Iodine In Groundwater Research Articles

Iodine nutrition status of children 3-13 years of age in areas with high groundwater iodine content in China

BackgroundAdequate iodine status is crucial for children's health and normal development. However, there is a paucity of research on the iodine status of children from areas with high groundwater iodine content. ObjectivesTo monitor the iodine status of children in Shandong, China (regions primarily characterized by high iodine concentrations in groundwater) and to describe the factors influencing children's iodine status. MethodsA cross-sectional study was conducted from 2013 to 2023 on 3,253 children aged 3-13 years. We collected drinking water, spot urine, and 24-hour urine samples from children to assess their iodine status (measuring drinking water iodine concentration (WIC), water iodine intake (WII), urine iodine concentration (UIC), 24-hour urine iodine excretion (24-h UIE), daily iodine intake (DII), etc.), and analyzed influencing factors. ResultsThe median WIC for children was 183 (IQR: 70.2, 362) μg/L, and the median spot UIC was 428 (IQR: 194, 737) μg/L, surpassing the WHO cutoff (300 μg/L). Children at risk of iodine excess numbered 1750 (61.8%). Approximately 61% of iodine intake came from drinking water. Boys had significantly higher iodine intake than girls (P < 0.001). Children's age showed positive correlations with spot UIC, 24-h UIC, and 24-h UIE. There were no significant differences in 24-h UIC and 24-h UIE among children with different BMIs. The logistic regression model revealed that the risk of iodine excess was increased by boy gender, increment in age (OR = 1.05, 95% CI: 1.02, 1.08), and every 10 μg (OR = 1.04, 95% CI: 1.03, 1.04) or 50 μg (OR = 1.19, 95% CI: 1.16, 1.22) increment in WII. ConclusionChildren in areas with high groundwater iodine content are at a risk of iodine excess. As age increases, the risk of iodine excess in children rises, with boys at a higher risk than girls.

Dissimilatory Iodate-Reducing Microorganisms Contribute to the Enrichment of Iodine in Groundwater.

Iodate reduction by dissimilatory iodate-reducing microorganisms (DIRMs) plays a crucial role in the biogeochemical cycling of iodine on Earth. However, the occurrence and distribution of DIRMs in iodine-rich groundwater remain unclear. In this study, we isolated the dissimilatory iodate-reducing bacteriumAzonexus hydrophilusstrain NCP973 from a geogenic high-iodine groundwater of China for the first time. The analysis of genome, transcriptome, and heterologous expression revealed that strain NCP973 uses the dissimilatory iodate-reducing enzyme IdrABP1P2 to reduce dissolved or in situ sediment-bound iodate to iodide. The location of IdrABP1P2 in the conjugative plasmid of strain NCP973 implies that IdrABP1P2 could be spread by horizontal gene transfer and allow the recipient microorganisms to participate in the enrichment of iodide in aquifers. Based on the global iodine-rich groundwater metagenomes and genomes, the identification of idrA showed that phylogenetically diverse DIRMs are widely distributed not only in geogenic high-iodine groundwater of China but also in radionuclide-contaminated groundwater of USA as well as in subsurface cavern waters in Germany and Italy. Moreover, the abundance of idrA was found to be higher in groundwater with a relatively high iodine content. Collectively, these results suggest that terrestrial iodine-affected groundwater systems are another important habitat for DIRMs in addition to marine environments, and their activity in aquifers triggers the mobilization and enrichment of iodine in groundwater worldwide.

Coupled transformation pathways of iron minerals and natural organic matter related to iodine mobilization in alluvial-lacustrine aquifer

