Organic Clay Research Articles

Assessment of health risks associated with prediction of vegetable inorganic arsenic concentrations given different soil properties.

Inorganic arsenic (iAs) is a carcinogen. Vegetables such as water spinach (Ipomoea aquatica Forssk.) and amaranth (Amaranthus mangostanus L.) are recognized as high-risk sources of iAs exposure because they can accumulate significant amounts of iAs and are widely consumed. To ensure safe cultivation conditions, this study aimed to establish prediction models for iAs concentration in the edible parts of water spinach and amaranth based on soil properties. Subsequently, health risk assessments associated with iAs exposure through the consumption of these vegetables were conducted using prediction models. Soil samples were collected from agricultural fields in Taiwan and used in the pot experiments. Pearson correlation and partial correlation analyses were used to explore the relationship between soil properties, including total As, clay, organic matter, iron oxides and available phosphates, and iAs concentration in edible parts of water spinach and amaranth. Prediction models based on soil properties were developed by stepwise multiple linear regression. Health risk assessments were conducted using the Monte Carlo algorithm. The results indicate that total As and organic matter contents in soil were major predictors of iAs concentration in water spinach, whereas those in amaranth were total As and clay contents. Therefore, higher health risks for consuming water spinach and amaranth are associated with higher levels of organic matter and clay contents in soil, respectively, and these are crucial factors to consider to ensure food safety. This study suggested that As-elevated soils enriched with organic matter and clay contents should be avoided when growing water spinach and amaranth, respectively.

Kajian Penyebab Rembesan pada Bendungan Situ Lembang di Kabupaten Bandung Barat

A dam is a construction structure built to hold back the flow of water from upstream to downstream. Geographically, the Situ Lembang Dam is located in Kertawangi Village, Cisarua District, West Bandung Regency, the Situ Lembang Dam has a length of 350 m. One of the problems with dams is seepage. Seepage is defined as the property of a porous material that allows fluid in the form of water to flow through the pore cavity. The aim of this research is to determine the effect of variations in hydrostatic height on seepage that occurs in the dam body. The material forming the dam body is a type of organic clay. Almost all of the instrumentation equipment at 'Situ Lembang' no longer functions. This research uses laboratory simulations to review seepage patterns and seepage discharge against variations in hydrostatic height. Seepage discharge (Qf) is calculated using 3 methods, namely the Dupuit method, Schaffernak method, and Cassagrande method. The hydrostatic height variations reviewed are H10, H15, and H20.

Performance of Nickel Slag as a Stabilization Material for Soft Soil

The chemical soil stabilization method is an effort to improve soil bearing capacity according to soil work specifications in construction. The use of conventional stabilization materials, such as cement and lime, is considered environmentally unfriendly. Utilizing by-products from the mining industry becomes an alternative that can be developed in soil improvement efforts. This research aims to examine the influence of nickel slag on the enhancement of soil bearing capacity as observed through its unconfined compressive strength value. In this study, the concentration of added nickel slag as a stabilization material is 3%, 6%, 9%, and 12% by dry soil weight. The test specimens used are cylinders with a diameter of 5 cm and a height of 10 cm. Unconfined compressive strength testing is conducted after the specimens are cured for 14 days. The results of this study indicate that the clay soil used is classified as organic clay with high plasticity based on the USCS classification, with an unconfined compressive strength value of 0.2 kg/cm2. The addition of nickel slag with concentrations of 3%, 6%, 9%, and 12% results in respective increases in unconfined compressive strength by 46%, 50%, 68%, and 47%. These findings demonstrate that the optimum nickel slag content of 6% provides the maximum unconfined compressive strength. Therefore, it can be concluded that nickel slag, as a source of silica, has the potential to be used as an alternative material in soft soil improvement.

