to be a cause of hyperexponential deposition often observed in experiments. Permeability reduction was small for strong repulsive forces because particles only deposited in paths of slow velocity. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3118–3131, 2017

Modelling dispersal of radioactive contaminants in Arctic waters as a result of potential recovery operations on the dumped submarine K-27

Of the wide variety of dumped objects containing radioactive materials in the Arctic seas, the submarine K-27 constitutes a major risk due to the large amount of highly enriched uranium onboard and its location in shallow waters. As the matter of potential operations involving raising of the submarine have entered the public arena, a priori assessment of the contamination in the Arctic marine environment that could result after a possible accident during such operations is a matter of some interest. The dispersion of contaminants within the Arctic has been assessed using a large scale hydrodynamic model for a series of plausible accident scenarios and locations under different oceanographic regimes. Results indicate that, depending primarily on the nature of a release (i.e. instantaneous or continuous), large areas of the Arctic marine environment will exhibit contamination to varying degrees.

Cytotoxic, genotoxic and mutagenic evaluation of surface waters from a coal exploration region

Coal mining generates a considerable amount of waste, which is disposed of in piles or dams near mining sites. As a result, leachates may reach rivers and streams, promoting the wide dispersion of contaminants in solution and as particulate matter. The present study evaluated the cytotoxic, genotoxic, and mutagenic action of surface waters collected around a thermoelectric power plant and the largest mining area in Brazil (Candiota). Four sites in Candiota stream were selected, and samples were collected in winter and summer. Water samples were analyzed using the comet and CBMN assays in V79 and HepG2 cells. Furthermore, genotoxicity of water samples was evaluated in vivo using the SMART in Drosophila melanogaster. In addition, polycyclic aromatic hydrocarbons and inorganic elements were quantified. The results indicate that water samples exhibited no genotoxic and mutagenic activities, whether in vitro or in vivo. On the other hand, surface water samples collected in sites near the power plant in both summer and winter inhibited cell proliferation and induced increased frequencies of V79 cell death, apoptosis, and necrosis. The cytotoxicity observed may be associated with the presence of higher concentration of inorganic elements, especially aluminum, silicon, sulfur, titanium and zinc at sites 1 and 2 in the stream, as well as with the complex mixture present in the coal, in both seasons. Therefore, the results obtained point to the toxicity potential of water samples with the influence of coal mining and combustion processes and the possible adverse effects on the health of exposed organisms.

A numerical study of indoor air quality in a ventilated room using different strategies of ventilation

This study aimed to numerically investigate the air flow and contaminant dispersion in a ventilated room. The URANS equations supplemented with energy and concentration equations are solved using the scStream code. We are targeting primarily the ventilation effectiveness (εc) and the index of indoor air quality (IIAQ). Different displacement and mixing ventilation modes are investigated in isothermal conditions. The ventilation flow rate is 50 m3.h-1 Here, our ultimate aim is to suggest an effective ventilation that can ensure a good indoor air quality. The RNG k − ε model was adopted to handle the turbulence. CFD simulations were systematically checked, whenever possible, through available results. The simulation results indicate that the ventilation effectiveness to remove a contaminant and the index of indoor air quality are substantially influenced by the ventilation mode and the location of inlet and outlet air. From this study, it appears that the air flow and contaminant dispersion in a ventilated room can be typically predicted or evaluated by computer simulations.

Natural Attenuation Capacity Indicators for Groundwater Remediation to the Northeastern Cairo

