Sand Surface Research Articles

Transport and retention patterns of fragmental microplastics in saturated and unsaturated porous media: A real-time pore-scale visualization

The environmental behaviors of microplastics (MPs) have garnered ever-increasing attention globally. To overcome the limitations of commonly used “black box”, a real-time pore-scale visualization system including microscope, charge coupled device (CCD) microscope camera, and flow cell (connected with pump and sample collector) was used to unravel the transport and retention mechanisms of fragmental microplastics (FMPs) in saturated and unsaturated porous media. The breakthrough curves (BTCs) of effluent concentrations from the flow cells were used to quantitatively analyze FMPs transport. The videos gathered from different transport scenarios indicated that FMPs can move along with the bulk flow in porous media, but also move around the sand surfaces via sliding, rolling, and saltating patterns. The FMPs were retained in porous media mainly via deposition and straining in saturated porous media. Interestingly, little FMPs were captured by the air-water interface in unsaturated conditions. The mobility of FMPs varied with environmental factors, which became lower at higher solution ionic strength (IS), smaller grain size, and lower water content in porous media. Flow rate barely affected the transport of FMPs under 0.1 mM IS with the mass recovery rate ranging between 65.8 and 67.5%, but significantly enhanced FMPs mobility under 10 mM IS through reducing the moving rate. The IS and grain size showed a more significant effect on the transport of FMPs in unsaturated porous media. Our findings, for the first time, visually deciphered the transport and retention patterns of MPs with fragmental shapes on pore-scale, expanding our current knowledge of the fate and transport of more realistic MPs in the environment.

A comparison of the aerodynamic characteristics of four kinds of land surface in wind erosion areas of northern China

Aerodynamic characteristics is a crucial factor influencing soil wind erosion, which is closely related to the properties of surface roughness elements. In the expansive arid and semi-arid northern China, grassland, farmland, mobile sandy land, and gobi are the main land surface types that suffer wind erosion to varying degrees. To investigate the aerodynamic characteristics of different surfaces, we used three-dimensional ultrasonic anemometers to observe the near-surface wind speed above grassland, farmland, mobile sand, and two types of gobi surfaces in areas of northern China (a total of five observation sites). We compared the aerodynamic characteristics of the five surfaces and their causes (i.e., the surface roughness length, wind speed pulsation, turbulence intensity, and drag coefficient), and analyzed how surface roughness elements weakened the airflow. The roughness length was greatest for grassland, followed by farmland, sand, fine gobi, and black gobi. The pulsation intensity of near-surface wind speed increased linearly with increasing wind speed at all sites. At a given wind speed, increasing roughness length increased the pulsation intensity of wind speed. The probability distributions for the drag coefficient and turbulence intensity of the five surfaces followed a positively skewed distribution. The drag coefficient and turbulence intensity were greatest for grassland, followed by farmland, sand, fine gobi, and black gobi surfaces. The drag force exerted on the roughness elements increased with increasing wind speed, but the ratio of drag force exerted on the roughness elements to the total drag force (τR/τ) for flexible roughness elements (i.e., plants) increased as the wind speed increased; for rigid roughness elements, τR/τ decreased with increasing wind speed. This confirms that the shelter capability of flexible roughness elements against soil wind erosion increases with the increase of wind speed, while that of rigid roughness elements is opposite.

Response of the Thoroughbred Forelimb to Perturbations Caused by a Change in Ground Surface