The complex of natural organic matter (NOM) and iron minerals in sediment is the main host and source of groundwater iodine. However, the transformation pathways of the complex remain unclear. The groundwater and sediment from the Hetao Basin were collected in this study to analyze multi-isotopes, NOM molecular characteristics, and iron mineral phases. The results showed that high-iodine groundwater was mainly observed in the discharge area, where biodegradation of NOM, sulfate reduction and methanogenesis occurred. Compared to the shallow clayey sediments, the confined sandy sediments had lower iodine content, a lower fraction of crystalline iron oxides, and a higher fraction of carbonate associated Fe(II) minerals, suggesting that the release of sediment iodine in the aquifer is related to the transformation of sediment Fe(III) hydroxides/oxides. Moreover, the molecular features of high-iodine groundwater NOM and sandy sediment NOM were characterized by a higher proportion of refractory compounds, suggesting that the reductive transformation of sediment Fe(III) hydroxides/oxides is fueled by degradable organic compounds. The microbial Fe-reducing and/or sulfate-reducing processes cause the enrichment of groundwater iodine in the form of iodide via the transformation of iodine species. These findings provide new insights into the genesis of high-iodine groundwater.

Spatial distribution and hydrogeochemical processes of high iodine groundwater in the Hetao Basin, China

To understand the genesis and spatial distribution of high iodine groundwater in the Hetao Basin, 540 groundwater samples were analyzed for the chemistry and isotope. Total iodine concentrations in groundwater range from 1.32 to 2897 μg/L, with a mean value of 159.2 μg/L. The groundwater environment was mainly characterized by the weakly alkaline and reducing conditions, with the iodide as the main species of groundwater iodine. High iodine groundwater (I > 100 μg/L) was mainly distributed in shallow aquifers (< 30 m) of Hangjinhouqi near the Langshan Mountain and the discharge areas along the main drainage channels. The δ18O and δ2H values ranged from −12.09 ‰ to −3.99 ‰ and − 91.58 ‰ to −52.80 ‰, respectively, and the correlation between groundwater iodine and isotopes indicates the dominant role of evapotranspiration in the enrichment of iodine in the shallow groundwater with depth <30 m. It was further evidenced by the correlation between groundwater iodine and Cl/Br molar ratio, and significant contributions of climate factors identified from the random forest and XGBoost. Moreover, irrigation practices contribute to high iodine levels, with surface water used for irrigation containing up to 537.8 μg/L of iodine, which can be introduced into shallow aquifer directly. The iodine in irrigation water can be retained in the soil or shallow sediment, and later leach into groundwater under favorable conditions.

A review of groundwater iodine mobilization, and application of isotopes in high iodine groundwater.

Excessive intake of iodine will do harm to human health. In recent years, high iodine groundwater has become a global concern after high arsenic and high fluorine groundwater. A deep understanding of the environmental factors affecting iodine accumulation in groundwater and the mechanism of migration and transformation is the scientific prerequisite for effective prevention and control of iodine pollution in groundwater. The paper comprehensively investigated the relevant literature on iodine pollution of groundwater and summarized the present spatial distribution and hydrochemical characteristics of iodine-enriched groundwater. Environmental factors and hydrogeological conditions affecting iodine enrichment in aquifers are systematically summarized. An in-depth analysis of the hydrologic geochemistry, physical chemistry, biogeochemistry and human impacts of iodine transport and transformation in the surface environment was conducted, the results and conclusions in the field of high iodine groundwater research are summarized comprehensively and systematically. Stable isotope can be used as a powerful tool to track the sources of hydrochemical components, biogeochemistry processes, recharge sources and flow paths of groundwater in hydrogeological systems, to provide effective research methods and means for the study of high iodine groundwater system, anddeepen the understanding of the formation mechanism of high iodine groundwater, the application of isotopic technique in high iodine groundwater is also systematically summarized, which enriches the method and theory of high iodine groundwater research. This paper provides more scientific basis for the prevention and control of groundwater iodine pollution and the management of groundwater resources in water-scarce areas.

