Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review.

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Industrial waste-based adsorbents as a new trend for removal of water-borne emerging contaminants.

Emerging contaminants in wastewater are one of the growing concerns because of their adverse effects on human health and ecosystems. Adsorption technology offers superior performance due to its cost-effectiveness, stability, recyclability, and reliability in maintaining environmental and health standards for toxic pollutants. Despite extensive research on the use of traditional adsorbents to remove emerging contaminants, their expensiveness, lack of selectivity, and complexity of regeneration remain some of the challenges. Industrial wastes viz. blast furnace slag, red mud, and copper slag can be used to develop efficacious adsorbents for the treatment of emerging contaminants in water. Advantages of the use of such industrial wastes include resource utilization, availability, cost-effectiveness, and waste management. Nevertheless, little is known so far about their application, removal efficacy, adsorption mechanisms, and limitations in the treatment of emerging contaminants. A holistic understanding of the application of such unique industrial waste-derived adsorbents in removing emerging contaminants from water is need of the hour to transform this technology from bench-scale to pilot and large-scale applications. This review investigates different water treatment techniques associated with industrial waste-based adsorbents derived from blast furnace slag, red mud, and copper slag. Besides, this review provides important insights into the growing trends of utilizing such novel types of adsorbents to remove emerging contaminants from water with an emphasis on removal efficacy, controlling measures, adsorption mechanisms, advantages, and limitations. The present timely review brings the current state of knowledge into a single reference which could be a strong platform for future research in understanding the latest advancements, decision making, and financial management related to the treatment of wastewater using industrial waste-based adsorbents.

Contribution of free hydroxyl radical to the formation of micro(nano)plastics and release of additives during polyethylene degradation in water.

The omnipresence of secondary microplastics (MPs) in aquatic ecosystems has become an increasingly alarming public health concern. Hydrogen peroxide (H2O2) is an important oxidant in nature and the most stable reactive oxygen species occurred in natural water. In order to explore the contribution of free ˙OH generated from H2O2-driven Fenton-like reactions on the degradation of polyethylene (PE) and generation of micro- and nano-scale plastics in water, a batch experiment was conducted over a period of 620 days in water treated with micromolar H2O2. The incorporation of H2O2 in water induced the formation of flake-like micro(nano)-sized particles due to intensified oxidative degradation of PE films. The presence of ˙OH significantly enhanced the generation of both micro- and nano-scale plastics exhibiting a higher proportion of particles in the range of 200-500 nm compared to the Control. Total organic carbon in the H2O2 treated solution was nearly 174-fold higher than that of the Control indicating a substantial liberation of organic compounds due to the oxidative degradation of native carbon chain of PE and subsequent decomposition of its additives. The highly toxic butylated hydroxytoluene detected from the gas chromatography-mass spectrometry (GC-MS) analysis implied the toxicological behavior of secondary micro(nano)plastics influenced by the oxidation and decomposition processes The findings from this study further expand our understanding of the role of ˙OH in degrading PE micro-scale plastics into nanoparticles as an implication of naturally occurring H2O2 in aquatic environments. In the future, further attention should be drawn to the underlying mechanisms of H2O2-driven in-situ Fenton reaction mediated by natural environmental conditions targeting the alternation of light and darkness on the oxidative degradation of plastics.

A review on constructive classification framework of research trends in analytical instrumentation for secondary micro(nano)plastics: What is new and what needs next?

