Seasonal dynamics and typology of microplastic pollution in Huixian karst wetland groundwater: Implications for ecosystem health.

This study offers an insightful and detailed examination of microplastic pollution in the Huixian karst wetland's groundwater, providing novel insights into the complex interplay of microplastic characteristics and their seasonal dynamics. We meticulously quantified microplastic concentrations, observing significant seasonal variation with values ranging from 4.9 to 13.4 n·L-1 in the wet season and 0.53-49.4 n·L-1 in the dry season. Our analysis pinpoints human activities and atmospheric deposition as key contributors to this contamination. A critical finding of our research is the pronounced disparity in microplastic levels between open wells and covered artesian wells, highlighting the vulnerability of open wells to higher pollution levels. Through correlation analysis, we unearthed the crucial influence of the karst region's unique hydrogeological characteristics on microplastic migration, distinctively different from non-karst areas. The karst terrain, characterized by its caves and subterranean rivers, facilitates the downward movement of microplastics from surface to groundwater, exacerbating pollution levels. Our investigation identifies agricultural runoff and domestic wastewater as primary pollution sources. These findings not only underscore the urgent need for environmental stewardship in karst regions but also provide a crucial foundation for formulating effective strategies to mitigate microplastic pollution in karst groundwater. The implications of this study extend beyond the Huixian karst wetland, offering a template for addressing microplastic pollution in similar ecosystems globally.

A long-ignored unique ecosystem of cavefishes in the southern karst: achievements, challenges, and prospects.

Cavefishes represent a taxon that has experienced natural selection pressures. This paper summarizes the results with respect to the taxonomy, diversity, phylogeny, and adaptation aspects of cavefishes research. It showed that: 1) These studies suggest that cavefishes play important roles in the study of geologic history and adaptation to extreme environments, but the mechanisms involved 168 species of cavefishes belonging to 17 genera, four families, and two orders have been recorded in China. Meanwhile, more new species are being discovered recently, and the species diversity of cavefishes are still underestimated, indicating the need to strengthen the survey in field. 2) The biogeography of cavefishes have focused on Sinocyclocheilus and Triplophysa, that have helped understand the geomorphology of karst areas in southern China and the spatial pattern of species diversity. These studies revealed the influences of evolution and geological history in Sinocyclocheilus, but there are still many species that have not been studied accordingly. 3) Some adaptive mechanistic studies have been conducted on cavefishes, primarily focusing on eye and body color degradation and energy metabolism in the genus Sinocyclocheilus to reveal adaptive mechanisms in the dark environment. 4) The IUCN list of protected cavefishes species in China only includes 21 species. The List of Key Protected Wild Animals for 2021 includes all species of Sinocyclocheilus as National Class II.It is necessary to strengthen the research on the biodiversity and adaptation and need consider the conservation actions for cavefishes.

Development of a new design of deironing granulated filter for joint removal of iron and ammonium nitrogen from underground water.

Providing the population with high-quality drinking water is one of the main state tasks. Rural water supply systems and water supply systems of small settlements in the region require special attention, namely, the development of technologies for individual, small-sized water treatment equipment, as well as equipment for collective use, designed to purify groundwater for drinking purposes. In many areas, there are groundwaters containing excess levels of several pollutants, which makes their purification much more difficult. Elimination of shortcomings in the known methods of water iron removal is possible by reconstructing existing water supply systems from underground sources in small settlements. A rational solution is to search for groundwater treatment technologies that make it possible to provide the population with high-quality drinking water at a lower cost. The result of increasing the concentration of oxygen in water was obtained in the process of modifying the filter by changing the excess air exhaust system, which was made in the form of a perforated pipeline located in the lower half of the granular filter layer connected to the upper branch pipe. At the same time, high-quality groundwater treatment, sufficient simplicity and reliability in operation are ensured, local conditions and the inaccessibility of many objects and settlements in the region are taken into account as much as possible. After the filter was upgraded, the concentration of iron decreased from 4.4 to 0.27 mg/L and ammonium nitrogen from 3.5 to 1.5 mg/L.