Atividade residual e adsorção do tebuthiuron em diferentes solos

ABSTRACT Applications of tebuthiuron can increase the risks of environmental contamination and hinder the cultivation of sensitive species in succession. The objective of this work was to assess the residual activity and sorption of the herbicide tebuthiuron in soils with different physical and chemical attributes. The experiments were conducted in a completely randomized design with four replicates. The experiment for determining residual activity was conducted in a 2 × 7 factorial arrangement consisted of two herbicide doses (0.6 and 1.2 kg a.i. [active ingredient] ha-1) and seven sowing times (0, 60, 120, 180, 240, 300, and 360 days after herbicide application) in sandy loam and sandy clay loam soils. The experiment for evaluating sorption was conducted in a sandy loam soil and two clay loam soils with applications of increasing tebuthiuron doses (0.025, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.50, 0.60, 0.70, and 0.80 kg a.i. ha-1). Regarding residual activity, the herbicide’s effect of the decreased over time, with no toxicity detected 360 days after application (DAA), regardless of the soils and doses used. Sandy loam soils had lower sorption, resulting in lower shoot dry weight and plant height and in higher phytotoxicity 21 days after emergence. Residual activity was detected 360 DAA in the studied soils. Tebuthiuron sorption was higher in soils with higher organic carbon and clay contents.

Simultaneous preparation and reinforcement of organic 2D clay layers/cis-1,4-polyisoprene composite latex and its high-performance films

Simultaneous preparation and reinforcement of organic 2D clay layers/cis-1,4-polyisoprene composite latex and its high-performance films

The effects of the rock stratigraphy on TPH/PAH absorption and transmission in some sections of the Gokana and Khana Local Government Areas

Concentration of TPH/PAH in soils in parts of Gokana and Khana local government areas of Rivers state were examined using samples from 30 shallow wells drilled with hand auger. The core intervals penetrated, ranged between 0 on the surface to 100cm at total depth and was composited into two sections corresponding to upper 0 – 0.5m and lower 0.51 – 0.1m sections respectively. The samples were described to determine their sedimentological characteristics and effect on absorption and transmission of fluids. The total hydrocarbon content in samples of the study area were determined following the EPA 1664 Hexane Method (Method No: EPA 418.1/413.2 & EPA 1664). Individual concentrations of identified PAH congeners were noted and combined to generate the PAH concentrations in each of the two composited sections of the 30 sampled locations. The sedimentology of the logged sections consists mostly of peaty clay, clayey sands and organic clay in the upper section and clayey silt and clayey sand in the lower section. TPH in the study area ranged between 20612mg/kg at Location 15 to 37.09mg/kg at Location 11 for the upper (0 – 0.5m) sections and 14731mg/kg at Location 12 to 14.67mg/kg at Location 17 for the lower (0.51 – 1m) section. PAH ranged from 9.55mg/kg at Location 12 to <0.01mg/kg at several other Locations for the upper (0 – 0.5m) sections and 5.71mg/kg at Location 11 to <0.01mg/kg at several other Locations for the lower (0.51 – 1m) section. Correlation of sedimentology descriptions with the geochemical analysis indicates high concentrations of total petroleum hydrocarbon (TPH) and polycyclic aromatic hydrocarbon (PAH) within the upper (0 – 0.5m) sections than in the lower (0.51 – 0.1m) sections in consonant with the stratigraphy of the logged section.

Comparative Soil Analysis from Different Crime Prone Areas of Kottayam and Kollam Districts of Kerala for Forensic Characterization

Soil is the loose surface material that covers land on which plants grow. It consists of a mixture of organic remains, clay, and rock particles, which gives it its uniqueness from place to place. Because of the uniqueness of soil, it has a high evidential value in the field of forensic science. In the present study, research has been conducted to check the range of variations in the soil collected from different crime-prone areas of Kottayam and Kollam districts of Kerala by physical, chemical, microscopic, and instrumental examination. In physical examination, soil colour, texture, consistency, and density were measured, and in chemical examination, pH and total soluble sulphate of the soil were measured. In instrumental examination, Heavy metal analysis was done by using Atomic Absorption Spectrometry (AAS), which helps to measure the amount of trace elements present in the soil. The study found that each soil has some significant variations that make it unique. In the field of forensic science, this can be highly helpful in determining the origin of soil by examining its colour, texture, structure, content, etc.

