Risk assessment of e-waste - Liquid Crystal Monomers re-suspension caused by coastal dredging operations.

The Pearl River Estuary (PRE), one of the primary e-waste recycling centers in the world, has been suffering from the pollution of Liquid Crystal Monomers (LCMs), critical materials with persistent, bio-accumulative, and toxic substances used in electronic devices. It has been detected in seabed sediment with both high frequency and concentration near PRE - Hong Kong (HK) waters. In the same area, dredging operations with in-situ sediment have been frequently used in the last decades for coastal land reclamation projects. Dredging is known to cause a huge amount of sediment re-suspension into water columns, with potential damage to marine ecosystems and biodiversity. In this study, we proposed a new risk assessment strategy to estimate the secondary pollution due to the re-suspension sediment highly contaminated by LCMs. We formulate a robust and reliable probabilistic approach based on unsupervised machine learning and hydrodynamic and sediment transport numerical simulation. New risk indexes were also proposed to better quantify the impact of contaminated sediments. We applied the methodology to assess the potential impact of dredging operations in the PRE and Hong Kong waters on the local marine ecosystem. The results of the analysis showed how the potentially contaminated areas depended on the dredging locations.

Marine plastic pollution detection and identification by using remote sensing-meta analysis.

The persistent plastic litter, originating from different sources and transported from rivers to oceans, has posed serious biological, ecological, and chemical effects on the marine ecosystem, and is considered a global issue. In the past decade, many studies have identified, monitored, and tracked marine plastic debris in coastal and open ocean areas using remote sensing technologies. Compared to traditional surveying methods, high-resolution (spatial and temporal) multispectral or hyperspectral remote sensing data have been substantially used to monitor floating marine macro litter (FMML). In this systematic review, we present an overview of remote sensing data and techniques for detecting FMML, as well as their challenges and opportunities. We reviewed the studies based on different sensors and platforms, spatial and spectral resolution, ground sampling data, plastic detection methods, and accuracy obtained in detecting marine litter. In addition, this study elaborates the usefulness of high-resolution remote sensing data in Visible (VIS), Near-infrared (NIR), and Short-Wave InfraRed (SWIR) range, along with spectral signatures of plastic, in-situ samples, and spectral indices for automatic detection of FMML. Moreover, the Thermal Infrared (TIR), Synthetic aperture radar (SAR), and Light Detection and Ranging (LiDAR) data were introduced and these were demonstrated that could be used as a supplement dataset for the identification and quantification of FMML.

Performance assessment of bubbles barriers for microplastic remediation.

We report the results of experiments designed to evaluate the performance of a bubble barrier device for microplastics collection in natural and artificial streams. Bubble barrier is an innovative device based on the principle that pumping air to produce a vertical curtain of small air bubbles along the depth of a waterway creates a sufficient current to direct floating and non-floating particle towards a catchment device. The bubble barrier has been designed and already tested in rivers. Despite its use, there is a lack of information on the fluid mechanical functioning and performance, i.e., its ability to catch the largest number of microplastic particles. The aim of the present study is to test different bubble barriers configurations (length of the bubble generator, alignment with the main current) in different hydraulic conditions. We used a laboratory channel to produce a scaled river flow and we performed velocity measurements, and particle tracking visualization to understand how the bubble curtain could influence the water flow. The catchment performance of the different barriers has been tested using two types of particles, lighter and heavier than water. The results show that the system performance is strongly linked to a combination of the bubble generator configuration and the main properties of the flow. This study is the first attempt to provide scientific data on the bubble barrier and future design strategies depending on its application.

Dynamic Pressure Measurements During Vitrectomy in a Model of the Eye.

Purpose: To accurately evaluate pressure changes during vitrectomy in a rigid model of the vitreous chamber and to test the efficiency of the EVA phacovitrectomy system (Dutch Ophthalmic Research Center) in terms of compensation of intraocular pressure variations. Methods: We tested 23-, 25-, and 27-gauge double-blade vitreous cutters in both vented global pressure control and automatic infusion compensation (AIC) modes in a vitreous chamber model, mimicking the real surgical procedure. Balanced salt solution and artificial vitreous, similar to the real vitreous body, were used. We tested both standard-flow (SF) and high-flow (HF) infusion systems, varying the infusion pressure between 20 and 40 mm Hg. In each experiment, flow rate was also measured. Results: Pressure drop was rapidly and efficiently compensated when 23- and 25-gauge cutters were used in AIC mode, with infusion pressures ranging between 30 and 55 mm Hg. The 27-gauge cutter was less efficient in compensating pressure variations. Pressure fluctuations related to the high-frequency motion of the cutter blade were small compared to the overall pressure variations. The use of the HF infusion system resulted in larger flow rates and lower pressure changes compared to the SF infusion system. Conclusions: Despite the rigid material of the model, the present pressure measurements are in line with previous studies performed on porcine eye. The use of AIC mode compensates intraoperative pressure drops efficiently, with both 23- and 25-gauge cutters. The HF infusion system is more efficient than the SF infusion system. Translational Relevance: The AIC infusion mode efficiently compensates intraoperative pressure drops, in both 23- and 25-gauge experimental vitrectomy. The HF infusion system resulted in larger flow rate and lower pressure changes.

