Daily dietary selenium intake in a high selenium area of Enshi, China

Effects of Selenium and Cadmium on Human Liver and Kidney Functions in Exposed Black Shale Areas

Animal experiments suggest that selenium (Se) may alleviate cadmium (Cd) toxicity in animal liver and kidneys, but its effect on human liver and kidneys remains uncertain. In China, areas with black shale have shown elevated levels of Se and Cd. According to the USEPA (U.S. Environmental Protection Agency) evaluation method, the soil and rice in these areas pose significant risks. In black shale regions such as Enshi and Zhuxi County, residents who long-term consume local rice may surpass safe Se and Cd intake levels. Significantly high median blood Se (B-Se) and urine selenium (U-Se) levels were detected in these areas, measuring 416.977 μg/L and 352.690 μg/L and 104.527 μg/L and 51.820 μg/L, respectively. Additionally, the median blood Cd (B-Cd) and urine Cd (U-Cd) levels were markedly elevated at 4.821 μg/L and 3.848 μg/L and at 7.750 μg/L and 7.050 μg/L, respectively, indicating substantial Cd exposure. Nevertheless, sensitive liver and kidney biomarkers in these groups fall within healthy reference ranges, suggesting a potential antagonistic effect of Se on Cd in the human body. Therefore, the USEPA method may not accurately assess Cd risk in exposed black shale areas. However, within the healthy ranges, residents in the Enshi study area had significantly greater median levels of serum creatinine and cystatin C, measuring 67.3 μmol/L and 0.92 mg/L, respectively, than those in Zhuxi did (53.6 μmol/L and 0.86 mg/L). In cases of excessive Se and Cd exposure, high Se and Cd levels impact the filtration function of the human kidney to some extent.

A preliminary predictive model for selenium nutritional status in residents based on three selenium biomarkers

BACKGROUND

Selenium (Se) is an essential nutrient and an important component of many selenoproteins that possess fundamental importance to human health. Selenium deficiency and excess will cause corresponding diseases in the human body. The nutritional health of Se in the human body mainly depends on the daily dietary Se intake of the human body, which in turn depends to a certain extent on the content of Se transmitted along the food chain. This study aims to research the transport of Se through the soil-crop-human chain in regions with different Se levels, and to establish the model between the residents' dietary Se intake and the three Se biomarkers (hair, nails, and plasma), to predict the nutritional health status of Se in residents through Se biomarkers.

METHOD

Carry out field and cross-sectional surveys of populations in Loujiaba Village and Longshui Village. Samples were collected from soil, crops, drinking water, residents' hair, nails, plasma, and diet. The concentration of available Se fractions was extracted from soil samples using 0.1 mol/L K2HPO4. The concentration of total Se for all samples was determined by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), and the relative standard deviation was less than 5%. In this study, hair, nails, and blood samples were collected from volunteers according to the Declaration of Helsinki and the Ethics Committee of Soochow University. The dietary nutritional structure and dietary Se intake of the population were randomly selected by 12 volunteers using the duplicate portion method. Data were described using mean ± standard deviation. We performed saliency analysis and correlation analysis (with Pearson correlation coefficient), and fitted a regression to evaluate the associations between these variables.

RESULTS

The soil total Se (5201 ± 609.2 μg/kg) and available Se (307.7 ± 83.5 μg/kg) in Luojiaba Village (LJB) were significantly higher than the soil total Se (229.2 ± 32.5 μg/kg) and available Se (21.9 ± 4.0 μg/kg) in Longshui Village (LS). The residents' dietary Se intake of LJB (150.3 ± 2.2 μg/d) was within the World Health Organization (WHO) recommended intake range, while LS (16.0 ± 0.4 μg/d) was close to the range of Keshan disease occurrence, and there was a risk of insufficient Se intake. The correlation analysis found significant positive correlations between residents' dietary Se intake and the three Se biomarkers. According to the preliminary model established in this study, if the daily dietary Se intake of residents reaches the WHO recommended value of 55-400 μg, the hair, nails, and plasma of Se concentration will be 522.1-2850.5 μg/kg, 1069.0-6147.4 μg/kg, and 128.3-661.36 μg/L, respectively.

CONCLUSION

Selenium is transmitted through the soil-crop-human chain, and the Se concentration that enters the human body through the food chain in high-Se areas is significantly higher than that in low-Se areas. The nutritional health status of Se in the human body depends on the daily dietary intake of the human body, and there is a significant correlation between the daily dietary Se intake of the human body and the three biomarkers of Se levels in the human body, so the three biomarkers can be used to evaluate the Se nutritional health of the human.

Micronuclei frequency and exposure to chemical mixtures in three Colombian mining populations

The Colombian mining industry has witnessed significant growth. Depending on the scale and mineral extracted, complex chemical mixtures are generated, impacting the health of occupationally exposed populations and communities near mining projects. Increasing evidence suggests that chromosomal instability (CIN) is an important link between the development of certain diseases and exposure to complex mixtures. To better understand the effects of exposure to complex mixtures we performed a biomonitoring study on 407 healthy individuals from four areas: three located in municipalities exploiting different-scale mining systems and a reference area with no mining activity. Large, medium, and small-scale mining systems were analyzed in Montelibano (Córdoba), artisanal and small-scale mining (ASGM) in Nechí (Antioquia), and a closed mining system in Aranzazu (Caldas). The reference area with no mining activity was established in Montería (Córdoba). ICP-MS measured multi-elemental exposure in hair, and CIN was evaluated using the cytokinesis-block micronucleus technique (MNBN). Exposure to mixtures of chemical elements was comparable in workers and residents of the mining areas but significantly higher compared to reference individuals. In Montelibano, increased MNBN frequencies were associated with combined exposure to Se, Hg, Mn, Pb, and Mg. This distinct pattern significantly differed from other areas. Specifically, in Nechí, Cr, Ni, Hg, Se, and Mg emerged as the primary contributors to elevated frequencies of MNBN. In contrast, a combination of Hg and Ni played a role in increasing MNBN in Aranzazu. Interestingly, Se consistently correlated with increased MNBN frequencies across all active mining areas. Chemical elements in Montelibano exhibit a broader range compared to other mining zones, reflecting the characteristics of the high-impact and large-scale mining in the area. This research provides valuable insights into the effects of exposure to chemical mixtures, underscoring the importance of employing this approach in the risk assessment of communities, especially those from residential areas.

Selenium intake and multiple health-related outcomes: an umbrella review of meta-analyses

Selenium is an essential trace metalloid element that is associated with fundamental importance to human health. Our umbrella review aimed to evaluate the quality of evidence, validity, and biases in the relationship between selenium intake and health-related outcomes according to published systematic reviews with pooled data and meta-analyses. Selenium intake is associated with a decreased risk of digestive system cancers, all-cause mortality, depression, and Keshan disease, when in children reduce the risk of Kashin-Beck disease. Additionally, selenium supplementation can improve sperm quality, polycystic ovary syndrome, autoimmune thyroid disease, cardiovascular disease, and infective outcomes. Selenium supplementation also has relationship with a decreased concentration of serum lipids including total cholesterol and very low-density lipoprotein cholesterol. However, no evidence has shown that selenium is associated with better outcomes among patients in intensive care units. Furthermore, selenium intake may be related with a higher risk of type 2 diabetes and non-melanoma skin cancers. Moreover, most of included studies are evaluated as low quality according to our evidence assessment. Based on our study findings and the limited advantages of selenium intake, it is not recommended to receive extra supplementary selenium for general populations, and selenium supplementation should not be continued in patients whose selenium-deficient status has been corrected.

