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1.
An oxidation state diagram was used to study the relative stability of inorganic iodine species in an aqueous system. It is shown that although iodate is the most stable form, iodide may exist as a metastable form in a basic solution. Molecular iodine may undergo disproportionation to form iodide and iodate. Results from laboratory studies suggest that molecular iodine is rapidly taken up by seawater, and hypoiodite is probably formed. Hypoiodite is also unstable in seawater, and may react with organic matter or undergo autodecomposition. Direct reactions between molecular iodine and organic matter were not observed.  相似文献   

2.
Toward assessing the biogeochemical significance of seaweeds in relation to dissolved iodine in seawater, the effect of whole seaweeds (Laminaria digitata and Fucus serratus) upon iodide and iodate, at essentially natural concentrations, has been studied. The weeds were carefully removed from the sub-littoral zone of the Menai Straits and exposed to iodide and iodate at their natural temperature (6 °C), but under continuous illumination. Laminaria digitata was found to decrease the concentration of iodate with an exponential rate constant of 0.008–0.24 h−1. This is a newly discovered process which, if substantiated, will require an entirely new mechanism. Generally, apparent iodide concentration increased except in a run with seawater augmented with iodide, where it first decreased. The rate constant for loss of iodide was 0.014–0.16 h−1. Meanwhile, F. serratus was found not to decrease iodate concentrations, as did L. digitata. Indeed, after ∼30 h iodate concentrations increased, suggesting that the weed may take in iodide before oxidising and releasing it. If substantiated, this finding may offer a way into one of the most elusive of processes within the iodine cycle – iodide oxidation. With both seaweeds sustained long-term increases of apparent iodide concentration are most easily explained as a secretion by the weeds of organic matter which is capable of reducing the Ce(IV) reagent used in determination of total iodine. Modelling of the catalytic method used is provided to support this contention. The possibility of developing this to measure the strain that seaweeds endure in this kind of biogeochemical flux experiment is discussed. A Chemical Oxygen Demand type of approach is applied using Ce(IV) as oxidant. The results of the iodine experiments are contrasted with the several investigations of 131I interaction with seaweeds, which have routinely used discs of weed cut from the frond. It is argued that experiments conducted with stable iodine may measure a different variable to that measured in radio-iodine experiments.  相似文献   

3.
A study of inorganic iodine speciation in the waters of seven Croatian coastal caves is described. These are anchialine caves as they are connected hydraulically with Adriatic Sea surface water, with the tide inside the cave rising and falling with that outside, but replenishment of the water is restricted by the karst rock. In effect, the water in the cave probably acts more like a piston, and although moving slightly vertically, has a long residence time compared to a fully-flushing cave. Anchialine environments display a number of unusual features, e.g., a well-developed pycnocline, hypoxia and endemic fauna. Iodate and iodide were determined by differential pulse voltammetry and cathodic stripping square wave voltammetry, respectively. Low iodide concentrations (< 10 nM) have been consistently identified in the bottom water of the caves where concentrations of 90–100 nM would ordinarily be expected from intrusion of Eastern Adriatic surface seawater. Where total inorganic iodine concentrations behave conservatively with salinity the loss of the iodide implies oxidation to iodate. As iodide oxidation remains one of the enduring academic problems of the marine iodine system the study of iodine in anchialine caves may help unravel it. Iodate reduction was observed in mid-water, at the halocline, and mechanisms for the reduction involving either respiration or chemolitho-autotrophic bacteria are considered. The respiration mechanism is favoured because of enhanced alkalinity found in the near surface waters of the caves.  相似文献   

4.
Shipboard incubations from the US JGOFS cruise to the Arabian Sea (TN045) March, 1995 showed evidence of iodate reduction in 0.45 μ (Gelman Supor membrane) filtered seawater samples collected from intermediate depths (200–600 m) within the oxygen minimum zone (OMZ). Inorganic chemical reduction of iodate in these samples was ruled out as no free sulfide was measurable and concentrations of ammonia and nitrite were found to be less than 5 μM. To examine whether the reduction of iodate observed at sea could have been the result of bacterial metabolism, reduction of iodate (IO3−) to iodide (I−) by Shewanella putrefaciens strain MR-4 was studied in artificial seawater using electrochemical methods. MR-4 is a ubiquitous marine bacterium which may be of considerable importance when considering redox zonation in the water column because it is a facultative anaerobe and may switch amongst a suite of electron acceptors to support metabolism. In all experiments MR-4 reduced all iodate to iodide. The rate of formation of [I−]in the culture followed pseudo-first order kinetics. This is the first report of the marine bacterial reduction of iodate where the concentrations of iodide and iodate were measured directly. Our results may help to explain the depth distribution of iodine speciation reported in productive waters like the Arabian Sea and for the first time couple iodine speciation with bacterial productivity in the ocean.  相似文献   

