Toxicity of organoclays to microbial processes and earthworm survival in soils

Colour and surface functional properties of wool fabrics coated with gallnut, feijoa skin, and mango seed kernel tannin-stabilised Ag nanoparticles

In the textile industry, textile materials are dyed and multi-functionalised by multi-step treatments that considerably increase the environmental impacts by increasing water and energy usage along with increasing the generation of volume of effluent. In this work, Ag nanoparticles (Ag NPs) were in situ formed and stabilised with gallnut, feijoa fruit skin, and mango seed kernel-derived tannins, and wool fabrics were coated simultaneously with these Ag NPs in the same bath. The Ag NP treatment produced dark to light olive-brown shades on wool fabrics. The treatment conditions for the treatment with Ag NPs were optimised to achieve the best results. The colour intensity, UV radiation absorption, antibacterial activity, surface electrical resistance, and durability of the treatment to washing were assessed by various methods. The gallnut-derived tannin (GNT)-stabilised Ag NP-coated wool fabrics showed overall the best results including excellent antibacterial activity against various types of bacteria. The treatment was durable to at least 20 cycles of IWS 7A washes (equivalent to 80 domestic washes). For the 0.5% Ag NPs on the weight of fibre (owf) dosage, the UV light transmission through the trisodium citrate-stabilised Ag NP-coated fabric at 365 and 311 nm was 6.37 and 0.95% respectively, which reduced to 1.63 and 0.20% for the fabric coated with GNT-stabilised Ag NPs providing excellent protection against UV radiation. The surface resistivity of wool fabric reduced from 1.1 × 1012 ohm cm-1 for the untreated fabric to 1.1 × 109 ohm cm-1 for the fabric coated with 2.0% owf GNT-stabilised Ag NPs. The stabilisation of Ag NPs with GNT prolonged the wash-durability by reducing the leaching of Ag NPs from the treated fabric. The developed method could be a sustainable alternative to traditional multi-stage treatments conducted in the textile industry with toxic synthetic dyes and finishing agents for the colouration and multifunctionalisation of wool fabrics.

Ecotoxicological effects of per- and polyfluoroalkyl substances (PFAS) and of a new PFAS adsorbing organoclay to immobilize PFAS in soils on earthworms and plants

A novel adsorptive organoclay (Intraplex A®) was developed for the in situ immobilization of per- and polyfluoroalkyl substances (PFAS) in the vadose zone. We provide the first evaluation of the effects of Intraplex A® on earthworms and plants in a PFAS-contaminated soil. Ecotoxicological tests were carried out on control soil with and without Intraplex A® (C + I and C, respectively) and PFAS-contaminated soil with and without Intraplex A® (PFAS + I and PFAS, respectively). We investigated the acute ecotoxicological effects of PFAS and Intraplex A® on the growth, reproduction and survival of earthworms (Eisenia fetida) and on plant growth (oat - Avena sativa and turnip - Brassica rapa L. silvestris). Earthworm lethality was 7.6 lower in PFAS + I than in PFAS soil. Earthworms avoided 100% C + I and PFAS + I soils, and reduced earthworms' reproduction was observed in both these soils. For both plant species, the PFAS + I soil yielded less fresh and dry shoot biomass than the PFAS soil, while root growth remained unaffected (all tests: p < 0.05). Soils with Intraplex A® had some negative effects on plants and earthworms, which must be balanced with its benefits as an in situ PFAS adsorbent.

Recovery, regeneration and sustainable management of spent adsorbents from wastewater treatment streams: A review

Adsorption is the most widely adopted, effective, and reliable treatment process for the removal of inorganic and organic contaminants from wastewater. One of the major issues with the adsorption-treatment process for the removal of contaminants from wastewater streams is the recovery and sustainable management of spent adsorbents. This review focuses on the effectiveness of emerging adsorbents and how the spent adsorbents could be recovered, regenerated, and further managed through reuse or safe disposal. The critical analysis of both conventional and emerging adsorbents on organic and inorganic contaminants in wastewater systems are evaluated. The various recovery and regeneration techniques of spent adsorbents including magnetic separation, filtration, thermal desorption and decomposition, chemical desorption, supercritical fluid desorption, advanced oxidation process and microbial assisted adsorbent regeneration are discussed in detail. The current challenges for the recovery and regeneration of adsorbents and the methodologies used for solving those problems are covered. The spent adsorbents are managed through regeneration for reuse (such as soil amendment, capacitor, catalyst/catalyst support) or safe disposal involving incineration and landfilling. Sustainable management of spent adsorbents, including processes involved in the recovery and regeneration of adsorbents for reuse, is examined in the context of resource recovery and circular economy. Finally, the review ends with the current drawbacks in the recovery and management of the spent adsorbents and the future directions for the economic and environmental feasibility of the system for industrial-scale application.

