Iodine Concentrations In Groundwater Research Articles

Molecular characteristics of natural organic matter in the groundwater system with geogenic iodine contamination in the Datong Basin, Northern China

Natural organic matter (NOM) plays an important role in the iodine mobilization in the groundwater system. In this study, the groundwater and sediments from iodine affected aquifers in the Datong Basin were collected to perform chemistry analysis and molecular characteristics of NOM by Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS). Total iodine concentrations in groundwater and sediments ranged from 1.97 to 926.1 μg/L and 0.001–2.86 μg/g, respectively. A positive correlation was observed between DOC/NOM and groundwater/sediment iodine. FT-ICR-MS results showed that the DOM in the high-iodine groundwater system is characterized by less aliphatic and more aromatic compounds with higher NOSC, indicating the features of more unsaturated larger molecule structures and more bioavailability. Aromatic compounds could be the main carriers of sediment iodine and were easily absorbed on amorphous iron oxides to form the NOM-Fe-I complex. More aliphatic compounds, especially those containing N/S, experienced a higher degree of biodegradation, which further mediated the reductive dissolution of amorphous iron oxides and the transformation of iodine species, thereby causing the release of iodine into groundwater. The findings of this study provide some new insights into the mechanisms of high-iodine groundwater.

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.

Iodine in major Danish aquifers

Iodine in groundwater can have direct importance for human dietary iodine intake in areas where drinking water is of groundwater origin, as in Denmark. Knowledge on the sources and processes for the varying iodine concentrations in groundwater is of utmost importance for understanding the variation in iodine intake of the population via drinking water. The aim of this study was to characterize groundwater with elevated iodine concentrations and to investigate the sources and processes controlling natural iodine speciation and concentration at four study sites in Denmark with postglacial sandy, Quaternary sandy, and Cretaceous limestone aquifers. Analyses included iodide (I−), iodate (IO3 −), total iodine (TI), major ions, and stable H and O isotopes. Dissolved organic iodine (DOI) was calculated by subtracting I− and IO− 3 from TI. A diagram of stable δ18O and δ2H isotopes in Danish groundwater was compiled in order to interpret the groundwater iodine geochemistry. Groundwater had TI concentrations from 5 to 14,500 µg/L. Iodine speciation reflected the prevailing neutral to alkaline and reduced conditions at the investigated sites with domination of I− and DOI correlated with dissolved organic carbon. We found three different explanations for elevated TI concentrations at the four Danish sites: (1) leaching from soil enriched in iodine due to atmospheric deposition and proximity to the sea, (2) influence from the marine origin of the aquifer sediment due to desorption of iodine from iodine-enriched organic matter or minerals, and (3) influence from residual saline water due to upward advective or/and diffusive transport of iodine.

Effects of water-sediment interaction and irrigation practices on iodine enrichment in shallow groundwater

High iodine concentrations in groundwater have caused serious health problems to the local residents in the Datong basin, northern China. To determine the impact of water-sediment interaction and irrigation practices on iodine mobilization in aquifers, isotope (2H, 18O and 87Sr/86Sr) and hydrogeochemical studies were conducted. The results show that groundwater iodine concentrations vary from 14.4 to 2180μg/L, and high iodine groundwater (>150μg/L) mainly occurs in the central area of the Datong basin. Sediment iodine content is between <0.01 and 1.81mg/kg, and the co-occurrence of high iodine and high DOC/TOC concentrations of groundwater and sediment samples in the deeper aquifer indicates that the sediment enriched in iodine and organic matter acts as the main source of groundwater iodine. The 87Sr/86Sr values and groundwater chemistry suggest that aluminosilicate hydrolysis is the dominant process controlling hydrochemical evolution along groundwater flowpath, and the degradation of TOC/iodine-rich sediment mediated by microbes potentially triggers the iodine release from the sediment into groundwater in the discharge area. The vertical stratification of groundwater 18O and 2H isotope reflects the occurrence of a vertical mixing process driven by periodic surface irrigation. The vertical mixing could change the redox potential of shallow groundwater from sub-reducing to oxidizing condition, thereby affecting the iodine mobilization in shallow groundwater. It is postulated that the extra introduction of organic matter and O2/NO3/SO4 could accelerate the microbial activity due to the supplement of high ranking electron acceptors and promote the iodine release from the sediment into shallow groundwater.