A revisit to the relationship between geothermal energy growth and underground water quality in EU economies.

This study's main goal is to evaluate how the research will look at the impact of geothermal energy production on the quality of the subterranean in the 27 European nations from 1990 to 2021. A considerable decline in the subterranean water supply can occur in EU14 emerging nations employing geothermal energy growth compared to EU13 emerging economies, according to research that uses the autoregressive distributed lag (ARDL). Fossil fuel use, population growth, and economic expansion are some factors that have a more detrimental effect on the subterranean water supply in EU14 emerging economies than in EU13 emerging nations. In contrast, the study's findings indicate that EU13 emerging nations may be better able to enhance their underground water supply than EU14 emerging economies because of more effective institutional qualities. The findings so indicate that increasing the amount of geothermal energy generation among the 27 European Union countries can accelerate subsurface water degradation at a high capacity and help achieve unionism's 2030 energy-related goals. When this is achieved, climate change will be put to check, as pollution of the environment. All calculations projected were seen to be of a good level of validity, and this is ascertained through three estimators considered in this study.

Unraveling the occurrence of contaminants of emerging concern in groundwater from urban setting: A combined multidisciplinary approach and self-organizing maps.

In recent decades, changes in human behavior and new technologies have introduced thousands of new compounds into the environment called "contaminants of emerging concern" (CEC). These compounds have been detected in different environmental compartments such as soil, surface water, air, and groundwater. The presence of these contaminants in groundwater may pose risks to human health when used as potable water. In some urban areas in Brazil, groundwater is normally consumed without previous treatment. This study aimed to use statistical analysis by self-organizing maps (SOM) to evaluate the trends of CEC in urban groundwater systems. A total of 23 CEC compounds including pesticides, pharmaceuticals, and hormones were determined in groundwater samples using solid phase extraction and liquid chromatography-mass spectrometry. The CEC most frequently detected were atrazine and degradation products, fipronil, simazine, tebuconazole, hexazinone, and caffeine in concentrations up to 300 ng L-1. All studied compounds were detected in groundwater at least in one sample. Patterns in the data through SOM have shown a strong positive correlation between atrazine, hexazinone, simazine, tebuthiuron, 2-hydroxyatrazine, and 17ß-estradiol. The hormones estrone and testosterone also show a positive correlation due to their similar chemical properties. On the other hand, caffeine was detected in 90% of the samples, likely due to a population habit of taking daily a hot drink made of yerba mate associated with low rates of treated domestic sewage in the study area.

Field Trial of an Automated Batch Chlorinator System at Two Shared Shallow Tubewells among Camps for Forcibly Displaced Myanmar Nationals (FDMN) in Cox's Bazar, Bangladesh.

Chlorination of shallow tubewell water is challenging due to various iron concentrations. A mixed-method, small-scale before-and-after field trial assessed the accuracy and consistency of an automated chlorinator, Zimba, in Rohingya camp housing, Cox's Bazar. From August-September 2018, two shallow tubewells (iron concentration = 6.5 mg/L and 1.5 mg/L) were selected and 20 households were randomly enrolled to participate in household surveys and water testing. The field-team tested pre-and post-treated tubewell and household stored water for iron, free and total chlorine, and E. coli. A sub-set of households (n = 10) also received safe storage containers (5 L jerry cans). Overall mean iron concentrations were 5.8 mg/L in Zimba water, 1.9 mg/L in household storage containers, and 2.8 mg/L in the project-provided safe storage containers. At baseline, 0% samples at source and 60% samples stored in household vessels were contaminated with E. coli (mean log10 = 0.62 MPN/100 mL). After treatment, all water samples collected from source and project-provided safe storage containers were free from E. coli, but 41% of post-treated water stored in the household was contaminated with E. coli. E. coli concentrations were significantly lower in the project-provided safe storage containers (log10 mean difference = 0.92 MPN, 95% CI = 0.59-1.14) compared with baseline and post-treated water stored in household vessels (difference = 0.57 MPN, 95% CI = 0.32-0.83). Zimba is a potential water treatment technology for groundwater extracted through tubewells with different iron concentrations in humanitarian settings.

