Toxicity assessments of nanoscale zerovalent iron and its oxidation products in medaka (Oryzias latipes) fish

Iron-based nanotechnologies are increasingly used for environmental remediation; however, toxicologic impacts of iron nanoparticles on the aquatic ecosystem remain poorly understood. We treated larvae of medaka fish (Oryzias latipes) with thoroughly characterized solutions containing carboxymethyl cellulose (CMC)-stabilized nanoscale zerovalent iron (nZVI), aged nanoscale iron oxides (nFe-oxides) or ferrous ion (Fe[II]) for 12–14 days’ aqueous exposure to assess the causal toxic effect(s) of iron NPs on the fish. With the CMC-nZVI solution, the dissolved oxygen level decreased, and a burst of reactive oxygen species (ROS) was generated as Fe(II) oxidized to ferric ion (Fe[III]); with the other two iron solutions, these parameters did not significantly change. CMC-nZVI and Fe(II) solutions caused acute lethally and sublethally toxic effects in medaka larvae, with nFe-oxide-containing solutions causing the least toxic effects. We discuss modes of toxic action of iron NPs and chronic toxic effects in terms of hypoxia, Fe(II) toxicity and ROS-mediated oxidative damage.     

Comparative embryotoxicity of phenanthrene and alkyl-phenanthrene to marine medaka (Oryzias melastigma)

Alkylated polycyclic aromatic hydrocarbons (alkyl-PAHs) are the predominant form of PAHs in oil, comprising 85–95% of total PAHs. However, little attention has been paid to these chemicals in ecological risk assessment of marine oil spill. A comparative study of the toxic effects of phenanthrene and retene (7-isopropyl-1-methylphenanthrene, an alkyl-phenanthrene) on the early life stage of marine medaka (Oryzias melastigma) was conducted. Results showed that retene was significantly more toxic than phenanthrene, and marine medaka could be more sensitive to retene than some freshwater fishes. Retene had a higher excretion rate than phenanthrene during the larvae stage. Both of compounds resulted in developmental malformation of marine medaka embryos, with phenanthrene affecting on peripheral vascular system and yolk sac, while retene affecting on cardiac tissues. The toxicity of phenanthrene might be mainly related to its anesthetic effects, and that of retene might be related to the CYP1A-mediated toxicity of its metabolites.     

Acute toxicities of five commonly used antifouling booster biocides to selected subtropical and cosmopolitan marine species

Since 1990s, various booster biocides have been increasingly used as substitutes of organotins. However, knowledge about their toxicities on tropical/sub-tropical marine species is significantly lacking. This study comprehensively investigated the acute toxicities of copper, tributyltin (TBT), and five commonly used booster biocides including Irgarol, diuron, zinc pyrithione (ZnPT), copper pyrithione (CuPT) and chlorothalonil on the growth or survival of 12 marine species in which eight of them are native species of subtropical Hong Kong. We found that Irgarol was more toxic than TBT on the growth of autotrophic species. The toxicity of CuPT was comparable to that of TBT on almost all test species, while it showed higher toxicity than TBT on medaka fish larvae. As the usage of these biocides is expected to further increase worldwide, accurate assessments of their ecological risks are required for better informed decision on their management. This study provided useful datasets for such purposes.     

Variations in the Fe/O value resulting from changes in the ion energy in flows of accelerated solar particles

Qualitative estimates of the relative iron and oxygen ions (Fe/O) in flows of solar cosmic rays from impulsive and long-duration solar flares are obtained for different ion energy ranges. The Fe/O value serves as a measuring unit for the known FIP effect in the solar atmosphere. It is shown that the FIP effect is most evident (maximum Fe/O values) in impulsive events for ions at energies <2 MeV/n. In long-duration events, the Fe/O value gradually decreases in parallel with ion energy and its maximum values are observable in the area of relatively low energies. The comparison of some flare models provided grounds for a qualitative explanation of the Fe/O behavior in response to changes in ion energies for both classes of solar cosmic ray (SCR) events.     