A seismic prediction method of reservoir brittleness based on mineral composition and pore structure

The Lucaogou Formation, a typical fine-grained mixed formation in the Jimusaer Sag of the Junggar Basin, exhibits considerable potential for hydrocarbon exploration. Accurate brittle prediction is a crucial factor in determining hydraulic fracturing effectiveness. However, the area features complex lithological characteristics, including carbonate rocks, clastic rocks, volcanic rocks, and gypsum interbeds, along with thin layering and sporadic sweet spots. Traditional prediction methods offer limited resolution and there is an urgent need for a seismic brittle prediction method tailored to this complex geological environment. This paper presents a multi-mineral composition equivalent model for complex lithologies that enables the accurate calculation of Vp and Vs These ratios serve as the foundation for pre-stack elastic parameter predictions, which include Poisson’s ratio and Young’s modulus. By comparing the predicted parameters with well-logging measurements, the prediction accuracy is improved to 82%, with particularly high conformity in intervals characterized by high organic matter and clay content. Additionally, a three-dimensional brittle modeling approach reveals that the brittleness of the reservoir exceeds that of the surrounding rock, showing a gradual improvement in brittleness with increasing burial depth from southeast to northwest. The central area exhibits relatively good brittleness, with a stable, blocky distribution pattern.

Assessing Suitability of Different Extractants for Estimating Plant Available Boron in Lateritic Soils (Alfisols)

ABSTRACT The depth-wise distribution of plant available boron (B) extracted by dilute HCl (HCl), tartaric acid (TA), hot calcium chloride (HCC), hot water (HW), ammonium acetate (AA), Ammonium Bicarbonate-Diethylene Triamine Penta Acetic acid (AB-DTPA) and mannitol calcium chloride (MCC) in some acidic lateritic soils (Alfisols) of Birbhum, West Bengal, India, was examined in relation to their physicochemical properties and grain yield, concentration and removal of B by rice grain to screen out the most suitable extractant for lateritic soils. The highest overall mean B concentration of surface soils (0.325 mg kg−1) was obtained by 0.05 M HCl, whereas its lowest content was obtained by MCC (0.145 mg kg−1) and with increasing depth its content was decreased for all the extractants used. The sequence of B extraction by various extractants was as follows: HCl > TA > HCC > HW > AA > AB-DTPA > MCC. Higher extractability of HCl is due to lower pH and attendant dissolution of soil minerals. Most often, decrease in organic carbon, clay, CEC, amorphous iron and aluminum oxides or increase in manganese oxide contributed to the observed drop in B along soil depth. The B extracted by different extractants showed significant positive correlations among themselves. The HCl extracted B showed the highest correlation with grain yield, concentration, and removal of B by rice grain. The HCl extractable B enhanced adjusted R2 value in multiple regression equation, boosting the predictability of the model. Thus, in acidic lateritic soils (Alfisols), the 0.05 M HCl is the best extract for estimating plant available B.

The effect of organic clay on the properties of TPI/NR composite materials

TPI shape memory materials’ low flexibility and poor mechanical properties currently limit their use in a broader range of applications. Most scholars use high performance fillers to improve their mechanical properties. However, the cost of high-performance fillers is high. Therefore, the introduction of flexible natural rubber (NR) and low-cost organic clay (OC) into the trans-1,4-polyisoprene (TPI) matrix as the reinforcing phase. A new shape memory polymer— TPI/NR/OC, was prepared by mechanical melt blending.The effect of the changes of filler content on the thermodynamic properties of the composite materials were revealed by series of tests. The results showed that OC formed a homogeneous intercalation structure with the composite matrix, and OC promoted the crystallization of TPI, and part of OC was able to form physical entanglements with the molecular chains of the composites, which led to the improvement of mechanical and shape memory properties. The tensile strength of the composite at an OC dosage of 3.6phr was 19.9 MPa, with a shape fixity ratio of 97.9% and a shape recovery ratio of 96.8%. The relevant findings of this research may provide valuable design references for more areas of application of shape memory composites.

Proximal and remote sensing – what makes the best farm digital soil maps?

