Selenium in modern agriculture

Selenium (Se) is a micronutrient necessary in small amounts for the proper organism functioning. Se‐rich agriculture, also known as special agriculture, has the potential to improve agricultural production and produce beneficial agricultural products. This review discusses the various applications of Se in agriculture, including animal husbandry, crop production and aquaculture. It covers Se metabolites, the function and regulation of selenogenomes and selenoproteomes of human and animal food and the recycling of Se in food systems and ecosystems. Finally, the review identifies research needs that will support the basic science and practical applications of dietary Se in modern agriculture.


INTRODUCTION
Modern agriculture is based on the development and application of agricultural science and technology which relies on modern natural science to improve agricultural production techniques and expand the scope of agricultural applications. 1 Selenium (Se) is a key element in modern agriculture and is used in three main sectors: pre-production, production and postproduction. Pre-production includes seed and feed, production includes planting and farming and postproduction includes processing and distributing products. Despite being rare in the earth's crust, 2 Se is essential for animals and humans due to its role in antioxidant enzymes and selenoproteins, which help to regulate redox balance in the body and improve animal immunity. 3 As a result, Se is widely used in poultry, livestock husbandry and aquaculture. Additionally, Se can extend the shelf life of agricultural products, counteract heavy metals and boost the metabolism of antibiotics in the body. 4 In the pre-production sector, Se is mixed with other substances to feed poultry, livestock and aquatic products; in the mid-production sector, plants and microorganisms absorb Se from the soil and use it to form Se-containing organic matter, which promotes the growth and development of organisms and in the postproduction sector, the addition of Se can improve the quality of certain food products, such as improving water retention in Se-enriched broilers. 5 Therefore, the effective development and use of Se is critical for agricultural performance.
In this review article, we provide an overview of Se through three key aspects: the mechanism of absorption and metabolism of Se; the functions of Se in soils and environment, plant growth, livestock industry and aquaculture and the application of Se in storage and transportation.

FUNCTIONS AND METABOLISM OF SELENIUM
Se is a metalloid trace element existing in the environment in both inorganic and organic forms. There are four different inorganic chemical forms: selenide (Se 2− ), elemental state selenium (Se 0 ), selenite (Se 4+ ) and selenate (Se 6+ ). The organic forms of Se include selenocysteine (SeCys) and selenomethionine (SeMet), which are formed through competition with sulphur (S) in the S-containing amino acids, cysteine (Cys), and methionine (Met). 4 In general, plants tend to absorb inorganic forms of Se more efficiently, while organic forms are more easily absorbed by mammals. In mammals, the absorption of Se occurs mainly in the duodenum, where it is actively transported through a sodium pump. Se absorption can also occur in the intestine, and the method of uptake varies depending on the chemical form of Se. Selenite is absorbed by simple diffusion and selenate is absorbed through a cotransport of sodium selenate and exchange selenate/OH −6 and organic forms (i.e., SeMet and SeCys) follow the same way as amino acid uptake. For example, the SeMet is actively carried via intestinal Met transporters and enters the Met pool of the body. 7 SeMet can also be metabolised in the liver through the Met cycle and transsulphuration pathways, yielding SeCys as a transient form, which is promptly converted into selenide, which in turn, is used for selenoprotein synthesis. 8 SeCys-containing selenoprotein is the primary form through which Se exercises its functions in humans and animals. 4 Due to the essential role in maintaining cell and tissue function, SeCys is considered to be the 21st amino acid. 9 Selenoproteins are involved in regulating various physiological and biochemical processes, including the activation and inactivation of thyroid hormones, the removal of glutathione-dependent hydroperoxide, the reduction of thioredoxins, the synthesis of selenophosphate, the repair of oxidised methionine residues and the folding and degradation of endoplasmic reticulum-associated proteins among others. 10 Twenty-five selenoprotein genes have been found in humans and animals, including the iodothyronine deiodinase family (DIO1, DIO2 and DIO3), the glutathione peroxidase family (GPX1, GPX2, GPX3, GPX4 and GPX5), the thioredoxin reductase family (TXNRD1, TXNRD2 and TXNRD3), MSRB1 (methionine-R-sulfoxide reductase 1), SELENOF, SELENOH, SELENOI, SELENOK, SELENOM, SELENON, SELENOO, SELENOP, SELENOS, SELENOT, SELENOV, SELE-NOW and SPS2 (Table 1). 11 The presence of selenoprotein genes varies in different organisms (Table 1), with 41 selenoprotein genes found in fish, in contrast to the lower gene copies in humans and animals (Table 1). 12 In addition, SELENOP is composed of two structural domains, with the larger N-terminal domain responsible for maintaining the intracellular redox potential and the smaller C-terminal domain responsible for mediating Se translocation. 13 It is considered a marker of Se concentration in vivo and plays an important role in the transport of Se in tissues and in maintaining homoeostasis in vivo.
Se has been shown to play a role in the prevention and management of various human diseases, such as cancer, cardiovascular disease, cognitive decline and thyroid dysfunction. 13 As a component of selenoproteins, Se is essential for proper immune function and play a role in preventing oxidative damage to cells. 14 Deficiency in Se can result in several health problems, including hypothyroidism, muscle weakness and a weakened immune system. 15 It is important to note that while adequate Se intake is important for overall health, excessive intake can also lead to health problems. Excessive intake of Se through supplements can lead to a condition called selenosis, which is characterised by a range of symptoms, including hair and nail brittleness, skin rashes, nausea, diarrhoea, fatigue and nervous system disorders. 4 The tolerable upper limit for Se intake is 400 μg per day for adults. 16 It is recommended to have an adequate intake of Se through a T A B L E 1 Comparison among selenoproteins found in the food of humans and animals. balanced diet, as excessive supplementation can lead to selenosis and other health problems.