Assessing the physico-chemical parameters and some metals of underground water and associated soil in the arid and semiarid regions of Tank District, Khyber Pakhtunkhwa, Pakistan.

Good-quality water and food are the basic needs of humans, plants, and animals. Polluted groundwater and soil directly and indirectly affect organisms, which is the main environmental concern. In the current study, standard protocols of atomic absorption spectrometry were adopted for the investigation of selected metals (lead, chromium, and iron) in the collected groundwater and soil samples. The Pearson correlation coefficient (r) applied to groundwater and soil samples shows a positive perfect correlation among water parameters (conductivity and total dissolved solids) in all three sources. In the hand pump samples between water table (WT) and water source depth (WSD), Pearson correlation coefficient (r) value was found (r = 0.87) while between EC and TDS, it was r = 1. Similarly, in the bore hole samples between WT and WSD (r = 0.66), EC and TDS (r = 1), EC and Cr (r = 0.70), and TDS and Cr (r = 0.70), which showed weaker correlation. In the tube well samples, correlation between EC and TDS was high (r = 1). The correlation coefficient (r) values of the soil parameters in the hand pump (soil) samples between Fe and Cr (r = 0.86), in bore hole samples between Fe and Cr (r = 0.77), in tube well samples between Fe and Cr (r = 0.69), while all the other parameter correlations were found lower (r = 0.60). Between electrical conductivity and total dissolved solids, high relation has been observed between them (r = 1). Overall, results showed that in most of the studied samples, contents of the target metals were found above the allowable limit set by the World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA).

A permeable electrochemical reactive barrier for underground water remediation using TiO2/graphite composites as heterogeneous electrocatalysts without releasing of chemical substances.

Permeable reactive barriers (PRBs) are well-studied and widely-applied technologies in underground water remediation. However, the releasing of chemical substances cannot be avoided during the PRBs operation. In this study, a novel permeable electrochemical reactive barrier (PERB) was fabricated for underground water remediation using a TiO2/graphite composite (TiO2/C) as the heterogeneous electrocatalyst. TiO2/C performed an electro-Fenton-like reaction on cathode and an anodic oxidation on anode respectively, along with the variety of the TiO2 lattice. The performance of this PERB system was evaluated using tetracycline hydrochloride (TTC) degradation. TTC could be degraded at a low applied potential and a wide range of pH. The degradation rate of about 60% was obtained at the optimized reaction condition: the interelectrode potential difference of 1.2 V, pH 3.0, the anode 10 cm above cathode. The relative position and spacing of the electrodes effected the mass transfer equilibrium of TTC. During the 25-day persistent degradation of TTC, the PERB system shown a perfect stability with rarely leaching of Ti. This work explored the potential for underground water remediation by the electrocatalysis with the goal of establishing a clean and eco-friendly PERB system.

Occurrence of 222Rn and 226,228Ra in underground water and 222Rn in soil and their mutual correlations for underground water supplies in southern Greater Poland.