Influencing mechanisms of siderite and magnetite, on naphthalene biodegradation: Insights from degradability and mineral surface structure

Biodegradation is the most economical and efficient process for remediating polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap). Soil composition is pivotal in controlling PAH migration and transformation. Iron minerals such as siderite and magnetite are the primary components of soil and sediment and play key roles in organic pollutant biodegradation. However, it is unclear whether siderite and magnetite promote or inhibit Nap biodegradation. The effects of siderite and magnetite on Nap biodegradation were investigated through batch experiments in this study. The results indicated that siderite increased Nap biodegradation efficiency by 7.87%, whereas magnetite inhibited Nap biodegradation efficiency by 3.54%. In the presence of siderite, Nap-degrading bacteria with acid-producing effects promoted siderite dissolution via metabolic activity, resulting in an increased Fe (II) concentration in solution which accelerated the iron reduction process and promoted Nap biodegradation. In addition, the presence of iron minerals altered the genus-level community structure. Anaerobic sulfate-reducing bacteria such as Desulfosporosinus occurred in the presence of siderite, indicating that sulfate reduction occurred in advance under the influence of siderite. In the presence of magnetite, Fe (III) in iron minerals were converted to Fe (II), and under the mediation of microorganisms, Fe (II) combined with carbonate to form secondary minerals (e.g., siderite). Secondary minerals were attached to the surface of magnetite, which inhibited magnetite dissolution and reduced the efficiency of Fe (III) utilization by microorganisms. Furthermore, as the reaction proceeds, acid-producing microorganisms promoted magnetite further dissolution, resulting in a longer duration of the Fe (III) reduction process. Bacteria utilizing sulfuric acid as the terminal electron acceptor consumed organic matter more rapidly than those using iron as the terminal electron acceptor. Therefore, magnetite inhibited Nap degradation. These observations enhance our understanding of the interaction mechanisms of iron minerals, organic pollutants, and degrading bacteria during the biodegradation process.

Natural and engineered clays and clay minerals for the removal of poly- and perfluoroalkyl substances from water: State-of-the-art and future perspectives

Poly- and perfluoroalkyl substances (PFAS) present globally in drinking-, waste-, and groundwater sources are contaminants of emerging concern due to their long-term environmental persistence and toxicity to organisms, including humans. Here we review PFAS occurrence, behavior, and toxicity in various water sources, and critically discuss their removal via mineral adsorbents, including natural aluminosilicate clay minerals, oxidic clays (Al, Fe, and Si oxides), organoclay minerals, and clay-polymer and clay‑carbon (biochar and graphene oxide) composite materials. Among the many remediation technologies, such as reverse osmosis, adsorption, advanced oxidation and biologically active processes, adsorption is the most suitable for PFAS removal in aquatic systems. Treatment strategies using clay minerals and oxidic clays are inexpensive, eco-friendly, and efficient for bulk PFAS removal due to their high surface areas, porosity, and high loading capacity. A comparison of partition coefficient values calculated from extracted data in published literature indicate that organically-modified clay minerals are the best-performing adsorbent for PFAS removal. In this review, we scrutinize the corresponding plausible mechanisms, factors, and challenges affecting the PFAS removal processes, demonstrating that modified clay minerals (e.g., surfactant, amine), including some commercially available products (e.g., FLUORO-SORB®, RemBind®, matCARE™), show good efficacy in PFAS remediation in contaminated media under field conditions. Finally, we propose future research to focus on the challenges of using clay-based adsorbents for PFAS removal from contaminated water due to the regeneration and safe-disposal of spent clay adsorbents is still a major issue, whilst enhancing the PFAS removal efficiency should be an ongoing scientific effort.