Selenium hyperaccumulator plant Cardamine enshiensis: from discovery to application

Selenium (Se) is an essential trace element for animals and humans. Se biofortification and Se functional agriculture are emerging strategies to satisfy the needs of people who are deficient in Se. With 200 km2 of Se-excess area, Enshi is known as the "world capital of Se." Cardamine enshiensis (C. enshiensis) is a Se hyperaccumulation plant discovered in the Se mine drainage area of Enshi. It is edible and has been approved by National Health Commission of the People's Republic of China as a new source of food, and the annual output value of the Se-rich industry in Enshi City exceeds 60 billion RMB. This review will mainly focus on the discovery and mechanism underlying Se tolerance and Se hyperaccumulation in C. enshiensis and highlight its potential utilization in Se biofortification agriculture, graziery, and human health.

Mercury and selenium co-ingestion assessment via rice consumption using an in-vitro method: Bioaccessibility and interactions

Mercury (Hg) was reported to accumulate in rice grains, and, together with the selenium (Se) was found in rice, the co-exposure of Hg-Se via rice consumption may present significant health effects to human. This research collected rice samples containing high Hg:high Se and high Se:low Hg concentrations from high Hg and high Se background areas. The physiologically based extraction test (PBET) in vitro digestion model was utilized to obtain bioaccessibility data from samples. The results showed relatively low bioaccessible for Hg (<60%) and Se (<25%) in both rice sample groups, and no statistically significant antagonism was identified. However, the correlations of Hg and Se bioaccessibility showed an inverse pattern for the two sample groups. A negative correlation was detected in the high Se background rice group and a positive correlation in the high Hg background group, suggesting various micro forms of Hg and Se in rice from different planting locations. In addition, when the benefit-risk value (BRV) was calculated, some "fake" positive results showed while Hg and Se concentrations were directly used, which indicated that bioaccessibility should not be neglected in benefit-risk assessment.

Toxicity of repeated oral intake of organic selenium, inorganic selenium, and selenium nanoparticles: A review

BACKGROUND

To protect from toxicity at supra-essential doses of selenium, it is important to determine dose levels at which adverse effects occur.

METHODS

We identified relevant literature on the repeated dosage of selenium and extracted dose descriptors on reported endpoints, except on genotoxicity/carcinogenicity.

RESULTS

Selenium forms with toxicological data were organic ones: selenomethionine, selenocystine/selenocysteine; and inorganic ones, including selenite (SeO₃^2-), selenate (SeO₄^2-), selenium sulphide (SeS₂), selenide (Se^2-) and selenium nanoparticles. Clinical signs of selenium toxicity in humans include a garlicky-smelling breath, hair loss, and nail changes. One human study showed increased mortality following daily ingestion of 300 µg Se per day for 5 years, equal to a lowest-observed-adverse-effect level (LOAEL) of ∼4.3 µg/kg bw/days. The corresponding no-observed-adverse-effect level (NOAEL) was ∼2.9 µg Se/kg bw/day. One study reported an increased risk of type 2 diabetes after ∼2.9 µg Se/kg bw/day, but other studies with similar doses found no increases in mortality or incidence of type 2 diabetes. NOAELs on affected body weight in animal studies were 0.24-1.2 mg Se/kg bw/day. Other endpoints of selenium toxicity in animals include hepatotoxicity with a NOAEL as low as 2 µg/kg bw/day in rats, as well as gastrointestinal, cardiovascular, and reproductive toxicities with NOAELs of 0.6 (gastrointestinal), 0.08, and 0.4 (cardiovascular) and ≥ 0.04 mg Se/kg bw/day (reproductive), respectively.

CONCLUSIONS

Dose descriptors describing selenium toxicity were as low as 2-3 µg Se/kg bw/day.

Do high soil geochemical backgrounds of selenium and associated heavy metals affect human hepatic and renal health? Evidence from Enshi County, China

It is unclear whether the United States Environmental Protection Agency (US EPA) method can accurately assess heavy metal risks in high-Se areas. Herein, a black shale outcropping in Enshi County, China, was taken as the study area, and a carbonate outcropping in Lichuan County was the control area. Selenium and associated heavy metal concentrations in rock, soil, rice, human blood and urine samples and human sensitive hepatic and renal biomarkers were measured. The results showed that the contents of selenium, cadmium, molybdenum and copper in the study area were 3.68 ± 2.72 μg/g, 2.65 ± 1.42 μg/g, 16.3 ± 15.5 μg/g, and 57.3 ± 17.6 μg/g, respectively, in soil (n = 47) and 1.072 ± 0.924 μg/g, 0.252 ± 0.310 μg/g, 2.800 ± 2.167 μg/g, and 10.91 ± 27.42 μg/g, respectively, in rice (n = 47). The daily adult intake levels of selenium, cadmium and molybdenum from rice consumption in the study area (exposure group) exceed the recommended tolerance values in China. According to the US EPA method, these environmental media pose a significant risk to human health. However, in the exposure group (n = 111), the median levels of the sensitive hepatic biomarkers alanine aminotransferase (18 U/L), aspartate aminotransferase (28 U/L) and total bilirubin (10.9 μmol/L) and the sensitive renal biomarkers serum creatinine (70.1 μmol/L), urinary nitrogen (5.73 mmol/L) and uric acid (303.80 μmol/L) were within reference ranges and had values equivalent to those of the control group (P > 0.05). The elements tended to differentiate during migration from one medium to another. Due to the complex interaction between selenium and heavy metals, a survey of human health indicators is indispensable when the US EPA method is used to assess the heavy metal risks in high-Se areas. The recommended molybdenum tolerable intake in the U.S. (2000 μg/d) is reasonable based on a comparison.

Selenium-enriched plant foods: Selenium accumulation, speciation, and health functionality

Selenium (Se) is an essential element for maintaining human health. The biological effects and toxicity of Se compounds in humans are related to their chemical forms and consumption doses. In general, organic Se species, including selenoamino acids such as selenomethionine (SeMet), selenocystine (SeCys₂), and Se-methylselenocysteine (MSC), could provide greater bioactivities with less toxicity compared to those inorganics including selenite (Se IV) and selenate (Se VI). Plants are vital sources of organic Se because they can accumulate inorganic Se or metabolites and store them as organic Se forms. Therefore, Se-enriched plants could be applied as human food to reduce deficiency problems and deliver health benefits. This review describes the recent studies on the enrichment of Se-containing plants in particular Se accumulation and speciation, their functional properties related to human health, and future perspectives for developing Se-enriched foods. Generally, Se's concentration and chemical forms in plants are determined by the accumulation ability of plant species. Brassica family and cereal grains have excessive accumulation capacity and store major organic Se compounds in their cells compared to other plants. The biological properties of Se-enriched plants, including antioxidant, anti-diabetes, and anticancer activities, have significantly presented in both in vitro cell culture models and in vivo animal assays. Comparatively, fewer human clinical trials are available. Scientific investigations on the functional health properties of Se-enriched edible plants in humans are essential to achieve in-depth information supporting the value of Se-enriched food to humans.

Multiple exposure pathways and health risk assessment of potentially harmful elements for children and adults living in a coal region in Brazil

Energy generated by coal can contaminate the environment by releasing toxic elements, including metals. The human health risk assessment (HHRA) associated with geographic information system (GIS) tools can assist the management of contaminated areas, such as coal mining areas. The objective of the study was to carry out the assessment and spatialization of the risk to human health of potentially hazards elements (PHEs) in the soil for children and adults, from multiple exposure routes (oral, inhalation and dermal) in the Candiota mines, largest coal mining region of Brazil. The non-carcinogenic risks (HQ) of PHEs (Cu, Pb, Zn, Ni, Cr, Fe, Mn, Cd, As and Se) and carcinogenic risks of As were estimated and spatialized. The results revealed a risk for children exposure to Mn, with greatest contribution through dermal route. Mn (HQ_derm 72.41-96.09% and HQ_inh 40.84-82.52%) and Fe (HQ_o 43.90-81.44%) were the metals with greatest contribution to human health risk among studied population. As did not present carinogenic risk to adults. The spatial distribution of non-carcinogenic risk showed that Cr, As, Fe, Pb, Ni, Zn and Cu have higher HInc close to the coal mining areas, while Mn, Se and Cd have the highest HInc values in surrounding municipalities (Pinheiro Machado; Pedras Altas and Hulha Negra). The use of HHRA associated with GIS tools provides important elements for decision-making in the management of contaminated sites, indicating chemical elements, locations, routes of exposure and priority target populations.

