Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

Stabilization of microbial network by co-digestion of swine manure and organic wastes

The production of biogas from organic waste has attracted considerable interest as a solution to current energy and waste management challenges. This study explored the methane (CH4) production potential of swine manure (SM), food waste (FW), and tomato waste (TW) and the changes in the microbial community involved in the anaerobic digestion process. The results revealed that the CH4 production potentials of the four kinds of SM samples were influenced by the characteristics of SM (e.g., age and storage period). Among the four kinds of SM samples, the CH4 yield from the manure directly sampled from primiparous sows (SM3) was the highest. The CH4 yield was significantly improved when SM3 was co-digested with FW, but not with TW. The addition of SM fostered a stable CH4 production community by enhancing the interaction between methanogens and syntrophic bacteria. Furthermore, the addition of FW as a co-substrate may improve the functional redundancy structure of the methanogenesis-associated network. Overall, the characteristics of SM must be considered to achieve consistent CH4 yield efficiency from anaerobic digestion since CH4 production potentials of SM can be different. Also, the contribution of co-substrate to the synergistic relationship between methanogens and syntrophic bacteria can be considered when a co-substrate is selected in order to enhace CH4 yield from SM.

Graphitic-carbon-nitride-hydrophilicity-dependent photocatalytic degradation of antibiotics with different log Kow

The surface hydrophilicity of a photocatalyst is an important factor that directly influences its interactions with organic pollutants and significantly impacts its degradation. In this study, we investigated the impact of increased hydrophilicity of g-C3N4 (CN) by alkaline solvothermal treatment on the degradations of three antibiotics (oxytetracycline (OTC), oxolinic acid (OA), and sulfamethoxazole (SMX)) with different log Kow values. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and Fourier-transform infrared (FT-IR) spectroscopy showed no significant differences in the morphology, crystalline structure, and surface functional groups of CN after alkaline solvothermal treatment (Nv-HPCN). However, contact angle analysis revealed that Nv-HPCN (31.8°) was more hydrophilic than CN (61.1°). To assess the hydrophilicity of the antibiotics, the log Kow values of SMX (0.77), OA (0.43), and OTC (-0.34) were measured. Nv-HPCN showed faster OTC degradation than CN, whereas the opposite pattern was observed for the degradation of OA. Scavenger tests showed that O2•- and h+ mainly contributed to the degradation of these antibiotics. Furthermore, the influences of NOM and coexisting anions on antibiotic degradation were investigated. This study thus offers perspectives on the impact of surface hydrophilicity of photocatalysts on the degradation of antibiotics.

Microplastic contamination in the agricultural soil-mitigation strategies, heavy metals contamination, and impact on human health: a review

Microplastic pollution has emerged as a critical global environmental issue due to its widespread distribution, persistence, and potential adverse effects on ecosystems and human health. Although research on microplastic pollution in aquatic environments has gained significant attention. However, a limited literature has summarized the impacts of microplastic pollution the agricultural land and human health. Therefore, In the current review, we have discussed how microplastic(s) affect the microorganisms by ingesting the microplastic present in the soil, alternatively affecting the belowground biotic and abiotic components, which further elucidates the negative effects on the above-ground properties of the crops. In addition, the consumption of these crops in the food chain revealed a potential risk to human health throughout the food chain. Moreover, microplastic pollution has the potential to induce a negative impact on agricultural production and food security by altering the physiochemical properties of the soil, microbial population, nutrient cycling, and plant growth and development. Therefore, we discussed in detail the potential hazards caused by microplastic contamination in the soil and through the consumption of food and water by humans in daily intake. Furthermore, further study is urgently required to comprehend how microplastic pollution negatively affects terrestrial ecosystems, particularly agroecosystems which drastically reduces the productivity of the crops. Our review highlights the urgent need for greater awareness, policy interventions, and technological solutions to address the emerging threat of microplastic pollution in soil and plant systems and mitigation strategies to overcome its potential impacts on human health. Based on existing studies, we have pointed out the research gaps and proposed different directions for future research.

Biochar derived from rice husk: Impact on soil enzyme and microbial dynamics, lettuce growth, and toxicity

This study was set to investigate the effects of rice husk biochar (RHB) on soil characteristics and growth of lettuce (Lactuca sativa). A comprehensive research approach was employed to examine the effect of different RHB concentrations (i.e., 0-1.5%) on soil pH, soil enzyme activities (i.e., alkaline phosphatase, beta-glucosidase, and dehydrogenase), soil microbial community, lettuce growth, and earthworm toxicity. The results showed that, within the studied RHB concentration range, the RHB application did not have significant effects on the soil pH. However, the enzyme activities were increased with increasing RHB concentration after the 28 d-lettuce growth period. The RHB application also increased the abundances of the bacterial genera Massilia and Bacillus and fungal genus Trichocladium having the plant growth promoting abilities. Furthermore, the study revealed that the root weight and number of lettuce leaves were significantly increased in the presence of the RHB, and the growth was dependent on the RHB concentration. The improved lettuce growth can be explained by the changes in the enzyme and microbial dynamics, which have resulted from the increased nutrient availability with the RHB application. Additionally, the earthworm toxicity test indicated that the tested RHB concentrations can be safely applied to soil without any significant ecotoxicity. In conclusion, this study underscores the potential of RHB as a soil amendment with positive effects on crop growth, highlighting the utilization of agricultural byproducts to enhance soil biological quality and plant growth through biochar application.