Simulation of the impacts of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe(II)-oxidizing biofilm

The microaerobic iron-oxidizing bacteria in circumneutral environment produce extracellular polymeric substances(EPS)with unique morphologic features,such as stalks or sheaths,which can be regarded as geobiological signatures.The Archean and early Palaeoproterozoic oceans were anoxic with high soluble Fe(II)that were suggested to have been oxidized through the metabolism of Fe(II)-oxidizing bacteria.The precursor of the ultrafine hematite in banded iron formation(BIF),e.g.,ferrihydrite,was suggested to be the mineral record of microbial Fe(II)-oxidation at that time.However,both the biological materials and primary iron minerals were prone to being altered by diagenetic or low-grade metamorphic processes.This makes it difficult to interpret the genesis of Precambrian BIFs.Here,we report experimental simulation on the effects of diagenesis or low-grade metamorphism on neutrophilic microaerobic Fe(II)-oxidizing bacteria and their biomass.Stalks,sheaths,and iron oxide spheroidal aggregates are partially preserved after the 100 MPa/300°C treatments,which indicates the mixed organic matters and iron oxides could survive the diagenetic or low-grade metamorphic processes.Some organic-mineral mixing structures carry information on microbial processes,though they appear similar to pseudomorphs of fossilized bacteria.     

Alteration of gene expression profiles in the brain of Japanese medaka (Oryzias latipes) exposed to KC-400 or PCB126

Polychlorinated biphenyls (PCBs) are known as neurotoxic chemicals and possibly alter animal behavior. We previously reported that PCB-exposure induced abnormal schooling behavior in Japanese medaka (Oryzias latipes). This abnormal behavior might be caused by the functional alteration of central or terminal nervous system. To understand the mechanism(s) of behavioral change by PCB-exposure, we analyzed the gene expression profiles in the brain of medaka exposed to 3,3',4,4',5-pentachlorobiphenyl (PCB126) or a PCB mixture (Kanechlor-400: KC-400) using a cDNA microarray that we constructed. Twelve FLF-II strain medaka (six individuals per treatment) were dietary exposed to PCB126 (0.01 microg/g b.w./day) or KC-400 (1 microg/g b.w./day) for three weeks. For the control, six fish were fed a control diet. After the exposure period, fish were dissected, and the brain samples were collected. The samples from control fish were pooled and used as a common reference in the microarray experiment. Microarray data were normalized by the LOWESS method, and we screened the genes whose expression levels were altered more than 1.5-fold. Gene expression profiling showed 97 down-regulated and 379 up-regulated genes in the brain of medaka exposed to PCB126. KC-400 exposure suppressed 15 genes and induced 266 genes in medaka brain. Among these genes, the expression levels of 7 and 188 genes were commonly down- or up-regulated, respectively in both treatment groups. On the other hand, 31 gene expressions were significantly different between PCB126 and KC-400 treatment groups, and three out of 31 genes were received opposite effects. In addition, the microarray data showed that thyroid hormone-responsive genes were up-regulated by PCB-exposure, which may imply that PCBs or their metabolites mimic thyroid hormone effects in the brain of PCB-exposed medaka.     

Alteration of gene expression profiles in the brain of Japanese medaka (Oryzias latipes) exposed to KC-400 or PCB126

Polychlorinated biphenyls (PCBs) are known as neurotoxic chemicals and possibly alter animal behavior. We previously reported that PCB-exposure induced abnormal schooling behavior in Japanese medaka (Oryzias latipes). This abnormal behavior might be caused by the functional alteration of central or terminal nervous system. To understand the mechanism(s) of behavioral change by PCB-exposure, we analyzed the gene expression profiles in the brain of medaka exposed to 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) or a PCB mixture (Kanechlor-400: KC-400) using a cDNA microarray that we constructed. Twelve FLF-II strain medaka (six individuals per treatment) were dietary exposed to PCB126 (0.01 μg/g b.w./day) or KC-400 (1 μg/g b.w./day) for three weeks. For the control, six fish were fed a control diet. After the exposure period, fish were dissected, and the brain samples were collected. The samples from control fish were pooled and used as a common reference in the microarray experiment. Microarray data were normalized by the LOWESS method, and we screened the genes whose expression levels were altered more than 1.5-fold. Gene expression profiling showed 97 down-regulated and 379 up-regulated genes in the brain of medaka exposed to PCB126. KC-400 exposure suppressed 15 genes and induced 266 genes in medaka brain. Among these genes, the expression levels of 7 and 188 genes were commonly down- or up-regulated, respectively in both treatment groups. On the other hand, 31 gene expressions were significantly different between PCB126 and KC-400 treatment groups, and three out of 31 genes were received opposite effects. In addition, the microarray data showed that thyroid hormone-responsive genes were up-regulated by PCB-exposure, which may imply that PCBs or their metabolites mimic thyroid hormone effects in the brain of PCB-exposed medaka.     