Biomaterials for human space exploration: A review of their untapped potential

As biomaterial advances make headway into lightweight radiation protection, wound healing dressings, and microbe resistant surfaces, a relevance to human space exploration manifests itself. To address the needs of the human in space, a knowledge of the space environment becomes necessary. Both an understanding of the environment itself and an understanding of the physiological adaptations to that environment must inform design parameters. The space environment permits the fabrication of novel biomaterials that cannot be produced on Earth, but benefit Earth. Similarly, designing a biomaterial to address a space-based challenge may lead to novel biomaterials that will ultimately benefit Earth. This review describes several persistent challenges to human space exploration, a variety of biomaterials that might mitigate those challenges, and considers a special category of space biomaterial. STATEMENT OF SIGNIFICANCE: This work is a review of the major human and environmental challenges facing human spaceflight, and where biomaterials may mitigate some of those challenges. The work is significant because a broad range of biomaterials are applicable to the human space program, but the overlap is not widely known amongst biomaterials researchers who are unfamiliar with the challenges to human spaceflight. Additionaly, there are adaptations to microgravity that mimic the pathology of certain disease states ("terrestrial analogs") where treatments that help the overwhelmingly healthy astronauts can be applied to help those with the desease. Advances in space technology have furthered the technology in that field on Earth. By outlining ways that biomaterials can promote human space exploration, space-driven advances in biomaterials will further biomaterials technology.

Remediation of poly- and perfluoroalkyl substances (PFAS) contaminated soils - To mobilize or to immobilize or to degrade?

Poly- and perfluoroalkyl substances (PFASs) are synthetic chemicals, which are introduced to the environment through anthropogenic activities. Aqueous film forming foam used in firefighting, wastewater effluent, landfill leachate, and biosolids are major sources of PFAS input to soil and groundwater. Remediation of PFAS contaminated solid and aqueous media is challenging, which is attributed to the chemical and thermal stability of PFAS and the complexity of PFAS mixtures. In this review, remediation of PFAS contaminated soils through manipulation of their bioavailability and destruction is presented. While the mobilizing amendments (e.g., surfactants) enhance the mobility and bioavailability of PFAS, the immobilizing amendments (e.g., activated carbon) decrease their bioavailability and mobility. Mobilizing amendments can be applied to facilitate the removal of PFAS though soil washing, phytoremediation, and complete destruction through thermal and chemical redox reactions. Immobilizing amendments are likely to reduce the transfer of PFAS to food chain through plant and biota (e.g., earthworm) uptake, and leaching to potable water sources. Future studies should focus on quantifying the potential leaching of the mobilized PFAS in the absence of removal by plant and biota uptake or soil washing, and regular monitoring of the long-term stability of the immobilized PFAS.

Bentonite-Based Organic Amendment Enriches Microbial Activity in Agricultural Soils

Bentonite-based organic amendments may have the potential to enhance soil microbial properties. The experiment was carried out from 2014 to 2017 comprising four treatments: NPK fertilizer (nitrogen, phosphorus and potassium mineral fertilizer as a control), NPK + cattle manure, NPK + bentonite, and NPK + combination of manure with bentonite (MB) to verify this hypothesis. The effect of treatments on seven different soil microbial properties was measured: dehydrogenase activity (DHA), bacterial phospholipid fatty acid content, fungal phospholipid fatty acid content, microbial biomass carbon (Cmic), 16S rDNA, 18S rDNA, and ammonia-oxidizing bacteria in soil. The results showed that solely bentonite treatment increases the bacterial and fungal biomass, which was further confirmed by the increased 16S rDNA and 18s rDNA gene copy numbers. The only significantly decreased values upon treatment with solely bentonite were recorded for DHA and Cmic. The ammonia-oxidizing bacteria population increased with the sole application of bentonite and reached its maximum value when bentonite was applied with manure. The MB treatment showed the highest value for all seven measured properties. In summary, the application of bentonite solely might increase or decrease the soil activity, but its addition, along with manure, always promotes an abundance of soil microorganisms and their activity. The co-application of bentonite with manure altered the soil microbial properties in a 3-year field experiment in favor of increased microbial biomass, which is beneficial for agriculture and environment and reveals the potential for the restoration of polluted lands.

