Soil Slurry Research Articles

A slurry approach to identify nutrient critical source areas from subtropical catchment erosion

Targeting catchment nutrient critical source areas (CSAs) (areas contributing most of the nutrients in a catchment) is an efficient way to prioritize remediation sites for reducing nutrient runoff to waterways. We tested if the soil slurry approach – with particle sizes and sediment concentrations representative of those in streams during high rainfall events – can be used to identify potential CSAs within individual land use types, examine fire impacts, and identify the contribution of leaf litter in topsoil to nutrient export in subtropical catchments. We first confirmed the slurry approach met the prerequisite to identify CSAs with relatively higher nutrient contribution (not absolute load estimation) by comparing the slurry sampling with stream nutrient monitoring data. We validated that: 1) differences in slurry total nitrogen to phosphorus mass ratios from different land uses were consistent with stream monitoring data; and 2) our estimated nutrient export contribution from agricultural land, via the slurry approach, was comparable to that derived from monitoring data. Additionally, we found nutrient concentrations in slurries differed across soil types and management practice within individual land uses, correlating with nutrient concentrations in fine particles. These results indicate the slurry approach can be used to identify potential small-scale CSAs. Slurry results from burnt soils were also comparable to other studies showing increased levels of dissolved nutrient loss and higher nitrogen than phosphorus loss, than non-burnt soils. The slurry method also showed the contribution of leaf litter to slurry nutrient concentrations from topsoil was greater for dissolved nutrients than particulate nutrients, indicating different forms of nutrients need to be considered for impacts of vegetation. Our study reveals that the slurry method can be used to identify potential small-scale CSAs within the same land use from erosion and can account for impacts of vegetation and bushfires, providing timely information to guide catchment restoration actions.

Efficiency and mechanism on photocatalytic degradation of fluoranthene in soil by Z-scheme g-C3N4/α-Fe2O3 photocatalyst under simulated sunlight.

Polycyclic aromatic hydrocarbons (PAHs) in soil have potential harm on human health. However, remediation of PAH-contaminated soils through photocatalytic technology remains a challenge. Therefore, the photocatalyst g-C3N4/α-Fe2O3 was synthesized and applied to photocatalytic degradation of fluoranthene in soil. The physicochemical properties of g-C3N4/α-Fe2O3 and various degradation parameters, such as catalyst dosage, the ratio of water/soil, and initial pH, were investigated in detail. In soil slurry reaction system (water/soil=10:1, w/w), the optimal degradation efficiency on fluoranthene was 88.7% after simulated sunlight irradiation for 12 h (contaminated soil=2 g, initial fluoranthene concentration=36 mg/kg, catalyst dosage=5%, and pH=6.8), and the photocatalytic degradation followed pseudo-first-order kinetics. The degradation efficiency of g-C3N4/α-Fe2O3 was higher compared with P25. Degradation mechanism analysis showed that •O2- and h+ are the main active species in photocatalytic degradation process of fluoranthene by g-C3N4/α-Fe2O3. Coupling g-C3N4 and α-Fe2O3 enhances the interfacial charge transport capacity via Z-scheme charge transfer route and inhibits the recombination of photogenerated electrons and holes of g-C3N4 and α-Fe2O3, then significantly improves the production of active species and photocatalytic activity. Results showed that photocatalytic treatment of soil by g-C3N4/α-Fe2O3 is an effective strategy for remediation of soils contaminated by PAHs.