SELENIUM IN THE SOIL
Soils are the source of our food and therefore many of our nutrients. In general, the soil will be considered as Se deficient if the Se content is lower than 0.5 mg/kg; on the contrary, it will be considered as Se-rich soil if the Se content is higher than 4 mg/kg. Although there are parts of the world with high Se content in the soil, such as Enshi (Se > 100 mg/kg, Hubei Province, China), northwest India (Se > 4 mg/kg) and northern California (Se~30 mg/ kg). A significant portion of the world's soil is deficient in Se. In China, there are 40 counties with Se-deficient soil, particularly in the northeastern region, the Loess Plateau, and the eastern region of the Tibetan Plateau, 4 where the Se content is below 0.2 mg/kg. Deficient Sesoils also exist in countries, such as Qatar (0.12-0.77 mg/kg) and Saudi Arabia (0.1-0.11 mg/kg). 17 In these regions, inadequate intake of Se usually leads to Keshan and Kaschin-Beck diseases. 18 To address this issue, people have developed Se-rich soils. The fugitive forms of Se in soil can be mainly classified into groups, including residual Se (RES-Se), Se bound to organic matters (OM-Se), acid soluble Se (FMO-Se), water soluble Se (SOL-Se), exchangeable Se and Se bound to carbonate (EX-Se). Se 4+ and Se 6+ make up 73%-76% of total soil Se. 19 These forms of Se in the soil are subject to interconversion. 20 Plants readily take up Se from the soil and use Se-assimilating enzymes to incorporate it into organic compounds. Because of the chemical similarity between Se and sulphur (S), Se is usually incorporated into plants by substituting S to form S-containing amino acids, mainly SeMet. 4 Humans and animals consume Se through the consumption of Se-rich plants, such as apples and black bean. A portion of Se is excreted in faeces, which is again decomposed and utilised by microorganisms, and finally recycled back to the soil. This is the ecological cycle of Se ( Figure 1).