Monitoring diclofenac adsorption by organophilic alkylpyridinium bentonites

Organoclays have been applied as efficient adsorbents for pharmaceutical pollutants from aqueous solution. In this work, dodecylpyridinium chloride (C₁₂pyCl) and hexadecylpyridinium chloride (C₁₆pyCl) cationic surfactants were used for the preparation of organobentonites destined for diclofenac sodium (DFNa) adsorption, an anionic drug widely detected in wastewater. The organofunctionalization of the clay samples was performed under microwave irradiation at 50 °C for 5 min with surfactant amounts of 100% and 200% in relation to the cation exchange capacity (CEC) of the pristine bentonite. The amount of incorporated ammonium salts based on CHN elemental analysis was higher for all samples prepared with 200% of the CEC. The basal spacings of the organoclays ranged from 1.54 to 2.13 nm, indicating the entrance of organic cations into the interlayer spacing of the clay samples, and the spacing depended on the size of the alkyl organic chain. The hydrophobic character of the organobentonites was verified by thermogravimetry and infrared spectroscopy (FTIR). The adsorption isotherms showed that the drug capacity adsorption was influenced by the amount of surfactant incorporated into the bentonite, the packing density and the arrangement of the surfactants in the interlayer spacing. Zeta potential measurements of the organobentonites and FTIR analysis after drug adsorption suggested that electrostatic and nonelectrostatic interactions contributed to the mechanism of adsorption.

Modified clays alter diversity and respiration profile of microorganisms in long-term hydrocarbon and metal co-contaminated soil

Clays and surfactant‐modified clays (organoclays) are becoming popular as pollutant sorbents due to their high reactivity and low‐cost availability. However, the lack of field testing and data on ecotoxicity limits their application. Considering such aspects, this study assessed the impact of clay amendments to polycyclic aromatic hydrocarbons (PAHs)/cadmium (Cd)‐contaminated soil on microbial respiration profiles (active vs. inactive cells) using redox staining and the relative abundance and diversity of bacteria and archaea. These clay products are bentonite, cationic surfactant‐modified bentonite and palmitic acid‐grafted surfactant‐modified bentonite). After 70 days, the addition of bentonite and its modified forms altered microbial community structure mainly among dominant groups (Actinobacteria, Proteobacteria, Firmicutes and Chloroflexi) with effects varying depending on material loading to soil. Among amendments, fatty acid (palmitic acid) tailored cationic surfactant‐modified bentonite proved to be microbial growth supportive and significantly increased the number of respiration‐active microbial cells by 5% at a low dose of material (e.g. 1%). Even at high dose (5%), the similarity index using operational taxonomic units (OTUs) also indicates that this modified organoclay‐mixed soil provided only slightly different environment than control soil, and therefore, it could offer more biocompatibility than its counterpart organoclay at similar dose (e.g. cationic surfactant‐modified bentonite). This study promotes designing ‘eco‐safe’ clay‐based sorbents for environmental remediation.

Biocompatible functionalisation of nanoclays for improved environmental remediation

Among the wide range of materials used for remediating environmental contaminants, modified and functionalised nanoclays show particular promise as advanced sorbents, improved dispersants, or biodegradation enhancers. However, many chemically modified nanoclay materials are incompatible with living organisms when they are used in natural systems with detrimental implications for ecosystem recovery. Here we critically review the pros and cons of functionalised nanoclays and provide new perspectives on the synthesis of environmentally friendly varieties. Particular focus is given to finding alternatives to conventional surfactants used in modified nanoclay products, and to exploring strategies in synthesising nanoclay-supported metal and metal oxide nanoparticles. A large number of promising nanoclay-based sorbents are yet to satisfy environmental biocompatibility in situ but opportunities are there to tailor them to produce "biocompatible" or regenerative/reusable materials.

