This article looks at the potential health benefits of selenium when a person consumes it from food or supplements, the recommended daily intake of selenium, and some possible health risks associated with selenium. According to the ODS , selenoproteins may affect heart health by preventing the oxidative modification of lipids, or body fats.
This may reduce inflammation and the buildup of platelets. However, there is no consistent clinical evidence to suggest that the mineral lowers the risk of cardiovascular disease, especially in healthy people who already get selenium from food. Some studies do indicate that people with less selenium in the blood are at higher risk of heart disease, but other studies refute this. However, doctors do not yet recommend selenium for this purpose.
Studies in the International Journal of Endocrinology and Nature Reviews Endocrinology suggest that having an optimal level of selenium in the body may help prevent thyroid disorders. This could especially be true for females. However, more research is underway to help inform how selenium supplements might support thyroid health.
However, this may depend on the type of selenium and the type of cancer a person has, according to a study. Other studies cited in a review indicate that selenium supplements may have little effect on cancer risk. Scientists have also suggested that selenium levels during pregnancy may be a factor in the development of childhood asthma.
However, although selenium has links with many aspects of human health, there is not enough evidence to indicate that taking selenium supplements can prevent any of these conditions. Selenium is most often found in whole grains and animal products such as fish and eggs. The amount of selenium in grains and grain-based foods depends on the soil content where they grew. The following foods are good sources of selenium:.
The recommended DV for selenium is 55 mcg per day for most adults. During pregnancy, a person should consume 60 mcg, and while lactating, they should consume 70 mcg per day.
The same origin policy will only allow randomScript. However, it cannot access pages from different sites such as yahoo. This is the reason why prior to Selenium RC, testers needed to install local copies of both Selenium Core a JavaScript program and the web server containing the web application being tested so they would belong to the same domain.
Unfortunately; testers using Selenium Core had to install the whole application under test and the web server on their own local computers because of the restrictions imposed by the same origin policy. This system became known as the Selenium Remote Control or Selenium 1.
Selenium Grid was developed by Patrick Lightbody to address the need of minimizing test execution times as much as possible. Shinya Kasatani of Japan created Selenium IDE , a Firefox extension that can automate the browser through a record-and-playback feature.
He came up with this idea to further increase the speed in creating test cases. Simon Stewart created WebDriver circa when browsers and web applications were becoming more powerful and more restrictive with JavaScript programs like Selenium Core. It was the first cross-platform testing framework that could control the browser from the OS level.
Currently, Selenium RC is still being developed but only in maintenance mode. The Name Selenium came from a joke which Jason cracked once to his team. Since Selenium is a well-known antidote for Mercury poisoning, Jason suggested that name and his teammates took it. So that is how we got to call this framework up to the present. It is a Firefox plugin that you can install as easily as you can with other plugins.
However, because of its simplicity, Selenium IDE should only be used as a prototyping tool. If you want to create more advanced test cases, you will need to use either Selenium RC or WebDriver. Selenium RC was the flagship testing framework of the whole Selenium project for a long time. This is the first automated web testing tool that allowed users to use a programming language they prefer.
In excess it is carcinogenic and teratogenic disturbs the development of an embryo or foetus. Natural abundance. Selenium is found in a few rare minerals. These muds are either roasted with sodium carbonate or sulfuric acid, or smelted with sodium carbonate to release the selenium.
Help text not available for this section currently. Elements and Periodic Table History. He had shares in a sulfuric acid works and he was intrigued by a red-brown sediment which collected at the bottom of the chambers in which the acid was made. At first he thought it was the element tellurium because it gave off a strong smell of radishes when heated, but he eventually realised that it was in fact a new element.
He also noted that it was like sulfur and indeed had properties intermediate between sulfur and tellurium. Berzelius found that selenium was present in samples of tellurium and gave that element its characteristic smell. He also became affected by it personally — it can be absorbed through the skin — and it caused him to experience the bad breath associated with those who work with this element.
Atomic data. Bond enthalpies. Glossary Common oxidation states The oxidation state of an atom is a measure of the degree of oxidation of an atom. Oxidation states and isotopes.
Glossary Data for this section been provided by the British Geological Survey. Relative supply risk An integrated supply risk index from 1 very low risk to 10 very high risk. Recycling rate The percentage of a commodity which is recycled. Substitutability The availability of suitable substitutes for a given commodity. Reserve distribution The percentage of the world reserves located in the country with the largest reserves. Political stability of top producer A percentile rank for the political stability of the top producing country, derived from World Bank governance indicators.
Political stability of top reserve holder A percentile rank for the political stability of the country with the largest reserves, derived from World Bank governance indicators. Supply risk. Relative supply risk 7. Young's modulus A measure of the stiffness of a substance. Shear modulus A measure of how difficult it is to deform a material. Bulk modulus A measure of how difficult it is to compress a substance. Vapour pressure A measure of the propensity of a substance to evaporate.