Biological Activity of Selenium and Its Impact on Human Health

Selenium (Se) is a naturally occurring metalloid element essential to human and animal health in trace amounts but it is harmful in excess. Se plays a substantial role in the functioning of the human organism. It is incorporated into selenoproteins, thus supporting antioxidant defense systems. Selenoproteins participate in the metabolism of thyroid hormones, control reproductive functions and exert neuroprotective effects. Among the elements, Se has one of the narrowest ranges between dietary deficiency and toxic levels. Its level of toxicity may depend on chemical form, as inorganic and organic species have distinct biological properties. Over the last decades, optimization of population Se intake for the prevention of diseases related to Se deficiency or excess has been recognized as a pressing issue in modern healthcare worldwide. Low selenium status has been associated with an increased risk of mortality, poor immune function, cognitive decline, and thyroid dysfunction. On the other hand, Se concentrations slightly above its nutritional levels have been shown to have adverse effects on a broad spectrum of neurological functions and to increase the risk of type-2 diabetes. Comprehension of the selenium biochemical pathways under normal physiological conditions is therefore an important issue to elucidate its effect on human diseases. This review gives an overview of the role of Se in human health highlighting the effects of its deficiency and excess in the body. The biological activity of Se, mainly performed through selenoproteins, and its epigenetic effect is discussed. Moreover, a brief overview of selenium phytoremediation and rhizofiltration approaches is reported.

Selenium and thyroid diseases

Selenium, a non-metallic element, is a micronutrient essential for the biosynthesis of selenoproteins containing selenocysteine. In adults, the thyroid contains the highest amount of selenium per gram of tissue. Most known selenoproteins, such as glutathione peroxidase, are expressed in the thyroid and are involved in thyroid hormone metabolism, redox state regulation, and maintenance of cellular homeostasis. Some clinical studies have shown that lack of selenium will increase the prevalence of several kinds of thyroid diseases. Selenium treatment in patients with Graves' orbitopathy has been shown to delay disease progression and improve the quality of life. Selenium supplementation in Hashimoto's thyroiditis was associated with the decreased levels of anti-thyroid peroxidase antibody and improved thyroid ultrasound structure. In thyroid cancer, various selenium supplements have shown variable anticancer activity. However, published results remain the conflicting and more clinical evidence is still needed to determine the clinical significance of selenium. This article reviews the strong association between selenium and thyroid disease and provides new ideas for the clinical management of selenium in thyroid disease.

Selenium Status: Its Interactions with Dietary Mercury Exposure and Implications in Human Health

Selenium is an essential trace element in humans and animals and its role in selenoprotein and enzyme antioxidant activity is well documented. Food is the principal source of selenium, and it is important that selenium status in the body is adequately maintained for physiological functions. There has been increasing attention on the role of selenium in mitigating the toxic effects of mercury exposure from dietary intake in humans. In contrast, mercury is a neurotoxin, and its continuous exposure can cause adverse health effects in humans. The interactions of selenium and mercury are multi-factorial and involve complex binding mechanisms between these elements at a molecular level. Further insights and understanding in this area may help to evaluate the health implications of dietary mercury exposure and selenium status. This review aims to summarise current information on the interplay of the interactions between selenium and mercury in the body and the protective effect of selenium on at-risk groups in a population who may experience long-term mercury exposure.

Exploring nanoselenium to tackle mutated SARS-CoV-2 for efficient COVID-19 management

Despite ongoing public health measures and increasing vaccination rates, deaths and disease severity caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its new emergent variants continue to threaten the health of people around the world. Therefore, there is an urgent need to develop novel strategies for research, diagnosis, treatment, and government policies to combat the variant strains of SARS-CoV-2. Since the state-of-the-art COVID-19 pandemic, the role of selenium in dealing with COVID-19 disease has been widely discussed due to its importance as an essential micronutrient. This review aims at providing all antiviral activities of nanoselenium (Nano-Se) ever explored using different methods in the literature. We systematically summarize the studied antiviral activities of Nano-Se required to project it as an efficient antiviral system as a function of shape, size, and synthesis method. The outcomes of this article not only introduce Nano-Se to the scientific community but also motivate scholars to adopt Nano-Se to tackle any serious virus such as mutated SARS-CoV-2 to achieve an effective antiviral activity in a desired manner.

Prediction models for monitoring selenium and its associated heavy-metal accumulation in four kinds of agro-foods in seleniferous area

Se-rich agro-foods are effective Se supplements for Se-deficient people, but the associated metals have potential risks to human health. Factors affecting the accumulation of Se and its associated metals in Se-rich agro-foods were obscure, and the prediction models for the accumulation of Se and its associated metals have not been established. In this study, 661 samples of Se-rich rice, garlic, black fungus, and eggs, four typical Se-rich agro-foods in China, and soil, matrix, feed, irrigation, and feeding water were collected and analyzed. The major associated metal for Se-rich rice and garlic was Cd, and that for Se-rich black fungus and egg was Cr. Se and its associated metal contents in Se-rich agro-foods were positively correlated with Se and metal contents in soil, matrix, feed, and matrix organic contents. The Se and Cd contents in Se-rich rice grain and garlic were positively and negatively correlated with soil pH, respectively. Eight models for predicting the content of Se and its main associated metals in Se-rich rice, garlic, black fungus, and eggs were established by multiple linear regression. The accuracy of the constructed models was further validated with blind samples. In summary, this study revealed the main associated metals, factors, and prediction models for Se and metal accumulation in four kinds of Se-rich agro-foods, thus helpful in producing high-quality and healthy Se-rich.

Lentinan-functionalized selenium nanoparticles induce apoptosis and cell cycle arrest in human colon carcinoma HCT-116 cells

Selenium nanoparticles (SeNPs) have gained extensive attention for their excellent biological activity and low toxicity. However, SeNPs are extremely liable to aggregate into non-bioactive or gray elemental selenium, which limits their application in the biomedicine field. This study aimed to prepare stable SeNPs by using lentinan (LNT) as a template and evaluate its anti-colon cancer activity. The average particle diameter of obtained lentinan-selenium nanoparticles (LNT-SeNPs) was approximately 59 nm and presented zero-valent, amorphous, and spherical structures. The monodisperse SeNPs were stabilized by LNT through hydrogen bonding interactions. LNT-SeNPs solution remained highly stable at 4°C for at least 8 weeks. The stability of LNT-SeNPs solution sharply decreased under high temperature and strong acidic conditions. LNT-SeNPs showed no obvious cytotoxic effect on normal cells (IEC-6) but significantly inhibited the proliferation of five colon cancer cells (HCT-116, HT-29, Caco-2, SW620, and CT26). Among them, LNT-SeNPs exhibited the highest sensitivity toward HCT-116 cells with an IC50 value of 7.65 μM. Also, LNT-SeNPs displayed better cancer cell selectivity than sodium selenite and selenomethionine. Moreover, LNT-SeNPs promoted apoptosis of HCT-116 cells through activating mitochondria-mediated apoptotic pathway. Meanwhile, LNT-SeNPs induced cell cycle arrest at G0/G1 phase in HCT-116 cells via modulation of cell cycle regulatory proteins. The results of this study indicated that LNT-SeNPs possessed strong potential application in the treatment of colorectal cancer (CRC).