Thoroughbred racehorses are often affected by musculoskeletal injuries, leading to involuntary rest, early retirement or death. Hardness and consistency of the track surface have been implicated as major risk factors for limb injury. The purpose was to test the utility of a preliminary AnyBody musculoskeletal model of the equine forelimb for its responses on two perturbing surfaces. A musculoskeletal model was developed using CT, muscle, tendon and ligament properties, and kinematic data were applied from ridden trials using five Thoroughbred horses. Horses were ridden at trot and canter on a baseline sand surface, and through two perturbation pits containing a harder and a softer surface for one stance phase. In response to the hard perturbation, the proximal limb was more compliant at trot and canter, as measured by increased shoulder flexion in the perturbed stance phase and increased elbow and carpal flexion in the subsequent swing phase. The suspensory ligaments and muscle-tendon units were less strained while lacertus fibrosus was more strained. In response to the soft perturbation, the coffin joint was more flexed and the elbow was more extended in the acute stance phase at trot, resulting in increased strain to the DDF, extensor branches and lacertus fibrosus. At canter, the coffin was more flexed, the fetlock less hyperextended and so the suspensory structures were less strained in the perturbed stance phase, but more strained in the second stance phase. Changes in ground surface affect both the perturbed stance phase, and the following stance phase.

Predicting the critical salt concentrations of monovalent and divalent brines to initiate fines migration using DLVO modeling

Fine particles are released from sandstone reservoirs at a salinity known as the critical salt concentration (CSC), which is strongly dependent on monovalent and divalent ions in the permeating liquid. Formation water is an ionic liquid, and when the salinity of the sand-fine-brine (SFB) system goes below the CSC, repulsive surface forces increase, and fine particles are dislodged from the sand surface plugging the pore throat as a result of fines migration. In this study, the effect of monovalent and divalent ions is modeled using the DLVO theory, and CSCs are predicted for monovalent and divalent salts individually and in different combinations. Using the average fine particle size and zeta potential of the SFB system, DLVO models are developed considering attractive and repulsive surface forces for various concentrations of monovalent and divalent salts to predict CSC. Zeta potentials were measured or collected from previous studies. The DLVO models predict the CSCs of 0.11 M, 0.04 M, 0.0001 M, and 0.0001 M for NaCl, KCl, CaCl2, and MgCl2, respectively, and all the results are found to be in close agreement with the experimental CSCs. Furthermore, several mixtures of NaCl and CaCl2 are utilized, and CSCs are predicted. This study showed that divalent ions significantly reduce the CSC, and their presence in the formation water and injection water is beneficial to control fines migration even at low salinity of the injection water. The application of our developed method to predict CSC yields reliable and accurate results without requiring extensive experimentation.

The study of ultralow interfacial tension SiO2-surfactant foam for enhanced oil recovery

Surfactant selection and formulation are key factors in technological and economic success in chemically enhanced oil recovery (cEOR) applications. In this study, the silica nanoparticle (SNP) was added in an ultralow interfacial tension foam (ULIFT), called SNP-ULIFT foam, which was successfully prepared by ternary surfactant systems. The Carboxylate-based extended surfactant (Carboxylate), Dioctyl Sulfosuccinate Sodium salt (AOT), and Sodium Diphenyl Oxide Disulfonate (DODS) at a 0.48:0.48:0.04 wt ratio were conducted as the surfactant system. Remarkable results in the selected surfactant system were observed in terms of the ability to form foaming and ultralow interfacial tension (IFT) at 60 ± 2 °C with the ADNOC crude oil (Abu Dhabi National Oil Company) as model oil. The optimum salinity of the surfactant system was found at 2.5 wt% (8:2 Na:Ca by weight), indicating a minimum IFT of 0.0019 mN/m. The adsorption capacities at the optimum salinity condition of each surfactant in the mixture onto the SNP's surface were 1.4, 7.3 and 19.4 molecule/nm2 for the DODS, Carboxylate and AOT surfactants, respectively; the calculated total surfactant adsorption was 2.6 mg surfactant/mg nanoparticles. While in the presence of SNP, the surfactant adsorption of the ternary surfactant foam system onto the sand surface was significantly reduced by 16.2% at 200 psi and 60 °C when compared with the neat ULIFT foam system. It was remarkably noted that the adsorption of the surfactant onto the SNP surface could result in a reduction of surfactant adsorption onto the sand surface. The oil recovery performance in the core flood by ULIFT foam was the greatest with 43% of Original Oil in Place (OOIP), and it further increased by 13% in the presence of 200 ppm SNP. In addition, the stress and viscosity of ULIFT microemulsion significantly decreased with SNP. This suspension exhibited the most non-Newtonian behavior with shear-thinning behavior over different ranges of shear rate. Therefore, SNP-ULIFT foam with the appropriate surfactant selection was a successful method for improving oil recovery performance.