Machine learning prediction of health risk and spatial dependence of geogenic contaminated groundwater from the Hetao Basin, China

Geogenic contaminated groundwater (GCG), characterized by elevated arsenic, fluoride, and iodine levels, present a significant challenge to public health and government management. Conventional survey-based approaches of collecting groundwater samples, conducting physicochemical tests, and performing spatial interpolation to obtain regional groundwater chemical component maps are inefficient and costly. More importantly, it does not take into account the actual hydrogeological conditions or the characteristics of pollutant transport and enrichment. To address this issue, we utilized Support Vector Machine (SVM), Random Forest (RF), Adaptive Boosting (AdaBoost), and Extreme Gradient Boosting (XGBoost) to analyze the likelihood of occurrence of arsenic, fluoride, and iodine as well as their spatial distribution in shallow groundwater from the Hetao Basin. Our study incorporated 20 indicators related to meteorology, soil physicochemical properties, and groundwater conditions, along with 1505 labeled samples consisting of groundwater arsenic, fluoride, and iodine concentrations and their corresponding coordinates. Subsequently, the study automatically analyzed the meteorological, soil physicochemical properties and groundwater conditions by constructing a machine learning model using the available data. In order to optimise and select the best prediction model, this paper presents a quantitative evaluation of the prediction performance of various machine learning models. The accuracy (AC), area under curve (AUC) and mean squared error (MSE) were calculated to predict the spatial distribution of CGC. Subsequently, the optimized model for predicting the spatial distribution of GCG was selected. The results showed that the XGBoost algorithm provided optimal predictions for groundwater with arsenic concentrations above 10 μg/L and fluoride concentrations exceeding 1.5 mg/L, whereas the RF model provided the best predictions for groundwater with arsenic concentrations surpassing 50 μg/L and iodine concentrations exceeding 100 μg/L. Subsequently, groundwater health risk zones were delineated based on an optimal prediction model, and demographic analysis was conducted in both the direct and potential groundwater risk zones. Model predictions indicated that hundreds of thousands of people in the Hetao Basin were facing a public health crisis caused by high concentrations of arsenic, fluoride and iodine in groundwater. These findings underscore the significant health challenge in the study area. Considering the agricultural development and increasing groundwater use in the area, our findings can guide local governments in managing the extent of groundwater development, establishing control zones, and enhancing protection measures for populations at risk from groundwater contamination.

Bacterial Sulfate Reduction Facilitates Iodine Mobilization in the Deep Confined Aquifer of the North China Plain.

Bacterial sulfate reduction plays a crucial role in the mobilization of toxic substances in aquifers. However, the role of bacterial sulfate reduction on iodine mobilization in geogenic high-iodine groundwater systems has been unexplored. In this study, the enrichment of groundwater δ34SSO4 (15.56 to 69.31‰) and its significantly positive correlation with iodide and total iodine concentrations in deep groundwater samples of the North China Plain suggested that bacterial sulfate reduction participates in the mobilization of groundwater iodine. Similar significantly positive correlations were further observed between the concentrations of iodide and total iodine and the relative abundance of the dsrB gene by qPCR, as well as the composition and abundance of sulfate-reducing bacteria (SRB) predicted from 16S rRNA gene high-throughput sequencing data. Subsequent batch culture experiments by the SRB Desulfovibrio sp. B304 demonstrated that SRB could facilitate iodine mobilization through the enzyme-driven biotic and sulfide-driven abiotic reduction of iodate to iodide. In addition, the dehalogenation of organoiodine compounds by SRB and the reductive dissolution of iodine-bearing iron minerals by biogenic sulfide could liberate bound or adsorbed iodine into groundwater. The role of bacterial sulfate reduction in iodine mobilization revealed in this study provides new insights into our understanding of iodide enrichment in iodine-rich aquifers worldwide.

Strontium isotopes as tracers for water-rocks interactions of groundwater to delineate iodine enrichment in aquifer of Datong Basin, northern China