Pressure and temperature data — advanced. Listen to Selenium Podcast Transcript :. You're listening to Chemistry in its element brought to you by Chemistry World , the magazine of the Royal Society of Chemistry.
Hello, this week flaky scalps, skunks, dead polo ponies and an element that makes you stink of garlic. But it's not all bad news. We know selenium is there, right under sulfur, in the periodic table, but it doesn't get much attention. The inorganic chemistry textbooks that I studied from talk extensively about sulphur and, where appropriate, say things like 'selenium also forms similar acids', or 'selenium also has many allotropic forms'. How slighted is this important element! When I was in my early 20s I developed a dry scalp condition for a few years, probably a result of anxiety over research grants I was trying to obtain.
The treatment for this was a shampoo containing selenium sulphide, surprising to me because I thought that selenium was highly toxic. In fact a little investigation showed me that it was perfectly safe in small amounts. Selenium is one of those all too common elements that is essential to life in small quantities, and very toxic in larger quantities.
But we require it as part of various enzymes, such as glutathione peroxidase, as well as in the thyroid. It is widespread, and accumulated in various foods, such as nuts, tuna, and lobster, so it is rare for humans to have a selenium deficiency. But for horses, with their more limited diet, selenium deficiency is common and often corrected with dietary supplements. Again, this requires great care. Recently 21 polo horses died from selenium overdose in Florida, the result of a veterinary pharmacist overdoing it in mixing the drugs.
It was Berzelius who discovered selenium in , as an impurity in sulphuric acid. Tellurium had already been discovered, and named after the Greek word for earth, so he named selenium using the Greek word for moon, selene.
It occurs in various minerals, together with sulphur as you would expect. We know its evolution in plants goes back a long ways, because we find selenium compounds in coals, and much of what is released into the atmosphere today comes from coal burning.
Indeed, the toxicity level of selenium to humans was established only 20 years ago by studies of Chinese victims of selenium poisoning, s elenosis , who grew corn on selenium rich coal rocks. Selenosis has some lovely symptoms: a garlic odor on the breath, hair loss, sloughing of nails, fatigue, irritability, and eventually cirrhosis of the liver and death.
It is the selenates and selenites that are the most toxic, since the elemental selenium is not readily incorporated into biological processes.
While some of the allotropic forms of selenium resemble those that we know well from study of sulphur, there are others that are different.
Most important, so called gray selenium consists of long chains of atoms forming extended helical structures. While selenium is not a metallic element, gray selenium is a good photoconductor, and was used in early photocells. Subsequently, selenium and various selenium compounds have been used in a variety of photoconductor and photovoltaic applications. Indeed, the newest and most promising class of mass produced solar cells are copper indium gallium selenide.
At one time virtually all copying machines used selenium ; this has now been largely replaced by organic photoconductors. But the diversity of uses of selenium does not stop with shampoo and horse food supplements and photovoltaics. Selenium is added to synthetic rubber to improve resistance to abrasion, it has been added to brass, along with bismuth, to replace lead in pipes, and it is used, as sodium selenate, as an insecticide to stop attacks on flowering plants such as chrysanthemums and carnations.
Selenium in its allotropic red form is added to glass to give it a scarlet color, but it also can be used to remove the greenish tint sometimes found in glass due to iron compounds. Well, this is something that we are going to discuss in detail in the article.
By the end of the article, you will be able to list out all the benefits of performing automation testing using Selenium and why is it preferred over other automation testing tools. Before we delve deep in the benefits of let us first understand what Selenium is and why it is used. Well, Selenium is an open-source automation testing tool which is used for automating tests carried out on different web-browsers.
It has a suite of tools which caters to different needs of organizations. It basically has four different tools:. Selenium is basically used to automate the testing across various web browsers. It supports various browsers like Chrome, Mozilla, Firefox, Safari, and IE, and you can very easily automate browser testing across these browsers using Selenium WebDriver.
You can see live automated tests being performed on your computer screen. When someone chooses a tool the first thing that comes to mind is: "Does my tool supports the language that I know? Well, this is not the case with Selenium as it supports all major languages like Java, Python, JavaScript, C , Ruby, and Perl programming languages for software test automation. You can write your scripts in any of these programming languages and Selenium converts it into Selenium compatible codes in no time.
So, there is no need for knowing Selenium only languages. Also, every Selenium supported language has dedicated frameworks which help in writing test script for Selenium test automation.
One of the many things that adds to the advantages of Selenium is its open source availability. So, being an open source tool, Selenium is a publicly accessible automation framework and is free, with no upfront costs. So, you can save bucks here and use them for other good causes. The Selenium community is continuously helping developers and software engineers in automating the web browser features and functionalities.
Selenium being open source also helps you customize the code for better code management and enhance the functionality of predefined functions and classes. Selenium has become the most reliable web automation tool because of the ease of generating test scripts to validate functionality.
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