Numerical analysis of a concrete foundation under a combination of a dynamic and a seismic load

Improving in assembling technology has provided machines of higher evaluation with better resistances and managed behavior. This machinery led to remarkably higher dynamic forces and therefore higher stresses. In this paper, a dynamic investigation of rectangular machine diesel and gas engines foundation at the top surface of one-layer dry sand with various states (i.e., loose, medium and dense) was carried out. The dynamic investigation is performed numerically by utilizing limited component programming, PLAXIS 3D. The soil is accepted as flexible totally plastic material submits to Mohr-Coulomb yield basis. A harmonic load is applied at the foundation with amplitude of 10 kPa at a frequency of (10, 15 and 20) HZ and seismic load is applied with acceleration – time input of earthquake hit Halabjah city north of Iraq. A parametric statement is completed to evaluate the effect of changing the relative density, embedded depth and frequency of the machine. It has been noticed that the relative density plays an important role in the resistance of settlement, as it increases the resistance of the soil to the applied loads because the dense soil is stiffer. While total stress and displacement of different relative density decrease at the time when increasing the foundations' embedding, the ratio was (15%) at the depths (Df=0 and Df=2). In addition, it has been noticed that there decrease of displacement when the frequency value changes from (10 to 20) Hz.

Comparison between the kinematics for kangaroo rat hopping on a solid versus sand surface.

In their natural habitats, animals move on a variety of substrates, ranging from solid surfaces to those that yield and flow (e.g. sand). These substrates impose different mechanical demands on the musculoskeletal system and may therefore elicit different locomotion patterns. The goal of this study is to compare bipedal hopping by desert kangaroo rats (Dipodomys deserti) on a solid versus granular substrate under speed-controlled conditions. To accomplish this goal, we developed a rotary treadmill, which is able to have different substrates or uneven surfaces. We video recorded six kangaroo rats hopping on a solid surface versus sand at the same speed (1.8 m s−1) and quantified the differences in the hopping kinematics between the two substrates. We found no significant differences in the hop period, hop length or duty cycle, showing that the gross kinematics on the two substrates were similar. This similarity was surprising given that sand is a substrate that absorbs mechanical energy. Measurements of the penetration resistance of the sand showed that the combination of the sand properties, toe-print area and kangaroo rat weight was probably the reason for the similarity.

The Effects of Seasonal Wind Regimes on the Evolution of Reversing Barchanoid Dunes

AbstractSeasonal changes in wind regime have driven the formation and emergence of reversing dunes and crest reversal in the inland arid and coastal areas of Asia, but due to the strong prevailing winds, the reversing dunes or reversing crest can be flipped. Therefore, the transient reversing dunes or crest reversal will be ignored and unobserved. To investigate dune morphology and sedimentology concerning seasonal alternation of the wind regime, we reconstructed dune topographies using aerial drone photos and analyzed the grain‐size parameters and internal sedimentary structures of dunes. Morphological results show that wind‐blown sands from the lee side are transported and deposited on the upper stoss side because of the reversing winds. Then, the dune crestal area is flattened, surface sand compositions were reorganized from fining to coarsening at the dune crest. Combining these field surveys with numerical simulation results, we found that the internal sedimentary structures are composed of high‐angle cross‐strata and low‐angle bounding surfaces. The dip angles of the bounding surfaces gradually decrease from the bottom to the top because of the reversing wind erosion on the lee side. The increase in sand flux on the lee side plays a critical role in shaping the dip angle of the bounding surfaces due to the speed‐up effect.

