pH, ionic strength and dissolved organic matter alter aggregation of fullerene C60 nanoparticles suspensions in wastewater

Impact of natural organic matter and inorganic ions on the stabilization of polystyrene micro-particles

The orthokinetic coagulation of irregularly shaped polystyrene micro-particles (PS-MP) was investigated in solutions of inorganic cations with different valence (NaCl, CaCl2, LaCl3) using a coagulation jar test set-up combined with light extinction particle counting. The stabilizing effect of model natural organic matter (NOM from reverse-osmosis (RO-NOM), humic (HA) & fulvic acid (FA)) and of surface water components (SW-NOM) was studied. Collision efficiencies were calculated from the decrease in particle concentration applying first order reaction kinetics. The coagulation of PS-MP followed Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with regard to ionic charge in solution. Highest collision efficiencies were obtained close to the suspected critical coagulation concentrations for CaCl2 (12 mM) and LaCl3 (5.5 mM) whereas for NaCl no CCC was found within the applied concentration range (10-1000 mM). The addition of NOM effectively stabilized PS-MP at low ionic strength (10 mM NaCl) in the order HA > RO-NOM > FA > SW-NOM at concentrations of dissolved organic carbon (DOC) as low as 0.2-0.5 mg/L DOC through electrostatic repulsion. PS-MP were effectively stabilized in 6.1 mg DOC/L of SW-NOM even at high ionic strength (100 mM MgCl2). Coagulation at intermediate ionic strength (10 mM MgCl2) was only observed for SW-NOM concentrations below 0.6 mg/L DOC. The results showed that even low NOM concentrations prevent PS-MP from orthokinetic coagulation in the presence of high ion concentrations. The study provides further insight in the orthokinetic coagulation behavior of PS-MP in the presence of NOM and highlights the importance of NOM for the stabilization of microplastics in aquatic suspensions. Further research is needed to elucidate the behavior of MP in turbulent systems to predict the mobility MP in aquatic systems such as rivers.

Cotransport of fullerene nanoparticles and montmorillonite colloids in porous media: Critical role of divalent cations of montmorillonite

While the cotransport of carbon nanoparticles (CNPs) and clay colloids in porous media has been widely studied, the influence of the cation exchange capacity (CEC) of clay colloids on the transport process remains unclear. In this study, batch adsorption and column transport experiments were conducted to investigate the fate and transport of CNPs and clay colloids in quartz sand, with respect to the effect of monovalent-cation exchange capacity (mono-CEC), divalent-cation exchange capacity (di-CEC) and total CEC of clays. Fullerene nanoparticles (nC60) and six types of montmorillonite (ML) with different CEC were selected as modeled CNPs and clay colloids, respectively. Transport behavior of nC60 and ML was characterized using breakthrough curves (BTCs) and fitted with two-kinetic-sites colloid transport model. Results of the adsorption experiments showed a good linear correlation between the deposition of nC60 on the sand surface and the di-CEC of ML. Transport of ML and nC60 was inhibited by each other. The calculated mass recovery of nC60, as well as the fitted maximum deposition capacity and attachment rate coefficients of nC60 exhibited a strong linear relationship with the di-CEC of ML. These results indicate that divalent cations in ML interlayers play a significant role in aggregation between nC60 and ML and their cotransport. Through measurements of the particle size and zeta potentials of sole nC60 and mixtures of ML and nC60, FTIR and XPS analysis of nC60 under different conditions, and a release experiment of nC60 in a sand column, it demonstrated cation bridging (Ca2+-π) between nC60 and ML mediated by the divalent cations in ML interlayers. The study highlighted the potential of using di-CEC of clays as an indicator to predict the mobility of nC60 in clay-containing porous media and added insights to the transport behavior of CNPs in porous media.