Secondary micro(nano)plastics generated from the degradation of plastics pose a major threat to environmental and human health. Amid the growing research on microplastics to date, the detection of secondary micro(nano)plastics is hampered by inadequate analytical instrumentation in terms of accuracy, validation, and repeatability. Given that, the current review provides a critical evaluation of the research trends in instrumental methods developed so far for the qualitative and quantitative determination of micro(nano)plastics with an emphasis on the evolution, new trends, missing links, and future directions. We conducted a meta-analysis of the growing literature surveying over 800 journal articles published from 2004 to 2022 based on the Web of Science database. The significance of this review is associated with the proposed novel classification framework to identify three main research trends, viz. (i) preliminary investigations, (ii) current progression, and (iii) novel advances in sampling, characterization, and quantification targeting both micro- and nano-sized plastics. Field Flow Fractionation (FFF) and Hydrodynamic Chromatography (HDC) were found to be the latest techniques for sampling and extraction of microplastics. Fluorescent Molecular Rotor (FMR) and Thermal Desorption-Proton Transfer Reaction-Mass Spectrometry (TD-PTR-MS) were recognized as the modern developments in the identification and quantification of polymer units in micro(nano)plastics. Powerful imaging techniques, viz. Digital Holographic Imaging (DHI) and Fluorescence Lifetime Imaging Microscopy (FLIM) offered nanoscale analysis of the surface topography of nanoplastics. Machine learning provided fast and less labor-intensive analytical protocols for accurate classification of plastic types in environmental samples. Although the existing analytical methods are justifiable merely for microplastics, they are not fully standardized for nanoplastics. Future research needs to be more inclined towards secondary nanoplastics for their effective and selective analysis targeting a broad range of environmental and biological matrices.

Global arsenic dilemma and sustainability.

Arsenic (As) is one of the most prolific natural contaminants in water resources, and hence, it has been recognized as an emerging global problem. Arsenic exposure through food exports and imports, such as As-contaminated rice and cereal-based baby food, is a potential risk worldwide. However, ensuring As-safe drinking water and food for the globe is still not stated explicitly as a right neither in the United Nations' Universal Declaration of Human Rights and the 2030 Sustainable Development Goals (SDGs) nor the global UNESCO priorities. Despite these omissions, addressing As contamination is crucial to ensure and achieve many of the declared human rights, SDGs, and global UNESCO priorities. An international platform for sharing knowledge, experience, and resources through an integrated global network of scientists, professionals, and early career researchers on multidisciplinary aspects of As research can act as an umbrella covering the activities of UN, UNESCO, and other UN organizations. This can deal with the mitigation of As contamination, thus contributing to global economic development and human health. This article provides a perspective on the global As problem for sustainable As mitigation on a global scale by 2030.

Seven potential sources of arsenic pollution in Latin America and their environmental and health impacts.

This review presents a holistic overview of the occurrence, mobilization, and pathways of arsenic (As) from predominantly geogenic sources into different near-surface environmental compartments, together with the respective reported or potential impacts on human health in Latin America. The main sources and pathways of As pollution in this region include: (i) volcanism and geothermalism: (a) volcanic rocks, fluids (e.g., gases) and ash, including large-scale transport of the latter through different mechanisms, (b) geothermal fluids and their exploitation; (ii) natural lixiviation and accelerated mobilization from (mostly sulfidic) metal ore deposits by mining and related activities; (iii) coal deposits and their exploitation; (iv) hydrocarbon reservoirs and co-produced water during exploitation; (v) solute and sediment transport through rivers to the sea; (vi) atmospheric As (dust and aerosol); and (vii) As exposure through geophagy and involuntary ingestion. The two most important and well-recognized sources and mechanisms for As release into the Latin American population's environments are: (i) volcanism and geothermalism, and (ii) strongly accelerated As release from geogenic sources by mining and related activities. Several new analyses from As-endemic areas of Latin America emphasize that As-related mortality and morbidity continue to rise even after decadal efforts towards lowering As exposure. Several public health regulatory institutions have classified As and its compounds as carcinogenic chemicals, as As uptake can affect several organ systems, viz. dermal, gastrointestinal, peptic, neurological, respiratory, reproductive, following exposure. Accordingly, ingesting large amounts of As can damage the stomach, kidneys, liver, heart, and nervous system; and, in severe cases, may cause death. Moreover, breathing air with high As levels can cause lung damage, shortness of breath, chest pain, and cough. Further, As compounds, being corrosive, can also cause skin lesions or damage eyes, and long-term exposure to As can lead to cancer development in several organs.

Handwashing with soap: A concern for overuse of water amidst the COVID-19 pandemic in Bangladesh.