5.
研究了离子色谱-电感耦合等离子体质谱（IC-ICPMS）联用技术直接进样测定海水中IO3^-和I^-的方法．采用IonPacAG23离子色谱保护柱分离IO3^-和I^-，以浓度4．0mmol／dm3的KOH为流动相，流量为1．0cm3／min，每个样品的分析时间为2．5min．采用2．5×10^-3cm^3的进样量，IO3^-和I^-的检出限分别达到0．6和0．4nmol／dm2，可满足海水中碘形态的定量分析．该方法的IO3^-和I^-浓度范围在2．0nmol／dm3～2．0μmol／dm3．  相似文献   

6.
The distributions of iodate, iodide and dissolved organic iodine (DOI) were determined in two deep sub-basins in the Chesapeake Bay, the shallow waters at the mouth of the Bay and the adjacent North Atlantic between the late spring and the early fall along the net flow-path of the water entering and exiting the Chesapeake Bay by using an improved analytical scheme designed for the quantitative recovery of DOI. The concentration of R-DOI found in the surface mixed layer in the upper Bay was about twice of those found at the same location in previous studies. (R-X was the concentration of a dissolved iodine species X that had been normalized to a constant salinity of 35.) Thus, DOI in estuarine waters might have been underestimated significantly in the earlier studies. Following the water along its net flow-path, iodate initially constituted more than 60% of total iodine (TI) in the source water in the Middle Atlantic Bight off the Delmarva Peninsula. As this water entered the Chesapeake Bay through the northern part of its mouth, the concentration of R-iodate decreased while that of R-iodide increased progressively until the former became undetectable in the surface mixed layer while the latter reached a maximum of 0.42 μM in the deep water in the upper Bay. Then, the concentration of R-iodate rebounded while that of R-iodide decreased in the outflowing water that exited through the southern part of the mouth of the Bay and was later entrained by the Gulf Stream. The concentration of R-DOI in the surface waters followed the same pattern as R-iodide and reached a maximum of 0.20 μM in the upper Bay. However, R-DOI was depleted in the deep water in the sub-basins. Its concentration dropped to around the detection limit in the suboxic waters in the upper Bay. R-TI in the Bay far exceeded that in the incoming Middle Atlantic Bight water and reached 0.55 μM in the upper Bay. These distributions of the iodine species suggest that, as water from the Middle Atlantic Bight intruded into the Chesapeake Bay, in the well oxygenated surface mixed layer, iodate was reduced to iodide, and the inorganic iodine species could also be converted to DOI. In the deep water, iodate and DOI were converted to iodide. Superimposed on these inter-conversions among the iodine species, dissolved iodine, possibly in the form of iodide, was also added to the water column from the underlying sediments and the process was especially significant in the suboxic deep water in the upper Bay. Mixing between the surface mixed layer and the deep water could also have increased the concentrations of iodide and total iodine in the former.  相似文献   

7.
The speciation of dissolved iodine and the distributions of the iodine species in the deep Chesapeake Bay underwent seasonal variations in response to changes in the prevailing redox condition. In the deep water, the ratios of iodate to iodide and iodate to inorganic iodine decreased progressively from the Winter through the Summer as the deep water became more poorly oxygenated before they rebounded in the Fall when the deep water became re-oxygenated again. The composition of the surface water followed the same trend. However, in this case, the higher biological activities in the Spring and the Summer could also have enhanced the biologically mediated reduction of iodate to iodide by phytoplankton and contributed to the lower ratios found during those seasons. Superimposed on this redox cycle was a cycle of input and removal of dissolved iodine probably as a result of the interactions between the water column and the underlying sediments. Iodine was added to the Bay during the Summer when the deep water was more reducing and removed from the Bay in the Fall when the deep water became re-oxygenated. A third cycle was the inter-conversion between inorganic iodine and ‘dissolved organic iodine’, or ‘‘DOI’’. The conversion of inorganic iodine to ‘DOI’ was more prevalent in the Spring. As a result of these biogeochemical reactions in the Bay, during exchanges between the Bay and the North Atlantic, iodate-rich and ‘DOI’-poor water was imported into the Bay while iodide- and ‘DOI’-rich water was exported to the Atlantic. The export of iodide from these geochemically reactive systems along the land margins contributes to the enrichment of iodide in the surface open oceans.  相似文献   

