Se In Groundwater Research Articles

Pollution and Ecological Risk Assessment of Metal Elements in Groundwater in the Ibinur Lake Basin of NW China

Groundwater pollution by metal elements is a serious issue due to its probable risks to the ecosystem and human health. In the present study, 75 groundwater samples were collected from the Ibinur Lake Basin (ILB) of NW China. The contents of As, Se, Pb, Cu, Cr(Ⅵ), Zn, Mn, and Cd were determined. The levels, pollution degrees, and potential ecological risks of metals in groundwater were systematically analyzed for the first time in this area. The potential sources of metals were also discussed. It was observed that the mean contents of metals in groundwater in the ILB were lower than the Class III thresholds of the Standard for Groundwater Quality of China (GB/T 14848–2017), whereas the maximum contents of As, Se, Pb, Cr(Ⅵ), and Mn exceeded the Class III thresholds values. The pollution index of each metal and the Nemerow comprehensive index (NPI) caused by the overall pollution by all these metals in groundwater showed the pollution-free level. The single and comprehensive potential ecological risk index of analyzed metals in groundwater showed a relatively low level of potential ecological risk. Additionally, spatial distribution patterns of contents, pollution levels, and ecological risks of metals in groundwater in the ILB were found to be substantially heterogeneous. Furthermore, As and Se in groundwater originated from anthropogenic sources such as agriculture and mining, whereas Mn mainly originated from natural factors, and Pb, Cu, Cr(Ⅵ), Zn, and Cd were correlated with both natural and anthropogenic sources. Overall, As was identified as the main pollution factor, while As and Se were identified as the main ecological risk factors in the groundwater in the ILB. These results can provide important information for groundwater management in the ILB and will guide authorities in taking the necessary measures to ensure the safety of groundwater supply in the northwestern arid regions of China.

Chemical association of copper and selenium in coals of Sindh by time saving single step strategy and their impact on groundwater.

The aim of the present study is to estimate the different chemical fractionations of copper (Cu) and selenium (Se) in coal samples of different coal mining areas. The Cu and Se bound to various chemical fractions of coal collected from two mining fields of Sindh, Pakistan, have been determined by BCR sequential extraction scheme (BCR-SES). The long duration of the BCR sequential scheme (51h) was reduced by a time-saving shaking device (ultrasonic bath) termed as ultrasonic-assisted extraction (USE) depending on the same operating conditions and extracting solutions used for BCR sequential extraction scheme. The both trace elements were determined in aquifer water, sampled from different depth of both coal mining fields. In addition, the groundwater of dug well in the vicinity of coal mining areas were also analyzed for Cu and Se using reported extraction methodologies. The partitioning of Cu and Se bound with different chemical fractions of coal was successfully made by proposed USE, within 2h as compared to long duration of BCR-SES (51h). The Cu and Se concentrations in acid-soluble fractions of coal samples were > 10%, enhanced by USE extraction procedure than those values gained via BCR-SES (p < 0.01). About 67 to 69% of Cu were found in the first three fractions, whereas their remaining amount corresponding to 31 to 33%, respectively bound with crystalline/residual fraction, while up to 66.1 to 71.1% of total Se contents extracted in three extractable phases, followed up to 28.9 to 33.8% of it was bound with residual phase. The concentrations of Cu and Se in groundwater of different aquifers were found in decreasing order as AQ1 > AQII > AQIII; the same trend was observed for two aquifers of Lakhra coal mining, whereas the groundwater samples have two to three folds higher levels of Se than WHO limit. The Cu levels in water samples were significantly lower than the recommended limit of WHO for drinking water (p < 0.01).

