Selenium was discovered by Jons Jacob Berzelius in 1808 and derived from the Greek word selene which means the moon. This element is the 69th most abundant element on the earth and belongs to the group V periodic table [15]. It exists in different oxidation states such as selenite (IV; SeO₃²⁻), selenate (VI; SeO₄²⁻), elemental Se (0), and organic forms such as dimethyl selenide, methyl selenide, selenomethionine, selenocysteine. According to Paul and Saha (2019), California (38%), Ireland (32%), Punjab (8%), Jaipur (9%), and China (2%) are the most selenium-polluted regions in the world. Selenium is released to the environment by natural and anthropogenic activities such as volcanic eruption, mining, weathering of rocks, coal mining (so-called selenium curse of the eastern range of the north American Rocky mountains) and combustion, and effluent waste by some industries and agriculture leading to polluted areas [16,17,18,19,20,21,22].

There is a narrow limit between selenium toxicity and the amount required for human health. Paradoxically, less than 40 µg/day of selenium is essential for the body and more than 400 µg/day is toxic to the human body [23]. Daily intake of selenium in food varies from 0.055 to 0.4 mg per day, required for crucial body functions such as antioxidant defense, protein folding, and cell signaling [24,25]. Some primary selenoprotein genes in mammals have central roles in Redox signaling (GPX1, GPX3, GPX4, TRXRD1, TRXRD2), Protein folding and degradation (SEP15, SELS), and metabolism (SEP1, SPS1, SPGS) [26,27]. Selenium deficiency is associated with Keshan disease [28,28,29,30,31], muscle weakness [32], Kashin Beck [33,34,35,36,37], cardiomyopathy [38,39,40,41], and redox dysregulation [42]. In contrast, exposure to excessive amounts of selenium can lead to disorders such as selenosis, loss of hair and nails, redox dysregulation, mitochondrial dysfunction, and cell growth inhibition [43,44,45,46,47,48].

Arsenic (As, group V periodic table) is the 20th most abundant elements in the earth’s crust with a terrestrial abundance of about 1.5–3 mg/kg and an average abundance of about 5 mg/kg [15]. Anthropogenic and natural activities are the main sources of arsenic pollution in the world. The groundwater of different regions of Asia (Bangladesh [49,50,51,52], India [53,54,55,56,57,58], China [59,60,61,62,63,64], Nepal [65,66], Cambodia [67], Vietnam [68], Myanmar [69], Pakistan [70,71,72,73,74,75], and Indonesia [76]), North and South America (USA [77,78], Canada [79,80], Argentina [81], Chile [82], and Mexico [83]), Europe (Hungary [84]) and Africa (South Africa [85]) are contaminated by arsenic [86]. Arsenic occurs in different oxidation states in nature, including arsenate (+5, AsO₄³⁻), arsenite (+3, AsO₃³⁻), elemental arsenic (0), and arsenide (−3). Akin to SeO₃²⁻, AsO₃³⁻ is the most toxic form among arsenic oxyanions in the environment [87,88]. Arsenic-containing compounds were applied in the manufacture of glass [89], semiconductors [90] and alloys [91], herbicides [92,93], wood preservatives [94], pesticides [95], animal feed additives [96], and medicine [97]. Disruption in cell signaling [98], reactive oxygen species (ROS) generation [99], high affinity to protein thiols or vicinal sulfhydryl groups [100], interruption in the binding of some hormones to their receptor [101], and prevention of oxidative phosphorylation [102] are the main effects of arsenic oxyanion on cells [88].

Depending on the concentration, oxidation state, and exposure time, arsenic can cause health problems such as cancer (skin [103], lung [104,105], bladder [106], and liver [107]), skin lesions [108], PNS (Peripheral Nervous System) disorder [109], liver failure [110], leukopenia [111], circulatory disease [112,113], anemia [114,115], and death [116,117].

Boron, the fifth element in the periodic table (group III), is a ubiquitous element in the environment that comprised an average concentration of around 10 mg/kg of the earth’s crust. Na₂B₄O₅(OH)₄·8H₂O is a common form of boron in ores widely distributed in California and Turkey [118]. Argentina, Russia, Chile, Peru, China, Libya, Egypt, Iraq, Morocco, and Syria are other countries containing many boron deposits [119,120]. This element forms approximately 230 compounds, and natural and anthropogenic activities such as volcanoes, commercial uses, fertilizers, wastewater treatment plants, forest fires, and coal combustion can release it into the atmosphere [121]. Boron has very useful applications in some industries such as the manufacture of glass and ceramics, fertilizer and detergent [122,123,124,125].

