Implications of a New Test Facility for Fragmentation Investigations on Virgin (Micro)plastics.

Littered plastics are partly introduced into water bodies, ultimately transporting this waste to the shores and oceans. At the shore, ultraviolet (UV) radiation (also present in other environmental compartments) and wave breaking cause plastics to degrade and fragment into smaller particles, called microplastics, if below 5 mm. Since these plastics' surfaces can act as vectors for hydrophobic (toxic) chemical substances (e.g., per- and polyfluoroalkyl substances (PFAS)) and leach (toxic) chemicals into the water, the increase in the surface area through the fragmentation of plastics becomes relevant. Studies investigating different effects on the fragmentation of plastics have mostly disregarded a sufficient mechanical component for fragmentation, focusing on degradation by UV radiation. Therefore, this study investigated the impact of the mechanical fragmentation drivers, wave impact, and sediment abrasion on the fragmentation of expanded polystyrene (EPS), high-density polyethylene (PE-HD), and polyethylene terephthalate (PET) particles. In a newly designed test facility called Slosh-Box, the mentioned impacts were investigated concurrently. The results reveal that the mechanical impacts alone are sufficient for plastic fragmentation, and the test facility is suitable for fragmentation investigations. Furthermore, the increase in surface area was determined via scanning electron microscopy. For EPS, the surface area increased more than 2370-fold, while for PE-HD and PET, surface areas increased between 1 and 8.6 times. Concluding from the results, the new test facility is suitable for plastic fragmentation studies. In addition, sediment was revealed to be a relevant fragmentation driver, which should be included in every experiment investigating the fragmentation of plastic in a nearshore environment independent of other drivers like UV radiation.

Determination of Microplastics' Vertical Concentration Transport (Rouse) Profiles in Flumes.

The transport behavior of microplastics (MPs) in the fluvial environment is scarcely researched. Besides settling velocities and critical shear stress for erosion, only a few investigations aim at MPs' vertical concentration profile and the underlying theory required. Therefore, this paper's experiments investigate vertical concentration profiles of approximately spherical MP particles (d = 1-3 mm) with densities close to water (0.91-1.13 g/cm3) in flow channels, coupling them with fundamental theory for the first time. The experiments were conducted in a tiling flume (slope of 0-2.4%) at 67 and 80 mm water depth, with a turbulent flow, velocities ranging from 0.4 to 1.8 m/s, and turbulence kinetic energy from 0.002 to 0.08 m2/s2. The measured profiles confirm the assumption that the concentration profile shapes of settling plastics are similar to those of sediments and running reversed for buoyant plastics. Furthermore, the hypothesis of the Rouse formula's applicability for floating and sinking plastics could be confirmed for approximately uniform flows. Future studies tying in with this research should increase particle properties and hydraulic parameter variation.

Remobilization of pollutants during extreme flood events poses severe risks to human and environmental health.

While it is well recognized that the frequency and intensity of flood events are increasing worldwide, the environmental, economic, and societal consequences of remobilization and distribution of pollutants during flood events are not widely recognized. Loss of life, damage to infrastructure, and monetary cleanup costs associated with floods are important direct effects. However, there is a lack of attention towards the indirect effects of pollutants that are remobilized and redistributed during such catastrophic flood events, particularly considering the known toxic effects of substances present in flood-prone areas. The global examination of floods caused by a range of extreme events (e.g., heavy rainfall, tsunamis, extra- and tropical storms) and subsequent distribution of sediment-bound pollutants are needed to improve interdisciplinary investigations. Such examinations will aid in the remediation and management action plans necessary to tackle issues of environmental pollution from flooding. River basin-wide and coastal lowland action plans need to balance the opposing goals of flood retention, catchment conservation, and economical use of water.

Application of Laser-Induced, Deep UV Raman Spectroscopy and Artificial Intelligence in Real-Time Environmental Monitoring-Solutions and First Results.

Environmental monitoring of aquatic systems is the key requirement for sustainable environmental protection and future drinking water supply. The quality of water resources depends on the effectiveness of water treatment plants to reduce chemical pollutants, such as nitrates, pharmaceuticals, or microplastics. Changes in water quality can vary rapidly and must be monitored in real-time, enabling immediate action. In this study, we test the feasibility of a deep UV Raman spectrometer for the detection of nitrate/nitrite, selected pharmaceuticals and the most widespread microplastic polymers. Software utilizing artificial intelligence, such as a convolutional neural network, is trained for recognizing typical spectral patterns of individual pollutants, once processed by mathematical filters and machine learning algorithms. The results of an initial experimental study show that nitrates and nitrites can be detected and quantified. The detection of nitrates poses some challenges due to the noise-to-signal ratio and background and related noise due to water or other materials. Selected pharmaceutical substances could be detected via Raman spectroscopy, but not at concentrations in the µg/l or ng/l range. Microplastic particles are non-soluble substances and can be detected and identified, but the measurements suffer from the heterogeneous distribution of the microparticles in flow experiments.

