Apparent Distribution Coefficients Research Articles

Unfolding the interaction of radioactive Cs and Sr with polyethylene-derived microplastics in marine environment

To unveil the interaction of radioactive Cs and Sr with polyethylene-derived microplastics in the marine environment, a mesocosm study was conducted in a stepwise manner by investigating the uptake capability of microplastics at three different stages: pristine, radiation-exposed, and marine-exposed microplastics. The study demonstrates that the physio-chemical properties of microplastics undergo significant alterations upon exposure to the environment, leading to the emergence of biofilm formation upon marine exposure, while radiation exposure induces surface roughness and cracks. Biofilm growth enhances the uptake of radionuclides by microplastics. However, the growth of biofilms increases the density of microplastics through aggregation, leading to a buoyancy transition from positive to negative buoyancy. Various interaction mechanisms, such as electrostatic, ion–dipole, and physical diffusion interactions, were identified as important mechanisms playing key roles in radionuclide binding to polyethylene-derived microplastics. Despite the significantly lower apparent distribution coefficients observed for radio Cs (in the range of 7.3–23.6 L/kg) and Sr (in the range of 4.3–8.06 L/kg) in the marine system, typically 2–3 orders of magnitude lower than those on marine suspended sediment, this study offers compelling evidence that microplastics in marine environments are capable of sequestering radio Cs and Sr. Consequently, microplastics can potentially accumulate these radionuclides, highlighting their role as potential reservoirs as well as vectors of radionuclides in marine environments.

Controls of temperature and mineral growth rate on lithium and sodium incorporation in abiotic aragonite

The use of Li/Ca, Na/Ca and Li/Mg ratios in biogenic aragonite exhibits high potential for reconstructing environmental parameters such as temperature and/or salinity. To date however, only a little is known about the mechanisms controlling the incorporation of monovalent metals such as Li+ and Na+ in aragonite. In this study, the effects of temperature and growth rate on Li and Na incorporation into abiotically precipitated aragonite were experimentally investigated. The results for aragonite overgrowths at 5, 15 and 25 °C and for the surface normalized growth rate range 10–8.6 ≤ rp ≤ 10–7.1 (mol/m2/s) suggest that apparent distribution coefficients (i.e., DMe+=CMe+CCaaragonitemMe+mCasolution) of Li and Na are mainly controlled by mineral growth rate, whereas temperature has a minor effect. The combined effect of growth rate and temperature on DLi and DNa can be described as:LogDLi=0.836±0.028Logrp−0.026±0.002T+2.958±0.221;R2=0.97LogDNa=0.456±0.030Logrp−0.018±0.002T−0.253±0.234;R2=0.90where Log rp is the growth rate in mol/m2/s and T is the temperature in degrees Celsius.The DLi and DNa values increase at increasing mineral growth rate, but also decrease as a function of temperature in experiments with similar normalized growth rate. These observations suggest that the incorporation of Li and Na in abiotic aragonite is controlled by the density of mineral surface defect sites that are correlated with the degree of saturation of the reactive solution with respect to aragonite. Interestingly, no correlation between Li/Mg in the aragonite overgrowths and temperature of formation was observed in this study. This difference of Li/Mg and temperature correlations between abiotic aragonite and natural biogenic samples is intriguing and underlines the need for robust understanding of elemental incorporation during carbonate mineral formation, and proxy calibrations specific for growth conditions (e.g., abiotic versus biogenic). The results of this study do not support the use of Li/Mg as a temperature proxy in abiotic aragonite.

Sorption behavior of cesium ions to Mg-containing calcium silicate hydrate in a co-precipitation process

The sorption behavior of Cs to Mg-containing calcium silicate hydrate (C–S–H) was examined to consider C–S–H formation under the water-saturated conditions around a radioactive waste repository. The amount of Cs sorption was slightly lower for Mg-containing C–S–H than for C–S–H, because Mg leads to a decrease in sorption sites by facilitating the polymerization of silicate chains. However, the apparent sorption distribution coefficient Kd of Cs on C–S–H with a Ca/Si molar ratio of 0.8 and Mg contents up to 20% was estimated to be 3.4–6.1 mL/g. Furthermore, the amount of Cs sorption was not decreased by the presence of Ba. The apparent Kd obtained in this study was about 10 times higher than that conventionally estimated for host rocks in the plutonic repository, indicating that C–S–H retains the effect of Cs immobilization even when it contains Mg.Graphical abstract