Handwashing is one of the vital public health measures. It helps to prevent the spread of the COVID-19 pandemic. However, water overuse during hand scrubbing with soap keeping the tap on may put enormous pressure on the already overstretched groundwater resources and households' economic well-being. Therefore, this study aimed to determine the overuse of water while scrubbing hands with soap for handwashing when the tap is on amid the COVID-19 pandemic in Bangladesh. Sociodemographic data were collected using a web-based survey tool among 1980 participants and an experiment was conducted among 126 participants to estimate the overuse of water during hand scrubbing while the tap is on. A total of 80% of the participants washed their hands regularly after returning home from outside. About 57.3% of participants did not turn off their tap throughout the handwashing process. A single participant, who kept his tap on throughout the handwashing process, overused approximately 1.7 L of water per handwash and 14.9 L of water per day. Hand scrubbing with soap keeping the tap on, raised the overuse of water 13-fold during this pandemic compared to the non-pandemic situation which cost an extra 225.0 BDT (2.7$) per day for 1980 participants. Minimize the speed of tap, using automatic taps, and using taps operated by legs might be an effective solution to reduce the water overuse. Furthermore, behavioral change interventions are needed to aware people turn off the tap during hand scrubbing with soap.

Microbe mediated immobilization of arsenic in the rice rhizosphere after incorporation of silica impregnated biochar composites.

This study mechanistically addressed for the first time, the contradiction between the application of many biochars to paddy soil and increased arsenic (As) release as employed by most of previous studies. Three types of biochar containing natural and chemical forms of Si: (i) unmodified rice husk biochar (RHBC), (ii) RHBC modified with Si fertilizer (Si-RHBC), and (iii) RHBC modified with nanoparticles of montmorillonite clay (NM-RHBC) were applied in As-contaminated paddy soil to examine their potential to control the mobility of As in the soil-microbe-rice system. Both Si-RHBC and NM-RHBC decreased As concentration in porewater by 40-65 %, while RHBC decreased by 30-44 % compared to biochar unamended soil from tillering to maturing stage. At tillering stage, RHBC, Si-RHBC and NM-RHBC amendments significantly decreased As(III) concentration in the rice rhizosphere by 57, 76 and 73 %, respectively compared to the control soil. The immobilization of As is due to: (i) lowering of microbe mediated As release from iron minerals, (ii) oxidation of As(III) to As(V) by aioA gene, and (iii) adsorption on a Si-ferrihydrite complex. The decrease of more toxic As(III) and its oxidation to less mobile As(V) by Si-rich biochar amendments is a promising As detoxification phenomenon in the rice rhizosphere.

Arsenic in Latin America: A critical overview on the geochemistry of arsenic originating from geothermal features and volcanic emissions for solving its environmental consequences.

Geothermal fluids and volcanic emissions are important sources of arsenic (As), resulting in elevated concentrations of As in ground-, surface-water and soil, which may adversely affect the environment. Arsenic originating from geothermal features and volcanic activities is common in Latin America forming a serious threat to the livelihoods of millions of people. This review attempts to provide a critical overview of the geochemistry of As originating from these sources in Latin America to understand what information exists about and what future research needs to be undertaken. This study evaluated 15 countries in Latin America. In total, 423 sites were characterized with As originating from geothermal sources, mostly related to present volcanic activity (0.001 < As<73 mg/L, mean: 36.5 mg/L) and the transboundary Guarani Aquifer System (0.001 < As<0.114 mg/L, mean: 0.06 mg/L). Many of the geothermal systems and volcanoes discussed in this study are close to densely populated cities, including Bogota, Managua, San José, Guatemala City and Mexico City, where total As concentrations in natural ground- and surface- water exceed the safe drinking water guideline of 0.01 mg/L, recommended by the World Health Organization (WHO). However, the wide geographical occurrence of As in geothermal fluids and volcanic emissions of this region is by far not fully understood, so that development of geographical maps based on geographic information system (GIS) is an urgent necessity to understand the real nature of the problem. The assessment of environmental risks and the potential impacts on human health both inadequate and scarce and hence, these gaps need to be addressed by future research. The present holistic assessment of As originating from geothermal features and volcanic emissions would be a driving force to formulate a plan for establishing a sustainable As mitigation in vulnerable areas of Latin America in the near future. An assessment of the geochemistry, mobility and distribution of As would augment the effectiveness of the plan.