Why analysing microplastics in floodplains matters: application in a sedimentary context.

Microplastics in the environment are a relatively new form of anthropogenic contamination. Right now, the research focus is on the detection of microplastic accumulation in different environmental compartments and understanding the processes that have led to its transport. Detailed information on microplastics in floodplain areas and their distribution in depth are still missing to better understand accumulation points. Therefore, this study presents on the one hand microplastic detection in fluvial sediments from nine sampling sites along a river course. Polymers were determined with infrared spectroscopy and additional sedimentary analysis of the grain size and heavy metal concentration was performed. In total, there was less microplastic in the upper than in the lower river course and slip-off slopes were identified as accumulation hotspots also in deeper sediment layers. Mostly, microplastic particles were detected in fine sediment and heavy metal concentrations along the river were similar to those of microplastics. On the other hand, besides the spatial distribution of microplastics and accumulation in floodplain areas, microplastic analysis offered information in a sedimentary context. Sedimentation rates (0.29-4.00 cm a-1) and patterns between temporal deposition and microplastic polymers were identified. The basis for the development of a dating method by detection of MPs in sediments was thus established. Microplastics as a contaminant provide, in addition to the identification of deposition areas, further data in a temporal and sedimentary perspective.

Canola oil extraction in conjunction with a plastic free separation unit optimises microplastics monitoring in water and sediment.

Microplastics are widely distributed in the environment and to define contamination hot spots, environmental samples have to be analysed by means of cost-as well as time-efficient and reliable standardised protocols. Due to the lipophilic characteristics of plastics, oil extraction as a fast and density-independent separation process is beneficial for the crucial extraction step. It was extensively validated (480 experiments) in two test setups by using canola oil and a cost-effective, plastic-free separation unit with spiked microplastics (19 different polymer types) in the density range from ρ = 11-1760 kg m-3 and in the size range from 0.02-4.4 mm. Thus, an innovative, new method combination was developed and profoundly validated for water and sediment samples using only a short settling time of 15 minutes. Some experiments were also carried out with zinc chloride to obtain additional reference data (particles ≤ 359 µm). The total mean recovery rate was 89.3%, 91.7% within the larger microplastic fraction and 85.7% for the small fraction. Compared to zinc chloride (87.6%), recovery rates differed not significantly with oil (87.1%). Furthermore, size limits were set, since the method works best with particles 0.02 mm ≥d≤ 3 mm. The proposed method exhibits higher efficiency (84.8% for 20-63 µm) for the potentially most harmful microplastic size fraction than the classic setup using brine solution. As a result, oil is a comparably effective separation medium and offers further advantages for separating water and sediment samples due to its density independence, simple and fast application and environmental friendliness. Based on this, a new extraction protocol is presented here that confirms oil separation as a sound and effective separation process in microplastic analysis and identifies previously missing information.

Settling and rising velocities of environmentally weathered micro- and macroplastic particles.

Microplastic is exposed to numerous weathering processes in the environment, which change particle properties and thus influence transport behaviors, including settling and rising velocities in aquatic environments. However, the extent to which particles in the environment differ from virgin particles in their transport behaviors has not yet been investigated. The settling and rising velocities of weathered fluvial microplastic and macroplastic particles collected from environmental samples are determined in this study and the transferability of theoretical approaches to predicting their transport behaviors is examined. The settling velocities of the environmental particles were between 0.16 and 3.52 cm/s and the rising velocities between 0.18 and 19.85 cm/s. Formulas were applied that were developed using experiments with virgin microplastic, but do not account for the effects of environmental impacts such as degradation, fragmentation and biofouling on the velocities. Accordingly, the transferability of the formulas to environmental particles must be verified. The formulas proved to be suitable for describing the settling and rising velocities of environmental microplastic particles in the shapes of pellets, fragments and foams, and were less suitable for describing the velocities of films and macroplastic particles. Further experiments will be necessary in the future to integrate effects from biofilm and particle deformation on the transport behaviors to adequately model the behavior of the highly diverse micro- and macroplastic particles in the aquatic environment.