Iodine in groundwater of the Guanzhong Basin, China: sources and hydrogeochemical controls on its distribution

Groundwater sampling at 179 sites in the Guanzhong Basin, China, indicated iodine concentrations ranging from 2 to 28,620 μg/L. 7.3 % of the sites have iodine concentrations 300 μg/L and are defined as “iodine excess water.” Sites with low groundwater iodine concentrations are mainly distributed at the edge of a piedmont alluvial–proluvial fan containing bicarbonate-rich water with a low mineral content, near-neutral pH values and low fluorine concentrations. The piedmont fan is characterized by a fast groundwater flow and active leaching of iodine from the sediments. Conversely, high groundwater iodine concentrations are principally located in silty or clayey sedimentary zones having low groundwater flow rates, weakly alkaline to alkaline pH values, and water containing HCO3·SO4, SO4·Cl and Cl·SO4 hydrochemical types. Elevated iodine concentrations in shallow groundwater commonly occur in discharge areas where there is a high rate of solute evaporation; elevated iodine concentrations in deep groundwater are likely attributed to microbial decomposition of organic matter under anaerobic conditions. Processes of iodine enrichment lead to correlations between high iodine and high fluorine contents in shallow groundwater, and between high iodine and high arsenic concentrations in deep groundwater. Moreover, redox processes and active water recycling are important factors for groundwater iodine enrichment.

Factors Controlling Spatial Variation of Iodine Species in Groundwater of the Datong Basin, Northern China

To better understand the distribution of iodine speciation composition and the controlling factors in groundwater from the Datong basin, hydrochemical studies were conducted. Total iodine concentrations in groundwater ranges from 6.2 to 1380μg/L, with the mean value of 243μg/L. Speciation of iodine in groundwater is mainly controlled by redox potential. Under reducing conditions, iodide is the dominant dissolved species, while in sub-oxic and oxic conditions, iodate is the major species, with a lower proportion of iodide. The evident existence of organic iodine in several groundwater samples may be related to anthropogenic activities.

Hydrogeochemistry of high iodine groundwater: a case study at the Datong Basin, northern China

High iodine concentrations in groundwater have seldom been reported and there have been few systematic studies on high iodine groundwater worldwide. To better understand the sources and processes responsible for iodine enrichment in the groundwater of the Datong Basin, the hydrochemical characteristics of groundwater and geochemical features of aquifer sediments were studied. High iodine groundwater mainly occurs in the center of the Datong Basin with iodine concentrations ranging between 3.31 and 1890 μg L(-1). Most samples with iodine concentrations higher than 500 μg L(-1) are from wells with depths between 75 and 120 m. High pH and a reducing environment are favorable for iodine enrichment in the groundwater, with iodide as the dominant species that accounts for 63.2-99.3% of the total iodine. Sediment samples from a borehole specifically drilled for this study contain 0.18-1.46 mg kg(-1) iodine that is moderately correlated with total organic carbon (TOC). The results of sequential extraction experiments show that iodine is mostly bound to iron oxyhydroxides and organic matter in the sediments. The mobilization processes of iodine are proposed to include reductive dissolution of iron oxyhydroxides and transformations among iodide, iodate and organic iodine driven by microbial activities under alkaline and reducing conditions.

Iodine in groundwater of the North China Plain: Spatial patterns and hydrogeochemical processes of enrichment

The North China Plain (NCP), with an area of 139,238km2, has concurrent occurrence of high-iodine (>150μg/L) and low-iodine (<10μg/L) groundwater regions that frequently result in iodine excess or deficiency disorders. The spatial distribution of iodine was delineated based on 6098 groundwater samples obtained through the “National Groundwater Quality Investigation and Assessment Program (2006–2010)” by the China Geological Survey. Of those, 4390 samples were from shallower depths (<100–150m) and 1708 were from deeper depths (>100–150m). In the piedmont alluvial fan and alluvial–pluvial plain along the northern and western margins of the NCP, groundwater iodine concentrations were low at both shallow and deep depths. Extensive areas in the flood plain adjacent to the Yellow River and the Haihe River and in the coastal plain had high-iodine groundwater, although the patterns were more patchy for the shallower depths than for the deeper depths. Cones of groundwater depression in the NCP were extensive due to excessive pumping of groundwater, and in turn, may contribute to complex spatial patterns of iodine distribution in the eastern NCP. Principal component analysis of hydrogeochemistry of 46 shallow and 48 deep groundwater samples (representative of the entire dataset) identified three factors (sea water, carbonate mineral dissolution and decomposition of organic matter) to account for 86.8% variance in 9 hydrogeochemical parameters. Decomposition of organic matter is the leading cause for high-iodine in groundwater, with sea water influence more important in the shallow groundwater than in the deep groundwater.

Geochemistry of iodine-rich groundwater in the Taiyuan Basin of central Shanxi Province, North China

This paper presents the results of studies on the geochemistry of iodine-rich groundwater in the southwest of the Taiyuan Basin, Shanxi Province, North China. A total of 950 water samples were collected from shallow (≤50m), medium-depth (50–200m) and deep (≥200m) wells in the southwestern Taiyuan Basin. Total and inorganic iodine concentrations, including species of iodide and iodate, were determined using inductively coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography- ICP-MS (HPLC-ICP-MS). The results indicate that there are 76.8%, 70.3% and 85.2% of groundwater samples from the above-mentioned three levels, respectively, that exceed the national drinking water standard for iodine (150μg/L), with the highest iodine concentration of up to 4117μg/L, 27 times higher than the standard, tested in shallow groundwater. The main species of iodine in the groundwater is iodide ion with a small proportion of iodate. Organic iodine was detected in about 60% of the water samples with relatively low content. The main factors causing the high iodine concentrations in groundwater include the unique topography, geomorphologic features and aquifer structures in the study area, resulting in hindered movement of groundwater. Furthermore, salinization of surface soil in the low-lying lands intensifies the elevation of iodine concentrations in shallow groundwater. The enrichment of iodine in groundwater is inextricably linked to the geological environment of marine, lacustrine and fluvial sedimentations. The results of this research could provide scientific bases for optimization of water supply scheme in China's iodine excess areas.

