Iodine's air of importance

Iodine uptake in brown seaweed exposed to radioactive liquid discharges from the reprocessing plant of ORANO La Hague

Iodine-129 is present in controlled liquid radioactive waste routinely released in seawater by the ORANO nuclear fuel reprocessing plant in La Hague (Normandy, France). Brown algae are known for their exceptional ability to concentrate iodine from seawater. They also potentially emit volatile iodine compounds in response to various stresses, such as during emersion at low tide. For these reasons, brown seaweed is routinely collected for radioactivity monitoring in the marine environment (Fucus serratus and Laminaria digitata). Despite the high concentration ratio, the exact mechanism of iodine uptake is still unclear. Chemical imaging by laser desorption/ionization mass spectrometry provided evidence that iodine is stored by kelps as I-. In this study we investigate in vivo iodine uptake in kelps (L. digitata) with an emphasis on seawater iodine chemical speciation. Our results showed that kelp plantlets were able to take up iodine in the forms of both IO3- and I-. We also observed transient net efflux of I- back to seawater but no IO3- efflux. Since the seaweed stores I- but takes up both IO3- and I-, IO3- was likely to be converted into I- at some point in the plantlet. One major outcome of our experiments was the direct observation of the kelp-based biogenic conversion of seawater IO3- into I-. On the basis of both IO3- and I- uptakes by the seaweed, we propose new steps in the possible iodine concentration mechanism used by brown algae.

Reactions of SO2 and NH3 with epoxy groups on the surface of graphite oxide powder

The reactions between the epoxy groups on graphite and graphite oxide surfaces and SO₂ as well as NH₃ were characterized using ToF-SIMS and XPS.

Investigation of the Halogenate-Hydrogen Peroxide Reactions Using the Electron Paramagnetic Resonance Spin Trapping Technique

The differences in the mechanism of the halogenate reactions with the same oxidizing/reducing agent, such as H₂O₂ contribute to the better understanding of versatile halogen chemistry. The reaction between iodate, bromate, and chlorate with hydrogen peroxide in acidic medium at 60 °C is investigated by using the electron paramagnetic resonance (EPR) spin trapping technique. Essential differences in the chemistry of iodate, bromate, and chlorate in their reactions with hydrogen peroxide have been evidenced by finding different radicals as governing intermediates. The reaction between KIO₃ and H₂O₂ is supposed to be the source of IO₂^• radicals. The KBrO₃ and H₂O₂ reaction did not produce any EPR signal, whereas the KClO₃-H₂O₂ system was found to be a source of HO^• radical. Moreover, KClO₃ dissolved in sulfuric acid without hydrogen peroxide produced HO^• radical as well. The minimal-core models explaining the origin of obtained EPR signals are proposed. Current findings suggested the inclusion of IO₂^• and HOO^• radicals, and ClO₂^• and HO^• radicals in the particular kinetic models of iodate-hydrogen peroxide and chlorate-hydrogen peroxide systems, as well as possible exclusion of BrO₂^• radical from the kinetic scheme of the bromate-hydrogen peroxide system. Obtained results may pave the way for understanding more complex, nonlinear reactions of these halogen-containing species.

Radioiodine Biogeochemistry and Prevalence in Groundwater

¹²⁹I is commonly either the top or among the top risk drivers, along with ⁹⁹Tc, at radiological waste disposal sites and contaminated groundwater sites where nuclear material fabrication or reprocessing has occurred. The risk stems largely from ¹²⁹I having a high toxicity, a high bioaccumulation factor (90% of all the body's iodine concentrates in the thyroid), a high inventory at source terms (due to its high fission yield), an extremely long half-life (16M years), and rapid mobility in the subsurface environment. Another important reason that ¹²⁹I is a key risk driver is that there is uncertainty regarding its biogeochemical fate and transport in the environment. We typically can define ¹²⁹I mass balance and flux at sites, but cannot predict accurately its response to changes in the environment. As a consequence of some of these characteristics, ¹²⁹I has a very low drinking water standard, which is set at 1 pCi/L, the lowest of all radionuclides in the Federal Register. Recently, significant advancements have been made in detecting iodine species at ambient groundwater concentrations, defining the nature of the organic matter and iodine bond, and quantifying the role of naturally occurring sediment microbes to promote iodine oxidation and reduction. These recent studies have led to a more mechanistic understanding of radioiodine biogeochemistry. The objective of this review is to describe these advances and to provide a state of the science of radioiodine biogeochemistry relevant to its fate and transport in the terrestrial environment and provide information useful for making decisions regarding the stewardship and remediation of ¹²⁹I contaminated sites. As part of this review, knowledge gaps were identified that would significantly advance the goals of basic and applied research programs for accelerating ¹²⁹I environmental remediation and reducing uncertainty associated with disposal of ¹²⁹I waste. Together the information gained from addressing these knowledge gaps will not alter the observation that ¹²⁹I is primarily mobile, but it will likely permit demonstration that the entire ¹²⁹I pool in the source term is not moving at the same rate and some may be tightly bound to the sediment, thereby smearing the modeled ¹²⁹I peak and reducing maximum calculated risk.