European Union Council Directive 2013/51/EURATOM recently sets out so-called indicator parameters for: radon, tritium and indicative dose of water intended for human consumption. The aim of this research was to elaborate an effective procedure for determination of radon and radium 226,228Ra isotopes (which are potentially the main contributors to the internal dose from drinking and cooking water) and to find the possible relationships between these radionuclides in underground water reservoirs and 222Rn concentration in the soil gas in their vicinity. The research was performed by applying a non-volatile and water-immiscible scintillation cocktail based on a pure diisopropylnaphthalene (Ultima Gold F: UGF), which allow for efficient radon extraction from 0.5 dm3 of water samples to 20 cm3 of scintillation phase and its direct determination with a detection limit of 5 × 10-3 Bq dm-3. The further preliminary concentration of 3 dm3 of crude water samples by evaporation to 0.5 dm3 samples led to the removal of all unsupported 222Rn activity and allowed the 226Ra determination via equivalent 222Rn detection after one-month samples storage using a low-background Triathler liquid scintillation counter in the α/ß separation counting mode. Together with determination of 226Ra isotope in water samples, the simultaneous measurements of 228Ra and 222Rn radionuclides concentrations in water as well as 222Rn activity in the soil gas around the water supply sites were performed. The achieved limit of 226Ra detection was at a very low level of 10-3 Bq dm-3. The measured values of 226Ra concentration in 50 public underground water supply units for the Kalisz district of Poland were relatively low and ranged from below detection limit to 28.5 × 10-3 Bq dm-3 with arithmetic mean and median values of 12.9 and 12.2 × 10-3 Bq dm-3, respectively. Weak correlations were observed between activity concentrations of 226Ra and 222Rn in the crude water samples (R2 = 0.31) and 222Rn in water and its concentration in the nearby soil gas (R2 = 0.48).

Joint effects of genomic markers and urinary methylation capacity associated with inorganic arsenic metabolism on the occurrence of cancers among residents in arseniasis-endemic areas: A cohort subset with average fifteen-year follow-up.

BACKGROUND: Chronic exposure to inorganic arsenic results in many cancers in susceptible persons. The metabolism of inorganic arsenic and genomic susceptibility are thought to be associated with cancer occurrence. METHODS: This study aims to examine the interaction of genomic susceptibility markers and urinary methylation capacity indicators involved in inorganic arsenic metabolism with all-cancer occurrence. This study conducted a follow-up on 96 residents to determine their urinary inorganic arsenic metabolites and genomic assay from an arseniasis area. Among them, 24 cancer developed. Multivariable Cox proportional hazards model was used to determine and estimate the candidate independent variables for cancer development. RESULTS: The residents with high inorganic arsenic exposure, high primary methylation index (PMI; MMA/InAs) (but lower secondary methylation index (SMI)), and non-heterogeneity type of genomic markers, including GSTO1, AS3MT, and MPO, tend to develop cancers. Subjects with higher PMI are at higher risk of developing cancers (HR = 1.66; 95% CI = 1.30-2.12). Cancer occurrence was greater among the CC type of GSTO1 (HR = 3.33; 95% CI = 1.11-10.00), CC type of AS3MT (HR = 19.21; 95% CI = 1.16-318.80), and AA type of MPO (HR = 13.40; 95% CI = 1.26-142.40). After adjusting confounders, a mutually moderating effect was revealed between genomic markers and methylation capacity on cancer occurrence. CONCLUSIONS: This study found the hypermethylation responses to inorganic arsenic exposure and an array of genomic markers may increase the susceptibility of a wide range of organ cancers. The findings indicated a high-risk arsenic-exposed population to develop cancers. The phenotype of arsenic metabolism and genomic polymorphism suggested a potential preventive strategy for arsenic carcinogenesis.

Characterization of Vibrio spp. in environmental water samples collected from flood prone areas of Bangladesh and their antibiotic resistance profile.