A fast analytical protocol for simultaneous speciation of arsenic by Ultra-High Performance Liquid Chromatography (UHPLC) hyphenated to Inductively Coupled Plasma Mass Spectrometry (ICP-MS) as a modern advancement in liquid chromatography approaches.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) hyphenated to High Performance Liquid Chromatography (HPLC) and Ion Chromatography (IC) are widely used for simultaneous speciation of arsenic (As). Longer retention time resulting in a slow separation is the major drawback of these existing approaches. Besides, fast separations achieved from HPLC based methods have always resulted in poor resolution and baseline separation between peaks. For the first time, the present study aimed to improve the existing HPLC related methods in order to develop a fast analytical protocol based on Ultra-High Performance Liquid Chromatography (UHPLC) hyphenated to ICP-MS detection for simultaneous separation and quantification of arsenite (As(III)), arsenate (As(V)), dimethylarsonate (DMA(V)) and monomethylarsenate (MMA(V)). Two types of ammonium-based mobile phases (i.e. NH4H2PO4 and NH4NO3) were examined at different eluent concentrations and pH to choose the most effective eluent system. Results demonstrated that the mixed mobile phase containing 8.5 mM of NH4H2PO4 and NH4NO3 (1:1) at pH 6.0 is the most effective eluent achieving the separation of As species with improved resolutions within 5 min which is almost a double saving in analysis time per sample compared to the existing methods (9-15 min). Faster separation is analytically cost effective in terms of ICP-MS running cost and energy consumption. Unlike HPLC, UHPLC did not generate a higher column back pressure with increasing flow rate up to 2.5 mL/min resulting in a faster separation with excellent resolution of peaks. Limits of detection for As species were in the range of 0.3-0.5 µg/L. The proposed method was applied to quantify As species present in commercially available rice varieties in Australia and Sri Lanka. Results of speciation analysis indicated that As(III) is the dominant species, ranging from 53 to 100% in the rice grains. The proposed analytical protocol based on UHPLC-ICP-MS provided an accurate and reliable identification and quantification of As species with the advantages of rapid separation, excellent resolution, and low detection limits. Such a recent trend in fundamental research could be a turning point for future environmental and biological research to further improve this strategy for the speciation of other toxic metal(loid)s in food, water and biological samples.

Hydrogeochemical controls on arsenic mobility in an arid inland basin, Southeast of Iran: The role of alkaline conditions and salt water intrusion.

Elevated inorganic arsenic concentrations in groundwater has become a major public and environmental health concern in different parts of the world. Currently, As-contaminated groundwater issue in many countries and regions is a major topic for publications at global level. However, there are many regions worldwide where the problem has still not been resolved or fully understood due to inadequate hydrogeochemical investigations. Hence, this study evaluates for the first time the hydrogeochemical behavior of the arid and previously unexplored inland basin of Sirjan Plain, south east (SE) Iran, in order to assess the controlling factors which influence arsenic (As) mobility and its distribution through groundwater resources. Total inorganic arsenic concentration was measured using inductive-coupled plasma optical emission spectrometry (ICP-OES). Arsenic content in groundwater of this region ranged between 2.4 and 545.8 µg/L (mean value: 86.6 µg/L) and 50% of the samples exceeded the World Health Organization (WHO) guideline value of 10 µg/L in drinking water. Groundwater was mainly of Na-Cl type and alkaline due to silicate weathering, ion exchange and evaporation in arid conditions. Elevated As concentrations were generally observed under weakly alkaline to alkaline conditions (pH > 7.4). Multivariate statistical analysis including cluster analysis and bi-plot grouped As with pH and HCO3 and demonstrated that the secondary minerals including oxyhydroxides of Fe are the main source of As in groundwater in this region. The desorption of As from these mineral phases occurs under alkaline conditions in oxidizing arid environments thereby leading to high levels of As in groundwater. Moreover, evaporation, ion exchange and saltwater intrusion were the secondary processes accelerating As release and its mobility in groundwater. Based on the results of this study, desorption of As from metal oxy-hydroxides surfaces under alkaline conditions, evaporation and intrusion of As-rich saline water are considered to be the major factors causing As enrichment in arid inland basins such as those in southeast Iran. This study proposes the regular monitoring and proper groundwater management practices to mitigate high levels of arsenic in groundwater and related drinking water wells of Sirjan Plain.