Molecular iodine (I2) emission from two Laminaria species (Phaeophyceae) and impact of irradiance and temperature on I2 emission into air and iodide release into seawater from Laminaria digitata

Kelps of the genus Laminaria accumulate iodine at high concentrations, but the iodine retaining capacity can be affected by emersion and physiological stress. In this study, I2 emission into the atmosphere from Laminaria digitata and Laminaria hyperborea was compared under controlled low irradiances and temperatures. The two species exhibited different I2 emission rates as blades of L. digitata emitted I2 at rates five times higher than those from newly-grown blades (current growth season) of L. hyperborea. I2 emission was not detectable from old blades (previous growth season) of L. hyperborea. Additionally, effects of irradiance and temperature on both I2 emission into air and net I(-) release into seawater where assessed for L. digitata while monitoring photo-physiological parameters as stress indicators. Irradiances between 30 and 120 μmol photons m(-2) s(-1) had only marginal effects on both I2 emission and I(-) release rates, but physiological stress, indicated by photoinhibition, was observed. The results suggest that the irradiances applied here were not stressful enough to impact on the iodine release. By contrast, at elevated temperatures (20 °C), photoinhibition was accompanied by an increase in I2 emission rates, but net I(-) release rates remained similar at 10-20 °C. High I2 emission rates into air and I(-) release into seawater observed from L. digitata underpin the fundamental function of this kelp as mediator of coastal iodine fluxes.

A review on 129I analysis in air

A review of literature focused on (129)I determination in air is provided. (129)I analysis in the environment represents a vital tool for tracing transport mechanisms, distribution pathways, safety assessment and its application as environmental tracer. To achieve that, specific chemical extraction methods and high sensitivity analytical techniques have been developed. This paper is intended to give an overview about the sample collection, extraction and distribution of (129)I in the air. Sensitivity of available measurement techniques for the determination of (129)I is compared. The article also provides the summary of current worldwide distribution of (129)I in air and respective radiation exposure of man.

Molecular iodine emission rates and photosynthetic performance of different thallus parts of Laminaria digitata (Phaeophyceae) during emersion

The emission of molecular iodine (I(2)) from the stipe, the meristematic area and the distal blade of the brown macroalga Laminaria digitata (Hudson) Lamouroux (Phaeophyceae) was monitored under low light and dark conditions. Photosynthetic parameters were determined to investigate both the extent of stress experienced by different thallus parts and the effects of emersion on photosynthesis. Immediately after air exposure, intense I(2) emission was detectable from all thallus parts. I(2) emission declined continuously over a period of 180 min following the initial burst, but was not affected by the light regime. The total number of mole of I(2) emitted by stipes was approximately 10 times higher than those emitted from other thallus parts. Initial I(2) emission rates (measured within 30 min of exposure to air) were highest for stipes (median values: 2,999 and 5,222 pmol g(-1) dw min(-1) in low light and dark, respectively) and lower, by one order of magnitude, for meristematic regions and distal blades. After exposure to air for between 60 and 180 min, I(2) emission rates of all thallus parts were reduced by 70-80%. Air exposure resulted in a decrease of the maximum photosystem II (PSII) efficiency (F(v)/F(m)) by 3%, and in a 25-55% increase of the effective PSII quantum efficiency (F(v)/F'(m)); this was caused by a higher fraction of open reaction centres (q(P)), whereas the efficiency of the latter in capturing energy (F'(v)/F'(m)) remained constant. The results indicate the presence of an iodine pool which is easily volatilised and depleted due to air exposure, even under apparently low stress conditions.