Land Surface Parameterization at Exposed Playa and Desert Region to Support Dust Emissions Estimates in Southern California, United States

Remote sensing technologies provide a unique opportunity to identify ground surfaces that are more susceptible to dust emissions at a large scale. As part of the Salton Sea Air Quality Mitigation Program (SSAQMP) of the Imperial Irrigation District (IID), efforts have been made to improve our understanding of fugitive, wind-blown dust emissions around the Salton Sea region in Southern California, United States. Field campaigns were conducted for multiple years to evaluate surface conditions and measure the dust emissions potential in the area. Data collected during the field work were coupled with remote sensing imagery and data mining techniques to map surface characteristics that are important in identifying dust emissions potential. Around the playa domain, surface crust type, sand presence, and soil moisture were estimated. Geomorphic surface types were mapped in the desert domain. Overall accuracy ranged from 91.7% to 99.4% for the crust type mapping. Sand presence mapping showed consistent and slightly better accuracy, ranging from 96.2% to 99.7%. Soil moisture assessment agreed with precipitation records. Geomorphic mapping in the desert domain achieved accuracy above 93.5%, and the spatial pattern was consistent with previous studies. These land surface condition assessments provide important information to support dust emissions estimates in the region.

Loading of Silver Nanoparticles onto Silica Sand Surface and Simulating of Heat Dissipation for Therapeutic Heat Applications

To develop the heat storage media for therapeutic heat applications, silver nanoparticles (AgNPs) were loaded onto silica sand surface using chemical reduction method. The thermal properties of these two materials were combined and the loading efficiency was verified by using UV-Visible spectroscopy, Scanning Electron Microscopy (SEM), and X-Ray Diffraction Spectroscopy (XRD). Observation by SEM revealed that the silver nanoparticles were homogeneously immobilized onto the silica sand surface and XRD results confirmed the formation of nanocrystalline silver. The crystallite size calculated by Scherrer formula was about 20 nm. It was also found that the particles increased in size and partially agglomerated when the concentration of AgNO3 solutions increased. Furthermore, to estimate the appropriate quantity of the nanoparticles for heating pad application, the finite element simulation by ANSYS was applied. The simulation results showed that the thermal dissipation of the silica sand was improved after loading of the silver nanoparticles. It was also found that the thermal dissipation increased with the silver proportion but 1.50% of silver concentration are sufficient to provide a significant thermal effect.

Kinetic insight on CO2 hydrate formation and dissociation in quartz sand in presence of brine

CO2 storage as hydrates in porous media is a promising method to sequester carbon dioxide (CO2) that need to be comprehended to guide its potential site selection prospects. In this study, CO2 hydrate formation and dissociation were studied in three quartz sand particles with varying petrophysical properties such as surface area, pore size, and porosities. The studied quartz sand particle sizes are QS-1 (<0.6 mm), QS-2 (0.6–0.8 mm), and QS-3 (0.8–2.0 mm). The hydrate formation experiments were conducted in a high-pressure hydrate reactor with and without brine (3.3 wt.% NaCl) at 4 MPa and temperatures of 274.15 K and 277.15 K in 100% sample saturation. The hydrate dissociation kinetics were studied at two different temperatures of 277.15 K and 279.15 K. The results show that hydrates form faster in deionized water (DI) than brine solution. The presence of brine reduced the CO2 storage capacity by 30% compared with deionized water. In addition, the presence of brine reduces the stability of CO2 hydrates. CO2 hydrate formation and dissociation behavior in porous media is highly controlled by the quartz sand porosity, pore size, and surface area. The quartz sand particles with low porosity were found to efficiently store more CO2 with a fast onset hydrate formation time of 6 hr and high gas to hydrate conversion of 55%. However, the CO2 hydrates in the sand particles with low porosity were less stable and averagely prolonged the time take to release 90% of CO2 of the systems with high porosity by 39%.