Effect of different types and shapes of microplastics on the growth of lettuce

The presence of microplastics in agricultural soils has emerged as a significant environmental concern due to their persistent nature. Microplastics of different properties (i.e., types, shapes, size, concentration) are present in the environment, but the studies on the effect of microplastics having different properties are limited. Thus, this study investigated the effects of different microplastics (low-density polyethylene (LDPE) fragments, polyvinyl chloride (PVC) fragments, and LDPE fiber) in soil on the growth of lettuce (Lactuca sativa L.). Pot tests were carried out to study the effect of a range of microplastic concentrations and different shapes and types of microplastics in soil on the lettuce growth. The different growth parameters such as lettuce weight, lengths, and chlorophyll contents were measured and compared. The results showed that the adverse effects of the microplastics on the lettuce growth increased with increasing microplastic concentration. The effects of LDPE fragments and fibers on the root weights and the chlorophyll contents were microplastic shape-dependent. Also, the effects of LDPE fragments and PVC fragments on the shoot and root weights and the chlorophyll contents were microplastic type-dependent. Among the three microplastics studied, LDPE fragments tend to have greater effects on the lettuce growth than the other microplastics. Overall, the results show that the effects of microplastics on different growth parameters of lettuce can be shape- and/or type-dependent. The presence of microplastics having different properties make the understanding the effects of microplastics on plants difficult, and this necessitates further studies.

Responses of earthworms exposed to low-density polyethylene microplastic fragments

The interest in the effect of microplastics (MPs) on the terrestrial environment has been increasing recently. Different species of earthworms have been used to study the effects of MPs on different aspects of earthworm health. However, there is still a need for more studies because different studies report different effects on earthworms depending on the properties (e.g., types, shapes, sizes) of MPs in the environment and exposure conditions (e.g., exposure period). This study used Eisenia fetida as a test earthworm species to investigate the effect of different concentrations of low-density polyethylene (LDPE) MPs (≤125 μm) in soil on the growth and reproduction of earthworms. The exposure of the earthworms to the different concentrations LDPE MPs (0-3% w/w) for 14 d and 28 d neither caused death of the earthworms nor showed significant effects on the earthworm weights in this study. The number of cocoons produced by the exposed earthworms were also similar to that of the controls (i.e., no exposure to MPs). Some previous studies reported similar results to what have been observe in this study, while some studies reported different results. On the other hand, the number of ingested MPs by the earthworms increased with increasing MPs concentrations in soil, suggesting a potential for damage to digestive tract. Also, the earthworm skin surface was damaged after exposure to MPs. The ingested MPs and the skin surface damage suggest that there is a potential for adverse effects on the earthworm growth after a longer-term exposure. Overall, the results of this study show that the effects of MPs on earthworms can be different depending on the properties of MPs and exposure conditions.

Fe(III)-doped activated biochar sorbents trigger mitochondrial dysfunction with oxidative stress on Daphnia magna

This study investigates the ecotoxicological effects of the synthesized Fe(III)-doped activated biochar (FeAB) sorbents using Daphnia magna and elucidates the underline mechanism of potential oxidative stress that may be induced by the sorbent. The EC50 value was determined to be 68.8 mg L^-1. The superoxide dismutase (SOD) activity of D. magna was generally inhibited and the glutathione (GSH) level was significantly reduced even at the lowest FeAB concentration used (i.e., 0.12 mg L^-1). This means that the antioxidant system of D. magna can be significantly inhibited by exposure to even a small amount of FeAB. While the higher reactive oxygen species (ROS)/reactive nitrogen species (RNS) levels in the exposed samples than the control at low FeAB concentrations (i.e., <15.63 mg L^-1) suggest the failure of the anti-oxidation mechanism of SOD and GSH, the lower average levels of ROS/RNS in the exposed samples than the control at relatively high concentrations (i.e., 31.25-1000 mg L^-1) can be explained by the reduced ROS/RNS production due to cell damage. Furthermore, the mitochondrial complex III activities were significantly inhibited in a FeAB concentration-dependent manner. Overall, the FeAB sorbent down-regulates the antioxidant mechanism, and this, together with the inefficient mitochondria, increases the ROS generation, leading to mitochondrial dysfunction again. The potential oxidative stress of FeAB on D. manga observed in this study suggests that the environmental application of FeAB needs to adopt a method that can minimize the direct contact between FeAB and organisms.

Restoring phosphorus from water to soil: Using calcined eggshells for P adsorption and subsequent application of the adsorbent as a P fertilizer

This study investigated the solution for two environmental issues: excess of P in water and its deficiency in soil, which is restored by transferring the adsorbed P from water into the soil using eggshell as an adsorbent. The eggshells were calcined at different temperatures to improve their adsorption capacity, and evaluated for their physical/chemical properties and P adsorption capacity. The eggshells calcined at 800 °C (CES-800) had the highest P adsorption; CaCO₃ decomposed into 23.6% of CaO and 40.8% of Ca(OH)₂, eluting more Ca that reacted with soluble P in water. X-ray diffraction analysis confirmed that CES-800 removed P as hydroxylapatite by reacting with Ca. Pseudo-first-order and Langmuir models suitably described the kinetic and equilibrium of P adsorption by CES-800, respectively. The maximum adsorption capacity of CES-800 was 108.2 mg g^-1. As the solution pH increased from 3 to 11, the adsorption amount decreased from 99.8 mg g^-1 to 62.3 mg g^-1. The feasibility of CES-800 as a filter medium was assessed using real lake water under dynamic flow conditions; > 90% of P removal was achieved at 158 h, and the P adsorbed was 11.5 mg g^-1. When CES-800 and P adsorbed CES-800 (P-CES-800) were applied to the soil at the studied rates, the earthworms were unaffected by toxicity, suggesting the use of both adsorbents in soil without adverse effects. The shoot fresh weight, tiller number, and total dry weight significantly increased in P-CES-800 applied rice plants compared to the control plants, indicating that P-CES-800 can be a good alternative to conventional P-fertilizer in rice cultivation.