8.
Dissolved iodine in waters overlying and in the Orca Basin,Gulf of Mexico   总被引：1，自引：0，他引：1  
The distribution and speciation of iodine, a biophilic redox-sensitive trace element, in waters overlying and in the Orca Basin, Gulf of Mexico, which contains hypersaline, anoxic and yet non-sulfide-bearing brine have been determined. The distribution of iodate and iodide in the oxic waters overlying the anoxic brine are similar to those reported in other oceans. However, in the oxic-anoxic mixing zone, iodate disappears while the concentration of iodide reaches a maximum of 8.1 μM, the highest concentration ever reported in open oceans. There is also a maximum in specific iodine of 30.7 nM‰?1 at this depth. Specific iodine in oxic seawater is only about 10–14 nM ‰?1. These features may be explained by the preferential dissolution of biogenic particles that have accumulated in a strong pycnocline. In the anoxic brine proper, the concentration of iodide is 3.8 μM and can be explained almost entirely by the simultaneous mobilization of chloride and iodide during the dissolution of evaporite beds as the specific iodine of 14.5 nM‰?1 is only slightly higher than those observed in the oxic waters.  相似文献   

9.
The distributions of iodide, iodate and total iodine were determined along a transect from the Sargasso Sea and across the Gulf Stream to the continental shelf of the South Atlantic Bight during November 1990. The western boundary of the Gulf Stream at the outer shelf-upper slope was characterized by steeply sloping isotherms and isopleths of iodide and iodate, resulting from a dome of cold water that was rich in iodate and nearly devoid of iodide at the slope. Both the mid and the inner shelf were relatively well mixed vertically. The concentration of iodate in the surface waters decreased shoreward from >0.3 μM in the Sargasso Sea/Gulf Stream/outer shelf, to 0.29 μM in the midshelf, 0.19 μM in the outer-inner shelf and 0.11 /IM in the inner-inner shelf. Concomitantly, the concentration of iodide increased from <161 nM to 175 nM, 257 nM and 300 nM. The concentration changes were more abrupt in the inner-inner shelf within about 30 km from the shore. There was no evidence of significant concentrations of organic iodine. These distributions of iodide and iodate suggest that the South Atlantic Bight may act as a geochemical processor of dissolved iodine. Iodate is added to the shelf during topographically induced upwelling and frontal exchange with the Gulf Stream. In the shelf waters, iodate is reduced to iodide in situ. Iodide is exported from the shelf to the Gulf Stream which may eventually further transport it to the ocean interior. A ☐ model calculation suggests that 28% and 43% of the iodate added to the Bight and the inner shelf, respectively, are converted to another form in these waters, almost all of which is iodide. About a third of the reduction of iodate to iodide in the Bight occurs in the inner shelf. Thus, the inner shelf may be the most geochemically active zone within the Bight. The residence times of iodide relative to its production and that of iodate relative to its removal are 3.1 and 3.6 months in the Bight and 0.9 and 1.8 months in the inner shelf.  相似文献   

10.
Existing methods for the determination of the various forms of iodine present in seawater are laborious or unwieldy in use. This paper describes modified forms of the iodate and total iodine methods described by Barkley and Thompson (1960), a spectrophotometric procedure for iodate determination derived from Johannesson's (1958) work, and an automatic method for total iodine determination. Procedures for iodate and total-iodine determination which are suitable for use aboard ship, are recommended. Both procedures for iodate determination returned a standard deviation close to 0.5 μg/l when several replicate samples of a seawater containing approximately 30 μg/l of iodate-iodine were analysed. The automatic method for total iodine determination yielded a standard deviation of 0.8 μg/l by the repeated analysis of a seawater containing a total of approximately 50 μg/l of iodine. Suitable methods for the filtration and storage of seawater are also described.  相似文献   