Infiltration Behavior of Microplastic Particles with Different Densities, Sizes, and Shapes-From Glass Spheres to Natural Sediments.

In this study, the infiltration behavior of 21 microplastic particles with different densities, diameters, and shapes was investigated using columns of glass spheres with different grain diameters. The glass spheres were considered as an analogy for natural sediment and the results were afterward transferred to natural sediment and compared to fine sediment infiltration. The infiltration depth of the microplastic particles increased with decreasing diameter of the microplastic particles (dMP) and with increasing diameter of the glass spheres (dGS). At ratios of dMP/dGS > 0.32, hardly any infiltration could be observed. In regard to the particle shape, the data shows that spherical particles infiltrate deeper than fragments and fibers. In case of fibers, the fiber diameter, in particular, influences the depth of infiltration, with thinner fiber diameters leading to deeper infiltration depths. Fragments, such as tire abrasion, infiltrated less deeply than spherical particles, probably due to the entanglement of the angular particles in the pores. Finally, based on the experiments, this study provides initial indications of reasonable sampling depths in dependence of the grain sizes of the bottom sediment and the microplastic particles. According to this, microplastics in detectable particle sizes (>100 µm) are only found on the surface of sediment consisting of coarse silt and fine sand, while the particles might infiltrate up to 13 cm into sediment consisting of coarse sand, fine gravel, and medium gravel. A statement of depth-variable microplastic concentrations is therefore mainly useful for these sediment types. Accordingly, in future sediment samples, the grain size distribution of the sediment should always be indicated to better evaluate the detected microplastic concentrations.

The way of microplastic through the environment - Application of the source-pathway-receptor model (review).

Microplastics in the environment is a highly relevant research topic. However, although more and more studies on environmental concentrations of microplastics are published, a profound risk assessment could not be carried out yet. This is mainly attributable to the fact that the current sampling and analysis methods do not provide a representative picture of the environmental pollution, as the fundamental knowledge about transport processes of microplastic is not present, and the ecotoxicological studies therefore cannot consider the relevant exposures of the organisms. To provide a methodological basis for further research and risk assessments, this paper applies the Source-Pathway-Receptor model to the context of microplastics, whereby the current state of knowledge can be compiled in a structured way and important knowledge gaps can be identified.

Erosion Behavior of Different Microplastic Particles in Comparison to Natural Sediments.

Microplastic (MP) has been detected in marine, limnic, terrestrial, and atmospheric environments. However, rivers are often only seen as transport paths for MPs from inland sources to the oceans, although transport rates in rivers can hardly be determined yet. MP in rivers can either be transported, or it settles to the bottom of the river and either remains there or is remobilized again at higher flow velocities. This remobilization, also known as erosion, depends on the critical shear stress of a particle and is influenced by the particle properties and the sediment bed. In this study, the critical shear stresses of 14 MP particles with different shapes, densities, and particle sizes on different sediment beds were experimentally determined and subsequently compared with the basic principles of erosion from sediment transport. Critical shear stresses of the MP particles were between 0.002 and 0.233 N/m2, depending on particle and sediment properties. Furthermore, the hiding-exposure effect was transferred to MPs and an equation was developed to determine the critical shear stress of different MP particles on natural sediment beds.

Effects of Particle Properties on the Settling and Rise Velocities of Microplastics in Freshwater under Laboratory Conditions.

Microplastic (MP) contaminates terrestrial, aquatic, and atmospheric environments. Although the number of river sampling studies with regard to MP concentrations is increasing, comprehension of the predominant transport processes of MP in the watercourse is still very limited. In order to gain a better process understanding, around 500 physical experiments were conducted to shed more light on the effects of particle shape, size and density on the rise and settling velocities of MP. The determined velocities ranged between 0.39 cm/s for polyamide fibers (settling) and 31.4 cm/s for expanded polystyrene pellets (rise). Subsequently, the determined velocities were compared with formulas from sediment transport and, as there were large differences between theoretically and experimentally determined velocities, own formulas were developed to describe settling and rise velocities of MP particles with a large variety of shapes, sizes and densities. This study shows that MP differs significantly from sediment in its behavior and that a transfer of common sediment transport formulas should be treated with caution. Furthermore, the established formulas can now be used in numerical simulations to describe the settling and rising of MP more precisely.

A decade of fluvial morphodynamics: relocation and restoration of the Inde River (North-Rhine Westphalia, Germany).