Alteration of gene expression profiles in the brain of Japanese medaka (Oryzias latipes) exposed to KC-400 or PCB126

Polychlorinated biphenyls (PCBs) are known as neurotoxic chemicals and possibly alter animal behavior. We previously reported that PCB-exposure induced abnormal schooling behavior in Japanese medaka (Oryzias latipes). This abnormal behavior might be caused by the functional alteration of central or terminal nervous system. To understand the mechanism(s) of behavioral change by PCB-exposure, we analyzed the gene expression profiles in the brain of medaka exposed to 3,3′,4,4′,5-pentachlorobiphenyl (PCB126) or a PCB mixture (Kanechlor-400: KC-400) using a cDNA microarray that we constructed. Twelve FLF-II strain medaka (six individuals per treatment) were dietary exposed to PCB126 (0.01 μg/g b.w./day) or KC-400 (1 μg/g b.w./day) for three weeks. For the control, six fish were fed a control diet. After the exposure period, fish were dissected, and the brain samples were collected. The samples from control fish were pooled and used as a common reference in the microarray experiment. Microarray data were normalized by the LOWESS method, and we screened the genes whose expression levels were altered more than 1.5-fold. Gene expression profiling showed 97 down-regulated and 379 up-regulated genes in the brain of medaka exposed to PCB126. KC-400 exposure suppressed 15 genes and induced 266 genes in medaka brain. Among these genes, the expression levels of 7 and 188 genes were commonly down- or up-regulated, respectively in both treatment groups. On the other hand, 31 gene expressions were significantly different between PCB126 and KC-400 treatment groups, and three out of 31 genes were received opposite effects. In addition, the microarray data showed that thyroid hormone-responsive genes were up-regulated by PCB-exposure, which may imply that PCBs or their metabolites mimic thyroid hormone effects in the brain of PCB-exposed medaka.     

The role of cytochrome P4501A activity inhibition in three- to five-ringed polycyclic aromatic hydrocarbons embryotoxicity of marine medaka (Oryzias melastigma)

The mode of action of PAHs that causes fish developmental malformations is unclear. The embryotoxicity of marine medaka (Oryzias melastigma) was investigated after individual exposure to three- to five-ring PAHs Phe, Py, and BaP or co-exposure with α-ANF for 18 days. We found that the relationships between EROD induction and developmental deformities of embryos showed a various pattern under different exposure scenarios of Phe, Py, and BaP, which suggested possibly different modes of action in determining the developmental toxicities. As for co-exposure scenarios of each PAH combined with ANF, it showed potentially synergistic effects. The inhibited CYP1A mediated enzyme activity by ANF after co-exposure did not effectively alleviate developmental toxicity of embryo. It showed potentially synergistic effects after co-exposure of marine fish embryos to CYP1A inhibitors and PAH-type CYP1A inducers. Heart deformities in the early life stages of marine medaka were recommended as a biomarker for indicating the extent of PAH pollution.     

Kinetics of redox cycling of iron coupled with fulvic acid

The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10^–4 M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the > Fe^III-OH/Fe(II) wheel coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)₃(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.     