Selenium as an important factor in various disease states - a review

Selenium (Se) is an element that has a pro-health effect on humans and animals. However, both the deficiency of this element and its excess may prove harmful to the body depending on the chemical form of the selenium, the duration of supplementation, and the human health condition. Many data indicate insufficient coverage of the demand for selenium in humans and animals due to its low content in soils and food products. A balance in the physiological process of the body can be achieved via the proper percentage of organically active minerals in the feed of animals as well as human beings. Selenium is a trace mineral of great importance to the body, required for the maintenance of a variety of its processes; primarily, selenium maintains immune endocrine, metabolic, and cellular homeostasis. Recently, this element has been emerging as a most promising treatment option for various disorders. Therefore, research based on Se has been increasing in recent times. The present review is designed to provide up-to-date information related to Se and its different forms as well as its effects on health.

Exploring the Role of Heavy Metals and Their Derivatives on the Pathophysiology of COVID-19

Many aspects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its disease, COVID-19, have been studied to determine its properties, transmission mechanisms, and pathology. These efforts are aimed at identifying potential approaches to control or treat the disease. Early treatment of novel SARS-CoV-2 infection to minimize symptom progression has minimal evidence; however, many researchers and firms are working on vaccines, and only a few vaccines exist. COVID-19 is affected by several heavy metals and their nanoparticles. We investigated the effects of heavy metals and heavy metal nanoparticles on SARS-CoV-2 and their roles in COVID-19 pathogenesis. AgNPs, AuNPs, gold-silver hybrid NPs, copper nanoparticles, zinc oxide, vanadium, gallium, bismuth, titanium, palladium, silver grafted graphene oxide, and some quantum dots were tested to see if they could minimize the severity or duration of symptoms in patients with SARS-CoV-2 infection when compared to standard therapy.

Understanding the translocation and bioaccumulation of cadmium in the Enshi seleniferous area, China: Possible impact by the interaction of Se and Cd

Selenium (Se) plays an indispensable role in minimizing cadmium (Cd) hazards for organisms. However, their potential interactions and co-exposure risk in the naturally Se-Cd enriched paddy field ecosystem are poorly understood. In this study, rice plants with rhizosphere soils sampled from the Enshi seleniferous region, China, were investigated to resolve this confusion. Here, translocation and bioaccumulation of Cd showed some abnormal patterns in the system of soil-rice plants. Roots had the highest bioaccumulation factors of Cd (range: 0.30-57.69; mean: 11.86 ± 14.32), and the biomass of Cd in grains (range: 1.44-127.70 μg, mean: 36.55 ± 36.20 μg) only accounted for ∼10% of the total Cd in whole plants (range: 14.67-1363.20 μg, mean: 381.25 ± 387.57 μg). The elevated soil Cd did not result in the increase of Cd concentrations in rice grains (r² = 0.03, p > 0.05). Most interestingly, the opposite distribution between Se and Cd in rice grains was found (r² = 0.24, p < 0.01), which is contrary to the positive correlation for Se and Cd in soil (r² = 0.46, p < 0.01). It is speculated that higher Se (0.85-11.46 μg/g), higher Se/Cd molar ratios (mean: 5.42 ≫1; range: 1.50-12.87), and higher proportions of reductive Se species (IV, 0) of the Enshi acidic soil may have the stronger capacity of favoring the occurrence of Se binding to Cd ions by forming Cd-Se complexes (Se^2- + Cd²⁺ =CdSe) under reduction conditions during flooding, and hence change the Cd translocation from soil to roots. Furthermore, the negative correlation (r² = 0.25, p < 0.05) between the Cd translocation factor (TF_{whole grains/root}) and the roots Se indicates that Cd translocation from the roots to rice grains was suppressed, possibly by the interaction of Se and Cd. This study inevitably poses a challenge for the traditional risk assessment of Cd and Se in the soils-crops-consumers continuum, especially in the seleniferous area.

Can Selenium Reduce the Susceptibility and Severity of SARS-CoV-2?-A Comprehensive Review

The SARS-CoV-2 infection is a highly contagious viral infection, which has claimed millions of lives in the last two years. The infection can cause acute respiratory distress, myocarditis, and systemic inflammatory response in severe cases. The interaction of the viral spike protein with the angiotensin-converting enzyme in various tissues causes damage to vital organs and tissues, leading to complications in the post-infection period. Vaccines and antiviral drugs have improved patient response to the infection, but the long-term effect on vital organs is still unknown. Investigations are now focused on supportive nutrient therapies, which can mitigate the susceptibility as well as the long-term complications of COVID-19. Selenium is one such micronutrient that plays a vital role in preventing oxidative stress induced by the virus. Further, selenium is important for effective immune response, controlling systemic inflammation, and maintain overall health of humans. We examine the role of selenium in various aspects of SARS-CoV-2 infection and address the importance of selenium supplementation in reducing the susceptibility and severity of infection in this review.

Enhanced phytoremediation of selenium using genetically engineered rice plants

Selenium (Se) is a micronutrient essential for human and animal health. However, Se is toxic at high levels because the nonspecific substitution of cysteine by selenocysteine could lead to protein malfunction. In an attempt to prevent nonspecific selenocysteine incorporation into proteins, we simultaneously overexpressed the gene encoding selenocysteine lyase from Homo sapiens (HsSL), which specifically catalyzes the decomposition of selenocysteine into elemental Se⁰ and alanine, and the gene encoding selenocysteine methyltransferase from Astragalus bisulcatus (AbSMT), which methylates selenocysteine into methylselenocysteine in rice. The transgenic plants showed normal growth under standard conditions. Se treatment resulted in higher levels of alanine and methylselenocysteine in transgenic plants than in wild-type plants, which indicated that this approach might have successfully redirected Se flow in the plant. Overexpression of HsSL and AbSMT in rice also endows transgenic plants with hyposensitivity to Se stress at the seed germination stage. The transgenic plants showed enhanced selenate and selenite tolerance, which was simultaneously supported by fresh weight values. Moreover, our phytoremediation assay revealed that the transgenic plants exhibited greatly improved Se elimination capabilities and accumulated about 38.5% and 128.6% more Se than wild-type plants when treated with selenate and selenite, respectively. This study offers hope that genetically modified plants could play a role in the restoration of Se-contaminated environment.

Seleno-Amino Acids in Vegetables: A Review of Their Forms and Metabolism

Seleno-amino acids are safe, health-promoting compounds for humans. Numerous studies have focused on the forms and metabolism of seleno-amino acids in vegetables. Based on research progress on seleno-amino acids, we provide insights into the production of selenium-enriched vegetables with high seleno-amino acids contents. To ensure safe and effective intake of selenium, several issues need to be addressed, including (1) how to improve the accumulation of seleno-amino acids and (2) how to control the total selenium and seleno-amino acids contents in vegetables. The combined use of plant factories with artificial lighting and multiple analytical technologies may help to resolve these issues. Moreover, we propose a Precise Control of Selenium Content production system, which has the potential to produce vegetables with specified amounts of selenium and high proportions of seleno-amino acids.