BACKGROUND: Relocations and restorations do not only change the ecological passability and sediment continuity of a river but also its flow behavior and fluvial morphodynamics. Sediment transport processes and morphological development can be assessed with field measurements, also taking the transport of sediment-bounded contaminants as a tracer material for fluvial morphodynamics into account. The objective of this study was to determine the morphological development of the Inde River (a tributary of the Rur River in North-Rhine Westphalia, Germany) towards its pre-defined guiding principle after a relocation and restoration in 2005 AD. METHODS: The fluvial morphodynamics of the Inde River were analyzed over a period of almost 15 years taking sediment samples, analyzing echo soundings of the river's bathymetry and determining the heavy metal content of the sediment as a tracer material for the morphological development. RESULTS: The results show that the relocation and restoration of the Inde River initiates new hydrodynamic processes, which cause morphological changes of the river widths, meander belts and channel patterns. The riverbed of the new Inde River has incised into the ground due to massive erosion, which has led to increased fine sediment transport in the downstream direction. The reasons for and consequences of this fine sediment transport are discussed and correlated to the sediment continuity of a river. CONCLUSIONS: Overall, the new Inde River has reached its goal of being a natural river as a consequence of the relocation and restoration and has adapted its new conditions towards a dynamic morphological equilibrium.

Institute of hydraulic engineering and water resources management (RWTH Aachen University): an overview of research focus and training.

Water is an essential element and highly valuable resource in life. Between the priorities of environment, people and economy, it is of increasing importance to fully understand the fundamental force of water to be capable of handling waterborne events-such as flooding-manage and ensure water quality and availability, and utilize hydraulic energy. The Institute of Hydraulic Engineering and Water Resources Management (IWW) at RWTH Aachen University has a long research tradition in this field. Going back to the founding year of the university in 1870, the chair is based on the work of civil engineer Otto Intze, who is best known for his pioneering contributions in construction of dams and elevated water tanks. Ever since then, the institute has broadened its research spectrum and is today focusing on flood protection structures, hydraulic engineering design, integrated coastal zone management, morphodynamics and ethohydraulics. In a comprehensive approach, physical model experiments are combined with field measurements and numerical simulations to investigate a wide range of projects. With its annually organized International Symposium on Hydraulic Engineering (IWASA), the institute also offers information to a wide audience on highly topical aspects in the field of water engineering works and water management, while at the same time bridging the gap between science and industry. The institute is part of the "Project House Water", a research network at RWTH Aachen University that was established within the framework of the German excellence initiative. Here, scientific competencies from the fields of ecotoxicology, process engineering, geography, sociology, economy and hydraulic engineering are focussed to allow for an interdisciplinary, holistic assessment of flooding events and their impacts.

Project house water: a novel interdisciplinary framework to assess the environmental and socioeconomic consequences of flood-related impacts.

Protecting our water resources in terms of quality and quantity is considered one of the big challenges of the twenty-first century, which requires global and multidisciplinary solutions. A specific threat to water resources, in particular, is the increased occurrence and frequency of flood events due to climate change which has significant environmental and socioeconomic impacts. In addition to climate change, flooding (or subsequent erosion and run-off) may be exacerbated by, or result from, land use activities, obstruction of waterways, or urbanization of floodplains, as well as mining and other anthropogenic activities that alter natural flow regimes. Climate change and other anthropogenic induced flood events threaten the quantity of water as well as the quality of ecosystems and associated aquatic life. The quality of water can be significantly reduced through the unintentional distribution of pollutants, damage of infrastructure, and distribution of sediments and suspended materials during flood events. To understand and predict how flood events and associated distribution of pollutants may impact ecosystem and human health, as well as infrastructure, large-scale interdisciplinary collaborative efforts are required, which involve ecotoxicologists, hydrologists, chemists, geoscientists, water engineers, and socioeconomists. The research network "project house water" consists of a number of experts from a wide range of disciplines and was established to improve our current understanding of flood events and associated societal and environmental impacts. The concept of project house and similar seed fund and boost fund projects was established by the RWTH Aachen University within the framework of the German excellence initiative with support of the German research foundation (DFG) to promote and fund interdisciplinary research projects and provide a platform for scientists to collaborate on innovative, challenging research. Project house water consists of six proof-of-concept studies in very diverse and interdisciplinary areas of research (ecotoxicology, water, and chemical process engineering, geography, sociology, economy). The goal is to promote and foster high-quality research in the areas of water research and flood-risk assessments that combine and build off-laboratory experiments with modeling, monitoring, and surveys, as well as the use of applied methods and techniques across a variety of disciplines.