DNRA and ANRA-centered microbial mechanism of biogas slurry on soil nitrogen leaching: An indication from a laboratory study

Biogas slurry has ammonia (NH4+-N) abundance and is applied in a major production region, Southwest China. This study compared the consequent environmental risk of nitrogen (N) leaching in two major soils, yellow soil and calcareous soil, in Southwest China, and investigated underlying microbial mechanisms. Biogas slurry was applied to soil columns packed with yellow soil and calcareous soil at the rates of 0 to 240 kg N/hm2. Soil N leaching, N contents, and N-related bacteria gene abundances were measured, with their responses to slurry application analyzed through partial least squares-structural equation modeling (PLS-SEM). Nitrate (NO3−-N) dominated in N leaching as a result of soil NO3−-N accumulation and microbial regulation. Nitrification increased yellow soil NO3−-N contents and leaching, however, both were inhibited by dissimilatory nitrate reduction to ammonium (DNRA) and assimilatory nitrate reduction to ammonium (ANRA) in the two soils. Further, NO3−-N leaching was enhanced by biogas slurry in yellow soil by promoting nitrification and preventing DNRA and ANRA; but it was not affected in calcareous soil. Accordingly, yellow soil has higher NO3−-N leaching than calcareous soil. The leaching can be regulated by the DNRA and ANRA in both soils, which were overlooked relative to nitrification but probably reactive to slurry, warranting further exploration.

Theoretical Approach to Predicting the Diffusion Radius of Fracture Grouting in Soil–Rock Mixtures

Previously conducted studies have established that the soil–rock mixture in the Chongqing area has the characteristics of loose structure, poor stability, strong permeability, and so on. When building a tunnel in a soil–rock mixture stratum, it is necessary to reinforce the surface rock mass and surrounding rock by grouting to improve the safety of tunnel excavation. To study the diffusion mechanism of cement slurry (Bingham fluid) in soil–rock mixtures, based on the Bingham fluid flow equation and slurry diffusion model, the Bingham fluid fracture diffusion formula was derived, and field grouting tests and indoor model tests were carried out with soil–rock mixtures in the Chongqing area as the research object. The fracture grouting diffusion formula was verified and analyzed using the test data. The research results show that the theoretical calculation results of various working conditions are close to the actual test results (the error of indoor model test results is less than 3%, and the error of field test results is less than 5%). A Bingham fluid fracture diffusion formula has been developed that applies to various working conditions of fracture grouting of soil–rock mixtures and has a good prediction effect on the value of the fracture diffusion radius.

Effect of Concentration on Shear Stress of Nanyang Expansive Soil Slurry

The yield stress of mud is the basis for analyzing the flow and desilting of debris flow. Nanyang expansive soil mud was used as experimental materials, and the rheological curves of mud with different solid volume concentrations were obtained by using the stress scanning rheological experiment of Antonpa mcr702 rheometer. For Nanyang expansive soil slurry with different solid volume concentration, the change process of shear stress with shear rate is analyzed. According to the experimental results, the rheological process of Nanyang expansive soil slurry is divided into three stages: stress growth, stress attenuation and stress stability. The slurry concentration has obvious influence on the dynamic and static shear stress of mud.

Complete Genome Sequence of Bacteriophage vB_Hercules_Set, Which Infects Enteric Pathogen Salmonella enterica Serovar Typhimurium.

We report the isolation, sequencing, and annotation of bacteriophage vB_Hercules_Set, a kuttervirus infecting human pathogen Salmonella enterica. vB_Hercules_Set was isolated from a slurry of soil and deli meat collected in New Hampshire in 2021. The genome length is 157,338 nucleotides, containing 210 protein-coding genes and five tRNAs.

The study of the separation and deposition of dredging soil slurry under physical disturbance.

Most existing research uses experimental designs for testing, which cannot efficiently analyse the migration and sorting rules of particles in the disturbed slurry. Therefore, based on the fluidized bed flow film theory, a slurry flow film structure system is established according to the disturbance state of the fluid. On this basis, the particle size and distribution law of the disturbing force formed by slurry disturbance are analyzed, and the calculation model of single particle lift in the flowing film is also analyzed. On this basis, using Markov probability model, the probability of particle lifting and sorting between layers is theoretically deduced. Then, according to the particle ratio of the original mud, the settlement gradation of the particles in the disturbance is analyzed. It can also predict the separation degree of particle in natural turbulence, fluidized beds, and sludge mechanical dewatering. Finally, according to the particle flow software PFC (Particle Flow Code), the main influencing parameters (disturbing force and gradation) were verified and analyzed. The results show that the particle flow simulation results are in good agreement with the calculation results. The model of slurry membrane separation proposed in this paper can provide a basis for studying the mechanism of slurry disturbance separation and particle deposition.