Airborne bacterial spore counts by terbium-enhanced luminescence detection: pitfalls and real values

Bacterial spore determination by terbium(III)-dipicolinate luminescence has been reported by several investigators. We collected spore samples with a cyclone and extracted dipicolinic acid (DPA) in-line with hot aqueous dodecylamine, added Tb(III) in a continuous-flow system and detected the Tb(III)-DPA with a gated liquid core waveguide fluorescence detector with a flashlamp excitation source. The absolute limit of detection (LOD) for the system was equivalent to 540 B. subtilis spores (for a 1.8 m3 sample volume (t = 2 h, Q = 15 L/min), concentration LOD is 0.3 spores/L air). Extant literature suggests that, from office to home settings, viable spore concentrations range from 0.1 to 10 spores/L; however, these data have never been validated. Previously reported semiautomated instrumentation had an LOD of 50 spores/L. The present system was tested at five different location settings in Lubbock, Texas. The apparent bacterial spore concentrations ranged from 9 to 700 spores/L and only occasionally exhibited the same trend as the simultaneously monitored total optical particle counts in the > or = 0.5 microm size fraction. However, because the apparent spore counts sometimes were very large relative to the 0.5+ microm size particle counts, we investigated potential positive interferences. We show that aromatic acids are very likely large interferents. This interference typically constitutes approximately 70% of the signal and can be as high as 95%. It can be completely removed by prewashing the particles.

Iodine transfers in the coastal marine environment: the key role of brown algae and of their vanadium-dependent haloperoxidases

Brown algal kelp species are the most efficient iodine accumulators among all living systems, with an average content of 1.0% of dry weight in Laminaria digitata, representing a ca. 30,000-fold accumulation of this element from seawater. Like other marine macroalgae, kelps are known to emit volatile short-lived organo-iodines, and molecular iodine which are believed to be a main vector of the iodine biogeochemical cycle as well as having a significant impact on atmospheric chemistry. Therefore, radioactive iodine can potentially accumulate in seaweeds and can participate in the biogeochemical cycling of iodine, thereby impacting human health. From a radioecological viewpoint, iodine-129 (129I, half-life of 1.6 x 10(7) years) is one of the most persistent radionuclide released from nuclear facilities into the environment. In this context, the speciation of iodine by seaweeds is of special importance and there is a need to further understand the mechanisms of iodine uptake and emission by kelps. Recent results on the physiological role and biochemistry of the vanadium haloperoxidases of brown algae emphasize the importance of these enzymes in the control of these processes.

Computational Studies of (HIO3) Isomers and the HO2 + IO Reaction Pathways

The geometries, harmonic vibrational frequencies, relative energetics, and enthalpies of formation of (HIO3) isomers have been examined using quantum mechanical methods. At all levels of theory employed, MP2, B3LYP, and CCSD(T), the lowest energy structure is found to be the HOIO2 form, which shows particular stability. The two isomers HOOOI and HOOIO are closely located at the CCSD(T) level of theory. The higher energy structure is HIO3. The interisomerization transition states have been determined, along with the transition states involved in the various pathways of the reaction HO2 + IO.

Rapid Formation of Sulfuric Acid Particles at Near-Atmospheric Conditions

We investigated the formation of new particles in a laboratory study, starting from H2SO4 produced in situ through the reaction of OH radicals with SO2. Newly formed particles were observed for H2SO4 concentrations above 7 x 10(6) per cubic centimeter. At 293 kelvin, a rough estimate yielded a nucleation rate of 0.3 to 0.4 particles per cubic centimeter per second for approximately 10(7) particles per cubic centimeter of H2SO4 (particle size >/= 3 nanometers). These findings are in agreement with observations from the atmosphere. The results demonstrate that under laboratory conditions similar to the atmosphere, particle formation occurs at atmospheric H2SO4 concentration levels.

Computational investigation of isomeric and conformeric structures of methyl iodoperoxide

Quantum mechanical electronic structure methods are employed to investigate the isomeric and conformeric stuctures of methyl iodoperoxide. Optimized geometries and harmonic vibrational frequencies are calculated at the MP2 level of theory using two types of basis sets, the 6-311G(d,p) for all atoms and the 6-311G(d,p) combined with the LANL2DZ relativistic ECP procedure for iodine. Refinement of the energetics has been accomplished by performing single-point CCSD(T) calculations. Five isomers were determined in total among which iodomethyl hydroperoxide (ICH2OOH) is found to be the lowest energy structure. Conformational barriers and transition states that connect the isomeric forms have been characterized.Key words: methyl iodoperoxide, isomers, conformers.

Atmospheric new particle formation enhanced by organic acids

Atmospheric aerosols often contain a substantial fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly affect human health and global climate.