Hair Selenium Content in Middle-Aged and Elderly Chinese Population

Selenium (Se) is an essential nutrient element for human health, and middle-aged and elderly people (age ≥ 45 years old) are at higher risk of nutrient deficiency including Se due to their physiological characteristics. This study investigated the hair Se content of middle-aged and elderly people in China with the purpose of providing a reference for prescription of hair Se normal range in this population. In this study, the hair Se content of 2155 middle-aged and elderly people was detected with atomic fluorescence photometry. The participants were recruited from 15 provinces or municipalities spreading from south to north of China with a diverse Se content in soil. Additionally, the relationships between hair Se content with sex, age, and BMI were analyzed. The results found that the median and 95% quantile of hair Se content were 0.36 μg/g and 0.60 μg/g respectively, with a range of 0.08 to 20.04 μg/g in middle-aged and elderly Chinese. The hair Se content mostly concentrated at 0.23~0.48 μg/g in 81.11% of participants. The participants in Guangdong and Hunan provinces had the highest hair Se levels (medians were 0.51 and 0.50 μg/g, respectively), while Henan and Shaanxi provinces had the lowest levels (medians were 0.30 and 0.29 μg/g, respectively). In addition, the Se content of males was higher than that of females (p < 0.05), whereas there was no significant difference between different ages and BMI (p > 0.05). In conclusion, this study found that the hair Se content of middle-aged and elderly Chinese ranges from 0.08 to 20.04 μg/g, with median and 95% quantile of 0.36 μg/g and 0.60 μg/g, respectively. Our results provide a reference for the establishment of hair Se content in this population and suggest that the differences of region and sex should be considered when setting up the range.

The interaction between selenium and cadmium in the soil-rice-human continuum in an area with high geological background of selenium and cadmium

Natural selenium (Se)-rich areas in China are generally characterized by high geological background of cadmium (Cd). However, the interaction between Se and Cd in the soil-rice-human continuum in such areas remains elusive. The concentrations, bioaccessibilities, and biomarkers of Se and Cd in a typical Se-Cd rich area were determined through chemical analysis, in vitro digestion model and cross-sectional study, respectively. The results showed that the molar ratio of available Se/Cd in the soil was averaged at 0.55 and soil Se did not reduce Cd accumulation and transportation in rice. Se bioaccessibility increased from the gastric phase to the intestinal phase, but the opposite was the case for Cd bioaccessibility. Moreover, bioaccessible concentration of Cd was positively correlated to corresponding total concentration in rice but negatively associated with the logarithm of molar ratio of Se/Cd. The risk of Cd-induced nephrotoxicity for the exposure group was not higher than the reference group, which could be ascribed to the mitigative effect of Se. Males and elders were at higher risk of Cd-induced injury owing to higher urinary Cd (U-Cd) and β2-microglobulin (U-β2-MG), and lower urinary Se (U-Se). Our results suggested that Cd-induced health risk should be assessed from a soil-rice-human perspective and the interaction between Se and Cd should be taken into account.

Supranutritional selenium suppresses ROS-induced generation of RANKL-expressing osteoclastogenic CD4+ T cells and ameliorates rheumatoid arthritis

OBJECTIVE

The benefit of Se supplementation in rheumatoid arthritis (RA) has been tested in clinical trials, but results remain inconclusive. The objective of this study was to specifically investigate the potential benefit of supranutritional Se by examining human samples from an area with supranutritional Se intake and testing a mouse model of RA.

METHODS

Peripheral blood mononuclear cells (PBMCs) from RA patients (N = 57) and healthy controls (HC, N = 71) from an area of supranutritional Se intake (Enshi, Hubei, China) were analysed by flow cytometry. Serum cytokine and Se levels were measured by cytometric beads array (CBA) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. With sufficient or supranutritional selenium intake, mice were induced with collagen-induced arthritis (CIA) and examined for disease activity and immunopathology. The influence of Se supplementation in the generation of RANKL-expressing osteoclastogenic CD4+ T cells was investigated by in vitro assays.

RESULTS

In Enshi city, HC showed the above-normal concentrations of serum Se concentrations while RA patients were enriched in the normal range (70-150 ng mL-1) or below. RA patients with higher Se levels demonstrated milder disease and lower levels of C-reactive protein, IL-6, RANKL and Th17 cells. In the mouse CIA model, supranutritional Se supplementation delayed disease onset, ameliorated joint pathology and reduced CD4+CD44+RANKL+ T cells. Se supplementation could suppress RANKL expression in cultured mouse Th17 cells.

CONCLUSION

Supranutritional Se suppresses RANKL-expressing osteoclastogenic CD4+ T cells and could be beneficial to RA, which warrants formal testing in randomised clinical trials.

The Relevance of Plant-Derived Se Compounds to Human Health in the SARS-CoV-2 (COVID-19) Pandemic Era

Dietary selenium (Se)-compounds accumulated in plants are essential for human metabolism and normal physiological processes. Inorganic and organic Se species can be readily absorbed by the human body, but are metabolized differently and thus exhibit distinct mechanisms of action. They can act as antioxidants or serve as a source of Se for the synthesis of selenoproteins. Selenocysteine, in particular, is incorporated at the catalytic center of these proteins through a specific insertion mechanism and, due to its electronic features, enhances their catalytic activity against biological oxidants. Selenite and other Se-organic compounds may also act as direct antioxidants in cells due to their strong nucleophilic properties. In addition, Se-amino acids are more easily subjected to oxidation than the corresponding thiols/thioethers and can bind redox-active metal ions. Adequate Se intake aids in preventing several metabolic disorders and affords protection against viral infections. At present, an epidemic caused by a novel coronavirus (SARS-CoV-2) threatens human health across several countries and impacts the global economy. Therefore, Se-supplementation could be a complementary treatment to vaccines and pharmacological drugs to reduce the viral load, mutation frequency, and enhance the immune system of populations with low Se intake in the diet.

Food Chemistry of Selenium and Controversial Roles of Selenium in Affecting Blood Cholesterol Concentrations

Hypercholesterolemia, one of the major risk factors of cardiovascular diseases, is a worldwide public health problem. Nutraceuticals and phytochemicals are attracting attention as a result of their cholesterol-lowering ability and minimal side effects. Among them, selenium (Se) is on the list. The amount of Se in foods varies by region. Se-enriched fertilizers and feeds can raise the Se content in plants and animals, while some processing methods decrease food Se content. This review summarizes recent studies on (1) the content distribution of Se in foods and factors influencing Se-enriched foods, (2) the bioavailability and metabolism of Se, and (3) the role of Se in affecting blood cholesterol and cholesterol metabolism. Although the hypocholesterolemic effect of Se is equivocal, its cholesterol-lowering activity may be more remarkable when the Se supplementation is 200 μg/day or the baseline blood total cholesterol is above 200 mg/dL in humans with low Se status.

Multiple exposure pathways and health risk assessment of selenium for children in a coal mining area

Selenium (Se) presents a dual role to human body, harmful or beneficial, depending on its concentration. The exposure to this element has been associated to coal mining. Health risk assessment allows estimating and evaluating the risks that environmental hazards pose to vulnerable groups of populations. The present study aimed to analyze the risk of exposure to Se through multiple exposure pathways in children living in Candiota city, where the largest coal reserve of Brazil is located. Data from previous environmental (air, soil, drinking water, and food) and population parameters (age, weight, and food intake) were used to assess the health risk, which was calculated with real values (extracted from the population) and fixed reference values, based on the USEPA recommendation. Most of the children had low health risk (HQ < 1); however, in the most conservative scenarios (higher Se values in the different matrices), there was a high health risk in both scenarios, using population data or the USEPA parameters. The mean HQ using reference values was twice higher than using real values. Se content in air, soil, and drinking water did not represent important average daily dose in both scenarios. While, food intake was a main source of Se exposure, contributing with 96.9% of total Se intake. The findings of this study reinforce the importance of food intake for exposure to Se and the difference between HQs using population measures and fixed parameters of the USEPA highlights the need for adaptations to local scenarios for a better dimensioning of toxicological risk management actions.

