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Rickard D.,University of Cardiff | Hatton B.,University of Cardiff | Murphy D.M.,University of Cardiff | Butler I.B.,University of Edinburgh | And 3 more authors.
Aquatic Geochemistry | Year: 2011

Plasmid DNA was incubated at 25°C with aqueous solutions of dissolved Fe(II), S(-II), and nanoparticulate FeS with a mackinawite structure, FeS m. At ≥ 0.1 mM total dissolved Fe(II) and S(-II), an increase in the proportion of the relaxed plasmid DNA occurs, through scission of the DNA backbone. In solutions where FeS m was precipitated, nanoparticulate FeS m binds to the DNA molecules. In solutions with concentrations below the FeS m solubility product, nicking of supercoiled pDNA occurs. Plasmid DNA appears to be a sensitive proxy for radical reactions. The reactant is proposed to be a sulfur-based radical produced from the iron-catalyzed decomposition of bisulfide, in a manner analogous to the Fenton reaction. This is further supported by experiments that suggest that sulfide free radicals are produced during the photolysis of aqueous solutions of polysulfides. Supercoiling of DNA affects nearly all DNA-protein transactions so the observation of relaxation of supercoiled forms through reaction with FeS solutions has direct implications to biochemistry. The results of this experimentation suggest that genotoxicity in FeS-rich systems is a further contributory factor to the limited survival of organisms in sulfidic environments. Mutations resulting from the interactions of organisms and mobile elements, such as plasmids, in sediments will also be affected in sulfide-rich environments. © 2011 Springer Science+Business Media B.V. Source

Holwell D.A.,University of Leicester | McDonald I.,University of Cardiff | Butler I.B.,University of Edinburgh | Butler I.B.,A joint research Institute of the Edinburgh Research Partnership in Engineering and Mathematics
Contributions to Mineralogy and Petrology | Year: 2011

Magmatic sulfide deposits are the most significant source of platinum-group elements (PGE) in the world. Key to understanding their genesis is determining the processes and timing of sulfide saturation, metal enrichment and crustal contamination. In this study, we have identified droplets of magmatic sulfide from the Platreef, South Africa, where droplets of sulfide have been trapped in the earliest crystallising phase, chromite. Due to their early entrapment at high temperatures, metal concentrations and ratios that they display are indicative of a very early-stage sulfide liquid in the system, as they will have cooled and fractionated within an essentially closed system, unlike interstitial blebs that crystallise in an open system as the magma cools. Analysis of these droplets in an opaque mineral like chromite by LA-ICP-MS is problematic as some of the fractionated inclusion is necessarily lost during cutting and polishing to initially identify the inclusion. This particularly affects the ability to representatively sample the most fractionated phases such as gold and platinum minerals. Here, using a novel technique whereby the inclusions are homogenized and quickly quenched, so that any cutting, polishing and subsequent LA-ICP-MS analysis samples a truly representative portion of the droplet. This has been used to show that early sulfide liquids in the Platreef were highly PGE-rich and had Pt/Pd ratios of close to unity that supports genetic models invoking sulfide saturation and metal enrichment prior to intrusion, with pre-enriched sulfides entrained within the Platreef magma. © 2010 Springer-Verlag. Source

Yucel M.,University of Delaware | Yucel M.,CNRS Benthic Ecogeochemistry Laboratory | Moore W.S.,University of South Carolina | Butler I.B.,University of Edinburgh | And 3 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2012

The Black Sea is the world's largest anoxic-sulfidic marine basin and has unique sedimentation conditions. Recent studies suggested that mass accumulation rates (MAR) in this environment have increased in the past century when compared to the last 2000 years (Unit 1 period). In this paper we test this hypothesis with new MAR data and further explore the relationship between the depositional pattern and pyrite-sulfur isotopic signature. Based on 15 cores sampled in 2001 and 2003, our dataset comprises radioactive isotopes ( 210Pb, 226Ra, 137Cs) and sulfur stable isotopes (δ 34S VCDT) along with organic, inorganic carbon and pyrite-sulfur. We calculated MARs using 210Pb profiles and/or Chernobyl-derived 137Cs horizon buried in the sediment column. Our turbidite-free deep basin sediment MARs (61 to 76gm -2yr -1) agreed with the previous results (50-100gm -2yr -1) and confirm the view that MARs of the deep Black Sea basin have been increasing. A unique feature of our dataset was the presence of Chernobyl-derived radionuclides below up to 20cm thick turbidite layers (deposited between 1986 and 2003), which enabled us to compute MARs for these coring locations. MARs were 1120±103 and 5230±125gm -2yr -1 for the last two decades in two turbidite-impacted western central basin cores, 20-100 times the long-term rates of the deep basin. This fast depositional pattern was reflected in the geochemical and isotopic data as well. Turbidites had isotopically heavier pyrite-sulfur compared to the Unit 1-type water column formed pyrite. This is probably because the turbidites originated from slope and transported slope pyrite isotopic signature to the deep basin. Diagenetic effects within the turbidite can make pyrite-sulfur even heavier. These tightly linked results demonstrate the importance of turbidites in recent sedimentation of the Black Sea. © 2012 Elsevier Ltd. Source