SELENIUM IN PLANTS
Se is also important for plant growth and development.
Moderate application of Se can enhance photosynthesis of plants, resulting in increased yield and increased resistance to stress and antioxidant capacity. 21 However, high concentration of Se plays a side effect. This is exemplified in Se hyperaccumulators where SeMet biosynthesis is limited by the conversion of the precursor SeCys into non-protein amino acids like Se-methylselenocysteine (MeSeCys), γ-glut-amyl-Semethylselenocysteine (GGMeSeCys) and selenocystathionine. The sequestration of Se into these metabolites The ecological cycle of selenium. Se is absorbed directly by plants from the soil. Once absorbed by plant roots, inorganic Se is converted into SeMet and other forms of Se chemicals through the plant sulphur assimilation pathway. In animals, Se is absorbed into the bloodstream mainly through the stomach and intestines. It binds to α and β globulins in the blood and is transported into the tissues via the plasma. Inorganic Se is passively diffused through the intestinal wall, and once absorbed, is converted into hydrogen selenide (H 2 Se) by the action of reduced coenzyme II, coenzyme A, adenosine-5 0 -triphosphate and magnesium. It is then synthesised as SeCys to form selenocytecontaining proteins or metabolised products for excretion. Organic Se is converted to seleno-substituted amino acids in the small intestine and are actively transferred as monomeric amino acids through the mucosal epithelium into the bloodstream. These amino acids are transported to the liver to bind with selenoproteins or directly to the tissues to bind with tissue proteins. After uptake of selenide by microorganisms, selenate or selenite can be reduced to monomeric Se. Finally, monomeric Se re-enters the ecological cycle.
reduces or completely circumvents the integration of SeCys and SeMet into proteins. 4 The biosynthesis of most Se compounds may depend on the enzymes involved in the S assimilation pathway. The concentration of Se also affects plant growth, with low concentrations promoting plant growth and high concentrations inhibit it. 22 For example, lower concentrations of selenite solution can promote the germination of many buckwheat seeds, while high concentrations (Se ≥ 3 mg/L) can be detrimental to the seeds. Studies have shown that sodium selenite is unlikely to affect the biomass of grown chard at peak bioconcentrations less than 10 mg/ kg. 20 By growing cabbage shoots hydroponically in an Se-nutrient solution, when the concentration of Se is less than 1.0 mg/L, it promotes the growth of cabbage shoots and the biomass gradually increases, while when the concentration of Se-nutrient solution is more than 2.5 mg/L, it inhibits growth and reduces biomass. 23 Se may affect photosynthesis in plants in two different ways: by directly affecting the accumulation of ROS and regulating the enzyme activities required for photosynthesis 24 or by directly affecting the electron transfer process necessary for photosynthesis by inhibiting of Fe-S haemoglobin synthesis. 25 Some studies have shown that Se application to rice that starts composting at an early stage could significantly increase the rate of multi net photosynthesis in rice, accelerating photosynthesis and resulting in an increase in photosynthetic yield. 26

Application of selenium in feed
Poultry and livestock feed are primarily plant-based with added nutrient supplements. Trace element nutrition, such as Se, is crucial for animal growth, health and reproductive performance. 20 In the poultry industry, it is common to supplement diets with various forms of Se, such as selenate, sodium selenite and organic forms, namely OH-SeMet, SeMet and Zine-SeMet, to improve the immunity and overall health of the animals. 27 Compared to inorganic Se, organic Se has been shown to produce a stronger immune response and result in higher Se concentrations in tissues. 8 An increase in dietary Se intake of poultry and livestock leads to a corresponding increase in Se content in eggs and meat. Se is a key component in antioxidant enzymes, such as GPX, SOD and catalase, which are important for avian growth and development. An increase in Se content increases GPX activity in birds. 28 To improve antioxidant homoeostasis and development in laying birds, Se supplementation in the form of sodium selenite, Se nanoparticles (SeNPs) or Se yeast is commonly used to increase GPX4 levels. 29 Studies have shown that supplementation with Bacillus Se-rich bacteria increased the levels of T-AOC, T-SOD and GPX in the pectoral muscle of chicks. 30 Selenoprotein genes that are sensitive to changes in Se levels in chickens include GPX1, GPX3, GPX4, SELENOM, SELENOP1 and SELENOU but genes such as DIO1, DIO2, DIO3, GPX2, SELENOP2 and TXNRD2 are not affected. 31 Dietary addition of Se increases ATPase activity and antioxidant levels in poultry arteries and veins. 32 Additionally, different forms of Se (e.g., sodium selenite and Se yeast) have similar effects in promoting antioxidant capacity in laying hens. 33 Earthworm meal supplemented with 1 mg/kg Se increased serum levels of GPX, SOD, IgG and IL-2, thereby improving antioxidant levels and immune function in laying hens. 34 Furthermore, dietary supplementation with SeNPs improved intestinal function and the development of broiler chickens. 35 These studies demonstrate the importance of Se in avian growth and development. In pigs, elevating dietary Se from 0.3 mg/kg to 3 mg/kg enhanced GPX activities in the liver, muscle, and thyroid. 36,37 Compared with 0.17 mg Se/kg, 0.5 mg Se/kg enhanced GPX1 activity in the porcine muscle. 38 The 3 mg/kg Se diet elevated SELENOP in the muscle 39 and thyroid, 40 and SELE-NOS in the thyroid. 40 Plasma GPX3 activity of pigs was decreased by dietary Se deficiency, but remained unchanged at week 8 41 or was elevated at week 16 after the treatment of the high Se diet. 40