Influential factors of long-term and seasonal 137Cs change in agricultural and forested rivers: Temperature, water quality and an intense Typhoon Event

In this study, the effect of temperature, water quality, and the impact of an intense typhoon event on change in 137Cs concentration in the water of agricultural and forested rivers near the Fukushima Daiichi nuclear power plant (Japan) was evaluated using monthly stationary observations obtained under baseflow conditions 2.8–10.6 years after the nuclear accident in 2011. The dissolved 137Cs concentration fluctuated seasonally with water temperature in all rivers, and the increase in dissolved 137Cs concentration for unit increase in temperature was higher in forested rivers than in agricultural rivers. The relationship between water temperature and the apparent distribution coefficient of 137Cs well followed the van ’t Hoff equation in the two agricultural rivers, where the enthalpy of reaction was estimated as −15.6 and −19.6 kJ mol−1. The van ’t Hoff equation was not well followed for a forested river, where the suspended solids mainly comprised organic matter, suggesting that the dominant process determining dissolved 137Cs concentrations in forested rivers is not only water temperature effect on ion exchange, but rather the input of 137Cs and K+ (competing with 137Cs for exchange sites on mineral particles) into the water phase via litter leaching. Suspended solids concentrations in agricultural rivers correlated negatively with 137Cs concentrations in suspended solids, suggesting an increased proportion of coarse particles or the input of soils with low 137Cs concentration from decontaminated agricultural land. At some sites, 137Cs concentrations in dissolved form and in suspended solids were reduced sharply in association with the passage of Typhoon Hagibis in October 2019, suggesting that Typhoon Hagibis caused large-scale surface erosion that removed the source of 137Cs.

Estimation of the Binding Constant of Sugar Alcohol to Sodium Ion by Using Its Apparent Distribution Coefficients to Cation-exchange Resins with Different Cross-linkages

Estimation of the Binding Constant of Sugar Alcohol to Sodium Ion by Using Its Apparent Distribution Coefficients to Cation-exchange Resins with Different Cross-linkages

Experimental and theoretical investigations of stable Sr isotope fractionation during its incorporation in aragonite

Strontium partitioning and isotope fractionation between aragonite and fluid have been determined experimentally at low values of the fluid saturation state (Ω) with respect to this mineral (1.1 ≤ Ωaragonite ≤ 2.2), and the measured isotope fractionation has been compared with the results of first-principles simulations. For the latter, Density Functional Theory (DFT) was used for estimation of the equilibrium Sr isotope fractionation between aragonite and Sr2+(aq). The obtained results suggest that, for values of Ωaragonite close to unity, the apparent distribution coefficient of Sr in aragonite (DSr,aragonite=XSrCO3XCaCO3(CaSr)fluid) exhibits values higher than one that rapidly decrease at increasing aragonite growth rate. Under equilibrium conditions (i.e. Ωaragonite=1) a DSr,aragoinite value of 2.7 can be extrapolated. Additionally, for aragonite growth rates rp ≤ 10−8.0±0.2 (mol/m2/s) the Sr isotope fractionation between aragonite and the fluid (i.e. Δ88/86Sraragonite-fluid) shows a constant value of −0.1±0.05‰, whereas it decreases to −0.40‰ when the growth rate increases to 10−7.7(mol/m2/s). The surface reaction kinetic model (SRKM) developed by DePaolo (2011) has been used to describe the dependence of DSr,aragonite and Δ88/86Sraragonite-fluid on mineral growth rate. In this model the best fit for DSr,aragonite and Δ88/86Sraragonite-fluid were 4 and −0.01‰, respectively, whereas the kinetic isotope fractionation factor for Δ88/86Sraragonite-fluid was −0.6‰. The results of first-principles calculations yield an equilibrium Sr isotope fractionation factor of −0.04‰ which is in excellent agreement with the experimental value of the present study. These results are the first experimental measurements of Sr isotope fractionation during inorganic aragonite precipitation as a function of growth rate and the first DFT calculations of Sr equilibrium fractionation in the aragonite-fluid system. The results of this study provide new insight into the mechanisms controlling stable Sr isotope composition in aragonite, which has implications for using Sr isotopes for paleo-reconstructions of natural archives, particularly those of abiogenic origin.

