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Phytoremediation by Constructed Wetlands
Published in Norman Terry, Gary Bañuelos, of Contaminated Soil and Water, 2020
Selenium (Se) is a metalloid with properties of both heavy metals and nonmetals such as sulfur, its close neighbor in the periodic table. It is a vital cofactor in antioxidant removal in mammals, but becomes toxic when more concentrated. Once thought to be a rare agricultural problem in dry inland regions (San Francisco Examiner, 1987), Se from agriculture, oil and coal industries, photocopying, and auto manufacturing has become a major concern in several areas of North America (Science, 1986; Frankenberger and Benson, 1994). Unfortunately, Se is unique in that the range between sufficiency and toxicity is much closer than for metals such as copper or cadmium (Combs and Combs, 1986). The range of needs and toxicity for each species overlaps to such an extent that the U.S. EPA primary maximum contaminant level in drinking water concentration for humans (50 μg/l) exceeds the threshold of chronic toxicity for freshwater aquatic biota by an order of magnitude. Bioconcentration of Se into the food chain by algae resulted in numerous grotesque deaths of birds in the past 2 decades. Mammals are also affected. Thus, the removal of excess Se in surface waters used by wildlife is imperative.
Chemicals in California Drinking Water: Source of Contamination, Risk Assessment, and Drinking Water Standards
Published in Rhoda G.M. Wang, Water Contamination and Health, 2020
Richard H. F. Lam, Joseph P. Brown, Anna M. Fan
Selenium is a known contaminant discharged from agricultural drainage. It is monitored in Delta water because of concern arising from the 1984 Kesterson National Wildlife Refuge episode in which deformities in young aquatic birds were attributed to high selenium levels in the refuge (39,40). The source of selenium was traced to the San Luis Drain, which emptied agricultural drain water containing selenium leached from soils in the western part of the San Joaquin Valley. Selenium is an essential nutrient to animals and humans at low levels of intake but can be toxic at high levels of exposure. Symptoms characteristics of overexposure in humans are nail changes and hair loss. Selenium concentrations in the Delta are meeting the 10 (xg/L drinking water standard. Selenium-laden waters enter the San Joaquin River between February and March each year from Mud Slough and Salt Slough. During this period, elevated levels can be traced down the San Joaquin River and through the southern Delta. In monitoring studies, the highest concentrations are found in the lower San Joaquin River: 3 fxg/L was measured in the Delta-Mendota intake, Banks Delta pumping plant, and Vernalis (28). Because of dilution and natural removal processes, selenium does not currently appear to constitute a health threat
Metals in the workplace
Published in Sue Reed, Dino Pisaniello, Geza Benke, Kerrie Burton, Principles of Occupational Health & Hygiene, 2020
Selenium is a non-metallic element that can occur in a metal-like form. This is obtained as a by-product of refining copper (and sometimes zinc) ore, so exposure to selenium fume can occur during the smelting and refining of these ores. Some of its forms are volatile and so more difficult to contain. Occupational exposure occurs primarily via inhalation, although in some cases it can be by direct skin contact. Selenium is used in the manufacture of glass, pigments, ceramics and semiconductors; in photocopiers and cameras; in photoelectric cells, steel, rectifiers in electronic equipment; as catalysts; and in the vulcanising of rubber. Selenium compounds are also used in the treatment of a number of animal and human diseases—it is a common ingredient in anti-dandruff shampoos. It is an essential trace element for animals and humans, but can concentrate to toxic levels in the body, causing selenosis.
