Particles In Natural Waters Research Articles

Chitosan in the treatment of mine spoil rainwater - An approach to protect the aquatic biota

The mining industry suppresses vegetation, exposing large soil areas in its ordinary operation. Water pollution and turbidity are caused by the carrying of solids, mainly colloidal particles, to the watercourses due to the effect of rainfall events. Therefore, the discharge of those effluents will lead to failure with watercourse quality parameters. Thus, there is a need to treat drainages (rainwaters) from the mining industry. However, using common coagulants and flocculants can result in acute or chronic ecotoxicity for aquatic biota. In this scenario, this research aimed to evaluate using a natural coagulant, the biopolymer Chitosan, to remove turbidity from mining industry spoiled water through bio-coagulation. The ecotoxicity of the natural coagulant was compared to the commonly used coagulants. For this purpose, we used synthetic rainwater (SRW) from the dispersion of fine (colloidal) particles in natural waters. Materials (water and soil) were collected in the mining area's sumps (sedimentation basins). The turbidity of the produced SRW ranged from between 500 and 4000 NTU. Jar Tests using Chitosan (CTS), polyaluminum chloride (PAC®12), and Superfloc®N100 variable doses were carried out to compare the effects of the coagulating/flocculating agents on the SRW turbidity reduction. The obtained results demonstrated the efficiency of CHS on turbidity reduction. The results were encouraging for low turbidity samples (<1000 NTU), making it possible to meet the limit parameters recommended by the Brazilian legislation. In addition, it was possible to conclude both CHS and the effluents treated with this coagulant have lower toxicity to aquatic biota than the combination of PAC®12 and Superfloc®N100.

Polarized lidar and ocean particles: insights from a mesoscale coccolithophore bloom.

Oceanographic lidar can provide remote estimates of the vertical distribution of suspended particles in natural waters, potentially revolutionizing our ability to characterize marine ecosystems and properly represent them in models of upper ocean biogeochemistry. However, lidar signals exhibit complex dependencies on water column inherent optical properties (IOPs) and instrument characteristics, which complicate efforts to derive meaningful biogeochemical properties from lidar return signals. In this study, we used a ship-based system to measure the lidar attenuation coefficient (α) and linear depolarization ratio (δ) across a variety of optically and biogeochemically distinct water masses, including turbid coastal waters, clear oligotrophic waters, and calcite rich waters associated with a mesoscale coccolithophore bloom. Sea surface IOPs were measured continuously while underway to characterize the response of α and δ to changes in particle abundance and composition. The magnitude of α was consistent with the diffuse attenuation coefficient (Kd), though the α versus Kd relationship was nonlinear. δ was positively related to the scattering optical depth and the calcite fraction of backscattering. A statistical fit to these data suggests that the polarized scattering properties of calcified particles are distinct and contribute to measurable differences in the lidar depolarization ratio. A better understanding of the polarized scattering properties of coccolithophores and other marine particles will further our ability to interpret polarized oceanographic lidar measurements and may lead to new techniques for measuring the material properties of marine particles remotely.

Discovery of High Abundances of Aster-Like Nanoparticles in Pelagic Environments: Characterization and Dynamics.

This study reports the discovery of Aster-Like Nanoparticles (ALNs) in pelagic environments. ALNs are pleomorphic, with three dominant morphotypes which do not fit into any previously defined environmental entities [i.e., ultramicro-prokaryotes, controversed nanobes, and non-living particles (biomimetic mineralo-organic particles, natural nanoparticles or viruses)] of similar size. Elemental composition and selected-area electron diffraction patterns suggested that the organic nature of ALNs may prevail over the possibility of crystal structures. Likewise, recorded changes in ALN numbers in the absence of cells are at odds with an affiliation to until now described viral particles. ALN abundances showed marked seasonal dynamics in the lakewater, with maximal values (up to 9.0 ± 0.5 × 107 particles·mL−1) reaching eight times those obtained for prokaryotes, and representing up to about 40% of the abundances of virus-like particles. We conclude that (i) aquatic ecosystems are reservoirs of novel, abundant, and dynamic aster-like nanoparticles, (ii) not all virus-like particles observed in aquatic systems are necessarily viruses, and (iii) there may be several types of other ultra-small particles in natural waters that are currently unknown but potentially ecologically important.

