Using yeast RNA as a probe for generation of hydroxyl radicals by earth materials

Coal mining pyritic waste in Fenton-like processes: Raw and purified catalysts in Reactive Blue 21 dye discoloration

Raw pyritic waste (RPW) from South Brazilian coal deposits and pure pyritic waste (PPW) were used as catalysts for organic dyes discoloration. Samples were characterized for their chemical, morphological, and structural properties. There was a significant content of Fe and S in both samples from the presence of iron sulfide. The average particle size is 10.9 μm for RPW and 7.4 μm for PPW, demonstrating that the beneficiation process could remove the larger quartz particles, interfered in the distribution, and average particle size. Smaller particle sizes promoted a larger surface area for the PPW. The influence of the pyritic waste in dosage, H₂O₂ concentration, and pH was evaluated, obtaining discoloration values above 95% for 0.5 g/L of pyritic waste, 2 g/L of H₂O_2, and pH 4.3 for both pyritic wastes. The degradation kinetics of the Reactive Blue 21 using the raw pyritic waste obtained a dye concentration removal above 93% in 90 min, with an iron release of 5.4 mg/L into the solution. Using PPW, the dye concentration removal was over 92% in 40 min, with the iron release of 15.5 mg/L into the solution. Discoloration rate for the PPW sample is 7 times greater than the rate obtained for RPW, indicating a faster decay rate for the purified sample. A decrease in discoloration efficiency is observed for PPW after 6 cycles of use, due to the higher concentration of iron leached into the medium. From the results, it was concluded that the raw pyritic waste has excellent potential for use as a catalyst for Fenton reaction, especially for dye-containing water discoloration, thus demonstrating the excellent applicability potential of pyritc waste in the degradation of organic pollutants in wastewater.

Geochemistry and oxidative potential of the respirable fraction of powdered mined Chinese coals

This study evaluates geochemical and oxidative potential (OP) properties of the respirable (finer than 4 μm) fractions of 22 powdered coal samples from channel profiles (CP₄) in Chinese mined coals. The CP₄ fractions extracted from milled samples of 22 different coals were mineralogically and geochemically analysed and the relationships with the OP evaluated. The evaluation between CP₄/CP demonstrated that CP₄ increased concentrations of anatase, Cs, W, Zn and Zr, whereas sulphates, Fe, S, Mo, Mn, Hf and Ge decreased their CP₄ concentrations. OP results from ascorbic acid (AA), glutathione (GSH) and dithiothreitol (DTT) tests evidenced a clear link between specific inorganic components of CP₄ with OP^AA and the organic fraction of OP^GSH and OP^DTT. Correlation analyses were performed for OP indicators and the geochemical patterns of CP₄. These were compared with respirable dust samples from prior studies. They indicate that Fe (r = 0.83), pyrite (r = 0.66) and sulphate minerals (r = 0.42) (tracing acidic species from pyrite oxidation), followed by S (r = 0.50) and ash yield (r = 0.46), and, to a much lesser extent, Ti, anatase, U, Mo, V and Pb, are clearly linked with OP^AA. Moreover, OP^GSH correlation was identified by organic matter, as moisture (r = 0.73), Na (r = 0.56) and B (r = 0.51), and to a lesser extent by the coarse particle size, Ca and carbonate minerals. In addition, Mg (r = 0.70), B (r = 0.47), Na (r = 0.59), Mn, Ba, quartz, particle size and Sr regulate OP^DTT correlations. These became more noticeable when the analysis was done for samples of the same type of coal rank, in this case, bituminous.

Olivine Dissolution in Simulated Lung and Gastric Fluid as an Analog to the Behavior of Lunar Particulate Matter Inside the Human Respiratory and Gastrointestinal Systems