Transfer of 129I to freshwater fish species within Fukushima and Chernobyl exclusion zones

Unique data is reported on the transfer of 129I iodine from freshwaters to fish as well as the internal distribution within fish from the Fukushima and Chernobyl exclusion zones (ChEZ). Samples of water, sediments and fish were collected in the contaminated ponds Inkyozaka and Suzuuchi, and in the less contaminated Abukuma river in Fukushima, as well as in the contaminated Glubokoye lake and in the less contaminated Starukha lake in ChEZ. In water, 129I was mainly present as low molecular mass (LMM) and negatively charged species, while a minor fraction was associated with colloidal fraction, most probably organic material in water. The sediment-water 129I apparent distribution coefficients, Kd, ranged from 225 to 329 L/kg, equal that of stable iodine, but did not correlate with 129I/127I ratio or 129I/137Cs ratio as the environmental distribution of radioactive iodine was different from that of stable iodine and radioactive cesium. Concentration ratios (CR) of 129I in muscle of freshwater fish ranged from 85 to 544 across waterbodies with limited water exchange, similar in Fukushima and Chernobyl, but varied with respect to fish species. Thus, this is the first results on the transfer of 129I to freshwater fish, showing that the CR for freshwater fish is higher than CR reported for marine fish. Concentrations of 129I in fish muscle were, however, lower than in the intestinal content, indicating the influence of more contaminated dietary ingredients probably of terrestrial origin based due to δ13C signal on as well as of biodilution. The present results highlighted also that the radiation dose in fish was highly inhomogeneously distributed. Based on the present 129I/127I atomic ratio of 10−5 in the most contaminated fish in the ponds in Fukushima and Glubokoye lake in Chernobyl, however, a radiation dose of 10 μSv/y would not pose any harm to the fish population.

Revisiting the distribution/permeability regularities exemplified by cationic drug amitriptyline hydrochloride: Impact of temperature and pH

The partition and permeation processes for ionizable tricyclic antidepressant amitriptyline hydrochloride (AMT•HCl) were studied. The apparent distribution coefficients in 1-octanol/aqueous buffer and n-hexane/aqueous buffer systems were determined at 6 temperatures (293.15–313.15 K). The thermodynamics and driving forces of the process were examined by calculating the main transfer thermodynamic parameters: ΔGtr0, ΔHtr0 and ΔStr0. The distribution experiments were carried out at different pH of the aqueous phase: pH 2.0, pH 4.0 and pH 6.8 from which the impact of the ionization state on the compound transferring was disclosed. To help explaining the distribution behavior, the data on the solubility in n-hexane (determined herein) and 1-octanol (from literature) were drawn into consideration. Two artificial membranes were used to investigate the permeability and to disclose the influence of the lipid layer in the content of the membrane.

Naturally grown duckweeds as quasi-hyperaccumulators of rare earth elements and yttrium in aquatic systems and the biounavailability of gadolinium-based MRI contrast agents