Selenium transport and metabolism in plants: Phytoremediation and biofortification implications

The aim of this review is to synthesize current knowledge of selenium (Se) transport and metabolism in plants, with a focus on implications for biofortification and phytoremediation. Selenium is a necessary human micronutrient, and around a billion people worldwide may be Se deficient. This can be ameliorated by Se biofortification of staple crops. Selenium is also a potential toxin at higher concentrations, and multiple environmental disasters over the past 50 years have been caused by Se pollution from agricultural and industrial sources. Phytoremediation by plants able to take up large amounts of Se is an important tool to combat pollution issues. Both biofortification and phytoremediation applications require a thorough understanding of how Se is taken up and metabolized by plants. Selenium uptake and translocation in plants are largely accomplished via sulfur (S) transport proteins. Current understanding of these transporters is reviewed here, and transporters that may be manipulated to improve Se uptake are discussed. Plant Se metabolism also largely follows the S metabolic pathway. This pathway is reviewed here, with special focus on genes that have been, or may be manipulated to reduce the accumulation of toxic metabolites or enhance the accumulation of nontoxic metabolites. Finally, unique aspects of Se transport and metabolism in Se hyperaccumulators are reviewed. Hyperaccumulators, which can accumulate Se at up to 1000 times higher concentrations than normal plants, present interesting specialized systems of Se transport and metabolism. Selenium hyperaccumulation mechanisms and potential applications of these mechanisms to biofortification and phytoremediation are presented.

Using nano-selenium to combat Coronavirus Disease 2019 (COVID-19)?

The coronavirus disease 2019 (COVID-19) pandemic represents a severe global health threat. Selenium (Se), as one of the essential trace elements in human body, is well known for its antioxidant and immunity-boosting capabilities that induce a strong antiviral effect. In response to the global pandemic, we highlight here the current status of Se in combating different viruses, as well as the potential application of nano-selenium (nanoSe) in combating COVID-19.

Selenium dietary intake, urinary excretion, and toxicity symptoms among children from a coal mining area in Brazil

Selenium (Se) is necessary for several physiological functions in the human body; however, high concentrations of this element in coal mining areas raise the possibility of Se-related health risks. Children are much more vulnerable and at risk to environmental hazards than adults. The largest coal mining area of Brazil is located in the city of Candiota, where previous studies point to significant urinary Se concentrations among children. Food intake is the main Se source. The study aimed to evaluate dietary Se intake, as well as urinary Se excretion and classic symptoms of Se intoxication among children from Candiota and a control city in the same region. A cross-sectional study was carried out, with participation from 242 children between 6 and 12 years old in two cities in Rio Grande do Sul state, Brazil. Socioeconomic variables, dietary intake, and Se toxicity symptoms were evaluated through a structured questionnaire, and urinary Se levels were measured. Children from both cities had normal levels of Se intake and urinary excretion; however, children from Candiota had significantly higher levels of Se in both parameters in relation to the control city, especially for Se urinary excretion. There was low prevalence of Se toxicity symptoms. We conclude that coal mining activities may increase Se intake in children and consequently its urinary excretion.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

Selenium Toxicity in Plants and Environment: Biogeochemistry and Remediation Possibilities

Selenium (Se) is a widely distributed trace element with dual (beneficial or toxic) effects for humans, animals, and plants. The availability of Se in the soil is reliant on the structure of the parental material and the procedures succeeding to soil formation. Anthropogenic activities affect the content of Se in the environment. Although plants are the core source of Se in animal and human diet, the role of Se in plants is still debatable. A low concentration of Se can be beneficial for plant growth, development, and ecophysiology both under optimum and unfavorable environmental conditions. However, excess Se results in toxic effects, especially in Se sensitive plants, due to changing structure and function of proteins and induce oxidative/nitrosative stress, which disrupts several metabolic processes. Contrary, Se hyperaccumulators absorb and tolerate exceedingly large amounts of Se, could be potentially used to remediate, i.e., remove, transfer, stabilize, and/or detoxify Se-contaminants in the soil and groundwater. Thereby, Se-hyperaccumulators can play a dynamic role in overcoming global problem Se-inadequacy and toxicity. However, the knowledge of Se uptake and metabolism is essential for the effective phytoremediation to remove this element. Moreover, selecting the most efficient species accumulating Se is crucial for successful phytoremediation of a particular Se-contaminated area. This review emphasizes Se toxicity in plants and the environment with regards to Se biogeochemistry and phytoremediation aspects. This review follows a critical approach and stimulates thought for future research avenues.

Selenium and selenoproteins in viral infection with potential relevance to COVID-19

Selenium is a trace element essential to human health largely because of its incorporation into selenoproteins that have a wide range of protective functions. Selenium has an ongoing history of reducing the incidence and severity of various viral infections; for example, a German study found selenium status to be significantly higher in serum samples from surviving than non-surviving COVID-19 patients. Furthermore, a significant, positive, linear association was found between the cure rate of Chinese patients with COVID-19 and regional selenium status. Moreover, the cure rate continued to rise beyond the selenium intake required to optimise selenoproteins, suggesting that selenoproteins are probably not the whole story. Nonetheless, the significantly reduced expression of a number of selenoproteins, including those involved in controlling ER stress, along with increased expression of IL-6 in SARS-CoV-2 infected cells in culture suggests a potential link between reduced selenoprotein expression and COVID-19-associated inflammation. In this comprehensive review, we describe the history of selenium in viral infections and then go on to assess the potential benefits of adequate and even supra-nutritional selenium status. We discuss the indispensable function of the selenoproteins in coordinating a successful immune response and follow by reviewing cytokine excess, a key mediator of morbidity and mortality in COVID-19, and its relationship to selenium status. We comment on the fact that the synthetic redox-active selenium compound, ebselen, has been found experimentally to be a strong inhibitor of the main SARS-CoV-2 protease that enables viral maturation within the host. That finding suggests that redox-active selenium species formed at high selenium intake might hypothetically inhibit SARS-CoV-2 proteases. We consider the tactics that SARS-CoV-2 could employ to evade an adequate host response by interfering with the human selenoprotein system. Recognition of the myriad mechanisms by which selenium might potentially benefit COVID-19 patients provides a rationale for randomised, controlled trials of selenium supplementation in SARS-CoV-2 infection.

Safe utilization and zoning on natural selenium-rich land resources: a case study of the typical area in Enshi County, China

Selenium (Se) is an essential trace element. However, Se in soil is often accompanied by heavy metals, such as cadmium (Cd), because of geological background. The safe utilization of such Se-rich land resources remains a challenge. A typical Se-rich area located in Enshi County, China, was systematically investigated with geochemical and epidemiological methods. The results show that Se in the topsoil is 0.84 ± 1.39 μg/g, whereas that of Cd is 0.93 ± 1.63 μg/g. And the concentration of Se and Cd in corn is 0.22 ± 0.96 μg/g and 0.15 ± 0.32 μg/g, respectively, which is mainly related to the high concentrations in soil. The benchmark dose limit of urinary Cd for β2-microglobulin in subjects (n = 160) was calculated as 3.27 µg/g Cr. In view of crop-human dose effect and combining the relationship among the concentrations of crops and human biomarkers and the concentrations of crops and topsoil, this study established the models of land resource safety zoning. With that, the risk screening value of Cd in the soil could be obtained as 0.98 μg/g in this typical area. The proportions of priority utilization, safe utilization, and strict management of agricultural land area were 58.85%, 22.90%, and 18.25%, respectively, in Enshi, China. These results could provide scientific support for local agricultural development and ecological sustainability.