The natural attenuation capacity of groundwater is considered to be an important factor for remediation purpose, it is also important for surveying suitability in the early phases of siting hazardous facilities. The present work has been devoted to explore the natural attenuation capacity of the groundwater system northeast Cairo. Some indicators (hydrogeological, hydrochemical and isotopic) have been insighted to explore the system retardability against contaminant dispersion. Groundwater flow and contaminant transport have been pointed out using GOD index which varied from 0.04 to 0.28 reflecting high protectability. The isotopic contents (18O, 3H, and 14C) showed a general comply with the GOD index and helped to delineate the sectors of high contaminate attenuation ability. Kelly index inferred significantly high adsorption potential on the aquifer clay content. The calcite and dolomite tend to precipitate on the aquifer contact providing a chance for specific contaminants to coprecipitate. The Eh-pH relation of the studied groundwater samples indicates high oxidation conditions and openness of the system. The attenuation capacity has been determined mathematically, it assumes the dispersive, advective, sorptive, and degradative processes acting on a solute in a one-dimensional flow system. The value of attenuation capacity increases by decreasing groundwater velocity and completely vanishes at a certain high velocity; determined for the relevant radioactive contaminants.

Investigating the performance of Ogata-banks' one-dimensional dispersion equation in oil contamination dispersion in Bentonite soil

In recent years, the soil and its surrounding environment have undergone and faced irrecoverable changes and contaminations due to human activities. From among contaminating sources, hydrocarbon compounds are very important because they easily permeate into soil and aquifers due to storage or leakage (when transferred). Investigating contamination transfer peculiarities is, in fact, a vital and basic issue in the environmental studies because of their high potential of permeation into soil and aquifers. In the present research, effort has been made to introduce the mechanism of contaminations' dispersion and the basic equation in the related theory while applying boundary conditions, and extending the equation to study one-dimensional dispersion. Next, the results of one-dimensional dispersion in Bentonite with and without surface absorption in time intervals of 15, 30, and 90 days from the beginning of dispersion have been compared using the C-Tran Software. The results of this research study have revealed that the oil contamination density (concentration) variations along the soil column experience a decreasing trend; under the conditions of one-dimensional dispersion, the reduction rate is nearly constant 90 days after the commencement of the dispersion process.

Investigating the performance of Ogata-banks' one-dimensional dispersion equation in oil contamination dispersion in Bentonite soil

In recent years, the soil and its surrounding environment have undergone and faced irrecoverable changes and contaminations due to human activities. From among contaminating sources, hydrocarbon compounds are very important because they easily permeate into soil and aquifers due to storage or leakage (when transferred). Investigating contamination transfer peculiarities is, in fact, a vital and basic issue in the environmental studies because of their high potential of permeation into soil and aquifers. In the present research, effort has been made to introduce the mechanism of contaminations' dispersion and the basic equation in the related theory while applying boundary conditions, and extending the equation to study one-dimensional dispersion. Next, the results of one-dimensional dispersion in Bentonite with and without surface absorption in time intervals of 15, 30, and 90 days from the beginning of dispersion have been compared using the C-Tran Software. The results of this research study have revealed that the oil contamination density (concentration) variations along the soil column experience a decreasing trend; under the conditions of one-dimensional dispersion, the reduction rate is nearly constant 90 days after the commencement of the dispersion process.

Development of Numerical Estimation Method of the Location and Amount of Materials Seeping from the Sea Floor

To mitigate global warming, it is necessary to reduce the large volume of CO2 released into the atmosphere. Carbon capture and storage technology is a promising means of achieving this purpose. Those who inject and store CO2 in sub-seabed geological formations may be legally required to monitor CO2 leakage, even when the likelihood of such an event is very low. In the case that the leaked CO2 is monitored by limited numbers of CO2 censors set on the sea bottom, it is required to elucidate the leakage location and rate immediately, in order to evaluate its impacts on the marine ecosystems and to minimize the impacts. In this study, we developed a numerical method to predict the location and rate of a contaminant seeping from the seafloor, using the adjoint marginal sensitivity method, based on the data monitored by limited numbers of sensors. A time-reversed numerical test was successfully conducted, using information obtained by the time-forward simulation of tidal current and contaminant dispersion.