Evaluation of continuous flow centrifugation as an alternative technique to sample microplastic from water bodies

The scientific and public interest regarding environmental pollution with microplastic has considerably increased within the last 15 years. Nevertheless, up to now there is no widely applied standard operation procedure for microplastic sampling, resulting in a lack of inter-study comparability. In addition, many studies on microplastic occurrences do not indicate a sound methodological validation of the applied methods and procedures. This study presents an alternative volume-reduced sampling technique to sample the entire load of suspended particulate matter including microplastic particles in natural waters, based on continuous flow centrifugation. For the lab-scale validation of the proposed instrumental setup, six different microplastic types (PE, PET, PS, PVDC, EPS and PP) were used. The particles covered a size range from 1 μm to 1 mm and a density range from 0.94 g mL-1 to 1.63 g mL-1. Recoveries ranged from 95.0% ± 2.3% - 99.1% ± 0.3% for virgin powders and from 96.1% ± 0.6% - 99.4% ± 0.2% (1 SD, n = 2 - 3) for microplastic suspended in river water for 40 days. Gravimetric and microscopic analysis of the effluent indicates efficient removal of microplastic from the suspensions. Static light scattering analysis of the microplastic suspensions prior to and after centrifugation confirmed that no change of the particle size distribution has occurred – neither through aggregation nor through size-discrimination during centrifugation. Moreover, the system was tested in the field and used twice to sample suspended particulate matter from the Elbe estuary directly on site. Based on these first lab-scale experiments, continuous flow centrifugation proves a promising technique bearing potential to alleviate drawbacks such as contamination, filter clogging and particle size-discrimination of commonly used volume-reduced microplastic sampling approaches.

Interactions between nano/micro plastics and suspended sediment in water: Implications on aggregation and settling

Interactions between nano/microplastics and suspended sediment (SS) in natural waters are important for the environmental fate of plastic particles. This study investigated the effect of heteroaggregation between nano/microplastics and SS on the settling of aggregates. In NaCl solutions (0.05–0.5 M), large SS (100–500 μm in diameter) significantly increased the settling ratio of polystyrene nanoplastics (PSNPs) with an average diameter of 100 nm due to the formation of PSNPs-SS aggregates. The settling ratio of the heteroaggregates increased significantly when the NaCl concentration increased from 50 to 200 mM. This was primarily because higher ionic strength reduced the electrostatic repulsion between large SS and PSNPs, and subsequently increased the heteroaggregation rate. No obvious differences in settling ratios were observed in 200 or 500 mM NaCl solutions because the heteroaggregation entered the diffusion-controlled regime. However, in HA solutions (10–50 mg L−1), the surface adsorption of HA on PSNPs and large SS reduced the heteroaggregation of PSNPs-SS and thus led to the low co-settling ratio due to the steric hindrance according to the DLVO theory. In contrast, polyethylene microplastics (PEMPs) with diameters of 1.0–1.2 mm were found to always float on water surface (up to 8 months), even after addition of 500 mg L−1 small SS (<10 μm in diameter). Clearly, the heteroaggregation of PEMPs and small SS had minor effect on the settling of PEMPs due to the overwhelming boyanccy. These results provided new insight into the fate and distribution of nano/microplastics in aquatic environment, which affect the bioavailability of plastic particles in natural waters.

Remote sensing of optical characteristics and particle distributions of the upper ocean using shipboard lidar

Passive ocean color remote sensing has revolutionized our ability to quantify the horizontal distribution of phytoplankton across the ocean surface. Lidar technology can provide remotely sensed estimates of the vertical distribution of optical properties and suspended particles in natural waters, significantly improving our ability to model upper ocean biogeochemical processes. In this study, we constructed and deployed a ship-based lidar system to measure laser backscattering and linear depolarization profiles in the coastal Mid-Atlantic ranging from estuarine to oceanic conditions, and across the Gulf of Maine (GoM). The instrument identified layers with different backscattering intensity in stratified waters of the coastal Mid-Atlantic and produced system attenuation coefficients (Ksys) approximating the absorption coefficient (apg) of particulate + dissolved matter. The linear depolarization ratio was strongly related to in situ measurements of the particulate backscattering ratio (bbp/bp). Measurements of Ksys and linear depolarization made across the GoM corresponded well with simultaneous in situ observations performed aboard the M/V Nova Star and by an autonomous glider deployed along the transect. The relationship between Ksys and apg differed between sampling schemes, likely due to differences in the deployment geometries (e.g., height, nadir angle). These results support the proposition that ship-based lidar systems can provide a powerful tool for remotely measuring the vertical distributions of optical properties and geochemical constituents (e.g., particles) in the upper ocean. Continued development of compact lidar systems for deployment on ships, moorings, and autonomous platforms has the potential to greatly improve the quality and scope of a variety of oceanographic investigations.