Silica nanofluid in low salinity seawater containing surfactant and polymer: Oil recovery efficiency, wettability alteration and adsorption studies

Production of crude oil from a matured oil reservoir is challenging due to the low recovery factor. Hybrid methods have demonstrated potential in oil recovery from the matured crude oil reservoir. In recent years, the low salinity water with chemicals (viz., surfactant, polymer) and nanoparticles have brought the attention of the researchers due to their ability in altering the interfacial properties of the rock-oil-water systems favorable for crude oil recovery. The current interest by industries in injection fluid (i.e., low salinity water injection) has prompted the invention of a hybrid oil recovery agent for matured crude oil reservoirs. In the current study, a novel silica-based hybrid nanofluids (NFs) of variable silica nanoparticles (NPs) concentration in low salinity seawater with anionic surfactant (AOT: dioctyl sodium sulfosuccinate) and polymer (PVP–K30: polyvinylpyrrolidone) (sometimes referred to as SMART LowSal) are used as an injection fluid in a sand-pack reactor. Oil recovery from oil saturated sand-pack reactor is observed to enhance due to NFs (hybrid) injection after secondary recovery. The characteristic study of relative permeability curves discloses that sand surface was initially water-wet and converted to strongly water-wet in the presence of NFs. A nuclear magnetic resonance (1H NMR) study reveals that adsorption of the chemical appeared on the sand surfaces, which could be the reason for wettability alteration, and thereby enhanced oil recovery. Similarly, the scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA) of the sand samples before and after injection disclosed desorption of hydrocarbon from the sand surfaces after NFs injection. An additional 5–10% oil recovery is achieved after chemical flooding due to the injection of NFs. Adsorption isotherm study well agreed with the monolayer adsorption of surfactant on the sand surface.

Preparation of super-hydrophobic/super-oleophilic quartz sand filter for the application in oil-water separation

In the present work, novel super-hydrophobic/super-oleophilic surface of quartz sand was prepared by constructing silica rough structure and modifying it with low-surface-energy hexadecyl-trimethoxysilane (HDTMS). The characterization results revealed that the water contact angle (WCA) of the modified quartz sand was more than 150° and the oil contact angle (OCA) was nearly 0°. Notably, the modified quartz sand could be used as a filter to separate oil and water and depicted a high separation efficiency. The water content in the filtrate was less than 0.5 wt%. In the meantime, the modified quartz sand can fully separate the oil film from water by adhesion. The WCA of the modified quartz sand remains above 148° even after repeated test, which indicated that the modified quartz sand had good stability and reusability.

Area Noise Assessment at Surface Stone, Sand, and Gravel Mines: Application for Reducing Worker Noise Exposure.

Repeated noise exposure and occupational hearing loss are common health problems across industries and especially within the mining industry. Large mechanized processes, blasting, grinding, drilling, and work that is often in close quarters put many miners at an increased risk of noise overexposure. In stone, sand, and gravel mining, noise is generated from a variety of sources, depending on the type of ore being mined as well as the final consumer product provided by that mine. Depending on the source of noise generation, different strategies to reduce and avoid that noise should be implemented. The National Institute for Occupational Safety and Health (NIOSH) has evaluated the noise profile at three operational surface stone, sand, and gravel mines. A-weighted sound level meter data as well as phase array beamforming data were collected throughout the mines in areas with high noise exposure or high personnel foot or vehicle traffic. Sound level meter data collected on a grid pattern was used to develop sound profiles of the working areas. These sound contour maps as well as phase array beamforming plots were provided to the mines as well as guidance to modify work areas or personnel traffic to reduce noise exposure.

Experimental Study of Evaporation Flux, Salt Precipitation, and Surface Temperature on Homogeneous and Heterogeneous Porous Media

Salt precipitation in porous media is widespread, which has garnered great research attention. However, the mechanisms governing the salt precipitation, water flux, and surface temperature changes in homogeneous and heterogeneous porous media remain unclear. This study investigated the dynamics of salt precipitation, evaporative loss, and surface temperature in homogeneous fine sand (0.1–0.25 mm), coarse sand (1‐2 mm), and a heterogeneous column with fine and coarse sand. All sand columns were initially saturated with NaCl solution. The experimental results showed that the salt was precipitated as efflorescence above the surface of the fine sand, whereas it was mainly precipitated as subflorescence below the surface of the coarse sand, causing the unconsolidated sand to form a strong stone‐like mass. The evaporated loss was significantly higher in heterogeneous than in homogeneous sand, but this difference in evaporation was insignificant in the stage where vapor diffuses through the precipitated salt to the external air. The salt crust formed not only decreased the surface temperature due to increased albedo by salt precipitation, but also resulted in a more discrete temperature distribution in the porous media. Our research results can promote further understanding of salt precipitation and evaporation in porous media.