A regional approach to the environmental risk assessment - Human health risk assessment case study in the Campania region

Environmental quality is fundamental for the wellbeing of human life. Environmental risk assessment and analysis have a crucial role in the evaluation of human health risk, especially in intensive urbanized and industrialized areas, such as the Campania region (Italy). In Italy, after the Legislative Decree 152/2006, the environmental risk assessment has become mandatory for contaminated lands such as brownfield sites.For the purposes of the present study 3535 topsoil samples were collected across the whole regional territory. The concentrations of 53 elements have been determined by aqua regia extraction followed by a combination of ICP-MS and ICP-AES methods.A new approach to assess/rank environmental risk was applied by using geospatial analysis in a GIS platform to adapt a European-wide accepted methodology for the preliminary assessment of human health risks at single contaminated sites to a regional scale.The methodology chosen for the risk assessment procedures is the PRA.MS (Preliminary Risk Assessment Model for the identification and assessment of probelm areas for Soil contamination in Europe). Following the PRA.MS guidelines, a conceptual model for the human health risk assessment in the Campania region has been based on four different exposure routes: 1) dispersion of contaminants in groundwater, 2) dispersion in surface water, 3) dispersion in air, and 4) direct contact with the contaminated media (soil). The source, pathway and receptor for each exposure route are scored fusing a quantitative or qualitative analysis of some characteristic features (parameters).A total of 14 representative parameters were chosen, based on the available regional data for Campania. Starting from the values of these parameters, the information is aggregated to higher levels in several steps, adopting a mixed additive and multiplicative algorithm, up to the overall risk score. The final risk map is classified into four risk classes. This map is useful for identifying high risk areas, where monitoring and more detailed analysis has to be carried out.

Experimental analysis of the air velocity and contaminant dispersion of human exhalation flows.

Human exhalation flow is a potential source of pathogens that can constitute a cross-infection risk to people in indoor environments. Thus, it is important to investigate the characteristics of this flow, its development, area of influence, and the diffusion of the exhaled contaminants. This paper uses phase-averaged particle image velocimetry together with a tracer gas (CO2 ) to study two different exhalation flows over time: the exhalation of an average male (test M) and an average female (test F), using a life-sized thermal manikin in a supine position. The exhalation jets generated for both tests are similar in terms of symmetrical geometry, vorticity values, jet opening angles, and velocity and concentration decays. However, there is a difference in the penetration length of the two flows throughout the whole exhalation process. There is also a time difference in reaching maximum velocity between the two tests. It is also possible to see that the tracer gas dispersion depends on the momentum of the jet so the test with the highest velocity decay shows the lowest concentration decay. All these results are of interest to better understand cross-infection risk.

Accuracy of Interpolated Bathymetry in Digital Elevation Models

ABSTRACT Amante, C.J. and Eakins, B.W., 2016. Accuracy of interpolated bathymetry in digital elevation models. In: Brock, J.C.; Gesch, D.B.; Parrish, C.E.; Rogers, J.N., and Wright, C.W. (eds.), Advances in Topobathymetric Mapping, Models, and Applications. Journal of Coastal Research, Special Issue, No. 76, pp. 123–133. Coconut Creek (Florida), ISSN 0749-0208. Digital elevation models (DEMs) are used to model numerous coastal processes, including tsunamis, contaminant dispersal, and erosion. In the bathymetric realm, the distance between measurements typically increases farther from shore (i.e., deeper water), such that gridding interpolation to build a bathymetric DEM is often across large distances. This study examined the accuracy of interpolation in bathymetric DEMs using three common interpolation techniques: inverse distance weighting, spline, and triangulation. The goal was to examine the relationship between interpolation accuracy and cell sampling density, distance to the nearest depth measureme...