Oxygen in the Earth's core: a first-principles study

First-principles electronic structure calculations based on DFT have been used to study the thermodynamic, structural and transport properties of solid solutions and liquid alloys of iron and oxygen at Earth's core conditions. Aims of the work are to determine the oxygen concentration needed to account for the inferred density in the outer core, to probe the stability of the liquid against phase separation, to interpret the bonding in the liquid, and to find out whether the viscosity differs significantly from that of pure liquid iron at the same conditions. It is shown that the required concentration of oxygen is in the region 25–30 mol%, and evidence is presented for phase stability at these conditions. The Fe/O bonding is partly ionic, but with a strong covalent component. The viscosity is lower than that of pure liquid iron at Earth's core conditions. It is shown that earlier first-principles calculations indicating very large enthalpies of formation of solid solutions may need reinterpretation, since the assumed crystal structures are not the most stable at the oxygen concentration of interest.     

Geochemical equilibria of iron in sediments of the roaring river alluvial fan,Rocky Mountain National Park,Colorado

Iron geochemistry of the sediments and interstitial waters of the Roaring River alluvial fan in the Rocky Mountain National Park, Colorado was studied using a chemical equilibria approach. Large concentrations of colloidal Fe in the filterable Fe of the interstitial waters results in considerable overestimation of Fe² + activity. The overestimation of Fe(II) seriously hampered the usefulness of chemical equilibria approach in the study of Fe geochemistry. Buried soil organic matter and a high water table within the alluvial fan has produced a highly reduced environment which results in elevated colloidal and filterable iron concentrations in the interstitial waters. The source of the iron is probably iron oxides within the buried soil and primary iron-bearing minerals in the sediments. When the iron-rich solutions reach the surface, the water rapidly oxidizes and amorphous ferric hydroxides precipitate. Between 190 to 370 mmol of iron per kg of surficial material were precipitated at the surface within two months. Noticeable decreases in the total amount of C and extractable iron (20 per cent and 30 per cent respectively) in the buried soil were observed during the study period (1985-1987) which implies a significant reduction in iron dissolution and subsequent deposition across the alluvial fan.     

Reconstructing the iron cycle from the horizontal distribution of metals in the sediment of Baldeggersee

In Baldeggersee, the distributions of solid phase Fe, Mn, V, Cr, As and Mo were determined in different sediment strata, deposited under various deep-water oxygen conditions. Iron concentrations are correlated with water depth when an anoxic sediment is in contact with an oxic water column. Benthic redox gradients trigger iron transport towards the deepest site (geochemical focusing) and loss of iron from the shallower parts through the outflow. Fe cycling in the lake is inhibited by oxygen penetration into the sediment. Vanadium and arsenic can be used as tracers for the internal Fe cycle. Their distribution patterns are highly correlated with iron. In case of a stable oxycline in the deep water, Mo is enriched in the sediment and correlates with Mn. The horizontal distribution patterns of Fe, V, As and the correlation of Fe and Mn with trace metals are promising proxy indicators for the reconstruction of deep-water oxygen conditions during deposition.     

The solubility of iron sulphides in synthetic and natural waters at ambient temperature

A critical evaluation of literature values for the solubility products, K _sp ^NBS = [Fe²⁺][HS^–] Fe²⁺ HS^– (H _NBS ⁺ )^–1, of various iron sulphide phases results in consensus values for the pKs of 2.95 ± 0.1 for amorphous ferrous sulphide, 3.6 ± 0.2 for mackinawite, 4.4 ± 0.1 for greigite, 5.1 ± 0.1 for pyrrhotite, 5.25 ± 0.2 for troilite and 16.4 ± 1.2 for pyrite.Where the analogous ion activity products have been measured in anoxic freshwaters in which there is evidence for the presence of solid phase FeS, the values lie within the range of 2.6–3.22, indicating that amorphous iron sulphide is the controlling phase. The single value for a groundwater of 2.65 (2.98 considering carbonate complexation) agrees. In seawater four values range between 3.85 to 4.2, indicating that mackinawite or greigite may be the controlling phase. The single low value of 2.94 is in a situation where particularly high fluxes of Fe (II) and S (–II) may result in the preferential precipitation of amorphous iron sulphide. Formation of framboidal pyrite in these sulphidic environments may occur in micro-niches and does not appear to influence bulk concentrations. Calculations show that the formation of Fe₂S₂ species probably accounts for very little of the iron or sulphide in most natural waters. Previously reported stability constants for the formation of Fe (HS)₂ and (Fe (HS)₃)^– are shown to be suspect, and these species are also thought to be negligible in natural waters. In completely anoxic pore waters polysulphides also have a negligible effect on speciation, but in tidal sediments they may reach appreciable concentrations and lead to the direct formation of pyrite. Concentrations of iron and sulphide in pore waters can be controlled by the more soluble iron sulphide phase. The change in the IAP with depth within the sediment may reflect ageing of the solid phase or a greater flux of Fe (II) and S (–II) nearer the sediment surface. This possible kinetic influence on the value of IAPs has implications for their use in geochemical studies involving phase formation.     

