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.

Organic Matter from Redoximorphic Soils Accelerates and Sustains Microbial Fe(III) Reduction.

Microbial reduction of Fe(III) minerals is a prominent process in redoximorphic soils and is strongly affected by organic matter (OM). We herein determined the rate and extent of microbial reduction of ferrihydrite (Fh) with either adsorbed or coprecipitated OM by Geobacter sulfurreducens. We focused on OM-mediated effects on electron uptake and alterations in Fh crystallinity. The OM was obtained from anoxic soil columns (effluent OM, efOM) and included-unlike water-extractable OM-compounds released by microbial activity under anoxic conditions. We found that organic molecules in efOM had generally no or only very low electron-accepting capacity and were incorporated into the Fh aggregates when coprecipitated with Fh. Compared to OM-free Fh, adsorption of efOM to Fh decelerated the microbial Fe(III) reduction by passivating the Fh surface toward electron uptake. In contrast, coprecipitation of Fh with efOM accelerated the microbial reduction, likely because efOM disrupted the Fh structure, as noted by Mössbauer spectroscopy. Additionally, the adsorbed and coprecipitated efOM resulted in a more sustained Fe(III) reduction, potentially because efOM could have effectively scavenged biogenic Fe(II) and prevented the passivation of the Fh surface by the adsorbed Fe(II). Fe(III)-OM coprecipitates forming at anoxic-oxic interfaces are thus likely readily reducible by Fe(III)-reducing bacteria in redoximorphic soils.

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.

Pharmacological Characterization of a Novel 5-Hydroxybenzothiazolone-Derived ß 2-Adrenoceptor Agonist with Functional Selectivity for Anabolic Effects on Skeletal Muscle Resulting in a Wider Cardiovascular Safety Window in Preclinical Studies.

The anabolic effects of ß 2-adrenoceptor (ß 2-AR) agonists on skeletal muscle have been demonstrated in various species. However, the clinical use of ß 2-AR agonists for skeletal muscle wasting conditions has been limited by their undesired cardiovascular effects. Here, we describe the preclinical pharmacological profile of a novel 5-hydroxybenzothiazolone (5-HOB) derived ß 2-AR agonist in comparison with formoterol as a representative ß 2-AR agonist that have been well characterized. In vitro, 5-HOB has nanomolar affinity for the human ß 2-AR and selectivity over the ß 1-AR and ß 3-AR. 5-HOB also shows potent agonistic activity at the ß 2-AR in primary skeletal muscle myotubes and induces hypertrophy of skeletal muscle myotubes. Compared with formoterol, 5-HOB demonstrates comparable full-agonist activity on cAMP production in skeletal muscle cells and skeletal muscle tissue-derived membranes. In contrast, a greatly reduced intrinsic activity was determined in cardiomyocytes and cell membranes prepared from the rat heart. In addition, 5-HOB shows weak effects on chronotropy, inotropy, and vascular relaxation compared with formoterol. In vivo, 5-HOB significantly increases hind limb muscle weight in rats with attenuated effects on heart weight and ejection fraction, unlike formoterol. Furthermore, changes in cardiovascular parameters after bolus subcutaneous treatment in rats and rhesus monkeys are significantly lower with 5-HOB compared with formoterol. In conclusion, the pharmacological profile of 5-HOB indicates superior tissue selectivity compared with the conventional ß 2-AR agonist formoterol in preclinical studies and supports the notion that such tissue-selective agonists should be investigated for the safe treatment of muscle-wasting conditions without cardiovascular limiting effects.

Biological effects of four iron-containing nanoremediation materials on the green alga Chlamydomonas sp.

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - 'pure' FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L-1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L-1), though such concentrations would rapidly decrease to mg or µg L-1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration.

Long-distance electron transfer by cable bacteria in aquifer sediments.