Flow and contaminant dispersion analysis around a model building using non-linear eddy viscosity model and large eddy simulation

In the present paper, the analysis of concentration and flow fields around a model building was performed using two different approaches in turbulence modeling. In the first approach, the non-linear model of Ehrhard and Moussiopoulos was employed as one of the best cubic non-linear eddy viscosity models, and large eddy simulation was utilized in the second approach. The obtained results suggest that although the non-linear model has the ability to predict the anisotropic normal components of Reynolds stress tensor, due to time-averaged nature of its governing equations, it is incapable of estimating the correct values of Reynolds stress components and turbulent characteristics in the wake region of the model building. So the predicted turbulence kinetic energy values by the non-linear model are 45% smaller than those of large eddy simulation approach in the wake region behind the model building. Also different predictions of the wake region structure by the non-linear model and large eddy simulation approach revealed that elongation of iso-surface for \(\left\langle K \right\rangle\) = 1.5 in non-linear model is 56% more than that of large eddy simulation approach. The large eddy simulation approach shows much consistent behavior to the physics governing the flow compared to the non-linear model. Also good agreement observed between the results obtained through this approach and the experimental data. However, the disadvantage of large eddy simulation approach is the high computational costs.

Vectorial statistics for the standard deviation of wind direction

The standard deviation of wind direction is an important parameter in atmospheric pollution management. It can be used to calculate the rate of horizontal diffusion and from this the transport and dispersion of air contaminants can be determined. The standard deviation of wind direction cannot be calculated directly from customary linear statistics, mainly because of its periodic nature which makes the zero position arbitrary. Various algorithms have been proposed to estimate its value. The methodologies adopted in meteorology implicitly assume that the wind angle can be treated independently of the wind speed. Such an assumption might not be appropriate in some instances, as will be shown in this work by means of an example. To overcome this limitation, a new algorithm that takes into account both the periodic and the vectorial nature of the wind direction will be proposed. This is done by weighing each sample value with the corresponding wind speed. The results obtained from the new method were compared to those determined from algorithms available in literature using measured data. The comparison indicates that while the behavior is similar, differences do exist. Further investigation indicated that while the differences can be small, they might be physically important.

Modelling the impacts of global change on concentrations of Escherichia coli in an urban river

Discharges of combined sewer system overflows (CSOs) affect water quality in drinking water sources despite increasing regulation and discharge restrictions. A hydrodynamic model was applied to simulate the transport and dispersion of fecal contaminants from CSO discharges and to quantify the impacts of climate and population changes on the water quality of the river used as a drinking water source in Québec, Canada. The dispersion model was used to quantify Escherichia coli (E. coli) concentrations at drinking water intakes. Extreme flows during high and low water events were based on a frequency analysis in current and future climate scenarios. The increase of the number of discharges was quantified in current and future climate scenarios with regards to the frequency of overflows observed between 2009 and 2012. For future climate scenarios, effects of an increase of population were estimated according to current population growth statistics, independently of local changes in precipitation that are more difficult to predict than changes to regional scale hydrology. Under “business-as-usual” scenarios restricting increases in CSO discharge frequency, mean E. coli concentrations at downstream drinking water intakes are expected to increase by up to 87% depending on the future climate scenario and could lead to changes in drinking water treatment requirements for the worst case scenarios. The greatest uncertainties are related to future local discharge loads. Climate change adaptation with regards to drinking water quality must focus on characterizing the impacts of global change at a local scale. Source water protection planning must consider the impacts of climate and population change to avoid further degradation of water quality.

A new statistical model for subgrid dispersion in large eddy simulations of particle-laden flows

Dispersed multiphase turbulent flows are present in many industrial and commercial applications like internal combustion engines, turbofans, dispersion of contaminants, steam turbines, etc. Therefore, there is a clear interest in the development of models and numerical tools capable of performing detailed and reliable simulations about these kind of flows. Large Eddy Simulations offer good accuracy and reliable results together with reasonable computational requirements, making it a really interesting method to develop numerical tools for particle-laden turbulent flows. Nonetheless, in multiphase dispersed flows additional difficulties arises in LES, since the effect of the unresolved scales of the continuous phase over the dispersed phase is lost due to the filtering procedure. In order to solve this issue a model able to reconstruct the subgrid velocity seen by the particles is required. In this work a new model for the reconstruction of the subgrid scale effects over the dispersed phase is presented and assessed. This innovative methodology is based in the reconstruction of statistics via Probability Density Functions (PDFs).