Changes in the aquatic ecotoxicological effects of Triton X-100 after UV photodegradation

Various spray adjuvants including surfactants are widely used in agricultural pesticide formulations, and some of them may remain in soils and waters and impose more adverse effects than active pesticide ingredients on organisms. However, previous studies are more focused on the active pesticide ingredients than the adjuvants. Thus, this study investigates the changes in toxic effects of surfactants during photodegradation, which is one way of naturally degrading contaminants in natural waters. Triton X-100, a water-soluble non-ionic surfactant, was degraded using different types of UV radiation (UVA, UVB, and UVC), and the changes in the toxic effects were determined using bioluminescent bacteria and water flea. The Triton X-100 removals were negligible with UVA within 24 h, while its removal was 81% with UVB and almost complete with UVC. The NMR spectra indicated possible molecule rearrangement after photolysis. On the other hand, the toxic effects based on the mortality of Daphnia magna and the bioluminescence of Aliivibrio fischeri increased (i.e., lower EC50 values) after photodegradation, suggesting the generation of photoproducts that are likely to have higher toxic effects or higher bioavailability. Furthermore, the sensitivities of D. magna and A. fischeri for Triton X-100 and the photodegraded Triton X-100 were different. This study suggests that the changes in the chemical composition of the Triton X-100 containing water with photodegradation can lead to changes in the relative toxic effects on different aquatic organisms. Therefore, not only the management of parent compound (i.e., Triton X-100) but also the photoproducts generated from the parent compound need to be considered when managing water environment subject to photodegradation.

Exploring reductive degradation of fluorinated pharmaceuticals using Al2O3-supported Pt-group metallic catalysts: Catalytic reactivity, reaction pathways, and toxicity assessment

Recently, an increasing number of pharmaceutical compounds has become fluorinated. Owing to their pharmacological efficacy, the use of these fluorinated pharmaceuticals continues to grow, and they constitute 20% of the drugs on the current market. However, only a few studies have investigated the fate and transformation of these emerging contaminants in natural and engineered aquatic environments. In the present study, the H₂-based reductive transformation of three fluorinated pharmaceutical compounds (levofloxacin, sitagliptin, and fluoxetine) were investigated using alumina-supported monometallic and bimetallic catalysts of the Pt-group noble metals (i.e., Ru, Rh, Pd, and Pt) under ambient temperature and pressure conditions. Degradation of all three compounds was observed with catalytic reactivity ranging from 4.0  ×  10^-3 to 2.14  ×  10² L/(min·g_cat), in which fluoxetine generally showed the highest reactivity, followed by sitagliptin and levofloxacin. The fluorination yields and transformation products were characterized for each fluorinated compound and three different degradation mechanisms were elucidated: 1) hydrodefluorination of C-F bond to CH bond, 2) hydrogenation of aromatic ring, and 3) reductive cleavage of CO bond from phenyl ether. Toxicity assessment using Aliivibrio fischeri showed there were no significant changes in toxicity over levofloxacin and sitagliptin degradation, suggesting the formation of no highly toxic by-products during catalytic reduction. For fluoxetine, an increased toxicity was observed during its degradation while ECOSAR-predicted toxicity values of all identified intermediates were lower than that of fluoxetine, suggesting the formation of unidentified secondary by-products that contribute to the overall toxicity. The study showed that catalytic reduction is a promising remediation process for treating and defluorinating the fluorinated pharmaceutical compounds.

Interaction among soil physicochemical properties, bacterial community structure, and arsenic contamination: Clay-induced change in long-term arsenic contaminated soils

Pyrosequencing analyses to determine soil bacterial communities were conducted with forty-two soil samples collected from rice paddy and forest/farmland soils (Group A and B, respectively) at a long-term As-contaminated site. Soil physicochemical properties, such as the concentrations of As, Fe, Al, and Mn, pH, organic matter content, and clay content, were found to be significantly different with land use, and more importantly, strongly affected the bacterial community structure of the soil samples. When fitting the soil properties onto a nonmetric multidimensional scale plot of soil bacterial communities, clay content was found to be the most important factor in clustering the bacterial communities (R² = 0.4831, p-value = 0.001). Phylum Chloroflexi (-1.03 of bioplot score) and Planctomycetes (1.31 of bioplot score) showed a significant relationship with clay content in soil samples. Interestingly, thebacterial phylotypes linked to clay content were only found in the soil samples of group B with low clay content, and had a strong relationship to As contamination in the redundancy analysis and the correlation analysis.Our results suggest that clay content seems to be negatively related to As contamination in soils, which, in turn, strongly influences the structure of bacterial communities in As-contaminated soil.

