Soil Se Concentrations Research Articles

Toxic or beneficial? What is the role of food‐relevant selenium species selenoneine?

Toxic or beneficial? What is the role of food‐relevant selenium species selenoneine?

Effects of microorganisms on soil selenium and its uptake by pak choi in selenium-enriched lateritic red soil

Data on selenium (Se) transformation, specifically the mineralization or activation of Se bound by microorganisms in natural Se-enriched soil, is limited. Therefore, this study investigates the effects of microorganisms on Se availability of Se-enriched lateritic red soil and Se uptake by pak choi. Following the incubation of Stenotrophomonas maltophilia S1 and arbuscular mycorrhizal (AM) fungi agent, the available Se content of soils increased from 35 to 66.69–117.04 μg/kg, corresponding to an increase of 90.50–234.40%. The Se bioconcentration and translocation factors in pak choi increased after adding the AM fungi agent and strain S1. The soil acid phosphatase activity, and pak choi root length, surface area, and diameter also increased. Moreover, the soil acid phosphatase activity showed a significant positive correlation with soil available Se and phosphorus content (p < 0.01). Overall, the AM fungi agent and strain S1 increased Se bioavailability by enhancing soil acid phosphatase and promoting root activity, ultimately increasing pak choi’s ability to absorb available Se.

Impact of selenium biofortification on production characteristics of forages grown following standard management practices in Oregon.

Low selenium (Se) concentrations in soils and plants pose a health risk for ruminants consuming locally-grown forages. Previous studies have shown that Se concentrations in forages can be increased using soil-applied selenate amendments. However, the effects of foliar selenate amendments applied with traditional nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizers on forage yields, and nutrient contents, and agronomic efficiencies are unknown. Using a split plot design, we determined the effects of springtime sodium selenate foliar amendment rates (0, 45, and 90 g Se ha-1) and NPKS application (none, NPK for grasses/PK for alfalfa, and NPKS/PKS fertilization at amounts adapted to meet local forage and soil requirements) on forage growth and N, S, and Se concentrations, yields, and agronomic efficiencies. This 2-year study was conducted across Oregon on four representative forage fields: orchardgrass (Dactylis glomerata L.) in Terrebonne (central Oregon), grass-clover mixture in Roseburg (southwestern Oregon), and both grass mixture and alfalfa (Medicago sativa L.) fields in Union (eastern Oregon). Grasses grew poorly and were low in N content without NPK fertilization. Fertilization with NPK/PK promoted forage growth, increased forage N concentrations, and had to be co-applied with S when plant available S was low. Without Se amendment, forage Se concentrations were low and further decreased with NPKS/PKS fertilization. Selenate amendment linearly increased forage Se concentration without adversely affecting forage yields, N and S concentrations, or N and S agronomic efficiencies. Importantly, S fertilization did not interfere with Se uptake in Se amended plots. In conclusion, co-application of NPKS/PKS fertilizers and foliar sodium selenate in springtime is an effective strategy to increase forage total Se concentrations, while maintaining optimal growth and quality of Oregon forages.

The Controlling Factors of Soil Selenium Content in a Selenium-Deficient Area in Southwest China

Selenium (Se) is a beneficial microelement for humans, and its varying abundances and shortages have attracted widespread concern. The accumulation process of soil Se is quite complicated, being controlled by multiple factors. However, the influence mechanism of soil properties, climate, and topographic conditions on Se distribution is still unclear in Se-deficient areas. For this study, we collected 2804 samples from cropland soil to assess the levels of Se and the factors that influence those levels in Se-deficient areas of southwestern China. The Se content in this area (0.17 mg/kg) was less than the mean value of China as a whole (0.29 mg/kg). Moran’s I index and a random forest (RF) model showed that higher Se levels were mostly observed in the southern and northern sections of the area we studied. The RF model had excellent performance in predicting soil Se content, with an accuracy of 64%. The use of Shapley additive explanations indicated that soil organic matter (SOM) and mean annual precipitation (MAP) were the critical factors determining Se distribution. The areas with high SOM and MAP showed high Se levels. The information obtained from this work can provide guidance for agricultural planning in Se-deficient areas.