Influencing mechanisms of hematite on benzo(a)pyrene degradation by the PAH-degrading bacterium Paracoccus sp. Strain HPD-2: insight from benzo(a)pyrene bioaccessibility and bacteria activity

Iron oxides are reactive inorganic soil components that play an important role in the fate and transport of organic pollutants. Here, hematite was selected to investigate its effect on the biodegradation of benzo[a]pyrene (BaP) by Paracoccus sp. strain HPD-2. Approximately 60% of the total BaP was degraded in the absence of hematite after 7 days but only 30.8 and 20.8% of that was degraded after the addition of 10 and 20 mg  mL^-1 hematite, respectively, indicating that the addition of hematite could significantly inhibit the biodegradation of BaP (P < 0.05). The hematite also lowered bacterium activity by coating the cells and by generating reactive oxygen species that destroyed the cells. Two-photon confocal laser scanning microscope images showed that the addition of hematite substantially decreased the amount of BaP combined with the bacterium, and this also enabled us to observe directly the migration and regression of BaP in the interaction between HPD-2 and hematite. Higher death ratio of HPD-2 might lower the BaP access to live cells because dead cells have a higher adsorption affinity for BaP than live cells. These observations enhance our understanding of the mechanisms by which metal oxides, organic pollutants and degrading-bacteria interact during the biodegradation process.

Influence of physico-chemical properties of soil clay fractions on the retention of dissolved organic carbon

This study investigated the effects of surface functional groups, cation exchange capacity (CEC), surface charge, sesquioxides and specific surface area (SSA) of three soil clay fractions (SCFs) (kaolinite-illite, smectite and allophane) on the retention of dissolved organic carbon (DOC) in soils. Physico-chemical properties of the SCFs before and after removing native carbon and/or sesquioxides were characterised, and the DOC adsorption-desorption tests were conducted by a batch method. Native organic carbon (OC)/sesquioxide removal treatments led to a small change in the CEC values of kaolinite-illite, but significant changes in those of smectite and allophane. The net negative surface charge increased in all samples with an increase in pH indicating their variable charge characteristics. The removal of native OC resulted in a slight increase in the net positive charge on soil clay surfaces, while sesquioxide removal increased the negative charge. Changes in the functional groups on the SCF surfaces contributed to the changes in CEC and zeta potential values. There was a strong relationship (R ² = 0.93, p < 0.05) between the Langmuir maximum DOC adsorption capacity (Q _max) and SSA. The Q _max value also showed a moderately strong relationship (R ² = 0.55, p < 0.05) with zeta potential (at pH 7). Q _max was only poorly correlated with CEC and native OC content. Therefore, along with SSA, the surface charge and functional groups of SCFs played the key role in determining the adsorption affinity and hence retention of DOC in soils.

Mild acid and alkali treated clay minerals enhance bioremediation of polycyclic aromatic hydrocarbons in long-term contaminated soil: A 14C-tracer study

Bioremediation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils requires a higher microbial viability and an increased PAH bioavailability. The clay/modified clay-modulated bacterial degradation could deliver a more efficient removal of PAHs in soils depending on the bioavailability of the compounds. In this study, we modified clay minerals (smectite and palygorskite) with mild acid (HCl) and alkali (NaOH) treatments (0.5-3 M), which increased the surface area and pore volume of the products, and removed the impurities without collapsing the crystalline structure of clay minerals. In soil incubation studies, supplements with the clay products increased bacterial growth in the order: 0.5 M HCl ≥ unmodified ≥ 0.5 M NaOH ≥ 3 M NaOH ≥ 3 M HCl for smectite, and 0.5 M HCl ≥ 3 M NaOH ≥ 0.5 M NaOH ≥ 3 M HCl ≥ unmodified for palygorskite. A¹⁴C-tracing study showed that the mild acid/alkali-treated clay products increased the PAH biodegradation (5-8%) in the order of 0.5 M HCl ≥ unmodified > 3 M NaOH ≥ 0.5 M NaOH for smectite, and 0.5 M HCl > 0.5 M NaOH ≥ unmodified ≥ 3 M NaOH for palygorskite. The biodegradation was correlated (r = 0.81) with the bioavailable fraction of PAHs and microbial growth as affected particularly by the 0.5 M HCl and 0.5 M NaOH-treated clay minerals. These results could be pivotal in developing a clay-modulated bioremediation technology for cleaning up PAH-contaminated soils and sediments in the field.