Mapping salinization and trace element abundance (including As and other metalloids) in the groundwater of north-central Mexico using a double-clustering approach

This study aimed to determine the reliability of the double-clustering method to understand the spatial association and distribution of major and minor constituents in the groundwater of an arid endorheic basin in central Mexico (Comarca Lagunera Region). The results of the double-clustering approach were compared with well-known spatial statistics such as spatial autocorrelations (Moran index) and the local indicator of spatial association (LISA). Fifty-five groundwater samples were collected from diverse wells within the basin, and the major ions, metalloids, and trace elements were determined. Overall, the double-clustering analysis was an effective tool for identifying lithogenic/anthropogenic processes occurring in the basin and for establishing zones with high or low abundance of major ions and trace elements, even where processes affecting the groundwater quality were spatially dispersed. Although 89% of the samples showed As higher than the threshold value of 10 μg/L proposed by the World Health Organization for drinking water, both the double-clustering and LISA analyses identified As hotspots in the alluvial aquifer, where the extraction of deeper and warmer groundwater might promote the concomitant release of the metalloids As, Sb, and Ge and the trace elements V and W. Similarly, both statistical analyses identified mountainous sectors where the weathering of silicates and carbonates plays a key role in the abundance of HCO3−, Ga, and Ba. However, the LISA analysis failed to identify hotspots of carbonate-derived elements such as Ca, Mg, Sr, and U and silicate-derived elements such as Ca, Mg, K, Sr, Rb, Cs, Pb, Ni, and Y. Otherwise, the double-clustering analysis clearly defined high- and low-concentration zones for all these elements in the study region. Unlike the LISA analysis, the double-clustering approach was also successful in determining alluvial areas with high concentrations of Si and Ti and areas where the concentrations of Na, Cl−, SO42−, NO3−, B, Li, Cu, Re, and Se in groundwater were elevated, increasing the groundwater salinity. Overall, this study demonstrated that the double-clustering is an easy-to-apply approach, capable of visualizing disperse zones where specific anthropogenic processes may threaten the groundwater quality.

Groundwater Selenium Level and its Enrichment Dynamics in Seawater Intrusion Area along the Northern Coastal Zones of Shandong Province, China

The variation of groundwater properties caused by seawater intrusion, such as OH–, TDS, $${\text{SO}}_{4}^{{2 - }},$$ can potentially affect the groundwater Se levels. But there are no researches detailing the mechanism of groundwater selenium characteristics in seawater intrusion areas along coastal zones. Buzhuang town has been selected for study and groundwater is sampled to discuss the behavior of groundwater selenium with the intrusion of seawater. The groundwater Se levels range from 1.43 to 15.60 µg/L, with an average of 6.23 µg/L. All are within the limit of 10 µg/L except Wanglu village, but the local groundwater Se levels in 8 villages exceed the chronic criterion of 5 µg/L, and the Se levels in local groundwater are higher than those in the supplied water which has a non-seawater source. The groundwater Se levels have been shown to be elevated by seawater intrusion. The groundwater Se levels are positively correlated with Cl–, TDS, Br–, Na+, Mg2+, $${\text{SO}}_{4}^{{2 - }},$$ Ca2+ and Fe and negatively correlated with pH. Ion competition effects and the Na-Mg-sulfate minerals play an important role in the adsorption and desorption for $${\text{SeO}}_{3}^{{2 - }}$$ and $${\text{SeO}}_{4}^{{2 - }}$$ , which are the important dynamic species for groundwater selenium enrichment. However, Ca and Fe ions have less contribution to groundwater Se variation because of the lower affinity for $${\text{SeO}}_{3}^{{2 - }}$$ and $${\text{SeO}}_{4}^{{2 - }}$$ and lesser content in groundwater of seawater intrusion areas.

Selenium and drinking water quality indicators in Mongolia.

Mongolia is characterized by restricted sources of drinking water and intensive water pollution due to high rates of urbanization, mining industry development, enormous amount of livestock, and ever-growing attempts in domestic production of cereals and vegetables. Among others, Se is the least studied element in Mongolian water resources. Based on fluorimetric method of analysis, the first results on Se levels in drinking water of five aimags, Ulaanbaatar, and Erdenet were obtained. Uneven distribution of Se in Mongolia was manifested, the highest Se concentrations being typical for the southern resources (up to 18,600μg/L) and the lowest, for the Northern ones (up to 0.022μg/L). ICP-MS data of Al, As, B, Ca, Cd, Co, Cr, Cu, Fe, Hg, I, K, Li, Mg, Mn, Na, Ni, P, Pb, Si, Sn, Sr, V, and Zn contents indicate poly-microelementosis existence in the South of Mongolia (Dorno-Gobi aimag) where ground water is characterized by elevated levels of As and extremely high levels of Se, Li, Na, F, Cl, B, and nitrates ions, exceeding maximum permissible levels by 1.86; 4.3; 3.1; 3.1; 2.7; 3.4; and 1.8 times respectively. Toxic concentrations of Se in groundwater of Dorno-Gobi aimag contradict with the published low human serum Se and low content of the element in horseflesh that suggests the possible effect of the above pollutants on Se bioavailability. Revealed phenomenon and mosaic distribution of heavy metals in areas with high and low Se content in water resources indicate the need of direct search for Se and other pollutant transfer in food chain in various ecological loading conditions, creation of a map of Se distribution in water resources of other Mongolian regions, and large-scale evaluation of the human poly-elemental status.