The biodegradation of organic pollutants in aquifers is often restricted to the fringes of contaminant plumes where steep countergradients of electron donors and acceptors are separated by limited dispersive mixing. However, long-distance electron transfer (LDET) by filamentous 'cable bacteria' has recently been discovered in marine sediments to couple spatially separated redox half reactions over centimeter scales. Here we provide primary evidence that such sulfur-oxidizing cable bacteria can also be found at oxic-anoxic interfaces in aquifer sediments, where they provide a means for the direct recycling of sulfate by electron transfer over 1-2-cm distance. Sediments were taken from a hydrocarbon-contaminated aquifer, amended with iron sulfide and saturated with water, leaving the sediment surface exposed to air. Steep geochemical gradients developed in the upper 3 cm, showing a spatial separation of oxygen and sulfide by 9 mm together with a pH profile characteristic for sulfur oxidation by LDET. Bacterial filaments, which were highly abundant in the suboxic zone, were identified by sequencing of 16S rRNA genes and fluorescence in situ hybridization (FISH) as cable bacteria belonging to the Desulfobulbaceae. The detection of similar Desulfobulbaceae at the oxic-anoxic interface of fresh sediment cores taken at a contaminated aquifer suggests that LDET may indeed be active at the capillary fringe in situ.

Size- and composition-dependent toxicity of synthetic and soil-derived Fe oxide colloids for the nematode Caenorhabditis elegans.

Colloidal iron oxides (FeOx) are increasingly released to the environment due to their use in environmental remediation and biomedical applications, potentially harming living organisms. Size and composition could affect the bioavailability and toxicity of such colloids. Therefore, we investigated the toxicity of selected FeOx with variable aggregate size and variably composed FeOx-associated organic matter (OM) toward the nematode Caenorhabditis elegans. Ferrihydrite colloids containing citrate were taken up by C. elegans with the food and accumulated inside their body. The toxicity of ferrihydrite, goethite, and akaganeite was dependent on aggregate size and specific surface area, with EC50 values for reproduction ranging from 4 to 29 mg Fe L(-1). Experiments with mutant strains lacking mitochondrial superoxide dismutase (sod-2) showed oxidative stress for two FeOx and Fe(3+)-ions, however, revealed that it was not the predominant mechanism of toxicity. The OM composition determined the toxicity of mixed OM-FeOx phases on C. elegans. FeOx associated with humic acids or citrate were less toxic than OM-free FeOx. In contrast, soil-derived ferrihydrite, containing proteins and polysaccharides from mobile OM, was even more toxic than OM-free Fh of similar aggregate size. Consequently, the careful choice of the type of FeOx and the type of associated OM may help in reducing the ecological risks if actively applied to the subsurface.

Metabolic efficiency of Geobacter sulfurreducens growing on anodes with different redox potentials.

Microorganisms respiring Fe(III) in the environment face a range of redox potentials of the prospective terminal ferric electron acceptors, because Fe(III) can be present in different minerals or organic complexes. We investigated the adaptation of Geobacter sulfurreducens to this range by exposing the bacteria to different redox potentials between the electron donor acetate and solid, extracellular anodes in a microbial fuel-cell set-up. Over a range of anode potentials from -0.105 to +0.645 V versus standard hydrogen electrode, G. sulfurreducens produced identical amounts of biomass per electron respired. This indicated that the organism cannot utilize higher available energies for energy conservation to ATP, and confirmed recent studies. Either the high potentials cannot be used due to physiological limitations, or G. sulfurreducens decreased its metabolic efficiency, and less biomass per unit of energy was produced. In this case, G. sulfurreducens "wasted" energy at high-potential differences, most likely as heat to fuel growth kinetics.

Iron oxide nanoparticles in geomicrobiology: from biogeochemistry to bioremediation.

Iron oxides are important constituents of soils and sediments and microbial iron reduction is considered to be a significant anaerobic respiration process in the subsurface, however low microbial reduction rates of macroparticulate Fe oxides in laboratory studies led to an underestimation of the role of Fe oxides in the global Fe redox cycle. Recent studies show the high potential of nano-sized Fe oxides in the environment as, for example, electron acceptor for microbial respiration, electron shuttle between different microorganisms, and scavenger for heavy metals. Biotic and abiotic reactivity of iron macroparticles differ significantly from nano-sized Fe oxides, which are usually much more reactive. Factors such as particle size, solubility, ferrous iron, crystal structure, and organic molecules were identified to influence the reactivity. This review discusses factors influencing the microbial reactivity of Fe oxides. It highlights the differences between natural and synthetic Fe oxides especially regarding the presence of organic molecules such as humic acids and natural organic matter. Attention is given to the transport behavior of Fe oxides in laboratory systems and in the environment, because of the high affinity of different contaminants to Fe oxide surfaces and associated co-transport of pollutants. The high reactivity of Fe oxides and their potential as adsorbents for different pollutants are discussed with respect to application and development of remediation technologies.

