Zhang, Luyuan

Jod er et essentielt grundstof for alle pattedyr. Derfor er det vigtigt at undersøge, hvorledes jod opfører sig og transporteres i miljøet. 129I, en langlivet radioisotop af jod (1.57107 år), udledes hovedsageligt til miljøet fra nukleare oparbejdningsanlæg (især Sellafield i Storbritannien og La Hague i Frankrig), som udgør unikke punktkilder med udslip til havet, som er velegnede til sporstofundersøgelser af jod i miljøet. Undersøgelser af kemiske former (speciering) af 129I benyttes ikke kun for at studere jods geokemiske kredsløb, men også for at undersøge processer i miljøet. Denne afhandling præsenterer metoder udviklet til kemisk analyse af speciering af 129I i miljøprøver og biologiske prøver (dvs. havvand, aerosoler, og tang), såvel som anvendelser til at undersøge processer i miljøet og det geokemiske kredsløb for stabilt 127I i havet, atmosfæren og tang. Baseret på tidligere erfaring blev en metode med nedbrydning med persulfat oxidation udviklet yderligere for at konvertere organisk jod til uorganiske former i naturlige vandprøver. Denne ny metode har vist sig at være effektiv og pålidelig til nedbrydning af organisk jod, og har været anvendt med succes til at bestemme 129I i naturlige vandområder og perkolat indeholdende organisk jod. En metode er udviklet til analyse af speciering af 129I og 127I i aerosoler indsamlet på luftfiltre af polypropylen. Sekventiel ekstraktion med vand og NaOH-opløsning blev brugt til at udvinde vandopløseligt jod (WSI) og NaOH opløselig jod (NSI), og alkalisk foraskning blev brugt til rester af uopløseligt aerosol jod (RII). WSI blev yderligere adskilt i iodid og iodat ved hjælp af anionbytningskromatografi. Parametre, såsom mængden af udvaskningsmidler, udvaskningstid, foraskningstid og temperatur, og tilsætning af jodbevarende reagenser, der kan påvirke stabiliteten af jodformer og kemisk udbytte af jodformer under kemisk separation, blev undersøgt med henblik på at opnå nøjagtige resultater af 129I-former i aerosoler. Analyseresultaterne af de samlede og forskellige kemiske former for 129I i aerosolprøver viser, at den udviklede metode er pålidelig til præcis angivelse af 129I og 127I i aerosoler. Fordeling af kemiske former (iodid og iodat) af 129I og 127I i prøver af havvand fra det centrale Arktis, Grønlands kyster, danske kyster og kysten ved Fukushima i Japan blev undersøgt. For både 129I og 127I er iodat den fremherskende form i havvand i det centrale Arktis og ved Grønlands kyster, mens iodid er den fremherskende form for 129I og 127I i danske kystfarvande. Et særligt fordelingsmønster af iod-former blev observeret i prøver af havvand fra kysten ved Fukushima, hvor I-/IO3 - atomforholdet for 127I var i intervallet 0.07-0.27, hvilket afspejler dominerende mængder af iodat i havvand, mens forholdene for 129I angiver, at iodid er den dominerende form . Disse resultater viser, at sammensætningen af jod-former afhænger af kilden til jod (nukleare oparbejdningsanlæg og nukleare ulykker), transportveje (langs kysten og i åbent område på havet) og biogeokemiske processer. Den bemærkelsesværdig store mængde 129I i det Arktiske Ocean i 2011 medfører, at Arktis virker som en sekundær kilde af 129I med udstrømning til sydligere have, såsom Grønlandshavet og det vestlige Atlanterhav, samt til atmosfæren og det arktiske økosystem. Aerosolprøver indsamlet to steder (Risø, Danmark, nær kysten, og Tsukuba Japan, 170 km sydvest for Fukushima Dai-ichi atomkraftværket) i løbet af foråret 2011 (kort efter Fukushima atomulykken) og vinteren 2014 blev analyseret for jodformer af 129I og 127I herunder opløselige og uopløselige former. Resultaterne viser, at koncentrationer og kemiske former af 129I og 127I i aerosoler er stærkt relateret til kilder og transportveje for luftmasser, og at 129I fra Fukushima bidrog med under 6% af den samlede mængde 129I i atmosfæren over Nordeuropa under ulykken. Kemiske former af 129I og 127I i tang (Fucus serratus og vesiculosus) indsamlet i danske kystområder i 2014 blev bestemt, herunder vandopløselig jod (iodid, iodat og opløselig organisk jod) og vanduopløselig jod. Mulige mekanismer for optag af jod i tang i naturlige marine systemer blev undersøgt ved at kombinere data for kemiske former af jod i prøver af vand og tang indsamlet samtidigt.Iodine is well known as an essential nutrient element for mammals. It has evoked extensive interests in investigation of its behaviours and transportation processes in various environmental components. 