The use of rare earths and yttrium (REY) in high-technology products is accompanied by their increasing release into the environment. Concerns regarding the (eco-)toxicity and bioaccumulation of these emerging contaminants highlight the need for research on REY uptake by (aquatic) plants.Duckweeds are widespread macrophytes in lentic waters and receive increasing attention as a potential protein-rich food additive. We here provide a baseline dataset for the complete set of REY in naturally grown duckweed assemblages and ambient freshwater and coastal brackish seawater. Our results show that duckweeds strongly bioaccumulate REY and incorporate them at the μg/kg level (dry matter basis). Their shale-normalised (SN) REY patterns are mildly fractionated relative to upper continental crust, regardless of sampling location and season. In contrast, the patterns of ambient waters increase from light to heavy REY (LREY and HREY, resp.) and may show prominent positive anthropogenic GdSN anomalies due to the presence of Gd-based contrast agents (Gd-CAs) applied for magnetic resonance imaging (MRI). The lack of GdSN anomalies in the duckweed assemblages reveals discrimination against the uptake of Gd-CAs by the macrophytes, providing further evidence for the conservative behaviour of these xenobiotics in the environment. High REY concentrations and apparent bulk distribution coefficients between duckweeds and ambient waters of up to 105 show that duckweeds are quasi-hyperaccumulators of REY. Uptake of LREY is up to two orders of magnitude higher than of HREY, possibly due to stronger complexation of HREY with dissolved ligands. The REY closely correlate with Mn but not with Ca, suggesting that uptake of REY and Mn occurs via the same pathway and revealing the negligible role of calcium oxalates. Our study demonstrates that while duckweeds are quasi-hyperaccumulators of REY, there is currently no risk that anthropogenic Gd from MRI contrast agents may enter the food chain via consumption of duckweeds.

Incorporation of Na and S in bamboo coral skeletons

Ocean environmental conditions can be inferred from the chemical composition of bamboo coral skeletons. The high magnesium calcite internodes of these long-living octocorals may therefore represent a potential archive for seawater properties such as salinity or temperature where instrumental time series are absent. To extend these time series into the past using a natural archive the principles of temperature and salinity signal incorporation into cold-water coral skeletal material need to be investigated. Since skeletal Na and S concentrations have been proposed as environmental proxies, we mapped the spatial distribution and concentration of these elements in two Atlantic specimens of Keratoisis grayi (family Isididae). These measurements were conducted with an electron microprobe applying a spatial resolution of 4 μm. The mean apparent distribution coefficient of Na/Ca for the two samples was within 2.5 and 2.8*10−4, while that of S shows a similar depletion relative to seawater with 3.8 and 3.6*10−3. The two elements show an inverse correlation in bamboo coral skeletons. The mean apparent distribution coefficient of Na is similar to that of abiotic calcites. This similarity can be interpreted as the absence of significant vital effects for skeletal Na/Ca. Hence it corroborates the idea that the average skeletal composition of bamboo corals holds the potential to record past seawater conditions. In contrast, it appears unlikely that the spatial variations of the element distribution of seemingly simultaneously precipitated material along growth rings are exclusively controlled by environmental factors. We further exclude Rayleigh fractionation, ion-specific pumping, and Ca/proton exchange as the driver of Na and S distribution in bamboo corals. Instead, we adapt a calcification model originally proposed for scleractinians to bamboo corals. This model can explain the observed distribution of Na and S in the skeleton by a combination of Ca/proton pumping, bicarbonate active transport, and the formation of an organic skeletal matrix. The adapted model can further be used to predict the theoretical behaviour of other elements and disentangle vital effects from external factors influencing compositional features. It is therefore a useful tool for future studies on the potential of bamboo corals as environmental archives.

Nickel retention by calcium silicate hydrate phases: Evaluation of the role of the Ca/Si ratio on adsorption and precipitation processes

The objective of the present study is to investigate Ni retention processes in Calcium Silicate Hydrate (CSH) phases, as the main cement hydration products, and to describe them in a generalized form for the first time. In particular, the effects of the CSH Ca/Si ratio (from 0.8 to 1.6) on the equilibrium water chemistry, Ni speciation, adsorption and solubility have been addressed. Nickel adsorption tends to decrease as the Ca/Si ratio increases, especially when Ca/Si is < 1.2, and then Ca/Si becomes less relevant. The “adsorption” region is limited to low final aqueous Ni concentrations (<5·10−9 M), and when the Ni concentration exceeds this limit, an increase in the (apparent) distribution coefficient, Kd, is observed, which is related to precipitation processes. The onset of precipitation depends on Ni solubility but also on the Ca/Si ratio: at the lowest ratio, the lowest Ni concentration occurs when the apparent Kd starts to increase. The existence of Ni–Si phases as surface precipitates could explain the observed experimental behaviour, which is not totally explicable assuming Ni(OH)2(s) as the unique phase limiting Ni solubility. Nickel retention on the CSH phases was analysed and interpreted with the help of surface complexation modelling using an electrostatic double layer approach and accounting for the major species present in solution for each CSH. The uncertainties in the available Ni thermodynamic database under alkaline conditions and in the presence of Si are underlined.