Numerical Study of the Hydraulic Effects of Modifying the Outlet Pipe and Diffuser Plate in Pressurized Sand Filters with Wand-Type Underdrains

HighlightsAn outlet pipe with twice the cross-sectional area reduced the filter pressure drop by 12%.Two-outlet designs did not improve the hydraulic performance of the central wand.Flow uniformity in the sand bed was improved with a central downward outlet pipe.Abstract. The pressurized sand filters used in drip irrigation systems have three zones (the water inlet, sand bed, and water outlet) with different hydraulic behaviors. Previous studies that aimed to improve the hydraulic performance of these filters focused on the water inlet and sand bed by redesigning the diffuser plate and underdrain elements, respectively. In this study, we analyzed the consequences of modifying the water outlet of a commercial porous medium filter without changing its underdrain design. The original design consisted of a horizontal pipe connected to ten horizontal wands. Five additional designs that varied in size, orientation, and number of outlets were numerically studied in four operating modes (including two sand bed heights and two superficial velocities). Comparison with the commercial design indicated that (1) an outlet pipe with twice the cross-sectional area reduced the overall filter pressure drop by up to 12% and increased the flow uniformity within the sand bed; (2) two outlets led to symmetrical behavior for the amount of water drained per wand but did not improve the water volume drained by the central wand, which drained the least amount; and (3) a central vertical outlet of equal diameter as the commercial outlet produced a similar pressure drop but increased the flow uniformity within the porous medium. For completeness, two additional diffuser designs were also studied. In comparison with the original design, the proposed designs improved the flow uniformity and weakened the water vortex above the sand surface. Keywords: Computational fluid dynamics, Drip irrigation, Filtration, Granular bed, Modeling.

Study on Triaxial Mechanical Properties and Micro Mechanism of Fly Ash Reinforced Cement Calcareous Sand

In order to study the mechanical properties and micro-mechanism of industrial waste fly ash-reinforced cement calcareous sand (FCS), the triaxial unconsolidated undrained (UU) test and scanning electron microscope tests (SEM) were carried out on it. The results of UU test show that the peak stress and energy dissipation of the FCS sample first increase and then decrease with the increase in fly ash content. Fly ash enhances the cement calcareous sand by increasing both the cohesion and internal friction angle, and adding 10% content of fly ash gives the largest values. The SEM test results shows that the hydration products of cement and fly ash filled the pores and cracks on the surface of the calcareous sand, which increased the compactness and structure of the FCS samples. The porosity of cement calcareous sand can be reduced from 27.6% to 12.8% by adding 10% fly ash. A brittleness evaluation index based on energy dissipation is proposed to quantitatively characterize the brittleness of FCS samples. The results show that when the content of fly ash is 5%, the brittleness of FCS samples is the lowest. This study shows that the mechanical properties of cement calcareous sand can be effectively enhanced by adding the appropriate amount of fly ash.

Wireless Underground Sensor Networks Channel Using Energy Efficient Clustered Communication

Wireless Underground Sensor Networks (WUSNs) refer to a group of nodes working underneath the earth plane that has been predicted to render concurrent observation capability in the hostile subversive and underwater surroundings. The accurate monitoring in places like underground earth, water, lubricates so on called non-conventional media need high accuracy of tiny sized sensors with antennas at a similar size. Therefore, an investigation is needed to study the opportunities and drawbacks of utilizing WUSNs without compromising the effectiveness of real-time monitoring procedures. With this, the major confrontation is to institute a trustworthy underground communication regardless of the complex environment that has the key difficulties like elevated path loss, and miniature communication range when piercing through the soil, sand, water, and oil surfaces. On the other hand, aside from on or after elevated pathway failure, it acknowledges continuously varying channel deeds owing to the underground communication. In non-conventional media, dealing with the concerns for scheming cluster-based cooperative communication protocols for sensors have been a tough task to improve the network lifetime and its energy effectiveness. The paper intends to concentrate on these problems to put forward a fresh cooperative communication channel model bearing in mind, the propagation belongings of terahertz EM waves in the underground sensor network. Besides, the work also focuses on the creation of energy-efficient Clustered Cooperative communication protocol (CCNU) for underground sensor network to yield better reliability and effective utilization of spectrum efficiency by obtaining better lifetime, throughput, packet loss, successful packet delivery, and energy utilization. The outcome of this proposal would yield an outcome in the form of better communication channel modeling for monitoring, intrusion detection, exploration, and sensing.