Potential methane production in oligohaline wetlands undergoing erosion and accretion in the Mississippi River Delta Plain, Louisiana, USA

Methane (CH4) is steadily increasing in the atmosphere from different sources including wetlands. However, there is limited landscape level CH4 flux data in deltaic coastal systems where the availability of freshwater is impacted by the combined effect of climate change and anthropogenic impacts. Here we determine potential CH4 fluxes in oligohaline wetlands and benthic sediments in the Mississippi River Delta Plain (MRDP), which is undergoing the highest rate of wetland loss and most extensive hydrological wetland restoration in North America. We evaluate potential CH4 fluxes in two contrasting deltaic systems, one undergoing sediment accretion as result of a freshwater and sediment diversions (Wax Lake Delta, WLD), and one experiencing net land loss (Barataria-Lake Cataouatche, BLC). Short- (<4 days) and long-term (36 days) incubations using soil and sediment intact cores and slurries were performed at different temperatures representing seasonal differences (10, 20, 30 °C). Our study revealed that all habitats were net sources of atmospheric CH4 in all seasons, and CH4 fluxes were generally the highest for the 20 °C incubation. The CH4 flux was higher in the marsh habitat of the recently formed delta system (WLD) with total carbon content of 5–24 mg C cm−3 compared to the marsh habitat in BLC, which had high soil carbon content of 67–213 mg C cm−3. This suggests that the quantity of soil organic matter might not be a determining factor in CH4 flux. Overall, benthic habitats were found to have the lowest CH4 fluxes indicating that projected future conversions of marshes to open water in this region will impact the total wetland CH4 emission, although the overall contribution of such conversions to the regional and global carbon budgets is still unknown. Further research is needed to expand the CH4 flux studies by simultaneously using several methods across different wetland habitats.

Zero-Material Cost Production of Soil-Coated Fabrics with Underwater Superoleophobicity for Antifouling Oil/Water Separation.

Soil-coated fabrics were fabricated by scrape-coating of soil slurry onto cotton fabrics. The raw materials, soil, and cotton fabrics were, respectively, obtained from farmland and waste bed sheets, making the method a zero-material cost way to produce superwetting membrane. The superhydrophilic/underwater superoleophobic soil-coated fabrics exhibit high efficiency (>99%), ultra-high flux (~45,000 L m-2 h-1), and excellent antifouling behavior for separating water from various oils driven by gravity. The simple fabrication and superior performance suggest that the soil-coated fabric could be a promising candidate as a filtration membrane for practical applications in industrial oily wastewater and oil spill treatments.

Changes in Selected Forage Parameters of Meadow Timothy (Phleum pratense L.) Biomass and in the Soil as a Response to Slurry Interaction with Soil Conditioners

The aim of the research was to assess the effect of slurry and soil conditioners on Phleum pratense yield and its selected parameters and on soil nutrients. The second aspect of the experiment was to obtain information whether slurry and soil conditioners applied together will increase the accumulation of nitrogen, phosphorus and potassium in the soil compared to slurry applied on its own or together with NPK fertilizers. The research was carried out on the basis of a three-year (2015–2017) field experiment. The interaction of soil conditioners or mineral fertilizers with slurry was tested on forage grass of the Meadow timothy species of the Secesja variety, sown in autumn 2014. Grass total protein, crude fiber and crude ash content and net energy concentration (NE) were determined; additionally, at the end of the experiment, total nitrogen, phosphorus and potassium content in the soil was measured. The results of plant material analyses were statistically developed using a three-factor analysis of variance, while the results of soil content determination were developed with a one-factor analysis. The interaction of slurry with Humus Active or Rosahumus significantly increased the amount of meadow timothy biomass in relation to plants fertilized with slurry on its own (by 22% and 26%, respectively) or supplemented with NPK fertilizers (by 9% and 7%). The interaction of slurry with the Rosahumus soil conditioner resulted in a significant increase in meadow timothy crude fiber content compared to the effect of slurry applied on its own or with NPK fertilizers (by 5% and 6.5%). The interaction of slurry with soil conditioners did not result in a significant increase in total protein and crude ash content or in the net energy concentration compared to slurry applied on its own or with NPK fertilizers. Soil nutrient content determined after the experiment proved a significant impact of the interaction of soil conditioners and slurry on the accumulation of nitrogen, phosphorus and potassium.