Reconstruction of the Long-Term Dynamics of Particulate Concentrations and Solid–Liquid Distribution of Radiocesium in Three Severely Contaminated Water Bodies of the Chernobyl Exclusion Zone Based on Current Depth Distribution in Bottom Sediments

Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of 137Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of 137Cs and its apparent distribution coefficient Kd, based on 137Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain 137Cs vertical profile. Assuming negligible sediment mixing and allowing for 137Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate 137Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate 137Cs concentrations, and the available long-term monitoring data for dissolved 137Cs, the dynamics of 137Cs solid–liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.

Reconstruction of time changes in radiocesium concentrations in the river of the Fukushima Dai-ichi NPP contaminated area based on its depth distribution in dam reservoir's bottom sediments

Radionuclide depth distribution in bottom sediments in deep-water zones of dam reservoirs, where no sediment mixing occurs, can be used to reconstruct time changes in particulate activity concentrations of radionuclides strongly bound to bottom sediments. This approach was used to analyze the 137Cs concentration profile in a bottom sediment core collected from Ogaki dam reservoir on the Ukedo River in the Fukushima Dai-ichi nuclear power plant contaminated zone in October 2019. The derived 137Cs particulate concentrations provided a basis for estimating the dissolved concentration and its temporal trend in the Ukedo River, using the mean value of the apparent 137Cs distribution coefficient. The reconstructed particulate and dissolved 137Cs concentrations and their temporal trends are consistent with monitoring data. The annual mean particulate and dissolved 137Cs wash-off ratios were also calculated for the period of eight years after the accident. Interestingly, the particulate 137Cs wash-off ratios for the Ukedo River at Ogaki dam were found to be similar to those for the Pripyat River at Chernobyl in the same time period after the accident, while the dissolved 137Cs wash-off ratios in the Ukedo River were an order of magnitude lower than the corresponding values in the Pripyat River. Both the particulate and dissolved 137Cs wash-off ratios in the Ukedo River declined faster during the first eight years after the FDNPP accident than predicted by the diffusional model, most likely, due to greater natural attenuation and, to some extent, remediation measures implemented on the catchments in Fukushima.

Geochemistry of barium ions associated with biogenic manganese oxide nanoparticles generated by a fungus strain: Implications for radium sequestration in uranium mill tailings

Biogenic Mn oxides are reactive and ubiquitous in many Earth surface environments, yet their role in radionuclide sequestration at U mill-tailings sites still require an improved understanding at the nano- and molecular-scales. This study concerns the uptake of Ba, utilized as a safe and chemically appropriate surrogate for radioactive Ra, by biogenic Mn oxides produced by a fungal species, Coprinopsis urticicola, isolated from the mine water of the Ningyo-toge U mine, Okayama, Japan. The biogenic Mn oxides were identified as birnessite nanocrystals <10 nm in width having many vacancy sites in the MnO6 octahedral layers. Ba2+ adsorption experiments using biogenic birnessite were conducted at pH 6.00 ± 0.02 with the initial Ba concentrations ranging from 10–8 to 10–3 mol/L. The apparent distribution coefficient, Kd, was calculated to be 103.8 L/g for biogenic birnessite, which is comparable to the apparent Kd of Ra in the mill tailings pond at Ningyo-toge. Both in adsorption and coprecipitation experiments, extended X-ray absorption fine edge structure analysis of Ba L3 edge revealed that the Ba atom forms an inner-sphere complex with O atoms of the MnO6 layer. A slightly greater coordination number for coprecipitated Ba may be attributed to the formation of BaO binding to the newly overlying MnO6 layer during coprecipitation. Static desorption experiments for 7 days reveal that the steady-state release rate of adsorbed Ba is ∼1.4 times faster than that of the coprecipitated Ba, when the Ba concentration in the initial loading solution was ∼10–8 mol/L, indicating that the release of intercalated (coprecipitation) Ba to solution is retarded. The present study demonstrates the importance of fungus-generated Mn oxides as an efficient absorber of Ba2+, and likely Ra2+, among soil compounds in U mill-tailings. This may be applicable to other contaminated sites due to the ubiquitous occurrence of fungi in the environment.