A versatile and low-cost open source pipetting robot for automation of toxicological and ecotoxicological bioassays.

In the past decades, bioassays and whole-organism bioassay have become important tools not only in compliance testing of industrial chemicals and plant protection products, but also in the monitoring of environmental quality. With few exceptions, such test systems are discontinuous. They require exposure of the biological test material in small units, such as multiwell plates, during prolonged incubation periods, and do not allow online read-outs. It is mostly due to these shortcomings that applications in continuous monitoring of, e.g., drinking or surface water quality are largely missing. We propose the use of pipetting robots that can be used to automatically exchange samples in multiwell plates with fresh samples in a semi-static manner, as a potential solution to overcome these limitations. In this study, we developed a simple and low-cost, versatile pipetting robot constructed partly using open-source hardware that has a small footprint and can be used for online monitoring of water quality by means of an automated whole-organism bioassay. We tested its precision in automated 2-fold dilution series and used it for exposure of zebrafish embryos (Danio rerio)-a common model species in ecotoxicology-to cadmium chloride and permethrin. We found that, compared to conventional static or semi-static exposure scenarios, effects of the two chemicals in zebrafish embryos generally occurred at lower concentrations, and analytically verified that the increased frequency of media exchange resulted in a greater availability of the chemical. In combination with advanced detection systems this custom-made pipetting robot has the potential to become a valuable tool in future monitoring strategies for drinking and surface water.

Physiologically-based toxicokinetic models help identifying the key factors affecting contaminant uptake during flood events.

As a consequence of global climate change, we will be likely facing an increasing frequency and intensity of flood events. Thus, the ecotoxicological relevance of sediment re-suspension is of growing concern. It is vital to understand contaminant uptake from suspended sediments and relate it to effects in aquatic biota. Here we report on a computational study that utilizes a physiologically based toxicokinetic model to predict uptake, metabolism and excretion of sediment-borne pyrene in rainbow trout (Oncorhynchus mykiss). To this end, data from two experimental studies were compared with the model predictions: (a) batch re-suspension experiments with constant concentration of suspended particulate matter at two different temperatures (12 and 24°C), and (b) simulated flood events in an annular flume. The model predicted both the final concentrations and the kinetics of 1-hydroxypyrene secretion into the gall bladder of exposed rainbow trout well. We were able to show that exhaustive exercise during exposure in simulated flood events can lead to increased levels of biliary metabolites and identified cardiac output and effective respiratory volume as the two most important factors for contaminant uptake. The results of our study clearly demonstrate the relevance and the necessity to investigate uptake of contaminants from suspended sediments under realistic exposure scenarios.

An attempt to assess the relevance of flood events-biomarker response of rainbow trout exposed to resuspended natural sediments in an annular flume.

There is a consensus within the scientific community that sediments act as a long-term sink for a variety of organic and inorganic pollutants, which, however, can re-enter the water column upon resuspension of deposited material under certain hydraulic conditions such as flood events. Within the implementation of the European Water Framework Directive, it is important to understand the potential short- and long-term impact of suspended particulate matter (SPM)-associated contaminants on aquatic organisms as well as the related uptake mechanisms for a sound risk assessment. To elucidate the effects of sediment-bound organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), rainbow trout (Oncorhynchus mykiss) were exposed to three resuspended natural sediments with different contamination levels. Physicochemical parameters including dissolved oxygen concentration, pH and temperature, total PAH concentration in sediments and SPM as well as different biomarkers of exposure in fish (7-ethoxyresorufin O-deethylase activity, biliary PAH metabolites, micronuclei, and lipid peroxidation) were measured following seven days of exposure within an annular flume, a device to assess erosion and deposition processes of cohesive sediment. Concentrations of PAHs in SPM remained constant and represented the different contamination levels in the un-suspended sediments. Significant differences in bile metabolite concentrations as well as in 7-ethoxyresorufin O-deethylase induction compared to control experiments (untreated animals and animals that were exposed in the annular flume without sediment) were observed for all exposure scenarios. The ratio between 1-hydroxypyrene in bile from fish exposed to the three different contamination levels was 1.0:3.6:10.7 and correlated well with (1) the ratio of pyrene concentrations in corresponding sediments which was 1.0:3.1:12.7 and (2) with the ratio of particle-bound pyrene in SPM which was 1.0:2.7:11.7. In contrast, hepatic lipid peroxidation and micronuclei formation represented the different contamination levels less conclusive. The results of this study clearly demonstrate that firmly bound PAH from aged sediments can become bioaccessible upon resuspension under flood-like conditions and are readily absorbed by aquatic organisms such as rainbow trout. Associated short-term effects were clearly documented and possible adverse long-term impacts due to genotoxicity are likely to follow.