Groundwater iodine has direct importance for human dietary iodine intake in areas where drinking water is of groundwater origin. Iodine affected aquifer system in Datong Basin of North China was studied with a focus on strontium isotopes and major ion chemistry, in order to estimate the controlling hydrological and geochemical processes. The data revealed a rather complicated mixing pattern of various groundwater source end-members that were subject to different water-rock interactions, such as silicate weathering, evaporite and carbonate dissolution. Groundwater from the recharge area of east margin was characteristic by 87Sr/86Sr ratios higher than 0.71643, which implied the silicate weathering process. Groundwater from the discharge area and west margin might be originated from evaporite and carbonate dissolution processes with low 87Sr/86Sr ratios. Mixing models of three end-members based on Sr isotope and contents reflected that the type of water-rock interactions shifted from silicate weathering towards evaporite dissolution along the groundwater flow path from east margin to basin center. Abundant iodine and natural organic matters (NOMs) were discovered in groundwater located at the discharge area with Sr isotopic values between 0.710 and 0.717, implying evaporite dissolution governing iodine and NOMs enrichment in groundwater. Silicate weathering process had negligible influence on iodine and NOMs enrichment in groundwater. While carbonate dissolution made negative contribution for iodine releasing to aqueous phases. The PHREEQC inverse modeling results illustrated that dissolution of halite, calcite, gypsum and kaolinite and cation exchange significantly changed chemical composition of groundwater along the groundwater paths from the two basin margins to central area.

Temporal variation of iodine in Danish groundwater

Iodine is an essential element for human health, and both high and low iodine intake could have negative health outcomes. The spatial variation of iodine in Danish groundwater has been studied before, but to the author’s knowledge, this is the first time that the temporal variation is characterised. Nationwide data from the Danish groundwater monitoring programme (GRUMO) were analysed between 2011 and 2021, including 2924 samples from 1242 well screens at 893 wells. The sampling frequency varied and so the robust coefficient of variation (rCV) was calculated for 930 (75%) of well screens, and time-series analysis was performed for 23 (2%). Key findings are (1) iodine in Danish groundwater varies over time (0–124%, median = 10%), (2) in one quarter of the well screens rCV exceeds 20% and (3) this variation cannot be attributed solely to analytical uncertainty at 14% of the well screens. The impact of temporal variation of iodine in Danish drinking water of groundwater origin should be evaluated in future exposure or epidemiological studies with respect to the study goal, location and time period. Since the temporal variation could not be quantified over the entire concentration range, monitoring of iodine in Danish groundwater should continue.

Iodine enrichment in the groundwater in South China and its hydrogeochemical control

In North China, iodine-rich groundwater has been extensively studied, but few in South China. This study aimed to investigate the characteristics of iodine-rich groundwater in South China and identify potential contamination sources. The results revealed that the average concentration of iodine in groundwater was 890 µg/L, with a maximum concentration of 6350 µg/L, exceeding the permitted levels recommended by the World Health Organization (5–300 µg/L). Notably, the enrichment of iodide occurred in acidic conditions (pH = 6.6) and a relatively low Eh environment (Eh = 198.4 mV). Pearson correlation and cluster analyses suggested that the enrichment of iodide could be attributed to the intensified redox process involving Mn(II), iodine (I2), or iodate (IO3−) in the soil. The strong affinity between Mn(II) and I2/IO3− facilitated their interaction, resulting in the formation and mobilization of I− from the soil to the groundwater. Leaching experiments further confirmed that reducing substances (such as sodium sulfides, ascorbic acids, and fulvic acids) in the soil with low dissolved oxygen (DO) levels (< 1.0 mg/L) enhanced the dissolution of iodine species. Conversely, higher DO content (> 3.8 mg/L) promoted the oxidation of I− into I2 or IO3−, leading to its stabilization. This research provides new insights into the characteristics and mechanisms of I− enrichment in groundwater in South China, and emphasizes the significance of the redox reactions involving Mn(II) and I2/IO3−, as well as the influence of soil properties in regulating the occurrence and transportation of iodine species within groundwater systems.

Enrichment mechanism of fluoride and iodine in saline groundwater in the lower flood plain of the Yellow River, northern China