Selenium accumulation characteristics of Cyphomandra betacea (Solanum betaceum) seedlings

A pot experiment was conducted to study the selenium (Se) accumulation characteristics and the tolerance of Cyphomandra betacea (Solanum betaceum) seedlings under different soil Se concentrations. The 5 mg/kg soil Se concentration increased the C. betacea seedling biomass and photosynthetic pigment contents (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), whereas the other soil Se concentrations (10, 25, and 50 mg/kg) inhibited seedling growth. Increases in the soil Se concentrations tended to decrease the superoxide dismutase activity and soluble protein content, but had the opposite effect on the peroxidase and catalase activities. The 5, 10, and 25 mg/kg soil Se concentrations decreased the DNA methylation levels of C. betacea seedlings because of an increase in demethylation patterns (versus 0 mg/kg), whereas the 50 mg/kg soil Se concentration increased the DNA methylation levels because of an increase in hypermethylation patterns (versus 0 mg/kg). Increases in the soil Se concentrations were accompanied by an increasing trend in the Se content of C. betacea seedlings. Moreover, the amount of Se extracted by the shoots was highest for the 25 mg/kg soil Se concentration. Therefore, C. betacea may be able to accumulate relatively large amounts of Se and its growth may be promoted in 5 mg/kg soil Se.

Selenoprotein P as Biomarker of Selenium Status in Clinical Trials with Therapeutic Dosages of Selenite

Selenoprotein P (SELENOP) is an established biomarker of selenium (Se) status. Serum SELENOP becomes saturated with increasing Se intake, reaching maximal concentrations of 5–7 mg SELENOP/L at intakes of ca. 100–150 µg Se/d. A biomarker for higher Se intake is missing. We hypothesized that SELENOP may also reflect Se status in clinical applications of therapeutic dosages of selenite. To this end, blood samples from two supplementation studies employing intravenous application of selenite at dosages >1 mg/d were analyzed. Total Se was quantified by spectroscopy, and SELENOP by a validated ELISA. The high dosage selenite infusions increased SELENOP in parallel to elevated Se concentrations relatively fast to final values partly exceeding 10 mg SELENOP/L. Age or sex were not related to the SELENOP increase. Western blot analyses of SELENOP verified the results obtained by ELISA, and indicated an unchanged pattern of immunoreactive protein isoforms. We conclude that the saturation of SELENOP concentrations observed in prior studies with moderate Se dosages (<400 µg/d) may reflect an intermediate plateau of expression, rather than an absolute upper limit. Circulating SELENOP seems to be a suitable biomarker for therapeutic applications of selenite exceeding the recommended upper intake levels. Whether SELENOP is also capable of reflecting other supplemental selenocompounds in high dosage therapeutic applications remains to be investigated.

Sources, Fraction Distribution and Health Risk Assessment of Selenium (Se) in Dashan Village, a Se-Rich Area in Anhui Province, China

Soil, rock, potable water, animal food and human hair samples were collected from the Dashan village, a typical selenium (Se)-rich area of China. Se content and fraction distribution were determined to trace the source of soil Se and evaluate the potential health risk to humans. Total Se contents in soils ranged from 0.60 to 10.46 mg kg^- 1. The fractions of soil Se followed the order: residual Se (R-Se) > organic-bound Se (O-Se) > acid soluble Se (A-Se) > exchangeable Se (E-Se) > water soluble Se (W-Se). Total Se contents in rocks ranged from 0.07 to 24.8 mg kg^- 1. The dietary Se intake of local residents was estimated to be 261.2 µg day^- 1 and hair Se content varied from 0.34 to 1.35 mg kg^- 1, suggesting that the potential health risk should be concerned. Weathering of carbonaceous rock was speculated to be the primary source of soil Se according to the contents of Se in rocks, the distribution of Se in soil profiles and the relationships between Se and other elements in soils and parent rocks.

Global survey of urinary selenium in children: A systematic review

BACKGROUND

Selenium (Se) is an essential element in the human body that plays an important role in numerous fundamental physiological functions. However, the distribution of Se in the environment varies widely resulting in this element being available in a large concentration range in the ecosystem, and thus, in the human body. Urinary Se is a biomarker considered to be involved in adaptive mechanisms that help prevent health problems.

OBJECTIVES

The purpose of the present study was to conduct a systematic review to identify studies reporting the status of urinary Se in healthy children and create a global map.

METHODS

A literature search was conducted using MEDLINE (United States National Library of Medicine), Web of Science, Toxicology Bibliographic Information (TOXLINE), Latin-American and Caribbean Literature on Health Sciences (LILACS), and the grey literature. This study was registered in PROSPERO (international prospective register of systematic reviews) and was conducted in accordance with the PRISMA guidelines.

RESULTS

We identified 322 relevant articles, out of which 15 were included in this systematic review. The study identified a total of 4038 healthy children worldwide with urinary Se concentrations from 7.7 to 145.0 μg/L.

CONCLUSION

This is a pioneering study that provides evidence for the presence of Se in the urine of healthy children; we have shown that the available data is restricted to a small number of individuals and specific groups. Furthermore, there is a lack of information on urinary Se, especially in Latin America, Africa, and Asia.

Assessing the uptake of selenium from naturally enriched soils by maize (Zea mays L.) using diffusive gradients in thin-films technique (DGT) and traditional extractions

A generally accepted method to predict selenium (Se) bioavailability of long-term contaminated soils has not yet been established, even if risk assessments in selenosis areas are crucial. In this study, a set of methods were tested to assess the bioavailability of Se to field maize. Fifty maize (Zea mays L.) samples and corresponding soils were collected from a selenosis area (Ziyang, China). The diffusive gradients in thin-films (DGT) technique and the traditional chemical extraction methods, including seven single-step extraction procedures and a five-step sequential extraction were used to predict the bioaccumulation of Se in plant. The result verified the presence of 50% of total Se in the form of residual Se fraction, followed by organic-bound and Fe-Mn oxide-bound Se fractions in soil. In addition, Se⁶⁺, Se⁴⁺, and Se^2- were all detected in the solution extracted by H₂O, KCl, phosphate-buffered solution (PBS), NaHCO₃, ethylenediaminetetraacetic acid-2Na (EDTA-2Na) and ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA), but Se⁶⁺ was not extracted by NaOH. The Se extracted by single-step extraction methods was weakly correlated with the Se uptake by plants with relatively high Se concentration (>3 mg·kg^-1). The abilities of the tested methods to predict Se bioavailability in naturally Se-enriched soils declined in the following order: DGT > soil solution > PBS > KCl > H₂O > NaHCO₃ > EDTA > DTPA > NaOH. The ratio of C_DGT to soil solution Se (C_soln) totaled 0.13, indicating an extremely low Se supply from the soil solid phase to the soil solution. Se measured by DGT was mainly derived from the soluble and exchangeable Se fractions that can accurately reflect the plant-absorbed Se pool. Therefore, the DGT technique is highly applicable in the simultaneous prediction of Se bioavailability in naturally Se-enriched soils.

Selenium status in lactating mothers-infants and its potential protective role against the neurotoxicity of methylmercury, lead, manganese, and DDT

A total of 206 lactating mothers and their infants (3-12 months) were included in this study to evaluate postnatal exposure to neurotoxic pollutants such as methylmercury (MeHg), lead (Pb), manganese (Mn), dichlorodiphenyltrichloroethane (DDT) and its metabolites [dichlorodiphenyldichloroethane (DDD), and dichlorodiphenyldichloroethylene (DDE)] and their association with delayed neurological development and to explore the protective role of selenium (Se) against chemical neurotoxicity. Neurodevelopmental performance was evaluated using Denver Developmental Screening Test II and Parents' Evaluation of Developmental Status (PEDS). Multivariate log-binomial regression modeling was applied for both single and multiple exposures to chemicals using a principal component analysis that generated six principal components. Both mothers and their infants had been exposed to metals and DDT metabolites, with some exceeding the accepted permissible limits. The geometric means of MeHg, Pb, Mn, DDD, DDE and DDT levels in breast milk were 1.333, 45.327, 15.576, 0.069, 0.542 and 1.08 μg/l, respectively. A single-exposure model identified a high risk of reduced PEDS performance significantly associated with DDD in breast milk [relative risk (RR) = 1.484; 95% confidence interval (95%CI) = 1.091-2.019] and marginally significantly associated with Pb in the mothers' blood (RR = 2.164; 95%CI = 0.87-5.382). We did not find a protective role of Se in neurodevelopment due to its high levels in the mothers. Models of multi-chemical exposure indicated that Mn in blood and breast milk, Se in blood and Pb in the mothers' urine were marginally significantly associated with a high risk of reduced PEDS performance (RR = 0.424; 95%CI = 0.176-1.022). The use of multi-chemical exposure approach in early life risk assessments is important because it indicates real-world exposure. Our results were not conclusive because the sample size was small, so future studies examining the implications to health of the impact of prenatal/postnatal exposure to a mixture of chemicals in the Saudi population are merited.