Disintegration of biochar adsorbent under the hydraulic conditions of fixed bed water treatment

Recent studies have provided promising evidence for potential applications of biochar in environmental engineering, including its use as an alternative carbonaceous adsorbent for water and wastewater treatment. Carbonaceous adsorbents, such as activated carbon and biochar, are prone to disintegration and erosion due to water flow, potentially leading to the co-transport of hazardous contaminants with eroded fine particles (1 μm or smaller). Despite its significance in overall performance assessment, the stability and erodibility of biochar as an adsorbent in fixed bed water treatment have received limited research attention. This paper presents the results of a series of filtration tests and microscopic examinations to evaluate the disintegration of activated carbon and three types of biochar filters under the hydraulic conditions of fixed bed filtration. A novel testing design was employed to study the effects of fluid velocities and ionic strengths on disintegration, mass loss, and the morphology of granular adsorbents before and after water flushing. The results indicate that disintegration of both activated carbon and biochar is continuous but exhibits different behaviour with pore volume. Although fluid velocity influenced erosion rates, minimal differences were observed in overall mass loss. Ionic strength had a more pronounced impact on the erodibility and stability of particles in suspension by altering electrical conductivity and Zeta potential. Disintegration of hardwood biochar was found to be comparable to that of activated carbon; however, impurities in biochar (elements other than carbon and oxygen) are more likely to be flushed out, creating additional pathways for co-transport of contaminants.

Measurement artifacts in the dithiothreitol (DTT) oxidative potential assay caused by interactions between aqueous metals and phosphate buffer

Metals in particulate matter (PM) are hypothesized to have enhanced toxicity based on their ability to catalyze reactive oxygen species (ROS) formation. Acellular assays are used to measure the oxidative potential (OP) of PM and its individual components. Many OP assays, including the dithiothreitol (DTT) assay, use a phosphate buffer matrix to simulate biological conditions (pH 7.4 and 37 °C). Prior work from our group observed transition metal precipitation in the DTT assay, consistent with thermodynamic equilibria. In this study, we characterized the effects of metal precipitation on OP measured by the DTT assay. Metal precipitation was affected by aqueous metal concentrations, ionic strength, and phosphate concentrations in ambient PM sampled in Baltimore, MD and a standard PM sample (NIST SRM-1648a, Urban Particulate Matter). Critically, differences in metal precipitation induced differing OP responses of the DTT assay as a function of phosphate concentration in all PM samples analyzed. These results indicate that comparison of DTT assay results obtained at differing phosphate buffer concentrations is highly problematic. Further, these results have implications for other chemical and biological assays that use phosphate buffer for pH control and their use to infer PM toxicity.

Colloidal Behavior and Biodegradation of Engineered Carbon-Based Nanomaterials in Aquatic Environment

Carbon-based nanomaterials (CNMs) have attracted a growing interest over the last decades. They have become a material commonly used in industry, consumer products, water purification, and medicine. Despite this, the safety and toxic properties of different types of CNMs are still debatable. Multiple studies in recent years highlight the toxicity of CNMs in relation to aquatic organisms, including bacteria, microalgae, bivalves, sea urchins, and other species. However, the aspects that have significant influence on the toxic properties of CNMs in the aquatic environment are often not considered in research works and require further study. In this work, we summarized the current knowledge of colloidal behavior, transformation, and biodegradation of different types of CNMs, including graphene and graphene-related materials, carbon nanotubes, fullerenes, and carbon quantum dots. The other part of this work represents an overview of the known mechanisms of CNMs' biodegradation and discusses current research works relating to the biodegradation of CNMs in aquatic species. The knowledge about the biodegradation of nanomaterials will facilitate the development of the principals of "biodegradable-by-design" nanoparticles which have promising application in medicine as nano-carriers and represent lower toxicity and risks for living species and the environment.

Fullerenes for the treatment of cancer: an emerging tool

Cancer is a most common cause of mortality globally. Available medicines possess severe side effects owing to their non-specific targeting. Hence, there is a need of an alternative in the healthcare system that should have high efficacy with the least side effects, also having the ability to achieve site-specific targeting and be reproducible. This is possible with the help of fullerenes. Fullerenes are having the unique physicochemical and photosensitizer properties. This article discusses the synthesis, functionalization, mechanism, various properties, and applications of C60 fullerenes in the treatment of cancer. The review article also addresses the various factors influencing the activity of fullerenes including the environmental conditions, toxicity profile, and future prospective.