A comparison between determination of trace amounts of sulfide in the presence and absence of micelle particles in natural waters (Qazvin, Iran): a kinetic spectrophotometric approach.

A new sensitive kinetic spectrophotometric method described for the determination of trace amounts of sulfides based on the addition reaction of sulfide ions with malachite green has been investigated in aqueous and micellar media at 25°C. The variables affecting the rate of the reaction were investigated, and the optimum conditions were established. Under the optimum experimental conditions, decreases in the absorbance of malachite green at 615nm in the absence and 630nm in the presence of micelle particles, their λ max, were proportional to the concentrations of sulfide ions at the first 15 and 25s from initiation of the reaction. The working curve was linear over the concentration range 50-1200ngmL(-1) of sulfide ions with a fixed time method at the first 15 and 25s from initiation of the reaction in aqueous medium and 25-1750ngmL(-1) with a fixed time method at the first 15s and 25-1500ngmL(-1) for primitive 25s in micellar medium. For the proposed kinetic method, the experimental and theoretical limit of detection (LOD) and limit of quantification (LOQ) in the presence and absence of micelle particles were obtained and tabulated at Δt = 15 and 25s. The effective range concentration was achieved from the plot of Ringbom in both media and reported. Different surfactants, such as nonionic surfactant (Triton-X100), anionic surfactant sodium dodecyl sulfate (SDS), and cationic surfactant cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC), were investigated and Triton X-100 selected as a suitable surfactant. To valuable vision into the reaction pathways, pseudo-first-order condition was applied and different kinetic parameters like ΔG (≠), ΔE (≠), ΔS (≠), and ΔH (≠) computed. The 2:1 stoichiometry of malachite green to sulfide ions was indicated by the results of mole ratio and Job's method of continuous variation. The effect of different environments on the interfering of various ions on sulfide determination with the suggested method was studied, and final results have been presented. To investigate the usefulness of the different media of the proposed method, sulfide ions were determined in natural waters such as river and spring samples without any purification or using masking reagents.

Experimental Investigation of the Effect of Flow Turbulence on the Adsorption of Phosphorus onto Sediment Particles

The mechanism of flow turbulence, sediment concentration and sediment grain size that effect the adsorption of phosphorus (P) onto sediment particles in natural waters are experimentally studied both in batch reactors and in an oscillating grid turbulence simulation device. In batch reactor experiments, both of phosphorus sorption isotherms and phosphorus sorption kinetics were studied, and the experimental data was fitted by Langmuir sorption model. The results indicated that both of the phosphorus sorption capacity and phosphorus sorption efficiency are closely related to sediment concentration and sediment grain size. In the oscillating grid turbulence simulation device, it is possible to control the turbulence intensity in two ways, by changing the frequency of the grid and controlling the oscillating stroke. According to this characteristic, the effect of flow turbulence on the adsorption of phosphorus onto sediment particles was experimentally simulated. Then a 1DV model is introduced in this paper to simulate sediment transport and phosphate sorption kinetics process.

Using solid-phase microextraction to evaluate the role of different carbon matrices in the distribution of PAHs in sediment-porewater systems of the Baltic Sea

Purpose The speciation of polycyclic aromatic hydrocarbons (PAHs) in sediment-porewater systems affects both the chemical fate and bioavailability of these compounds. PAHs may be dissolved or sorbed to sediment particles or dissolved organic carbon (DOC). Furthermore, soot carbon has been shown to control the sorption of PAHs onto particles in natural waters. The present study investigates the distribution of individual PAHs among these three phases by examining sediments from the western Baltic Sea, focusing on a highly contaminated former dumping area and evaluating the importance of soot-carbon partitioning.