To identify the enrichment mechanism of fluoride and iodine in saline groundwater and reveal the impact of salinization on it, hydrogeochemical studies were conducted in different zones from the lower flood plain of the Yellow River, China. The results showed that high-F and high-I groundwater is mainly distributed in the paleo–Yellow River alluvial plain (Zone 2) and alluvial–lacustrine plain (Zone 3) rather than the piedmont alluvial–proluvial plain (Zone 1), with exceedances of groundwater guidelines reaching up to 57.69 %–80.77 %. The high-F and high-I groundwater is characterized by high total dissolved solids (TDS) concentrations, which ranged between 475 and 7002 mg/L, with 47 % and 77 % of groundwater samples from Zone 2 and Zone 3 having TDS over 1000 mg/L, respectively. Groundwater F– mainly originated from geogenic sources of fluorite dissolution and silicate weathering, and its release was promoted by alkaline conditions, cation exchange processes, and the competitive adsorption of HCO3–. With increasing TDS concentration in the groundwater, F– concentration showed a trend of first increasing and then slightly decreasing. Furthermore, the Cl/Br molar ratio in groundwater and Gibbs diagram indicated that water–rock interactions could lead to F– enrichment in slightly saline water (TDS < 3000 mg/L), and strong evaporation would restrict F– concentration in saline water (TDS > 3000 mg/L) due to the limitation of fluorite solubility. In contrast, no close correlation between I– and TDS was observed, indicating that salinization of groundwater is not the dominant reason for I– enrichment. In Zone 2 and Zone 3, large amounts of alluvial–lacustrine sediments with abundant organic matter are probably the reason for high-I groundwater, which is supported by the significantly positive correlation between I– and Br–. The reduction of iodate and nitrate could be the direct cause of elevated I– concentration in groundwater. In addition, results of factor analysis further confirm contrasting behaviors of fluoride and iodine in saline groundwater.

Microbial Contributions to Iodide Enrichment in Deep Groundwater in the North China Plain.

Microorganisms play crucial roles in the global iodine cycling through iodine oxidation, reduction, volatilization, and deiodination. In contrast to iodate formation in radionuclide-contaminated groundwater by the iodine-oxidizing bacteria, microbial contribution to the formation of high level of iodide in geogenic high iodine groundwater is poorly understood. In this study, our results of comparative metagenomic analyses of deep groundwater with typical high iodide concentrations in the North China Plain revealed the existence of putative dissimilatory iodate-reducing idrABP1P2 gene clusters in groundwater. Heterologous expression and characterization of an identified idrABP1P2 gene cluster confirmed its functional role in iodate reduction. Thus, microbial dissimilatory iodate reduction could contribute to iodide formation in geogenic high iodine groundwater. In addition, the identified iron-reducing, sulfur-reducing, sulfur-oxidizing, and dehalogenating bacteria in the groundwater could contribute to the release and production of iodide through the reductive dissolution of iron minerals, abiotic iodate reduction of derived ferrous iron and sulfide, and dehalogenation of organic iodine, respectively. These microbially mediated iodate reduction and organic iodine dehalogenation processes may also result in the transformation among iodine species and iodide enrichment in other geogenic iodine-rich groundwater systems worldwide.

Spatiotemporal Variability of Groundwater Iodine in the Northern Arid Basins: Significance for Safe Water Supply.

The genesis of geogenic iodine (I)-contaminated groundwater poses a significant threat to long-term water exploitation. Safe and sustainable water supply, particularly in the northern arid basins, demands a quantitative prediction of the high variability of I distribution over hydrogeological timescales. Here, bioenergetics-informed reactive transport modeling was combined with high-resolution molecular characterization of fueling organic matter to decipher the time-controlled interactions between vertical flow and (bio)geochemical processes in I transport within the Datong aquifers. The declining reactivities of I-bearing organic matter and Fe oxides in the 15-40 m depth decreased the rate of I release, while a growing number of pore volumes flushed through the aquifers to leach out I- and organic I. This removal effect is compensated by the desorption of I- from Fe oxides and secondary FeS generated from the concurrent reduction of Fe oxides and SO42-. Consequently, peak concentrations of groundwater I- may have appeared, depending upon the vertical recharge rate, at the first several pore volumes flushed through the aquifers. The current vertical distributions of the various I species likely represent a quasi-steady state between I mobilization and leaching. These new mechanistic insights into the dynamic hydrogeological-(bio)geochemical processes support secure groundwater use in the I-affected northern arid basins.