Context Digital soil maps (DSM) across large areas have an inability to capture soil variation at within-fields despite being at fine spatial resolutions. In addition, creating field-extent soil maps is relatively rare, largely due to cost. Aims To overcome these limitations by creating soil maps across multiple fields/farms and assessing the value of different remote sensing (RS) and on-the-go proximal (PS) datasets to do this. Methods The value of different RS and on-the-go PS data was tested individually, and in combination for mapping three different topsoil and subsoil properties (organic carbon, clay, and pH) for three cropping farms across Australia using DSM techniques. Key results Using both PS and RS data layers created the best predictions. Using RS data only generally led to better predictions than PS data only, likely because soil variation is driven by a number of factors, and there is a larger suite of RS variables that represent these. Despite this, PS gamma radiometrics potassium was the most widely used variable in the PS and RS scenario. The RS variables based on satellite imagery (NDVI and bare earth) were important predictors for many models, demonstrating that imagery of crops and bare soil represent variation in soil well. Conclusions The results demonstrate the value of combining both PS and RS data layers together to map agronomically important topsoil and subsoil properties at fine spatial resolutions across diverse cropping farms. Implications Growers that invest in implementing this could then use these products to inform important decisions regarding management of soil and crops.

Spatio-temporal trends of mercury levels in alluvial gold mining spoils areas monitored between rainy and dry seasons in the Peruvian Amazon

Artisanal and small-scale gold mining (ASGM) in the Amazon has degraded tropical forests and escalated mercury (Hg) pollution, affecting biodiversity, ecological processes and rural livelihoods. In the Peruvian Amazon, ASGM annually releases some 181 tons of Hg into the environment. Despite some recent advances in understanding the spatial distribution of Hg within gold mine spoils and the surrounding landscape, temporal dynamics in Hg movement are not well understood. We aimed to reveal spatio-temporal trends of soil Hg in areas degraded by ASGM.,. We analyzed soil and sediment samples during the dry and rainy seasons across 14 ha of potentially contaminated sites and natural forests, in the vicinities of the Native community of San Jacinto in Madre de Dios, Peru. Soil Hg levels of areas impacted by ASGM (0.02 ± 0.02 mg kg−1) were generally below soil environmental quality standards (6.60 mg kg−1). However, they showed high variability, mainly explained by the type of natural cover vegetation, soil organic matter (SOM), clay and sand particles. Temporal trends in Hg levels in soils between seasons differed between landscape units distinguished in the mine spoils. During the rainy season, Hg levels decreased up to 45.5% in uncovered soils, while in artificial pond sediments Hg increased by up to 961%. During the dry season, uncovered degraded soils were more prone to lose Hg than sites covered by vegetation, mainly due to higher soil temperatures and concomitantly increasing volatilization. Soils from natural forests and degraded soil covered by regenerating vegetation showed a high capacity to retain Hg mainly due to the higher plant biomass, higher SOM, and increasing concentrations of clay particles. Disturbingly, our findings suggest high Hg mobility from gold mine spoil to close by sedimentary materials, mainly in artificial ponds through alluvial deposition and pluvial lixiviation. Thus, further research is needed on monitoring, and remediation of sediments in artificial to design sustainable land use strategies.

Lead in paint-contaminated residential soils with varying physicochemical properties from three large US cities: assessment of geochemical forms and recommendations on amendments for immobilization