Experimental assessment of the performance of vitreous cutters with fluids with different rheological properties.

PURPOSE: To assess the influence of rheological properties of an artificial vitreous (AV) on the performance of double-blade (DB) and single-blade (SB) guillotine vitreous cutters, with 23-, 25-, and 27-gauge (G) probes. METHODS: We evaluate the aspiration flow rate, using an optical method, based on image processing. Experiments are conducted using ten viscoelastic vitreous phantoms, with different properties that are measured with rheological tests. RESULTS: Aspiration rate strongly varies with fluid properties. Regardless of cutter geometry and operational conditions, the flow rate significantly decreases as vitreous viscosity and elasticity increase. CONCLUSIONS: All tested vitreous probes are very sensitive to changes in fluid rheology. SB cutters produce smaller flow rates compared with DB ones of the same caliber; however, they are less sensitive to fluid properties at low aspiration pressures. The use of vitreous substitutes for test performance guarantees comparability between flow rate results achieved with different vitrectomy systems operating in different media. This outcome is further confirmed by the low values of estimated flow rate relative errors.

Fluid Dynamic Assessment of Hypersonic and Guillotine Vitrectomy Probes in Viscoelastic Vitreous Substitutes.

Purpose: To assess the fluidics of 23-gauge (G) large-port (L) and tear drop-port (TD) hypersonic vitrectomy probes (HVPs) compared with guillotine vitrectomy probes (GVPs) of various calibers (23G, 25G, and 27G) and geometries (single and double blades). Also, to identify the working parameters that provide the best balance between acceleration and flow rate, and, for HVPs, to measure temperature variations in the fluid. Methods: We used particle image velocimetry to measure flow fields in balanced salt solution and viscoelastic artificial vitreous. We analyzed acceleration, kinetic energy, and volumetric flux. The parameters considered were vacuum pressure, ultrasound stroke, and cut rate. Temperature measurements were taken using an infrared thermal camera. Results: The flow rate was significantly higher for HVPs than GVPs. With both probes, flow rate and acceleration increased with vacuum pressure. Flow rate depended weakly on the ultrasound stroke or cut rate. In HVPs, the acceleration peaked at a stroke of 30 µm, whereas in GVPs it peaked at a cutting rate of 4000 to 5000 cuts per minute (cpm). The HPV/TD combination generated higher flow rates and lower accelerations than did HPV/L. The increase in temperature was small. Conclusions: Under the present experimental setup and medium, HVPs offered better fluidics compared with GVPs in terms of flow and acceleration; however, the flow structure for HVPs is more complicated and unsteady. The HPV/TD combination produced larger flows than did the HPV/L combination and slightly smaller accelerations. HPVs generated a small temperature increase. Translational Relevance: In the tested artificial vitreous, HVPs were found to be more efficient in terms of generating lower acceleration for a given flow rate. The slight increase in temperature observed with HVPs is unlikely to be clinically significant.

Correction to: Microplastics in seawater: sampling strategies, laboratory methodologies, and identification techniques applied to port environment.

The article Microplastics in seawater: sampling strategies, laboratory methodologies, and identification techniques applied to port environment.

Behaviour of plastic litter in nearshore waters: First insights from wind and wave laboratory experiments.

Plastic litter in nearshore waters is an environmental pollutant with increasing impact on coastal environments. At present, knowledge on basic plastic particle dynamics and the interaction with complex hydrodynamics is lacking. The present laboratory study, performed under controlled wave and wind conditions, demonstrates the dispersion of plastics in shallow waters. The study presents a simple case looking solely at cross-shore particle transport. The results show that both wind and waves as well as plastic properties (shape and density) govern the behaviour of plastic litter in the nearshore zone. Heavy particles behave like natural sand with accumulation in the wave breaking zone. Light particles have varying accumulation along the coastal profile depending on the wind, waves and particle shapes. More extensive characterization remains to be done in future studies.

Microplastics in seawater: sampling strategies, laboratory methodologies, and identification techniques applied to port environment.