Biochar versus bone char for a sustainable inorganic arsenic mitigation in water: What needs to be done in future research?

Arsenic (As) is an emerging contaminant on a global scale posing threat to environmental and human health. The relatively brief history of the applications of biochar and bone char has mapped the endeavors to remove As from water to a considerable extent. This critical review attempts to provide a comprehensive overview for the first time on the potential of bio- and bone-char in the immobilization of inorganic As in water. It seeks to offer a rational assessment of what is existing and what needs to be done in future research as an implication for As toxicity of human health risks through acute and chronic exposure to As contaminated water. Bio- and bone-char are recognized as promising alternatives to activated carbon due to their lower production and activation cost. The surface modification via chemical methods has been adopted to improve the adsorption capacity for anionic As species. Surface complexation, ion exchange, precipitation and electrostatic interactions are the main mechanisms involved in the adsorption of As onto the char surface. However, arsenic-bio-bone char interactions along with their chemical bonding for the removal of As in aqueous solution is still a subject of debate. Hence, the proposed mechanisms need to be scrutinized further using advanced analytical techniques such as synchrotron-based X-ray. Moving this technology from laboratory phase to field scale applications is an urgent necessity in order to establish a sustainable As mitigation in drinking water on a global scale.

Mechanistic understanding of crystal violet dye sorption by woody biochar: implications for wastewater treatment.

Dye-based industries, particularly small and medium scale, discharge their effluents into waterways without treatment due to cost considerations. We investigated the use of biochars produced from the woody tree Gliricidia sepium at 300 °C (GBC300) and 500 °C (GBC500) in the laboratory and at 700 °C from a dendro bioenergy industry (GBC700), to evaluate their potential for sorption of crystal violet (CV) dye. Experiments were conducted to assess the effect of pH reaction time and CV loading on the adsorption process. The equilibrium adsorption capacity was higher with GBC700 (7.9 mg g-1) than GBC500 (4.9 mg g-1) and GBC300 (4.4 mg g-1), at pH 8. The CV sorption process was dependent on the pH, surface area and pore volume of biochar (GBC). Both Freundlich and Hill isotherm models fitted best to the equilibrium isotherm data suggesting cooperative interactions via physisorption and chemisorption mechanisms for CV sorption. The highest Hill sorption capacity of 125.5 mg g-1 was given by GBC700 at pH 8. Kinetic data followed the pseudo-second-order model, suggesting that the sorption process is more inclined toward the chemisorption mechanism. Pore diffusion, π-π electron donor-acceptor interaction and H-bonding were postulated to be involved in physisorption, whereas electrostatic interactions of protonated amine group of CV and negatively charged GBC surface led to a chemisorption type of adsorption. Overall, GBC produced as a by-product of the dendro industry could be a promising remedy for CV removal from an aqueous environment.

Thiolated arsenic in natural systems: What is current, what is new and what needs to be known.

Thiolated arsenic compounds are the sulfur analogous substructures of oxo-arsenicals as the arsinoyl (As = O) is substituted by an arsinothioyl (As = S) group. Relatively brief history of thioarsenic research, mostly in the current decade has endeavored to understand their consequences in the natural environment. However, thioarsenic related aspects have by far not attached much research concern on global scale compared to other arsenic species. This review attempts to provide a critical overview for the first time on formation mechanisms of thioarsenicals, their chemistry, speciation and analytical methodologies in order to provide a rational assessment of what is new, what is current, what needs to be known or what should be done in future research. Thioarsenic compounds play a vital role in determining the biogeochemistry of arsenic in sulfidic environments under reducing conditions. Thioarsenic species are widely immobilized by naturally occurring processes such as the adsorption on iron (oxyhydr)oxides and precipitation on iron sulfide minerals. Accurate measurement of thioarsenic species is a challenging task due to their instability upon pH, temperature, redox potential, and concentrations of oxygen, sulfur and iron. Assessment of direct and indirect effects of toxic thioarsenic species on global population those who frequently get exposed to high levels of arsenic is an urgent necessity. Dimethylmonothioarsinic acid (DMMTAV) is the most cytotoxic arsenic metabolite having similar toxicological effects as dimethylarsinous acid (DMAIII) in human and animal tissues. The formation and chemical analysis of thioarsenicals in soil and sediments are highly unknown. Therefore, future research needs to be more inclined towards in determining the molecular structure of unknown thioarsenic complexes in various environmental suites. Contemporary approaches hyphenated to existing technologies would pave the way to overcome critical challenges of thioarsenic speciation such as standards synthesis, structural determination, quantification and sample preservation in future research.