Fibrous and filmy microplastics exert opposite effects on the mobility of nanoplastics in saturated porous media

This study explored the influence of fibrous and filmy polyethylene terephthalate (PET) on the transportation of nanoplastics (NPs) in saturated porous media. With the strong electrostatic repulsion, the negatively charged PET fibers (-57.5 mV) improved the transport of NPs, and the mass percentage of NPs recovered from the effluent (M_eff) increased from 69.3% to 86.7%. However, PET films (-49.7 mV) showed the opposite result, that is, M_eff decreased from 69.3% to 57.0%. X-ray micro-computed tomography quantitatively revealed the change in effective porosity of porous media before and after adding various PET MPs. The addition of 10 mm fiber increased the porosity from 0.39 to 0.43, whereas the addition of 10 × 10 mm² film reduced the porosity from 0.39 to 0.29. The fiber-facilitated transport of NPs is presumably due to the formation of new connected pores between fibers and sand grains, whereas the film-inhibited transport of NPs may be due to the partial truncation of transport path of NPs. Overall, the effect of coexisting MPs on the mobility of NPs strongly relies on the shape and size of MPs.

Toxicological effects and bioaccumulation of fullerene C60 (FC60) in the marine bivalve Ruditapes philippinarum

Fullerene C₆₀ (FC₆₀), with its unique physical properties, has been used in many applications in recent decades. The increased likelihood of direct release into the environment has raised interest in understanding the biological effects of FC₆₀ to aquatic organisms. Nowadays, only few studies have analysed FC₆₀ effects and bioaccumulation in marine organisms following in vivo exposure. To provide new data about FC₆₀ toxicity, Ruditapes philippinarum was selected as target species to assess potential adverse effects of the contaminant. Clams were exposed for 1, 3 and 7 days to predicted environmental concentrations of FC₆₀ (1 and 10 μg/L) and cellular and biochemical responses were evaluated in clams' gills, digestive gland and haemolymph. The FC₆₀ content in gills and digestive gland was determined in all experimental conditions after 7 days of exposure. Results showed an increase in oxidative stress. In particular, a significant modulation in antioxidant enzyme activities, and changes in glutathione S-transferase activity were observed in gills. Moreover, damage to lipids and proteins was detected in FC₆₀-treated (10 µg/L) clams. In digestive gland, slighter variations in antioxidant enzyme activities and damage to molecules were detected. CAT activity was significantly affected throughout the exposure, whereas damage to lipids was evident only at the end of exposure. FC₆₀ accumulation was revealed in both gills and digestive gland, with values up to twelve-fold higher in the latter. Interestingly, haemolymph parameters were slightly affected by FC₆₀ compared to the other tissues investigated. Indeed, only Single Cell Gel Electrophoresis and Neutral Red uptake assays showed increased values in FC₆₀-exposed clams. Moreover, volume and diameter of haemocytes, haemocyte proliferation, and micronucleus assay highlighted significant variations in treated clams, but only in the first phases of exposure, and no changes were detected after 7 days. Our results suggested clam gills as the target tissue for FC₆₀ toxicity under the exposure conditions tested: the high damage detected to lipids and proteins could contribute to long-term problems for the organism.

Magnetic porous NiLa-Layered double oxides (LDOs) with improved phosphate adsorption and antibacterial activity for treatment of secondary effluent

The removal of phosphate (nutrient) and E. coli (pathogen) from secondary effluent is of great importance to control the water quality of the receiving water bodies. In this study, magnetic porous NiLa-layered double oxides (NiLa-LDOs/Fe₃O₄) were synthesized using a simple co-precipitation method. NiLa-LDOs/Fe₃O₄ exhibited a high phosphate adsorption capacity of 203.10 mg g^-1 in batch adsorption experiments, which can mostly be maintained within the pH range (5.5-8.5) and ionic strength range (5-20 mM) of secondary effluent, and in the presence of commonly co-existing species (anions and organics). NiLa-LDOs/Fe₃O₄ were further evaluated in real secondary effluent and the homogenous surface diffusion model (HSDM) was used to predict the performance in field applications. Under typical conditions, NiLa-LDOs/Fe₃O₄ can last for ∼1845-2448 bed volumes (BVs) before the phosphate concentration in the effluent exceeds the monthly average limit of 1 mg L^-1 P. Good regeneration capacities were also demonstrated in cyclic adsorption-desorption runs in both synthetic solution and secondary effluent. In addition, the presence of Ni and La species greatly enhanced the antibacterial performance of the NiLa-LDOs/Fe₃O₄ toward E. coli. Results obtained from this study indicate porous NiLa-LDOs/Fe₃O₄ can be a promising multifunctional material for the treatment of secondary effluent.