Last cholera epidemic has been recorded in Bangladesh between 1992-1993, while few sporadic localized outbreaks have been reported as recent as 2005. Serotype O1 of Vibrio cholera is considered as the principal causative agent which transmits through contaminated drinking water resulting that epidemic. Therefore, the objective of this research was to isolate V. cholera in 3 different water sources; River, pond and tube-well, in 5 different locations of Gazipur, Bangladesh, and to analyze their antibiogram study. A total of 45 water samples were randomly collected for the isolation and identification of Vibrio spp. Samples are then serially diluted in alkaline peptone water and streak on Thiosulfate Citrate Bile Salt Sucrose-TCBS agar for quantification of V. spp. For V. cholera isolation water samples were first enriched in nutrient broth at 37 °C for 16 hours followed by cultivation in selective media; TCBS agar at 37 °C for 24 hours. Yellow colonies on TCBS agar were screed as V. cholera and was confirmed by analyzing their biochemical characteristics like Catalase, Oxidase, MR, VP, Indole, Sugar fermentation. Following isolation antibiotic sensitivity test was performed on each V. cholera isolates to determine their antibiotic sensitivity profile. The results showed, out of 45 samples 12 contained V. cholera. Tube-well water has significantly lower concentration (log CFU/mL) of V. spp. than river and pond water (P < 0.05). Bacterial concentration doesn't deviate (P > 0.05) significantly in 5 different location the sample was collected from. All the 12 isolates were sensitive to Gentamicin and ciprofloxacin (100%), while Chloramphenicol (91.67%), Sulfamethoxazole (91.67%), Azithromycin (66.67%) showed high sensitivity. Isolates showed marginal sensitivity towards Tetracycline (33.33%), and Cephalexin (16.67%) and 100% resistance against antibiotics like Vancomycin, Penicillin, Erythromycin, and Nalidixic Acid. Based on these data we recommend using tube-well water instead of river and pond water for drinking purposes. Furthermore, we suggest selective use of sensitive antimicrobials listed here for therapeutics of cholera outbreak.

Effects of drought on environmental health risk posed by groundwater contamination.

This publication presents a comparison of the content of pollutants in groundwater samples taken at 117 measurement points in four regions of Poland during a drought period and in the reference period without drought. Based on the chemical analyses of water, an assessment of the health risk resulting from the use of underground water for consumption was carried out. The study aimed to determine whether drought affects the increase in health risk exposure of the population. It was found that despite the occurrence of drought, the expected increase in the concentration of pollutants in water does not take place in all locations. This study found that in some cases the occurrence of drought did not cause an increase in the non-cancerogenic threat expressed by the hazard index. There were also no clear changes in excess lifetime cancer risk values except for selected measurement points. On the other hand, the statistical analysis of all data collected in the regions where the research was conducted showed a general trend of increasing environmental health risk caused by changes in groundwater pollution during drought.

Detection of ultra-low field NMR signal with a commercial QuSpin single-beam atomic magnetometer.

We experimentally demonstrate the nuclear magnetic resonance (NMR) detection at 1.9 kHz using a detection system comprised of a high-sensitivity single-beam atomic magnetometer and a flux transformer. The single-beam atomic magnetometer has been commercialized by QuSpin for typical operation at low frequencies below 200 Hz with a bandwidth of 135 Hz [1]. However, this magnetometer operation can be extended to much higher frequencies about 2 kHz by applying optimal-bias magnetic fields. The sensitivity of the detection system with a demonstrated signal-to-noise ratio of about 50 for a 20 ml water sample, even without magnetic field shimming, is quite competitive with that in other ultra-low field NMR detection systems, such as the Magritek Terranova system or the system based on our home-built atomic magnetometer installed inside a magnetically shielded room [2]. This ultra-low field NMR approach can be applied to Earth-field NMR detection and imaging. We estimate that the detection system with a modified flux transformer can be sensitive to underground-water detection at depth of 1 meter and deeper, and to field mapping applications.

New approach for inert filtering media modification by using precipitates of deironing filters for underground water treatment.

The anthracite granules were coated with iron oxide by a solution combustion synthesis method in a muffle furnace oven. As for iron precursor, an iron-containing precipitate of water treatment plants was used. The influence of four different reducing reagents on surface phase composition and properties of the modified materials was investigated. Obtained samples were investigated using different diffraction and spectroscopic methods. Using the solution combustion synthesis method, anthracite granules formed fine dispersed and crystalline structures of iron oxides on their surface with the iron content up to 40.7 wt%. This had a positive effect on the catalytic capacity of the material for deironing of underground water as well as for the increase in specific surface area. The catalytic properties of the obtained samples and the effectiveness of deferrization of groundwater were investigated. The use of tested materials makes it possible to reduce of catalytic layer height of the filter media from 50 to 20 cm for the filtration rate 12 m/h and enhance the treatment efficiency during the first start-up of filters after regeneration up to 3 times.