With the Artemis III mission scheduled to land humans on the Moon in 2025, work must be done to understand the hazards lunar dust inhalation would pose to humans. In this study, San Carlos olivine was used as an analog of lunar olivine, a common component of lunar dust. Olivine was dissolved in a flow-through apparatus in both simulated lung fluid and 0.1 M HCl (simulated gastric fluid) over a period of approximately 2 weeks at physiological temperature, 37°C. Effluent samples were collected periodically and analyzed for pH, iron, silicon, and magnesium ion concentrations. The dissolution rate data derived from our measurements allow us to estimate that an inhaled 1.0 μm diameter olivine particle would take approximately 24 years to dissolve in the human lungs and approximately 3 weeks to dissolve in gastric fluid. Results revealed that inhaled olivine particles may generate the toxic chemical, hydroxyl radical, for up to 5-6 days in lung fluid. Olivine dissolved in 0.1 M HCl for 2 weeks transformed to an amorphous silica-rich solid plus the ferric iron oxy-hydroxide ferrihydrite. Olivine dissolved in simulated lung fluid shows no detectable change in composition or crystallinity. Equilibrium thermodynamic models indicate that olivine in the human lungs can precipitate secondary minerals with fibrous crystal structures that have the potential to induce detrimental health effects similar to asbestos exposure. Our work indicates that inhaled lunar dust containing olivine can settle in the human lungs for years and could induce long-term potential health effects like that of silicosis.

Chemical Generation of Hydroxyl Radical for Oxidative 'Footprinting'

BACKGROUND

For almost four decades, hydroxyl radical chemically generated by Fenton chemistry has been a mainstay for the oxidative 'footprinting' of macromolecules.

OBJECTIVE

In this article, we start by reviewing the application of chemical generation of hydroxyl radical to the development of oxidative footprinting of DNA and RNA and the subsequent application of the method to oxidative footprinting of proteins. We next discuss a novel strategy for generating hydroxyl radicals by Fenton chemistry that immobilizes catalytic iron on a solid surface (Pyrite Shrink Wrap laminate) for the application of nucleic acid and protein footprinting.

METHOD

Pyrite Shrink-Wrap Laminate is fabricated by depositing pyrite (Fe-S2, aka 'fool's gold') nanocrystals onto thermolabile plastic (Shrinky Dink). The laminate can be thermoformed into a microtiter plate format into which samples are deposited for oxidation.

RESULTS

We demonstrate the utility of the Pyrite Shrink-Wrap Laminate for the chemical generation of hydroxyl radicals by mapping the surface of the T-cell co-stimulatory protein Programmed Death - 1 (PD-1) and the interface of the complex with its ligand PD-L1.

CONCLUSION

We have developed and validated an affordable and reliable benchtop method of hydroxyl radical generation that will broaden the application of protein oxidative footprinting. Due to the minimal equipment required to implement this method, it should be easily adaptable by many laboratories with access to mass spectrometry.

Measurement of OH* Generation by Pulverized Minerals Using Electron Spin Resonance Spectroscopy and Implications for the Reactivity of Planetary Regolith

Mineral analogs to silicate phases common to planetary regolith, including olivine; the pyroxenes augite and diopside; the plagioclase feldspars labradorite, bytownite, and albite; the Johnson Space Center-1A lunar regolith simulant; as well as quartz (used as a reference), were subjected to mechanical pulverization by laboratory milling for times ranging from 5 to 45 min. Pulverized minerals were then incubated in an aqueous solution containing the free radical spin trapping compound 5,5-Dimethyl-1-Pyrroline-N-Oxide for times ranging from 5 to 30 min. These slurries were then analyzed by Electron Paramagnetic Resonance spectroscopy to quantify the amount of hydroxyl radical (the neutral charge form of the hydroxide ion, denoted as OH*) formed in solution. We find that all tested materials generate an Electron Paramagnetic Resonance spectrum indicating the formation of OH* with concentrations ranging between 0.1 and 1.5 μM. We also find that, in general, mineral pulverization time is inversely correlated to OH* generation, while OH* generation is positively correlated to mineral fluid incubation time for phases that have iron in their nominal chemical formulae, suggesting the possible action of Fenton reaction as a cofactor in increasing the reactivity of these phases. Our results add to a body of literature that indicates that the finely comminuted minerals and rocks present in planetary regolith are capable of generating highly reactive and highly oxidizing radical species in solution. The results provide the foundation for further in vitro and in vivo toxicological studies to evaluate the possible health risks that future explorers visiting the surfaces of planetary bodies may face from these reactive regolith materials.

Oxidation of arsenite to arsenate on birnessite in the presence of light

The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (k_obs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04 h^-1, respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Post-reaction XAS analysis of As(III) exposed birnessite showed that arsenic was present on the surface as As(V). Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process.