Influence of bioenergy waste biochar on proton- and ligand-promoted release of Pb and Cu in a shooting range soil.

Presence of organic and inorganic acids influences the release rates of trace metals (TMs) bound in contaminated soil systems. This study aimed to investigate the influence of bioenergy waste biochar, derived from Gliricidia sepium (GBC), on the proton and ligand-induced bioavailability of Pb and Cu in a shooting range soil (17,066mg Pb and 1134mg Cu per kg soil) in the presence of inorganic (sulfuric, nitric, and hydrochloric) and organic acids (acetic, citric, and oxalic). Release rates of Pb and Cu in the shooting range soil were determined under different acid concentrations (0.05, 0.1, 0.5, 1, 5, and 10mM) and in the presence/absence of GBC (10% by weight of soil). The dissolution rates of Pb and Cu increased with increasing acid concentrations. Lead was preferentially released (2.79×10-13 to 8.86×10-13molm-2s-1) than Cu (1.07×10-13 to 1.02×10-13molm-2s-1) which could be due to the excessive Pb concentrations in soil. However, the addition of GBC to soil reduced Pb and Cu dissolution rates to a greater extent of 10.0 to 99.5% and 15.6 to 99.5%, respectively, under various acid concentrations. The increased pH in the medium and different adsorption mechanisms, including electrostatic attractions, surface diffusion, ion exchange, precipitation, and complexation could immobilize Pb and Cu released by the proton and ligands in GBC amended soil. Overall, GBC could be utilized as an effective soil amendment to immobilize Pb and Cu in shooting range soil even under the influence of soil acidity.

Correction to: Effects of carbon nanotube and biochar on bioavailability of Pb, Cu and Sb in multi-metal contaminated soil.

Unfortunately, in the original publication of the article, Prof. Yong Sik Ok's affiliation was incorrectly published. The author's affiliation is as follows.

Effects of carbon nanotube and biochar on bioavailability of Pb, Cu and Sb in multi-metal contaminated soil.

This study examined the effects of carbon nanotube and biochar on the bioavailability of Pb, Cu and Sb in the shooting range soils for developing low-cost remediation technology. Commercially available multi-walled carbon nanotube (MWCNT) and biochar pyrolyzed from soybean stover at 300 °C (BC) at 0.5, 1 and 2.5% (w w-1) were used to remediate the contaminated soil in an incubation experiment. Both DTPA (bioavailable) and TCLP (leaching) extraction procedures were used to compare the metal/loid availability and leaching by the amendments in soil. The addition of BC was more effective in immobilizing mobile Pb and Cu in the soil than that in MWCNT. The BC reduced the concentrations of Pb and Cu in the soil by 17.6 and 16.2%, respectively. However, both MWCNTs and BC increased Sb bioavailability by 1.4-fold and 1.6-fold, respectively, in DTPA extraction, compared to the control. The toxicity characteristic leaching procedure (TCLP) test showed that the leachability of Pb in the soil amended with 2.5% MWCNT was 1.3-fold higher than that the unamended soil, whereas the BC at 2.5% decreased the TCLP-extractable Pb by 19.2%. Precipitation and adsorption via electrostatic and π-π electron donor-acceptor interactions were postulated to be involved in the interactions of Pb and Cu with surfaces of the BC in the amended soils, whereas ion exchange mechanisms might be involved in the immobilization of Cu in the MWCNT-amended soils. The application of BC derived from soybean stover can be a low-cost technology for simultaneously immobilizing bioavailable Pb and Cu in the shooting range soils; however, neither of amendments was effective in Sb immobilization.