Land-Use Types Regulate Se:Cd Ratios of Natural Seleniferous Soil Derived from Different Parent Materials in Subtropical Hilly Areas

As natural selenium (Se)-rich soil in China is generally characterized by a high geological background of cadmium (Cd), the safe utilization of such seleniferous soil remains a challenge. The accumulating evidence shows that the threshold value of the Se:Cd ratio is a determinant of regulating Cd accumulation in plants. However, the factors modulating the soil’s Se:Cd ratio in selenium-enriched regions are not well understood. Here, a comprehensive study aimed at quantitatively analyzing the effects of land-use types, parent-material types, and soil properties on the distribution and influencing factors of Se, Cd, and the Se:Cd ratios. According to land use and parent-material types, 77 soil samples were collected in Yuanzhou District, a typical naturally seleniferous area in the subtropical hilly area. The results suggested that, compared with quaternary red clays (qrc), the Se content of soils derived from river and lake sediments (rls) and weathered acidic crystalline rocks (wacr) decreased by 5.81%–19.75%, while the weathered quartzite (wq)-derived soils was increased significantly. The soil Cd content in an orchard was significantly reduced compared with that in a paddy field. A redundancy analysis (RDA) revealed that SOM, Total K, and Total P significantly affected the changes in Se and Cd contents. In addition, the land-use type had the most significant effect on the Se:Cd ratio, with a regression coefficient of −0.6999 analyzed by the binary logistic regression model (p &lt; 0.05). Furthermore, pH and Total K were the critical soil properties in controlling the Se:Cd ratio. The study indicated that the Se:Cd ratio in natural selenium-rich soil was mainly regulated by land-use types. Therefore, it is a feasible measure to regulate the Se:Cd ratio by using agronomic practices, mainly regulating soil pH, for the safe utilization of selenium-rich soil with a high Cd background.

Differences in selenium concentration and bioavailability between paddy and dryland soils of China: A study based on literature collection and field sampling.

Lack systematic understanding of differences in environmental behavior of selenium between paddy and dryland soils affects Se biofortification and leads to human Se-related health risks. Therefore, this study investigated differences in Se concentration and bioavailability between paddy and dryland soils using data collected from literatures and field sampling. Our analysis showed paddy soil Se concentration in Se-rich area of China was significantly lower than that in dryland soil. Selenium biological concentration factor of rice grain (BCFgrain) in Se-rich area was lower than that in non-Se-rich area attributed to higher percentage of selenite in available Se. Concentration and percentage of available Se were in dryland soil lower than those in paddy soil and this affected BCFgrain of maize, whereas BCFgrain of rice was further influenced by its Se transport capacity. The ranges of Se concentration in Se-rich paddy (0.14-3.63mgkg-1) and dryland (0.45-1.17mgkg-1) soils were derived using a linear regression model. The current soil Se concentration evaluation standard was only suitable for dryland but overestimated Se-deficiency and Se-toxicity levels in paddy field. The present study provides theoretical foundations for understanding Se concentrations and bioavailability in soils and selecting efficient and safe approach on cultivated land use.

Distribution and attribute analysis of soil selenium in Hebei Province, China

From 2004 to 2018, c. 73% of the land area in Hebei Province was surveyed by a 1:250 000 land quality geochemical survey of the National Geochemistry Survey of Land Quality. Based on the topsoil (0–20 cm) datasets (50 724 analysis samples) and attribute analysis of the key area with a semivariance function model, geographic detector model and random forest model, the content and spatial distribution of soil selenium (Se) in Hebei Province and the influencing factors of the distribution of Se in the Shijiazhuang–Xingtai–Handan area were obtained. The soil Se content in Hebei Province is low, ranging from 0.02 to 3.23 mg kg –1 , with an average of 0.20 mg kg –1 . The spatial distribution of soil Se was heterogeneous, and the marginal Se (0.125–0.175 mg kg –1 ) area and the sufficient Se (0.175–0.40 mg kg –1 ) area were widely distributed, but the acreage of the Se-rich (0.40–3.0 mg kg –1 ) area was very limited, accounting for only 2.43% of the total survey area. However, the Shijiazhuang–Xingtai–Handan area was a significant Se enrichment area. The spatial distribution of Se in this area was restricted by natural and socioeconomic factors. Soil organic matter was the most influential factor and showed good coordination with Se. Coal burning superimposed on natural factors promotes the spatial differentiation of soil Se to a certain extent.