Sequential biowashing-biopile processes for remediation of crude oil contaminated soil in Kuwait

The application of biological processes for remediation of the aged crude oil-contaminated soil of Kuwait can be an inefficient way, thus, this study developed 20 d-sequential biowashing and biopile processes where the biowashing step uses an enrichment culture of the indigenous soil bacterial community and the biopile step includes hemoglobin-catalyzed oxidation (HCO). The residual total petroleum hydrocarbons (TPH) concentrations and CO₂ generation were measured to determine the removal efficiency, and the bacterial community changes were studied to investigate the effect of the sequential processes on the soil indigenous bacterial community. The enrichment culture grown on hemoglobin showed an increased surface activity, and this promoted desorption and emulsification of crude oil from the soil sample in the biowashing step resulting in 75% TPH removal. Potential surfactant-producing bacterial species were observed in the soil sample after biowashing. The HCO in the beginning of the biopile step removed 21% of the residual TPH, and further TPH removal was observed with a longer biopile period. Overall, the sequential biowashing and biopile processes removed 86% TPH. The results show that the developed sequential biowashing and biopile processes can be used to efficiently remediate the aged crude oil-contaminated soil of Kuwait.

Effect of initial pH, operating temperature, and dissolved oxygen concentrations on performance of pyrite-fuel cells in the presence of Acidithiobacillus ferrooxidans

Fuel cell technology can be applied to remove pyrite from pyrite containing mine waste (PCMW) and to generate electricity. This study investigated the effect of pH, presence of Acidithiobacillus ferrooxidans, operating temperature, and dissolved oxygen (DO) concentration on the performance of pyrite-fuel cells (PFCs). These factors affect the pyrite dissolution rate, which affects the electron movement for electricity generation, hence electrical performance. The PFCs performance based on the maximum power density and maximum current density, obtained on the 28th day, was better at pH 2.2 (0.74 mW m^-2, 28 mA m^-2) than at pH 4.3 and pH 6.5 and in the presence of A. ferrooxidans (i.e., biotic PFCs) than in the abiotic PFCs. The biotic PFCs showed more consistent performance regardless of the operating temperature than the abiotic PFCs. The PFCs performance was better at higher DO concentrations (30-33 mg L^-1) than at lower DO concentrations (8-9 and 0-2 mg L^-1); however, gas purging used to adjust DO concentrations could adversely affect the biotic PFCs performance. This study demonstrates that PCMW treatment and electricity generation can be achieved using the fuel cell-based technology, and the PFCs performance can be optimized by adjusting the operating conditions.

Heavy metal and sulfate removal from sulfate-rich synthetic mine drainages using sulfate reducing bacteria

The removals of heavy metals and sulfate in the synthetic acid mine drainages (AMDs) by Desulfovibrio desulfuricans, sulfate-reducing bacteria (SRB), and the indigenous bacteria isolated from the mine area soil sample were studied to compare the AMD treatment efficiencies. The AMD treatment by the D. desulfuricans grown in the Desulfovibrio medium was used to represent bioaugmentation, while the AMD treatment by the indigenous bacteria grown in the Desulfovibrio medium was used to represent biostimulation. The consumption of lactate and sulfate suggested that the zinc (Zn) removal in the Zn-spiked Desulfovibrio medium by D. desulfuricans involved chemical precipitation and biosorption. The complete Zn removal by D. desulfuricans took 24 h, while the indigenous bacteria took 360 h. The significantly lower rate can probably be attributed to the composition of the culture. The removal of Zn in the sulfate-rich synthetic AMD-containing Desulfovibrio medium (i.e., AMD) was adversely affected by the presence of other heavy metals. Also, the sulfate reduction by D. desulfuricans and the indigenous bacteria was reduced from 47% to 20% and from 36% to 6%, respectively. The inhibitive effects on the removal of heavy metals and sulfate were greater with the Zn/Cu-spiked AMD than the Zn-spiked AMD. Overall, the indigenous bacteria showed potential for removing heavy metals and sulfate in AMDs, while the removal efficiency was lower than D. desulfuricans. The continuous supply of carbon sources with an adaptation period may be required to enhance the AMD treatment efficiency by the indigenous bacteria.

Role of hemoglobin in hemoglobin-based remediation of the crude oil-contaminated soil

This study investigated the changes in the indigenous microbial community structure with hemoglobin (Hb) application to determine the role of Hb in Hb-based remediation of crude oil-contaminated soil. The phylogenetic diversity of the bacterial community showed that the Hb addition selected surfactants-producing species, thereby, promoting TPH degradation. The significant increase in the CO₂ generation, which can be related to the increase in the bacterial abundance inferred from the 16S rRNA gene copy number, supports the enhanced TPH degradation with Hb application. The similar residual TPH concentrations in the presence of only hydrogen peroxide (H₂O₂) and both Hb and H₂O₂ suggested that the role of Hb as a catalyst was not as significant as the role of Hb as a nutrient. Also, in the presence of H₂O₂, a greater recovery of the microbial community structure was observed with the double Hb injection than the single Hb injection. Overall, this study shows that the Hb-based remediation strategies via microbial metabolism can be successfully applied to remediate the crude-oil contaminated Kuwaiti soil.