Heavy metal(loid)s and organic contaminants in groundwater in the Pearl River Delta that has undergone three decades of urbanization and industrialization: Distributions, sources, and driving forces

Urbanization and industrialization have increased groundwater resource demands, and may drive the change of heavy metal(loid)s and organic chemicals in groundwater in the Pearl River Delta (PRD), southern China. Thus, a comprehensive understanding of the distributions, sources, and driving forces of heavy metal(loid)s and organic chemicals in groundwater in the PRD is vital for water resource management in this region. In this study, eight heavy metal(loid)s and fifty-five organic chemicals in groundwater across the PRD were investigated. The results show that undrinkable groundwater related to heavy metal(loid)s was mainly due to high concentrations of Fe (19.3%) and As (6.8%). Eighteen organic contaminants were detected in groundwater in the PRD, where the most frequently detected organic contaminant was naphthalene, and its detection rate was 2.51%. In 5.3% of all groundwater samples, one or more organic contaminants were found. All detected organic contaminants, except ones without allowable limits, in groundwater were at concentrations below allowable limits of China. The mean concentrations of heavy metal(loid)s in granular aquifers were higher than those in fissured and karst aquifers, especially for Fe and As. Except Se, the mean concentrations of other heavy metal(loid)s and the frequency of detection of organic contaminants in groundwater in urbanized and peri-urban areas were higher than those in non-urbanized areas, especially for Hg, Co, and organic contaminants. Fe, As, and Se in groundwater mainly originated from the release of Fe/As/Se rich sediments. The former two were driven by reduction reactions, while the latter was driven by oxidation resulting from the infiltration of NO3−. In contrast, other five heavy metal(loid)s and organic contaminants in groundwater mainly originated from the anthropogenic sources, such as the infiltration of industrial sewage. It is evident that urbanization and industrialization are two powerful driving forces for heavy metal(loid)s and organic contaminants in groundwater in the PRD.

Land Use Modification and Changing Redox Conditions Releases Selenium and Sulfur from Historic Marsh Sediments

AbstractSan Diego Creek Watershed forms the southern end of the Coastal Plain that covers much of Los Angeles County and Orange County, California. Prior to 1900, the central part of the watershed was marshland, and the edges of the watershed were used for grazing sheep and cattle. After 1900, cattle and sheep grazing were displaced by irrigated agriculture. Drainage ditches and channels were constructed to drain the marshes to “reclaim” the land for agriculture. Today, the drainage ditches and channels still exist in the watershed, which has undergone massive urban growth. Shallow groundwater discharges into these channels and ditches, which then flows as surface water, into Upper Newport Bay a thriving ecological habitat. Surface flows in these channels usually exceed the United States Environmental Protection Agency (EPA) aquatic water quality criterion for selenium (Se) of 3.1 μg/L (lotic) for protection of aquatic life. Selenium in surface flows is caused by groundwater inflows. The highest concentrations of Se in shallow groundwater in the watershed coincide with the marshland area that was displaced by agriculture. Concentrations of Se in shallow groundwater beneath the former marsh area often exceed 25 μg/L and are as high as 478 μg/L. In areas where marshes were absent, concentrations of Se in groundwater are usually less than 25 μg/L. In the marsh, Se accumulated due to chemically reducing conditions in the organic‐rich marshland soils that caused it to precipitate as elemental Se(0) and metal selenides, Se(−II). We hypothesize that the elevated concentrations of Se in groundwater where the marshes once existed are a direct result of the destruction of the marsh. Today, oxidizing groundwater flows through the soils where the marshes once existed, remobilizing Se as selenate, a water soluble and oxidized form of Se(+VI) that is highly mobile in aquifer systems.