The mechanism of melanocytes-specific cytotoxicity induced by phenol compounds having a prooxidant effect, relating to the appearance of leukoderma

Specific phenol compounds including rhododendrol (RD), a skin-brightening ingredient in cosmetics, are reported to induce leukoderma, inducing a social problem, and the elucidation of mechanism of leukoderma is strongly demanded. This study investigated the relationship among the cytotoxicities of six phenol compounds on B16F10 melanoma cells and HaCaT keratinocytes and generated reactive oxygen species (ROS). As a result, the cytotoxicity of RD on B16F10 cells was higher than that on HaCaT cells, and RD significantly increased intracellular ROS and hydrogen peroxide (H2O2) levels in B16F10 cells. Furthermore, although raspberry ketone (RK), RD derivative, also increased intracellular ROS in B16F10 cells, increase in ROS was suppressed by disodium dihydrogen ethylenediaminetetraacetate dehydrate (EDTA). The amounts of increased ROS with RK in HaCaT cells without melanocyte were further increased by tyrosinase. Therefore, tyrosinase, a metalloprotein having copper, was speculated to be one of causative agents allowing phenol compounds to work as a prooxidant. Hydroxyl radical was generated by adding a mixture of tyrosinase and H2O2 to RD, and the amount of the radical was further increased by UVB, indicating that RD cytotoxicity was caused by intracellularly increased ROS, which possibly related to phenol induced prooxidants.

The effect of pyrite on Escherichia coli in water: proof-of-concept for the elimination of waterborne bacteria by reactive minerals

We present proof-of-concept results for the elimination of waterborne bacteria by reactive minerals. We exposed Escherichia coli MG1655 suspended in water to the reactive mineral pyrite (FeS₂) at room temperature and ambient light. This slurry eliminates 99.9% of bacteria in fewer than 4 hours. We also exposed Escherichia coli to pyrite leachate (supernatant liquid from slurry after 24 hours), which eliminates 99.99% of bacteria over the same time-scale. Unlike SOlar water DISinfection (SODIS), our results do not depend on the presence of ultraviolet (UV) light. We confirmed this by testing proposed SODIS additive and known photo-catalyst anatase (TiO₂) for antibacterial properties and found that, in contrast to pyrite, it does not eliminate E. coli under our experimental conditions. Previous investigations of naturally antibiotic minerals have focused on the medical applications of antibiotic clays, and thus have not been conducted under experimental conditions resembling those found in water purification. In our examination of the relevant literature, we have not found previously reported evidence for the use of reactive minerals in water sanitization. The results from this proof-of-concept experiment may have important implications for future directions in household water purification research.

Core-shell upconversion nanoparticle - semiconductor heterostructures for photodynamic therapy

Core-shell nanoparticles (CSNPs) with diverse chemical compositions have been attracting greater attention in recent years. However, it has been a challenge to develop CSNPs with different crystal structures due to the lattice mismatch of the nanocrystals. Here we report a rational design of core-shell heterostructure consisting of NaYF₄:Yb,Tm upconversion nanoparticle (UCN) as the core and ZnO semiconductor as the shell for potential application in photodynamic therapy (PDT). The core-shell architecture (confirmed by TEM and STEM) enables for improving the loading efficiency of photosensitizer (ZnO) as the semiconductor is directly coated on the UCN core. Importantly, UCN acts as a transducer to sensitize ZnO and trigger the generation of cytotoxic reactive oxygen species (ROS) to induce cancer cell death. We also present a firefly luciferase (FLuc) reporter gene based molecular biosensor (ARE-FLuc) to measure the antioxidant signaling response activated in cells during the release of ROS in response to the exposure of CSNPs under 980 nm NIR light. The breast cancer cells (MDA-MB-231 and 4T1) exposed to CSNPs showed significant release of ROS as measured by aminophenyl fluorescein (APF) and ARE-FLuc luciferase assays, and ~45% cancer cell death as measured by MTT assay, when illuminated with 980 nm NIR light.

High-dispersive FeS2 on graphene oxide for effective degradation of 4-chlorophenol

High-dispersive FeS₂ particles on graphene oxide (FeS₂@GO) was prepared by a one-pot hydrothermal method for efficient removal and mineralization of aqueous 4-chlorophenol (4-CP) under slightly acidic or alkaline conditions.