Functional Filaments: Creating and Degrading pH-Indicating PLA Filaments for 3D Printing

With the rapid pace of advancements in additive manufacturing and techniques such as fused filament fabrication (FFF), the feedstocks used in these techniques should advance as well. While available filaments can be used to print highly customizable parts, the creation of the end part is often the only function of a given feedstock. In this study, novel FFF filaments with inherent environmental sensing functionalities were created by melt-blending poly(lactic acid) (PLA), poly(ethylene glycol) (PEG), and pH indicator powders (bromothymol blue, phenolphthalein, and thymol blue). The new PLA-PEG-indicator filaments were universally more crystalline than the PLA-only filaments (33-41% vs. 19% crystallinity), but changes in thermal stability and mechanical characteristics depended upon the indicator used; filaments containing bromothymol blue and thymol blue were more thermally stable, had higher tensile strength, and were less ductile than PLA-only filaments, while filaments containing phenolphthalein were less thermally stable, had lower tensile strength, and were more ductile. When the indicator-filled filaments were exposed to acidic, neutral, and basic solutions, all filaments functioned as effective pH sensors, though the bromothymol blue-containing filament was only successful as a base indicator. The biodegradability of the new filaments was evaluated by characterizing filament samples after aging in soil and soil slurry mixtures; the amount of physical deterioration and changes in filament crystallinity suggested that the bromothymol blue filament degraded faster than PLA-only filaments, while the phenolphthalein and thymol blue filaments saw decreases in degradation rates.

Online chemiluminescence determination of the hydroxyl radical using coumarin as a probe.

The hydroxyl radical (˙OH) is one of the strongest oxidizing species, which can react with a variety of organic and inorganic chemicals. Although ˙OH is widely used for degradation of environmental pollutants, detection of ˙OH remains a major challenge due to its high reactivity and short lifetime, especially online detection. In this study, a novel method for online detection of ˙OH by flow oxidization chemiluminescence (F-OCL) using coumarin as a probe was established. The concentrations of ˙OH determined by this new method were consistent with those determined by HPLC analysis. Because the new method has a short response speed, it was successfully used to quantify the dynamic change of ˙OH in the TiO2 photocatalytic process and Fenton reaction in real time. Furthermore, a combination of two chemiluminescence systems was developed to track the dynamics of ˙OH and hydrogen peroxide (H2O2) in homogeneous or heterogeneous Fenton reactions occurring in soil slurry. The proposed method and strategy have good application potential in online ROS monitoring of both natural and engineered systems.

The laterally confined consolidation of initially compacted and wetted swelling clay

This paper describes the laterally confined consolidation of an Israeli clay following compaction and swelling on wetting, including the measurement of lateral stresses. The results of the tests are compared to those obtained during consolidation of the clay from an initially slurried condition. In comparing the compression and expansion indices relative to vertical, lateral and mean stress, it was found that they varied, depending on the initial, preparation conditions; the values approached the slurried values with decreasing initial dry density. During unloading, the expansion indices were found to be independent of initial conditions, and essentially the same as those of the slurried soil. The coefficient of lateral earth pressure at rest during loading, K0, of the compacted and then wetted specimens was found to be reasonably constant regardless of initial soil conditions, but significantly higher than the value of the slurried soil. However, during unloading, the relationship between the normalized coefficients of lateral earth pressure at rest, K0'/K0, and the overconsolidation ratio, OCR, was found to be essentially the same as that obtained for the slurried soil.