Institutional Constraints on Cost‐Effective Water Management: Selenium Contamination in Colorado's Lower Arkansas River Valley

AbstractGround and surface water selenium (Se) contamination is problematic throughout the world, leading to harmful impacts on aquatic life, wildlife, livestock, and humans. A groundwater reactive transport model was applied to a regional‐scale irrigated groundwater system in the Lower Arkansas River Basin in southeastern Colorado to identify management practices that remediate Se contamination. The system has levels of surface water and groundwater Se concentrations exceeding the respective chronic standard and guidelines. We evaluate potential solutions by combining the transport model with an assessment of the cost to employ those practices. We use a framework common in economics and engineering fields alike, the Pareto frontier, to show the impact of four different best management practices on the tradeoffs between Se and cost objectives. We then extend that analysis to include institutional constraints that affect the economic feasibility associated with each practice. Results indicate that although water‐reducing strategies have the greatest impact on Se, they are the hardest for farmers to implement given constraints common to western water rights institutions. Therefore, our analysis shows that estimating economic and environmental tradeoffs, as is typically done with a Pareto frontier, will not provide an accurate picture of choices available to farmers where institutional constraints should also be considered.

Controls on selenium distribution and mobilization in an irrigated shallow groundwater system underlain by Mancos Shale, Uncompahgre River Basin, Colorado, USA

Elevated selenium (Se) concentrations in surface water and groundwater have become a concern in areas of the Western United States due to the deleterious effects of Se on aquatic ecosystems. Elevated Se concentrations are most prevalent in irrigated alluvial valleys underlain by Se-bearing marine shales where Se can be leached from geologic materials into the shallow groundwater and surface water systems. This study presents groundwater chemistry and solid-phase geochemical data from the Uncompahgre River Basin in Western Colorado, an irrigated alluvial landscape underlain by Se-rich Cretaceous marine shale. We analyzed Se species, major and trace elements, and stable nitrogen and oxygen isotopes of nitrate in groundwater and aquifer sediments to examine processes governing selenium release and transport in the shallow groundwater system. Groundwater Se concentrations ranged from below detection limit (<0.5μgL−1) to 4070μgL−1, and primarily are controlled by high groundwater nitrate concentrations that maintain oxidizing conditions in the aquifer despite low dissolved oxygen concentrations. High nitrate concentrations in non-irrigated soils and nitrate isotopes indicate nitrate is largely derived from natural sources in the Mancos Shale and alluvial material. Thus, in contrast to areas that receive substantial NO3 inputs through inorganic fertilizer application, Se mitigation efforts that involve limiting NO3 application might have little impact on groundwater Se concentrations in the study area. Soluble salts are the primary source of Se to the groundwater system in the study area at-present, but they constitute a small percentage of the total Se content of core material. Sequential extraction results indicate insoluble Se is likely composed of reduced Se in recalcitrant organic matter or discrete selenide phases. Oxidation of reduced Se species that constitute the majority of the Se pool in the study area could be a potential source of Se in the future as soluble salts are progressively depleted.

Contaminants in sediment, food-chain biota, and bird eggs from the Newport Bay watershed, Orange County, California.

Groundwater-related discharges in the San Diego Creek/Newport Bay watershed in Orange County, California have the potential to adversely affect the surface waters within the watershed and would likely not comply with the established total maximum daily loads (TMDLs) for the watershed. In 2004 and 2005, we studied the concentrations of contaminants of TMDL concern (particularly selenium [Se]) in birds that are at risk of exposure to contaminated food items because they feed and nest in the Newport Bay watershed. Most bioaccumulation is from elevated Se in groundwater downstream of a historic terminal swamp. Se bioaccumulation was observed in all biota tested, and DDE was found in fish and bird egg samples. Effects of contaminants on fish and birds are inconclusive due to the management disturbances in the watershed (e.g., flood control) and lack of bird nesting habitat. Although a significant relationship was observed between DDE concentrations and eggshell thinning in American avocet (Recurvirostra americana) eggs, the shell thinning in avocet and other species examined was not enough to result in hatching failure. Further focused monitoring efforts will be needed to characterize the exposure and risk levels.