Influence of impressed current cathodic protection systems on chemical characteristics of underground water.

Despite well-known corrosion inhibition behavior of cathodic protection (CP) system, this process might be a potential hazard to surrounding ecosystem resulted mostly from continuous electrical current which is applied to the adjacent environment and metallic anode dissolution as well. In this research, deepwater CP wells at different locations of Golestan province, Iran, were taken into consideration to evaluate the impact of these protective systems on underground waters from viewpoint of chemical and physicochemical characteristics resulted from anode dissolution. For this purpose, concentration of metallic constituents of the anode as well as the amount of pH, total dissolved solids (TDS), electrical conductivity (EC), and total hardness were determined. On the basis of obtained results, the concentration of Mn, Cr, and Fe in CP well located nearby an industrial district (i.e., 0.087, 0.475, and 8.5 mg/L, respectively) was higher than both WHO and USEPA standards. This fact can be resulted from the position where the well was dug as well as the CP anode dissolution within the deep CP water wells. PRACTITIONER POINTS: The impact of impressed current cathodic protection (ICCP) system on chemical and physicochemical characteristics of underground water has been evaluated. Anode dissolution of ICCP systems influences the water characteristics nearby the anodes. Despite low dissolution rate of high silicon cast iron anodes, their long-term utilization might be harmful for adjacent ecosystem. The amount of heavy metals in underground waters was demonstrated to be influenced by the employment of ICCP system. Both anode dissolution and the geological properties of the Earth`s crust surrounding the wellbore might be responsible for significant increase of heavy metals concentration.

Potential Effect of Porosity Evolution of Cemented Paste Backfill on Selective Solidification of Heavy Metal Ions.

Cemented paste backfill (CPB) is a common environmentally friendly mining approach. However, it remains undetermined whether CPB pollutes underground mine water. Tank leaching analysis of a CPB mass in distilled water was performed for 120 d, and water quality was tested in situ for a long-term pollution assessment. Computerized tomography was also used to determine the CPB micro-pore structure and ion-leaching mechanism. The dissolved Zn2+, Pb2+ and As5+ concentrations in the leachate peaked at 0.56, 0.11 and 0.066 mg/L, respectively, whereas the Co2+ and Cd2+ concentrations were lower than the detection limit. The CPB porosity decreased from 46.07% to 40.88% by soaking, and 80% of the pore diameters were less than 13.81 µm. The permeability decreased from 0.8 to 0.5 cm/s, and the quantity, length, and diameter of the permeate channels decreased with soaking. An in-situ survey showed novel selective solidification. The Zn2+ concentration in the mine water was 10-20 times that of the background water, and the Pb2+ concentration was 2-4 times the regulated value. Although the Pb2+ content decreased significantly with mining depth, there remains a serious environmental risk. Mine water pollution can be reduced by adding a solidifying agent for Pb2+ and Zn2+, during CPB preparation.

Impact of gas flaring on surface and underground water: a case study of Anieze and Okwuibome areas of Delta State, Nigeria.

Gas flaring is a major activity in oil exploration processes in Nigeria with concerns on its effects on the oil communities. This study investigated the contribution of flare gases to pollution burden of Anieze and Okwuibome communities. Water samples were displayed at 10-m, 50-m, and 100-m locations from gas-flaring stations, and control samples were taken in another location. After a month, the water samples were examined for heavy metals, polycyclic aromatic hydrocarbons, and physico-chemical parameters. Pb was found only in the 50-m location and above the WHO standard. Fe, Zn, and Cr were detected in the order 10 m > 50 m > 100 m > control whereas Cd was detected in the order 100 m > 50 m > 10 m > control. Fe, Zn, Cr, and Cd were linked to gas-flaring activities. The total PAHs were found in the order 10 m (1929.43 µg/L) > 100 m (1759.64 µg/L) > 50 m (620.27 µg/L) > control (389.37 µg/L). The signature ratio related the PAH sources to combination of petroleum and combustion sources. The sources of the PAHs were linked to the flare gas. The study implicates gas-flaring activities for the increased pollution burden in the communities and suggests policies that guide its reduction in petroleum explorations.