Humic acid induced weak attachment of fullerene nC60 nanoparticles and subsequent detachment upon reduction of solution ionic strength in saturated porous media

Sand column experiments were performed under saturated conditions to investigate impact of humic acid (HA) on attachment of nC₆₀ nanoparticles (NPs) in NaCl and CaCl₂ at ionic strengths (ISs) from 1 mM to 100 mM and subsequent detachment via reducing solution IS. The attachment increased with increasing IS due to reduced repulsive Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy and accordingly increased retention in primary energy wells. More attachments occurred in CaCl₂ compared to NaCl because Ca²⁺ exhibited greater charge screen ability and served as a bridging agent between the NPs and sand surfaces. The presence of HA significantly reduced nC₆₀ NPs attachment on sand surfaces (especially on nanoscale physical heterogeneities) in 10 mM NaCl and 1 mM CaCl₂ because of enhanced electrostatic and steric repulsions. Interestingly, although the HA did not cause reduction of attachment in 100 mM NaCl and 10 mM CaCl₂ compared to the case in absence of HA, the HA caused weak attachment of nC₆₀ on sand surfaces and then much more significant detachment by decreasing IS. The HA did not alter both attachment and detachment in 100 mM CaCl₂, because the Ca²⁺ at the high concentration caused formation of very stable complex of HA and NPs, and strong interaction of the complex with the sand surfaces via cation bridge. Our study highlighted that the HA can not only enhance the transport of NPs by inhibiting attachment as revealed in the literature, but also by the continuous capture and release of the NPs from surfaces in subsurface environments.

Generation and properties of aqu/nC60: the combined effects of humic acid, sunlight, and agitation intensity

Once released into natural water, the environmental behavior and fate of C₆₀ could inevitably been affected by humic acid (HA), sunlight, and hydrodynamic conditions. However, the combined effects of these factors are not so clear. Therefore, in the present study, effects of HA, sunlight, and agitation intensity on generation and properties of aqu/nC₆₀ were investigated. The results indicated that HA could increase the concentration of aqu/nC₆₀ mainly through the steric hindrance effect. The higher agitation intensity led to higher concentrations of aqu/nC₆₀ and more efficient steric stabilization was formed by HA. Sunlight irradiation promoted the surface oxidization and consequently enhanced the dispersion of C₆₀. The relative order of the influence on the UV/vis concentration was sunlight > agitation intensity > HA. In addition, HA might not always enhance the dispersion of aqu/nC₆₀ due to light screening/ROS scavenging, over-coating, or chain-like bridging mechanism. Therefore, evaluating the environmental behavior and fate of C₆₀ should take these factors into account together.

The dispersion, stability, and resuspension of C60 in environmental water matrices

Environmental waters cover a range of water quality characteristics which could greatly affect the behavior and fate of C₆₀ in the aquatic environment. In this study, the dispersion and stability of C₆₀ in several environmental water matrices during a 70-day extended mixing period were investigated to better understand its environmental behavior and fate in environmental waters. Relatively stable nanoscale aggregates in water (aqu/nC₆₀) could be formed in wastewater influent, while unstable suspensions were obtained in river water, wastewater effluent, seawater, and estuarine water. During the extended mixing under sunlight, oxygen-containing moieties were produced on the surface of the C₆₀ aggregates, independent of the kind of environmental water matrices. Once the mixed system went under quiescent condition, aggregation and sedimentation of aqu/nC₆₀ occurred. However, an extremely short-time disturbance could easily resuspend the C₆₀ aggregates deposited and increase the concentration of aqu/nC₆₀ in the overlying water column. Therefore, the effects of resuspension should be considered when investigating the environmental behavior and fate of C₆₀.