Characteristics of Soil Selenium Enrichment And Its Effects on the Aboveground Parts Of Abelmoschus Manihot (L.) Medic

Pot experiments were carried out to study characteristics of soil selenium (Se) enrichment and its influence on Chinese medicinal plant Abelmoschus manihot, and selenium contents in aboveground parts of A. manihot under conditions of natural Se-rich, low soils and exogenous Se addition were analyzed. Results indicated that contents of total Se and various Se fractions of natural Se-rich soil were significantly higher than that of Se-low soil (P &lt; 0.05), and Se content in aboveground parts of A. manihot grown in natural Serich soil was significantly higher than that in natural Se-low soil (P &lt; 0.05). The Se content in aboveground parts of A. manihot increased with the increase of soil total Se content, soil pH and contents of various Se fractions, showing significant tolerance to high Se. Moreover, it was initially found that A. manihot could effectively absorb soil Se even in relatively low Se soil conditions (soil Se content of 0.11~0.12 mg/kg) and thus reaching the standard of Se-rich crops. Bangladesh J. Bot. 51(4): 961-970, 2022 (December) Special

Study on the Migration and Accumulation of Selenium between Soil and Vegetations

Selenium (Se) is an essential trace element for human health, and humans mainly consume Se through diet. China is recognized as a Se-deficient country, and the study of Se migration and accumulation relationships between crops and soils is essential for Se-deficient areas. In this experiment, the greenhouse pot experiment of Chinese cabbage (Brassica rapa L. ssp. pekinensis), wheat (Triticum aestivum L.) and pepper (Capsicum annuum L.) were carried out with the Guanzhong region of Shaanxi Province and common farmland soils from Beijing Province. The relationship between the Se content in soil and crops organs (e.g., roots, stems, leaves, grain and fruit) and the differences in the Se-enriching capacity of the organs were analyzed. The following results were obtained: (1) all three field crops could absorb Se from soil, including Se-rich and -regulated soil and reach the standard of Se-enriched vegetables; (2) different organs of Chinese cabbage had different Se-enriching capacity, which can be arranged as leaf &gt; stem &gt; root, while the Se enrichment capacity of wheat was root &gt; leaf &gt; stem &gt; grain, and for pepper it was root &gt; leaf &gt; fruit &gt; stem; (3) when the soil Se regulation content reached 1.0–1.5 mg/kg, the utilization rate of Se in Chinese cabbage and pepper were higher, but when the soil Se regulation reached 4.0–5.0 mg/kg, the utilization rate of Se in wheat was higher.

Effects of anthropogenic and natural environmental factors on the spatial distribution of trace elements in agricultural soils

The concentrations of trace elements in agricultural soils directly affect the ecological security and quality of agricultural products. A comprehensive study aimed at quantitatively analyze the effects of anthropogenic and natural environmental factors on the spatial distribution of heavy metals (HMs) and selenium (Se) in agricultural soils in a typical grain producing area of China. Factors considered in this study were parent rock, soil physicochemical properties, topography, precipitation, mine activity, and vegetation. Results showed that the median values of Zn, Cd, Cr, and Cu of 111 topsoil samples exceeded the background values of Guangxi province but were lower than the relevant national soil quality standards, and 85% of soil samples were classified as having rich Se levels (0.40 −3.0 mg kg−1). The potential ecological risk index of soil heavy metals as a whole was low, with Cd in 9% of the samples posing moderate ecological risk. The concentrations of heavy metals and Se were relatively high in soils from shale rock. Soil properties, mainly Fe2O3 and Mn played a dominant role on soil HMs and Se concentrations. Based on GeoDetector, we found that the interaction effects of two factors on the spatial differentiation of soil HMs and Se were greater than their sum effect. Among the factors, Mn enhanced the explanatory power of the model the most when interacting with other factors for soil Zn; the greatest interactive effect was between distance from mining area and Mn for Cd (q = 0.70); Fe2O3 significantly promoted the spatial differentiation of soil Cr, Cu and Se when interacting with other factors (q > 0.50). These findings contribute to a better understanding of the factors that drive the distribution of HMs and Se in agricultural soils.