Optimization of hydrogen peroxide-to-hemoglobin ratio for biocatalytic mineralization of polycyclic aromatic hydrocarbons (PAHs)-contaminated soils

This study investigates the efficiency of hemoglobin (Hb)-catalyzed biocatalytic reactions for removal of polycyclic aromatic hydrocarbons (PAHs) in a historically PAHs-contaminated soil and of benzo(a)pyrene (BaP) in an artificially BaP-contaminated soil. PAHs removal tests at various H₂O₂-to-Hb mass ratios (0-3.7) showed that the PAHs removal was greater at H₂O₂-to-Hb mass ratio of ≥3. This was attributed to the greater removal of high molecular weight PAHs at higher H₂O₂-to-Hb mass ratios. The BaP removal increased from 36% to 85% with increasing H₂O₂-to-Hb mass ratio from 1 to 3, and further increase in H₂O₂-to-Hb mass ratio decreased the BaP removal. Thus, the optimal H₂O₂-to-Hb mass ratio for BaP removal was determined to be 3 in the artificially BaP-contaminated soil. The BaP removal in the presence of only Hb can be attributed to the capture of BaP by Hb. The increased BaP removal in the presence of H₂O₂ is likely due to BaP mineralization as the BaP removal and the CO₂ generated showed a strong positive correlation (R² = 0.999). Overall, this study shows that the Hb-catalyzed biocatalytic reactions can effectively remove PAHs in soil.

Utilization of waste bittern from saltern as a source for magnesium and an absorbent for carbon dioxide capture

During solar salt production, large quantities of bittern, a liquid by-product containing high inorganic substance concentrations, are produced. The purpose of this research was to examine the utilization of waste bittern generated from salterns as a source for Mg production and as an absorbent for carbon dioxide (CO₂) capture. The study was conducted in a sequential two-step process. At NaOH/Mg molar ratios of 2.70-2.75 and pH 9.5-10.0, > 99% Mg precipitation from the bittern was achieved. After washing with water, 100-120 g/L of precipitate containing 94% Mg(OH)₂ was recovered from the bittern. At the optimum NH₄OH concentration of 5%, 120 g of sodium bicarbonate precipitate per liter of bittern were recovered, which was equivalent to 63 g CO₂ captured per liter of bittern. These results can be used to support the use of bittern as a resource and reduce economic losses during solar salt production.

Importance of chemical binding type between As and iron-oxide on bioaccessibility in soil: Test with synthesized two line ferrihydrite

Bioaccessible concentrations of As associated with Fe oxide as different chemical binding types were determined in soils using the in vitro Physiologically Based Extraction Test (PBET). When compared to the five-step sequential extraction data, most of the As extracted by in vitro PBET originated from the amorphous Fe oxide-bound fraction, and more importantly, the bioaccessibility of As ranged from 0 to 58.8% in 24 soil samples. Two batches of ferrihydrite were synthesized separately. For one batch, As was adsorbed onto the ferrihydrite after synthesis; for the other one, As was added while synthesizing ferrihydrite to co-precipitate. The bioaccessible concentration of As determined by in vitro PBET of the former was 415mg of As/kg of ferrihydrite and that of the latter was 67mg of As/kg of ferrihydrite. X-ray photoelectron spectra (XPS) analysis indicated that As-O-Fe bonds were evident in As-associated ferrihydrite sample and especially, As was found within the Fe oxide lattice in the co-precipitated sample. Our data suggest that binding type between As and Fe oxide should be considered when determining the bioaccessibility of As in soil, which, in turn, greatly influences the realistic risk of As present in soil.

Effect of biogeochemical interactions on bioaccessibility of arsenic in soils of a former smelter site in Republic of Korea

The total concentration-based regulations for soil remediation do not consider the possible changes in bioaccessibility of remaining arsenic (As) in soils due to biogeochemical interactions after remediation. This study used As-contaminated soil and pore water samples that were collected from the rice paddy and forest/farmland located in the vicinity of a former smelter site in Republic of Korea to elucidate the changes in As bioaccessibility due to biogeochemical interactions. Bioaccessibility and chemical forms of As in soils were determined by using an in vitro method and sequential extraction, respectively, and soil microbial community was evaluated. Bioaccessibility of As in the rice paddy soil samples was higher than that in the forest/farmland soil samples. This could be attributed to relatively higher dependence of bioaccessible As in the rice paddy soils on the soil concentration of iron (Fe), aluminum, or manganese, which could lead to greater changes in bioaccessible As via reductive dissolution. The strong linear relationship (R ² = 0.90, p value ≤0.001) between the pore water As and Fe concentrations, and the greater portion of bacterial species related to reductive dissolution of Fe oxides in the rice paddies can support the higher As bioaccessibility promoted by reductive dissolution. Therefore, it is necessary to consider the potential changes in the bioaccessible As due to biogeochemical interactions in remediation of As-contaminated soils, particularly when soils are likely to be reused under reductive dissolution-promoting conditions (e.g., flooded conditions).