Hydrogen peroxide thermochemical oscillator as driver for primordial RNA replication

This paper presents and tests a previously unrecognized mechanism for driving a replicating molecular system on the prebiotic earth. It is proposed that cell-free RNA replication in the primordial soup may have been driven by self-sustained oscillatory thermochemical reactions. To test this hypothesis, a well-characterized hydrogen peroxide oscillator was chosen as the driver and complementary RNA strands with known association and melting kinetics were used as the substrate. An open flow system model for the self-consistent, coupled evolution of the temperature and concentrations in a simple autocatalytic scheme is solved numerically, and it is shown that thermochemical cycling drives replication of the RNA strands. For the (justifiably realistic) values of parameters chosen for the simulated example system, the mean amount of replicant produced at steady state is 6.56 times the input amount, given a constant supply of substrate species. The spontaneous onset of sustained thermochemical oscillations via slowly drifting parameters is demonstrated, and a scheme is given for prebiotic production of complementary RNA strands on rock surfaces.

Degradation of Acid Orange 7 in aqueous solution by dioxygen activation in a pyrite/H₂O/O₂ system

Increasing attention has been paid to pyrite due to its ability to generate hydroxyl radicals in air-saturated solutions. In this study, the mineral pyrite was studied as a catalyst to activate molecular oxygen to degrade Acid Orange 7 (AO7) in aqueous solution. A complete set of control experiments were conducted to optimize the reaction conditions, including the dosage of pyrite, the AO7 concentration, as well as the initial pH value. The role of reactive oxygen species (ROS) generated by pyrite in the process was elucidated by free radical quenching reactions. Furthermore, the concentrations of Fe(II) and total Fe formed were also measured. The mechanism for the production of ROS in the pyrite/H2O/O2 system was that H2O2 was formed by hydrogen ion and superoxide anion (O2(·-)) which was produced by the reaction of pyrite activating O2 and then reacted with Fe(II) dissolved from pyrite to produce (·)OH through Fenton reaction. The findings suggest that pyrite/H2O/O2 system is potentially practical in pollution treatment. Moreover, the results provide a new insight into the understanding of the mechanism for degradation of organic pollutants by pyrite.

Pyrite-driven reactive oxygen species formation in simulated lung fluid: implications for coal workers' pneumoconiosis

The origin of coal worker's pneumoconiosis (CWP) has been long debated. A recent epidemiological study shows a correlation between what is essentially the concentration of pyrite within coal and the prevalence of CWP in miners. Hydrogen peroxide and hydroxyl radical, both reactive oxygen species (ROS), form as byproducts of pyrite oxidative dissolution in air-saturated water. Motivated by the possible importance of ROS in the pathogenesis of CWP, we conducted an experimental study to evaluate if ROS form as byproducts in the oxidative dissolution of pyrite in simulated lung fluid (SLF) under biologically applicable conditions and to determine the persistence of pyrite in SLF. While the rate of pyrite oxidative dissolution in SLF is suppressed by 51% when compared to that in air-saturated water, the initial amount of hydrogen peroxide formed as a byproduct in SLF is nearly doubled. Hydroxyl radical is also formed in the experiments with SLF, but at lower concentrations than in the experiments with water. The formation of these ROS indicates that the reaction mechanism for pyrite oxidative dissolution in SLF is no different from that in water. The elevated hydrogen peroxide concentration in SLF suggests that the decomposition, via the Fenton mechanism to hydroxyl radical or with Fe(III) to form water and molecular oxygen, is initially inhibited by the presence of SLF components. On the basis of the oxidative dissolution rate of pyrite measured in this paper, it is calculated that a respirable two micron pyrite particle will take over 3 years to dissolve completely.

Quantification of particle-induced inflammatory stress response: a novel approach for toxicity testing of earth materials

BACKGROUND

Reactive oxygen species (ROS) are vital regulators of many cellular functions in the body. The intracellular ROS concentration is highly regulated by a balance between pro-oxidants and anti-oxidants. A chronic excess of pro-oxidants leads to elevated ROS concentrations and inflammation, possibly initiating or enhancing disease onset. Mineral-induced generation of ROS, the role of minerals in upregulating cellular ROS, and their role in the development of several occupational diseases are now widely recognized. However, there is no standard protocol to determine changes in ROS production in cells after exposure to mineral dust or earth materials in general. In this study, a new method for determining the degree of cellular toxicity (i.e., cytotoxicity) of particles is described that will help bridge the gap in knowledge.