Highland barley grain and soil surveys reveal the widespread deficiency of dietary selenium intake of Tibetan adults living along Yalung Zangpo River

ObjectiveIn order to assess selenium (Se) flux through the soil-plant-human chain in Tibet plateau and explore the reason why local Tibetan adult residents from large scale agricultural production areas in Tibet lacked daily Se intake.MethodsA total of 210 intact highland barley plants and their corresponding cultivated topsoil samples were collected in fields of 14 agricultural counties along Yalung Zangpo River and quantitative dietary data were collected from a cross-sectional survey using a cultural-specific food frequency questionnaire that contained all local Tibetan foods in 2020.ResultsThe mean value of The estimated daily Se dietary intake by each participant was 17.1 ± 1.9 μg/day/adult, the Se concentration in topsoil and highland barley grain were 0.128 ± 0.015 mg/kg and 0.017 ± 0.003 mg/kg, respectively. Although highland barley was the first contributor of dietary Se in local adult residents (34.2%), the dietary Se intake provided by highland barley only about 10% of the EAR value (50 μg/day/adult) currently. A significantly positive relationship was determined between soil total Se content (STSe), available Se content (SASe) and highland barley grain Se content (GSe). The amount of Se in food system depends on a number of soil properties (TOC, pH, clay content, Fe/Mn/Al oxides), climate variables (MAP, MAT) and terrain factor (altitude).ConclusionTo sum up, it can be inferred that the insufficient dietary Se intake of Tibetan adult population living along Yalung Zangbo River is mainly caused by the low Se content in highland barley grain, which was result from the low Se content in cultivated soil. In order to enable adult participants in the present study to achieve recommended dietary Se-intake levels, agronomic fortification with selenised fertilizers applied to highland barley could be a great solution. It is necessary to combine the influencing factors, and comprehensively consider the spatial variation of local soil properties, climatic and topographic conditions, and planting systems.

Vertical distribution and major influencing factors of soil selenium in tropical climate: A case study of Chengmai County, Hainan Island

Soil selenium is of great significance to human health. Soil-forming parent rocks are the most critical factor that influences soil Se levels. Chengmai County, Hainan Island, has a tropical climate and diverse types of parent rocks, in which soil Se content is high. This study investigated the vertical distribution of soil Se from various parent rock substrates under tropical climatic conditions, and the factors that influence these soil Se contents, with 69 vertical soil profiles covering Chengmai County. The vertical distribution of soil Se and correlations with CIA (chemical alteration index), Al2O3, TFe2O3 (total iron oxide expressed as Fe2O3), total iodine, SOC (soil organic carbon), and pH were analysed. As per the results, the mean ± standard error of Se content in the A, B, and C horizons was 0.88 ± 0.13 mg/kg, 0.77 ± 0.08 mg/kg and 0.45 ± 0.05 mg/kg, respectively. The parent rock strictly controlled the horizon distribution of Se in the A-horizon. Soil Se showed A-B-horizons-enrichment in the vertical profile, especially in soil profiles overlying granite and basalt. It is hypothesised that the Se enriched in soils developed from the Tuolie Formation due to the release of Se from the weathering process of Se-rich rocks. Meanwhile, Se in soils developed from granite and basalt is more closely associated with exogenous input. Another crucial factor for the high level of Se in Chengmai County is the tropical climate, which has led the rocks to generally undergo intense chemical weathering. This results in soils rich in clay minerals and Fe/Al oxyhydroxides, which easily absorb and retain Se. Furthermore, the Se content of the B-horizon was generally higher than that of the A-horizon due to leaching. These results provide further knowledge and understanding of the geochemical behaviour of soil Se and guide the evaluation of Se-rich land resources under tropical climatic conditions.