Lead in yard soils has been recognized as the principal source of excess lead absorption among young children. The hazard imposed by soil lead is dependent on the geochemical forms of lead in soils. Soil properties such as pH, soil organic matter, clay, and carbonate content influence the geochemical forms of lead in soil. This study was conducted to investigate the correlation between soil properties and the geochemical speciation of lead in lead paint-contaminated residential soils from three major US cities. A comprehensive field survey was conducted, involving the collection of soils from ten houses in each of the cities: Baltimore, San Antonio, and Detroit. The influence of soil properties on geochemical speciation was analyzed to identify effective immobilization amendments for each soil type. Results showed that soils collected from San Antonio were slightly alkaline, whereas those from Baltimore were slightly acidic. Soils collected from Detroit were neutral to mildly alkaline in pH. San Antonio soils had relatively high soil salinity, high clay content, moderate to high soil organic matter (SOM), and high total carbon (TC). In contrast, soils collected from Baltimore had lower salinity and clay content, low SOM, and total carbon. Soils from Detroit exhibited relatively high salinity, clay, SOM, and TC contents. The average total soil lead concentrations were as follows; San Antonio 4,073 mg/kg, Baltimore 2,706 mg/kg, and Detroit 850 mg/kg. Geochemical speciation studies revealed significant differences in lead distribution among the studied soils. San Antonio soils exhibited high carbonate-bound and organic matter-bound fractions, while Baltimore soils had elevated soluble + exchangeable fractions. Detroit soils showed substantial lead in organic matter-bound fractions. Correlation analysis showed that the soil properties influencing exchangeable lead, were pH, total Al, and total Ca for San Antonio soils; pH and total P for Baltimore soils; and SOM and total Al for Detroit soils. Correlation analysis showed that there is a significant negative correlation (p < 0.05) between exchangeable lead and total Al (r = −0.653), and total Ca (r = −0.438) for San Antonio soils; pH (r = −0.286) and total p (r = −0.314) for Baltimore soils; and SOM (r = −0.628) and total Al (r = −0.408) for Detroit soils. Based on these results, the best potential immobilization amendments for each of these cities were predicted.

Prediction of the mobility and persistence of eight antibiotics based on soil characteristics

Antibiotics are widely used in intensive animal husbandry in the Netherlands and are subsequently emitted to soil via manure. To predict degradation and mobility in soil, generic sorption models have been derived. However, most of the coefficients used in generic models are based on a limited range of soils and have not been validated for agricultural soils in the Netherlands. To improve model predictions and assess to what extent differences among soils affect sorption and degradation, an experimental study has been performed. Using a recently developed experimental approach, both the degradation (DT50) and mobility (Kd) of eight selected commonly used antibiotics were determined in 29 typical Dutch agricultural soils. Median DT50 values range from 5.3 days for Sulfadiazine to 120 days for Trimethoprim but are affected by soil type. The ratio of the lowest and highest DT50 for a given antibiotic among soils can be as large as 151, for Tylosin. Measured values of the logKd also range from 0.19 for Sulfadiazine to more than 2 for Doxycycline, Flumequine, Trimethoprim, Tylosin and Enrofloxacine. The impact of soil on Kd is large, especially for more mobile antibiotics such as Sulfadoxine and Sulfadiazine. Both the range in DT50 and Kd can be predicted reasonably well using a Freundlich type regression model that accounts for the variation in soil type and sampling depth. Organic matter, iron oxides, pH and clay content appear to be the main constituents and explain between 29 % (Trimethoprim) and 77 % of the variation in DT50 and between 64 % (Lincomycin) and 87 % (Sulfadoxine and Sulfadiazine) of the variation of Kd. The effect of depth on DT50 and Kd is however limited. The information thus obtained in combination with local data on soil type can be used to more accurately predict the potential risk of relevant antibiotics in soil and transport to ground- and nearby surface waters.

Soil Properties Affecting Mercury (Hg) Adsorption-Desorption: Determine The Extent of Soil Pollution Risk

One of the hazardous wastes generated from unlicensed gold mining is mercury. Mercury is a toxic metal that can have a negative impact on the environment such as reducing soil and water quality and disturbing human health. The presence of mercury in the soil is completely controlled by adsorption-desorption of various sorbents. Soil properties greatly affect the adsorption and desorption of mercury in the soil. Because different soil properties will adsorb and desorb mercury in different ways and amounts. The purpose of writing this article is to review the results of previous research on the adsorption-desorption of mercury in soil so as to determine the extent of the risk of soil and environmental pollution. The method used in this writing is to collect and process data sources from previous research published in scientific articles, books, and discussion results. The results show that soils with high organic matter, iron oxide and clay content can absorb more Hg2+. In addition, lower pH has more hydroxylated surfaces that can adsorb more Hg2+. Irreversibility was found where the amount released or desorbed was less than the adsorption of mercury.