Revisiting the Village Where Arsenic Contamination of Underground Water Was First Discovered in Bangladesh: Twenty-Five Years Later.

A survey was conducted in an As-affected village of Bangladesh-the first discovery of As contamination in the country-to assess the current situation and how implementation activities have worked to mitigate the problem. The As testing showed that the levels were less than the Bangladesh standard (50 µg/L) in all shallow tube-wells throughout the village. The questionnaire survey was conducted in the village as well as a neighboring As-affected village for comparison. The results revealed that there was a significant number of people using shallow tube-wells in both villages despite knowing that these wells could be contaminated with As and that safe water was available through a pipeline water supply. About 70% of responding households possessed their own water sources, mostly shallow tube-wells, and owners were less likely to choose tap water for drinking purpose than nonowners. In the village where As contamination was first reported, those individuals with a higher level of education and strong ties with neighbors were more likely to use shallow tube-well water for drinking purposes rather than tap water. This study suggests several measures to mobilize people to get safe water, namely providing subsides to install private taps, supplying public taps, and marketing and distributing handy water quality tests for households.

Modified activated carbon for deironing of underground water.

Successful water treatment is one of the most important aspects for a healthy human life and environmental protection. This study deals with the investigation of a modified catalytic material that is used in water treatment as one of the most promising filter media for water deironing. The activated carbon granules were coated with iron oxide by solution combustion synthesis (SCS) method in a muffle furnace oven. We investigated obtained samples using different diffraction and spectroscopic methods. The elemental composition of the surface and phases of produced materials and the results of comparative analysis with initial samples of the raw material used for the underground water deironing were presented. Using the SCS method, active coal granules were modified with a formation of fine dispersed and crystalline structures of magnetite on their surface. This had a positive effect on the catalytic capacity of the material for deironing of underground water as well as for the specific surface area increase. The residual concentration of total iron in the first portions of the filtrate when using modified samples was almost 3 times lower than for initial material.

[Pollution Characteristics and Migration of BTEX at a Chemical Contaminated Site in the Guangdong-Hong Kong-Macau Greater Bay Area].

In this study, we analyzed 247 soil and 20 groundwater samples from a typical chemical site in the Guangdong-Hong Kong-Macau Greater Bay Area and simulated the solute transport of pollutant benzene with the GMS software, in order to reconstruct the distribution and migration mechanism of benzene series (BTX) pollutants. The detected concentrations of benzene, ethylbenzene, m,p-xylene, and o-xylene exceeded the screening values in some soil and groundwater samples, indicating that the pollution of BTX in shallow groundwater was serious. Our simulation indicated an elliptical flow of benzene in groundwater (from northwest to southeast), mainly through convection, dispersion, and molecular diffusion. Along the vertical direction, the BTX was mainly distributed in the form of floating benzene, and some of the constituents were dissolved in the groundwater. Due to hydrodynamic mechanisms, the dissolved benzene tended to migrate faster and had hence a greater impact on the downstream groundwater. Through the model validation and analysis, we obtained a linear fitting correlation coefficient (R2) of 0.995 between the simulated and actual monitoring values, which indicates a good agreement between these two sets of data. The model had a high prediction accuracy, and could hence accurately determine the migration and distribution characteristics of benzene. Therefore, it provides a scientific basis for the accurate control and remediation of chemical contaminated sites in the Guangdong-Hong Kong-Macao Greater Bay Area.