Prediction method of soil horizontal displacement caused by non-uniform distribution of disturbance force in shield construction

Based on the Mindlin solution, this paper considers the influence of factors such as the non-uniform distribution of additional thrust of the cutter head influenced by lateral earth pressure in shield excavation, the non-uniform distribution of friction of shield shell influenced by soil softening and slurry spreading, and the non-uniform distribution of grouting pressure influenced by slurry spreading on the horizontal displacement of soil. The existing prediction formula is revised and verified by engineering examples. It is found that: affected by the shield construction disturbance force, the horizontal displacement behind the excavation surface is larger than that in front of the excavation surface, and the peak value of the horizontal displacement appears around the tunnel axis; through the verification of engineering case, when calculating the horizontal displacement in front of the excavation surface, the calculation results of both the modified formula and the original formula are in good agreement with the measured values, which can reflect the change trend of the measured horizontal displacement; when calculating the horizontal displacement behind the excavation surface, the calculation result of the existing formula has a great error due to the assumption of uniform distribution of disturbance force, which is different from the law of the measured result; the calculation result of the modified prediction formula is obviously in better agreement with the measured deformation value, and the error is smaller, which is more in line with the engineering reality.

Insights into enhanced removal of fluoranthene by sulfidated nanoscale zero-valent iron: In aqueous solution and soil slurry

In this study, 90.9% fluoranthene (FLT) was degraded in sodium percarbonate (2Na2CO3·3H2O2, SPC) oxidation system by Fe(II) combined with sulfidated nano zero valent iron (S-nZVI) activation within 60 min in aqueous solution. Scavenging experiments and electron paramagnetic resonance detection suggested that HO•, O2−•, and 1O2 contributed to the removal of FLT in SPC/Fe(II)/S-nZVI system. Based on the FLT degradation intermediates that were analyzed by GC-MS in SPC/Fe(II)/S-nZVI process, three potential FLT degradation pathways were speculated. The removal efficiency of FLT was inhibited with the presence of humic acid (HA) unless the concentration of HA was controlled at 1.0 mg L−1, and the presence of 1.0 mg L−1 HA favored the generation of HO•. The excellent removal performance of FLT (88.6%) could be achieved in actual groundwater by increasing the chemical dosages and adjusting the initial solution pH to acid environment. In soil slurry tests, the optimal reaction time and soil/water ratio were obtained as 24 h and 2/10, respectively, and the desired FLT degradation performances were obtained at pH 3 and 5 with the soil/water ratio of 2/10. This work effectively demonstrates the application potential of SPC/Fe(II)/S-nZVI system for the remediation of PAHs contamination in actual industrial sites.

Iron speciation changes and mobilization of colloids during redox cycling in Fe-rich, Icelandic peat soils

Soils of Iceland are characterized by an abundance of short-range order (SRO) iron (Fe) minerals and aluminosilicates. Interactions between these SRO mineral phases and soil organic carbon (OC) promote long-term stabilization of the latter through the formation of mineral-organic complexes and aggregates. However, Icelandic soils are also exposed to high rainfall events, which induce anoxic conditions, facilitate microbial reduction of ferric Fe, and may lead to the mobilization of mineral-associated OC. Here, we explored the fate of OC during Fe redox cycling by incubating six organic-rich soil horizons from three typical soil types across Iceland (Histosols, Histic and Gleyic Andosols) as soil slurries under anoxic conditions for up to 5 weeks and followed the effects of re-oxidation after 1, 2, and 5 weeks. Changes in solid-phase Fe speciation were assessed by combining Fe K-edge X-ray absorption spectroscopy with time-resolved parallel selective chemical extractions, and trends in aqueous element contents were measured in both the dissolved (<3 kDa) and fine colloidal fractions (3 kDa to 0.45 µm). In all soils, anoxic incubation resulted in microbial reduction of Fe(III) and concomitant increases in soil solution pH. However, soils containing SRO Fe minerals underwent more extensive Fe reduction. Rapid (<1 wk) increases in aqueous element contents (including Fe, Al, and OC) were recorded in all soil slurries, and mobilization of colloids occurred in soil horizons which reached the highest pH values (>4.6). Mobilized colloids persisted during re-oxidation of the soil slurries, which also resulted in the formation of new Fe mineral phases, the composition of which was influenced by initial soil Fe mineralogy. Collectively, our results suggest that increases in the frequency of redox cycles in Icelandic soils are likely to result in shifts in Fe mineralogy and may contribute to the increased mobilization of soil OC as organic-Fe-/Al-colloids.