Rates and potential mechanism of anaerobic nitrate-dependent microbial pyrite oxidation.

Pyrite (FeS2) is a major iron- and sulfur-containing mineral phase in the environment. Oxidation of pyrite by aerobic micro-organisms has been well investigated. However, the reactivity of pyrite under anoxic conditions is still an open question. In the present paper, we summarize field and laboratory data on this chemolithotrophic respiration process with nitrate as terminal electron acceptor. Geochemical and stable isotope field data indicate that this process is occurring. Laboratory studies are more ambiguous, but recent positive results provide evidence that anaerobic microbial pyrite oxidation can, in fact, occur with nitrate as electron acceptor.

Reevaluation of colorimetric iron determination methods commonly used in geomicrobiology.

The ferrozine and phenanthroline colorimetric assays are commonly applied for the determination of ferrous and total iron concentrations in geomicrobiological studies. However, accuracy of both methods depends on slight changes in their protocols, on the investigated iron species, and on geochemical variations in sample conditions. Therefore, we tested the performance of both methods using Fe(II)((aq)), Fe(III)((aq)), mixed valence solutions, synthetic goethite, ferrihydrite, and pyrite, as well as microbially-formed magnetite and a mixture of goethite and magnetite. The results were compared to concentrations determined with aqua regia dissolution and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Iron dissolution prior to the photometric assays included dissolution in 1M or 6M HCl, at 21 or 60°C, and oxic or anoxic conditions. Results indicated a good reproducibility of quantitative total iron determinations by the ferrozine and phenanthroline assays for easily soluble iron forms such as Fe(II)((aq)), Fe(III)((aq)), mixed valence solutions, and ferrihydrite. The ferrozine test underestimated total iron contents of some of these samples after dissolution in 1M HCl by 10 to 13%, whereas phenanthroline matched the results determined by ICP-AES with a deviation of 5%. Total iron concentrations after dissolution in 1M HCl of highly crystalline oxides such as magnetite, a mixture of goethite and magnetite, and goethite were underestimated by up to 95% with both methods. When dissolving these minerals in 6M HCl at 60°C, the ferrozine method was more reliable for total iron content with an accuracy of ±5%, related to values determined with ICP-AES. Phenanthroline was more reliable for the determination of total pyritic iron as well as ferrous iron after incubation in 1M HCl at 21°C in the Fe(II)((aq)) sample with a recovery of 98%. Low ferrous iron concentrations of less than 0.5mM were overestimated in a Fe(III) background by up to 150% by both methods. Heating of mineral samples in 6M HCl increased their solubility and susceptibility for both photometric assays which is a need for total iron determination of highly crystalline minerals. However, heating also rendered a subsequent reliable determination of ferrous iron impossible due to fast abiotic oxidation. Due to the low solubility of highly crystalline samples, the determination of total iron is solely possible after dissolution in 6M HCl at 60°C which on the other hand makes determination of ferrous iron impossible. The recommended procedure for ferrous iron determination is therefore incubation at 21°C in 6M HCl, centrifugation, and subsequent measurement of ferrous iron in the supernatant. The different procedures were tested during growth of G. sulfurreducens on synthetic ferrihydrite. Here, the phenanthroline test was more accurate compared to the ferrozine test. However, the latter provided easy handling and seemed preferable for larger amounts of samples.

Transport of ferrihydrite nanoparticles in saturated porous media: role of ionic strength and flow rate.