Spatial variability of soil selenium as affected by geologic and pedogenic processes and its effect on ecosystem and human health

Selenium (Se) deficiency and excess in agricultural ecosystems are related to many human health problems through the food chain and depend on the spatial variability and bioavailability of Se in soils. This paper examines the spatial variability of Se in soils as affected by geologic and pedogenic processes and its effects on rice grains, groundwater, and human health using Rugao County, Jiangsu Province, an agricultural area in Yangtze River Delta Region, which has a high level of nonagenarians, as a case study. The results showed that total soil Se (T-Se) concentration in the study area (average 0.13 ± 0.02 mg kg-1, n = 203) was close to the Se Clark value, the Se mean concentration in earth crust, and had narrow spatial variation as a result of consistent geological processes. As a fraction of the potential bio-available Se in ecosystems, soil water soluble Se (WS-Se) (average 2.27 ± 1.09 μg kg-1, n = 203) had wide spatial variation. The higher concentrations of WS-Se were spatially distributed on loamy and highly weathered soils in the east and north of the county. Spatial heterogeneity of WS-Se was primarily due to changes in soil physicochemical properties caused by pedogenic processes related to cultivation. Average Se concentration in the rice grains and groundwater were 97 ± 69 μg kg-1 (n = 93) and 0.19 ± 0.21 μg L-1 (n = 95), respectively. Similar spatial variability and correlation between WS-Se and rice Se, groundwater Se, and longevity ratio (an index of nonagenarians per 100,000 inhabitants), were found, indicating that the soluble fractions of Se in soils play an important role in biogeochemical cycling in the ecosystem and might be an important indicator of Se deficiency or excess in soils. Thorough small-scale surveys of element availability in the soil should be emphasized where geologic settings are simple but pedogenic processes are complex due to intensive human activities. So WS-Se in soils was advised as a better indicator for Se environmental effect than T-Se, especially when dealing with simple geologic settings and complex pedogenic processes on a small scale.

Comparative study on sorption of individual and coupling cesium and selenium on mudrock

This study focused on sorption mechanism of Cs and Se in mudrock by batch techniques. Batch kinetics tests have been conducted with carriers 10−4M CsCl and SeO2 by using individual and coupling radiotracers of 137Cs and 75Se. The distribution coefficients (Kd) of Cs in synthetic groundwater (GW) and seawater (SW) showed that there is no interference between individual and coupling value (13 and 6 ml/g). Moreover, individual and coupling Kd) (80 and 40 ml/g) of Se in GW and SW are in agreement with Cs. It is quite clear that the sorption mechanisms of Cs and Se on mudrock are independent and different by using radiotracer’s technique.

Inorganic selenium speciation in groundwaters by solid phase extraction on Dowex 1X2

A Dowex 1X2 resin separation technique followed by analysis with atomic absorption spectroscopy was evaluated for the study of inorganic selenium speciation in groundwaters. After Se(IV) and Se(VI) were retained on the resin column, Se(IV) and Se(VI) were eluted out by 0.1 and 1 M nitric acid solutions. The method detection limit was 5.6 ng/L for both Se(IV) and Se(VI). Analysis of synthetic solutions consistently yielded more than 90% recovery of these two selenium forms with negligible cross-contamination. The results of spiked well waters show that this method can be applied at ultra-trace level of Se in groundwater and the interference of chloride ion can be neglected. Water samples collected from the monitoring wells in the Science-based Industrial Park, Hsin-Chu, Taiwan, were analyzed. Average dissolved selenium concentrations were 32.1 ± 17.6 ng/L. The proportion of Se(VI) to the total dissolved selenium ranged from 47.6 to 61.2% and an average of 53.8% in water samples analyzed.