Differential responses of soil nirS- and nirK-type denitrifying microbial communities to long-term application of biogas slurry in a paddy soil

Biogas slurry (BS) has been widely used as an organic fertilizer in rice paddy fields in China, with potential impacts on the diversity and activity of many biogeochemically important microbial communities. Among these communities, denitrifiers play a significant role in nitrogen (N) transformation and loss in such ecosystems. Here, we examined the abundance, diversity, and community composition of nirS- and nirK-type denitrifiers in paddy soils after long-term application of BS with different N contents using quantitative PCR and high-throughput sequencing. The experiment included four treatments: 1) mineral fertilizer with 270 kg N ha−1; 2) BS with 270 kg N ha−1; 3) BS with 405 kg N ha−1; and 4) BS with 540 kg N ha−1. Our results showed that BS application increased the soil nitrite reductase (NIR) activity by 5.9–27.5 % compared to mineral fertilizer application. Higher nirS gene abundance was observed in BS fertilized soils with increasing N content and was significantly correlated with NIR activity, but nirK gene abundance did not change with different fertilization intensities. Biogas slurry as a substitute for mineral fertilizer significantly decreased the alpha-diversity of only nirS-type denitrifiers at low application rate, but such negative effect was offset by increasing BS fertilization intensity. The community compositions of both nirS- and nirK-type denitrifiers shifted following changes in fertilizer type or intensity, and were significantly influenced by soil organic carbon (SOC), available phosphorus (AP), zinc (for both groups), and copper (for only nirK-type denitrifiers). The structural equation model indicated that the differences in soil NIR activity were mainly explained by SOC, AP, Zn, and the nirS-type denitrifier communities. Sulfurifustis, Thiobaclillus, Microvirgula and Duganella appeared to be the main genera governing NIR activity in the studied paddy fields. In conclusion, increasing BS application intensity can greatly alter the abundance and structure of the nirS-type denitrifying communities, and to a lesser extent, those of the nirK-type denitrifiers in paddy soils.

MgAl-layered double hydroxides/sodium alginate beads for nitrate adsorption from groundwater and potential use as a slow-release fertilizer

The excessive occurrence of nitrate in water can be a threat to the environment and human health. Yet, nitrate is an essential nutrient for plant growth. In this study, MgAl-layered double hydroxides/sodium alginate (MgAl-LDHs/SA) beads, synthesized via the crosslinking of MgAl-LDHs and sodium alginate, were employed for nitrate adsorption in both synthetic solution and groundwater, and then tested for slow nitrate release. The effects of pH on nitrate adsorption were insignificant within a wide range (pH 4–10, Langmuir maximum adsorption capacity ∼20–22 mg NO3−/g), while the presence of co-existing anions may negatively affect nitrate removal (HCO3− ≫ Cl− ≈ SO42−). The spent beads slowly swelled for 47 days at pH 7 (to ∼800%) in water before gradually dissolving. In soil slurries, the beads also enhanced the water retention capacity of the soil, implying their ability to retain water for plant growth. Nitrate release from the spent beads in water was slow (still in progress after 40 days) and in soil slurries was low (cumulative desorption <30%), due to the strong complexes formed between LDHs and nitrate molecules. However, the release behavior can be manipulated by changing the physical form of the beads (e.g., grinding; duration in water shortened to ∼5 days, desorption in soil doubled). Results of this study show the MgAl-LDHs/SA beads have the potential of being adsorbents for pump-and-treat water purification and then slow release fertilizers (SRFs) for better nutrient management for crop growth.