Partitioning and transformation of organic and inorganic phosphorus among dissolved, colloidal and particulate phases in a hypereutrophic freshwater estuary

Phosphorus (P) loadings to the Great Lakes have been regulated for decades, but re-eutrophication and seasonal hypoxia have recently been increasingly reported. It is of paramount importance to better understand the fate, transformation, and biogeochemical cycling processes of different P species across the river-lake interface. We report here results on chemical speciation of P in the seasonally hypoxic Fox River-Green Bay system and variations in sources and partitioning of P species along the aquatic continuum. During midsummer when productivity is generally high, phosphate and dissolved organic P (DOP) were the major species in river water while particulate-organic-P predominated in open bay waters, showing a dynamic change in the chemical speciation of P along the river-bay transect with active transformations between inorganic and organic P and between colloidal and particulate phases. Colloidal organic P (COP, >1 kDa) comprised 33‒65% of the bulk DOP, while colloidal inorganic P was generally insignificant and undetectable especially in open bay water. Sources of COP changed from mainly allochthonous in the Fox River, having mostly smaller sized colloids (1–3 kDa) and a lower organic carbon to phosphorus (C/P) ratio, to predominantly autochthonous in open bay waters with larger sized colloids (>10 kDa) and a higher organic C/P ratio. The observed high apparent distribution coefficients (Kd) of P between dissolved and particulate phases and high-abundant autochthonous colloidal and particulate organic P in the hypereutrophic environment suggest that, in addition to phosphate, colloidal/particulate organic P may play a critical role in the biogeochemical cycling of P and the development of seasonal hypoxia.

Salinity-independent dissipation of antibiotics from flooded tropical soil: a microcosm study

River deltas are frequently facing salinity intrusion, thus challenging agricultural production in these areas. One adaption strategy to increasing salinity is shrimp production, which however, heavily relies on antibiotic usage. This study was performed to evaluate the effect of increasing salinity on the dissipation rates of antibiotics in tropical flooded soil systems. For this purpose, paddy top soil from a coastal Vietnamese delta was spiked with selected frequently used antibiotics (sulfadiazine, sulfamethazine, sulfamethoxazole, trimethoprim) and incubated with flood water of different salt concentrations (0, 10, 20 g L−1). Antibiotic concentrations were monitored in water and soil phases over a period of 112 days using liquid chromatography and tandem mass spectrometry. We found that sulfamethazine was the most persistent antibiotic in the flooded soil system (DT50 = 77 days), followed by sulfadiazine (DT50 = 53 days), trimethoprim (DT50 = 3 days) and sulfamethoxazole (DT50 = 1 days). With the exception of sulfamethoxazole, the apparent distribution coefficient increased significantly (p < 0.05) for all antibiotics in course of the incubation, which indicates an accumulation of antibiotics in soil. On a whole system basis, including soil and water into the assessment, there was no overall salinity effect on the dissipation rates of antibiotics, suggesting that common e-fate models remain valid under varying salinity.

Uranium and neptunium retention mechanisms in Gallionella ferruginea/ferrihydrite systems for remediation purposes

The ubiquitous β-Proteobacterium Gallionella ferruginea is known as stalk-forming, microaerophilic iron(II) oxidizer, which rapidly produces iron oxyhydroxide precipitates. Uranium and neptunium sorption on the resulting intermixes of G. ferruginea cells, stalks, extracellular exudates, and precipitated iron oxyhydroxides (BIOS) was compared to sorption to abiotically formed iron oxides and oxyhydroxides. The results show a high sorption capacity of BIOS towards radionuclides at circumneutral pH values with an apparent bulk distribution coefficient (Kd) of 1.23 × 104 L kg−1 for uranium and 3.07 × 105 L kg−1 for neptunium. The spectroscopic approach by X-ray absorption spectroscopy (XAS) and ATR FT-IR spectroscopy, which was applied on BIOS samples, showed the formation of inner-sphere complexes. The structural data obtained at the uranium LIII-edge and the neptunium LIII-edge indicate the formation of bidentate edge-sharing surface complexes, which are known as the main sorption species on abiotic ferrihydrite. Since the rate of iron precipitation in G. ferruginea-dominated systems is 60 times faster than in abiotic systems, more ferrihydrite will be available for immobilization processes of heavy metals and radionuclides in contaminated environments and even in the far-field of high-level nuclear waste repositories.