Selenium and reproduction
Previous studies have established a relationship between Se deficiency and reproductive problems in animals. 42 In mammals, Se deficiency can lead to placental retention in dairy cattle, reduced fertilisation rates in beef cattle 43 and decreased conception rates in sheep. 44 Previous reports have also shown that Se deficiency in chickens can lead to a reduction in body weight. 45 Supplementing broiler diets with Se-yeast has been shown to improve the primary immune response 46 and the hatching rate of fertilised eggs in hens. 47 Se is also important for the reproductive capacity of boars. Boar sperm are particularly sensitive to lipid peroxidation, 48 As they contain a high proportion of polyunsaturated fatty acids (PUFAs) in the phospholipid fraction of their membranes. 49 This allows for easy sperm motility and fusion with the egg, but also makes them vulnerable to free radical attack and lipid peroxidation. Therefore, antioxidant protection is an important determinant of boar semen quality.
Se is vital for boars and has a similar impact on sows as well. Organic Se has a greater effect on sows than inorganic Se, and the addition of inorganic Se to the diet of sows during gestation can increase Se levels in sow serum (7.7%), colostrum (44.8%) and milk (69.5%). 50 Gestation is a period of sustained oxidative stress 51 and sows experience increased DNA damage and reduced antioxidant protection. 52 At around 60 days postpartum, GPX activity decreases with a decrease in serum Se. 53 Se levels in the body are also positively correlated with the production of certain antioxidants. One study showed that sows supplemented with organic Se produced piglets with serum Se concentrations and GPX activity that were 29.44% and 6.4% higher, respectively, compared to piglets produced by sows supplemented with inorganic Se. Moreover, organic Se not only increased the weaning MODERN AGRICULTURE -37 weight of piglets (6.93%), but also improved the ability of piglets to adapt to intestinal infections and adverse environments during early growth. 54 Overall, Se plays a key role in the growth, reproduction and survival of females.

Selenium and growth performance
Se plays a crucial role in animal production, mainly by participating in the synthesis of antioxidant enzymes associated with selenoproteins. One of the most studied enzymes is GPX, which is the earliest and high level of selenoprotein-involved enzymes found in mammals. GPX enzymatic reactions protect cells from oxidative damage by scavenging hydrogen peroxide and lipid peroxides, derivatives of superoxide anion radicals, thus maintaining normal structure and function. 55 The antioxidant enzymes involved in the synthesis of selenoproteins together create an antioxidant barrier for the animal organism. Additionally, Se has been found to affect the metabolism of nonenzymatic antioxidants by binding to cell membranes, acting against free radicals and protecting cell membrane. 55 Regarding the effect of Se on animal performance, most studies have shown that Se has a positive effect on promoting animal growth and development, and the effect of organic Se is superior. Chicks fed the Sedeficient diet developed NPA, along with poor growth, poor feathering and mortality as early as on day 18. 56 Huang et al. also showed that chicks fed the Sedeficient diet manifested typical clinical signs of exudative diathesis and showed poor growth performance, decreased plasma concentrations of Se and ɑtocopherol and low plasma GPX activity and liver and muscle GPX activities. 31 The final body weight and overall average daily gains (ADG) of chicks were additively decreased by dietary Se (34%-38%) and vitamin E (7%-10%) deficiencies. Average daily feed intake (ADFI) and gain/feed efficiency were decreased (20%) by dietary Se deficiency. 31 A study comparing the effects of Se methionine and sodium selenite on growth performance in Xianju chickens found that the body weight gain and feed conversion ratio of the organic Se group were higher than those of the inorganic Se group with significant differences. The results showed that yeast Se improved the ADG and ADFI of piglets and reduced the feed-to-weight ratio and diarrhoea rate, with significant improvement in ADFI and reduction of diarrhoea rate (p < 0.05). 57 Research has also found that the weaning litter weight, weight gain per litter and average daily weight gain of piglets were significantly higher than those of sodium selenate in the experimental group with 0.5 mg/kg yeast Se in the diet. 58 In an experiment conducted in China, the effect of organic Se in the form of Se-Yeast on growth performance and diarrhoea incidence of weaning piglets from days 21 through 42 was investigated. 59 When dietary sodium selenite (0.2 mg/kg) was replaced by the same amount of organic Se in the form of Se-Yeast, the following advantages were seen: ADG significantly increased (290.9 vs. 274.1 g/day) and decreased incidence of diarrhoea (1.32% vs. 1.72%) decreased the feed cost/kg weight gain by 11%. 59