Guilbaud R.,University of Edinburgh | Guilbaud R.,A joint research Institute of the Edinburgh Research Partnership in Engineering and Mathematics | Butler I.B.,University of Edinburgh | Butler I.B.,A joint research Institute of the Edinburgh Research Partnership in Engineering and Mathematics | And 3 more authors.
Earth and Planetary Science Letters | Year: 2010

We detail the results of an experimental study on the kinetics of Fe isotope exchange between aqueous Fe(II)aq and nanoparticulate mackinawite (FeSm) at 25°C and 2°C over a one month period. The rate of isotopic exchange decreases synchronously with the growth of FeSm nanoparticles. 100% isotopic exchange between bulk FeSm and the solution is never reached and the extent of isotope exchange asymptotes to a maximum of ~75%. We demonstrate that particle growth driven by Ostwald ripening would produce much faster isotopic exchange than observed and would be limited by the extent of dissolution-recrystallisation. We show that Fe isotope exchange kinetics are consistent with i) FeSm nanoparticles that have a core-shell structure, in which Fe isotope mobility is restricted to exchange between the surface shell and the solution and ii) a nanoparticle growth via an aggregation-growth mechanism. We argue that because of the structure of FeSm nanoparticles, the approach to isotopic equilibrium is kinetically restricted at low temperatures. FeSm is a reactive component in diagenetic pyrite forming systems since FeSm dissolves and reacts to form pyrite. Isotopic mobility and potential equilibration between FeSm and Fe(II)aq thus have direct implications for the ultimate Fe isotope signature recorded in sedimentary pyrite. © 2010 Elsevier B.V. Source

Guilbaud R.,University of Edinburgh | Guilbaud R.,A joint research Institute of the Edinburgh Research Partnership in Engineering and Mathematics | Butler I.B.,University of Edinburgh | Butler I.B.,A joint research Institute of the Edinburgh Research Partnership in Engineering and Mathematics | And 4 more authors.
Geochimica et Cosmochimica Acta | Year: 2011

We report the first experimentally-determined metal isotope equilibrium fractionation factors for a metal sulphide at ambient temperatures and pressures. Mackinawite, referred here as FeSm (where the subscript m indicates mackinawite), can be a reactive component in diagenetic pyrite formation and the extent of equilibration between FeSm and dissolved Fe(II) has direct implications the δ56Fe signatures recorded in diagenetic pyrite. The measured equilibrium Fe isotope fractionation between Fe(II)aq and FeSm is Δ56FeFe(II)-FeS=-0.52±0.16‰ at 2°C and Δ56FeFe(II)-FeS=-0.33±0.12‰ at 25°C and pH 4. At the experimental pH the equilibrium fractionation factor between all dissolved Fe(II) species and FeSm (Δ56FeFe(II)-FeS) equates to the fractionation factor between Feaq2+ and FeSm (Δ56FeFe2+-FeS). The measured fractionations are of the same order as other non-redox fractionations measured in low-temperature Fe-C-O systems. We show that at low temperature, the Fe(II)aq-FeSm system is slowly asymptotic to isotopic equilibrium and consequently, FeSm is likely to partially conserve kinetically derived isotopic signatures generated on precipitation. Combined with the range of published kinetic fractionations measured on FeSm precipitation, our data suggest that, subject to the degree of isotope exchange during equilibration, FeSm can display δ56Fe compositions encompassing a range of ~1.4‰. © 2011 Elsevier Ltd. Source

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