RESULTS

By measuring the production of ROS and the viability of cells, an inflammatory stress response (ISR) indicator is defined. This approach normalizes the ROS upregulation with respect to the number of viable cells at the time of measurement. We conducted experiments on a series of minerals and soils that represent materials that are inert (i.e., glass beads, anatase, and a soil with low trace element content), moderately reactive (i.e., soil with high trace element content), and highly reactive (i.e., pyrite). Inert materials generated the lowest ISR, averaging 350% compared to the control. Acid washed pyrite produced the highest ISR (1,100 fold higher than the control). The measurements conducted as a function of time showed a complex response. Most materials showed an increase in ISR with particle loading.

CONCLUSIONS

The amount of cellularly generated ROS and cell viability combined provide a better understanding of particle-induced oxidative stress. The results indicate that some earth materials may solicit an initial burst of ROS, followed by a second phase in which cell viability decreases and ROS production increases, leading to a high ISR value. Hence, measurements conducted over a range of particle loading combined with multiple data measurements up to 24 hours can provide new insights in the possible effect of exposure to earth materials on human health.

Multiple aspects of the interaction of biomacromolecules with inorganic surfaces

The understanding of the mechanisms involved in the interaction of biological systems with inorganic materials is of interest in both fundamental and applied disciplines. The adsorption of proteins modulates the formation of biofilms onto surfaces, a process important in infections associated to medical implants, in dental caries, in environmental technologies. The interaction with biomacromolecules is crucial to determine the beneficial/adverse response of cells to foreign inorganic materials as implants, engineered or accidentally produced inorganic nanoparticles. A detailed knowledge of the surface/biological fluids interface processes is needed for the design of new biocompatible materials. Researchers involved in the different disciplines face up with similar difficulties in describing and predicting phenomena occurring at the interface between solid phases and biological fluids. This review represents an attempt to integrate the knowledge from different research areas by focussing on the search for determinants driving the interaction of inorganic surfaces with biological matter.

Estimation of the postmortem duration of mouse tissue by electron spin resonance spectroscopy

Electron spin resonance (ESR) method is a simple method for detecting various free radicals simultaneously and directly. However, ESR spin trap method is unsuited to analyze weak ESR signals in organs because of water-induced dielectric loss (WIDL). To minimize WIDL occurring in biotissues and to improve detection sensitivity to free radicals in tissues, ESR cuvette was modified and used with 5,5-dimethtyl-1-pyrroline N-oxide (DMPO). The tissue samples were mouse brain, hart, lung, liver, kidney, pancreas, muscle, skin, and whole blood, where various ESR spin adduct signals including DMPO-ascorbyl radical (AsA(∗)), DMPO-superoxide anion radical (OOH), and DMPO-hydrogen radical (H) signal were detected. Postmortem changes in DMPO-AsA(∗) and DMPO-OOH were observed in various tissues of mouse. The signal peak of spin adduct was monitored until the 205th day postmortem. DMPO-AsA(∗) in liver (y = 113.8-40.7 log (day), R1 = -0.779, R2 = 0.6, P < .001) was found to linearly decrease with the logarithm of postmortem duration days. Therefore, DMPO-AsA(∗) signal may be suitable for detecting an oxidation stress tracer from tissue in comparison with other spin adduct signal on ESR spin trap method.

Trichloroethylene transformation in aerobic pyrite suspension: pathways and kinetic modeling

The pathways and kinetics of trichloroethylene (TCE) degradation in aerobic pyrite suspension were investigated. The detection of hydroxyl radical in aqueous pyrite suspension suggested that TCE was degraded by this strong oxidant The reaction pathways of TCE degradation were proposed in which the degradation of TCE to formic acid and finally to CO2 was the main route. Degradation of TCE to oxalic acid and to dichloroacetic acid were found as minor pathways. Degradation rates of TCE to formic acid, glyoxylic acid, and dichloroacetic acid were obtained using kinetic model at 1.2 x 10(-2), 9.8 x 10(-4) and 4.6 x 10(-4) h(-1), respectively.