Antimony as a global dilemma: Geochemistry, mobility, fate and transport.

Elevated concentrations of antimony (Sb) in environmental, biological and geochemical systems originating from natural, geological and anthropogenic sources are of particular global concern. This review presents a critical overview of natural geochemical processes which trigger the mobilization of Sb from its host mineral phases and related rocks to the surrounding environments. The primary source of Sb contamination in the environment is geogenic. The geochemical characteristics of Sb are determined by its oxidation states, speciation and redox transformation. Oxidative dissolution of sulfide minerals and aqueous dissolution are the most prevalent geochemical mechanisms for the release of Sb to the environment. Transformation of mobile forms of Sb is predominantly controlled by naturally occurring precipitation and adsorption processes. Oxyhydroxides of iron, manganese and aluminum minerals have been recognized as naturally occurring Sb sequestrating agents in the environment. Antimony is also immobilized in the natural environment via precipitation with alkali and heavy metals resulting extremely stable mineral phases, such as schafarzikite, tripuhyite and calcium antimonates. Many key aspects, including detection, quantification, and speciation of Sb in different environmental systems as well as its actual human exposure remain poorly understood. Identification of global distribution of most vulnerable Sb-contaminated regions/countries along with aquifer sediments is an urgent necessity for the installation of safe drinking water wells. Such approaches could provide the global population Sb-safe drinking and irrigation water and hinder the propagation of Sb in toxic levels through the food chain. Hence, raising awareness through the mobility, fate and transport of Sb as well as further transdisciplinary research on Sb from global scientific communities will be a crucial stage to establish a sustainable Sb mitigation on a global scale.

Efficacy of woody biomass and biochar for alleviating heavy metal bioavailability in serpentine soil.

Crops grown in metal-rich serpentine soils are vulnerable to phytotoxicity. In this study, Gliricidia sepium (Jacq.) biomass and woody biochar were examined as amendments on heavy metal immobilization in a serpentine soil. Woody biochar was produced by slow pyrolysis of Gliricidia sepium (Jacq.) biomass at 300 and 500 °C. A pot experiment was conducted for 6 weeks with tomato (Lycopersicon esculentum L.) at biochar application rates of 0, 22, 55 and 110 t ha-1. The CaCl2 and sequential extractions were adopted to assess metal bioavailability and fractionation. Six weeks after germination, plants cultivated on the control could not survive, while all the plants were grown normally on the soils amended with biochars. The most effective treatment for metal immobilization was BC500-110 as indicated by the immobilization efficiencies for Ni, Mn and Cr that were 68, 92 and 42 %, respectively, compared to the control. Biochar produced at 500 °C and at high application rates immobilized heavy metals significantly. Improvements in plant growth in biochar-amended soil were related to decreasing in metal toxicity as a consequence of metal immobilization through strong sorption due to high surface area and functional groups.

Insights into aqueous carbofuran removal by modified and non-modified rice husk biochars.

Biochar has been considered as a potential sorbent for removal of frequently detected pesticides in water. In the present study, modified and non-modified rice husk biochars were used for aqueous carbofuran removal. Rice husk biochars were produced at 300, 500, and 700 °C in slow pyrolysis and further exposed to steam activation. Biochars were physicochemically characterized using proximate, ultimate, FTIR methods and used to examine equilibrium and dynamic adsorption of carbofuran. Increasing pyrolysis temperature led to a decrease of biochar yield and increase of porosity, surface area, and adsorption capacities which were further enhanced by steam activation. Carbofuran adsorption was pH-dependant, and the maximum (161 mg g-1) occurred in the vicinity of pH 5, on steam-activated biochar produced at 700 °C. Freundlich model best fitted the sorption equilibrium data. Both chemisorption and physisorption interactions on heterogeneous adsorbent surface may involve in carbofuran adsorption. Langmuir kinetics could be applied to describe carbofuran adsorption in a fixed bed. A higher carbofuran volume was treated in a column bed by a steam-activated biochar versus non-activated biochars. Overall, steam-activated rice husk biochar can be highlighted as a promising low-cost sustainable material for aqueous carbofuran removal.