The European Interreg Italy-France 2014-2020 Maritime Project SPlasH! (Stop to Plastics in H2O!) focused on the study of microplastics (MPs) in the marine port environment to evaluate their presence, abundance, and mechanisms of diffusion to the open sea. In the framework of this project, a worldwide review of 74 studies was carried out, providing an overview of MP investigation techniques, focusing on sampling strategies, laboratory methodologies, and identification of MPs collected in seawater, and specifically evaluating their applicability to the marine port environment. Nets were the most commonly used device for MP surface sampling, but their use can be difficult in narrow spaces within the port basins, and they must be coupled to discrete sampling devices to cover all port basins. In the laboratory, density separation (NaCl, ZnCl2, NaI, sodium lauryl sulfate (SLS)), filtration (polycarbonate, polyamide, glass, cellulose, ANOPORE inorganic membrane filters), sieving, visual sorting, and digestion methods (acidic, enzymatic, alkaline, oxidative) were used to separate MPs from seawater. Digestion becomes essential with water samples with great inorganic and organic loads as deriving from a port. Although many studies are based only on visual MP identification under a microscope, analytical identification techniques unequivocally determine the particle nature and the identity of the plastic polymers and are necessary to validate the visual sorting of MPs. Fourier-transform infrared spectroscopy (FTIR) is the most used analytical identification technique.

Influence of initial conditions on absolute and relative dispersion in semi-enclosed basins.

Absolute and relative dispersion are fundamental quantities employed in order to assess the mixing strength of a basin. There exists a time scale called Lagrangian Integral Scale associated to absolute dispersion that highlights the occurrence of the transition from a quadratic dependence on time to a linear dependence on time. Such a time scale is commonly adopted as an indicator of the duration needed to lose the influence of the initial conditions. This work aims to show that in a semi-enclosed basin the choice of the formulation in order to calculate the absolute dispersion can lead to different results. Moreover, the influence of initial conditions can persist beyond the Lagrangian Integral Scale. Such an influence can be appreciated by evaluating absolute and relative dispersion recursively by changing the initial conditions. Furthermore, finite-size Lyapunov exponents characterize the different regimes of the basin.

Fluidics of Single and Double Blade Guillotine Vitrectomy Probes in Balanced Salt Solution and Artificial Vitreous.

PURPOSE: To assess the fluidics of double-vitreous cutter blade (DB) compared with single-blade (SB) guillotine with 23-, 25-, and 27-gauge vitrectomy probes. To assess flow characteristics and flow rates in viscous and viscoelastic fluids. METHODS: We used Particle Image Velocimetry to measure the flow field close to the tip of each cutter probe and we derived kinematic quantities of interest, such as kinetic energy and acceleration. We performed measurements both on a balanced salt solution (BSS) and on a viscoelastic artificial vitreous (AV). RESULTS: The flow rate is significantly higher with DB than SB vitrectomy probes, for a given pumping pressure and cutting rate. The fluid flow observed is very different between BSS and AV tests. CONCLUSIONS: The DB has more efficient fluidics than SB vitrectomy probe in all tested conditions. Fluid acceleration depends on the cutting frequency, especially in the case of measurements in AV. The flow rate strongly depends on the pressure and it is little affected by the cutting frequency, in a range of clinical interest. The 27-G DB produces flow rates similar to the 23- and 25-G SB, with significantly smaller acceleration. The flow induced in the AV is different from that in BSS and oscillates at different frequencies. TRANSLATIONAL RELEVANCE: DB cutters prove to be more efficient in terms of lower acceleration for a given flow rate. The latter is mainly controlled by aspiration pressure and less by cut rates. The influence of vitreous rheology deserves further investigations.

In Vitro Evaluation of Upstream and Downstream Influences on Blood Pressure of the Hybrid Treatment of Thoracoabdominal Aortic Aneurysms.

BACKGROUND: The aim of our study was to assess, by means of an experimental model, whether different geometries in retrograde bypass and stent-graft deployment may affect upstream and downstream blood pressure in hybrid treatment. METHODS: An in vitro model of the arterial circulation has been prepared, which consists of a peristaltic pump, silicon tubes with geometrical and mechanical properties close to realistic arteries, a terminal reservoir kept at constant pressure, and a sequence of pressure transducers. The system allows us to study the pressure wave propagation in physiological conditions and simulate the patient's conditions as a result of debranching in 2 different configurations. RESULTS: In configuration 1, the mean pressure value (Kpa) was 4.72 in silicone tube before stent graft and debranching, 4.59 in visceral and renal bypass, and 4.38 in silicone tube after stent graft and debranching. In configuration 2, the mean pressure value (Kpa) was 5.22 in silicone tube before stent graft and debranching, 4.48 in visceral and renal bypass, and 4.99 in silicone tube after stent graft and debranching. CONCLUSION: The experimental data suggest that the debranching geometry and the material of the grafts and stent grafts change significantly the physiological arterial pressure possibly leading to an augmented pressure upstream of the stent grafts, owing to retrograde pressure waves toward the heart, and a decreased pressure downstream visceral and renal arteries.