Bioaccumulation and Health Risk Assessment of Heavy Metals in the Soil-Rice System in a Typical Seleniferous Area in Central China

Heavy metals are rich in seleniferous areas; however, the bioaccumulation and health risk of heavy metals are poorly understood, given the fact that selenium (Se) can inhibit the phytotoxicity and bioavailability of many heavy metals. The present study investigated the bioaccumulation of heavy metals in the soil-rice system in the Enshi seleniferous area of central China. Soils were contaminated by Mo, Cu, As, Sb, Zn, Cd, Tl, and Hg caused by the weathering of Se-rich shales. Among these heavy metals, Cd and Mo had the highest bioavailability in soils. The bioavailable fractions of Cd and Mo accounted for 41.84 and 10.75% of the total Cd and Mo in soils, respectively. Correspondingly, much higher bioaccumulation factors (BAFs) of Cd (0.34) and Mo (0.46) were found in rice, compared with those of other heavy metals (Zn 0.16, Cu 0.05, Hg 0.04, and Sb 0.0002). For the first time-to our knowledge-we showed that the uptake of Hg, Cd, and Cu by rice could be inhibited by the presence of Se in the soil. The probable daily intake (PDI) of Se, Cd, Mo, Zn, and Cu through consumption of local rice was 252 ± 184, 314 ± 301, and 1774 ± 1326 μg/d; and 7.4 ± 1.68 and 0.87 ± 0.35 mg/d, respectively. The high hazard quotients (HQs) of Mo (1.97 ± 1.47) and Cd (5.22 ± 5.02) suggested a high risk of Cd and Mo for Enshi residents through consumption of rice. Environ Toxicol Chem 2019;38:1577-1584. © 2019 SETAC.

Altered dietary selenium influences brain iron content and behavioural outcomes

Selenium (Se) is an essential micronutrient that provides antioxidant defence through selenoproteins, but at high concentrations, deleterious effects have been reported. The present study examines the antioxidant response in brain regions and behavioural functions in mice under various dietary Se paradigms; Se-deficient, Se-adequate and Se-excess. Se levels were found to be reduced in the cortex and hippocampus of Se-deficient animals, whereas no change was observed in animals on Se-excess diet. In the hippocampus, iron (Fe) levels increased in animals on Se-deficient and Se-excess diets. Moreover, in Se-deficient animals, Fe levels increased in cortex also. Interestingly, Se content in the hair positively correlated with the dietary Se intake. Total and Se-dependent glutathione peroxidase activity decreased in the cortex, hippocampus and cerebellum of animals on Se-deficient diet. On the other hand, the activity of these enzymes decreased in the cortex of animals on Se-excess diet. Further, lipid peroxidation increased in the cortex of animals on Se-deficient diet and in the hippocampus of animals on Se-excess diet. Cognitive functions assessed by Morris water maze and Y-maze tests revealed deficits in Se-deficient state. However, in Se-excess state cognitive deficits were observed only in Y-maze test. These findings suggest that long-term dietary variation in Se influences oxidative stress that impacts cognitive functions. Therefore, it is suggested that maintenance of Se status during postnatal development may be crucial for mental health.

Selenium translocation in the soil-rice system in the Enshi seleniferous area, Central China

Rice is an important source of selenium (Se) exposure; however, the transformation and translocation of Se in the soil-rice system remain poorly understood. Here, we investigated the speciation of Se in Se-rich soils from Enshi, Central China and assessed which Se species is bioavailable for rice grown in Enshi. Extremely high Se concentrations (0.85 to 11.46 mg/kg) were observed in the soils. The soil Se fractions, which include water-soluble Se (0.2 to 3.4%), ligand-exchangeable Se (4.5 to 15.0%), organically bound Se (57.8 to 80.0%) and residual Se (6.1 to 32.9%), are largely controlled by soil organic matter (SOM) levels. Decomposition of SOM promotes the transformation of organically bound Se to water-soluble Se and ligand-exchangeable Se, thereby increasing the bioavailability of Se. The bioaccumulation factors (BAFs) of Se decrease in the following order: roots (0.84 ± 0.30) > bran (0.33 ± 0.17) > leaves (0.18 ± 0.09) > polished rice (0.14 ± 0.07) > stems (0.12 ± 0.07) > husks (0.11 ± 0.07). Selenium levels in rice plants are affected by multiple soil Se fractions in the soil. Water-soluble, ligand-exchangeable and organically bound Se fractions are the major sources of Se in rice tissues.

Selenium and mercury concentration in drinking water and food samples from a coal mining area in Brazil

Selenium (Se) is an essential element for human health and can also alleviate the toxicity of elements such as mercury (Hg), which is considered deleterious to health. The study area is an important coal mineral region in Brazil, generating 40% of all Brazilian coal. During the coal mining process, Se and Hg are released, which can induce potential human health risks via the food chain. The purpose of the present study is to determine total Se and its species and total Hg in drinking water and food locally produced from a coal mining area, to assess the impact of coal mining. The samples were collected in two cities, with and without coal mining influence. Total Se levels in drinking water and food were assessed by inductively coupled plasma mass spectrometry (ICP-MS) and its species by high-performance liquid-ICP-MS, while total Hg was determined by cold vapor atomic fluorescence spectrometry. Drinking water (1.1 ± 0.2 mg L^-1 dry weight) (p = 0.02) and tomatoes (1.5 ± 0.1 mg kg^-1 dry weight) (p = 0.01) from the coal mining area had higher total Se concentration than the control area. The highest Se concentrations were found in animal-based food (6.4 ± 0.8 mg kg^-1 dry weight) with an important contribution of Se IV (65%). The analyzed sample did not accumulate a significant amount of Hg. Future studies on the estimates of daily intake of these elements and dietary pattern of the population are needed to make appropriate dietary recommendations and support public health action.

A comprehensive review on environmental transformation of selenium: recent advances and research perspectives

Selenium (Se) is an important micronutrient and essential trace element for both humans and animals, which exist in the environment ubiquitously. Selenium deficiency is an important issue worldwide, with various reported cases of its deficiency. Low selenium contents in some specific terrestrial environments have resulted in its deficiency in humans. However, high levels of selenium in the geochemical environment may have harmful influences and can cause a severe toxicity to living things. Due to its extremely narrow deficiency and toxicity limits, selenium is becoming a serious matter of discussion for the scientists who deals with selenium-related environmental and health issues. Based on available relevant literature, this review provides a comprehensive data about Se sources, levels, production and factors affecting selenium bioavailability/speciation in soil, characteristics of Se, biogeochemical cycling, deficiency and toxicity, and its environmental transformation to know the Se distribution in the environment. Further research should focus on thoroughly understanding the concentration, speciation, Se cycling in the environment and food chain to effectively utilize Se resources, remediate Se deficiency/toxicity, and evaluate the Se states and eco-effects on human health.