An Interfacial Label-Free Electrochemical Approach to in-Situ Soil pH Monitoring

Soil is a critical entity of Earth’s ecosystem. Healthy soil supports a landscape that is more resilient to the impacts of drought, flood, or fire. It also helps regulate the Earth’s climate. Real time assessment of soil health is imperative to improving crop yield as well to sustain an ever growing human population. Soil health encompasses moisture content, phosphorus, pH, nitrate, and other parameters. One of the most important parameters is soil pH which affects nutrients availability to plants and nutrients leaching in the soil. Current soil pH assessment techniques require destructive sampling of the soil where a core of soil is collected then treated at a lab before measuring the pH. This method measures pH at time points and doesn’t provide a continuous real time monitoring of pH. This work utilizes commercial screen printed electrodes with a pH sensitive coating for low cost continuous in-situ soil pH measurement. The coating is made up from alizarin an anthraquinone compound that undergoes a redox reaction in the presence of hydrogen ions and nafion an ion permeable membrane. Square wave voltammetry (SWV) is utilized since the output current signal shows the redox of alizarin while rejecting the capacitive current that’s inherent in soil. This redox peak current potential is dependent on the concentration of hydrogen ions which is gives a direct measure of pH. Due to the sensitivity of SWV, it is possible to measure unbuffered soil ph (without CaCl2 and KCl to improve the electrolyte ionic strength) accurately. The nafion layer protects the alizarin from dissolving in water present in soil as well as promoting the diffusion of hydrogen ions into the coating thus improving sensitivity. The alizarin has been used previously in screen printed electrodes however, this is the first work to our knowledge to utilize it to measure soil pH in-situ over a period of time. The sensor output was first calibrated in different unbuffered soil textures against the gold standard glass electrode. The calibrated response of the sensor in unbuffered sandy loam soil slurry is shown in Fig. 1. Then the sensor accuracy was validated by testing different soil samples using the sensor and later mixing it with deionized water and measuring the pH using the glass electrode. The sensor’s stability was evaluated by taking a measurement every hour for 48 hours without removing it from the soil sample. The temporal study showed a coefficient of variation less than 1% and an average reading of within 0.3 pH of the actual pH of the soil sample.Fig. 1 Calibrated response of proposed sensor in sandy loam soil slurries with 40% water Figure 1

Comprehensive Multi-compartment Sampling for Quantification of Long-Term Accumulation of PAHs in Soils.

Long-term accumulation in the soils of ubiquitous organic pollutants such as many polycyclic aromatic hydrocarbons (PAHs) depends on deposition from the atmosphere, revolatilization, leaching, and degradation processes such as photolysis and biodegradation. Quantifying the phase distribution and fluxes of these compounds across environmental compartments is thus crucial to understand the long-term contaminant fate. The gas-phase exchange between soil and atmosphere follows chemical fugacity gradients that can be approximated by gas-phase concentrations, yet which are difficult to measure directly. Thus, passive sampling, measured sorption isotherms, or empirical relationships to estimate sorption distribution have been combined in this study to determine aqueous (or gas) phase concentrations from measured bulk concentrations in soil solids. All these methods have their strengths and weaknesses but agree within 1 order of magnitude except for ex situ passive samplers employed in soil slurries, which estimated much lower concentrations in soil water and gas likely due to experimental artifacts. In field measurements, PAH concentrations determined in the atmosphere show a pronounced seasonality with some revolatilization during summer and gaseous deposition during winter, but overall dry deposition dominates annual mean fluxes. The characteristic patterns of PAHs in the different phases (gas phase, atmospheric passive samplers, bulk deposition, and soil solids) confirm the expected compound-specific distribution pattern and behavior. Since revolatilization fluxes in summer are only minor and wet and dry deposition is ongoing, our results clearly show that the PAH loads in topsoils will continue to increase.