Experimental investigation of the effect of flow turbulence and sediment transport patterns on the adsorption of cadmium ions onto sediment particles

The mechanism of flow turbulence, sediment supply conditions, and sediment transport patterns that affect the adsorption of cadmium ions onto sediment particles in natural waters are experimentally simulated and studied both in batch reactors and in a turbulence simulation tank. By changing the agitation conditions, the sediment transport in batch reactors can be categorized into bottom sediment-dominated sediment and suspended sediment-dominated sediment. It is found that the adsorption rate of bottom sediment is much less than that of suspended sediment, but the sediment transport pattern does not affect the final (equilibrium) concentration of dissolved cadmium. This result indicates that the parameters of an adsorption isotherm are the same regardless of the sediment transport pattern. In the turbulence simulation tank, the turbulence is generated by harmonic grid-stirred motions, and the turbulence intensity is quantified in terms of eddy diffusivity, which is equal to 9.84 F ( F is the harmonic vibration frequency) and is comparable to natural surface water conditions. When the turbulence intensity of flow is low and sediment particles stay as bottom sediment, the adsorption rate is significantly low, and the adsorption quantity compared with that of suspended sediment is negligible in the 6 h duration of the experiment. This result greatly favors the simplification of the numerical modeling of heavy metal pollutant transformation in natural rivers. When the turbulence intensity is high but bottom sediment persists, the rate and extent of descent of the dissolved cadmium concentration in the tank noticeably increase, and the time that is required to reach adsorption equilibrium also increases considerably due to the continuous exchange that occurs between the suspended sediment and the bottom sediment. A comparison of the results of the experiments in the batch reactor and those in the turbulence simulation tank reveals that the adsorption ability of the sediment, and in particular the adsorption rate, is greatly over-estimated in the batch reactor.

Environmental Colloids and Particles: Behaviour, Separation and Characterisation

List of Contributors. Series Preface. Preface. 1 Environmental Colloids and Particles: Current Knowledge and Future Developments (Jamie R. Lead and Kevin J. Wilkinson). 2 Colloidal Properties of Submicron Particles in Natural Waters (Montserrat Filella). 3 Colloid-Trace Element Interactions in Aquatic Systems (Frederic J. Doucet, Jamie R. Lead and Peter H. Santschi). 4 Ultrafiltration and its Applications to Sampling and Characterisation of Aquatic Colloids (Laodong Guo and Peter H. Santschi). 5 Characterisation of Aquatic Colloids and Macromolecules by Field-flow Fractionation (Martin Hassell ov, Frank von der Kammer and Ronald Beckett). 6 Modern Electrophoretic Techniques for the Characterisation of Natural Organic Matter (Philippe Schmitt-Kopplin and Jens Junkers). 7 Electrophoresis of Soft Colloids: Basic Principles and Applications (Jerome F. L. Duval). 8 Strategies and Advances in the Characterisation of Environmental Colloids by Electron Microscopy (Denis Mavrocordatos, Didier Perret and Gary G. Leppard). 9 Force Microscopy and Force Measurements of Environmental Colloids (Eric Balnois, Georg Papastavrou, and Kevin J. Wilkinson). 10 Laser Scanning Microscopy for Microbial Flocs and Particles (John R. Lawrence and Thomas R. Neu). 11 Study of Environmental Systems by Means of Fluorescence Correlation Spectroscopy (Nicolas Fatin-Rouge and Jacques Buffle). 12 Laser-induced Breakdown Detection (Jae-il Kim and Clemens Walther). 13 Probing Environmental Colloids and Particles with X-rays (Jean-Francois Gaillard). Index.

Impact of iron particles in groundwater on the UV inactivation of bacteriophages MS2 and T4

To investigate the impact of iron particles in groundwater on the inactivation of two model viruses, bacteriophages MS2 and T4, by 254-nm ultraviolet (UV) light. One-litre samples of groundwater with high iron content (from the Indianapolis Water Company, mean dissolved iron concentration 1.3 mg l(-1)) were stirred vigorously while exposed to air, which oxidized and precipitated the dissolved iron. In parallel samples, ethylenediaminetetra-acetic acid (EDTA) was added to chelate the iron and prevent formation of iron precipitate. The average turbidity in the samples without EDTA (called the 'raw' samples) after 210 min of stirring was 2.7 +/- 0.1 NTU while the average turbidity of the samples containing EDTA (called the 'preserved' samples) was 1.0 +/- 0.1 NTU. 'Raw' and 'preserved' samples containing bacteriophage MS2 were exposed to 254-nm UV light at doses of 20, 40, or 60 mJ (cm(2))(-1), while samples containing bacteriophage T4 were exposed to 2 or 5 mJ (cm(2))(-1), using a low pressure UV collimated beam. The UV inactivation of both phages in the 'raw' groundwater was lower than in the EDTA-'preserved' groundwater to a statistically significant degree (alpha = 0.05), due to the association of phage with the UV-absorbing iron precipitate particles. A phage elution technique confirmed that a large fraction of the phage that survived the UV exposures were particle-associated. Phages that are associated with iron oxide particles in groundwater are shielded from UV light to a measurable and statistically significant degree at a turbidity level of 2.7 NTU when the phage particle association is induced under experimental conditions. While the particle association of the phage in this study was induced experimentally, the findings provide further evidence that certain particles in natural waters and wastewaters (e.g. iron oxide particles) may have the potential to shield viruses from UV light.