Applicability of a submersible microbial fuel cell for Cr(VI) detection in water

Two-chamber microbial fuel cells (MFCs) were used to study the applicability of MFCs for hexavalent chromium (Cr(VI)) detection in water. The microbial acetate oxidation in the anode and the Cr(VI) reduction in the cathode together generated voltages, which were used to indicate the change in Cr(VI) concentrations of the cathode under varying conditions of pH, ionic strength, co-existing Fe(II) concentration, and organic matter concentration. The MFC-based Cr(VI) detector showed a significant change in voltage with increasing Cr(VI) concentration at pH 1 and 2, but not at higher pH conditions. The detector also successfully measured the changes in Cr(VI) concentration at a range of ionic strength (i.e., 10-300 mM), and in the presence of different concentrations of fulvic acid (0-50 mg/L), which was used as a surrogate of organic matters, without interference. The Cr(VI) detection was not interfered by the presence of Fe(II) at the Cr(VI)/Fe(II) ratio of 1:1 and 1:15, but it was interfered at higher ratios (i.e., 1:164 and 1:848). The detector could measure the Cr(VI) concentration from 0.1 to 15 mg/L at pH 2. Overall, the MFC-based Cr(VI) detector may be applied to meet the growing need of real-time Cr(VI) monitoring in water.

Lithium sorption properties of HMnO in seawater and wastewater

The lithium concentration in seawater is 0.17 mg/L, which is very low, but the overall quantity is approximately 2.5 × 10(14) kg. Therefore, seawater, which contains a vast amount of lithium, could be a major alternative source that might supply the rising demand for lithium. This research was undertaken to evaluate the feasibility of a manganese oxide (HMnO) adsorbent, which was produced after leaching lithium from lithium manganese oxide, for lithium collection from seawater. The HMnO was synthesized and deformed to a plastic after wet blending of manganese oxide and lithium hydroxide, and subsequently, the influence of pH, sorption isotherms, sorption rates, sorption energies, and effects of the co-ions were measured. Thermodynamic parameters such as ΔG°, ΔH°, and ΔS° indicated that the nature of the lithium sorption was both spontaneous and endothermic. The used HMnO could be regenerated by washing it with an HCl solution. The results demonstrated that HMnO could be effectively used for the collection of lithium from seawater with good selectivity.

Effect of different soil washing solutions on bioavailability of residual arsenic in soils and soil properties

The effect of soil washing used for arsenic (As)-contaminated soil remediation on soil properties and bioavailability of residual As in soil is receiving increasing attention due to increasing interest in conserving soil qualities after remediation. This study investigates the effect of different washing solutions on bioavailability of residual As in soils and soil properties after soil washing. Regardless of washing solutions, the sequential extraction revealed that the residual As concentrations and the amount of readily labile As in soils were reduced after soil washing. However, the bioassay tests showed that the washed soils exhibited ecotoxicological effects - lower seed germination, shoot growth, and enzyme activities - and this could largely be attributed to the acidic pH and/or excessive nutrient contents of the washed soils depending on washing solutions. Overall, this study showed that treated soils having lower levels of contaminants could still exhibit toxic effects due to changes in soil properties, which highly depended on washing solutions. This study also emphasizes that data on the As concentrations, the soil properties, and the ecotoxicological effects are necessary to properly manage the washed soils for reuses. The results of this study can, thus, be utilized to select proper post-treatment techniques for the washed soils.

Effect of dissolved humic acid on the Pb bioavailability in soil solution and its consequence on ecological risk

Current risk characterization in ecological risk assessment does not consider bioavailability of heavy metals, which highly depends on physicochemical properties of environmental media. This study was set to investigate the effect of humic acid (HA), used as a surrogate of organic matter, on Pb toxicity and the subsequent effect on risk characterization in ecological risk assessment. Pb toxicity was assessed using Microtox(®) in the presence and absence of two different forms of HA, particulate HA (pHA) and dissolved HA (dHA). With increasing contact time, the EC10 values increased (i.e., the toxic effects decreased) and the dissolved Pb concentrations of the filtrates decreased. The high correlation (R = 0.88, p < 0.001) between toxic effects determined using both the mixture and its filtrate as exposure media leads us to conclude that the Pb toxicity highly depends on the soluble fraction. Also, reduced Pb toxicity with increasing dHA concentrations, probably due to formation of Pb-dHA complexes, indicated that Pb toxicity largely comes from free Pb ions. Overall, this study shows the effect of HA on metal toxicity alleviation, and emphasizes the need for incorporating the bioavailable heavy metal concentrations in environmental media as a point of exposure in ecological risk assessment.

Changes in soil toxicity by phosphate-aided soil washing: effect of soil characteristics, chemical forms of arsenic, and cations in washing solutions

This study was set to investigate the changes in the toxicity of arsenic (As)-contaminated soils after washing with phosphate solutions. The soil samples collected from two locations (A: rice paddy and B: forest land) of a former smelter site were contaminated with a similar level of As. Soil washing (0.5 M phosphate solution for 2 h) removed 24.5% As, on average, in soil from both locations. Regardless of soil washing, Location A soil toxicities, determined using Microtox, were greater than that of Location B and this could be largely attributed to different soil particle size distribution. With soils from both locations, the changes in As chemical forms resulted in either similar or greater toxicities after washing. This emphasizes the importance of considering ecotoxicological aspects, which are likely to differ depending on soil particle size distribution and changes in As chemical forms, in addition to the total concentration based remedial goals, in producing ecotoxicologically-sound soils for reuse. In addition, calcium phosphate used as the washing solution seemed to contribute more on the toxic effects of the washed soils than potassium phosphate and ammonium phosphate. Therefore, it would be more appropriate to use potassium or ammonium phosphate than calcium phosphate for phosphate-aided soil washing of the As-contaminated soils.

