Evaluation of dissolution flux of iodine from brackish lake sediments under different temperature and oxygenic conditions

Preparation and characterizations of antibacterial iodine-containing coatings on pure Ti

Iodine-containing coatings were prepared on pure Ti surfaces via electrochemical deposition to enhance their antibacterial properties. The factors influencing iodine content were analyzed using an orthogonal experiment. The electrochemically deposited samples were characterized using scanning electron microscopy with energy dispersive spectroscopy and X-ray photoelectron spectroscopy, and their antibacterial properties and cytotoxicity were evaluated. The results showed that changing the deposition time is an effective way to control the iodine content. The iodine content, coating thickness, and adhesion of the samples increased with deposition time. Iodine in the coatings mainly exists in three forms, which are I2, I3-, and pentavalent iodine. For samples with iodine-containing coatings, the antibacterial ratios against E. coli and S. aureus were greater than 90% and increased with increasing iodine content. Although the samples with iodine-containing coatings showed some inhibition of the proliferation of MC3T3-E1 cells, the cell viabilities were all higher than 80%, suggesting that iodine-containing coatings are biosafe.

Large seasonal fluctuations of groundwater radioiodine speciation and concentrations in a riparian wetland in South Carolina

Recent studies evaluating multiple years of groundwater radioiodine (¹²⁹I) concentration in a riparian wetland located in South Carolina, USA identified strong seasonal concentration fluctuations, such that summer concentrations were much greater than winter concentrations. These fluctuations were observed only in the wetlands but not in the upland portion of the plume and only with ¹²⁹I, and not with other contaminants of anthropogenic origin: nitrate/nitrite, strontium-90, technecium-99, tritium, or uranium. This unexplained observation was hypothesized to be the result of strongly coupled processes involving hydrology, water temperature, microbiology, and chemistry. To test this hypothesis, an extensive historical groundwater database was evaluated, and additional measurements of total iodine and iodine speciation were made from recently collected samples. During the summer, the water table decreased by as much as 0.7 m, surface water temperature increased by as much as 15 °C, and total iodine concentrations were consistently greater (up to 680%) than the following winter months. Most of the additional iodine observed in the summer could be attributed to proportional gains in organo-iodine, and not iodide or iodate. Furthermore, ¹²⁹I concentrations were observed to be two-orders-of-magnitude greater at the bottom of the upland aquifer than at the top. A coupled hydrological and biogeochemical conceptual model is proposed to tie these observations together. First, as the surface water temperature increased during the summer, microbial activity was enhanced, which in turn stimulated the formation of mobile organo-I. Hydrological processes were also likely involved in the observed iodine seasonal changes: (1) as the water table decreased in summer, the remaining upland water entering the wetland was comprised of a greater proportion of water containing elevated iodine concentrations from the low depths, and (2) water flow paths in summer changed such that the wells intercepted more of the contaminant plume and less of the diluting rainwater (due to evapotranspiration) and streamwater (as the lower levels promote a predominantly recharging system). These results underscore the importance of coupled processes influencing contaminant concentrations, and the need to assess seasonal contaminant variations to optimize long-term monitoring programs of wetlands.

Flux and pathway of iodine dissolution from brackish lake sediment in the northeast of Japan

Sediment is one of the most important entities controlling the environmental dynamics of iodine. We previously evaluated the dissolution flux of iodine from aquatic sediment to its overlying water in a brackish lake through an incubation experiment with a sediment core sample, reporting the regulation factors of this flux, such as the temperature and oxygenic conditions. In this study, factors controlling the seasonal variation in the dissolution flux of iodine were investigated via an incubation experiment using the sediment core samples collected in autumn and summer. The dissolution flux in this study was significantly smaller than that reported in our previous study. The iodine concentration detected in the overlying water of the sediment during incubation in this study was positively correlated with the concentrations of some inorganic ions, such as Na⁺, Cl^-, and SiO₄^2-, while these correlations were not confirmed in our previous study. As the dissolution of sedimentary iodine includes two pathways, which are the diffusion of sedimentary pore water and degradation of organic matter on surface sediment, correlations potentially indicate that the dissolution flux estimated in this study has a larger contribution from sedimentary pore water than that in our previous study. In addition, the higher flux estimated in our previous study was considered to be caused by the larger contribution from iodine derived from the degradation of phytoplanktonic organic matter on surface sediment. Assuming that the dissolution fluxes estimated in the previous and present studies are representative of the fluxes during and excluding the high productivity season in Lake Obuchi, respectively, we estimated the annual flux at 2.7 g y^-1 m^-2, which is comparable with our previous estimation.

Evaluation of radioiodine (129I) dissolution from sediment of a brackish lake beside a spent nuclear fuel reprocessing plant in Japan

Dissolution fluxes of stable (¹²⁷I) and radioactive (¹²⁹I) isotopes of iodine from a brackish lake sediment beside a spent nuclear fuel reprocessing plant in Japan were evaluated through two kinds of experiments: incubation using a sediment core sample for 24 h, and observation of ¹²⁷I and ¹²⁹I concentrations in sedimentary pore water. For ¹²⁷I, the dissolution flux evaluated in the incubation experiment was comparable with that obtained from the vertical gradient of ¹²⁷I concentration in pore water in the observation experiment. This suggests that degradation of organic matter in the surface sediment is an important source of dissolved ¹²⁷I found in the water. For ¹²⁹I, the dissolution flux estimated in the incubation experiment showed negative values, indicating the transfer of ¹²⁹I to the sediment from the overlying water (i.e., absorption). Moreover, the flux evaluated from the observation experiment was positive. This result suggests that degradation of organic matter in the surface sediment is scarcely important to the supply of ¹²⁹I from the sediment to the water in the studied lake. The dissolution flux of ¹²⁹I estimated in the observation experiment was smaller than the absorption flux of ¹²⁹I in the incubation experiment. This potentially indicates that the dissolution of sedimentary ¹²⁹I does not significantly change ¹²⁹I concentrations in the water and sediment of the lake. This hypothesis was consistent with previous research conducted for the studied lake.