Kinetic mechanism of selenium leaching from selenium-rich acid sludge in NaOH solution
Published in Canadian Metallurgical Quarterly, 2023
Xijian Pan, Yan Hong, Tu Hu, Libo Zhang, Kun Yang
At present, domestic and foreign methods of selenium extraction mainly include pyrometallurgy and hydrometallurgy. The mainstream thermal method includes oxidation roasting and sulfuric acid roasting, through which selenium is converted into selenium dioxide and reduced to monolithic selenium by passing sulfur dioxide or sodium sulfite into the aqueous solution. However, the selenium obtained by this process has low purity, low recovery, high slag production, relatively high energy consumption, and the fumes produced during the roasting process tend to corrode the equipment and pollute the environment [12–14]. Wet recovery of selenium mainly consists of acid leaching and alkaline leaching. Although some wet metallurgical methods can extract selenium effectively, the whole process becomes complicated because solvent extraction, ion exchange is needed to separate other elements [15–18]. To avoid this problem, selenium can be leached by sodium hydroxide, which is easy to operate, simple to set up and pollution-free. Liu [19] et al. studied the leaching of selenium from anode sludge with sodium hydroxide and oxygen under pressure, and the leaching rate of selenium can reach 99%. Yasin [20] et al. suggested that sodium hydroxide can leach elemental selenium effectively. Peng [21] et al. studied the leaching of selenium by sodium hydroxide using hydrogen peroxide as oxidant. The leaching of selenium from selenium-containing materials by sodium hydroxide has been extensively conducted, so it is important to study the leaching kinetics of selenium by sodium hydroxide.
Carcinogenic and non-carcinogenic health risk assessment of heavy metals contamination in groundwater in the west of Minia area, Egypt
Published in Human and Ecological Risk Assessment: An International Journal, 2023
Ahmed Abdelhalim, Guy Howard, Nicholas J. K. Howden, Mohamed Ahmed, Esam Ismail
Selenium accumulates in the sediments as a metal in the form of ores including other elements. Humans obtain the majority of their selenium through plant meals, which concentrate the selenium contained in soil or collected from groundwater used for irrigation. Selenium is an essential human micro-nutrient in low amounts, however higher concentrations cause unique harmful effects. The United States Environmental Protection Agency has revealed that when people are exposed to selenium at levels above the permissible limit of 40 µg/l for relatively short periods, it can cause the following health impacts: hair and nails changes; damage to the peripheral nervous function; tiredness and irritation. In the study area, roughly 14% (Table 2) of the groundwater samples exceed the permitted limit in the extreme northern section of the study area.
The occurrence, transformation and control of selenium in coal-fired power plants: Status quo and development
Published in Journal of the Air & Waste Management Association, 2022
Shuangchen Ma, Fang Xu, Dao Qiu, Shuaijun Fan, Ruimin Wang, Yang Li, Xiangyang Chen
Selenium exists in soil, water and air as a trace element in nature. It is not only important for biological life activities, but also a rare resource with strategic significance Chang et al. (2019a). Selenium can play a positive and important role in organisms only in a narrow concentration range. The Food and Nutrition Board of the US National Research Council established an estimated safe and adequate daily dietary intake for humans is 11–280 Hadrup and Ravn-Haren (2020). In drinking water, World Health Organization provisional guideline for Se was set at 40 Santos et al. (2015a). When the concentration is too high, it will cause harm to organisms and induce serious selenium-related diseases Zhang et al. (2020a). Selenium has also been identified by the European Commission as an important raw material for strategic low-carbon energy technology. It has application prospects in photovoltaic applications and has a medium risk of bottleneck Qin et al. (2017). Since selenium pollution occurs at a lower concentration than other pollution situations, the treatment of selenium pollution has not attracted enough attentions Dodig and Čepelak (2004). For example,many countries such as the United States, China, Japan, Ireland and Indiahavegroundwater selenium pollution Liu et al. (2020). The highest concentration in parts of India is 4475 Malhotra, Pal, and Pal (2020). At the same time, selenium will bioaccumulate in higher nutritional level organisms through the food chain, which will cause concerns about long-term environmental impact. In recent years, people’s strong interest in the effects of selenium in cancer Vinceti et al. (2018), genetics Shu et al. (2020), health Park et al. (2020), technology, renewable energy, and sustainable energy Chang et al. 2019b) has also increased the attention of selenium pollution Lenz and Lens (2009) Table 1, Table 2, Table 3, Table 4, Table 5.