Size-dependent adsorption of antibiotics onto nanoparticles in a field-scale wastewater treatment plant

This work present aims to evaluate the effect of a conventional wastewater treatment process on the number of nanoparticles, and the role of nanoparticles as a carrier of antibiotics. A set of methods based on asymmetrical flow field flow fractionation coupled with multi-angle light scattering to separate and quantify nanoparticles in real wastewater was established. The characterization of nanoparticles was conducted by transmission electron microscopy, energy dispersive spectrometer, UV-visible spectrophotometer and three-dimensional excitation-emission matrix fluorescence spectroscopy. The adsorption of different sizes of nanoparticles separated from the real wastewater for four targeted antibiotics (sulfadiazine, ofloxacin, tylosin and tetracycline) was studied. The results show that the number of nanoparticles were increased in the wastewater treatment process and the size range between 60 and 80 nm was predominant in wastewater samples. The nanoparticles were mainly composed of O, Si, Al and Ca elements and organic components were in the size range of 0-10 nm. Targeted antibiotics were dominantly adsorbed onto nanoparticles with 60-80 nm size range at each stage. The concentrations of tetracycline adsorbed on nanoparticles were surprisingly increased in the end of the treatment process, while ofloxacin and tylosin had the completely opposite phenomenon to tetracycline. The pH and ionic strength definitely affected the aggregation of nanoparticles and interaction with the antibiotics. It is of great significance to give insights into nanoparticle-antibiotic assemblages for the effective treatment and avoiding the water risks due to nanoparticles' ubiquitous and their risks of carrying antibiotics.

Cotransport of nanoplastics (NPs) with fullerene (C60) in saturated sand: Effect of NPs/C60 ratio and seawater salinity

Nanoplastics (NPs) have been identified as newly emerging particulate contaminants. In marine environments, the interaction between NPs and other engineered nanoparticles remains unknown. This study investigated the cotransport of NPs with fullerene (C₆₀) in seawater-saturated columns packed with natural sand as affected by the mass concentration ratio of NPs/C₆₀ and the hydrochemical characteristics. In seawater with 35 practical salinity units (PSU), NPs could remarkably enhance C₆₀ dispersion with a NPs/C₆₀ ratio of 1. NPs behaved as a vehicle to facilitate C₆₀ transport by decreasing colloidal ζ-potential and forming stable primary heteroaggregates. As the NPs/C₆₀ ratio decreased to 1/3, NPs mobility was progressively restrained because of the formation of large secondary aggregates. When the ratio continuously decreased to 1/10, the stability and transport of colloids were governed by C₆₀ rather than NPs. Under this condition, the transport trend of binary suspensions was similar to that of single C₆₀ suspension, which was characterized by a ripening phenomenon. Seawater salinity is another key factor affecting the stability and associated transport of NPs and C₆₀. In seawater with 3.5 PSU, NPs and C₆₀ (1:1) in binary suspension exhibited colloidal dispersion, which was driven by a high-energy barrier. Thus, the profiles of the cotransport and retention of NPs/C₆₀ resembled those of single NPs suspension. This work demonstrated that the cotransport of NPs/C₆₀ strongly depended on their mass concentration ratios and seawater salinity.

Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review

Adsorption is one of the most widely used and effective wastewater treatment methods. The role of ionic strength (IS) in shaping the adsorption performances is much necessary due to the ubiquity of electrolyte ions in water body and industrial effluents. The influences of IS on adsorption are rather complex, because electrolyte ions affect both adsorption kinetics and thermodynamics by changing the basic characteristics of adsorbents and adsorbates. For a given adsorption system, multiple or even contradictory effects of IS may coexist under identical experimental conditions, rendering the dominant mechanism recognition and net effect prediction complicated. We herein reviewed the key advancement on the interaction and mechanisms of IS, including change in number of active sites for adsorbents, ion pair for metal ions, molecular aggregation and salting-out effect for organic compounds, site competition for both inorganic and organic adsorbates, and charge compensation for adsorbent-adsorbate reciprocal interactions. The corresponding fundamental theory was thoroughly described, and the efforts made by various researchers were explicated. The structural optimization of adsorbents affected by IS was detailed, also highlighting polyamine materials with exciting "salt-promotion" effects on heavy metal removal from high salinity wastewater. In addition, the research trends and prospects were briefly discussed.