Comparison of the lethal effect of CO2 and acidification on red sea bream (Pagrus major) during the early developmental stages

To compare the acute toxicity of CO(2)- and HCl-acidified seawater, eggs and larvae of a marine fish, Pagrus major, were exposed to seawater equilibrated with CO(2)-enriched gas mixtures (CO(2)=5% or 10%, O(2)=20.95% balanced with N(2)) or seawater acidified with 1 N HCl at two pH levels (pH 6.2 (=5% CO(2)) and 5.9 (=10% CO(2))) for 6 h (eggs) or 24 h (larvae). Mortalities of eggs were 85.8% (CO(2)) and 3.6% (HCl) at pH 6.2, and 97.4% (CO(2)) and 0.9% (HCl) at pH 5.9, while those of larvae were 61.2% (CO(2)) and 1.6% (HCl) at pH 6.2, and 100% (CO(2)) and 5.0% (HCl) at pH 5.9. Thus, previous research on the effects of acidified seawater on marine organisms, as a substitute for CO(2), has largely underestimated the toxic effects of CO(2).     

Biogeochemistry of iron in an acidic lake

In this paper, the fate of iron in Lake Cristallina, an acidic lake in the Alps of Switzerland, is discussed. A simple conceptual model is developed in order to explain the observed diel variation in dissolved iron(II) concentration. Biotite weathering provides reduced iron that is oxidized and subsequently precipitated in the lake. The amorphous Fe(III)hydroxide (FeOOH xH₂O), found in the sediments of Lake Cristallina, is an Fe(II) oxidation product. This oxygenation reaction is most probably catalyzed by bacteria surfaces, as indicated by the relatively high estimated oxidation rate compared to the oxidation rate of the homogeneous oxidation of inorganic Fe(II) species at the ambient pH of Lake Cristallina (pH 5.4 at 4 °C) and by the scanning electron micrograph pictures. Under the influence of light, these amorphous iron(III)hydroxide phases are reductively dissolved. The net concentration of Fe(II) reflects the balance of the reductive dissolution and the oxidation/precipitation reactions and tends to parallel the light intensity, leading to a diurnal variation in the Fe(II) concentration. The rate of the photochemical reductive dissolution of Lake Cristallina iron(III)hydroxides is greatly enhanced in situ and in the laboratory by addition of oxalate to the lake water.     

Quantitative Separation of As(III) and As(V) from a Synthetic Water Solution Using Ion Exchange Columns in the Presence of Fe and Mn Ions

The quantitative separation of As(III) from a water sample containing As(III) and As(V) in the presence of Fe and Mn in an ion exchange resin (AG1 X8) column for the speciation of arsenic is described. Individual and combined effects of Fe and Mn on the separation of As(III) from the solution have been studied separately. In absence of Fe and Mn, the ratio between the As(T) concentration in the eluent and the As(III) concentration in the original sample has been found to be 0.9717 under optimum process conditions. The presence of Fe(II) in the water sample increased the As(T) concentration in the eluent whereas Mn(II) decreased it. Combined effects of Fe and Mn on the percentage increment in the eluent arsenic concentration have been expressed by additive and interactive models. The interactive model has been developed by a statistical software with a 95 % confidence level. In most of the cases the error on the determination of the As(III) concentration had a minimum when using the interactive model.