Probability of cultivating Se-rich maize in Se-poor farmland based on intensive field sampling and artificial neural network modelling

Selenium (Se) is a necessary micronutrient for humans, and its supplementation from crop grains is important to address the ubiquitous Se deficiency in people worldwide. Se uptake by crops largely depend on soil bioavailable Se rather than soil total Se content, which provides possibilities to explore the Se-rich crops in Se-poor area. Here, the possibility of cultivating Se-rich maize grains in Se-poor farmland was tested based on intensive field sampling and mathematical modelling. Sampling was conducted at county scale, and a total of 7779 topsoil samples and 109 maize samples with paired rhizosphere soils samples were collected. Results showed that although the soil Se content in the study county from southwestern China was at a low level (0.01–2.75 mg kg−1), 54.1% of the maize grain samples satisfied the standard for Se-rich products (0.02–0.30 mg kg−1). Soil organic matter, iron oxide, and phosphorus levels were correlated negatively with Se bioconcentration factor (BCF) of maize grain. Compared with the multivariate linear regression model, the artificial neural network (ANN) model was more accurate and reliable in predicting maize Se BCF. Prediction using the ANN model showed that 22.7% of the county's farmland was suitable for cultivating naturally Se-rich maize, which increased 21.3% growing areas than that from cultivation based on simply soil total Se. This study provided a new methodological framework for natural Se-rich maize production and verified the probability of cultivating naturally Se-rich maize in Se-poor farmland.

Analysis of phosphorus and sulfur effect on soil selenium bioavailability based on diffusive gradients in thin films technique and sequential extraction.

Human intake of selenium (Se) mainly occurs through the food chain, and is largely dependent on the bioavailability of soil Se. Sulfur (S) and phosphorus (P) also as essential nutrients for plants, their antagonistic with Se effects on Se bioavailability should be considered. We conducted pot experiments to investigate the interaction effect on the bioavailability of Se in the soil using a sequential extraction method and diffusive gradients in thin films (DGT). The results showed that the root and shoot Se of pak choi increased at most 340%-360% with S and P application, while the Se uptake by pak choi was slightly inhibited when S and P application was 100mgkg-1. With high S and P application, pak choi Se had a high bioaccumulation factor (BAF) and low translocation factor (TF), and soil Soluble-Se (SOL-Se) increased 178%-299%, which due to the competitive adsorption of S, P with Se and changes in soil pH that lead to the transformation of soil Se fractions. In addition, the available Se concentration in soil measured by the DGT (CDGT-Se) increased by 866% with exogenous S and P application, and its source was HA-Se. However, CDGT-Se failed to show a good linear relationship with the Se content of pak choi. The application of DGT to assess the bioavailability of Se in soils where Se is present in the steady state needs to be further explored. We discuss the effect of S and P application on the bioavailability of soil Se and provide evidence for agricultural production and rational fertilizer use on Se-rich land.

Linkages between soil, crop, livestock, and human selenium status in Sub-Saharan Africa: a scoping review.

Selenium (Se) is essential for human health, however, data on population Se status and agriculture-nutrition-health linkages are limited in sub-Saharan Africa (SSA). The scoping review aims to identify linkages between Se in soils/crops, dietary Se intakes, and livestock and human Se status in SSA. Online databases, organisational websites and grey literature were used to identify articles. Articles were screened at title, abstract and full text levels using eligibility criteria. The search yielded 166 articles from which 112 were excluded during abstract screening and 54 full text articles were assessed for eligibility. The scoping review included 34 primary studies published between 1984 and 2021. The studies covered Se concentrations in soils (n = 7), crops (n = 9), animal tissues (n = 2), livestock (n = 3), and human Se status (n = 15). The evidence showed that soil/crop Se concentrations affected Se concentration in dietary sources, dietary Se intake and biomarkers of Se status. Soil types are a primary driver of human Se status and crop Se concentration correlates positively with biomarkers of Se dietary status. Although data sets of Se concentrations exist across the food system in SSA, there is limited evidence on linkages across the agriculture-nutrition nexus. Extensive research on Se linkages across the food chain is warranted.