Determining parameters of peat soil for finite-element analysis using the Cam Clay model

A practical procedure for determining soil parameters when analysing the deformation of peat by finite-element analysis (FEA) using the Cam Clay model is presented. FEA has not been frequently used to predict the deformation of peat soil, even though it can be a powerful prediction tool. The main reason for this is that a practical method for determining parameters has not been established. In this paper, the remarkable correlation between the soil parameters required for FEA using the Cam Clay model and the natural water content (wn) and ignition loss (Li) of peat and organic clay is presented. Then, based on this correlation, a flow chart for determining the soil parameters of peat and organic clay is proposed. Using this chart, it is possible to determine soil parameters directly from triaxial compression, oedometer and other detailed tests or to estimate them from wn, Li and other physical indexes. A trial embankment on peat soil in Hokkaido, Japan, was also created. FEA was performed on the trial embankment using the proposed procedure for determining the soil parameters. The results of the FEA corresponded to the measured settlement behaviour in the trial embankment with an accuracy in the range −4% to +8%. The FEA results also modelled the measured behaviour of pore water pressure and lateral and vertical displacements in the trial embankment very well.

Temporal variability of saturated hydraulic conductivity on a typical black soil slope of northeast China

Saturated hydraulic conductivity (Ks) is highly variable in both space and time. Compared to its spatial variability, however, the temporal Ks variability has rarely been studied or taken into account in the hydrological modelling. The objectives were to characterize the slope-scale temporal variability of Ks and to diagnose the primary factors regulating Ks variation during the growing season. In the black soil region of northeast China, a typical slope farmland dominated by silt loam was selected and divided into five sections with respect to soil erosion. Soil samples were collected in each section at approximately every 3 weeks during the maize growing season, and Ks, bulk density (BD), land surface roughness, wet-aggregate stability (WAS), soil organic carbon content (SOC), clay and sand contents (SAND) were investigated. Mainly owing to root growth, precipitation and agricultural management, strong temporal variability of Ks was observed in each of the five sections, as the corresponding coefficients of variation all exceeded 35 %. Using the redundancy analysis (RDA) and classical correlation analyses, the primary variables controlling Ks distribution varied among sections, i.e., precipitation (P) and SAND in the erosive section and BD in the others. The predominance of BD was also manifested when performing RDA and structural equation modelling (SEM) over the entire slope covering all five sections.The other significant factors included SAND, SOC, P and WAS, in the decreasing order of direct path coefficient. In addition, these factors also indirectly affected Ks through their influence on BD and/or other factors. These findings demonstrate the strong temporal variability of Ks throughout the maize growing season and intricate interactions of Ks with related factors, and have important implications for hydrological modelling and agricultural production in the black soil region of northeast China and other similar regions.

Physico-Chemical Properties of Surface Soil in Ashoknagar District of Madhya Pradesh for Agricultural Production

Looking at the crop production and soil related constraints in different village of Ashoknagar District of Madhya Pradesh we found it important to characterize the soils of the village. For this purpose, one hundred twenty-five GPS-based surface soil samples (0-15 cm) were collected from five blocks (Mungaoli, Chanderi, Ishagarh, Ashoknagar and Sadora) of Ashoknagar district from April to May 2017-2018. Soils were studied for their physical and chemical characteristics - status of sand,silt,clay percent varied from 36.6-56.7%, 3.9-38% and 25.2-42.4%, with the mean value of 47.5%, 17.2% or 35.1%, respectively and soil pH, EC, OC, Calcium carbonate, total Nitrogen or available sulphur were observed in the range of 7.2– 8.6, 0.32 - 0.62dSm‑1, 2.14 - 7.06 gkg-1, 0.5 –3.5 % 0.01-0.24 % and 4.36 – 40.25 mg kg-1under different villages of the investigated area with the average value of 8.0, 0.45dSm‑1, 4.35gkg-1, 1.7% and 0.11 %,14.68 mg kg-1 respectively. The availability of sulphur increased with an increase in organic carbon and clay content in the soil.

