Journal of contaminant hydrology最新文献

The residual air saturation plays a crucial role in modeling hydrological processes of groundwater and the migration and distribution of contaminants in subsurface environments. However, the influence of factors such as media properties, displacement history, and hydrodynamic conditions on the residual air saturation is not consistent across different displacement scenarios. We conducted consecutive drainage-imbibition cycles in sand-packed columns under hydraulic conditions resembling natural subsurface environments, to investigate the impact of wetting flow rate, initial fluid state, and number of imbibition rounds (NIR) on residual air saturation. The results indicate that residual air saturation changes throughout the imbibition process, with variations separated into three distinct stages, namely, unstable residual air saturation (S_gr-u), momentary residual air saturation (S_gr-m), and stable residual air saturation (S_gr). The results also suggest that the transition from S_gr-u to S_gr is driven by changes in hydraulic pressure and gradient; the calculated values followed the following trend: S_gr > S_gr-u > S_gr-m. An increase in capillary number, which ranged from 1.46 × 10⁻⁷ to 3.07 × 10⁻⁶, increased S_gr-u and S_gr-m in some columns. The increase in S_gr ranged from 0.034 to 0.117 across all the experimental columns; this consistent increase can be explained by water film expansion at the primary wetting front along with a strengthening of the hydraulic gradient during water injection. Both the pre-covered water film on the sand grain surface and a pore-to-throat aspect ratio of up to 4.42 were identified as important factors for the increased residual air saturation observed during the imbibition process. Initial air saturation (S_ai) positively influenced all three types of residual air saturation, while initial capillary pressure (P_ci) exhibited a more pronounced inhibitory effect on residual air saturation, as it can partly characterized the initial connectivity of the air phase generated under different drying flow rates. Under identical wetting flow rate conditions, S_gr was higher during the second imbibition than during the first imbibition due to variations in initial fluid state, involving both fluid distribution and the concentration of dissolved air in the pore water. In contrast, NIR did not have an obvious effect on the three types of residual air saturation. This work aims to provide empirical evidences and offer further insights into the capture of non-wetting phases in groundwater environments, as well as to put forward some potential suggestion for future investigations on the retention and migration of contaminants that involves multiphase interface interactions in subsurface environments.

The catalytic performance of nano-${\mathrm{FeS}}_2$ in the sonoelectrochemical activation of peroxymonosulfate (PMS) and ozone to remove aspirin (ASP) was studied for the first time. The crystal structure and Fe bonds in the catalyst were confirmed through XRD and FTIR analysis. Within 30 min, ASP (TOC) was removed by 99.2 % (81.6 %) and 98.6 % (77.4 %) in nano-${\mathrm{FeS}}_2$/PMS and nano-${\mathrm{FeS}}_2$/$O_3$ sonoelectrochemical systems, respectively. Water anions, especially${\mathrm{HCO}}_3^{-}$ (almost 50 %), had an inhibitory effect on ASP removal. The probes confirmed that ${\mathrm{SO}}_4^{•-}$and ${\mathrm{HO}}^{•}$ were the key to ASP degradation in nano-${\mathrm{FeS}}_2$/PMS and nano-${\mathrm{FeS}}_2$/$O_3$ systems, respectively. The effective activation of oxidants due to the ideal distribution of ${\mathrm{Fe}}^{2+}$ by catalyst was the main mechanism of ASP removal, in which electric current (EC) and ultrasound (US) played a crucial role through the recycling of Fe ions, dissolution and cleaning of the catalyst. LC-MS analysis identified thirteen byproducts in the ASP degradation pathways. The energy consumption of the proposed sonoelectrochemical systems was lower than previous similar systems. This study presented economic and sustainable hybrid systems for pharmaceutical wastewater remediation.

In order to assess sites for a deep geological repository for storing high-level nuclear waste safely in Germany, various numerical models and tools will be in use. For their interaction within one workflow, their reproducibility, and reliability version-controlled open-source solutions and careful documentation of model setups, results and verifications are of special value. However, spatially fully resolved models including all relevant physical and chemical processes are neither computationally feasible for large domains nor is the data typically available to parameterize such models. Thus, simplified models are crucial for the pre-assessment of possible sites to narrow down the list of suitable candidates for which detailed site investigations and fully resolved models will be done at a later stage. Still, the accuracy of these simplified models is of importance as the pre-assessment of suitable sites will be based on them. In this study, we compare the modelling capabilities of TransPyREnd, a one-dimensional transport code based on finite differences, specifically developed for the fast estimation of radionuclide transport by the German federal company for radioactive waste disposal (BGE), with OpenGeoSys, which is a modelling platform based on finite elements in up to three spatial dimensions. Both codes are used in the site selection procedure for the German nuclear waste repository. The comparison of the model results of TransPyREnd and OpenGeoSys is augmented by comparisons with an analytical solution for a homogeneous material. For the purpose of numerical benchmarking, we consider a geological profile located in southern Germany as an example where the hypothetical repository is located in a clay-stone formation. TransPyREnd and OpenGeoSys yield overall similar results. However, both codes use different discretizations which impact is the highest for strongly sorbing compounds, while the difference gets negligible for less sorbing and more diffusive compounds as higher diffusion tends to blur the initial conditions. Overall, the OpenGeoSys model is more exact whereas the TransPyREnd model has considerable faster run times. We found in our example, that significant substance amounts are only leaving the host rock formation, if apparent diffusion is high, for which case both codes give similar results, while relative differences are considerable for strongly sorbing compounds. However, in the latter case no significant substance amount of radionuclides leaves the host-rock formation, thus deeming the differences in the model results minor for the overall safety assessments of sites.