Quaternary ammonium-based biomedical materials: State-of-the-art, toxicological aspects and antimicrobial resistance

Microbial infections affect humans worldwide. Many quaternary ammonium compounds have been synthesized that are not only antibacterial, but also possess antifungal, antiviral and anti-matrix metalloproteinase capabilities. Incorporation of quaternary ammonium moieties into polymers represents one of the most promising strategies for preparation of antimicrobial biomaterials. Various polymerization techniques have been employed to prepare antimicrobial surfaces with quaternary ammonium functionalities; in particular, syntheses involving controlled radical polymerization techniques enable precise control over macromolecular structure, order and functionality. Although recent publications report exciting advances in the biomedical field, some of these technological developments have also been accompanied by potential toxicological and antimicrobial resistance challenges. Recent evidenced-based data on the biomedical applications of antimicrobial quaternary ammonium-containing biomaterials that are based on randomized human clinical trials, the golden standard in contemporary medicinal science, are included in the present review. This should help increase visibility, stimulate debates and spur conversations within a wider scientific community on the implications and plausibility for future developments of quaternary ammonium-based antimicrobial biomaterials.

Specific adsorption of cadmium on surface-engineered biocompatible organoclay under metal-phenanthrene mixed-contamination

Bioremediation of polycyclic aromatic hydrocarbons (PAHs) is extremely challenging when they coexist with heavy metals. This constrain has led to adsorption-based techniques that help immobilize the metals and reduce toxicity. However, the adsorbents can also non-selectively bind the organic compounds, which reduces their bioavailability. In this study we developed a surface-engineered organoclay (Arquad^® 2HT-75-bentonite-palmitic acid) which enhanced bacterial proliferation and adsorbed cadmium, but elevated phenanthrene bioavailability. Adsorption models of single and binary solutes revealed that the raw bentonite adsorbed cadmium and phenanthrene non-selectively at the same binding sites and sequestrated phenanthrene. In contrast, cadmium selectively bound to the deprotonated state of carboxyl groups in the organoclay and phenanthrene on the outer surface of the adsorbent led to a microbially congenial microenvironment with a higher phenanthrene bioavailability. This study provided valuable information which would be highly important for developing a novel clay-modulated bioremediation technology for cleaning up PAHs under mixed-contaminated situations.

Organophilic treatments of bentonite increase the adsorption of aflatoxin B1 and protect stem cells against cellular damage

Bentonite clays exhibit high adsorptive capacity for contaminants, including aflatoxin B1 (AFB1), a mycotoxin responsible for causing severe toxicity in several species including pigs, poultry and man. Organophilic treatments is known to increase the adsorption capacity of bentonites, and the primary aim of this study was to evaluate the ability of Brazilian bentonite and two organic salts - benzalkonium chloride (BAC) and cetyltrimethylammonium bromide (CTAB) to adsorb AFB1. For this end, 2(2) factorial designs were used in order to analyze if BAC or CTAB was able to increase AFB1 adsorption when submitted in different temperature and concentration. Both BAC and CTAB treatment (at 30°C and 2% of salt concentration) were found to increase the adsorption of AFB1 significantly compared with untreated bentonite. After organophilic bentonite treatments with BAC or CTAB, a vibration of CH stretch (2850 and 2920cm(-1)) were detected. A frequency of the SiO stretch (1020 and 1090cm(-1)) was changed by intercalation of organic cation. Furthermore, the interlayer spacing of bentonite increases to 1.23nm (d001 reflection at 2θ=7.16) and 1.22 (d001 reflection at 2θ=7.22) after the addition of BAC and CTAB, respectively. Another aim of the study was to observe the effects of these two bentonite salts in neural crest stem cell cultures. The two materials that were created by organophilic treatments were not found to be toxic to stem cells. Furthermore the results indicate that the two materials tested may protect the neural crest stem cells against damage caused by AFB1.

Surface tailored organobentonite enhances bacterial proliferation and phenanthrene biodegradation under cadmium co-contamination

Co-contamination of soil and water with polycyclic aromatic hydrocarbon (PAH) and heavy metals makes biodegradation of the former extremely challenging. Modified clay-modulated microbial degradation provides a novel insight in addressing this issue. This study was conducted to evaluate the growth and phenanthrene degradation performance of Mycobacterium gilvum VF1 in the presence of a palmitic acid (PA)-grafted Arquad® 2HT-75-based organobentonite in cadmium (Cd)-phenanthrene co-contaminated water. The PA-grafted organobentonite (ABP) adsorbed a slightly greater quantity of Cd than bentonite at up to 30mgL(-1) metal concentration, but its highly negative surface charge imparted by carboxylic groups indicated the potential of being a significantly superior adsorbent of Cd at higher metal concentrations. In systems co-contained with Cd (5 and 10mgL(-1)), the Arquad® 2HT-75-modified bentonite (AB) and PA-grafted organobentonite (ABP) resulted in a significantly higher (72-78%) degradation of phenanthrene than bentonite (62%) by the bacterium. The growth and proliferation of bacteria were supported by ABP which not only eliminated Cd toxicity through adsorption but also created a congenial microenvironment for bacterial survival. The macromolecules produced during ABP-bacteria interaction could form a stable clay-bacterial cluster by overcoming the electrostatic repulsion among individual components. Findings of this study provide new insights for designing clay modulated PAH bioremediation technologies in mixed-contaminated water and soil.