Selenium and meat quality improvement
Se is also essential for the meat quality of livestock products. 60 A typical disease that occurs in chickens with Se deficiency is nutritional muscle atrophy, 31 highlighting Se's irreplaceable role in the composition and integrity of muscle. 61 Many reports have shown that Triiodothryonine (T 3 ) controls animal growth by controlling the assimilation of energy and protein in the body. 5 0 deiodinase is the key enzyme for the synthesis of triiodo adenine (T 3 ) and that Se is a cofactor and activator of 5 0 deiodinase. 62 It has been reported that increasing Se levels from 0.10 mg/kg to 0.25 mg/kg can improve body weight in broilers, 63 indicating that Se is readily absorbed by broilers. Se can enhance the activity of serum GPX in animals, improve the oxidative capacity of the body, prevent the oxidation of myoglobin or oxy-myoglobin, improve meat colour, meat quality and muscle water retention. 64

Application of selenium in aqua feeds
The addition of different ingredients to fish feed may cause changes in various biochemical parameters in the organism. Alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities can indicate liver damage in fish and the health status of the organism. It has been shown that the addition of SeNPs to the diets of Nile tilapia, carp, Caspian roach and grass carp reduced serum levels of AST, ALT and ALP, 60 suggesting that SeNPs have a protective effect on the liver and other organs of fish. Elevated AST and ALT activity in serum may be associated with liver damage or dysfunction in fish. Although an increase in transaminases can lead to organismal organ damage, a decrease in transaminase levels may improve these problems in fish. Increases in glutathione and ghrelin levels may indicate stress conditions in fish.

Selenium and growth performance of aquatic animals
Se is an important component of the enzyme deiodinase and plays a role in the secretion of pituitary growth hormone. 65 Adding Se to fish feed can promote increased activity of thyroid hormones, which in turn promotes growth and development. Se is also involved in the composition of enzymes for digestive enzyme synthesis and can induce the release of more nutrients from the intestinal epithelium that improve food digestion. 66 SeNPs can increase the intracellular protein content of the intestinal epithelial cells of carp (Carassius auratus gibelio), which may lead to improved feed utilisation and growth performance. 67

Selenium and quality enhancement of aquatic products
The addition of a specific concentration of Se glucosamine can promote the growth of South American white shrimp, increase the Se and amino acid contents and improve the diversity of intestinal flora, thus enhancing the quality of the shrimp culture. Supplementing grass carp bait with 2-4 mg/kg of yeast Se has been shown to significantly improve the weight gain rate, end-of-test weight and feed conversion rate of grass carp. Studies on the effects of different levels of Se on the growth performance and antioxidant function of juvenile carp have revealed that while different levels of Se did not have a positive effect on the growth performance of juvenile carp, they did significantly enhance its antioxidant function. 68 Research on the effects of different Se sources and levels on the growth performance and immune enzyme activity of juvenile slanted grouper has found that the optimum level of Se addition in the bait for juvenile slanted grouper was sodium selenite 0.98 mg/kg and SeMet 1.01 mg/kg. Juvenile slanted grouper showed the best growth performance under these conditions. 67 These findings suggest that the selection of an appropriate Se source and level of addition in aquatic fish bait can improve the growth performance of fish organisms, which may be related to the strong antioxidant function of Se, and its ability to improve the antistress capacity of fish.

APPLICATION OF SELENIUM IN STORAGE AND TRANSPORTATION
The application of Se during the growth of fruit trees can enhance the storage resistance of the fruit. This is due to its positive impact on a range of intrinsic qualities, including flesh hardness and soluble solids content. Additionally, increased antioxidant enzyme activity and cell membrane integrity further improve the storage tolerance of the fruit. Foliar application of Se was found to be effective in improving the Se content and nutritional properties of 'Red Star' apples, slowing down the rate of ethylene biosynthesis, maintaining fruit hardness and delaying fruit ripening, thus positively affecting fruit storability. 68 The same holds true for grapes, where Se application increased the Se content, delayed fruit ripening, and improved the nutritional quality of the fruit, allowing for better post-harvest quality preservation and mature stage sales with less quality loss. 68 These findings suggest that pre-harvest Se treatment is an effective way to improve the storability of fruits and other horticultural crops.