Selenium in soils and groundwater of Moldova

High levels of selenium (Se) were detected in the shallow groundwaters in the rural Carpineni region of Moldova. Selenium concentrations in groundwater exceed the maximum allowable limit by 1.5–24 times (range: 15.0–240.0 g/L). To identify the source of Se in the groundwater, we analyzed the Se content of groundwater, soils, aquifer strata, and stream sediments. Samples were taken from a variety of locations, each of different land use including both rural agricultural regions and urban areas. Neogene middle Sarmatian clays in the Carpineni region contain both elemental and residual Se. Groundwaters in Carpineni are in intimate contact with these easily weathered units, and weathering of aquifer strata leads to increased Se in rural Moldovan groundwaters. Concentrations of soluble Se are low in soils from Carpineni, and Se remobilization in these soils caused by infiltration is a negligible source of Se in the groundwater. Anthropogenic Se sources also occur in rural Moldova and may contribute to Se in groundwater. Sediments from ponds holding waters used to cool the Cuciurgan Power Station, a former coal-burning plant, contained high Se concentrations. Seepage from these ponds, as well as from similar ponds in Carpineni, may occur, although the contribution to the Se budget of the groundwaters may be minor. In the urban regions of Chisinau City, higher soil concentrations of soluble and ligand-exchangeable Se and the low Se concentrations in the Quaternary loess aquifer strata suggest that the Se in groundwaters in Chisinau are derived from anthropogenic sources, including coal burning and domestic waste discharge with Se mobilized from soils during rain events.

Selenium Behavior in Open Bulk Precipitation, Soil Solution and Groundwater in Alluvial Fan Area in Tsukui, Central Japan

A monitoring study was carried out in an alluvial fan area in Tsukui, Central Japan during the study period of 1999–2003, in order to explain selenium (Se) behaviors in ecosystem combined with air, soil and groundwater. Monthly Se concentrations in open bulk precipitation (rainfall+aerosol, gaseous deposition and etc.), soil solution (collected by porous ceramic-cup) and groundwater ranged from 0.1 to 1.4 μg L−1 (volume-weighted average: 0.34 μg L−1), 0.21 to 1.0 μg L−1 (0.48 μg L−1) and 1.6 to 2.4 μg L−1 (2.2 μg L−1), respectively. Se concentration in open bulk precipitation was negatively correlated with the rainfall amount. Se concentration in soil solution significantly increased with DOC concentration in soil solution. Besides, despite atmospheric Se input and rainfall to the grassland study area, Se concentration in soil solution and groundwater received no significant effect from the rainfall amount, pH, Se, DOC, SO42−, NO3− and EC in rainfall. Even though Se concentrations in groundwater were significantly correlated with soil solution volume, Se, DOC and NO3− and groundwater level, the result of multiple regression analyses (MRA) indicated that the groundwater Se was negatively influenced by groundwater level, which depended on groundwater recharge. Se was transported into the groundwater through the groundwater recharge that largely increased in this alluvial fan study area after heavy rain.

Estimation Of Selenium Concentration In Shallow Groundwater In Alluvial Fan Area In Tsukui, Central Japan

Total selenium (Se) and water-soluble Se in soil, and Se in a shallow groundwater were hydrogeochemically researched in an alluvial fan area in Tsukui, Central Japan. The water-soluble Se was estimated at average level of 2.6 +/- 1.2 microg Se kg(-1) dry soil (+/- SD, n = 25), showing less than 1% of the total Se (349-508 microg Se kg(-1) dry soil) in soil. The monthly Se concentration in groundwater was average 2.2 microg,L(-1), ranging 1.6-2.4 microg,L(-1) during 2001-2003. The Se in groundwater significantly decreased with increasing groundwater level after rainfall. This result indicated that Se-bearing water percolated with relatively low Se concentration through the soil layer. According to our prediction model of linear regression curve on the observation data, Se concentration in the groundwater was estimated to be increasing with the very low rate of 4.35 x 10(-3) microg Se L(-1),yr(-1). The hydrogeochemical research and the result of the prediction model showed that any explosive increase of Se will hardly occur in this groundwater without an anthropogenic Se contamination.