The use of nanoscale ferrihydrite particles, which are known to effectively enhance microbial degradation of a wide range of contaminants, represents a promising technology for in situ remediation of contaminated aquifers. Thanks to their small size, ferrihydrite nanoparticles can be dispersed in water and directly injected into the subsurface to create reactive zones where contaminant biodegradation is promoted. Field applications would require a detailed knowledge of ferrihydrite transport mechanisms in the subsurface, but such studies are lacking in the literature. The present study is intended to fill this gap, focusing in particular on the influence of flow rate and ionic strength on particle mobility. Column tests were performed under constant or transient ionic strength, including injection of ferrihydrite colloidal dispersions, followed by flushing with particle-free electrolyte solutions. Particle mobility was greatly affected by the salt concentration, and particle retention was almost irreversible under typical salt content in groundwater. Experimental results indicate that, for usual ionic strength in European aquifers (2 to 5 mM), under natural flow condition ferrihydrite nanoparticles are likely to be transported for 5 to 30 m. For higher ionic strength, corresponding to contaminated aquifers, (e.g., 10 mM) the travel distance decreases to few meters. A simple relationship is proposed for the estimation of travel distance with changing flow rate and ionic strength. For future applications to aquifer remediation, ionic strength and injection rate can be used as tuning parameters to control ferrihydrite mobility in the subsurface and therefore the radius of influence during field injections.

Use of metal-reducing bacteria for bioremediation of soil contaminated with mixed organic and inorganic pollutants.

Mixed contamination by organic and inorganic compounds in soil is a serious problem for remediation. Most laboratory studies and field-scale trials focused on individual contaminant in the past. For concurrent bioremediation by biodegradation and bioleaching processes, we tested metal-reducing microorganism, Geobacter metallireducens. In order to prove the feasibility of the coupled process, multiple-contaminated soil was prepared. Mineralogical analyses have shown the existence of labile forms of As(V) as amorphous and/or weakly sorbed phases in the secondary Fe oxides. In the biotic experiment using G. metallireducens, biodegradation of toluene and bioleaching of As by bacteria were observed simultaneously. Bacteria accelerated the degradation rate of toluene with reductive dissolution of Fe and co-dissolution of As. Although there have been many studies showing each individual process, we have shown here that the idea of concurrent microbial reaction is feasible. However, for the practical use as a remediation technology, more details and multilateral evaluations are required in future studies.

Anaerobic, nitrate-dependent oxidation of pyrite nanoparticles by Thiobacillus denitrificans.

Pyrite is a key mineral in the global biogeochemical cycles of sulfur and iron, yet its anaerobic microbial oxidation has eluded geochemists and microbiologists for decades. Recent reports indicated that anaerobic oxidation of pyrite is occurring, but the mechanism remains unclear. Here, we provide evidence for the capability of Thiobacillus denitrificans to anaerobically oxidize a putatively nanosized pyrite particle fraction with nitrate as electron acceptor. Nanosized pyrite was readily oxidized to ferric iron and sulfate with a rate of 10.1 µM h(-1). The mass balance of pyrite oxidation and nitrate reduction revealed a closed recovery of the electrons. This substantiates a further "missing lithotrophy" in the global cycles of sulfur and iron and emphasizes the high reactivity of nanominerals in the environment.

Nanosized iron oxide colloids strongly enhance microbial iron reduction.

Microbial iron reduction is considered to be a significant subsurface process. The rate-limiting bioavailability of the insoluble iron oxyhydroxides, however, is a topic for debate. Surface area and mineral structure are recognized as crucial parameters for microbial reduction rates of bulk, macroaggregate iron minerals. However, a significant fraction of iron oxide minerals in the subsurface is supposed to be present as nanosized colloids. We therefore studied the role of colloidal iron oxides in microbial iron reduction. In batch growth experiments with Geobacter sulfurreducens, colloids of ferrihydrite (hydrodynamic diameter, 336 nm), hematite (123 nm), goethite (157 nm), and akaganeite (64 nm) were added as electron acceptors. The colloidal iron oxides were reduced up to 2 orders of magnitude more rapidly (up to 1,255 pmol h(-1) cell(-1)) than bulk macroaggregates of the same iron phases (6 to 70 pmol h(-1) cell(-1)). The increased reactivity was not only due to the large surface areas of the colloidal aggregates but also was due to a higher reactivity per unit surface. We hypothesize that this can be attributed to the high bioavailability of the nanosized aggregates and their colloidal suspension. Furthermore, a strong enhancement of reduction rates of bulk ferrihydrite was observed when nanosized ferrihydrite aggregates were added.