SEGH Articles

Modeling global Iodine in Global Atmosphere and its Deposition

08 September 2014
Tomas Sherwen is an Atmospheric Chemistry PhD Student and won the SEGH 2014 student prize for best poster.

 

Iodine is a crucial element for human health. Iodine deficiency in both developing and developed nations is implicated in multiple developmental conditions. The iodine in the food chain originates from the ocean where it is emitted into the atmosphere as either organic (e.g. CH3I, CH2IX) or inorganic (e.g. I2, HOI) compounds. To understand the global environmental distribution of we need to bring together knowledge of the emissions and interactions in the atmosphere that transform and transport iodine and lead to eventual deposition. There are significant uncertainties of atmospheric processing and uptake into the biosphere, but recent and continuing work has providing new insight into the sources iodine and their processing within the global atmosphere. Our work aims to bring together this understanding of atmospheric iodine within a global atmospheric chemistry – transport model, enabling evaluation including spatial understanding that can enable estimation of iodine deposition.

As a PhD student in atmospheric chemistry I am interested in understanding the impacts and interactions of the chemistry of iodine on our atmosphere from its sources in the ocean to its deposition to either the ocean or land surface, and everything in between. The emitted iodine containing compounds are quickly broken down by sunlight to form reaction iodine compounds (I, IO) which undergo further reactions with chemicals compounds in the air. Some of these reactions catalytically destroy ozone, which is key atmospheric oxidant and climate gas, whilst others can impact the concentration of methane (another climate gas). By combining our knowledge of these emissions with our understanding of the atmospheric chemistry and physics that process these species in the atmosphere we can model the resultant transport of iodine and it deposition to the land.

Our iodine simulations are implemented into a community chemical transport model (GEOS-Chem, www.geos-chem.org). This approach splits the world in boxes, vertically and horizontally, integrating the changes due to chemical reaction and physical processes (dry & wet deposition, photolysis, heterogeneous reactions, etc ) over time. The chemical species are then transported between the boxes via metrology derived from observations. Thus we can compare observation of iodine compounds with predictions from our model. We can then answer quantitative questions about the global iodine system, pulling together experimental knowledge together with our theoretical understanding of chemistry and physics. Through simulations, uncertainties and their impacts can be explored, helping to highlight future research directions.

The ability to understand Iodine from oceanic emission through to photochemical transformations and atmospheric deposition, allows for an estimation of depositional iodine fluxes and comparison with previous approaches. To develop this understanding to estimate resultant bioavailable iodine from these depositional fluxes will require further work considering terrestrial and ecological processing.

by Tomas Sherwen, PhD student

Wolfson Atmospheric Chemistry Laboratories (WACL)

Department of Chemistry

University of York

 

Further information can be found:

Saiz-Lopez, A., et al., Atmospheric Chemistry of Iodine. Chemical Reviews, 2012. 112(3): p. 1773-1804.

Carpenter, L.J., et al., Atmospheric iodine levels influenced by sea surface emissions of inorganic iodine. Nature Geosci, 2013. 6(2): p. 108-111. 

Chance, R., et al., The distribution of iodide at the sea surface. Environmental Science: Processes & Impacts, 2014. 16(8): p. 1841-1859.

The International Council for the Control of Iodine Deficiency Disorders (ICCIDD) - www.iccidd.org

GEOS-Chem - www.geos-chem.org

Keep up to date

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Fertilizer usage and cadmium in soils, crops and food 2018-06-23

    Abstract

    Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent \(\hbox {Cd}^{2+}\) , \(\hbox {Mg}^{2+}\) and \(\hbox {F}^-\) ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

  • Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

    Abstract

    Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

  • Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

    Abstract

    Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.