11.
Dimethylsulfide(DMS) is generally thought to be lost from the surface oceans by evasion into the atmosphere as well as consumption by microbe.However,photochemical process might be important in the removal of DMS in the oceanic photic zone.A kinetic investigation into the photochemical oxidation of DMS in seawater was performed.The photo-oxidation rates of DMS were influenced by various factors including the medium,dissolved oxygen,photosensitizers,and heavy metal ions.The photo-oxidation rates of DMS were higher in seawater than in distilled water,presumably due to the effect of salinity existing in seawater.Three usual photosensitizers(humic acid,fulvic acid and anthroquinone),especially in the presence of oxygen,were able to enhance the photo-oxidation rate of DMS,with the fastest rate observed with anthroquinone.Photo-oxidation of DMS followed first order reaction kinetics with the rate constant ranging from 2.5×10-5 to 34.3×10-5 s-1.Quantitative analysis showed that approximately 32% of the photochemically removed DMS was converted to dimethylsulfoxide.One of the important findings was that the presence of Hg2 could markedly accelerate the photo-oxidation rate of DMS in seawater.The mechanism of mercuric catalysis for DMS photolysis was suggested according to the way of CTTM(charge transfer to metal) of DMS-Hg2 complex.  相似文献   

12.
Recent experiments which purport to show that molecular iodine added to seawater is rapidly converted entirely to another oxidized form of iodine, hypoiodite, are shown to be defective. The earlier suggestion that the disappearance is due to chemical reduction of molecular iodine by organic matter remains the most plausible reason.  相似文献   

13.
A number of field and laboratory studies on the impact of marine macroalgae on dissolved inorganic iodine speciation are presented. Within tidally isolated rock pools, the brown macroalga Fucus serratus was found to both release stored iodide and to facilitate the reduction of iodate to iodide. In contrast, no discernible changes in iodine speciation were observed in rock pools containing green macroalgae of the genus Ulva. Incubation experiments confirmed that the macroalgae Laminaria digitata, F. serratus and Kallymenia antarctica release iodide, though the rate of release varied between species and between specimens of the same species. Application of oxidative stress by treatment with cell wall derived oligoguluronate elicitors increased the efflux of iodide by L. digitata approximately 20-fold. The release of iodide by macroalgae may impact upon the formation of volatile iodine species (molecular iodine and iodocarbons) that are of importance in the coastal atmosphere.  相似文献   

14.
Dissolved iodine species and the relationship between its distribution and salinity in Jiulong River estuarine water have been determined. It has been found that the total iodine, iodate and iodide are positive linear with salinity. This indicates that dissolved iodine species (IO-3 and I- ) in estuarine water .how conservative behaviour. The river water contains 2. 40μg/1 as iodide and less than 1. 0μg/1 as iodate, and iodide is the predominant species. Whereas the sea water contains 39. 4μg/1 as iodate and 4. 00μg/1 as iodide, and iodate is the dominant form. The distribution of dissolved iodine in pore water, as a function of depth, has been studied. Iodine in pore water occurs as iodide. The apparent fluxes of soluble iodine from the sediment to the overlying water in the estuary have been determined. The values are 2. 4 (15℃) and 27μmol/(m2·d) (30℃) respectively.  相似文献   

15.
Three methods for the determination of dissolved organic carbon in seawater were compared. Samples were analysed using persulphate oxidation, high-temperature combustion, and ultraviolet photo-oxidation. The dissolved organic carbon content of the seawater samples ranged from 0.6 to 1.6 mg C/I. This study shows that results of high-temperature oxidation and photo-oxidation procedures differ by less than 5%, whereas results with persulphate oxidation are about 15% less than those obtained with the high-temperature oxidation. The relative merits of each of the oxidation techniques for the determination of organic matter in seawater are discussed.  相似文献   

16.
This study was performed in order to obtain information on the influence of an acute anoxic event (September, 1997) on distribution and speciation of inorganic iodine in the water column of a small, intensely eutrophicated salt lake. The variations in iodate and iodide depth distributions during the investigated period (1998–2000) were in accord with seasonal changes in redox conditions. During the stratification period (spring and summer), the concentration ratio between iodate and iodide in the upper layers was high, whereas during late summer and autumn, as a result of water column de-stratification and mixing of highly reducing deep water with the oxic layer, lower ratios and more uniform depth distributions were observed.The massive mortality of lake organisms induced by anoxic conditions and sulphide presence throughout the water column was registered by the end of September 1997, when overturn of the lake occurred. The concentrations of iodate in the oxic upper layers were elevated for more than a year after the mass-mortality event (up to 0.55 μmol L−1), whereas iodide concentrations remained high for more than 2 years in deep anoxic water (up to 2.27 μmol L−1). These data suggest that biogeochemical renewal processes affecting the concentrations of inorganic iodine in the lake water are slow compared to those that govern the speciation of iodine. The role of sediment–water interactions and iodine-rich organic species in the production of iodide are discussed.  相似文献   