Selenium Remobilization Due To Destruction Of Wetlands In The Irvine Subbasin, Orange County, California

The Irvine Subbasin forms part of the coastal edge of Orange County, California. Prior to 1900, the central part of the Subbasin was marshland. After 1900, drainage ditches and channels were constructed to drain the marshes for agriculture. Today, the drainage ditches still exist in the Irvine Subbasin, which is undergoing massive urban growth. Shallow groundwater discharges into these channels, and the surface water eventually flows into Upper Newport Bay, a thriving habitat. Surface flows in these channels usually exceed the U.S. Environmental Protection Agency chronic criterion for selenium (Se) of 5 ppb for protection of aquatic life. Se in surface flows is caused by groundwater inflows. The highest concentrations of Se in shallow groundwater in the Irvine Subbasin coincide with the marshland areas that were displaced by agriculture. Concentrations of Se in groundwater in the former marsh areas often exceed 50 ppb and are as high as 200 ppb. In areas where marshes were absent, concentrations of Se in groundwater are usually 10 ppb. The marshes are presumed to have been oxygen-deficient, following modern analogs in undisturbed habitats along the California coast. In oxygen-deficient marshlands, Se is usually in the form of selenite or elemental Se, two relatively insoluble forms of Se that collect in the sediment at the bottom of the marsh. We hypothesize that the elevated concentrations of Se in groundwater where the marshes once existed are a direct result of the destruction of the marsh. Today, oxygenated groundwaters flow through the soils where the marshes once existed, remobilizing Se as selenate, a water-soluble form of Se that is highly mobile in aquifer systems.

The geochemistry of selenium in groundwaters in Finland

The background level, seasonal variation, speciation, and geographical distribution of selenium (Se) were studied in dug and drilled wells and in natural groundwaters in Finland. The total Se concentration of well water samples (n = 256) ranged from 4.1 to 2720 ng/l, with a median of 68.4 ng/l. The median Se concentration of groundwater from locations in natural surroundings was 51.5 ng/l (n = 41) and 50.5 ng/l (n = 39) in 1989 and 1990, respectively. The season had only a minor effect on both well and groundwater Se concentrations. Selenate was the most abundant species in groundwater. Locally, high concentrations of groundwater Se may originate from bedrock. The proportions of both selenite and Se associated with humic substances were less than 8 and 15%, respectively. The median Se concentration of 37 infiltration water samples was 28.6 ng/l (range 6.1–137 ng/l). The annual net deposition of Se from precipitation into soils was estimated to be 0.49 g/ha in the southern and 0.33 g/ha in the northern parts of Finland. Se from precipitation had no impact on groundwater Se. The effect of agricultural activities including Se supplemented fertilization on the Se concentration of groundwater in cultivated areas could not be demonstrated.

Selenite and Selenate Determination in Surface Coal Mine Backfill Ground Water

A majority of Wyoming`s public water supplies are based on ground water resources. It is necessary, therefore, to protect these resources from contamination by pollutants (e.g., selenium), which can be harmful to human health. Dissolved selenium (Se) in ground water may contain different species, including selenite (SeO{sup 2-}{sub 3}), selenate (SeO{sup 2-}{sub 4}), organic Se, and Se ion pairs (e.g., MgSeO{sup {degrees}}{sub 4}, CaSeO{sup {degrees}}{sub 4}). For an understanding of the toxicity potential of Se, it is necessary to know the concentrations of SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4}, as well as total Se content in ground water. The hydride generation atomic absorption spectrometry (HGAAS) method of Se analysis requires oxidation of organic matter, which destroys the natural distribution of Se. Ion chromatography (IC) can determine SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} concentrations, but other common anions (e.g., SO{sup 2-}{sub 4}) will interfere with SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} measurements. The objective of this study was to determine SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} concentrations to evaluate the chemical speciation of Se in ground water. Both SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} from ground water samples were adsorbed onto copper oxide (Cu) at pHmore » 5.5 and subsequently desorbed with NaOH solution at pH 12.5. Extracted SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} were determined using HGAAS and IC. From the SeO{sup 2-}{sub 3} and SeO{sup 2-}{sub 4} measurements, Se speciation in ground water was calculated. Results showed that dissolved Se concentrations in ground water ranged from 22 to 151 {mu}g/L. These results also show that mobility of dissolved Se will depend on the chemical form in which Se is present in the ground water.« less