Trichloroethylene transformation by natural mineral pyrite: the deciding role of oxygen

The transformation of trichloroethylene (TCE) in natural mineral iron disulfide (pyrite) aqueous suspension under different oxygen conditions was investigated in laboratory batch experiments. TCE transformation was pursued by monitoring its disappearance and products released with time. The effect of oxygen was studied by varying the initial dissolved oxygen concentration (DO(i)) inside each reactor. Transformation rates depended strongly on DO(i) in the system. In anaerobic pyrite suspension, TCE did not transform as it did under aerobic conditions. The transformation rate increased with an increase in DO(i). The TCE transformation kinetics was fitted to a pseudo-first-order reaction with a rate constant k (h(-1)) varying from 0.004 to 0.013 for closed systems with DO(i) varying from 0.017 to 0.268 mmol/L under the experimental conditions. In the aerobic systems, TCE transformed to several organic acids including dichloroacetic acid, glyoxylic acid, oxalic acid, formic acid, and finally to CO2 and chloride ion. Dichloroacetic acid was the only chlorinated intermediate found. Both TCE and the pyrite surface were oxidized in the presence of O2. Oxygen consumption profiles showed O2 was the common oxidant in both TCE and pyrite oxidation reactions. Ferric ion cannot be used as an alternative oxidant to oxygen for TCE transformation.

Role of pyrite in formation of hydroxyl radicals in coal: possible implications for human health

BACKGROUND

The harmful effects from inhalation of coal dust are well-documented. The prevalence of lung disease varies by mining region and may, in part, be related to regional differences in the bioavailable iron content of the coal. Pyrite (FeS2), a common inorganic component in coal, has been shown to spontaneously form reactive oxygen species (ROS) (i.e., hydrogen peroxide and hydroxyl radicals) and degrade nucleic acids. This raises the question regarding the potential for similar reactivity from coal that contains pyrite. Experiments were performed to specifically evaluate the role of pyrite in coal dust reactivity. Coal samples containing various amounts of FeS2 were compared for differences in their generation of ROS and degradation of RNA.

RESULTS

Coals that contain iron also show the presence of FeS2, generate ROS and degrade RNA. Coal samples that do not contain pyrite do not produce ROS nor degrade RNA. The concentration of generated ROS and degradation rate of RNA both increase with greater FeS2 content in the coals.

CONCLUSION

The prevalence of coal workers' pneumoconiosis can be correlated to the amount of FeS2 in the coals. Considering the harmful effects of generation of ROS by inhaled particles, the results presented here show a possible mechanism whereby coal samples may contribute to CWP. This suggests that the toxicity of coal may be explained, in part, by the presence of FeS2.

Pyrite-induced hydroxyl radical formation and its effect on nucleic acids

BACKGROUND

Pyrite, the most abundant metal sulphide on Earth, is known to spontaneously form hydrogen peroxide when exposed to water. In this study the hypothesis that pyrite-induced hydrogen peroxide is transformed to hydroxyl radicals is tested.

RESULTS

Using a combination of electron spin resonance (ESR) spin-trapping techniques and scavenging reactions involving nucleic acids, the formation of hydroxyl radicals in pyrite/aqueous suspensions is demonstrated. The addition of EDTA to pyrite slurries inhibits the hydrogen peroxide-to-hydroxyl radical conversion, but does not inhibit the formation of hydrogen peroxide. Given the stability of EDTA chelation with both ferrous and ferric iron, this suggests that the addition of the EDTA prevents the transformation by chelation of dissolved iron species.

CONCLUSION

While the exact mechanism or mechanisms of the hydrogen peroxide-to-hydroxyl radical conversion cannot be resolved on the basis of the experiments reported in this study, it is clear that the pyrite surface promotes the reaction. The formation of hydroxyl radicals is significant because they react nearly instantaneously with most organic molecules. This suggests that the presence of pyrite in natural, engineered, or physiological aqueous systems may induce the transformation of a wide range of organic molecules. This finding has implications for the role pyrite may play in aquatic environments and raises the question whether inhalation of pyrite dust contributes to the development of lung diseases.