An experimental model of vitreous motion induced by eye rotations.

BACKGROUND: During eye rotations the vitreous humour moves with respect to the eye globe. This relative motion has been suggested to possibly have an important role in inducing degradation of the gel structure, which might lead to vitreous liquefaction and/or posterior vitreous detachment. Aim of the present work is to study the characteristics of vitreous motion induced by eye rotations. METHODS: We use an experimental setup, consisting of a Perspex model of the vitreous chamber that, for simplicity, is taken to have a spherical shape. The model is filled with an artificial vitreous humour, prepared as a solution of agar powder and hyaluronic acid sodium salt in deionised water, which has viscoelastic mechanical properties similar to those of the real vitreous. The model rotates about an axis passing through the centre of the sphere and velocity measurements are taken on the equatorial plane orthogonal to the axis of rotation, using an optical technique. RESULTS: The results show that fluid viscoelasticity has a strong influence on flow characteristics. In particular, at certain frequencies of oscillation of the eye model, fluid motion can be resonantly excited. This means that fluid velocity within the domain can be significantly larger than that of the wall. CONCLUSIONS: The frequencies for which resonant excitation occurs are within the range of possible eye rotations frequencies. Therefore, the present results suggest that resonant excitation of vitreous motion is likely to occur in practice. This, in turn, implies that eye rotations produce large stresses on the retina and within the vitreous that may contribute to the disruption of the vitreous gel structure. The present results also have implications for the choice of the ideal properties for vitreous substitute fluids.

Investigation of the motion of a viscous fluid in the vitreous cavity induced by eye rotations and implications for drug delivery.

Intravitreal drug delivery is a commonly used treatment for several retinal diseases. The objective of this research is to characterize and quantify the role of the vitreous humor motion, induced by saccadic movements, on drug transport processes in the vitreous chamber. A Perspex model of the human vitreous chamber was created, and filled with a purely viscous fluid, representing eyes with a liquefied vitreous humor or those containing viscous tamponade fluids. Periodic movements were applied to the model and the resulting three-dimensional (3D) flow fields were measured. Drug delivery within the vitreous chamber was investigated by calculating particle trajectories using integration over time of the experimental velocity fields. The motion of the vitreous humor generated by saccadic eye movements is intrinsically 3D. Advective mass transport largely overcomes molecular diffusive transport and is significantly anisotropic, leading to a much faster drug dispersion than in the case of stationary vitreous humor. Disregarding the effects of vitreous humor motion due to eye movements when predicting the efficiency of drug delivery treatments leads to significant underestimation of the drug transport coefficients, and this, in turn, will lead to significantly erroneous predictions of the concentration levels on the retina.

Ultrasound imaging velocimetry of the human vitreous.

Knowledge of vitreous motion in response to saccades is a prerequisite for understanding vitreous rheology. Purpose of present paper is to introduce Ultrasound Image Velocimetry of the human eye, measure scleral and vitreous velocity fields and test the reproducibility of the proposed technique. Twelve patients with varying diagnosis underwent Ocular Dynamic Ultrasound; scleral angular velocity (V(S)) was measured by 2 different operators and reproducibility calculated. Squared velocity of the vitreous (E), which is representative of kinetic energy per unit mass, was computed from velocity. The time evolution of the energy of the vitreous was described by its spatial average (E(S)), whereas spatial distribution was described by its time average (E(T)). Peak and average E(S), the ratio K(p) of the peak of the spatially averaged kinetic energy per unit mass to the maximum squared scleral angular velocity, vitreous motion onset time (T(O)) and vitreous motion decay time (T(D)) were also defined. Inter-operator reproducibility coefficient was 0.043 and correlation between operators was significant. V(S), peak and average E(S), K(p) ratio and T(D) differed among patients but not among operators. V(S) correlated with E(S) and T(D). E(S) and T(D) but not V(S), were significantly different in patients with Posterior Vitreous Detachment. Patients with retinal detachment showed significantly higher V(S) and E(S). K(p) was inversely correlated to age and refraction. Measures proved accurate and reproducible. E is related to V(S), retinal traction and mechanical stimulation. Identified variables varied with age, refraction pathologic conditions.