In recent years, everyone has recognized microplastics as an emerging contaminant in aquatic ecosystems. Polypropylene is one of the dominant pollutants. The purpose of this study was to examine the effects of exposing zebrafish (Danio rerio) to water with various concentrations of polypropylene microplastics (11.86 ± 44.62 μm), including control (0 mg/L), group 1 (1 mg/L), group 2 (10 mg/L), and group 3 (100 mg/L) for up to 28 days (chronic exposure). The bioaccumulation of microplastics in the tract was noted after 28 days. From the experimental groups, blood and detoxifying organs of the liver and brain were collected. Using liver tissues evaluated the toxic effects by crucial biomarkers such as reactive oxygen species, anti-oxidant parameters, oxidative effects in protein & lipids, total protein content and free amino acid level. The study revealed that the bioaccumulation of microplastics in the organisms is a reflection of the oxidative stress and liver tissue damage experienced by the group exposed to microplastics. Also, apoptosis of blood cells was observed in the treated group as well as increased the neurotransmitter enzyme acetylcholine esterase activity based on exposure concentration-dependent manner. The overall results indicated bioaccumulation of microplastics in the gut, which led to increased ROS levels. This consequently affected antioxidant biomarkers, ultimately causing oxidation of biomolecules and liver tissue injury, as evidenced by histological analysis. This study concludes that chronic ingestion of microplastics causes considerable effects on population fitness in the aquatic environment, as well as other ecological complications, and is also critical to understand the magnitude of these contaminants' influence on ichthyofauna.

Composite with a high specific surface area of 224.62 m² g⁻¹ was prepared by adding urea as a nitrogen source to hazelnut shell biochar (HSB). Nitrogen doping significantly enhanced the ability of biochar for Cr(VI) elimination, achieving twice the removal efficiency of unmodified biochar. The impacts of varying the pH and initial concentrations on Cr(VI) removal by urea-modified biochar (N-HSB) were investigated. The Cr(VI) removal by N-HSB was better described by intra particle diffusion model and pseudo-second order kinetic model under optimal conditions. Furthermore, XPS, FTIR, SEM, and BET analyses were used to verify the pivotal roles of oxygen- and nitrogen-containing functional groups. Electrostatic attraction, redox reaction, and complexation constituted the principal mechanisms facilitating Cr(VI) elimination by N-HSB. This study demonstrated that the modification of biochar with urea as a nitrogen source represented a promising strategy for enhancing the removal capacity of biochar for Cr(VI) in aqueous environments.

Soil degradation, characterized by the deterioration of soil physical and chemical properties, nutrient loss, and an increase in toxic substances, is a key ecological concern in mining activities. This study explores the use of waste black shale from mining development as an additive to loess to enhance soil properties for reclamation in mining areas. The research includes resistivity and organic carbon content tests on modified reclaimed loess with varying black shale and water contents. Additionally, the electrical properties of these modified soils are investigated across different AC frequencies. The results highlight the significance of soil plasticity and a 1.5% black shale content in influencing reclaimed loess's electrical properties. Moisture content and black shale influence changes in soil conductive paths and resistivity. The abundance of clay minerals in black shale plays a crucial role in altering soil electrical resistivity due to the adsorption of cations in water and the directional transport under an electric field. Considering soil's three-phase composition and diffuse bilayer structure, the study elucidates the mechanism behind changes in the electrical properties of improved reclaimed loess, accounting for water and black shale content. This research demonstrates the feasibility of using black shale as a soil additive and emphasizes the non-destructive assessment potential of electrical resistivity test (ERT) measurements for modified reclaimed soils.

Biochar amendment has emerged as a potential solution for preventing, remediating, and mitigating agricultural compound pollution. This groundbreaking technique not only improves crucial soil properties like porosity, water retention capacity, cation exchange capacity, and pH, but also intricately impacts the interaction and retention mechanisms of polluting molecules. In this study, we investigate the dynamic of the herbicide Imazapic when subjected to applying pyrolyzed biochars, specifically at temperatures of 300 and 500 °C, within the context of a low-fertility soil characterized as dystrophic Yellow Ultisol (YUd) in a sugarcane cultivation area in Igarassu-PE, Brazil. The biochars were produced from sugarcane bagasse by pyrolysis process in a muffle furnace. In laboratory conditions, with saturated soil columns under steady-state, analyses of the mechanisms involved in interaction and transport and determining hydrodispersive parameters for Imazapic were performed by the two-site nonequilibrium transport model using the CXTFIT 2.0 program. Samples of YUd soil amended with biochar pyrolyzed at 300 °C presented a negligible interaction with Imazapic. However, adding biochar pyrolyzed at 500 °C (BC500) to the soil samples enhanced the adsorption coefficient and improved the interaction with Imazapic. This research points out that biochar produced from agricultural waste biomass, such as sugarcane bagasse specifically pyrolyzed at 500 °C, offers a potential means to adsorb herbicides, reducing their leaching to deeper layers of the amended soils and the risk of groundwater contamination and potential environmental negative impacts.

