is a vital necessity to human, aquatic, and terrestrial organisms. The presence of Se in the diet has nutritional benefits to the organisms on the Earth while its deficiency or excess consumption can lead to an adverse effect in humas as well as in aquatic and terrestrial life.
3.4.1 Human Population
Se is an essential micronutrient required for the human body. It is an important part of selenoproteins which will be required for various biological functions such as antioxidants defense, thyroid hormone formation, DNA synthesis, fertility, and reproduction. In organisms Se is converted into different metabolites. Se plays an important role in slowing down the aging process and improvement of endurance of muscles besides vitamin E. Methylselenol also plays a part in cancer prevention (Papp et al. 2007).
Table 3.1 Drinking water and surface water limits of different countries (EPA 2020; WHO 2012).
| Country | Limit (μg/l) | |
|---|---|---|
| Drinking water | Surface water | |
| United States | 50 | 5 |
| Canada (British Columbia, Ontario, Quebec) | 10 | – |
| Canada (Alberta, Nova Scotia, Prince Edward Island) | 50 | – |
| South Africa | 20 | – |
| Germany | 10 | 3 |
| Ireland | 10 | – |
| Japan | 10 | – |
| India | 10 | – |
| Malaysia | 10 | – |
| Russia | 10 | – |
| Abu Dhabi | 40 | – |
| New Zealand | – | 10 |
| Australia | – | 10 |
The deficiency of Se causes biochemical changes which may lead to additional stress in humans and causes certain type of illness (Du et al. 2012). A combination of Se deficiency and another stress such as viral infection can cause Keshan disease. A disease, namely cardiomyopathy, (also termed as Keshan disease) occurred in China during 1970 due to deficiency of Se. It was recommended that a daily intake of 20 mcg can protect the adults from this disease. Kashin–Beck disease is a type of osteoarthritis which is associated with male infertility due to Se deficiency (Sanmartin et al. 2012).
Se supplementation has an antiviral effect in the human body which lowers the risk of autoimmune thyroid disease. Excessive Se can generate reactive oxygen species which may leads to carcinogenesis. A few pieces of research also specify that high Se concentration may develop tumorigenesis by uplifting TR 1 expression and to diabetes. Besides a close relation with carcinogenesis, Se is related to development of chronic degenerative diseases such as cardiovascular disease and amyotrophic lateral sclerosis (Ralston et al. 2008). Se is 40 times more neurotoxic in inorganic form than in organic form.
3.4.2 Aquatic and Terrestrial Life
Se concentrations characteristically are higher in oceanic organisms than in those from river ecosystems, and they are greater in areas having seleniferous soils or deposits along with the areas with industrial, agricultural, or municipal wastes dump sites. It is observed that the egg‐laying vertebrates, namely fish and water birds, are the most sensitive organisms and could be at greatest risk in Se‐contaminated environments. These organisms at the base of the food web have been detected to concentrate Se 102 to 106 times exceeding that present in the water column (Sharma et al. 2017). There are some reports of high levels of Se in fish, primarily from seleniferous areas of the western United States and from reservoirs contaminated by fly ash from combustion of coal. The transfer of organic Se to eggs in egg‐laying vertebrates results in the production of reactive species that can cause not only oxidative stress but cellular dysfunction, which results in embryo mortality or teratogenic malformations observed in fish larvae and its population reduction (Chapman 2009).
Industries such as mining, agriculture, and petrochemicals discharge the waste generated by different operations into the water bodies, which causes contamination of Se in water. Generally the Se background concentrations in terrestrial invertebrates is found to be 0.1–2.5 mg/kg. Earthworms were found to bioaccumulate elevated concentrations of Se from selenite‐enriched soil (up to 7.5 mg Se/kg). There are fewer reports regarding terrestrial habitat, Se bioaccumulation, and toxicity.
The USEPA recently recommended strict guidelines for water quality criterion for the protection of aquatic life: 1.2 μg/l in lentic ecosystems (still freshwater) and 3.1 μg/l in lotic ecosystems (Holmes and Gu 2016). These new stringent guidelines may be useful for the protection of aquatic and terrestrial life from Se contamination.
3.4.3 Biological Role
Se forms unusual amino acids: selenocysteine and selenomethionine. In humans Se is a nutrient that functions as a co‐factor for reduction of antioxidant enzymes such as thioredoxin reductase and glutathione peroxidises found in some animal and plants (not all plants require Se). Dietary Se also reduces the effects of mercury toxicity, but it will be effective only at low doses of mercury. The excessive poisoning of Se can be measured through determination of Se in body fluids namely blood plasma, urine, and serum. There are some reports regarding cancer patients consuming selenomethionine through medicine that may achieve very high concentration of Se in plasma and urine of a person (Stadtman 1974).
3.5 Industrial Applications
Se is widely used in many industrial applications. More than 80% of global Se is produced as a by‐product of the copper refining process. It is collected from the anode residue (Hoffmann 1989). The production of Se through refinery processes has increased to 2800 tons (in the year 2018) due to its huge demand in industrial applications (USGS 2020). Refinery production by country is depicted in Figure 3.1. Ammonium selenite is used in glass manufacturing processes to neutralize coloration that has occurred due to iron oxide. Sodium selenate is also used as the soil additive in Se‐deficient areas. Ruby red glass, a variety of glass utilized in tableware, traffic, and other signal lenses and infrared equipment, was manufactured using 1–50 pounds of Se per ton of glass (Weyl 1981). Se in its high purity forms is also employed in semiconductors, specialty transformers, thermo elements, etc. About 23% of the total Se demand is for duplicating machine use. The Se‐coated metal cylinders are employed in the dry photographic copying process in which electricity transfers the photographic image (Joannopoulos 1979). For the