Energy-efficient ultrasonic release of bacteria and particulates to facilitate ingestion by phagotrophic algae for waste sludge treatment and algal biomass and lipid production

Wastewater treatment generates large amounts of waste activated sludge (WAS) that contains concentrated bacteria and particulate organics and requires costly treatment prior to disposal. This study develops an approach to harness the unique capability of oleaginous phagotrophic microalgae for treating WAS and producing algal biomass and lipids. WAS ultrasonication is studied for releasing particulates and bacteria suitable for direct ingestion by phagotrophic microalgae, without bacterial destruction/lysis, and thus minimizing energy requirement. Particle release into supernatant was followed by optical density at 610 nm (OD610) and volatile solid concentration (VS); OD610 correlated well with micron-size particle count rates measured by dynamic light scattering. Microalgae (Ochromonas danica) grew with a 7.6-h doubling time in sonication-generated WAS supernatant alone, giving approximately 66% (w/w) cell yield from consumed VS and ∼30% intracellular lipids. Effects of sonication power (P in W), WAS volume (V in mL) and sonication duration (t in s) were studied with a 3 × 3 × 6 factorial design. Supernatant OD610 increased with increasing P and t and decreasing V. Multiple linear regression gave the following equation with only significant terms: OD610TS=-0.0536+0.000592P-0.000213t+0.000003P×t+0.000274P×tV (R² = 0.94). Sonicating 500-mL WAS at 180 W for 240 s was selected for giving high particulate release (∼29% VS) with maximal energy efficiency, corresponding to a specific energy input of 4320 kJ (kg TS)^-1, which was much lower than the range (15,000-250,000 kJ (kg TS)^-1) reported previously for WAS ultrasonication. The results supported development of new ultrasonication-phagotrophic algae processes for WAS treatment and algae production.

Aggregation kinetics of microplastics in aquatic environment: Complex roles of electrolytes, pH, and natural organic matter

Microplastics are an emerging contaminants of concern in aquatic environments. The aggregation behaviors of microplastics governing their fate and ecological risks in aquatic environments is in need of evaluation. In this study, the aggregation behavior of polystyrene microspheres (micro-PS) in aquatic environments was systematically investigated over a range of monovalent and divalent electrolytes with and without natural organic matter (i.e., Suwannee River humic acid (HA)), at pH 6.0, respectively. The zeta potentials and hydrodynamic diameters of micro-PS were measured and the subsequent aggregation kinetics and attachment efficiencies (α) were calculated. The aggregation kinetics of micro-PS exhibited reaction- and diffusion-limited regimes in the presence of monovalent or divalent electrolytes with distinct critical coagulation concentration (CCC) values, followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The CCC values of micro-PS were14.9, 13.7, 14.8, 2.95 and 3.20 mM for NaCl, NaNO₃, KNO₃, CaCl₂ and BaCl₂, respectively. As expected, divalent electrolytes (i.e., CaCl₂ and BaCl₂) had stronger influence on the aggregation behaviors of micro-PS as compared to monovalent electrolytes (i.e., NaCl, NaNO₃ and KNO₃). HA enhanced micro-PS stability and shifted the CCC values to higher electrolyte concentrations for all types of electrolytes. The CCC values of micro-PS were lower than reported carbonaceous nanoparticles CCC values. The CCC[Ca²⁺]/CCC [Na⁺] ratios in the absence and presence of HA at pH 6.0 were proportional to Z^-2.34 and Z^-2.30, respectively. These ratios were in accordance with the theoretical Schulze-Hardy rule, which considers that the CCC is proportional to z^-6-z^-2. These results indicate that the stability of micro-PS in the natural aquatic environment and the possibility of significant aqueous transport of micro-PS.

Adsorption behavior and mechanism of chloramphenicols, sulfonamides, and non-antibiotic pharmaceuticals on multi-walled carbon nanotubes

The adsorption behavior of different emerging contaminants (3 chloramphenicols, 7 sulfonamides, and 3 non-antibiotic pharmaceuticals) on five types of multi-walled carbon nanotubes (MWCNTs), and the underlying factors were studied. Adsorption equilibriums were reached within 12h for all compounds, and well fitted by the Freundlich isotherm model. The adsorption affinity of pharmaceuticals was positively related to the specific surface area of MWCNTs. The solution pH was an important parameter of pharmaceutical adsorption on MWCNTs, due to its impacts on the chemical speciation of pharmaceuticals and the surface electrical property of MWCNTs. The adsorption of ionizable pharmaceuticals decreased in varying degrees with the increased ionic strength. MWCNT-10 was found to be the strongest adsorbent in this study, and the Freundlich constant (KF) values were 353-2814mmol(1-n)L(n)/kg, 571-618mmol(1-n)L(n)/kg, and 317-1522mmol(1-n)L(n)/kg for sulfonamides, chloramphenicols, and non-antibiotic pharmaceuticals, respectively. The different adsorption affinity of sulfonamides might contribute to the different hydrophobic of heterocyclic substituents, while chloramphenicols adsorption was affected by the charge distribution in aromatic rings via substituent effects.