129I, a long-lived radioisotope of iodine (1.57×107 years), is predominantly discharged to the environment from nuclear reprocessing plants (especially Sellafield in United Kingdom and La Hague in France), providing a unique point source for environmental tracing studies. Speciation analysis of 129I can be used not only for studying the geochemical cycle of iodine, but also for investigating various environmental processes. This thesis presents the methods developed for chemical speciation analysis of 129I in environmental and biological samples (i.e. seawater, aerosols, and seaweed), as well as its applications for tracing environmental processes and investigating geochemical cycle of stable 127I in ocean, atmosphere and seaweed. Based on the previous work, a persulfate oxidation decomposition method was further investigated for converting organic iodine to inorganic forms in natural water samples. This method was proved to be efficient and reliable for decomposing organic iodine, and has been successfully applied for determination of 129I in natural waters and leachates containing organic iodine species. A method has been established for speciation analysis of 129I and 127I in aerosol samples collected on polypropylene filter. Sequential extraction using water and NaOH solution was employed to extract water-soluble iodine (WSI) and NaOH soluble iodine (NSI), and alkaline ashing for residue insoluble aerosol iodine (RII). WSI was further partitioned to iodide and iodate using anion exchange chromatography. Parameters, such as amount of leaching agents used, leaching time, ashing time and temperature, and addition of iodine protecting reagent that might influence stability of iodine species and chemical yield of iodine species during chemical separation, were investigated in order to obtained accurate results of 129I species in aerosol. The results on the analysis of total and different species of 129I in real samples demonstrate that the developed method is reliable for accurate determination of 129I and 127I species in aerosol samples. Distributions of chemical species (iodide and iodate) of 129I and 127I in the seawater from the central Arctic, Greenland coast, Danish coast and offshore Fukushima, Japan were investigated. Iodate for both 129I and 127I is the predominant form for the seawater in the central Arctic and Greenland coast, whereas iodide is the major specie of 129I and 127I in Danish coast. A distinct distribution pattern of iodine species was observed in Fukushima offshore seawater, where the I-/IO3 ratios for 127I were in the range of 0.07-0.27 reflecting a dominant iodate in the seawater, but the I-/IO3 - ratios for 129I indicated that iodide is the major iodine specie. These investigations demonstrate that variation of iodine species is dependent on origins of iodine (nuclear reprocessing plants and nuclear accident), transportation pathways (along the coast and open area of ocean) and biogeochemical processes. The remarkably increased 129I inventory in the Arctic by 2011 suggests that it may acts as a secondary source of 129I that outflows to the downstream seas, such as the Greenland Sea, and the western Atlantic Ocean, as well as to the atmosphere and the Arctic ecosystem. Aerosol samples collected at two locations (Risø, Denmark, a coastal site, and Tsukuba Japan, about 170 km southwest of the Fukushima Dai-ichi nuclear power plant) during spring 2011 (shortly after the Fukushima nuclear accident) and winter 2014 were analyzed for iodine species of 129I and 127I including soluble and insoluble iodine. The results indicate that the concentrations and species of 129I and 127I in aerosols are strongly related to the sources and pathways of air masses, and that Fukushima-derived 129I only contributed less than 6% of total 129I in the northern Europe during the accident period. Chemical species of 129I and 127I in seaweed (Fucus Serratus and Vesiculosus) collected in Danish coastal areas in 2014 were determined including water-soluble iodine (iodide, iodate and soluble organic iodine) and water insoluble iodine. In combination of iodine species in seawater simultaneously collected with seaweed, possible mechanism of iodine uptake by seaweed was explored in natural marine system. - atomi

Online Research Database In Technology

Speciation Analysis and Environmental Tracer Studies of <sup>129</sup>I

http://orbit.dtu.dk/ws/files/111797433/Luyuan_Zhang_PhD_thesis.pdf

Speciation Analysis and Environmental Tracer Studies of <sup>129</sup>I

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