Experimental study on characteristics of pore water conversion during methane hydrates formation in unsaturated sand

Understanding the pore water conversion characteristics during hydrate formation in porous media is important to study the accumulation mechanism of marine gas hydrate. In this study, low-field NMR was used to study the pore water conversion characteristics during methane hydrate formation in unsaturated sand samples. Results show that the signal intensity of<i> T</i>₂ distribution isn’t affected by sediment type and pore pressure, but is affected by temperature. The increase in the pressure of hydrogen-containing gas can cause the increase in the signal intensity of<i> T</i>₂ distribution. The heterogeneity of pore structure is aggravated due to the hydrate formation in porous media. The water conversion rate fluctuates during the hydrate formation. The sand size affects the water conversion ratio and rate by affecting the specific surface of sand in unsaturated porous media. For the fine sand sample, the large specific surface causes a large gas-water contact area resulting in a higher water conversion rate, but causes a large water-sand contact area resulting in a low water conversion ratio (<i>C</i>_w=96.2%). The clay can reduce the water conversion rate and ratio, especially montmorillonite (<i>C</i>_w=95.8%). The crystal layer of montmorillonite affects the pore water conversion characteristics by hindering the conversion of interlayer water.

Qualitative Evaluation of Factors Inducing Environmental Pollution of the Sandy Beaches of Jeju Island Using Styrene Oligomers

Objectives : Plastic pollution is a very important environmental issue in Korea as well as abroad. The objective of this study is to evaluate the internal and external factors that cause pollution of the coastal environment of Jeju Island using styrene oligomers (SOs) originated from polystyrene (PS) plastic.Methods : In order to achieve the above objective, this study is conducted to quantitatively measure the concentration of 12 individual SOs chemicals, through gas chromatography/mass spectroscopy (GC/MS) analyzing seawater and beach sand samples around sandy beaches in Jeju Island. This study evaluates the degree of environmental pollution according to internal or external factors of the sandy beach by using the physicochemical characteristic that SOs species are adsorbed on the surface of sand particles.Results and Discussion : The average concentration of SOs in the beach sand of Jeju Island ranges from a minimum of 9.80 ng/g to a maximum of 13.62 ng/g, and the average concentration of SOs in seawater is relatively low with a constant 0.05 to 0.11 µg/L. Although the concentration distribution of SOs species differs considerably depending on the sample collected, the concentration of SOs decreases in the order of styrene trimers (7 isomers) &gt; styrene dimers (4 isomers) &gt; styrene monomer. As a result of monitoring, the concentration of SOs at the sandy beaches of Jeju Island is much higher in the beach sand than in the seawater. This result means that the major beaches of Jeju Island can be polluted mainly by internal factors (e.g. population density, number of travelers according to population movement, and so on), because SOs species are adsorbed on the surface of the sand particles and their mobility is limited.Conclusions : This study shows that the sandy beaches of Jeju Island are mainly polluted by internal factors. It is thought that the pollution degree of the sandy beaches is the highest in the order of Gwakji Beach &lt; Samyang Beach, Hamdeok Beach, Pyoseon Beach &lt; Ihoteho Beach, Sagye Beach &lt; Seopjikoji Beach, Gimnyeong Beach, and Hyeopjae Beach. This study is expected to contribute to the evaluation of the causes of plastic pollution in the coastal environment of Jeju Island.