Changes in abiotic dissipation rates and bound fractions of antibiotics in biochar-amended soil

To understand the impacts of molecular structures and biochar types on abiotic dissipation and bound fractions of antibiotics in soil, nine biochar types were applied into a soil contaminated with 16 antibiotics. In soil without biochar, the abiotic dissipation rates of antibiotics were generally tetracyclines (TCs) > sulfonamides (SAs) > quinolones (QLs). The trend was quite consistent with the total amounts of oxygen (O), nitrogen (N) and/or sulphur (S) atoms in antibiotic molecular structures. The dissipation trends of TCs (excluding oxytetracycline) and QLs (excluding ofloxacin) were just opposite the order of their logKow values, indicating that hydrophobic adsorption played the key role in their abiotic dissipation. The reason why oxytetracycline and ofloxacin were unique is they had one more O-containing functional group, when compared with the other TCs and QLs, respectively, resulting in their different hydrophobic adsorption affinities. For SAs, sulfadiazine and sulfachinoxalin had the highest and lowest abiotic dissipation rates, respectively. QLs and TCs were the dominant tightly bound fractions, while molecular structures influenced the bound fractions of SAs. In biochar-treated soils, biochars produced at 250 °C generally had a positive effect on the abiotic dissipation rates of antibiotics. The effect sizes of biochars produced at 400 °C and 600 °C for the abiotic dissipation of antibiotics were influenced by both biochar type and antibiotic molecular structure. Biochar type had the strongest impact on SA bound fractions, followed by TCs, while it had minimal influence on QLs. Biochars generally decreased the apparent distribution coefficients (Kapp) of antibiotics in soil, indicating an increase in antibiotic leaching following biochar addition.

Removal of sulfonamide antibiotics from water by high-silica ZSM-5.

Adsorption characteristics of high-silica zeolites (HSZSM-5) for two selected sulfonamide antibiotics (SAs) (sulfamethoxazole and sulfadiazine) were investigated. The SAs were almost completely (>90%) removed from the water by HSZSM-5. Adsorption followed second-order kinetics with liquid-film diffusion as the dominant mechanism. SA adsorption capacity on high-silica zeolites was examined in terms of pH, temperature, and the presence of natural organic matter (NOM). HSZSM-5 had better adsorption performance in acidic conditions, and the apparent distribution coefficient indicated that SA0 species were the major contribution to the overall adsorption at pH of 2-10. Adsorption of SAs on HSZSM-5 was a spontaneous and exothermic physisorption process. SA removal by HSZSM-5 was a mixed mechanism through ion-exchange and hydrophobic interaction. HSZSM-5 has potential application prospects in removing SAs from wastewater.

Time resolution effect on the apparent particle dynamics confined in a nanochannel evaluated by the single particle tracking subject to Brownian motion

Experimental observation of fluid dynamics including the diffusion due to the Brownian motion in confined nanospace, e.g., nanochannels and biological cells, and at the interface between the fluid and solid wall in general relies on the tracking of nanoparticles. Combination of finite time resolution with force field between the particle and the wall can cause significant deviation of apparent position distribution and diffusion coefficient from the actual ones. In this article, we show that the exposure time and the frame interval affect the apparent particle dynamics in a nanochannel in different manners. Sufficiently short exposure time enables precise evaluation of the force field with a long frame interval, whereas sufficiently short frame interval is also required in the precise evaluation of the diffusion coefficient. The dependences of the apparent diffusion coefficient and force field on the frame interval with a fixed force field for different particle sizes collapse into a single curve with appropriate nondimensional characterization. These findings are ubiquitously important in the fields of fluid dynamics, chemistry, biology, and their related engineering, where single particle or molecule tracking in the vicinity of solid–fluid interface is the subject of study.