Forces between colloid particles in natural waters.

The origin and nature of interparticle forces acting on colloid surfaces in natural waters has been examined using an atomic force microscope. Natural colloids were represented by a surface film of iron oxide precipitated onto spherical SiO2 particles, and the effects of adsorbed natural organic matter (NOM), solution pH, and ionic composition on the force-separation curves were investigated. NOM from both riverine and marine environments was strongly adsorbed to the iron oxide surface. Under conditions of low ionic strength, the interparticle forces were dominated by electrostatic repulsion arising from negative functional groups on the NOM, except at very small separations (<10 nm) where repulsive forces arising from steric interference of the NOM molecules were also present. At high ionic strength (e.g., seawater) or low pH, the electrostatic forces were largely absent, allowing steric repulsion forces to dominate. In addition, adhesive bridging between surfaces by adsorbed NOM was observed, creating a strong energy barrier to spontaneous disaggregation of colloid aggregates. Our results demonstrate that adsorbed NOM dominates the surface forces and thus stability with respect to aggregation of natural water colloids.

Role of Soot Carbon and Other Carbon Matrices in the Distribution of PAHs among Particles, DOC, and the Dissolved Phase in the Effluent and Recipient Waters of an Aluminum Reduction Plant

The speciation of polycyclic aromatic hydrocarbons (PAHs) in natural waters affects both the chemical fate and the bioavailability of these compounds. PAHs may be dis solved or sorbed to particles or dissolved organic carbon (DOC). Furthermore, soot carbon has recently been shown to control the sorption of PAHs onto particles in natural waters. The present study investigated the distribution of individual PAHs among these three phases by examining the effluent and recipient waters of a Soderberg aluminum plant and evaluating the importance of soot carbon partitioning. The results showed that soot carbon may control partitioning between the dissolved and particulate phases and that the partition coefficients were orders of magnitude higher than would be expected on the basis of organic carbon−water partitioning alone. The carbon-normalized partition coefficient for the distribution of individual PAHs between DOC and the dissolved phase (KDOC) exhibited no more than a weak correlation with hydrophobicity (K...

Electrokinetic properties of oxide particles in natural waters

Microelectrophoresis measurements have been made on haematite and on quartz particles equilibrated with and dispersed in two different river waters; a basic hard water obtained from the Sherston Avon (SA) and an acidic soft water obtained from Whitray Beck (WB). Information concerning the reversibility of surface-modifying adsorption processes has been obtained from studies of the effects of extensive washing of river-water-equilibrated particles with distilled water and with indifferent electrolyte solutions. Additional information concerning the influences of specific river water constituents on the oxide surface properties has been obtained from electrokinetic studies of particles dispersed in synthetic electrolyte solutions. The results obtained indicate that in the case of haematite, the surface electrical properties are controlled by a combination of inorganic cation and organic anion interactions with the particle surfaces. Whilst adsorbed cation species were found to be readily and completely removed from the particle surfaces by washing the particles with simple electrolyte solutions, adsorbed organic anion materials were found to be held far more tenaciously. This evidence suggests that the combined effects of cation and anion species on the surface electrical properties of haematite dispersed in these river waters arises either by the adsorption of these species at different surface sites or by adsorbed anions providing surface sites for cation species. Organic anion interactions with haematite particles appear to occur to essentially the same extent in the different river waters in spite of the significantly different pH values (pH ≈ 8.4 for SA pH ≈ 5.5 for WB) and humic concentrations (3 mg dm −3 for SA, 7 mg dm −3 for WB) of the two waters. In the case of quartz particles, surface interactions with organic anion species present in the river waters are of negligible importance with regard to modification of the surface electrical properties. The quartz surface properties appear to be determined essentially by interactions with inorganic cations, principally Ca 2+ and Mg 2+ in the basic SA water, and additionally, Al species in the acidic WB water.