Spatial distribution and partition of polycyclic aromatic hydrocarbons (PAHs) in the water and sediment of the southern Bohai Sea: Yellow River and PAH property influences

The marginal Bohai Sea, connected to the northwestern Pacific Ocean, is threatened by human activity. The Yellow River, the second largest river in China, drains large amounts of water, silts, and polycyclic aromatic hydrocarbons (PAHs) into the southern Bohai Sea; however, to what extent the Yellow River inputs influence the spatial distributions and partitions of PAHs in the southern Bohai Sea is not well known. Therefore, this study collected surface water, bottom water, and sediment samples from the southern Bohai Sea and analyzed them to examine the spatial distributions and partitions of 15 priority PAHs. The results showed that PAH concentrations ranged from 26.9 to 50.1 ng L–1 in surface water, 18.8 to 44.1 ng L–1 in bottom water, and 7.4 to 143.9 ng g–1 in sediment, with higher proportions of four-, five-, and six-ring PAHs in sediment than in water. PAH inputs from the Yellow River and sea coastal currents determined the spatial distribution of PAH concentrations in water and sediment, with an overall decrease from the estuary to the southeast. However, the solid dilution effect of input silts from the Yellow River and the liquid dilution effect of water from the Yellow River and Yellow Sea led to lower PAH concentrations in the water and sediment of the southern Bohai Sea than those in other areas of the Bohai Sea. PAH exchange between the atmosphere and seawater led to significantly higher individual PAH concentrations (except for acenaphthylene) in the surface water than in the bottom water, with ratios significantly related to the PAH n-octanol-water partition coefficient, organic carbon-water partition coefficient, and Henry's law constants. These parameters also determined PAH partitioning between the bottom water and sediment. Individual and total PAH concentrations in the sediment were significantly correlated with organic matter, clay, and silt contents. Therefore, the partitions and spatial distributions of PAHs in the southern Bohai Sea comprehensively depend on PAH properties, PAH inputs from the Yellow River and the atmosphere, sea currents, and seawater and sediment properties. The ecological risks posed by individual PAHs in both water and sediment were negligible or acceptable.

The Phase Inversion Mechanism of the pH-Sensitive Reversible Invert Emulsion.

Reversible emulsification drilling fluids can achieve conversion between oil-based drilling fluids and water-based drilling fluids at different stages of drilling and completion, combining the advantages of both to achieve the desired drilling and completion effects. The foundation of reversible emulsion drilling fluids lies in reversible emulsions, and the core of a reversible emulsion is the reversible emulsifier. In this study, we prepared a reversible emulsifier, DMOB(N,N-dimethyl-N'-oleic acid-1,4-butanediamine), and investigated the reversible phase inversion process of reversible emulsions, including the changes in the reversible emulsifier (HLB) and its distribution at the oil-water interface (zeta potential). From the perspective of the acid-alkali response mechanism of reversible emulsifiers, we explored the reversible phase inversion mechanism of reversible emulsions and reversible emulsification drilling fluids. It was revealed that the reversible phase inversion of emulsions could be achieved by adjusting the pH of the emulsion system. Then the proportion of ionic surfactants changed in the oil-water interface and subsequently raised/lowered the HLB value of the composite emulsifier at the oil-water interface, leading to reversible phase inversion of the emulsion. The introduction of organic clays into reversible emulsification drilling fluid can affect the reversible conversion performance of the drilling fluids at the oil-water interface. Thus, we also investigated the influence of organic clays on reversible emulsions. It was demonstrated that a dosage of organic clay of ≤2.50 g/100 mL could maintain the reversible phase inversion performance of reversible emulsions. By analyzing the microstructure of the emulsion and the complex oil-water interface, we revealed the mechanism of the influence of organic clay on the reversible emulsion. Organic clay distributed at the oil-water interface not only formed a complex emulsifier with surfactants, but also affected the microstructure of the emulsion, resulting in a difficult acid-induced phase transition, an easy alkali-induced phase transition, and improved overall stability.