This essential element plays a pivotal role in immune response [126,127], mineral metabolisms [128], and the endocrine system [129]. It can also inhibit osteoporosis in postmenopausal women [130] and decrease cardiovascular disease [131]. Similar to other metalloids, it can be toxic in higher concentrations and causes many problems such as an increase in the oxidative state of a cell, DNA damage, impairment of DNA repair systems and membrane functions, or the inhibition of protein folding, protein function, and activities in living organisms [119,132,133]. Boron is found in some antibiotics such as boromycin [134], tartrolons [135], aplasmomycin [136], and biomolecules such as the bacterial autoinducer 2 (AI-2] vibrioferrin (a siderophore) [137] and borolithochromes (pigment in algae Solenopora jurassica) [138]. Additionally, some nitrogen-fixing bacteria need boron as a cofactor for growth and nitrogen fixation [119].

Antimony belongs to subgroup 15 of the element periodic table (atomic number 51) with average concentrations less than 1 μg/L in nature. Most of the world’s antimony reserves are located in South Africa, China, Russia, Bolivia, Tajikistan, and Mexico [139]. Due to the chalcophilic nature of antimony and its presence in ores containing chalcogen, smelting, and mining of ores containing these compounds, especially sulfide ores [140] are among the polluting sources of this element [141].

Antimonate (Sb (V); Sb(OH)₆⁻) and antimonite (Sb (III); Sb(OH)₃) are the two common inorganic forms of antimony present in natural waters, and Sb(OH)₃ is more toxic than the other one [142]. Antimony’s other toxic compound is antimony trichloride (SbCl₃), used in alloys, as a constituent of paint pigments, and in rubber compounding. Other major applications of antimony are included in various industries and use such as semiconductor, alloys, batteries, catalyst, and medicine [143,144,145]. In ancient times, antimony was used to purify precious metals such as gold and silver. Furthermore, antimony is used with other compounds to make textiles, paper, and plastics as a fire retardant agent [140].

Antimony is not present in living systems and, such as arsenic, is highly toxic to humans and living organisms. Eye, skin, lung, mucous membrane irritation, oxidative DNA damage, pneumoconiosis, and increased lung, heart, and gastrointestinal diseases are some problems caused by long-term exposure to antimony [146,147]. Antimony can affect the nitrogen cycle in soil by influencing urease function under pH 7 [148].

Tellurium is an element that belongs to the 16th group of the periodic table with atomic number 52 and has two allotropic forms, including white crystalline metal and black amorphous powder [149,150]. The concentration of tellurium in the earth’s crust is very low and about 1–5 µg/kg [151]. Tellurium is found as oxyanions tellurite (IV; TeO₃²⁻) and tellurate (VI; TeO₄²⁻). Tellurium is found in industries such as petroleum refining plants, glass, electronic and photoelectronic industries, optics, and sensors [152]. Tellurium can be found in a variety of ores as well as coal. Another tellurium application is in medicine and has traditionally been exploited as an antimicrobial agent in treating some infectious diseases, including leprosy, tuberculosis, dermatitis, cystitis, and severe eye infections [153]. Tellurium is also used in labeling, imaging, and targeted drug delivery systems and has some anti-inflammatory, anti-fungal, anti-leishmaniasis, and immunomodulatory activities [154,155,156,157,158,159]. Exposure to a high amount of tellurium can cause several health issues, such as respiratory irritation, headache, drowsiness, weakness, malaise, lassitude, gastrointestinal symptoms, dizziness, and dermatitis [160]. Both Se and Te are mixed with Cadmium to make quantum dots (used in phone and TV screens) and photoreceptors in solar cells leading to concerns of their disposal and subsequent release into water systems [161].

Germanium is another metalloid that belongs to group 14 and period 4 of the periodic element table. This metalloid is ranked 54th among the most abundant elements in the earth’s crust and has two stable oxidation states +2 and +4 in nature. Only a few compounds of germanium such as GeO₂, GeH₄, GeCl₄, and GeF₄ have toxic properties and their organic forms have no effect on human health. Due to similar outer electron structure and properties, Germanium is also called a pseudo isotope of silicon [162,163]. Germanium is used in small quantities in some fields such as fiber optics [164,165], micro- and nano electronics [166], infrared detectors [167], and polymerization catalysts [168].

After oxygen, silicon (Si) with 27% is the most abundant element in the earth’s crust. This element is found in many human organs and its deficiency is related to infection and bone weakness. Si is mostly biologically inert, and it can be used as a drug carrier in ointments and hydrogel coatings in medical devices [169]. There are no specific reports on the devastating effects of astatine and silicon in the literature.