Novel insight into iodine enrichment in alluvial-lacustrine aquifers: Evidence from stable carbon and iron isotopes

Reductive dissolution of Fe (oxyhydr)oxides triggered by biodegradation of organic matter (OM) are considered to be key processes controlling iodine (I) release in groundwater systems. However, the precise mechanisms involved in release from organic matter degradation and from Fe (oxyhydr)oxides are unclear. In this study, dual stable isotope analysis (δ13C and δ56Fe) was combined with ultraviolet–visible spectral characterization of dissolved organic matter to elucidate the mechanisms of iodine enrichment in groundwater of the central Yangtze River basin, China, which represents Quaternary alluvial-lacustrine floodplains. High iodine groundwater mainly occurs along the Yangtze River (YR) and Han River (HR), with a maximum concentration of 1220 μg/L. The results suggest that methanogenesis driven by the biodegradation of high molecular weight organic compounds can promote the reductive dissolution of amorphous Fe (oxyhydr)oxides, which is the predominant process controlling iodine enrichment in the YR groundwater system. In addition, fermentation accompanied by sulfate reduction can also trigger the release of iodine into groundwater. The reductive dissolution of crystallized Fe (oxyhydr)oxides driven by the fermentation of small-molecule organic compounds is the dominant process responsible for iodine enrichment in the HR groundwater system. This study provides novel insight into the mechanisms of iodine enrichment in Quaternary alluvial-lacustrine aquifers.

Deficiency and excess of groundwater iodine and their health associations

More than two billion people worldwide have suffered thyroid disorders from either iodine deficiency or excess. By creating the national map of groundwater iodine throughout China, we reveal the spatial responses of diverse health risks to iodine in continental groundwater. Greater non-carcinogenic risks relevant to lower iodine more likely occur in the areas of higher altitude, while those associated with high groundwater iodine are concentrated in the areas suffered from transgressions enhanced by land over-use and intensive anthropogenic overexploitation. The potential roles of groundwater iodine species are also explored: iodide might be associated with subclinical hypothyroidism particularly in higher iodine regions, whereas iodate impacts on thyroid risks in presence of universal salt iodization exhibit high uncertainties in lower iodine regions. This implies that accurate iodine supply depending on spatial heterogeneity and dietary iodine structure optimization are highly needed to mitigate thyroid risks in iodine-deficient and -excess areas globally.

Mechanisms of iodine enrichment in the pore-water of fluvial/lacustrine aquifer systems: Insight from stable carbon isotopes and batch experiments

• High iodine groundwater occurs in discharge area of fluvial/lacustrine aquifer systems. • Local transformation of sediment Fe minerals explains the enrichment of pore-water iodine in the deep sediments. • Iodine-rich pore-water in the shallow sediments near the coastal area is related to the marine transgressions. The wide occurrence of high iodine groundwater is posing negative effects on human health. The land subsidence due to groundwater over-exploitation causes the release of iodine-rich pore-water trapped in clayey sediment into groundwater, however, the mechanisms of iodine enrichment in pore-water were still unclear. In this study, we selected the Datong Basin (DB) and North China Plain (NCP) with few and severe land subsidence, respectively, to understand the contributions of complex hydro-biogeochemical processes on the enrichment of iodine in groundwater and pore-water by using the inorganic/organic carbon isotope and batch experiments. The results showed that at the DB, the range of groundwater iodine was 4–2175 µg/L, and the enrichment of groundwater iodine is mainly related to the transformation of iron oxyhydroxides triggered by microbial degradation of organic matter, which was reflected by the more depleted δ 13 C DIC signatures of groundwater and gradual increasing trend of ratio of HCl-extractable Fe(II)/sediment Fe total and sediment δ 13 C DOC signatures with depth. In comparison, groundwater iodine at the NCP had the range of 2–1106 µg/L, and pore-water rich in iodine preserved in the clayey sediment serves as the main source. The depth profiles of sediment iron mineral fractions and δ 13 C DOC signatures suggested that the NCP sediments experienced lower degree of reductive transformation of iron minerals and microbial degradation of natural organic matter. At some specific depths higher than 300 m, the evident higher ratios of HCl-extractable Fe(II)/sediment Fe total indicate that the local transformation of iron minerals can explain the pore-water rich in iodine at deep sediments, which was supported by the results of microbial batch experiments. The pore-water with high iodine concentration preserved in the shallow sediment is more likely related to the marine transgressions. This study helps to improve our understanding of the mechanisms of high iodine groundwater, which may provide some new insights on further groundwater management.