Vulnerability of drinking water supplies to engineered nanoparticles

The production and use of engineered nanoparticles (ENPs) inevitably leads to their release into aquatic environments, with the quantities involved expected to increase significantly in the future. Concerns therefore arise over the possibility that ENPs might pose a threat to drinking water supplies. Investigations into the vulnerability of drinking water supplies to ENPs are hampered by the absence of suitable analytical methods that are capable of detecting and quantifiying ENPs in complex aqueous matrices. Analytical data concerning the presence of ENPs in drinking water supplies is therefore scarce. The eventual fate of ENPs in the natural environment and in processes that are important for drinking water production are currently being investigated through laboratory based-experiments and modelling. Although the information obtained from these studies may not, as yet, be sufficient to allow comprehensive assessment of the complete life-cycle of ENPs, it does provide a valuable starting point for predicting the significance of ENPs to drinking water supplies. This review therefore addresses the vulnerability of drinking water supplies to ENPs. The risk of ENPs entering drinking water is discussed and predicted for drinking water produced from groundwater and from surface water. Our evaluation is based on reviewing published data concerning ENP production amounts and release patterns, the occurrence and behavior of ENPs in aquatic systems relevant for drinking water supply and ENP removability in drinking water purification processes. Quantitative predictions are made based on realistic high-input case scenarios. The results of our synthesis of current knowledge suggest that the risk probability of ENPs being present in surface water resources is generally limited, but that particular local conditions may increase the probability of raw water contamination by ENPs. Drinking water extracted from porous media aquifers are not generally considered to be prone to ENP contamination. In karstic aquifers, however, there is an increased probability that if any ENPs enter the groundwater system they will reach the extraction point of a drinking water treatment plant (DWTP). The ability to remove ENPs during water treatment depends on the specific design of the treatment process. In conventional DWTPs with no flocculation step a proportion of ENPs, if present in the raw water, may reach the final drinking water. The use of ultrafiltration techniques improves drinking water safety with respect to ENP contamination.

Towards better understanding of C60organosols

The C₆₀colloidal species in acetonitrile are negatively charged owing to formation of anion-radicals. Electrolytes coagulate the organosol, and multi-charged cations cause the re-charging of the particles.

A zeta potential value determines the aggregate's size of penta-substituted [60]fullerene derivatives in aqueous suspension whereas positive charge is required for toxicity against bacterial cells

Background

The cause–effect relationships between physicochemical properties of amphiphilic [60]fullerene derivatives and their toxicity against bacterial cells have not yet been clarified. In this study, we report how the differences in the chemical structure of organic addends in 10 originally synthesized penta-substituted [60]fullerene derivatives modulate their zeta potential and aggregate’s size in salt-free and salt-added aqueous suspensions as well as how these physicochemical characteristics affect the bioenergetics of freshwater Escherichia coli and marine Photobacterium phosphoreum bacteria. Dynamic light scattering, laser Doppler micro-electrophoresis, agarose gel electrophoresis, atomic force microscopy, and bioluminescence inhibition assay were used to characterize the fullerene aggregation behavior in aqueous solution and their interaction with the bacterial cell surface, following zeta potential changes and toxic effects.

Results

Dynamic light scattering results indicated the formation of self-assembled [60]fullerene aggregates in aqueous suspensions. The measurement of the zeta potential of the particles revealed that they have different surface charges. The relationship between these physicochemical characteristics was presented as an exponential regression that correctly described the dependence of the aggregate’s size of penta-substituted [60]fullerene derivatives in salt-free aqueous suspension from zeta potential value. The prevalence of DLVO-related effects was shown in salt-added aqueous suspension that decreased zeta potential values and affected the aggregation of [60]fullerene derivatives expressed differently for individual compounds. A bioluminescence inhibition assay demonstrated that the toxic effect of [60]fullerene derivatives against E. coli cells was strictly determined by their positive zeta potential charge value being weakened against P. phosphoreum cells in an aquatic system of high salinity. Atomic force microscopy data suggested that the activity of positively charged [60]fullerene derivatives against bacterial cells required their direct interaction. The following zeta potential inversion on the bacterial cells surface was observed as an early stage of toxicity mechanism that violates the membrane-associated energetic functions.