Barriers to transport induced by periodic oscillations in a physical model of the human vitreous chamber.

Understanding mixing processes that occur in the human vitreous chamber is of fundamental importance due to the relevant clinical implications in drug delivery treatments of several eye conditions. In this article we rely on experimental observations (which demonstrated that dispersion coefficients largely dominate diffusive coefficients) on a physical model of the human eye to perform an analysis based on Lagrangian trajectories. In particular, we study barriers to transport in a particularly significant two-dimensional section of the eye model by using nonlinear dynamical systems theoretical and numerical tools. Bifurcations in the system dynamics are investigated by varying the main physical parameters of the problem.

Mixing processes in the vitreous chamber induced by eye rotations.

In this paper, we study a model of flow in the vitreous humour in the posterior chamber of the human eye, induced by saccadic eye rotations. We concentrate on the effect of the shape of the chamber upon the mixing properties of the induced flows. We make particle image velocimetry measurements of the fluid velocity in a transparent plastic (Perspex) model of the posterior chamber during sinusoidal torsional oscillations about a vertical axis. We use a Newtonian fluid to model the vitreous humour, which is most realistic when either the vitreous humour is liquefied or has been replaced by purely viscous tamponade fluids. The model of the posterior chamber is a sphere with an indentation, representing the effect of the lens. In spite of the purely periodic forcing, a steady streaming flow is generated, which plays a fundamental role in the mixing processes in the domain. The streaming flow differs markedly from that in a perfect sphere, and its topological characteristics change substantially as the frequency of oscillation varies. We discuss the flow characteristics in detail and show that, for physiological parameter values, the Péclet number (based on a suitable measure of the steady streaming velocity) is large, suggesting that advection strongly dominates over diffusion for mass transport phenomena. We also compute particle trajectories based on the streaming velocity and use these to investigate the stirring properties of the flow.

Eye rotation induced dynamics of a Newtonian fluid within the vitreous cavity: the effect of the chamber shape.

The dynamics of the vitreous body induced by eye rotations is studied experimentally. In particular, we consider the case in which the vitreous cavity is filled by a Newtonian fluid, either because the vitreous is liquefied or because it has been replaced, after vitrectomy, by a viscous fluid. We employ a rigid Perspex container which models, in a magnified scale, the vitreous cavity of the human eye. The shape of the cavity closely resembles that of the real vitreous chamber; in particular, the anterior part of the container is concave in order to model the presence of the eye lens. The container is filled with glycerol and is mounted on the shaft of a computer-controlled motor which rotates according to a periodic time law. PIV (particle image velocimetry) measurements are taken on the equatorial plane orthogonal to the axis of rotation. The experimental measurements show that the velocity field is strongly influenced by the deformed geometry of the domain. In particular, the formation of a vortex in the vicinity of the lens, which migrates in time towards the core of the domain, is invariably observed. The vortex path is tracked in time by means of a vortex identification technique and it is found that it is significantly influenced by the Womersley number of the flow. Particle trajectories are computed from the PIV measurements. Particles initially located at different positions on the equatorial horizontal plane (perpendicular to the axis of rotation) tend to concentrate in narrow regions adjacent to the lens, thus suggesting the existence, in such regions, of a vertical fluid ejection. Such a strong flow three-dimensionality, which is essentially induced by the irregular shape of the domain, may play a significant role in the mixing processes taking place inside the eye globe. The tangential stresses acting on the rigid boundary of the domain are also computed from the experimental measurements showing that regions subject to particularly intense stresses exist along the boundary close to the lens.

Experimental investigation of vitreous humour motion within a human eye model.

We present an experimental study of the vitreous motion induced by saccadic eye movements. A magnified model of the vitreous chamber has been employed, consisting of a spherical cavity carved in a perspex cylindrical container, which is able to rotate with a prescribed time law. Care has been taken to correctly reproduce real saccadic eye movements. The spherical cavity is filled with glycerol and the flow field is measured on the equatorial plane orthogonal to the axis of rotation, through the PIV technique. Visualizations of the fully three-dimensional flow suggest that it essentially occurs on planes perpendicular to the axis of rotation, the motion orthogonal to such planes being smaller by three to four orders of magnitude. Theoretical results, based on a simplified solution, are in very good agreement with the experimental findings. The maximum value of the shear stress at the wall, which is thought to play a possibly important role in the pathogenesis of retinal detachment, does not significantly depend on the amplitude of saccadic movements. This suggests that relatively small eye rotations, being much more frequent than large movements, are mainly responsible for vitreous stresses on the retina. Results also illustrate the dependence of the maximum shear stress at the wall from the vitreous viscosity.