17.
Robert M. Moore   《Marine Chemistry》2006,101(3-4):213-219
Experiments were conducted in the field to determine the non-chemical loss rate of methyl iodide in seawater and to examine production rates of methyl halides. The loss rate of added C13 labelled methyl iodide, present at concentrations similar to those found in seawater, corrected for chemical loss due to reaction with Cl− varied from < 1 to 18% day− 1, with a mean value of 7%. This rate of loss is much lower than that which was proposed by Bell et al. [Bell, N., Hsu, L., Jacob, D. J., Schultz, M. G., Blake, D. R., Butler, J. H., King, D. B., Lobert, J. M., Maier-Reimer, E., 2002. Methyl iodide: Atmospheric budget and use as a tracer of marine convection in global models, Journal of Geophysical Research-Atmospheres 107(D17), 4340-4351.] to account for the large discrepancies between observed and predicted mid-latitude concentrations of CH3I based on their global photochemical source model. The suitability of several types of container for seawater incubations was studied and only quartz tubes appeared to be free of experimental artifact. Collapsible polyvinyl fluoride containers showed major production of methyl halides on irradiation with simulated sunlight. Polyethylene containers caused spurious production of methyl iodide at lower rates.  相似文献   

18.
Pentachlorophenol (PCP) and 3,4-dichloroaniline (DCA) were used as models to examine photochemical reactions in seawater.The photolysis of PCP in seawater differed in both rate and product distribution from that in distilled water; rates were slower in seawater due to the photonucleophilic interaction of PCP with chloride ions, demonstrated by the formation of 36Cl-labeled PCP in irradiated PCP solutions containing Na36Cl. DCA showed no rate change and gave identical products in both systems. Both PCP and DCA yielded greater amounts of photoreduction products in seawater than in distilled water, and tetrachloromuconic acid was isolated and identified as a new and unstable PCP photoproduct resulting from ringfission. This study demonstrates the operation of photooxidation, photonucleophilic substitution, and photoreduction reactions which differ in detail between seawater and distilled water and suggests that photochemical reactions can be a major factor in the breakdown of organic pollutants and other chemicals in the marine environment.  相似文献   

19.
海洋石油光化学降解的研究   总被引：1，自引：0，他引：1  
石油进入海水会发生各种物理、化学变化,以往的研究已证明光化学氧化在石油及其精炼产品风化过程中具有重要意义.光化学氧化机理主要在于接受日光照射的能量,以不同的方式与溶解氧结合,从而最终降解石油烃.生成的光氧化产物一般为羧酸、醇、醚、羰基化合物等几类,还有一些产物尚不能确定其结构.光氧化产物仍然存在毒性,对海洋生物等十分有害.在动力学方面,针对其某一组分已证实为一级反应动力学行为,并定量地得出了速率常数.光降解速率会受到光照条件、溶解氧、金属离子等因素的影响.目前的研究表明,对石油光化学进行深入探讨具有较高的研究价值和现实意义.  相似文献   

20.
The development of procedures for the determination of iodate- and total-iodine content of seawater, which use a Technicon Auto-Analyser, is described. In both procedures the appropriate iodine species is first converted to iodate-iodine. Then, this is reacted with acid and excess iodide to give the iodonium ion, I3?, which is detected spectrophotometrically. In the total-iodine procedure the pre-oxidation is accomplished using bromine water. In the iodate procedure a pre-oxidation step using iodine-water can be included. It is anticipated that this will be used to test for the presence of naturally occurring reducing agents in seawaters, which by their action on iodonium ions could lead to an underestimate in iodate concentration. Seawaters, particularly coastal and surface oceanic ones, are known to contain iodine-reducing substances. Therefore, the validity of results obtained through the iodometric method for iodate must remain in some doubt until these tests have been made. The use of this method on anoxic waters which contain sulphides appears to be a prime example of where caution should be observed. The iodate procedure, both with and without pre-oxidation, has been tested on approximately 50 samples of waters from the Eastern Pacific Ocean; these waters did not appear to contain significant amounts of reducing agents. In a similar study, it was found that there was no significant difference between the results obtained by the new total-iodine procedure and an earlier automatic catalytic one.  相似文献   

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