Active capping technology: a new environmental remediation of contaminated sediment

The management and treatment of contaminated sediment is a worldwide problem and poses major technical and economic challenges. Nowadays, various attempts have been committed to investigating a cost-effective way in contaminated sediment restoration. Among the remediation options, in situ capping turns out to be a less expensive, less disruptive, and more durable approach. However, by using the low adsorption capacity materials, traditional caps do not always fulfill the reduction of risks that can be destructive for human health, ecosystem, and even natural resources. Active caps, therefore, are designed to employ active materials (activated carbon, apatite, zeolite, organoclay, etc.) to strengthen their adsorption and degradation capacity. The active capping technology promises to be a permanent and cost-efficient solution to contaminated sediments. This paper provides a review on the types of active materials and the ways of these active materials employed in recent active capping studies. Cap design considerations including site-specific conditions, diffusion/advection, erosive forces, and active material selection that should be noticed in an eligible remediation project are also presented.

Bioremediation of PAHs and VOCs: Advances in clay mineral-microbial interaction

Bioremediation is an effective strategy for cleaning up organic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). Advanced bioremediation implies that biotic agents are more efficient in degrading the contaminants completely. Bioremediation by microbial degradation is often employed and to make this process efficient, natural and cost-effective materials can serve as supportive matrices. Clay/modified clay minerals are effective adsorbents of PAHs/VOCs, and readily available substrate and habitat for microorganisms in the natural soil and sediment. However, the mechanism underpinning clay-mediated biodegradation of organic compounds is often unclear, and this requires critical investigation. This review describes the role of clay/modified clay minerals in hydrocarbon bioremediation through interaction with microbial agents in specific scenarios. The vision is on a faster, more efficient and cost-effective bioremediation technique using clay-based products. This review also proposes future research directions in the field of clay modulated microbial degradation of hydrocarbons.

Heavy metal-immobilizing organoclay facilitates polycyclic aromatic hydrocarbon biodegradation in mixed-contaminated soil

Soils contaminated with a mixture of heavy metals and polycyclic aromatic hydrocarbons (PAHs) pose toxic metal stress to native PAH-degrading microorganisms. Adsorbents such as clay and modified clay minerals can bind the metal and reduce its toxicity to microorganisms. However, in a mixed-contaminated soil, an adsorption process more specific to the metals without affecting the bioavailability of PAHs is desired for effective degradation. Furthermore, the adsorbent should enhance the viability of PAH-degrading microorganisms. A metal-immobilizing organoclay (Arquad(®) 2HT-75-bentonite treated with palmitic acid) (MIOC) able to reduce metal (cadmium (Cd)) toxicity and enhance PAH (phenanthrene) biodegradation was developed and characterized in this study. The MIOC differed considerably from the parent clay in terms of its ability to reduce metal toxicity (MIOC>unmodified bentonite>Arquad-bentonite). The MIOC variably increased the microbial count (10-43%) as well as activities (respiration 3-44%; enzymatic activities up to 68%), and simultaneously maintained phenanthrene in bioavailable form in a Cd-phenanthrene mixed-contaminated soil over a 21-day incubation period. This study may lead to a new MIOC-assisted bioremediation technique for PAHs in mixed-contaminated soils.