Enrichment mechanisms for the co-occurrence of arsenic-fluoride-iodine in the groundwater in different sedimentary environments of the Hetao Basin, China

Abnormal levels of co-occurring arsenic (As), fluoride (F−) and iodine (I) in groundwater at the Hetao Basin are geochemically unique. The abnormal distribution of As, F− and I is obviously related to the sedimentary environment. It is necessary to study the enrichment mechanisms for the co-occurrence of As, F− and I in groundwater under the influence of the sedimentary environment in Hetao Basin. In this study, 499 groundwater samples were collected. Sedimentary environments, hydrogeochemical process, isotopes were analyzed to elucidate their enrichment mechanisms. The environment of groundwater is weakly alkaline. The hydrochemical types of groundwater are mainly Na–Cl–HCO3. The distribution of isotope δ18O demonstrates that irrigation from the Yellow River is the main recharge source. The main drainage channel is the discharge area in the Hetao basin. Based on the clay-sand ratio (R), the number of clay layers (N) and terrain slope (S), Hetao Basin was divided into four sedimentary environmental zones. The distribution of As (0–916.70 μg/L), F− (0.05–8.60 mg/L) and I (0.01–3.00 mg/L) was featured by a clear zonation of the sedimentary environment. The high As and high I groundwater were mainly distributed in the paleochannel zone of the Yellow River, with exceedance rates of 80.28% and 52.58%, and the median values of 73.91 μg/L and 0.11 mg/L, respectively. In the reducing environment, the release of As initially adsorbed on iron hydrogen and iron oxide, the reductive of iron hydroxide itself, rock weathering and evaporation are the key factors affecting the enrichment of As in groundwater. In this area, large amounts of aquatic organisms and plankton deposited in the sediment and channel filling deposits abundant with organic matter is the premise of high-I groundwater. The reduction of iodate and nitrate directly leads to the high concentration of I in groundwater. The high F− groundwater was mainly distributed in the piedmont alluvial-pluvial fan and the north margin of Ordos Plateau, with exceedance rates of 58.62% and 43.30%, and the median values of 1.10 mg/L and 0.86 mg/L, respectively. High F− groundwater in the two zones is affected by the abundant biotite and hornblende in Langshan Mountain and Ordos Plateau. Under evaporation, the precipitation rate of CaF2 and pH plays key roles in the enrichment of F− in groundwater. In the Hetao Basin, sedimentary environment is the main controlling factor for the co-mobilization of As, F− and I in groundwater.

The mechanism of iodine enrichment in groundwater from the North China Plain: insight from two inland and coastal aquifer sediment boreholes.

As an element relevant to human health, iodine is highly worthy of researchers' attention, especially the mechanism of iodine migration and enrichment in groundwater systems. A total of 43 groundwater, 1 seawater, 107 sediment, and 111 pore water samples from two boreholes (toward to Bohai Sea: BT, HH) were collected along a groundwater flow path at the North China Plain to investigate hydro-geochemical processes controlling groundwater iodine. High iodine groundwater (> 100μg/L) was characterized by Na-Cl type, with high TDS values (827-2,400mg/L) and high Cl (110-705mg/L) and Br (416-1,180μg/L) concentrations, which may be related to marine influence. Borehole BT and HH had pore water I concentration ranges of 1.4-132μg/L and 3.6-830μg/L, with high level that occurred near to coastline and corresponded to ancient transgression events. The results of sequential extraction of borehole sediments indicate that the fractions of sediment inorganic iodine mainly consisted of exchangeable, carbonate, and Fe-oxides associated fractions. Fe-oxides associated iodine was the main occurrence state in borehole BT far from the coastline, but high exchangeable iodine fractions (up to 92% of total extracted iodine) were observed in a high salinity borehole HH located near Bohai Bay, corresponding to the occurrence of high iodine pore water and groundwater. The analysis of iodine species indicates that iodide with strong migration ability dominated high iodine groundwater, pore water, and exchangeable sediment iodine, reflecting the occurrence of adsorption/desorption processes of iodine in groundwater system. High iodine groundwater and pore water exhibited iodine enrichment relative to Cl and Br, which suggests that iodine adsorbed on sediment desorbed under suitable pH and high solution ionic strength and subsequently released to pore water and aquifers. Inverse geochemical modeling stressed that ion exchange plays an important role in iodine enrichment of groundwater system.