Dissolved iodine in rainfall, cloud, stream and groundwater in the Plynlimon area of mid-Wales

Abstract. Iodine concentrations in rainfall, cloud water, throughfall, stemflow, stream water and groundwater are described for the upper River Severn Plynlimon catchments in mid-Wales. Iodine concentrations average 1.55 µg l−1 in rainfall while the corresponding averages of iodine concentrations in cloud water, throughfall and stemflow iodine concentrations are three to eight times higher. For the atmospheric inputs, there are both marine and anthropogenic sources while, for stemflow and throughfall, humic substances may be a dominant component. The average concentrations in the streams and groundwaters vary between 1.00 to 4.22 µg l−1 and 0.57 to 8.51 µg l−1, respectively. The higher averages are for waters associated with gley soils that are high in dissolved organic carbon (DOC). For the streams draining forested catchments, iodine concentrations have increased over time, probably due to wetting up of the soils because of reduction in transpiration as the trees are maturing and felling activities. The increases vary between 0.025±0.003 and 0.044±0.010 µg l−1 per year and are associated partly with an increase in DOC concentration: adjusted for the effect of DOC, the increases range between 0.013±0.003 and 0.023±0.009 µg l−1 per year. For the moorland areas, no such trend is observed but the value is lower. For most of the Plynlimon catchments, a net uptake of iodine of around 40% is lower for streams draining gley soils with even a net export for the smaller streams. Within the streams, iodine concentrations are highly correlated with DOC and there is an annual cycle of iodine and DOC concentration change, with maxima between July and November. For the groundwaters, a loss of iodine and DOC relative to the streams probably reflects within catchment losses in the lower inorganic soils and bedrock areas. However, in one case, groundwater iodine concentrations were relatively high and this coincided with high DOC concentrations.

Geographic variation in groundwater iodine and iodine deficiency in Israel, The West Bank and Gaza.

Iodine deficiency during pregnancy and infancy is the world's most common preventable cause of mental retardation. Previous studies have shown a high incidence of goiter and low groundwater iodine concentrations in northern Israel. We examined the relationship between low groundwater iodine and iodine deficiency in pregnant women and schoolchildren. We measured the urinary iodine excretion of school-children in the West Bank and Gaza and rural and urban pregnant women in Western Galilee (an area known to have low groundwater iodine concentrations). We also measured iodine concentrations in groundwater in various locations in the West Bank and Gaza. Lower urinary iodine excretion was found among pregnant Arab women living in rural Western Galilee (101+/-7 microg iodine/g creatinine). 20% of them excreted <50 microg I/g creatinine. This is relatively less than found among pregnant Jewish women living in cities in the same area (154+/-13 microg I/g creatinine). Low iodine concentrations (<5 microg/l) were found in groundwater in the Nablus, Ramallah, Bethlehem highlands, as compared to normal concentrations in the lowland districts of the West Bank and Gaza. In a cohort of 728 schoolchildren aged 8-10, 10% (range 8-13%) of children from areas of low groundwater iodine had low levels of urinary iodine excretion, as compared to only <5% of those from districts with groundwater iodine concentrations >10 microg/l. Lower concentrations of groundwater iodine are related to low urinary iodine excretion in Israel, the West Bank and Gaza.

Iodine concentrations in groundwater of northern Israel and their relation to the occurrence of goiter

A high incidence of goiter has been reported in the population of the northern Golan Heights in Israel. In the early 1960s, endemic goiter was reported from Upper and Western Galilee and from northwestern Samaria. Assuming that low levels of iodine in water contribute to the etiology of goiter, its concentration was investigated in the main water-sources of northern Israel. In atmospheric precipitation, the I −-content is <2 μg/l, in the tributaries of the river Jordan 2–2.5 μg/l and in Lake Kinneret, 13–15 μg/l. In groundwater, the I −-content fluctuates between<5 μg/l in the upper flow course and 10 μg/l downflow. The very low concentrations are explained by the low level of iodine in local atmospheric precipitation, by the filtering-effect of terra-rossa and rendzina soils, and by the rapid flow of groundwaters through thoroughly leached pipe-like karstic cavities which preclude enrichment of groundwaters in iodine. During the last decade, there have been no reports of endemic goiter in the northern part of the country. This is attributed to the establishment of integrated regional water-supply systems and to the operation of the National Water Carrier Network distributing water with an I −-content of 14 μg/l.