Quaternary ammonium compounds (QACs): a review on occurrence, fate and toxicity in the environment

Quaternary ammonium compounds (QACs) are widely applied in household and industrial products. Most uses of QACs can be expected to lead to their release to wastewater treatment plants (WWTPs) and then dispersed into various environmental compartments through sewage effluent and sludge land application. Although QACs are considered to be aerobically biodegradable, the degradation is affected by its chemical structures, dissolved oxygen concentration, complexing with anionic surfactants, etc. High abundance of QACs has been detected in sediment and sludge samples due to its strong sorption and resistance to biodegradation under anoxic/anaerobic conditions. QACs are toxic to a lot of aquatic organisms including fish, daphnids, algae, rotifer and microorganisms employed in wastewater treatment systems. And antibiotic resistance has emerged in microorganisms due to excessive use of QACs in household and industrial applications. The occurrence of QACs in the environment is correlated with anthropogenic activities, such as wastewater discharge from WWTPs or single source polluters, and sludge land application. This article also reviews the analytical methods for determination of QACs in environmental compartments including surface water, wastewater, sewage sludge and sediments.

Toxicological evaluation of clay minerals and derived nanocomposites: a review

Clays and clay minerals are widely used in many facets of our society. This review addresses the main clays of each phyllosilicate groups, namely, kaolinite, montmorillonite (Mt) and sepiolite, placing special emphasis on Mt and kaolinite, which are the clays that are more frequently used in food packaging, one of the applications that are currently exhibiting higher development. The improvements in the composite materials obtained from clays and polymeric matrices are remarkable and well known, but the potential toxicological effects of unmodified or modified clay minerals and derived nanocomposites are currently being investigated with increased interest. In this sense, this work focused on a review of the published reports related to the analysis of the toxicological profile of commercial and novel modified clays and derived nanocomposites. An exhaustive review of the main in vitro and in vivo toxicological studies, antimicrobial activity assessments, and the human and environmental impacts of clays and derived nanocomposites was performed. From the analysis of the scientific literature different conclusions can be derived. Thus, in vitro studies suggest that clays in general induce cytotoxicity (with dependence on the clay, concentration, experimental system, etc.) with different underlying mechanisms such as necrosis/apoptosis, oxidative stress or genotoxicity. However, most of in vivo experiments performed in rodents showed no clear evidences of systemic toxicity even at doses of 5000mg/kg. Regarding to humans, pulmonary exposure is the most frequent, and although clays are usually mixed with other minerals, they have been reported to induce pneumoconiosis per se. Oral exposure is also common both intentionally and unintentionally. Although they do not show a high toxicity through this pathway, toxic effects could be induced due to the increased or reduced exposure to mineral elements. Finally, there are few studies about the effects of clay minerals on wildlife, with laboratory trials showing contradictory outcomes. Clay minerals have different applications in the environment, thus with a strict control of the concentrations used, they can provide beneficial uses. Despite the extensive number of reports available, there is also a need of systematic in vitro-in vivo extrapolation studies, with still scarce information on toxicity biomarkers such as inmunomodulatory effects or alteration of the genetic expression. In conclusion, a case by case toxicological evaluation is required taking into account that different clays have their own toxicological profiles, their modification can change this profile, and the potential increase of the human/environmental exposure to clay minerals due to their novel applications.

Processing of abasic site damaged lesions by APE1 enzyme on DNA adsorbed over normal and organomodified clay

The efficiency of the apurinic/apyrimidinic endonuclease (APE1) DNA repair enzyme in the processing of abasic site DNA damage lesions at precise location in DNA oligomer duplexes that are adsorbed on clay surfaces was evaluated. Three different forms of clay namely montmorillonite, quaternary ammonium salt modified montmorillonite and its boiled counterpart i.e. partially devoid of organic moiety were used for a comparative study of adsorption, desorption and DNA repair efficiency on their surfaces. The interaction between the DNA and the clay was analysed by X-ray diffraction, Atomic force microscopy, UV-Vis spectroscopy and Infrared spectroscopy. The abasic site cleavage efficiency of APE1 enzyme was quantitatively evaluated by polyacrylamide gel electrophoresis. Apart from the difference in the DNA adsorption or desorption capacity of the various forms of clay, substantial variation in the repair efficiency of abasic sites initiated by the APE1 enzyme on the clay surfaces was observed. The incision efficiency of APE1 enzyme at abasic sites was found to be greatly diminished, when the DNA was adsorbed over organomodified montmorillonite. The reduced repair activity indicates an important role of the pendant surfactant groups on the clay surfaces in directing APE1 mediated cleavage of abasic site DNA damage lesions.