Conclusions

The novel data about interrelations between physicochemical parameters and toxic properties of amphiphilic [60]fullerene derivatives make possible predicting their behavior in aquatic environment and their activity against bacterial cells.

Chitosan nanoparticles loaded the herbicide paraquat: the influence of the aquatic humic substances on the colloidal stability and toxicity

Polymeric nanoparticles have been developed for several applications, among them as carrier system of pesticides. However, few studies have investigated the fate of these materials in the environment in relation to colloidal stability and toxicity. In nature, humic substances are the main agents responsible for complexation with metals and organic compounds, as well as responsible for the dynamics of these nanoparticles in aquatic and terrestrial environments. In this context, the evaluation of the influence of aquatic humic substances (AHS) on the colloidal stability and toxicity of polymeric nanoparticles of chitosan/tripolyphosphate with or without paraquat was performed. In this study, the nanoparticles were prepared by the ionic gelation method and characterized by size distribution measurements (DLS and NTA), zeta potential, infrared and fluorescence spectroscopy. Allium cepa genotoxicity studies and ecotoxicity assays with the alga Pseudokirchneriella subcapitata were used to investigate the effect of aquatic humic substances (AHS) on the toxicity of this delivery system. No changes were observed in the physical-chemical stability of the nanoparticles due to the presence of AHS using DLS and NTA techniques. However some evidence of interaction between the nanoparticles and AHS was observed by infrared and fluorescence spectroscopies. The ecotoxicity and genotoxicity assays showed that humic substances can decrease the toxic effects of nanoparticles containing paraquat. These results are interesting because they are important for understanding the interaction of these nanostructured carrier systems with species present in aquatic ecosystems such as humic substances, and in this way, opening new perspectives for studies on the dynamics of these carrier systems in the ecosystem.

Aggregation behaviour of engineered nanoparticles in natural waters: characterising aggregate structure using on-line laser light scattering

Adsorption of natural organic matter, aggregation and disaggregation have been identified as three of the main processes affecting the fate and behaviour of engineered nanoparticles (ENPs) in aquatic environments. However, although several methods have been developed to study the aggregation behaviour of ENPs in natural waters, there are only a few studies focusing on the fate of such aggregates and their potential disaggregation behaviour. In this study, we proposed and demonstrated a simple method for characterising the aggregation behaviour and aggregate structure of ENPs in different natural waters. Both the aggregate size of ENPs and their adsorption capacity for dissolved organic matter (DOM) were strongly related (R(2)>0.97, p<.05) to the combined effect of initial concentration of dissolved organic matter (DOM) and the ionic strength of the natural waters. The structure of the formed aggregates was strongly correlated (R(2)>0.95, p<.05) to the amount of DOM adsorbed by the ENPs during the aggregation process. Under high ionic strength conditions, aggregation is mainly governed by diffusion and the aggregates formed under these conditions showed the lowest stability and fractal dimension, forming linear, chain-like aggregates. In contrast, under low ionic strength conditions, the aggregate structure was more compact, most likely due to strong chemical binding with DOM and bridging mechanisms involving divalent cations formed during reaction-limited aggregation.

Engineered nanoparticles and organic matter: a review of the state-of-the-art

Growth in the development and production of engineered nanoparticles (ENPs) in recent years has increased the potential for interactions of these nanomaterials with aquatic and terrestrial environments. Carefully designed studies are therefore required in order to understand the fate, transport, stability, and toxicity of nanoparticles. Natural organic matter (NOM), such as the humic substances found in water, sediment, and soil, is one of the substances capable of interacting with ENPs. This review presents the findings of studies of the interaction of ENPs and NOM, and the possible effects on nanoparticle stability and the toxicity of these materials in the environment. In addition, ENPs and NOM are utilized for many different purposes, including the removal of metals and organic compounds from effluents, and the development of new electronic sensors and other devices for the detection of active substances. Discussion is therefore provided of some of the ways in which NOM can be used in the production of nanoparticles. Although there has been an increase in the number of studies in this area, further progress is needed to improve understanding of the dynamic interactions between ENPs and NOM.