A Multi-country Association Analysis of Maternal Selenium (Se) Levels and Infant Birth Outcomes: Findings From the Women First Study

ObjectivesSelenium (Se) soil content varies worldwide impacting population levels. Maternal Se deficiency may be related to preterm birth, small for gestational age (SGA), and low birth weight (LBW, < 2,500g) possibly through its roles in antioxidant and thyroid hormone function particularly during the first trimester. We examined associations of Se levels and birth outcomes in a multi-country nutritional intervention trial of pregnant women.MethodsThis is a secondary analysis of the Women First trial (NCT01883193), a randomized controlled study investigating timing of maternal multiple micronutrient (with 130 mcg Se) and protein-energy supplementation (MNS) on fetal growth. MNS was started 3 months prior to conception (Arm 1), at ∼12 wk of gestation (Arm 2), or not at all (Arm 3) in women in India, Guatemala, and Pakistan. Gestational age was determined by first trimester ultrasound. At 12 and 34 wk gestation, maternal serum Se was measured by ICP-MS (n = 143–325 per timepoint per site). TSH was measured by 1-step sandwich (Guatemala and Pakistan) or chemiluminescence immunoassay (India). We used t-test or ANOVA to test group differences and linear models to test association of Se with infant outcomes and TSH, adjusting for treatment arm and study site.ResultsSe levels were highest in Guatemalan women (mean ± SD, 12 wk: 102.1 ug/L ± 12.6; 34 wk: 103.9 ± 14.2) and lowest in Pakistani women (12 wk: 85.7 ± 14.5; 34 wk: 77.9 ± 14.8) at both timepoints (P < 0.0001). MNS supplementation before or during gestation increased serum Se levels at 34 wk in Guatemalan women only (p = 0.038). In Pakistan a negative association between maternal Se at 34 wk and LBW was seen in female (n = 153; p = 0.041) but not male (n = 143; p = 0.97) infants. Se levels were not associated with preterm birth or SGA status at any site. TSH levels did not differ by study arm but were lower in Pakistan at 12 and 34 wk compared to other sites. There was no association between TSH and Se levels at any timepoint at any site.ConclusionsMaternal Se levels may impact fetal birth weight in vulnerable populations in a sexually dimorphic manner. Preconception Se supplementation as part of a comprehensive MNS did not increase Se levels in Pakistan where soil Se content is low. Although Se did not correlate with TSH levels in this study, future work will incorporate co-influence of iodine.Funding SourcesBill & Melinda Gates Foundation, NIH NICHD/ODS.

Selenium Effect Threshold for Soil Nematodes Under Rice Biofortification.

Crop biofortification with inorganic selenium (Se) fertilizer is a feasible strategy to improve the health of residents in Se-deficient areas. For eco-friendly crop Se biofortification, a comprehensive understanding of the effects of Se on crop and soil nematodes is vital. In this study, a rice pot experiment was carried out to test how selenite supply (untreated control (0), 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 100, or 200 mg Se kg−1) in soil affected rice growth, rice Se accumulation, and soil nematode abundance and composition. The results showed that selenite supply (5–200 mg kg−1) generally increased the number of rice tillers, rice yield, and Se concentrations in rice grains. In soil under 10 mg kg−1 Se treatment, the genus composition of nematodes changed significantly compared with that in the control soil. With increased Se level (> 10 mg kg−1), soil nematode abundance decreased significantly. Correlation analysis also demonstrated the positive relationships between soil Se concentrations (total Se and bioavailable Se) with rice plant parameters (number of rice tillers, rice yield, and grain Se concentration) and negative relationships between soil Se concentrations (total Se and bioavailable Se) with soil nematode indexes (nematode abundance and relative abundance of Tobrilus). This study provides insight into balancing Se biofortification of rice and soil nematode community protection and suggests the effective concentrations for total Se (1.45 mg kg−1) and bioavailable Se (0.21 mg kg−1) to soil nematode abundances at 20% level (EC20) as soil Se thresholds. At Se concentrations below these thresholds, rice plant growth and Se accumulation in the grain will still be promoted, but the disturbance of the soil nematodes would be negligible.

Use of Site-Specific Data for Modeling Selenium Bioaccumulation by Terrestrial Animals.