RISK OF EXCESSIVE SELENIUM APPLICATION IN AGRICULTURE
Inappropriate Se application can pose several risks to crops, soil organisms and the wider environment. One of the main risks is toxicity. Excessive Se application can lead to toxicity in crops, livestock and aquatic organisms, which can result in decreased growth, decreased productivity and even death. 69 Additionally, excessive Se application can lead to toxicity in soil organisms, including beneficial microorganisms, which can have a negative impact on soil health and fertility. 70 Another risk associated with Se application in agriculture is interaction with other essential nutrients in the soil and/or diets, such as nitrogen, phosphorus and potassium. 71 Inappropriate Se application can result in imbalances in soil nutrient status, which can be harmful to other species and the wider ecosystem.
It is important to consider these risks for optimal application of Se in agriculture. Careful dosing, using organic Se sources, regular monitoring of Se concentrations in agricultural environment and exploring alternative strategies for improving Se status in various conditions can help to minimise the risks associated with Se supplementation and ensure its safe and effective application in agriculture.

INDUSTRIALISATION OF SELENIUM APPLICATION
Despite the risks, the industrialisation of Se is in strong demand. It involves the production and commercialisation of Se-enriched food and probiotics, the establishment of Se industrial demonstration bases and the creation of Se branding strategies. To produce Se-enriched food and probiotics, various methods can be employed such as soil amendment with Se-enriched fertilisers, foliar application of Se and the addition of Se to animal feed for meat and dairy products. Additionally, the use of Se-enriched yeast as a probiotic supplement has also been explored. 4 The establishment of Se industrial demonstration bases can help to showcase the benefits of Se and its potential applications in modern agriculture. These demonstration bases can also serve as training centres for farmers and other stakeholders, providing practical information on Se application methods and the benefits of Se-enriched crops and livestock. Finally, creating a strong Se branding strategy can help to raise awareness about the benefits of Se and increase demand for Se-enriched food and probiotics. This can be done through targeted marketing campaigns, partnerships with relevant organisations and the creation of a recognisable Se brand.
In summary, the industrialisation of Se involves a combination of production, demonstration and branding efforts to promote the benefits of Se and increase its utilisation in agriculture and related industries.

CONCLUSION
Se is known to have a strong antioxidant and antiinflammatory capacity as well as potential antimicrobial properties. As a result, various forms of inorganic and organic Se are widely used in food fortification and MODERN AGRICULTURE -39 animal feed production. However, there are some challenges associated with Se use in these applications. In particular, the optimal dose for different forms of organic Se is currently unknown. This means that there is a risk of toxicity if high doses of organic Se are consumed. Inorganic forms of Se, on the other hand, are easy to get or cheap but can be less effective in providing the desired health benefits compared to organic forms. 72 Therefore, it is important to carefully consider the type and dose of Se used in food fortification and animal feed production in order to ensure safety and effectiveness. Further research is needed to determine the optimal dose and form of Se for different applications and to fully understand its potential health benefits.
To promote a robust, healthy and sustainable development of the Se industry, it is critical to establish standards and regulations for Se-enriched agricultural products and foods. Currently, there are various tools and methods available for evaluating the total Se status in individuals, including both organic and inorganic forms of Se. These methods typically involve analysis of blood, urine or hair samples to determine Se levels. 73 However, while these tools are useful for assessing overall Se status, they may not provide a comprehensive picture of the organic Se status, which is thought to be the most biologically active form of Se. As a result, there is a growing interest in developing more advanced technologies for assessing organic Se. This is important because improved methods for organic Se assessment could provide a more comprehensive understanding of Se status and its impact on health. Additionally, the development of a rapid Se detection kit is in high demand to monitor dietary Se intake and in vivo Se dynamics.
The rapid Se detection kit can be a handheld device or a point-of-care test that can quickly and easily measure Se levels in biological and environmental samples. The device would likely use a variety of analytical techniques, including spectrophotometry, immunoassay or mass spectrometry, to determine Se levels in a sample. The tool will be very useful for monitoring Se status and greatly enhance our understanding of Se and its impacts on agriculture, environment and human health.

AUTHOR CONTRIBUTIONS
Jia-Qiang Huang, Zhao-Hui Wang, Le-Li Wang and Lv-Hui Sun wrote and edited the paper; Yu-Long Yin and Jia-Qiang Huang were primarily responsible for the final content and all authors read and approved the final manuscript.