Size-Distribution Analysis of Sub-Micron Colloidal Particles in River Water

The particle size spectra of sub-micron colloidal particles collected from a river water, the Water of Leith in Dunedin, New Zealand, have been determined by transmission electron microscopy (TEM). Particles were isolated onto hydrophilic carbon films by ultracentrifugation at 300,000 g for 1 hr. Size spectra were found to conform to a power-law size distribution dn/dr = A r − s, behaviour also found for much larger-sized particles in natural waters and marine colloids. Values of the exponent s for unfiltered samples were in the range 2.3–2.9, consistent with Brownian aggregation as the principal mechanism maintaining the size spectrum. Comparison with spectra obtained from sampled prefiltered through Nuclepore 0.4µm filters showed clear evidence of particle removal down to 100–120 nm radius by filtration. Particles exhibited a range of electron densities under TEM, indicating a mixture of inorganic minerals and organic matter in the colloidal size range. Examples of fractal aggregates were also found.

Adsorption of poly(ethylene glycol) s on mercury/aqueous solution interface 2. Influence of the chain length

The adsorption on a mercury/aqueous solution interface of poly(ethylene glycol)s (PEGs) with molecular weights from 200 to 20 000 was studied by a.c. voltammetry in order to understand better the adsorption of linear components of fulvic acids on hydrophobic particles in natural waters, and the influence of their adsorption on voltammetric signals. As a general trend it was noted that the equilibrium adsorption constant increases with the molecular weight while the adsorption rate decreases. The values of the maximum surface concentration F. suggest a flat configuration for adsorbed molecules for all PEGs studied.

Vertical Distribution of Particles in Stratified Lake

A model to account for the distribution of particulate matter in a lake is presented. This model represents the coupling of a stratified lake mixing model with a particle settling, coagulation, and diffusion model. Using parameterizations of the fundamental mixing processes, the lake model simulates the response of the stratified water column to external forcing. At the same time, the particle model simulates the settling, aggregation, and diffusion of a given distribution of particles within this changing water column. Three different situations have been chosen in order to test the model. In the first, an input of mineral particles for different size classes has been attributed to an inflow. In the second, the evolution of a distribution of particles initially set up in the epilimnion of a strongly stratified lake has been described and in the third, the same initial distribution of particles has been set up for a weakly stratified lake. These cases show the importance of the different mechanisms (settling, aggregation and diffusion) affecting the dynamics of the particles in natural waters.

Settling and coagulation characteristics of fluorescent particles determined by flow cytometry and fluorometry

A new technique for detecting particles in natural waters relies upon analysis of fluorescent emission by flow cytometry. Fluorescent pigment particles ranging in radius from -0.1 to 5 pm are available in sufficient quantity to be useful as model particles. Laboratory coagulation and settling experiments analyzed by fluorometry demonstrate that the efficiency with which the pigment particles coagulate with sewage particles is very low (less than 5 X lo-*). Hence, in field applications these particles provide the limiting case of low-interaction behavior relative to natural particles. Removal from laboratory columns occurs primarily by noninteractive settling while thermal convection currents maintain nearly uniform particle concentration within the columns. Observed decreases in particle number are exponential (first order) for each size class as predicted for settling from well-mixed suspensions. The decrease in total suspended particle mass is higher order as a result of the difference in settling rates among particles. Thus, a system in which noninteractive settling dominates mimics systems in which coagulation processes are important. Flow cytometric analysis of particles removed by noninteractive settling shows the fluorescent emission from individual particles to be proportional to the particle surface area. These results enable flow cytometry to be used to detect, count, and size large numbers of particles rapidly.

The role or organic matter and ionic composition in determining the surface charge of suspended particles in natural waters

The surface charge behaviour of riverine and estuarine particles from the Yarra River system (Australia) was monitored using particle microelectrophoresis. The surface charge was invariably negative and decreased in magnitude as the ionic strength of the water increased. Laboratory mixing experiments involving river water and salt solutions revealed that the minor cations in seawater (Ca 2+ and Mg 2+) were much more effective than the major cation (Na +) in reducing the magnitude of the surface charge of suspended particles during estuarine mixing. The charge on the particles appears to be controlled by an adsorbed layer of natural organic matter and the concentration of divalent cations in the water. Evidence for this was found by the fact that the charge behaviour of both freshwater and estuarine particles can be modelled closely by a goethite colloid coated with an adsorbed layer of humic substances.