How flood events affect rainbow trout: evidence of a biomarker cascade in rainbow trout after exposure to PAH contaminated sediment suspensions.

Increasing frequency and intensity of flood events are major concerns in the context of climate change. In addition to the direct hydrological implications of such events, potential ecotoxicological impacts are of increasing interest. It is vital to understand mechanisms of contaminant uptake from suspended particulate matter (SPM) and related effects in aquatic biota under realistic conditions. However, little is known about these processes. Due to recent changes in climate, during summer temperatures of German rivers frequently exceed 25°C. Effects of re-suspension of sediments on biota under elevated temperature regimes are likely to differ from those under lower temperature regimes. To elucidate this differential response of aquatic vertebrates, rainbow trout were exposed to suspensions of sediment from the Rhine River that was spiked with a mixture of polycyclic aromatic hydrocarbons (PAH). The experiments were conducted under two different temperature regimes (24°C or 12°C). Physicochemical parameters, including concentration of PAHs in SPM, and biomarkers in fish (biliary PAH metabolites, 7-ethoxyresorufin O-deethylase activity, lipid peroxidation (LPO), mRNA expression of some genes and micronuclei) were measured over the course of a 12d study. Concentrations of pyrene and phenanthrene decreased over time, while no decrease was observed for chrysene and benzo[a]pyrene. The biomarker cascades, more specifically the temporal dynamics of biomarker reactions, did not only show quantitative differences (i.e. different induction intensity or rate of biomarker responses) at the two temperatures but also qualitative differences, i.e. different biomarker responses were observed. A slight significant increase of biliary metabolites in fish was observed in un-spiked sediment at 24°C. In bile of fish exposed to PAH spiked sediment concentrations of 1-hydroxypyrene and 1-hydroxyphenanthrene increased significantly during the first two days, and then decreased. At 12°C uptake of PAHs was slower and maximum metabolite concentrations in bile were less than in fish exposed at 24°C. Following a latency of two days, concentrations of PAH metabolites in bile of fish exposed at 24°C were followed by a peak in LPO. PAHs spiked into sediments under laboratory conditions were significantly more bioavailable than the PAHs that were already present in un-spiked field-collected sediments.

Simulation of ammonium and chromium transport in porous media using coupling scheme of a numerical algorithm and a stochastic algorithm.

The migration of the species of chromium and ammonium in groundwater and their effective remediation depend on the various hydro-geological characteristics of the system. The computational modeling of the reactive transport problems is one of the most preferred tools for field engineers in groundwater studies to make decision in pollution abatement. The analytical models are less modular in nature with low computational demand where the modification is difficult during the formulation of different reactive systems. Numerical models provide more detailed information with high computational demand. Coupling of linear partial differential Equations (PDE) for the transport step with a non-linear system of ordinary differential equations (ODE) for the reactive step is the usual mode of solving a kinetically controlled reactive transport equation. This assumption is not appropriate for a system with low concentration of species such as chromium. Such reaction systems can be simulated using a stochastic algorithm. In this paper, a finite difference scheme coupled with a stochastic algorithm for the simulation of the transport of ammonium and chromium in subsurface media has been detailed.

A probabilistic cellular automaton for two dimensional contaminant transport simulation in ground water.

In recent years evolutionary computing algorithms have been proposed to solve many engineering problems. Genetic algorithms, Neural Networks, and Cellular Automata are the branches of evolutionary computing techniques. In this study, it is proposed to simulate the contaminant transport in porous media using a Cellular Automaton. The physical processes and chemical reactions occurring in the ground water system are intricately connected at various scales of space, time, transport coefficients and molecular concentration. The validity of continuous approach for the simulation of chemical systems with low concentration of species and intracellular environments has become subtle. Due to the difference in scales of various processes that occur in the ground water system, the description of the system can be well defined in the intermediate scale called mesoscopic scale, which is in between microscopic and macroscopic description. Mesoscopic models provide the relationship between various parameters and their evolvement in time, thus establishing the contact between modeling at various scales at the interface. In this paper, a Probabilistic Cellular Automaton (PCA) model has been developed based on the transport and reaction probability values. The developed model was verified and validated for one, two dimensional transport systems and also for the simulation of BTEX transport in two dimensional system in ground water.