Prediction of Cd and Pb toxicity to Vibrio fischeri using biotic ligand-based models in soil

Biotic ligand-based models to predict site-specific toxicity of Cd and Pb contaminated soil were developed by using a Vibrio fischeri toxicity test. Firstly, competition effect by cations (i.e., Ca, Mg, K) commonly found in soil solution was incorporated into the models. For this purpose, biotic ligand-based model parameters including conditional binding constants of cations and metal ions to binding sites (i.e., biotic ligands) and the fractions of binding sites occupied by the metal ions were determined. Data from aqueous phase toxicity test showed that the difference between model-predicted EC(50) values of Cd and Pb and experimentally determined EC(50) values ranged within a factor of two, suggesting that the developed model parameters were reliable. Secondly, the use of soil solution to predict soil toxicity of Cd and Pb was experimentally verified with freshly spiked and field-aged soils. The results showed linear relationships in both soils, meaning that toxicity of soil solution can be representative of toxicity of soil. Finally, applicability of the developed models in Cd- or Pb-spiked soils was investigated by comparing predicted toxic effects (i.e., % bioluminescence inhibition at given cations and metal activities in soil solution) and experimentally obtained toxic effects determined by Microtox(®) solid phase toxicity test. Our data demonstrate that toxicity of Cd- or Pb-contaminated soil can be predicted by using the developed biotic ligand-based model with the chemical analysis data of soil solution as input data.

Extended biotic ligand model for prediction of mixture toxicity of Cd and Pb using single metal toxicity data

The combined toxic effects of Cd and Pb in the presence of different concentrations of Ca(2+) were predicted using the biotic ligand model (BLM), with the parameters derived from the Cd-only and Pb-only toxicity data. The BLM-based toxic unit (TU) approach and the proposed BLM-based f(mix) approach were used for prediction. The predicted mixture toxic effects using the BLM-based f(mix) approach were closer to the observed mixture effects (root mean square error [RMSE] = 9.7 at 25 mM Ca(2+) ) than that using the BLM-based TU approach (RMSE = 25.6 at 25 mM Ca(2+) ). This can be attributed to the fact that the BLM-based TU approach only considers the competition between Ca(2+) and Cd or Pb, whereas the BLM-based f(mix) approach considers both the competition between Cd and Pb and the competition between Ca(2+) and Cd or Pb for biotic ligand sites. In addition, the parameters derived from the Cd-only and Pb-only solutions in the presence of the background Ca(2+) concentration (0.025 mM) could be used to predict the mixture toxic effects at higher Ca(2+) concentrations. The BLM-based f(mix) approach proposed in the current study suggests a new way of predicting the Cd-Pb mixture toxicity from the single metal toxicity data by adopting the f(mix) values.

Facilitated desorption and stabilization of sediment-bound Pb and Cd in the presence of birnessite and apatite

Desorption of lead (Pb) and cadmium (Cd) from contaminated sediments was investigated to clarify the effect of stabilizing agents on Cd and Pb desorption kinetics. The desorbed aqueous Cd and Pb concentrations and the residual amounts of Cd on the sediments in the desorption tests were best fitted to a pseudo-second-order kinetics with the highest R(2) values among the models used in the kinetic studies. The average residual Cd on sediments were 24% and 19% less in the presence of apatite and birnessite, respectively, than in the absence of them. However, the Pb desorption was not affected by the stabilizing agents. The negligible aqueous concentrations of desorbed Cd and Pb in the presence of apatite and birnessite suggest the stabilization of desorbed Cd that was facilitated by apatite and birnessite and Pb. The kinetics study with Cd shows that the rate constants are not affected, but the desorption extents are affected in the presence of apatite and birnessite. The Tessier sequential extraction method and toxicity characteristic leaching procedure indicate that Pb is more strongly bound on the stabilizing agents than Cd. Overall, birnessite and apatite can be successfully applied in remediation of Cd and Pb contaminated sediment.

Fenton degradation of tetrachloroethene and hexachloroethane in Fe(II) catalyzed systems

The degradation of tetrachlorothene (PCE) and hexachloroethane (HCA) using Fe(II) and Fe(II)-citrate at different H(2)O(2) concentrations was studied to clarify the role of oxidation and reduction pathways in Fenton chemistry. The interactions between oxidative and reductive radicals, and the cyclic nature of the Fe(II)-Fe(III) ions make for a complex system that displays a suppression or enhancement of PCE or HCA degradation as the experimental conditions are varied. PCE degradation decreased, while HCA degradation increased, for larger H(2)O(2) concentration. The degradations of PCE and HCA were lower in vials where they were individually present compared to vials with the PCE-HCA mixture. Using Fe(II)-citrate instead of Fe(II) resulted in slower PCE and insignificant HCA degradation. These observations indicate that degradation efficiency losses arise from interactions between the oxidant and reductant radical moieties, and that the production of reduction radicals is only significant when the hydroxyl radical (OH) production is rapid.