Household Water Is the Main Source of Iodine Consumption among Women in Hargeisa, Somaliland: A Cross-Sectional Study

BackgroundIodine status surveys of women in Somaliland present widely conflicting results. Previous research indicates elevated concentrations of iodine (IQR 18–72 μg/L) in groundwater used for drinking and cooking, but the relation with iodine intake is not well characterized. ObjectivesWe aimed to investigate the contributions of household water iodine concentration (WIC), breastfeeding, total fluid intake, hydration levels, and urine volume on urinary iodine concentration (UIC) and excretion (UIE) over a 24-h period and to define iodine status from iodine intake estimates and median UIC, normalized to a mean urine volume of 1.38 L/d (hydration adjusted). MethodsThe study sample comprised 118 nonpregnant, healthy women aged 15–69 y. All participants resided in Hargeisa, and 27 were breastfeeding. Data collection consisted of a 24-h urine collection, a 24-h fluid intake diary, a beverage frequency questionnaire, and a structured recall interview. We measured UIC and WIC in all urine and in 49 household water samples using the Sandell-Kolthoff reaction. ResultsWIC ranged between 3 and 188 μg/L, with significant median differences across the water sources and city districts (P < 0.003). Nonbreastfeeding women were borderline iodine sufficient [hydration-adjusted median urinary iodine concentration (mUIC) 109 μg/L; 95% CI: 97, 121 μg/L], whereas breastfeeding women showed a mild iodine deficiency (73 μg/L; 95% CI: 54, 90 μg/L). There were strong correlations (ρ: 0.50–0.69, P = 0.001) between WIC and UIC, with iodine from household water contributing more than one-half of the total iodine intake. Multivariate regression showed hydration and breastfeeding status to be the main predictors of UIC. ConclusionsIodine from household water is the main contributor to total iodine intake among women in Hargeisa, Somaliland. Variation in female hydration and spatial and temporal WIC may explain diverging mUIC between studies. Water sources at the extremes of low and high iodine concentrations increase the risk of subpopulations with insufficient or more than adequate iodine intake.

Prediction modeling of geogenic iodine contaminated groundwater throughout China

Geogenic iodine-contaminated groundwater represents a threat to public health in China. Identifying high-iodine areas is essential to guide the mitigation of this problem. Considering that traditional analytical techniques for iodine testing are generally time-consuming, laborious, and expensive, alternative methods are needed to supplement and enhance existing approaches. Therefore, we developed an artificial neural network (ANN) model and assessed its feasibility in terms of predicting high iodine levels in groundwater in China. A total of 22 indicators (including climate, topography, geology, and soil properties) and 3185 aggregated samples (measured groundwater iodine concentrations) were utilized to develop the ANN model. The results showed that the accuracy and area under the receiver operating characteristic curve of the model on the test dataset are 90.9% and 0.972, respectively, and climate and soil variables are the most effective predictors. Based on the prediction results, a high-resolution (1-km) nationwide prediction map of high-iodine groundwater was produced. The high-risk areas are mainly concentrated in the central provinces of Henan, Shaanxi, and Shanxi, the eastern provinces of Henan, Shandong, and Hebei, and the northeastern provinces of Liaoning, Jilin, and Heilongjiang. The total number of people estimated to potentially be at high-risk areas because they use untreated high-iodine groundwater as drinking water is approximately 30 million. Considering the growing demand for groundwater in China, this work can guide the prioritization of groundwater contamination mitigation efforts based on regional groundwater quality levels to enhance environmental management.