We developed a bioaccumulation model from an extensive set of monitoring data to predict selenium (Se) concentrations in biota within a terrestrial system (Kesterson Reservoir, CA). The model uses water-extractable Se and total Se concentrations in soil to estimate the expected mean and ranges of Se concentrations in biota at Kesterson for future scenarios. Biological monitoring data collected at Kesterson from 1989 to 1994 were used to parameterize the initial model. The model was tested and updated with additional sample results from 1995 through 2001 biological monitoring and validated and calibrated using Se concentrations from sampling conducted in 2004 and 2006. Minor adjustments were made to the model based on each additional year's results, and the model was used in 2014 to assess whether there were continuing threats to wildlife at Kesterson. The model predicts Se concentrations in small mammals, bird blood, and bird eggs in common species found at Kesterson. This model was used for the final assessment of Kesterson in 2014 and performed well, but there was variability in results, probably due to differences in individual diets and feeding ranges of animals. The model has been further refined since 2014, as we describe here. The model performs well for predicting central tendency and is conservative as the predicted upper limits of the biotic exposure distributions were mostly similar or higher than the measured. The trophic and tissue transfer factors and regression equations should be applicable to other Se-contaminated sites; adjusting weighting factors based on diet and range allows the model to be adapted and used at other sites.

Geochemistry of selenium, barium, and iodine in representative soils of the Brazilian Amazon rainforest

The Amazon rainforest is a heterogeneous ecosystem and its soils exhibit geographically variable concentrations of trace elements. In this region, anthropic activities - e.g., agriculture and mining - are numerous and varied, and even natural areas are at risk of contamination by trace elements, either of geogenic or anthropogenic origin. A reliable dataset of benchmark values for selenium (Se), barium (Ba), and iodine (I) concentrations in soils is needed for use as a reference in research and public policies in the region. In this study, 9 selected sites in the Brazilian Amazon rainforest within areas represented by Oxisols and Ultisols were assessed for relevant soil physicochemical characteristics, along with the concentrations of total Se (SeTot), total Ba (BaTot), and sequentially-extracted soluble Se (SeSol) and adsorbed Se (SeAd) in 3 different soil layers (0–20, 20–40, and 40–60 cm). In addition, organically bound-Se (SeOrg) and total I (ITot) concentrations in the surface layer (0–20 cm) were measured. Soil Se concentrations (SeTot) were considered safe and are likely a result of contributions of sedimentary deposits from the Andes. Available Se (SeSol + SeAd) accounted for 4.5% of SeTot, on average, while SeOrg in the topsoil accounted for more than 50% of SeTot. Barium in the western Amazon (state of Acre) and central Amazon (Anori, state of Amazonas) exceeded national prevention levels (PVs). Furthermore, the average ITot in the studied topsoils (5.4 mg kg−1) surpassed the worldwide mean. Notwithstanding, the close relationship found between the total content of the elements (Se, Ba, and I) and soil texture (clay, silt, and sand) suggests their geogenic source. Finally, our data regarding SeTot, BaTot, and ITot can be used to derive regional quality reference values for Amazon soils and also for updating prevention (PV) and investigation (IV) values established for selected elements by the Brazilian legislation.

Selenium in Wheat from Farming to Food.

Selenium (Se) plays an important role in human health. Approximately 80% of the world's population does not consume enough Se recommended by the World Health Organization. Wheat is an important staple food and Se source for most people in the world. This review summarizes literature about Se from 1936 to 2020 to investigate Se in wheat farming soil, wheat, and its derived foods. Se fortification and the recommended Se level in wheat were also discussed. Results showed that Se contents in wheat farming soil, grain, and its derived foods around the world were 3.8-552 μg kg-1 (mean of 220.99 μg kg-1), 0-8270 μg kg-1 (mean of 347.30 μg kg-1), and 15-2372 μg kg-1 (mean of 211.86 μg kg-1), respectively. Adopting suitable agronomic measures could effectively realize Se fortification in wheat. The contents in grain, flour, and its derived foods could be improved from 93.94 to 1181.92 μg kg-1, from 73.06 to 1007.75 μg kg-1, and from 86.90 to 587.61 μg kg-1 on average after leaf Se fertilizer application in the field. There was a significant positive correlation between the Se content in farming soil and grain, and it was extremely the same between the foliar Se fertilizer concentration rate and the grain Se increased rate. The recommended Se fortification level in cultivation of wheat in China, India, and Spain was 18.53-23.96, 2.65-3.37, and 3.93-9.88 g hm-2, respectively. Milling processing and food type could greatly affect the Se content of wheat-derived food and should be considered seriously to meet people's Se requirement by wheat.