Degradation of hexachloroethane by Fenton's reagents

The effect of hydrogen peroxide (H2O2) concentrations on the degradation of hexachloroethane (HCA) in the absence and the presence of tetrachloroethene (PCE) by Fenton's reagent was investigated at pH 3 with 1 mM iron(II) and H2O2 concentrations ranging from 0.01 M to 2 M. HCA degradation in the absence of PCE increased with increasing H2O2 concentration between 0.2 M and 2 M. In the presence of PCE, HCA degradation was similar to that in the absence of PCE for H2O2 concentration up to 1 M, but significantly higher for 2 M H2O2. We propose that this increase is a result of elevated reductant radicals when PCE is present. This study highlights the need for further investigation into the degradation of contaminant mixtures at higher H2O2 concentrations.

The opposing effects of bacterial activity and gas production on anaerobic TCE degradation in soil columns

This laboratory study explores the effect of growth substrate concentration on the anaerobic degradation of trichloroethylene (TCE) in sand packed columns. In all columns the growth substrate rapidly degraded to gas, that formed a separate phase. Biomass accumulated in the 0-4.8 cm section of the columns in proportion to the influent growth substrate concentration and biomass concentrations in the remaining sections of all columns were similar to the column receiving the lowest substrate concentration. Increases in growth substrate concentration up to 3030 mg-CODl(-1) promoted TCE degradation, but a further increase to 14300 mg-CODl(-1) reduced the amount of TCE completely dechlorinated but did not affect the production of chlorinated TCE intermediates. The mathematical model developed here satisfactorily described the enhancement in TCE dehalogenation for substrate concentration up to 3030 mg-CODl(-1); reproducing TCE dehalogenation for 14300 mg-CODl(-1) required that the moisture content used in simulation be lowered to 0.1. The study shows that volatilization of TCE can be significant and volatilization losses should be taken into account when anaerobic activity in in-situ bioremediation applications is stimulated via addition of growth substrates. An implication of the modeling simulations is that maintaining a lower, but uniform, substrate concentration over the contaminated region may lead to faster contaminant degradation.

Purification of GSK-3 by affinity chromatography on immobilized axin

Glycogen synthase kinase 3 (GSK-3), an element of the Wnt signalling pathway, plays a key role in numerous cellular processes including cell proliferation, embryonic development, and neuronal functions. It is directly involved in diseases such as cancer (by controlling apoptosis and the levels of beta-catenin and cyclin D1), Alzheimer's disease (tau hyperphosphorylation), and diabetes (as a downstream element of insulin action, GSK-3 regulates glycogen and lipid synthesis). We describe here a rapid and efficient method for the purification of GSK-3 by affinity chromatography on an immobilized fragment of axin. Axin is a docking protein which interacts with GSK-3ss, beta-catenin, phosphatase 2A, and APC. A polyhistidine-tagged axin peptide (residues 419-672) was produced in Escherichia coli and either immobilized on Ni-NTA agarose beads or purified and immobilized on CNBr-activated Sepharose 4B. These "Axin-His6" matrices were found to selectively bind recombinant rat GSK-3 beta and native GSK-3 from yeast, sea urchin embryos, and porcine brain. The affinity-purified enzymes displayed high kinase activity. This single step purification method provides a convenient tool to follow the status of GSK-3 (protein level, phosphorylation state, kinase activity) under various physiological settings. It also provides a simple and efficient way to purify large amounts of active recombinant or native GSK-3 for screening purposes.

Galpha12 and Galpha13 mediate differentiation of P19 mouse embryonal carcinoma cells in response to retinoic acid

P19 mouse embryonal carcinoma cells can be stimulated to differentiate into endodermal-like, mesodermal-like, and neuronal-like phenotypes in response to specific morphogens. At low concentrations, retinoic acid stimulates P19 embryonal cells to differentiate to cells displaying an endodermal phenotype, whereas at higher concentrations it stimulates differentiation to neuroectoderm. The Galpha12 and Galpha13 subunits of heterotrimeric G-proteins are expressed in the embryonal P19 cells and stimulated in response to retinoic acid as the cells differentiate to endodermal or neuroectodermal phenotypes. Suppression of the expression of either Galpha12 or Galpha13 by antisense RNA is shown to promote cell detachment from substratum and apoptosis. Expression of the constitutively active, mutant form of Galpha12 (Q229L), in contrast, stimulates loss of the embryonal phenotype. Expression of the constitutively active form of Galpha13 (Q226L) stimulates differentiation of the cells from embryonal to endodermal, in the absence of retinoic acid. Thus, both Galpha12 and Galpha13 are essential to stimulation of cell differentiation by retinoic acid. Deficiency of either Galpha12 or Galpha13 increases programmed cell death.

c-Jun amino-terminal kinase is regulated by Galpha12/Galpha13 and obligate for differentiation of P19 embryonal carcinoma cells by retinoic acid

Retinoic acid induces P19 mouse embryonal carcinoma cells to differentiate to endoderm and increases expression of the heterotrimeric G-protein subunits Galpha12 and Galpha13. Retinoic acid was found to induce differentiation and sustained activation of c-Jun amino-terminal kinase, but not of ERK1,2 or of p38 mitogen-activated protein kinases. Much like retinoic acid, expression of constitutively active forms of Galpha12 and Galpha13 induced differentiation and constitutive activation of c-Jun amino-terminal kinase. Expression of the dominant negative form of c-Jun amino-terminal kinase 1 blocked both the activation of c-Jun amino-terminal kinase and the induction of endodermal differentiation in the presence of retinoic acid. These data implicate c-Jun amino-terminal kinase as a downstream element of activation of Galpha12 or Galpha13 obligate for retinoic acid-induced differentiation.