The co-occurrence of microplastics (MPs) and heavy metals in aquatic systems has raised significant concerns, yet their relationship in freshwater ecosystems remains poorly understood. This study aims to evaluate the prevalence of MPs and factors controlling their distribution in both water and sediment in the Markanda River, Northwest India. MPs were extracted from sediment and water samples using density separation and classified through fluorescence microscopy and Raman spectroscopy. Metal concentrations in river water samples were analyzed using ICP-MS, and their correlation with MP abundance was explored. The results indicated the widespread occurrence of MP pollution across the Markanda River basin, with particle concentrations ranging from 10 to 530 particles L⁻¹ in surface water and 1330–4330 particles kg⁻¹ dry weight (dw) in sediment samples. The variability in MP abundance at sampling sites along the Markanda River courses results from factors such as the proximity of industrial establishments and human habitation, while the influence of grain size on MP distribution appears to be limited. Pellets (88.5 %) and fragments (8.5 %) were the most abundant types of MPs, with polyethylene (45.45 %) and polystyrene (30.9 %) being the dominant forms in water samples. The ICP-MS analysis of heavy metals in water samples indicated elevated levels of As (1.67 to 32.31 ppb) in downstream areas of the river system, influenced by human activities. While metals exhibited correlation with each other, there was a weak association, except for As, with the levels of MPs in the Markanda River. The SEM-EDX analyses to characterize chemical elements absorbed onto the surface of MP showed distinct variations in upstream and downstream sites, with the presence of elements such as Mn, Ni, Cr, Zn, As, Se, and Cu found in downstream areas. We conclude that MPs contaminated with heavy metals potentially threaten the ecological security of freshwater aquatic systems and highlight the importance of management action to reduce plastic pollution worldwide.

Microplastics have been ubiquitous in our environment for decades, and numerous studies have revealed their extensive dispersion, reaching far beyond the surface of the land, soil, aquatic ecosystems. They have infiltrated the food-chain, the food web, even the air we breathe, as well as the water we drink. Microplastics have been detected in the food we consume, acting as vectors for hazardous chemicals that adhere to their hydrophobic surfaces. This can result in the transfer of these chemicals to the aquatic life, posing a threat to their well-being. The release of microplastics into different environmental settings can give rise to various eco-toxicological implications. The substantial body of literature has led scientists to the consensus that microplastic pollution is a global problem with the potential to impact virtually any type of ecosystem. This paper aims to discuss crucial information regarding the occurrence, accumulation, and ecological effects of microplastics on organisms. It also highlights the new and emerging disease named “Plasticosis” that is directly linked to microplastics and its toxicological effects like permanent scarring and long-term inflammation in the digestive system of the seabirds. By comprehending the behaviour of these microplastic pollutants in diverse habitats and evaluating their ecological consequences, it becomes possible to facilitate a better understanding of this toxicological issue.

In this study, we focused on the 3D dispersion of colloids. To our knowledge, we were the first to do so. Thereto, we injected silica encapsulated DNA tagged superparamagnetic particles (SiDNAmag) in a homogeneous coarse grain sand tank. At four downstream locations, SiDNAmag concentrations were determined as a function of time. Longitudinal and transverse dispersivity values and associated uncertainties of SiDNAmag were determined using Monte Carlo modelling approach. The parameter associated uncertainties of hydraulic conductivity as well as of the effective porosity estimated from SiDNAmag breakthrough curves were statistically similar to those estimated from salt tracer breakthrough curves. Further, the SiDNAmag dispersivity uncertainty ranges were then statistically compared with the salt tracer (NaCl, and fluorescein) dispersivities. Our results indicated that time to rise, time of peak concentration and shape of the breakthrough curves of SiDNAmag were similar to those of the salt tracer breakthrough curves. Despite the size difference between the salt tracer molecules and SiDNAmag, size exclusion did not occur, probably due to the large pore throat diameter to SiDNAmag diameter ratio. The median longitudinal dispersivity (α_L) of salt tracer and SiDNAmag were 4.9 and 5.8 × 10⁻⁴ m, respectively. The median ratio of horizontal and vertical transverse dispersivities to α_L, (α_TH /α_L and α_TV /α_L, respectively), for salt tracer and SiDNAmag ranged between 0.52 and 0.56. Through the statistical tests, we concluded that the longitudinal and traverse dispersivities of SiDNAmag were not statistically significantly different from salt tracer in 3 dimensions and could be used to characterize the dispersive properties of the medium we used. Our work contributes to a better understanding of 3D dispersion of SiDNAmag in saturated porous media.